- Flash Flooding
Models are nowhere close to one another yet for Thursday, while they're in fairly good agreement for Friday. GFS, for example. forms the low in central CO and has it in NW Kansas by 7pm Thursday. ECMWF (Euro) and CFS (Canadian Forecast Agency model) depict the low in a more usual southwest corner of Kansas location.
What I'm seeing in common is winds mostly coming from the south-southwest at all levels of the atmosphere. This would tend toward squall line development, or perhaps multi-cell clusters with storms training over the same few areas.
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Will Shear Develop?
It appears from the lates GFS forecast some shear (changing of direction and/or speed with height) may develop. My concern is, right along or just behind the front the surface and 500mb (about 18,00 to 20,000 feet up) wind barbs are the exact same direction in a line roughly along US 183. That’s where I’d expect the front to lay, which would put it in an area where wind does not change direction with height (little to no directional shear). The wind speeds do increase with altitude, which would tend to tilt a storm’s mesocyclone (the tower) and allow the rainfall to occur away from the inflow area of the storm. That would lead to longer-lived storms.
Where on the plains is the surface low?
The main factor that’s still in disagreement as I look at the models is the positioning of the low. There are the forecast position of three of the models:
The Euro and CFS model forecasts for the center of the low are pretty close, while the GFS puts it more than 100 miles further north. I expect the models to converge on the Euro solution, give or take. If that happens there would be more opportunity for changes in wind direction between the surface and higher altitudes. This would lead to more of a multi-cluster evolution, bringing severe hail into the picture. A solution closer to the GFS would tend to be a linear system, a shelf cloud extending the width of Kansas. Wind becomes the primary damage risk.
In both scenarios flash flooding becomes a fairly large risk. The limiting factor in this risk is a lack of good-quality moisture in the low levels…the Gulf moisture will have little time to fill back in after a cold front sweeps the area Tuesday. At this point, highest rainfall totals are forecast in the 1/4 to 1/3 of an inch range. But we’re six days out, and the amount of moisture available for these storms will likely remain in question right u until initiation.
Due to work commitments I will not be chasing Thursday. I’m leaning toward making my annual “shake-down cruise” Friday, where storms are a bit stronger chance and forecast to have potentially better quality in central and southern Oklahoma. Since that’s not our core coverage area I’ll be doing most of the coverage of that chase on Facebook, Twitter, and a few posts on the site if I get good video or photos. Of course, the model forecasts…especially the GFS…tend to slow down a few hours from the forecast this far out. Right now, I’m planning to do an updated briefing for this system on Tuesday, once it’s come into the timeframe of the shorter-term models like the NAM.