Friday, January 10, 2020

Severe storms likely early Saturday morning - what to expect

[ Updated at 5:00PM - timing of storms, increasing flooding risk, updated graphics ]

A surface low pressure system with a connecting cold front is situated over north central Texas and southern Oklahoma. This low will deepen and dig toward Arkansas Friday night before it begins lifting out toward the northeast. Most of the models agree that the low will move right up the Mississippi River. This may serve to prolong the period of thunderstorms some, as the line will not move east as fast while the low pressure center is moving parallel to it. 

Detailed outlook for the metro

Thanks to a strong surface high pressure system situated to our east, winds are fairly strong and from the south. In fact, a  Wind Advisory has been posted for the entire area as gusts could reach 25-30 mph this afternoon and 30-40 mph tonight. This will allow abundant moisture from the Gulf of Mexico to reach the Mid-South. With abundant moisture and a strong front to lift the moist air, a line of convective storms will form ahead of the cold front in eastern Texas and propagate through northern Louisiana and Arkansas before crossing the Mississippi River into western Tennessee and Mississippi. The main concern with this event will be the squall line as most models show little in the way of discrete storms ahead of the line. Models have focused in on a potential severe weather window of 3:00-9:00am Saturday morning.




The high-resolution NAM3 model forecast radar valid from midnight tonight through 6pm Saturday gives us an idea of what to expect as the line crosses Memphis proper in the 5-9am window. (WeatherModels.com)


Flooding threat

Over the past couple weeks, we have received 1.5-3" inches of rain across the area. This means our ground is pretty wet and a Flash Flood Watch has been issued due to the expectation of additional heavy rain. Ahead of the line, showers are possible, which will only aid in saturating the ground. However, this system may produce 2-3" of rainfall by mid-morning Saturday. A significant concern with this event will be flooding. Low lying areas should be avoided or monitored closely to ensure your safety. It is especially important that you exercise extreme caution when driving at night in or after heavy rain. The condition of the roadways is difficult to gauge in the dark! Remember: Turn Around, Don’t Drown!

Straight-line wind threat

The wind energy associated with this system is very significant. With surface wind gusts over 30 mph and wind of 80-90 mph at just 5,000' above us, the stage is set for a potential damaging event as wind with this system could reach hurricane strength in spots. That means we may be seeing surface wind on the magnitude of 70+ mph! A Severe Thunderstorm Warning with winds this high should be taken as seriously as a Tornado Warning! Take action and take cover in an interior room on the lowest floor, away from windows, if a Severe Thunderstorm Warning is issued. With saturated ground, it won’t take much for trees or possibly power poles to be knocked over, so make sure to charge all devices are charging overnight to ensure you can still receive weather updates and other information if the power goes out.

Tornado threat

The tornado threat with this event appears to be limited to a low potential for spin-ups, however these cannot be ruled out. Higher tornado threats exist to our southwest in southern AR, northern Louisiana, and western Mississippi. However, with storms moving at highway speeds due to the magnitude of the wind, even a spin-up tornado can move very quickly. Be ready to act if a warning is issued!


We also highly recommend you have multiple ways of receiving warning information. That includes commercial TV and radio, NOAA Weather Radio, Wireless Emergency Alerts on your cell phone, as well as a configurable mobile warning app like SW+ Alerts in the MemphisWeather.net app. SW+ Alerts is a low-cost, highly-customizable method of receiving warnings for specific locations you program in. It will even wake you up for the most severe warnings overnight! Learn more and download the app at App.MemphisWeather.net.



After the storm

Despite all the excitement Saturday morning, Saturday afternoon looks much better! There may be trees down or power outages, but weather conditions themselves improve. A few straggling showers are possible and it will remain breezy, but clouds will begin to decrease into the evening hours with temperatures hanging out in the mid 50s during the afternoon before falling into the 30s overnight. 

Paige Davide
MWN Meteorologist Intern

Erik Proseus
MWN Meteorologist

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Follow MWN on Facebook and Twitter for routine updates and the latest info!
Complete MWN Forecast: MemphisWeather.net on the mobile web or via the MWN mobile app
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MWN is a NOAA Weather Ready Nation Ambassador Meteorologist Erik Proseus is an NWA Digital Seal Holder

Saturday, January 4, 2020

December 2019 Climate Data for Memphis, TN

December Climate Recap

Following one of the colder Novembers on record, the script flipped in December as a major pattern change over the U.S. resulted in very warm temperatures across the eastern 2/3 of the country, an area which had been well below average in November. The mid-month period featured relatively "average" temperatures, and even a couple of very minor frozen precipitation events. However, warmth to start, and especially end, the month set the tone. In fact, the week surrounding Christmas Day (Dec. 23-29) was one of the warmest such weeks on record. Overall, the month ended more than four degrees above average.

The U.S. temperature anomaly (departure from normal) for the month of December shows well above normal temperatures across much of the nation east of the Rocky Mountains, while predominantly below average temperatures were present in the western U.S. The pattern was nearly a completely reversal of November temperatures. (WeatherBell)
December precipitation typically averages just under six inches, being one of the wetter months of the year climatologically. In 2019, rainfall was fairly well spread out with no prolonged wet or dry periods. For the month, just over four inches fell. Thunderstorms occurred on the 6th and 16th, but no severe weather was reported, nor warnings issued. Heavy rain on the 16th prompted a Flood Advisory for the southern portion of the greater metro.

There were two minor winter precipitation events, both on the backside of rain events, on the 10th and 17th. Only a trace or sleet or snow was recorded on each day. The most impact-ful "cold weather" event though was a coating of black ice on elevated roadways the morning of the 18th, resulting in dozens of crashes and major bridges and overpasses shutting down until the ice melted. More on this heavy frost/black ice event can be found in this blog post.

Google traffic data from the morning of the 18th when black ice caused major issues city-wide.


Memphis International Airport, Memphis, TN


Temperature
Average temperature: 47.7 degrees (4.1 degrees above average)
Average high temperature: 56.7 degrees (4.6 degrees above average)
Average low temperature: 38.8 degrees (3.7 degrees above average)
Warmest temperature: 71 degrees (28th)
Coolest temperature: 26 degrees (11th, 18th)
Heating Degrees Days: 526 (139 below average)
Cooling Degree Days: 0 (2 below average)
Records set or tied: None.
Comments: Nine days recorded a low temperature at or below freezing, 3.4 days less than average for the month.

Precipitation
Monthly total: 4.04" (1.70" below average)
Days with measurable precipitation: 7 (2.7 days below average)
Wettest 24-hour period: 1.42" (16th)
Snowfall: Trace
Records set or tied: Record snowfall tied - trace (10th).
Comments: Two days had rainfall exceeding one inch. A trace of snow and sleet fell on the 10th and snow flurries fell on the 17th.

Miscellaneous
Peak wind: West/25 mph (29th)
Average wind: 7.0 mph
Average relative humidity: 73%
Average sky cover: 60%

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

Cirrus Weather Solutions / MemphisWeather.net, Bartlett, TN


Temperature
Average temperature: 46.1 degrees
Average high temperature: 56.0 degrees
Average low temperature: 36.8 degrees
Warmest temperature: 70.1 degrees (25th)
Coolest temperature: 23.8 degrees (19th)
Comments: None

Precipitation
Monthly total: 3.69" (automated rain gauge), 3.99" (manual CoCoRaHS rain gauge)
Days with measurable precipitation: 11
Wettest date: 1.43" (29th) (via automated gauge)
Snowfall: Trace
Comments: A bit of sleet and snow fell on the 10th and snow flurries fell on the 17th.

Miscellaneous
Peak wind: West/32 mph (29th)
Average relative humidity: 81%
Average barometric pressure: 30.08 in. Hg
Comments: None

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

MWN Forecast Accuracy

MWN average temperature error: 2.41 degrees
MWN forecast temperatures within 2 degrees of actual: 67%
MWN average dewpoint error: 2.50 degrees
MWN forecast dewpoints within 2 degrees of actual: 61%

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

Climate Outlook - January 2020

The January climate outlook for the United States from the Climate Prediction Center is shown below. Above average temperatures are forecast for the southeast, spreading north towards the Ohio Valley and west into the Southern Plains. Below average temperatures are expected in the western U.S. Odds favor above average temperatures for Memphis, at 43% (versus only a 24% chance of below average temperatures). Memphis averages 41.2 degrees for the month.



Wetter than normal weather is expected for the Ohio and Tennessee Valleys into the Mid-Atlantic and southeast U.S., as well as the High Plains. For Memphis, odds favor above average rainfall (43% chance), which historically averages nearly four inches.

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Follow MWN on Facebook and Twitter for routine updates and the latest info!
Complete MWN Forecast: MemphisWeather.net on the mobile web or via the MWN mobile app
Download our iPhone or Android apps, featuring StormWatch+ severe weather alerts!
MWN is a NOAA Weather Ready Nation Ambassador Meteorologist Erik Proseus is an NWA Digital Seal Holder