Sunday, March 18, 2018

Volatile weather may miss Memphis, but Monday storms still expected

A potent low pressure system will pass just north of Memphis on Monday, but the timing and track of the system will likely result in muted effects for the area as compared to places to our east and south.

Sunday / Sunday night

Before that though, a cold front that slid south through the metro last evening has pushed our beautiful weather from Saturday southward, with a healthy mixture of clouds and sun dominating your Sunday and temperatures remaining about 15 degrees cooler than yesterday. As the aforementioned low pressure starts to energize in the southern plains, a "scout" upper level disturbance ahead of it, combined with yesterday's cold front returning north as a warm front, will result in evening showers tonight and a chance of rain overnight.

A strong upper level low pressure center will move from the KS/OK border at midnight tonight eastward to near Louisville by midnight Monday night. That low, and an accompanying surface low, will generate favorable conditions for severe weather along its southern flank. (NAM model, PivotalWeather)

Monday storms

By Monday morning, wind will shift to the south, a sure sign that the warm front will have moved to our north - but just barely. The low pressure to our west will be moving into the Ozarks, riding the fast train towards Nashville, and triggering scattered thunderstorms ahead of it. Accompanying the low, very strong upper level wind will result in high amounts of wind shear - one ingredient necessary in the production of severe storms. Another key ingredient, instability, will be less than ideal though, given the timing of the storms during the morning to mid-day hours, before the warm sector of the storm has a chance to really boil over. Thus, the lift generated by the approaching low will result in scattered thunderstorms, but the lack of appreciable instability (the main "fuel" for storms) will likely be insufficient to take advantage of the high amounts of shear over the area.

The result: scattered storms for the Memphis area during the post-morning rush hour through lunchtime period (about 9am-2pm) on Monday that could contain a few strong wind gusts and small hail, but likely not producers of damaging wind or hail, nor tornadoes. We are in a Marginal Risk of severe weather (level 1 on the 5-point scale) for Monday, with areas not far to our east a level higher and under a Slight Risk.

An Enhanced Risk of severe weather exists Monday for middle TN and north MS. The Memphis metro is on the edge of a Marginal Risk, category 1 on the 5-point scale. (SPC)

Meanwhile, to our east...

As the low moves east however, it will encounter an even warmer airmass with strong wind shear that could be capable of very large hail, damaging wind gusts, and even a few tornadoes. The most likely area for that to occur is from southern middle TN into north AL and northwest GA during the afternoon and evening hours, where an Enhanced Risk of severe weather is currently forecast (level 3 on the scale). In other words, the nearby track of the low earlier in the day will likely keep the Memphis metro from being under as volatile an airmass as areas to our east.

The Supercell Composite index, a measure of the capability of the atmosphere to produce supercells capable of severe storms, is maximized near the TN/AL border at mid-afternoon (4pm) according to the high-resolution NAM3 model. This index remains very low, mainly south of I-40, during the morning hours when we are most likely to see thunderstorms. (PivotalWeather)
As those areas to our east remain weather-aware, we're likely to see some afternoon sunshine that allows temperatures to rise into the mid 70s again. Gusty southwest wind is also expected as the low passes just to our north.

Remainder of the week

Behind this system, clouds wrap around back into the Mid-South as much cooler air filters back in on northerly wind. An embedded upper level system wrapping around the departed low will bring scattered showers on Tuesday with temperatures about 20° cooler than Monday, or in the mid 50s. A couple of cool mornings are expected with lows in the upper 30s Wednesday and Thursday mornings, but highs will slowly climb back into the mid 60s by week's end. Southerly flow re-establishes itself by Friday with more rain chances arriving in time for the weekend.

Stay in touch with our weather updates tomorrow via our social media feeds and mobile app and prepare for a few more chilly days to interrupt the blossoming of spring in Memphis!

Erik Proseus
MWN Meteorologist

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Sunday, March 11, 2018

February 2018 Climate Data for Memphis, TN

February Climate Recap

With a wet pattern dominating the weather in February, temperatures also were well above average due to increased moisture content in the atmosphere. For the month, the average temperature was 4.3 degrees above average, which ranks in the 88th percentile for warmth or 17th warmest February on record. High and low temperatures both averaged 4.3 degrees above average, so neither contributed more to the daily anomaly than the other.Three daily records were set or tied during the latter half of the month. Only six days saw average temperatures more than 2 degrees below the climatological average.

Precipitation was the big story for the month with three days recording near or more than two inches of rain, including 1.99" on the 10th, 2.82" on the 21st, and 3.12" on the 28th. Overall, two-thirds of the days in February had measurable rain with an average cloud cover for the month of 80%. With all of the rain came some periods of minor flash flooding, although river flooding at the end of the month into the first few days of June was the bigger impact as the Mississippi River climbed above flood stage and local tributaries such as the Loosahatchie and Wolf Rivers also overflowed their banks.
February 2018 was the in the top 3 wettest on record for ten states that drain into the Ohio or Mississippi Rivers, resulting in flooding late in the month into early March in both basins, including the Mississippi River at Memphis. (NOAA/CPC)

For the months comprising meteorological winter (November 2017-January 2018), the average temperature was 43.0 degrees, which is 0.4 degrees below the long-term average. Precipitation totaled 24.95", which was 10.84" above average and ranks seventh wettest on record.

Memphis International Airport, Memphis, TN

Average temperature: 49.8 degrees (4.3 degrees above average)
Average high temperature: 59.0 degrees (4.3 degrees above average)
Average low temperature: 40.6 degrees (4.3 degrees above average)
Warmest temperature: 77 degrees (19th, 20th)
Coolest temperature: 24 degrees (2nd, 5th)
Heating Degrees Days: 433 (115 below average)
Cooling Degree Days: 14 (12 above average)
Records set or tied: February 19th: 77° (tied record high); February 15th: 65° (record warmest low); February 20th: 66° (record warmest low)
Comments: February 2018 was the 17th warmest on record.

Monthly total: 13.43" (9.04" above average)
Days with measurable precipitation: 19
Wettest 24-hour period: 3.12" (28th)
Snowfall: 0.0" (1.3" below average)
Records set or tied: February 28th: 3.12" (daily record set); February 1-28: 13.43" (monthly record set)
Comments: Precipitation for the month set the all-time February record. Nine days recorded more than 0.5" and 2 days saw more than an inch fall.

Peak wind: West/41 mph (24th)
Average wind: 9.5 mph
Average relative humidity: 75%
Average sky cover: 80%

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

Cirrus Weather Solutions /, Bartlett, TN

Average temperature: 48.7 degrees
Average high temperature: 58.8 degrees
Average low temperature: 38.9 degrees
Warmest temperature: 78.6 degrees (19th)
Coolest temperature: 21.7 degrees (8th)
Comments: None

Monthly total: 11.79" (automated rain gauge), 13.75" (manual CoCoRaHS rain gauge)
Days with measurable precipitation: 19
Wettest date: 2.56" (28th) (via automated gauge)
Snowfall: None
Comments: Four days recorded more than 1" of rain, while two days have more than 2" of rain.

Peak wind: Northwest/29 mph (4th)
Average relative humidity: 80%
Average barometric pressure: 30.20 in. Hg

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

MWN Forecast Accuracy

MWN average temperature error: 2.84 degrees
MWN forecast temperatures within 2 degrees of actual: 56%
MWN average dewpoint error: 3.01 degrees
MWN forecast dewpoints within 2 degrees of actual: 49%

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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Friday, March 9, 2018

Spring break arrives - wish the weather were better!

The past couple of days have been cold relatively speaking - compared to both early March averages and recent history - but that trend ends for a few days as the pattern turns wet once again.

As high pressure shifts east, wind has turned around to the south and will be quite breezy today with afternoon gusts to 25 mph. However, that will help to push the mercury back into the 60s despite more cloud cover than previous days. Heading into the overnight, the next system to our west starts to organize and the southerly flow (resulting in increased moisture from the Gulf) brings a chance of showers before dawn Saturday morning.

With high pressure along the southeast coast, southerly flow over the Mid-South means increasing moisture and chances of rain. Low pressure over west TX will move east, grazing just south of the metro Saturday night. Surface map valid midnight tonight. (NWS)

Our computer models that are normally pretty reliable within 3-4 days have been struggling with the pattern for the first weekend of Spring Break. There are still some differences, but all now forecast a weak low pressure system to move by just south of Memphis Saturday night. The differences lie in the strength of the low and placement of heavier rainfall. While Saturday looks to feature scattered showers (likely not all-day rain), overnight Saturday night likely will be the wettest period of the weekend. The axis of heaviest precipitation will likely be across north MS/AL, where over 2" of rain could fall this weekend. In the Memphis area, an inch would not be unexpected and also would not result in additional flooding issues given the recent dry days of late, allowing the ground to dry some and the smaller rivers/creeks to return to normal levels. With the track of the low just to our south, we can't rule out a few thunderstorms, but most will be to our south and southwest, as will any chances of severe weather. Temperatures should also remain mild with highs Saturday in the lower 60s.

The severe weather outlook for Saturday and Saturday night shows that a few thunderstorms will be possible in the metro (lightest green), but the severe weather chances (darker green to yellow) will remain south of the area. (SPC)
As the low departs Sunday, "backlash" cloudiness and scattered showers will be possible as an upper level low pushes the system to the east, but brings those rain chances as well. Temperatures will also remain in the 50s all day and a north wind will kick up quite a bit by afternoon. Overall, not a real promising way to start an extended break for most of the school kids in the area!

Total precipitation through Sunday evening as forecast by the NWS. It shows an inch or a little more in the Memphis area, while I believe we could trend down a bit more and end up with a little less than that. Saturday night appears to be the wettest part of the weekend, but neither Saturday or Sunday will likely be completely dry. (WxBell)

If you don't like the rain on Spring Break, then there is good news - the rest of the week looks to be dry. However... cooler air arrives again, lasting much of the week. Lows will be back down into the 30s with highs only in the 50s from Monday through Thursday. We should start to see a warming trend heading into the final weekend of the break, though it could also become wet again. Sunny and 70° just isn't in the forecast quite yet - but we'll be there soon enough! Early March weather always tends to feature a few surprises as the seasons really start to change.

Erik Proseus
MWN Meteorologist

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MWN is a NOAA Weather Ready Nation Ambassador Meteorologist Erik Proseus is an NWA Digital Seal Holder