Saturday, September 24, 2011

Possible severe weather threat on Sunday

It's been a while since the Mid-South was positioned in a Slight Risk of severe weather by the Storm Prediction Center.  However, that is exactly what we find ourselves dealing with on Sunday.

An unseasonably strong upper-level low pressure system is retrograding (moving east to west) from the western Great Lakes towards the Corn Belt over the next 24 hours (see upper left panel in the graphic below).  Rotating around the upper low are a series of disturbances, one of which brought a band of light showers to the region early this afternoon.  Another of these disturbances will be quite potent tomorrow and will be accompanied by a surface cold front.

With a southerly flow ahead of the front today and tomorrow, increasing moisture is being carried north from the Gulf of Mexico. Due to the potency of the upper-level disturbance, thunderstorms will be likely along the front.  A few of these storms could become severe, since the front will also be moving across the Mississippi River around the same time as peak heating on Sunday - late afternoon to early evening.  See the lower left panel of the graphic below for the area where severe storms are possible.

The main threats in this possible severe weather scenario will be large hail in discrete (individual) thunderstorms and damaging straight-line wind if the storms can congeal into a squall line.  Tornadoes are not expected.  The most likely time for severe storms appears to be from mid afternoon (after 2pm) through early evening (8pm) in east AR and from late afternoon (after 4pm) through midnight in west TN and northwest MS.  MWN will be monitoring the situation and provide updates as conditions warrant.  Severe weather nowcasting is planned for tomorrow on our Facebook and Twitter pages (linked below).

GFS forecast for 7pm Sunday.
Upper left: forecast at 500mb (18,000 feet), showing a very large closed low over IA/IL with upper -level disturbances rotating around it (purple-ish colors). Lower left: Storm Prediction Center outlook area for Slight Risk of severe weather on Sunday. Right: GFS precip forecast for 1pm-7pm Sunday, indicating showers/t'storms possible to likely.
NOTE: The MWN iPhone app is currently not available in the App Store.  An updated version of the app will be available early next week, complete with StormWatch+.  For more on StormWatch+, visit this page on MWN.

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

2 comments:

Kathy Hannings said...

Erik, FYI the app can still be downloaded from the App Store, but it's not working. I accidentally cleared all my purchased apps from my iPad, and I just downloaded it, but it won't stay up - it tries to start but closes right back down. I'll watch for word that the download is working, but thought you'd want to know.

MWN/Erik said...

Kathy - I'm surprised you can still download it actually. I wasn't able to see it in the App Store. New update should be available any day now. It will fix your issues. My apologies!
--Erik