:: May Storms...will they come?
As the seasons continue to shift, the models are finally looking towards a promise of instability and precipitation that is more characteristic of the month. Weekend is ending on a mainly cloudy note...stratus deck riding on a cool low level adevection push from Lake Superior moved in overnight, plunging the low here at Lakeville to 40. Surface front responsible for keeping yesterday's 85°F heat at bay overnight has started moving back NE over the southwestern part of the state after noon today. GFS is much more aggressive with this feature, accenting the WAA and publishing max surface temps for the metro well into mid-70's in MOS. This has been stymied by the st deck and a few splash-and-dash showers that have sprouted late this afternoon across the area. As of 15Z, 990-1000mb low cirulating around the Powder River basin of WY, and its extent of eastern progress was main key to placement of the aforementioned front. Models have struggled (as they always do with the badland lows) with placement, depth, and effect of this low. Current data plots are now showing definitve troughing over the western Dakota badlands, with some central circulation over the Black Hills. The sat img and UDX 88D img confirm the central pressure defecit, coupled with current LLJ position fired off some +TSRA just off the Hills. Looking at the 00Z and then again 12Z model runs today, I have to toss off NAM...it just never pinpointed these features, whereas the GFS - especially in the 12Z run - is almost dead-center.
This follows guidance used by the local NWS-WFO's as well, and looking ahead on the GFS we can start to piece together the outlook for the next 72-120hrs with a little more certainty. As the Black Hills-Powder River low continues to deepen over the next 24 hrs, pressure gradient will intensify over our area as a southerly LLJ accelerates overnight and into Monday, streaming TX heat and Gulf moisture into the region. By noon tomorrow, it should be breezy and much warmer as the WAA takes over. Convection will most likely fire on the nose of the LLJ, which looks to hook up with the ULJ in a couplet near JMS-FAR by mid-tuesday. ABR and MPX WFO's are looking at these features with some certainty of a MCS or at least a training-type squall that moves out of the James River valley and into wrn MN by late tuesday-early wednesday. After that round, however, we are all scratching our heads about the main longwave upper trough, and associated cold front to roll off the front range in the wake. Upper winds will be the definitive ingregient for Wednesday...any veering off of the coupled structure will spell severe potential. A more agressive couplet could either push the system through faster, or just create more instability for rainmakers. One GFS element having some bearing is the prog of PWATs and TD's acrs the area. 1.5" to 1.75" pot's acrs the Dakotas were remaked as abv climatological norm for this time of yr. That same area of moisture will be backed in earnest by lusher, greener fields in MN. TD progs show us in a mid-60's range, against max heating of only mid-upper 70's for Wednesday. Shld the front be pushing acrs the ern Dakotas by 00Z/24th, we could see some heavy rains Wednesday night.
Tonight...Partly Cloudy, 30% chance of a stray shower. Low 52. Southeast wind 5-10mph.
Monday...Sunny. Warm and breezy. High of 83. South wind 15-20mph. Low 70.
Tuesday...Partly Cloudy and humid. High 85. Chance of thunderstorms after 4pm. Low 72.
Wednesday...Mostly Cloudy, but warm and still humid. High 76. Good chance of thunderstorms.