Wednesday, August 31, 2011

Could "Lee" bring tropical conditions to the Gulf Coast for Labor Day?

I've mentioned on social media a couple of times the strong possibility of a Gulf of Mexico tropical system this Labor Day weekend.  Computer models are not in good agreement with exactly where and how strong, but it appears that the central and or western Gulf Coast could see heavy rain and breezy conditions this weekend as the system moves northwest from the southern Gulf.

Below are a couple of model comparisons - all valid at 7pm Saturday evening - to demonstrate what I am talking about with model spread.  (Note also all 3 models showing Hurricane Katia northeast of the Leeward Islands on the far right edge of the images.) If this system does indeed develop and gets named, it will be "Lee."  The MWN Tropical page will have the latest on this developing system once it becomes a Tropical Depression.
GFS forecast - T.S. Lee off the southeast LA coast

NAM forecast for Saturday, 7pm - T.S. Lee off the TX coast

ECMWF forecast with a weak T.D. Lee near the south TX coast
For weather information for Memphis and the Mid-South, where and when you need it, visit on the web, on your mobile phone, download our iPhone or Android apps, or visit us on Facebook or Twitter.

Thursday, August 25, 2011

Weekend forecast looks nice in the Mid-South, but not in the northeast U.S!

The blog has been quiet of late, owing to many things going on behind the scenes, as well as other obligations that have prevented me from writing.

One of the big things going on behind the scenes is the imminent release of our newest service for smartphone users - StormWatch+. I am very excited about this new service, which will revolutionize the way you receive severe weather information!  If you haven't already downloaded the apps, I encourage you to do so so that you will be ready for the upgrades when they are released.  The iPhone update should be ready next week and then we'll get to work on porting it to Android.  You can download the apps by searching for "" in the App Store, iTunes, or Android Market or by clicking on the links on

So, back to the weather at hand... A cold front is passing through the region today with little fanfare. However, we will begin to see a marked difference in one thing with this front - the humidity!  By tomorrow afternoon, even though temperatures will still be near 90, the humidity will bottom out near 40%, which will make it feel much more comfortable. The lower humidity values will also allow overnight temperatures to drop down into the 60s for the next few nights everywhere except perhaps on the concrete of the big city. Pleasantly warm high pressure that takes hold behind the front will hang on through the weekend and right into next weekend thanks to Hurricane Irene moving up the East Coast and keeping weather systems over our part of the country at bay for a few days.

Hurricane Irene over the Bahamas as seen by Astronaut Ron Garan aboard the International Space Station
Speaking of Irene, I've been closely following the model tracks and forecast intensity of the storm as it moved into and through the Bahamas and now begins a beeline up the eastern seaboard.  Given the current track and models trends, my biggest concern right now is for the major metros of the northeast which have not dealt with a system like this in decades.  Besides significant wind (currently category 3 and expected to remain a hurricane right into the NYC metro) and torrential rainfall that could inundate sewer systems in large cities and cause flash flooding, storm surge could be particularly dangerous for coastal areas from the Delmarva up to Massachusetts. For a great read on the potential effects of this storm on the northeastern U.S., please check out Weather Underground's Tropical expert Dr. Jeff Master's blog post from earlier today.  Other links that are worth checking out:

MWN Tropical - everything the rubber-necker from Memphis needs in one concise package - the best interactive presentation on the tropical web
Crown Weather's Irene page - extremely comprehensive, no stone left unturned - complete coverage by the weather authorities

That's it for today. Thanks for reading and enjoy the great weather this weekend!

For weather information for Memphis and the Mid-South, where and when you need it, visit on the web, on your mobile phone, download our iPhone or Android apps, or visit us on Facebook or Twitter.

Friday, August 19, 2011

Keeping an eye on Mid-South storms with StormWatch and StormWatch+


On August 14, re-branded and expanded it's severe weather alerting services under the name "StormWatch." Previously, visitors could sign up for e-mail weather alerts for seven Memphis-area counties (Shelby, Fayette, and Tipton in TN; Crittenden, AR; and DeSoto, Marshall, and Tunica in MS), as well as receive severe weather alerts on Twitter for Shelby County only (@shelbyalerts).

With the official release of StormWatch, one additional county has been added to the coverage area ( Tate County, MS) with e-mail alerts available, and Twitter feeds have been set up for all eight metro counties - @fayettealerts, @tiptonalerts, @desotoalerts, @marshallalerts, @tunicaalerts, @tatealerts, and @crittendenalert (no trailing 's'), in addition to @shelbyalerts. This expansion now allows any of the over 1.25 million residents of the Memphis metro area to receive e-mail or Twitter alerts when severe weather arrives. See map below of the StormWatch coverage area.

StormWatch coverage area - eight Memphis metro counties

StormWatch+ is a unique service that sends alerts to smartphone users whenever severe weather threatens their specific location. Combining storm-based warnings issued by the National Weather Service (referred to as polygons) and a user’s precise location, alerts are sent only if the location registered is directly threatened, not if the storm is 20 miles away or on the other side of the county.

In 2007, the National Weather Service began issuing Tornado, Severe Thunderstorm, and Flash Flood Warnings as storm-based warning polygons (see images below), alerting only the areas in the path of the storm rather than entire counties. However, for various reasons, and in almost all cases, outdoor warning sirens still sound over the entire county even if the storm is only tracking only a small portion of that county. This overwarns the public and increases the perceived false alarm rate, thereby reducing the siren's effectiveness. It creates a "Boy Who Cried Wolf" scenario. StormWatch+ keeps residents from becoming siren-weary by only warning those directly in the path of the storm. If sirens are going off, but the StormWatch+ user did not receive an alert for their location, that person is likely not in harm's way.

StormWatch+ will be released as an in-app purchasable upgrade for those with the MWN app for iPhone by the end of the month! The technology will then be added to the MWN Android app (likely in September). For less than the cost of a combo meal at your favorite fast food restaurant, you can have peace of mind for an entire year!

Features of StormWatch+:
  • Push notifications in the event of: 
    • Tornado Watches and Warnings 
    • Severe Thunderstorm Watches and Warnings 
    • Flash Flood Watches and Warnings 
    • Winter Storm Watches, Warnings, and Advisories 
  • Notifications sent even if app is not running and device is not in use 
  • Audio AND voice alert when watches/warnings are received 
  • Auto-updating list of active alerts, which “roll off” when expired or canceled 
  • Registration of up to two locations anywhere in the U.S., which can be changed at any time and can be set using: 
    • Current GPS location 
    • City, ST 
    • Postal address 
  • Access to full warning text of the alerts 
  • Google map showing warning area and your location 
  • Quiet time – to temporarily stop alerts during a specified time of day 
  • Status button to disable notifications (i.e., vacation stop) 
  • Regional map showing all active Mid-South alerts 
  • Free re-install if the app is deleted
For more information on StormWatch and StormWatch+, visit the MWN StormWatch web page.

For weather information for Memphis and the Mid-South, where and when you need it, visit on the web, on your mobile phone, download our iPhone or Android apps, or visit us on Facebook or Twitter.

Thursday, August 18, 2011

Another heat wave - will it be the last of the summer?

As the calendar gets into the latter half of August, many are wondering just how much summer we have left in the Mid-South.  Well, by the numbers, beginning tomorrow, the average high temperature for Memphis starts slowly falling back from it's high for the year.  Since July 5, our average daily high temperature has been 92 degrees. That average drops to 91 tomorrow and by the first of September will be falling into the 80s - a sign of cooler weather to come.

In addition, I include the 8-14 day (week 2) temperature and precipitation forecast from the Climate Prediction Center in the MWN Forecast daily. For (seemingly) forever, it has indicated above to well above normal temperatures expected in that week 2 period.  This week, we are starting to see a general trend towards slightly below normal temperatures for the period beginning next week.  That is also promising.

So what about the actual forecast?  Are there any signs that we mid 90s to 100 degree heat is truly behind us? Well, the next several days (through the weekend at least), very warm high pressure continues to control the weather pattern in the Mid-South.  The only reason we wouldn't hit the mid 90s daily through the weekend will be more days like today - where abundant cloud cover and more than minimal rain chances keep the sun from beating down on us for 10 hours-plus. With nearly full sun, the atmosphere favors mid 90s for the next several days.  Also, humidity is fairly high (not excessive, but certainly noticeable), so heat indices will be in the upper 90s to lower 100s. There will be small rain chances in the forecast through early next week, so perhaps some of those will become more definite and provide some heat relief.

Once we get into the early part of next week, the models are indicating we could see a cooler pattern begin to take shape.  The exact timing of any frontal passage that would mark the start of that pattern change is not certain, but we'll be trying to pinpoint that better in the next few days.  In the meantime, know that with September not too far away, the threat of Heat Advisories and mid 90s temperatures begins to decline and we'll be headed towards fall!  Hang in there!

For weather information for Memphis and the Mid-South, where and when you need it, visit on the web, on your mobile phone, download our iPhone or Android apps, or visit us on Facebook or Twitter.

Friday, August 12, 2011

Back to average, and then below?

Long-suffering Memphians ready for a break from summer heat finally have a forecast they can smile about! Thanks to a retreat and slight weakening of the massive high pressure centered over the southern Plains, the Mid-South has been positioned in "northwest flow" - where the upper air flow is from northwest to southeast - that has brought some relief from the heat of June and July.  Though not everyone has benefited from scattered showers and thunderstorms, the closer-to-average temperatures have been a welcome respite.

As we head into the weekend, a cold front will move into and completely THROUGH the Mid-South on Saturday.  It's been a long time since we've had a front that actually moves far enough south to usher in some more forgiving air that will be less humid and cooler, but that is what this one brings. Along the front, expect scattered thunderstorms that could bring some gusty wind and heavy downpours on Saturday.  By Sunday, the humidity will be dropping and temperatures could struggle to reach 90 under full sun.  The same is expected for early next week.  Though temperatures will slowly rise a degree or two each day next week, humidity will still be decent with dewpoints in the 60s. The best part of lower dewpoints is the morning low temperatures.  Everyone (including in the city) will see lows in the 60s to start next week.


For weather information for Memphis and the Mid-South, where and when you need it, visit on the web, on your mobile phone, download our iPhone or Android apps, or visit us on Facebook or Twitter.

Tuesday, August 9, 2011

Well-documented pair of gravity waves move over the Memphis metro

A set of gravity waves (click link for a description of gravity waves) trained over the Memphis area between 7:00-8:00 this morning. The waves were visible on radar imagery as well as visually - as a pair of linear cloud features that moved quickly by from north to south at about 1,000 feet.

Below is a short video I took of the waves passing over Bartlett (with narration), as well as several photos submitted by Twitter and Facebook followers.  Thanks to all those who submitted their pics!

For weather information for Memphis and the Mid-South, where and when you need it, visit on the web, on your mobile phone, download our iPhone or Android apps, or visit us on Facebook or Twitter.

Sunday, August 7, 2011

Chance of evening storms "under the ridge," then a pattern shift means cooler weather

Massive high pressure has maintained a grip on Mid-South weather for several days, bringing nearly daily chances of eclipsing the 100 degree mark. A respite on Friday was caused by thunderstorms that managed to move under the ridge thanks to a disturbance in the mid levels of the atmosphere.

After nearly reaching 100 again today, another one of these disturbances is moving slowly across AR and causing scattered storms over the central part of the state. This impulse should move just south of the metro area this evening, but will bring a chance of t'storms, mainly over northwest MS and east-central AR, between 6-11pm.

As we head into the new work week and the first week of school for many area children, the strong ridge of high pressure will begin to retrograde to the west, putting the Mid-South in a northwest flow.  This means that the upper level wind will be flowing from northwest to southeast over the area.  In the summertime, this pattern lends itself to the possibility of repeated rounds of thunderstorms, particularly at night or in the morning hours.  These rounds of thunderstorms are hard to time more than a day or two in advance, so for now the MWN Forecast includes a daily chance of thunderstorms this week as the pattern could stick around for a while.

The bad part of this pattern is that, depending on the timing of the storms, they could bring chances of damaging wind and hail. The good news, other than the rain chances, is that it will also mean reduced high temperatures. So, the end of the upper 90s to lower 100s is within sight.  An Excessive Heat Warning remains in effect through Monday evening with heat indices near 110 again Monday.  Excessive Heat Warnings are not anticipated for the remainder of the week after Monday.

For weather information for Memphis and the Mid-South, where and when you need it, visit on the web, on your mobile phone, download our iPhone or Android apps, or visit us on Facebook or Twitter.

Friday, August 5, 2011

July 2011 Climate Data and MWN Forecast Accuracy

An extremely hot June continued into July with the June-July period averaging 84.9 degrees - tied with 1980 as the warmest June-July on record in Memphis and was just 0.2 degrees warmer than the same period in 2010. Despite the very hot temperatures, only one record was set - the maximum record low was tied on July 12 at 82 degrees.  Precipitation was below average for the month.

Memphis International Airport, Memphis, TN

The average July temperature was 86.0 degrees, which was 3.5 degrees above normal. The average high temperature was 94.9 degrees and the average low was 77.2. The coolest temperature of the month was 72 degrees on the 1st and the highest temperature was 99 degrees on the 11th, 12th, and 31st.

Precipitation for the month of July totaled 2.95", which was 1.27" below average. There were 9 days with measurable rainfall; 3 of those measured more than one-half inch.  The greatest 24-hour total was 0.82" on the 24th-25th. The peak wind gust was 51 mph in a thunderstorm on the 3rd with an average wind speed for the month of 5.6 mph. Click here for a daily statistical recap for Memphis International Airport.

Cirrus Weather Solutions, Bartlett, TN

The average temperature for July at Cirrus Weather Solutions in north Bartlett was 83.8 degrees with a maximum of 100.4 degrees on the 11th and 12th and a minimum of 64.5 degrees on the 1st.  July precipitation ended below normal with a total of 3.07". A co-located manual gauge used for the CoCoRaHS program measured 3.13". The peak wind gust was 20 mph on the 21st. Average relative humidity was a high 72%. Click here for a daily recap on

MWN Forecast Accuracy

For the month of July, the average temperature error in all MWN temperature forecasts was 1.63 degrees, lower than all compared computer models and our most accurate month since August 2010. Nearly 80% of the MWN temperature forecasts for the month were within 2 degrees of the actual temperature. MWN's forecasts extend out five periods (or 2.5 days). For dewpoint accuracy, the MWN forecast beat all data sources, averaging 1.65 degrees error and falling within 2 degrees of the actual dewpoint 82% of the time. Historical accuracy statistics can be found here.

For weather information for Memphis and the Mid-South, where and when you need it, visit on the web, on your mobile phone, download our iPhone or Android apps, or visit us on Facebook or Twitter.

Wednesday, August 3, 2011

Oppressive heat envelopes the Mid-South - records fall

Very strong high pressure built in from the west, where temperatures have routinely been above 100 for days to even weeks.  Even a fair amount of humidity (dewpoints in the low to mid 70s), which would typically be a deterrent to extreme heat, could not keep temperatures from reaching the mid 100s area-wide.  In fact, the combination of heat and humidity resulted in heat indices well into the danger category, topping out between 115-120 degrees.

The following temperature records were set today:

Memphis International Airport, TN - 106 degrees. This marks a daily record (previously 103 set last year) and ties for the 4th hottest day on record.  The all-time record in Memphis is 108, set July 13, 1980.

NWS Office, Germantown, TN - 105 degrees. This marks a new daily record, previously 103 set last year.

Cirrus Weather Solutions, Bartlett, TN - 105.1 degrees. This is the second hottest temperature recorded in Bartlett since WXLIVE was installed in 2005, trailing only August 15, 2007 (106.0 degrees).

Jackson McKellar-Sipes Airport, TN - 105 degrees. This marks a daily record (previously 102 set in 1987) and ties for the 5th hottest day on record.  The all-time record in Jackson is 107, set July 27, 1952.

Tupelo Regional Airport, MS - 106 degrees. This marks a daily record (previously 102 set in 2006) and ties for the 8th hottest day on record.  The all-time record in Tupelo is 109, set July 29, 1930.

Jonesboro, AR - 107 degrees. The daily record was missed by 2 degrees.  The all-time high temperature at Jonesboro is 116.

Little Rock Adams Field, AR - 114 degrees. This sets both a daily record (previously 107 set last year) and a new all-time record for Little Rock.  The previous all-time high was 112 set July 31, 1986.

North Little Rock, AR - 111 degrees. This marks a daily record (previously 104 set last year) and ties the all-time record set August 30, 2000. 

The very hot start to August is on the heels of the warmest June-July period on record.  The average temperature for June-July was 84.9 degrees, which tied 1980 for the top spot.

The MWN Forecast calls for a slight reduction in the heat, but more humidity Thursday and Friday as a cold front moves into the region but stops short of passing all the way through.  Moisture typically "pools" ahead of these summer front, thereby increasing humidity and making it feel worse.  Expect heat indices of 115 again on Thursday and about 110 on Friday.  Excessive Heat Warnings continue through Friday morning and could be extended into the weekend.  Please exercise extreme caution in the oppressive heat and follow the safety tips we have published on this blog.

Metro area temperatures as of mid-afternoon, August 3, 2011
For weather information for Memphis and the Mid-South, where and when you need it, visit on the web, on your mobile phone, download our iPhone or Android apps, or visit us on Facebook or Twitter.

Tuesday, August 2, 2011

How many ways is there to say "it's hot??"

Do all of the recent Heat Advisories, Excessive Heat Watches, and Excessive Heat Warnings have you confused and wondering why we can't just say "IT'S HOT"??  I'll get to that in a minute.

First a few stats about the Memphis summer of 2011:

  • Since May 28, there have only been 5 days that the temperature has NOT reached at least 90.  In July, we reached 90 every day except the 7th (it was 86).
  • So far, there have been 7 days in which the low has not dropped below 80.
  • The average temperature for June-July 2011 is 84.9 degrees, which ties 1980 for the warmest June-July period on record.  Yes, THAT 1980!
So, about all those watches and warnings.  What do they mean and why does the NWS issue one over another?  The following criteria are used by the Memphis NWS office, as well as many other offices that have not adopted their own criteria (which they are allowed to do).

Heat Advisory - Generally issued when the heat index will be 105-109 degrees for at least a couple of hours during the day and the overnight temperature will remain at or above 80 in the city (many times 70s are experienced in the suburbs).  Issued when the criteria will be met within 12-36 hours.

Excessive Heat Watch - Issued when the heat index is forecast to be at or above 110 degrees within 24-72 hours.

Excessive Heat Warning - Issued when the heat index is expected to reach 110+ degrees and overnight temperatures will remain above 75 degrees in the upcoming 12-48 hours.

So, the main threshold to watch for is the 110-degree heat index.  An Excessive Heat Watch may be issued 3 days in advance of a forecast heat index of 110.  Then, the day before the event, if the heat index is expected to only reach 105-109, a Heat Advisory will replace the Watch.  If the heat index is still expected to hit 110, the Warning will be issued instead.  An Advisory is basically a "toned-down" Warning.  A Watch is issued for longer lead times (similar to a Tornado Watch, which means conditions are favorable, versus a Warning, which means the event is imminent).

Hopefully this helps sort out the plethora of headlines the NWS has used during this heat wave.  By the way, the Memphis office has put together a well-done summary of all of their watch and warning products.  You can find it here: Headlines Issued by NWS-Memphis.

For weather information for Memphis and the Mid-South, where and when you need it, visit on the web, on your mobile phone, download our iPhone or Android apps, or visit us on Facebook or Twitter.