:: Approaching Severe Weather Outbreak
On the basis of an even more explosive scenario in the cards, SPC has now placed us under a severe threat for today and tomorrow, with more emphasis on tomorrow's conditions. The low pressure system, now gaining strength as it rolls down the front ranges, is forecast to deepen to around 970mb by the time it is in the open plains later this evening. The southerly flow ahead of the low will increase as a result and the upper jet will be coming across the trough and maxing out its nose over the 970mb sfc low. Placement of these features look to be western SD in all models by 00Z tonight, in conjunction with a very strong (50kt) south-southwestly H85 flow. With shear in place, and CAPE in the 3000J/kg range over the central dakotas, explosive MCS could develop quickly today and be showing large hail and tornadoes by 5pm CDT across especially Eastern SD.
That MCS will propagate ENE into MN as upper jet turns slightly to couple with the southerly LLJ overnight, and I would expect remnants to affect much of central, but more likely NW and NC MN overnight. As this happens, any warm upper level fetch that could have capped us Thursday will be destabilized. The next piece of the puzzle is timing of the cold front as it sweeps across the area thurs. NAM and GFS both push the front to a DLH-MGG-FRM line by 23Z, and if initiation does not occur between 18Z and 22Z, I would say that the Twin Cities metro will be on the back side of the weather. However, if that front slows up today and tonight, or if there is initiation just along and ahead of the front tomorrow AM and early afternoon, our threat becomes exponentially higher for severe weather. The forecasts coming out of all offices are very categorical due to this fine-tuning of timing issue. It will be windy, warmer, getting humid through today. There is a chance we will get rain showers and thunderstorms, but not as severe today. There is a chance that we will get more thunderstorms tomorrow, and possibly more severe, but the timing is going to be a close call. Instinctively, I am going to hunch on the front slowing up a tick, as the low trajects more northbound over the next 18 hrs, and thusly my forecast...
Wednesday...40% chance of rain showers in the AM, then partly cloudy and breezy through the day. Warmer and more humid with high of 76. Gusty south winds 20-30mph, with gusts to 45. 40% chance of showers and thunderstorms after 6pm, low 65.
Thursday...50%of showers and thunderstorms before noon. Then an 80% chance of showers and thunderstorms after 2pm. Some storms could be severe with damaging winds, hail, and a possible tornado. High 84. Winds south turning southwest 15-20 mph. Rain ending after 9pm, low 55.
Friday, Mostly Sunny, High 74. Wind NW 5-10mph, low 56.