Wednesday, April 2, 2014

Storms, and then more (severe) storms

A setup favoring multiple rounds of thunderstorms is in place across the region as the Mid-South shifts into severe weather season with calendar changing to April.  Let's start with today.

Atmospheric Setup

A couple of ingredients are depicted below, the first (dewpoint) indicates plenty of low-level moisture across the southern Plains and Mid-South streaming in on southerly wind off the Gulf. The second represents deep moisture throughout the atmosphere (not just at the surface) in the form of precipitable water (PW).  PW is at 1.5" which is an indicator that storms that form could be prolific rain-producers, in addition to any severe weather threat.
Surface dewpoint forecast at 3pm this afternoon. The orange area (in the 60s) is plenty of moisture to feed storms.

Precipitable water values at 7pm tonight of nearly 1.5" across the region indicate heavy rain could be a threat, in addition to severe weather.
In addition to these, instability - the fuel for the fire - will be moderate this afternoon until after sunset when it will diminish some.  The lifting mechanism for storms today is a shortwave disturbance, or "fly in the ointment" as we sometimes call it, in the mid levels of the atmosphere. Finally, necessary shear for supporting severe thunderstorms is also present.

This afternoon & evening

As far as what to expect today, scattered thunderstorms will likely form over the Mid-South by mid-afternoon and could quickly become strong to possibly severe. Though the overall coverage of the storms is not expected to be widespread (50/50 chance of rain at any one point), any storms that form will exist in an environment capable of producing damaging wind gusts, hail, and possibly an isolated tornado as low level wind shear is fairly high.  A Slight Risk of severe storms exists today according to the Storm Prediction Center.  Storms should gradually diminish by sunset as heating wanes and the shortwave moves out of the area.

Thursday morning

Early Friday, another disturbance could affect the area, which would bring another round of showers and thunderstorms. Models disagree on the nature of this "fly" but overall severe weather parameters are not impressive. Don't be surprised if rain is falling or thunder rumbling during the morning hours Thursday though.

Thursday afternoon and night

That all changes by Thursday afternoon as severe weather indices ramp back up, shear and instability increase, a dynamic upper-level jet stream moves closer, and a potent trough of low pressure moves in from the west.  These ingredients set the stage for additional thunderstorm development, most likely to our west initially, by Thursday afternoon. Scattered supercell storms could again become severe quickly with the threat continuing into the evening.  Later in the night - in the wee hours Friday morning - a cold front will cross the area, likely bringing a squall line and then an end to the severe weather.

All modes of severe weather are possible on Thursday, including large hail, damaging wind to 70-80 mph, and tornadoes.  Overnight with the cold front, the primary threat would be damaging wind.  Currently, the Storm Prediction Center has the entire region in a Moderate Risk for severe storms Thursday with a 45% probability of severe weather within 25 miles of anyone in the moderate risk area.

A Moderate Risk of severe weather exists Thursday into Thursday night for the entire region.
Probability of severe weather Thursday/Thursday night within 25 miles of you.  Black hatch indicates "significant severe" is possible.
Besides severe weather, flash flooding could also be an issue with Thursday's storms.  With very high water content in the air and widespread convection, perhaps including training storms that affect the same area multiple times, rain amounts of 1-3" (locally higher) are likely.  The map below shows the 3-day precipitation forecast from NOAA, courtesy NWS-Memphis.

Forecast rainfall amounts through Saturday morning. 1-3", locally higher, are expected, causing flash flooding concerns.
With severe weather season on our doorstep, now is the time to prepare for possible severe storms.  The first step is checking out our brand new MWN Significant Weather Outlook below for a quick glance overview of the hazards in the next 3 days. It's also linked off the front page of and updated daily.
In addition, the safety tips below should assist in preparation.  We highly recommend multiple ways of receiving severe weather alerts and one of those should include the mobile app with StormWatch+ added in-app. StormWatch+ will alert you if the locations you choose are going to be in the path of severe weather. It will even wake you up at night - but only if a severe thunderstorm or possible tornado is heading for your location, not the other side of the county.  Check it out via the links below.

We'll continue to update our social media feeds, including live nowcasting during storms, to keep you informed, educated, and safe!  We're also planning a Google+ Hangout tonight at 9pm to further discuss tomorrow's severe weather potential and bring you the latest information.  You can watch live here, where it will also be archived to watch later if you can't join us tonight.

Be prepared, not scared!

Erik Proseus, MWN Meteorologist

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