A cold front is currently stretched from the Great Lakes region down to Arkansas. Along and ahead of the cold front, a squall line has developed in MO and AR already and broken lines of storms has been observed on radar further south. I expect this to form one solid line before much longer as it moves toward the east. Low pressure has developed over Oklahoma and will move north and eastward through the night.
A few widely scattered showers will develop out ahead of the main precipitation shield; however, the heaviest weather is not due in until around 6am or perhaps slightly later. The low level winds are fairly ROBUST with H85 winds of 60-70kts forecast. Since the strong winds will not have far to go to reach the surface, it will not take much convection for them to reach the surface and possibly cause issues.
The 0-1km helicity forecasts are a bit worrisome with 350-400m2/s2 right over us as the line of storms move closer toward the area. One limiting factor is the time of day and lack of instability. SBCAPE values of 250j/kg are not out of the question; however, with such a volatile wind profile I would tend to think weaker updrafts (updrafts that will be fed on upper level ascent) would easily get rolled and eventually destroyed.
This event is very classic in terms of cool season severe with low instability and high shear. The best chance for tornadoes in general appears to be west of here where instability values are higher; however, given strong shear and strong forcing I can’t rule out a spin up here or there. EHI (0-1km) values of around 1 or slightly higher are forecast for this time period. This value is relatively low considering higher end events; however, given the time of year it is still rather impressive. Again, for that reason I simply can’t rule out a possible spin up.
With that said, I do not expect a widespread tornado outbreak by any means. I am very concerned about the possibility of strong damaging winds that will accompany the line of storms as it moves eastward. Even heavier shower activity may be enough to pull some of the wind energy down to the surface. Due to the lack of instability and fairly low topped convection, lightning may be limited with these cells as well.
Again, timing looks to be between 6am and 10am given model disagreement. Often times squall lines tend to surge forward a bit faster than forecast so that is why I’m thinking 6am at the earliest and 10am given the slower guidance. The morning rush looks very wet and windy. Be sure to keep both hands on the wheel as you drive and use extra caution if you drive a high profile vehicle.
-Severe storms are possible
-Strong possibly damaging winds are the primary threat
-Can’t rule out an isolated tornado; however, no widespread tornado outbreak is expected
-Brief heavy rainfall
Residents are urged to be ready to act and know what to do if a watch or warning is issued for the area. Stay safe and stay informed.
Meteorologist: Robert Frye
Updated: 7:00pm CST 1/29/13