- Flash Flooding
I'm looking for discrete cells to form by 4-5pm. There's only a few our window before the system lines out and the risk for damage shifts mostly to wind and flash flooding. Some of these storms will be copious rain producers, especially as they get further south and east into areas that won't take much rain at all to get flash flooding.
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I’m not going to put a lot of imagery into today’s briefing, just enough to show the similarity between the models now that latest model runs were 8-12 hours out from the event, mostly around 7am CDT today.
There is a caution to pass along with this first loop especially: don’t take the simulated radar image literally, but look more at the pattern. As you’ll see in the later images the models differ within maybe a 50-75 mile corridor east to west with their placement of initiation and where the front is by 7pm.
For the most part, wind near the surface will be south to southwest. It stays from the south and southwest up to the middle layers of the troposhpere, about 25-thousand feet or so. Above that the influence of the jet stream starts to swing things around to the west. Usually south to southwest wind at the surface means any discrete storm’s main threat is large hail. But in a small area of north central Kansas, there is a chance for a tornado or two while the storms say discrete. That’s reflected in the SPC tornado risk graphic just issued. The brown area is a 5% risk for any tornado.
The hail remains the largest damage-causing concern today, with the yellow area having a 15% probability for hail larger than one inch (quarter-size). In the lighter area, SPC forecasters have outlined a 10% probability for large (tennis-ball or larger) hail.
There is another brief area of tornado risk that I’m not sure SPC is keying on as much. That would be in Rice, Ellsworth or McPherson county as the cold front starts to zipper over the top of the dry line. Right at that zipper point we could see a brief, high-based landspout tornado. I think once any portion of the cold front overtakes the dry line, the chance for tornadoes in that southern zone effectively goes away.
Regardless of what happens before sunset, afterwards the storms are forecast to line out and move gradually southeast along with the cold front. The primary risk by 10pm or so will be flash flooding. The storms will be moving into areas where an inch of water in an hour will produce farily significant flooding because it’ll nearly all run off. These storms look like they’ll easy produce an inch or more per hour.