588 FXUS63 KMPX 210019 AFDMPX Area Forecast Discussion National Weather Service Twin Cities/Chanhassen MN 619 PM CST Wed Nov 20 2019 .Updated for 00Z Aviation Discussion... Issued at 608 PM CST Wed Nov 20 2019 && .SHORT TERM...(This evening through Thursday night) Issued at 250 PM CST Wed Nov 20 2019 Forecast remains on track regarding the widespread rainfall developing this evening into tonight, with rainfall eventually expected to change over to light snow tomorrow morning. Forcing aloft will continue to increase this evening as a shortwave approaches out of ND, aided by plenty of strong warm air advection and isentropic ascent in the low levels. As the atmosphere saturates tonight, a widespread shield of rainfall will develop out ahead of a surface low tracking from western IA through central WI, with a shield of light continuing to our north along a cold front dropping south through northern Minnesota. Rainfall is expected to be heaviest during the overnight hours, especially just from southern Minnesota through west-central WI, where models depict a frontogenesis band developing to the northwest of the track of the surface low. PW values will range from 0.75-1" across the area which are near record values for late November, so this looks to be an efficient rainfall producer for this late in the year. Rainfall amounts look to range from a quarter of an inch to half an inch across central Minnesota, to 0.75-1 inch across southeastern MN and west-central WI. While the rain is ongoing, the cold front to our north will pass through the area and cause temperatures to quickly drop below freezing. Expect to see a changeover from rain to light snow during the morning tomorrow, but this changeover looks to occur after the bulk of precipitation has already fallen. Snow accumulations of half an inch to an inch are possible across central Minnesota and along/north of the US-8 corridor in WI where an early transition will allow for snow to fall for a few hours. Elsewhere, expect only a dusting to a rain/snow mix as snow only falls for an hour or two on the back end of the precipitation. This transition is expected to occur for most of the area during the morning commute so there could be a few slick spots on the roads, especially on elevated surfaces as temperatures continue to fall during the morning. The precipitation is expected to be mostly east of the CWA by noon, with strong northwest winds developing as the precipitation ends. Temperatures will only reach the mid 20s to mid 30s Thursday afternoon, and fall into the teens across most of the CWA by Friday morning. Some additional slick spots on roads Thursday evening into Friday morning as any moisture remaining on the roads from Thursday morning quickly freezes. .LONG TERM...(Friday through Wednesday) Issued at 250 PM CST Wed Nov 20 2019 The extended period will remain progressive as the mean flow aloft continues from the west/northwest, with a slow transition to west/southwest by the end of the period. With the progressive nature, timing, and amplitude of the short waves embedded in this flow, confidence in the forecast will remain below average in the extended period. Even the ensembles have too much spread to determine which system next week will actually affect the Upper Midwest. The EC/GFS deterministic model run for this morning are fairly similar in the long wave pattern through early next. Although the overall mean remains similar, differences arise in the amplitude of a short wave moving across the region late in the weekend, and especially next week. First, the EC has a stronger signal on a developing short wave vs. the GFS on Sunday/Sunday night. Surface feature are similar with a trough of low pressure moving through, but the EC has developed an area of QPF along this trough. The GFS remains dry, and holds the frontal boundary just to the south of Minnesota on Monday. The EC moves this frontal boundary well to the south across the central Plains. A blend of models support a slight chance, but due to the lack of deep moisture, and no strong upper level features, am leaning toward a drier forecast, at least until Monday evening. The differences are even larger by mid week as the GFS supports a very strong storm system ejecting out of the Rockies, and into the Plains, Upper Midwest. The EC, and the GEM support a more southerly track for early/midweek, but still develop a large storm system by the end of the week. This is due to differences short wave energy and associated surface features, along with timing. Therefore, very low confidence on any one solution, especially considering temperatures and the potential of significant snowfall during the holiday week. Even though next week is highly uncertain in terms of where/when and how much precipitation develops, the long wave pattern is conducive on an active period. Each individual run of the models will get more refined as we get closer to the weekend, and into early next week on the potential of a large storm system. It is just too early to follow individual model runs. But, the large scale trough does support an active period. && .AVIATION...(For the 00Z TAFS through 00Z Thursday evening) Issued at 608 PM CST Wed Nov 20 2019 VFR/MVFR conditions will give way to IFR/LIFR conditions as a large storm system lifts up from the south and brings rain across the region. Should see the rain change over to snow as the system departs Thursday morning, but the heaviest precipitation should be over by then so no significant accumulations are expected. A cold front will push through the region tomorrow and bring brisk northwest wind gusts of 25 to 30 kts. KMSP... Rain should begin at KMSP between 2 and 4Z. The heaviest rain will fall after midnight. Should see a change over to snow around 13Z, and could have a couple hours of IFR vsbys. Then expect lingering light snow showers through the morning. Brisk northwest winds will develop Thursday morning as the rain changes to snow, but skies will clear during the afternoon as drier air moves across the region. /OUTLOOK FOR KMSP/ Fri...VFR. Wind W 5 kts. Sat...VFR. Wind W 5-10 kts. Sun...VFR. Wind S at 10 kts. && .MPX WATCHES/WARNINGS/ADVISORIES... WI...None. MN...None. && $$ SHORT TERM...ETA LONG TERM...JLT AVIATION...JRB