Monday, June 30, 2014

Recap of significant flash flooding in the Memphis metro - June 29, 2014 #memflood

A once-in-a-generation rainfall event resulted in significant flooding across portions of the metro on Sunday. Thunderstorms containing torrential rain began entering the area during the wee hours of the morning (between 1-2am) and continued nearly unabated in waves for nearly 10 hours, resulting in rainfall totals of about double the typical monthly totals for the month of June. Local rivers and tributaries to the Mississippi River quickly rose and created an urban flooding scenario as water backed up into streets and low-lying areas, including a mobile home park west of the airport, where 100 trailers were flooded and rescues were performed.

Several atmospheric factors came together to produce the copious rainfall amounts we saw locally. These included a very moist atmosphere with precipitable water (PW - the amount of water in a column of air) values of over 2" (or nearly a "worst case" for this time of year), a southwesterly flow of about 45-50 mph into the lower levels of the region, blowing over a stationary outflow boundary positioned just to our south which helped generate lift and storm initiation, and finally unstable air just south of the boundary which also provided some lift (see below). Storms continuously developed just west of the metro and trained over the same areas for many hours.

Strong flow into the storm from the southwest, overriding a boundary just south of the metro, contributed to significant precipitation rates, as forecast by the Weather Prediction Center during the event on Sunday morning.
Below is a map of radar-estimated rainfall amounts for the weekend, highlighting the areas from west of the city, across Shelby and Fayette Counties where rainfall amounts were highest. Following that, the departure from normal precipitation for the past week, dominated by the weekend precipitation.

Two-day storm total precipitation based on radar estimates, ending late Sunday afternoon
Departure from normal precipitation for the past seven days. Note the swath of 4-10" departures across the metro and into east-central AR.
A radar screenshot (below) taken early Sunday morning shows the mass of storms between Memphis and Little Rock in the storm initiation zone with waves moving east from that area paralleling I-40 into Shelby and Fayette Counties. At this time, Flash Flood Warnings (green boxes) were in effect from Little Rock to Arlington, TN, which subsequently were extended further east into Fayette and northern Marshall Counties.

At one point yesterday morning,Flash Flood Warnings were in effect from Little Rock to Arlington, then got extended east even further!

Selected rainfall totals for this event:

June 29th rain totals

  • Memphis Int'l Airport - 5.87"
  • in north Bartlett - 4.69" (est.)
  • Agricenter in Cordova - 6.13"

June 28-29th rain totals

  • Memphis Int'l Airport - 7.09"
  • in north Bartlett - 6.06"
  • Agricenter in Cordova - 7.48"
  • West Memphis, AR airport - 6.86"
  • Collierville - 5.77"
  • Germantown - 6.99"
  • Somerville - 3.95"
  • Olive Branch - 5.94"
  • Pleasant Hill, MS - 5.66"
  • Madison, AR - 10.80"

As far as records go, Memphis International Airport broke a daily record for rainfall on Sunday with 5.87". In addition, that total is the seventh highest daily rainfall amount in Memphis recorded history (dating to the 1870s)! The June total at Memphis will be 13.40", which makes this month the 2nd wettest June on record, trailing only June 1877 which recorded 18.16" of rain.

The Mississippi River experienced a slight rise Sunday morning, but that was largely due to the effects of the larger tributaries dumping huge amounts of water in the river. The Mississippi River is primarily affected by rainfall upstream, not in the immediate area, but the fact that it was relatively low allowed the tributaries like the Wolf River, Loosahatchie River, and Nonconnah Creek to effectively flow into it, therefore the flooding that occurred along these bodies of water abated fairly quickly once the rain stopped (within a few hours). Had the Mississippi River been several feet higher (say at spring levels in the 25-32 foot range), the tributaries would not have drained as efficiently and flooding along their banks would have been much worse and more prolonged.

The Mississippi River gauge in downtown Memphis rose almost two feet between 3am and 3pm Sunday due to excessive flow from the area tributaries into the river.
The Wolf River at Hollywood Street in Frayser climbed Saturday with storms in the area, then jumped more than 10 feet again Sunday and is receding much more slowly.
The Nonconnah Creek near Memphis Int'l Airport rose about 22 feet Sunday, but had fallen back to pre-storm levels by 3am Monday. This gauge is very near the mobile home park that was flooded.
Nonconnah Creek at Winchester Road rose 4 feet on Saturday afternoon then another 14 feet on Sunday morning, falling back to pre-storm levels by Monday morning.
The Loosahatchie River in Frayser also rose about 15 feet Sunday and has dropped a few feet but remains very high on Monday.
A similar situation on the Loosahatchie River at Brunswick Road, which is just below flood stage on Monday
Overall, this once-in-a-generation storm caught most forecasters off guard until it was in progress, but it was definitely a learning event. We're thankful that, despite people being displaced and losing possessions, no lives were lost and no major injuries were reported. Let's hope we don't see anything like this again in a long time!

How were you impacted by the flooding on Sunday? You can find more pictures and video of the mobile home park flooding in the timelines on our social channels listed below.

Erik Proseus
MWN Meteorologist

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Sunday, June 29, 2014

Flash Flood Emergency for Memphis/Shelby County - heavy rain continues

UPDATE - 12:45pm:

The bulk of the precipitation is now exiting the metro, leaving behind only a few light showers. Mainly dry conditions for the next couple of hours will help the smaller streams and tributaries absorb remaining runoff and push it into the larger creeks and rivers, which will continue to remain high (likely near or above flood stage) throughout the afternoon and evening hours. Use extra caution on roads near the larger tributaries, such as the Wolf River, Nonconnah Creek, and Loosahatchie River.

As for the rest of the afternoon, unfortunately some peeks of sunshine could mean scattered showers and t'storms redevelop. Whether they affect the metro is TBD, however we're keeping a chance of rain in the forecast into early evening and remain hopeful that it'll be gone for most evening activities. (It's worth noting that the latest high-resolution model data keeps rain chances around until 8-9pm.)

After this evening, we expect dry and hot conditions until Wednesday when a weak cold front arrives. The abundant rain may temper the expected mid 90s highs on Monday and Tuesday a bit as saturated ground is harder to heat than dry ground. That could be offset by higher humidity values though as the water evaporated from the ground. One more "worth mentioning" is that one model is trying to form more precip over us in the early morning hours Monday. Not sure that will happen, but I'll throw it out there!

As of noon, we have had the 7th wettest day in recorded Memphis history at 5.87" of rain and are now the second wettest June on record at 13.40" for the month. Unbelievable.

Rain and thunderstorms began around 2am this morning and have continued, mainly in a heavy manner, ever since. I posted this at 8:30am and last updated at noon. Earlier this morning, the National Weather Service pulled the trigger on a very rare "Flash Flood Emergency" for Memphis and Shelby County, and DeSoto and northern Tunica Co. in MS and has since extended it until 4:30pm this afternoon. Flash Flood Warnings are also in effect for Crittenden Co in AR, Fayette Co in TN, and northern Marshall Co in MS.

Flash Flood Warnings are in maroon hatch, river Flood Warnings in green outline, and Flash Flood Watches in green shading. A Flash Flood Emergency is in effect for Memphis and Shelby County

Records are seemingly falling as fast as the rain does. As of noon, the Memphis International Airport has received 5.87" of rain since midnight. The daily rainfall record has been shattered and we're now into the top 10 wettest days on record at #7. In addition, the month of June has now seen 13.40" of rain, becoming the second wettest June on record. The top spot belongs to June 1877, which saw 18.16" of rain.

Storm total rainfall estimates from the NWS Doppler show 5-8" across portions of the metro since yesterday.

Top 10 wettest days in Memphis (through 11:30am today)

Top 10 wettest Junes in Memphis (through 11:30am today)

Beyond the stats, the situation is becoming life-threatening. Already reports are coming in of stranded motorists and water rescues by the Memphis Fire Department. Local rivers and creeks are rising above flood stage due to massive runoff, which will cause further backup of water on streets and low lying areas as the water has no place to go.

The latest hydrograph (plotted river stage) for the Wolf River in Raleigh (Austin  Peay).

With continued periods of rainfall and thunderstorms with heavy rain expected through the afternoon hours, this will likely be the worst flooding in the Memphis metro since the first weekend in May 2010, when the National Guard was called in to help with rescues in Millington.

When will we see a break? Well, for good, by early evening when the entire system exits. However, it appears areas north of the TN/MS line still have a couple of hours of rain and thunder to deal with, though late morning. Then scattered "summertime" thunderstorms will begin to pop after lunch time and will affect mainly north MS and east AR, but we could also see a few southwest TN. All of the activity looks to be done by about 6pm, I hope! That's the best educated guess I have right now.

In the meantime, if you don't have to go out this morning, don't. If you do, use EXTREME caution, plan your route on roads that you know are not prone to flooding or that cross creeks that flood, and if you do encounter water across the road...

... it could save your life!

Erik Proseus
MWN Meteorologist

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Saturday, June 28, 2014

"Real Memphis summer" arrives, then a cool front in time for Independence Day

As several days of unsettled weather comes to an end this weekend and we head into the July 4th holiday week, high pressure aloft builds in. The only fly in the ointment will be a weak cool front around mid-week that, at best, lowers humidity values a bit and brings brief rain chances.

One more day of scattered storms is expected on Sunday before the high pressure ridge squashes thunderstorm chances for a couple of days. The extra heating under the ridge with a lack of cooling precipitation will mean highs soar above 90 Monday and Tuesday - likely into the mid 90s. With dewpoints (i.e., low level humidity) remaining near seasonal summertime levels, we'll likely see heat indices above 100, perhaps flirting with the 105-degree danger level.

High pressure aloft (pink) dominates the southern half of the U.S. in this GFS forecast model valid Monday evening.
A weak cold front will undercut the high pressure cell aloft, bringing a slight chance of rain at mid-week (most likely Wednesday, but possibly Thursday), followed by surface high pressure over the Ohio Valley building south. The high pressure ridge should hopefully end the rain chances by the first fireworks exhibitions on Thursday night. The hope is that the Ohio Valley high builds far enough south to end rain chances and also lower temperature and humidity values a bit heading into the the 3rd and 4th.

GFS forecast model temperatures and precipitation for the upcoming week. Mid 90s are possible Mon-Wed with slightly cooler temperatures after a bit of rain on Wed or Thu (other models indicate Wed; GFS says Thu).
After a couple of "cooler" days to end the week, the heat looks to build again heading into next weekend. Stay updated on the latest expectations from MWN for the short holiday week and local 4th of July celebrations with the MWN Forecast on the web, mobile web, and MWN mobile apps.

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Tuesday, June 24, 2014

Rain chances this week, then drier/hotter weather returns

A weak cold front is moving through the region bringing an end to the rounds of showers and t'storms we have experienced for the past few days. Although an isolated shower is possible Wednesday, mostly dry conditions will allow temperatures to climb once again back to the 90 degree mark.

By Wednesday night into Thursday, the pattern becomes more unsettled once again with higher rain chances returning  for a couple days. Scattered t'storms are expected both Thursday and Friday though severe weather is not expected outside of a brief strong wind gust as we've had with some of the stronger cells the past few days.

NAM model - total precipitation forecast for Thursday and Friday. The metro is in an area of 1/2"-1".

High pressure re-emerges this weekend though with diminishing rain chances and rising temperatures. In fact, as we reach the first days of July, the hottest weather of the summer could be on us with highs in the mid 90s and heat indices likely to exceed 100 if the medium-range models are right. This trend could continue right into the July 4th holiday weekend! For the complete MWN Forecast, click here.

Tuesday (July 1) max temperature forecast from the GFS model. Note the mid 90s just south of the metro.

Erik Proseus
MWN Meteorologist

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Monday, June 16, 2014

Memphis tech community loses one of its great leaders

Earlier this evening, I was reading my Twitter feed and came across the following tweet from a friend in the Memphis tech scene:

I read it a couple of times, first not thinking I had read it right, then understanding - but not believing - what I was reading.

This past weekend, Memphis unexpectedly lost (as Elizabeth aptly points out) one of the great champions of the thriving, yet still growing, tech community in Memphis. Dave Barger Jr. was an entrepreneur, the founder and CEO of LunaWeb, Inc. But perhaps as importantly as that job, he was dedicated to "raising the tech tide in Memphis" by providing multiple outlets for small business owners, those in social media and marketing, and "techies" in general to hone their skills and network with others in the area. Dave's passion for raising the bar in Memphis from a technology perspective matched well with his generosity as he gave freely of his time, and dollars, to see that vision come to fruition.

There are many Memphians whose lives he touched. This is my story of Dave. A little over two years ago, in early 2012, Dave recognized and Cirrus Weather Solutions as a fledgling start-up, appreciated the service that was provided, and decided he would be vocal about his support. Keen to the power of social media, Twitter in particular, he saw that MWN had early-adopted the use of the #memstorm hashtag and asked to incorporate our content into a new mobile-friendly website he wanted to build - I readily agreed, and within 2 days was born as severe storms rolled through the area. Dave provided early visibility for our social media presence and for that I am grateful.

It doesn't end there though. Not long after, Dave believed enough in what we were doing to put some of his company's advertising dollars into MWN's web presence with banner advertising that promoted upcoming tech camps and meet-ups - and then renewed the contract a couple of times. This small but important "boost" in revenue provided the necessary funds to begin development of the StormWatch+ mobile app that is now available nationwide in the App Store and is protecting people across the U.S. from severe storms.

Continuing to invest in the MWN brand, he then invited me to be a speaker at the inaugural "TechCamp Memphis" event that he was organizing for the social/tech community, asking me specifically to speak about using social media as a method of crisis communication - again because of how quickly the #memstorm fire had spread. Though we haven't spoken personally in perhaps a year or so, Dave continued to tweet me once in a while and recognize the work that I was doing. That is who Dave was - a person with a mission to support and mentor, in any way he could, those who were attempting to make a difference in Memphis.

There are many who seem to pride themselves in tearing down this city and reminding us constantly of our differences and struggles. Dave was the antithesis of those naysayers. He found movements and people that were starting off down the right path and encouraged them.

Dave Barger, you will be greatly missed in this city and by the people that you have touched. Godspeed.

Erik Proseus
Founder/Owner, Cirrus Weather Solutions, LLC

Sunday, June 15, 2014

Summertime pattern builds into the Mid-South

As everyone knows, the first half of June featured a lot of rain in the Memphis metro. Perhaps this blog on the first lengthy summertime pattern is a welcome change! Although things look to warm up a bit, it is hardly unbearable (seasonal even) and the decrease in precipitation chances is certainly alright with me. Let's take a look at some of the specifics regarding the coming week.

Mean sea level pressure and 3-hourly precipitation totals valid for 7 AM Tuesday
By Tuesday morning the typical summer-time pattern is quite apparent when viewing a mean sea level pressure map. Surface high pressure (the Bermuda high) is situated to our east, ushering in moist Gulf air into the region via its clockwise rotation. This will keep humidity values at levels that allow heat indices approaching the century mark during the day.

GFS Temperature and Heat Index values for the work week
A visual picture of model output shows temperatures nearly the same each day this week - near 90 (we expect temperatures to be a bit warmer than this, around 92). Similarly, heat indices approach 100 just about every day. This is only slightly above average for this time of year, as the weather this week will be nearly seasonal. It is worth pointing out that temperatures will remain in the 70s overnight due to the high humidity. With  heat indices near 100 in the afternoons, it's also time to give some thought to summer heat safety tips if you work outdoors. Make sure you're drinking plenty of water and wearing light-colored, loose-fitting clothing, taking breaks as necessary. 

To recap, highs in the lower 90's and lows in the mid 70's are expected for the work week. Partly cloudy skies can be expected for the vast majority of the week with only slight chances of thunderstorms by the end of the work week (beginning Thursday). As always you can find a full MWN forecast here.

--William Churchill (MWN Social Media Intern)

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Thursday, June 12, 2014

Rainfall recap, one more storm chance, and a lunar rarity

It's been a wet couple of weeks in the Mid-South! The proverbial ark jokes had started, but seemed to be quelled a bit by the beauty in the skies Monday and Tuesday evenings as gorgeous rainbows graced the horizon and sunsets were spectacular both nights!

Photo taken Monday night in Shelby Forest by photog Brian Anderson.

The rain stats for the recent fortnight are, if not surprising, still pretty amazing. At Memphis International Airport, since May 27, 15 of the 16 days have had precipitation fall in some amount with 12 days of measurable rain totaling 5.47"! Even more jaw-dropping are the totals from west TN outside the metro over to the western outskirts of Nashville. The graphic below shows "departure from normal" precip totals for the past 14 days. Notice that while the metro was anywhere from 1-4" above normal for that period, parts of the Tennessee River Valley were 8"+ above normal! (Not 8" of rain, but ABOVE NORMAL - which is in the 2" range.)

We will have one more shot at rain tonight as a weak cold front moves through the area. The main energy with this system, provided by upper-level support, will be southwest of the metro, across southern AR, east TX, and northern Louisiana. Clusters of thunderstorms across these areas will likely form into a squall line and move east into the Lower Mississippi River Valley. Due to the possibility of severe storms, a Slight Risk of severe weather covers these areas and extends to just southwest of Memphis (as shown below).

While I don't expect severe storms in the metro, thunder is a definite possibility with scattered storms possible after 7pm tonight. If you have evening ball games, the later they go, the more likely lightning and thunder will be in the area. Higher rain and thunder chances will exist from about 10pm through the wee hours Friday morning. By Friday morning rush hour, most all of the precipitation will be gone, but a few lingering showers will be possible through Friday morning.

Tonight's event will probably be the last chance of rain in the metro for a number of days as summertime high pressure builds in and causes temperatures to rise to 90+ by the end of the weekend. This pattern will carry us into next week before small thunderstorm chances re-emerge by the middle of the week. I hope you're ready for some more typical Memphis summer weather! (Click here for the complete MWN Forecast.)

Friday the 13th Full Moon

One final note on a phenomena that has been making the rounds on social and traditional media: Tomorrow is the only "Friday the 13th" of 2014. Coincidentally, for some, it is also a full moon! Why do I say "for some?" While most outlets tout the full moon on Friday the 13th and note its historical significance (first occurrence since 2000 and it won't happen again until 2049), they fail to provide full detail. A full moon is actually not a day-long phenomena, it occurs at a particular minute. Tonight, the full moon occurs at 12:13am EDT - which is on Friday. So for those in Eastern Time, it is indeed a full moon on Friday the 13th. For those of us west of  Eastern Time (Central, Mountain, Pacific Time), the full moon actually occurs before midnight - 11:12pm CDT in Memphis to be exact. (This article on Vox has a good description of the event and the reason it's so rare.) So while we will TECHNICALLY miss out on this double harbinger of bad luck (who's complaining?), I wouldn't blame you for going along with the story and calling tonight's full moon a Friday the 13th lunar event. Too bad it'll be cloudy and you won't see it anyway...

Erik Proseus
MWN Meteorologist

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Monday, June 9, 2014

Details from the NWS on our severe weather risk today and tonight

Severe weather outlook and probabilities of various threats within 25 miles of a point for Monday and Monday night. Click image for larger version.

The National Weather Service in Memphis has issued the following synopsis regarding the risk for severe weather in the Mid-South today and tonight.

There is a Slight Risk for severe thunderstorms today and tonight across the entire Mid South. 
A stationary front is stretched across north Mississippi this morning with widespread showers and thunderstorms. These storms will pose a threat for flash flooding through mid morning. These storms should diminish later this morning which should allow the front to lift back north as a warm front. By mid afternoon, an upper level disturbance will approach from the west. New showers and thunderstorms should redevelop over the Mid South and may initially focus along the northward moving warm front. An ongoing line of storms to our west will also continue to move east through the day. As the atmosphere becomes unstable along and south of the warm front, storms that form will have the potential to become severe. Any severe storms that form later today could produce damaging winds, large hail, and a few tornadoes. The greatest tornado threat will likely be near the warm front or with any supercell thunderstorms that form south of the warm front. These storms ahead of the approaching line from the west will move quickly northeast from mid afternoon through the evening. The line of storms should move east across the area later this evening and overnight with a continued threat for mainly damaging winds and large hail. In addition, a flash flood threat continues for the morning hours over portions of north Mississippi and across the entire region this afternoon through tonight.
Check in with us on social media throughout the day for the latest on the potential severe weather threat and be sure StormWatch+ is activated in the mobile app for immediate push notification of any watches or warnings issued.

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Friday, June 6, 2014

May 2014 Weather Recap and MWN Forecast Accuracy

May Recap

Each month in 2014 has seen below normal average temperatures and May continued the trend, but just barely. The average temperature for the month was just 0.3 degrees below normal at 71.4 degrees. There was a cool spell in the middle of the month that resulted in one record low temperature of 46 degrees and the month started with a low of 44 on the 1st, though it was not a record. Conversely, Memphis reached 89 on 3 occasions, but there were no 90 degree readings.

Precipitation for the month was about an inch below the long-term climate average with no records set or tied. The annual precipitation is now less than 2" above normal. Despite typically seeing severe weather in May, the cooler temperatures that existed for much of the month prevented severe weather from being a problem. In fact, it was probably the best weather for Memphis in May activities in some time!

For the period March-May, which is defined as "meteorological spring," temperatures were cooler than normal by 1.9 degrees (61.0 degree average) and precipitation was above normal by nearly 2" (17.84", +1.93" compared to normal).

Memphis International Airport, Memphis, TN

Average temperature: 71.4 degrees (0.3 degrees below average)
Average high temperature: 80.8 degrees
Average low temperature: 62.0 degrees
Warmest temperature: 89 degrees (12th, 24th, 26th)
Coolest temperature: 44 degrees (1st)
Records set or tied: Record low temperature: 46 degrees on the 16th
Comments: 21 days had maximum temperatures above 80 and no days had a high temperature of 90. For the year, the average temperature at Memphis is 52.0 degrees, which is 3.1 degrees below average.

Monthly total: 4.32 " (0.93" below average)
Snow/ice total: 0"
Days with measurable precipitation: 12
Wettest 24-hour period: 1.02" (May 27-28)
Records set or tied: None
Comments: Zero days had more than 1" of rain and three days recorded more than 0.50". For the year, the total precipitation has been 25.96", which is 1.68" above average.

Peak wind: Southwest/38 mph (8th)
Average wind: 8.2 mph
Average relative humidity: 65%
Average sky cover: 60%

Click here for a daily statistical recap for Memphis International Airport.

Cirrus Weather Solutions /, Bartlett, TN

Average temperature: 71.8 degrees
Average high temperature: 81.6 degrees
Average low temperature: 60.5 degrees
Warmest temperature: 90.6 degrees (24th)
Coolest temperature: 40.6 degrees (1st)
Comments: 22 days had high temperatures above 80 and three days topped 90 degrees.

Monthly total: 4.35" (automated rain gauge), 4.66" (manual CoCoRaHS rain gauge)
Snow/ice total: 0"
Days with measurable precipitation: 12
Wettest date: 0.96" (13th)
Comments: No days with more than 1" of rain and four days with more than 0.50".

Peak wind: Southwest/25 mph (14th)
Average relative humidity: 75%

Click here for a daily statistical recap for Bartlett, TN.

MWN Forecast Accuracy

MWN average temperature error: 1.80 degrees
MWN forecast temperatures within 2 degrees of actual: 77%
MWN average dewpoint error: 1.96 degrees
MWN forecast dewpoints within 2 degrees of actual: 72%

MWN's forecasts extend out five periods (2.5 days, or roughly 60 hours). Historical accuracy statistics can be found here.

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Convective system packs a punch Thursday - another today?

UPDATE - 11:00am
Temps are soaring in the metro and are well into the mid 80s with dewpoints (measure of low-level moisture) in the mid 70s. With cloud cover just to our north holding temperatures back in the 70s, a gradient of atmospheric instability (CAPE) has developed right over the metro. Why is this important? Convective complexes like the one moving into western AR now, tend to follow this gradient.

A storm complex (MCS) over western MO will likely move across areas with high atmospheric instability (CAPE - plotted above with red lines). The projected path of the MCS is shown with the red arrow. Memphis is the gold star.
With plenty of heating and available moisture already realized across central and southern AR into the metro and north MS, I expect the MCS thunderstorm complex in west AR to continue moving this way fairly quickly and reach the metro by mid-late afternoon, or maybe a couple hours later than yesterday's. The other difference from yesterday is that the strongest portion of the storm will likely be near and south of I-40 rather than north of I-40 (this does not discount north Shelby or Tipton County however).

Metro residents need to be prepared for storms possibly as strong as yesterday's (since we didn't get the brunt of that system) late this afternoon (after 3pm). The main threat will be high wind of 60+ mph, with a small threat of hail and a very low threat of a tornado. Before mid-afternoon, scattered strong storms with heavy rain, copious lightning, and gusty wind are possible anytime after noon to 1pm.

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A quick-hitting mesoscale convective system, or large thunderstorm complex, swept through the metro yesterday afternoon with the strongest wind hitting in the northern sections of the area. Below are the preliminary storm reports showing a lot of high wind gusts and damage. Trees and power lines were down in many sections of the metro and MLGW reported over 37,000 customers without power at the peak following the storm and still nearly 10,000 as of this writing (8:00am Friday).

You'll see from the storm reports that high wind was reported from near Wichita, KS right through the metro and east to nearly Atlanta. There is some debate about whether this was a "derecho" - a long-lived wind event that must meet several criteria to receive the label. The only one that seems to be in question being multiple well-separated reports of 75+ mph wind, though we're pretty sure a hurricane-force wind was required to throw this ATV into the air near Jonesboro yesterday! In addition, a train was derailed and tractor trailers blown over in northeast AR.

A flying four-wheeler ended up in a precarious position yesterday in Nettleton, AR in one of the more iconic images of the storms!
So what's in store for today? The stalled frontal system continues to linger in the area with a weak northwest flow aloft over the area, allowing upper-level disturbances from the Plains to move into the region. The Storm Prediction Center has placed a large area, including the Mid-South, in a Slight Risk for severe storms, as shown below, with the main threat again being high wind.

Scattered showers and t'storms will become possible mainly this afternoon. In fact, the HRRR high-resolution model (which handled yesterday's storms well) is predicting scattered activity after lunch with another complex of storms (perhaps not as strong as yesterday) moving through around rush hour tonight. Once again, we recommend battening down the hatches and securing outdoor objects that might have been loosened yesterday just in case. Also, a Flash Flood Watch remains in effect until midnight so some areas could see ponding of water or low-lying flooding front heavy rain produced by any storms.

HRRR modeled reflectivity (radar precip) at 2pm showing the chance of scattered storms.

HRRR modeled reflectivity (radar precip) at 6pm showing a line of storms moving through. 
The weekend shows a similar pattern to the past couple of days with a stalled front near the Mid-South. Saturday appears to produce another convective system, but there's a better chance that this one misses the metro, likely pulling to the north. By Sunday, a low pressure system ejects out of the plains and makes a run down the stalled front, perhaps producing more storms for our area. The whole system then tries to slowly advance east early next week, but takes it's sweet time. Thus scattered showers and thunderstorms remain in the forecast through at least the middle of the week. Click here for our complete forecast.

As with yesterday, stay with us on our social media channels (listed below) for the latest info and keep an eye to the sky. Our mobile apps also put the latest information at your fingertips.

Erik Proseus
MWN Meteorologist

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Thursday, June 5, 2014

Severe thunderstorms expected this afternoon in the metro

The first in possibly a series of mesoscale convective systems (MCS, or "macho thunderstorm complex") will move through the Mid-South this afternoon. This system is currently in the Ozarks and moving east-southeast towards the region at 50-60 mph.

Radar image at 10:20am. Green square icons in and behind the line are damaging wind reports. Yellow boxes are Severe T'storm Warnings.
The Storm Prediction Center (SPC) has issued a Severe Thunderstorm Watch for the entire metro until 5pm.  They provide probabilities of various severe weather events within the watch box. For this one, there is a 70% chance of 10 or more wind events of 60+ mph, a 50% chance of a 75 mph wind report, a 30% chance of 10 or more 1" hail reports, and only a 10% chance of 2 tornadoes. Thus, the main threat with these storms will be straight-line damaging wind of 50-60 mph.

Severe Thunderstorm Watch in pink. A Flash Flood Watch is also in effect.

SPC has also placed AR and points along the river in west TN under a Moderate Risk for severe weather today. I expect this to be extended eastward a bit later this morning.

A Moderate Risk zone extends from the Ozarks to the Mid-South at mid-morning. This could be extended east by late morning.

The estimated time of arrival for this complex of storms is between 2-4 pm in the metro with rain continuing for a few hours behind the line. The worst of the severe storms will hopefully be done by the time rush hour kicks into full gear, but expect wet streets, including residual ponding or minor flash flooding, and some traffic light failures due to power outages from high wind. If your car windows are rolled down at work, roll them up at lunch time. If you're attending the FESJC golf tournament, find suitable shelter WELL BEFORE the line arrives this afternoon. It will hit quickly and pack a significant punch when it gets here.

With any luck, most of the rain will be done by 7-8 pm tonight, but I make no promises on that. If you have outdoor plans tonight (such as a concert at Snowden Grove or an outdoor party), be prepared for possible rain and some thunder through at least mid-evening.  If you have outdoor objects that are not tied down and you have the ability to move them in or secure them prior to 2pm, we recommend doing that.

Stay with MWN on our social media channels below for the latest info. We make no guarantees of seeing everything we post to Facebook due to the way Facebook filters posts from Fan Pages like ours. Twitter is always a great option. Of course, we also highly recommend multiple ways of getting severe weather warnings, including the MWN apps with StormWatch+. A one-time upgrade fee for StormWatch+ (in the MWN app) will provide peace of mind with instant weather alerts for the locations you care about.

Erik Proseus
MWN Meteorologist

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Wednesday, June 4, 2014

Northwest flow MCS's result in chances of severe storms

An upper-level high pressure ridge over the southern plains extends eastward over the Mid-South and is suppressing thunderstorm activity, despite warm and humid conditions. However, this ridge will be pushed back to the west slightly the next few days, putting the Mid-South in a weak northwest flow situation. Northwest flow is when the winds at the steering level (around 15-20,000', which dictate the direction storm complexes move) blow from the northwest to the southeast over the area. This is shown pretty well below.

The steering flow for thunderstorm complexes will be from the northwest (thus "northwest flow") the next couple of days. The northwest flow is created by a ridge of high pressure to our southwest and a weak trough to our northeast.

In addition to the northwest flow aloft, a cold front will be oriented east-west just north of the metro tomorrow and just south of the metro on Friday. This front will act like the highway in the sky for complexes of thunderstorms triggered by upper-level disturbances over the Plains to move near or over the region.

A cold front sits over the Mid-South on Thursday evening, creating a "storm track" for systems moving in from the Plains.

These complexes (MCS's, or mesoscale convective systems) can bring rounds of strong to severe thunderstorms, primarily in the form of damaging wind and hail. Northwest flow MCS's are fairly predictable while in their mature stage, but can be very difficult to predict when they will fall apart. They frequently form in the Plains overnight and move east into the Mississippi Valley during the morning hours during summertime northwest flow events.

So, you guessed it, we'll be watching carefully as probably more than one MCS moves near, or into, the Mid-South the next few days. The Storm Prediction Center is also monitoring and forecasting the same thing, thus they have placed the Mid-South and areas upstream in the northwest flow in a Slight Risk zone for potential severe weather on both Thursday and Friday.

There is a Slight Risk of  damaging wind and large hail on Thursday over the Mid-South.

Another Slight Risk exists on Friday in weak northwest flow.

I believe the most likely day for strong storms from an MCS will be Friday and that the threat for Thursday could be just north of the metro, however we have chances of t'storms in the forecast tomorrow as well as Friday (and for that matter right through the weekend). By the way, don't be surprised to see one of these complexes tonight over southern Missouri and Kentucky that moves into northern TN. Although we could get a few showers early Thursday from this system, it should be in a dissipation state as it drops further south towards the metro.

We'll obviously be watching closely and provide updates on our social channels as things come into focus a little better. Just be prepared for the possibility of strong to severe storms the next couple of days as storms roll into the area from the northwest! If you're headed out to the FESJC golf tournament, heed all weather warnings from tournament officials and seek shelter if the sky looks threatening! (And also pack plenty of sunscreen and stay hydrated as heat and humidity will result in afternoon heat indices well above 90.)

One last side note: you can now monitor our severe weather risk and upstream weather systems even easier with the latest update to the MWN mobile app! We've added satellite imagery and SPC severe weather outlooks to MWN for iPhone users with Android users getting the same update within the next day or two. Download the app (or the most recent update if you already have it) by clicking here.

Erik Proseus
MWN Meteorologist

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Monday, June 2, 2014

Golf tournament week means muggy weather and thunderstorms

Some of the best golfers in the world are in town this week and, as usual, Memphis will be serving up a helping of heat, humidity, and scattered thunderstorms with their slabs of ribs!

The upper-level low that lingered over the region late last week and into the weekend and brought rounds of showers and thunderstorms nearly daily has weakened and is lifting out today, taking with it the rain chances. That low (rather a "trough" now) will be replaced by an upper level ridge of high pressure "nosing" into the area the next couple of days. This will mean nearly nil chances of thunderstorms and less cloud cover, which also means temperatures will warm up.

A ridge of high pressure over Texas and northern Mexico will push into the Mid-South the next couple days, suppressing thunderstorms and pushing the storm track to our north.

With low-level moisture still in place, muggy conditions will combine with the heat, resulting in the return of the dreaded heat index! Memphis has so far (officially) avoided reaching 90 degrees in 2014, but that streak comes to an end Wednesday, if not tomorrow. Wednesday's projected high is 93, but the heat index could briefly reach the century mark in the afternoon. This is a hazardous level for those unaccustomed to a Memphis summer, as well as those who are young, old, or not physically well. For the rest of us, a heat index of 105 is considered hazardous, though frequent breaks are still a good idea with temperatures in the 90s.

By Thursday, another cold front moves towards the area from the north. It is being pushed south by low pressure that will move across the Plains tomorrow and into the Ohio Valley Wednesday, bringing with it a good chance of severe weather to that region of the country. As the front sinks into our area Thursday morning, it will weaken considerably as it encounters high pressure and eventually stall out near or just south of the area. It will bring our next chance of thunderstorms on Thursday and, with it hanging around into the early part of the weekend, periods of thunderstorms and showers will be possible (especially during daytime heating) Friday and Saturday as well. If you're headed to the FESJC tournament, plan for muggy and very warm conditions (temps likely near 90) with scattered t'storms.

A cold front will stall out, or become stationary, across the region from Thursday into Saturday, bringing additional chances of rain and t'storms.

By Sunday, models differ slightly but indicate a retreat of that front back to our north. That retreat could reduce rain chances slightly, however it looks to make one more run at us early next week, perhaps pushing all the way through Monday or Tuesday. We'll have more details on that as it gets closer.

In the meantime, if you were complaining about cool weather a few weeks ago, your hot weather is back! If you love humidity, you'll love this week. And if you didn't like all the rain, you get a few dry days. However, if you want cool crisp mornings and pleasant afternoons, hang tight. October is only 5 months away!

View the complete MWN Forecast with details on this week's conditions here (or for mobile users, here). You'll find us on social media at the channels below. And don't forget to download our mobile apps (links below)! An app update bringing new features to MWN is coming to Android imminently and iOS within a week.

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Bartlett changes outdoor warning siren policy

As of June 1, Bartlett officials have modified the city's outdoor siren warning system policy to sound less often during adverse weather, just as Germantown did last fall and Collierville did previously. The primary reason for the change is an increase in complacency caused by perceived overwarning of residents, while still letting Bartlett citizens know when their community is threatened. Emergency Management Officials with the City of Bartlett feel that better public response to tornado warnings can be achieved by only sounding tornado sirens in the City Limits of Bartlett if the city is directly threatened by a storm capable of producing a tornado.

A new siren next to the water tower at Rivercrest Elementary School

As with Germantown and Collierville, Bartlett officials will only sound their outdoor sirens when a Tornado Warning (issued by the National Weather Service) intersects or overlays the Bartlett corporate limits, rather than anytime any portion of Shelby County is warned. Bartlett operates twelve (12) sirens with an effective radius of about 1 mile (or 3.5 square miles coverage) to warn their 58,000+ residents in the city limits. (Read the Press Release describing the change.)

In addition, the updated siren policy states that sirens will be sounded for 3 minutes, followed by a 2 minute pause, with the cycle repeated until the Tornado Warning is no longer in effect. This cycle will prevent the siren's mechanical parts from "burning up" that sometimes occurs when they have been running for tens of minutes with no break.

Background on polygon warnings

In 2007, the National Weather Service ceased warning entire counties for tornadoes, severe thunderstorms, and flash floods. Instead, these warnings are now issued on a storm basis. As we've described before, a polygon is drawn around the area in the path of these events, irrespective of county or state boundaries. However, many warning systems including NOAA Weather Radio still send alerts on a county-wide basis, resulting in larger areas being warned than the NWS intended via their polygon system. County-wide alerting result in "perceived overwarning" because people using those warning systems perceive a threat, when oftentimes they are not actually in the warned area. In the cases of Germantown and Bartlett, software designed by Earth Networks will show the polygon warning and the city limits and make the decision whether or not to sound the sirens straight-forward.

A Tornado Warning polygon issued for parts of Shelby County on January 23, 2012, is an example of one that would NOT require the sounding of Bartlett sirens, as the polygon does not touch the city limits. All other sirens in Shelby County would sound if this warning were issued again.

Caveats of outdoor warning sirens 

We cannot have a discussion of sirens though without talking about the main drawback of sirens. They are called OUTDOOR warning sirens for a reason! Sirens are to alert people outdoors that may be away from a news or weather source that dangerous weather is nearby and to seek additional information. They are not designed to wake you up in the middle of the night or be heard in a well-insulated structure over television, air conditioners, heavy rain or wind.

When indoors or asleep, ALWAYS have other sources of severe weather alerts that will grab your attention, such as our MWN mobile apps with StormWatch+ precision weather alert technology or a NOAA Weather Radio. In fact, everyone should have MULTIPLE ways of receiving life-saving severe weather bulletins, as any one can fail at any time.

Bottom line for those in Bartlett and Germantown - if sirens are sounding, you can expect that it is because your towns are within the tornado warned area and you should seek shelter immediately!  (Sirens in both communities are tested on Saturdays at noon, weather-dependent.)

Additional links/info:
Outdoor Warning Sirens page on
Bartlett Fire Department page on City of Bartlett website
Bartlett Fire Department on Facebook

Outdoor warning sirens series on the MWN Blog:
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