Saturday, April 6, 2013

Spring weather pattern means the beginning of severe weather season

While most Mid-Southerners are grateful for consecutive days in the 70s (especially on the weekend!), Mid-South meteorologists and weather weenies are keenly aware that a persistent southerly flow of moisture off the Gulf of Mexico and warm temperatures are harbingers of convective weather. And those same people, including yours truly, have been closely monitoring a potent storm system that will sweep across the Mississippi Valley the middle of next week.  This blog serves as a heads up to the rest of you that this strong spring cold front will bear watching in the coming days.

The Storm Prediction Center is giving ample notice to the southern plains and mid/lower Mississippi Valley that a storm system that will move across the region next week will have the main ingredients in place to produce severe weather.  There are several issues that must still be resolved, including exact timing of the front, that must be worked out. However, very warm air (75-80 degree temps locally for several days) and plenty of moisture from the Gulf courtesy of 4-5 days of south winds, plus the front and strong wind at all levels of the atmosphere, are the main ingredients necessary to produce what may become a widespread multi-day severe weather event.  The graphic below highlights the areas that SPC believes are at the greatest threat for severe weather Tuesday and Wednesday.  These are subject to change in the coming days, but likely more in the fine-scale details than in whether or not severe weather occurs.

SPC outlook for severe t'storms April 9-10, 2013

For the Mid-South, MWN is targeting Wednesday night as our most likely time for storms, some of which could easily be severe. The two main long-range models we use (GFS and European) are still several hours apart in their timing, but both indicate that severe weather is a good possibility.  (Remember that model output is NOT a forecast, but one possibility of how a very complex situation might turn out.) With strong wind from the ground up to the jet stream, and sufficient "turning" of those winds in the lowest several thousand feet, the main concerns we have at this early date are damaging straight line winds (primarily) and tornadoes (secondarily).  Hail is also a possibility, while widespread flooding does not at this time look too likely.

00Z European model output precipitation for Thursday, April 11, 1am CDT
Latest European model output showing leading edge of an area of storms near the MS River  overnight Wednesday night.

06Z GFS model output precipitation for Wednesday, April 10, 7pm CDT
Overnight model output from the GFS showing storms into the metro by early evening Wednesday, about 6-9 hours faster than the European model above.

06Z GFS model output Lifted Index for Wednesday, April 10, 7pm CDT
GFS model output of atmospheric instability, as measured by the Lifted Index.  Plenty of instability would be in place  to support severe thunderstorms if they arrive during the evening Wednesday, according to this model.
We'll continue to monitor and let you know of any changes, as well as provide more specific details as they become clearer.  Check in with us via our social channels listed below.  However, between outdoor time and "spring cleaning," it would be a good idea to review severe thunderstorm and tornado safety tips and be prepared for the spring severe weather season that some doubted would EVER come after the 2nd coolest March in the past 40 years!

Included in your severe weather safety plan should be multiple ways of getting severe weather warnings, including overnight.  Do NOT count on sirens to warn you, especially if you are inside or asleep!  (Why? Click here.)  We highly recommend a smartphone app solution that will pinpoint warnings to the locations you select, as well as NOAA Weather Radio with battery backup.  If you need a suggestion for a truly "smart" phone app, may we recommend our app (mobile link) with StormWatch+ for Android and iPhone.  It will wake you up if a dangerous storm is heading for your location, but not if it's headed for another part of your county.

--Erik Proseus, MWN Meteorologist

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