:: Ominous
Well, since our last severe weather outbreak -- just over a week back -- Lakeville and the surrounding region has enjoyed an early summer. Today things have turned almost tropical, with a current Temp and DP of 88/65. Between breeze rushes, that brings the heat index to about 100. And, although the southerly breeze is helping keep things somewhat bearable outdoors, it has also ushered in the moisture and heat needed to fuel severe convection. Now we need the other elements - lift, maybe a bit of spin, and some cooler air aloft to allow the storms to grow.
Currently, that is the only stymie for a convective eruption - capping is present at the mid layer of the troposphere from the central Dakotas eastward towards the Great Lakes. That is rapidly changing attm for a couple reasons now evolving on both a meso- and synoptic-scale. First, mesoscale analysis over the region of frontogenesis (currently western SD, NE, and eastern WY) shows a very abrupt dryline has formed from the Black Hills southwestward over the NE panhandle. Temps are at or near the century mark, but there is a 30 degree F drop in dewpoints over a span of 50 miles in the region. Add to that evidence that the cap over SoDak is weakening as shown in the 18Z RAOB from ABR. And now convection has fired from the SoDak badlands southwest along the dryline.
Frontogenesis should wrap up behind this line, and push east through the evening hours. Currently, it looks as though gut instinct is going to have to weigh in heavilly on system timing for our area. Supposing that the cap continues to weaken ahead of the system, and supposing that the upper jet flow remains in its swift zonal pattern until the trough arrives, we are looking at a fropa of mid-monday AM. Most WFO forecast grids have been focusing on that timeframe with earlier model runs as well. The next factor in handicapping this system is whether or not a MCS/and or squall line forms ahead of, or along the frontal boundary.
I am going to hedge my bets towards "ahead and possibly along"...and here is why: should the cap continue to weaken tonight from west to east, we could see impulse initiation over western to central MN by midnight. Then is is a matter of propogation, and with TD's in the mid-60's, PWats in the 1.5" to 2" range in all previous modeling available, propogation should be easy enough. We then move to supercell indicies...which are at high levels across the rapidly destabilizing central Dakotas. This area should move east, and if conditions hold tonight, we could see round one glance the metro around 3am and round two -- a more substantial round possibly -- just in advance of the front between 7am and 10am.
For some reason, models are not publishing fully on normally available internet sources, so this near-term outlook is all I can muster for now. MPX just published a short and generalized FD, and may be due to other activity now cropping up in Nrn MN (WW410 was just issued for the northern 1/3 of MN til midnight, and a tornado touched down near Crookston about 20 minutes ago). Will have to keep watching conditions as the night wears on...
Tonight...Warm and humid. Partly turning mostly cloudy, 40% chance of thunderstorms after 1am. Low 72. Winds south southwest 10-15mph, gusting to 30.
Monday...Stormy wakeup with thunderstorms likely until 10am. Heavy rain, damaging wind, and hail possible. Chance of rain 80%. Mostly cloudy turning partly cloudy by noon. High 82. Southwest winds turning northwest in the afternoon 5-15mph. Low monday night 62 with winds diminishing after 7pm.
Tuesday...Sunny and dry with a high of 76. Northwest wind 5-10 mph.