© 2019 Terry Swails

ENHANCED RISK OF SEVERE WEATHER

April 19, 2017

The situation and set up is still a complex one for this afternoon and evening across the state of Iowa.  The cold front from last night has started to stall down near I-80 as of noon today. Here's the surface pattern:

That front will lift back north has a warm front as the low pressure in Nebraska/Kansas moves closer to Iowa. The warm front will likely set up in between Highway 30 and I-80. This would typically be the focus for severe thunderstorms across the entire warm front. However, because of morning convection/clouds, the location of the low pressure, and the timing, the better forcing and instability will be closest to the low in far eastern Nebraska and west/central Iowa. Here's the latest risk from the Storm Prediction Center:

While the higher risk will likely be in the orange shaded (enhanced) area, the slight risk area still has the potential to see all modes of severe weather (large hail, winds, and tornadoes). Here are the probabilities from the SPC:

Large hail will be possible with these storms (ping pong size and larger) and really is the greatest threat of the day (and is also highest closest to the low).

There are a few factors that could still change - if the sun comes out for a long period of time in eastern Iowa and the atmosphere destabilizes then the severe risk could go up later this evening. Here's the latest HRRR which keeps much of the convection confined to west/central Iowa early, then northeast Iowa later on in the night:

Early afternoon/evening in western Iowa is where supercells will be most likely (and the potential for tornadoes). Those cells will likely form into a line and as the cold front moves into eastern Iowa there is the potential for more of a hail/wind threat. Because there will be a lot of wind shear in the atmosphere, there will be the potential for a tornado or two within that line. In my local area, the severe threat may continue well after sunset.

 

Still a lot of factors and some uncertainty today. Stay tuned... RK

 

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