Scientific Forecaster Discussion

000 fxus63 kmkx 212347 afdmkx Area forecast discussion National Weather Service Milwaukee/Sullivan WI 647 PM CDT Thu Mar 21 2019 Update...more clearing is expected through the evening as first surface trof moving through with little fanfare early this evening. Gusty winds will accompany the trof passage, and should linger through the evening as breezy west-northwest winds are expected just above the shallow low level inversion. Still thinking some mid- level clouds will sweep into eastern areas later tonight into Friday morning, in wake of passing stronger cold front. && Aviation(00z tafs)...VFR conditions expected for much of this forecast period. Still a concern for a period of MVFR sct-bkn late tonight into Friday morning in eastern areas in wake of passing cold front. Confidence lower on MVFR so trended to a tempo group in the east for now. Gusty winds in the lowest 2k feet will remain just below low level wind shear criteria but will be in the 25 to 30kt range. && Previous discussion... (issued 317 PM CDT Thu Mar 21 2019) Short term... Late this afternoon through Friday night...forecast confidence is high. Clouds are clearing across the area, bringing clearing skies. A cold front will pass through this evening, which may bring additional clouds to the area tonight. These additional clouds will help keep lows tonight in the 30s. Conditions will clear up Friday, as drier air pushes in along with northerly wind gusts around 25 to 30 mph for the afternoon. Northerly winds will keep temperatures Friday in the upper 30s to low 40s. High pressure will then settle in Friday night, bringing weaker winds and clear skies, which will allow lows to drop back into the 20s. Saturday...forecast confidence is high. Models are in good agreement with high pressure moving to the southeast of the area Saturday. Some modest warm air advection develops over the area, with southwest winds. Look for a dry day with mild temperatures. Highs should be in the upper 40s to lower 50s, and they may get a little higher given the dry southwesterly flow with the snowpack gone. Model certainty places forecast highs a little above the 75th percentile, so am leaning in the warmer direction. Saturday night through Sunday night...forecast confidence is medium. Models are generally showing a 500 mb low slowly weakening as it moves slowly east from the Central Plains into southeast Iowa Saturday night into Sunday. It then becomes more of an open wave as it accelerates southeast of there Sunday night. There is a fair amount of differential cyclonic vorticity advection Sunday afternoon and evening. Associated 850 mb deformation occurs near or south of the Wisconsin/Illinois border Sunday afternoon and evening, and frontogenesis response is rather weak. The 850 mb low level jet and focused warm air advection points into northern Illinois Sunday as well. The upward vertical motion is not strong, but enough saturation in the air column should occur, so kept generally higher end pops for light rain Sunday into Sunday evening. Some uncertainty here, as the European model (ecmwf) keeps this system a bit further to the south than the other models, and keeps drier air over the area. This limits the precipitation to the far southern counties on Sunday. Cold front then moves south through the area later Sunday into Sunday evening, with gusty northeast winds behind it bringing strong cold air advection into the area. This may bring a mix or changeover to light snow for a brief time, before dry air moves in and ends the precipitation later Sunday night. No snow accumulations are expected. Any rainfall should be on the light side, around 0.20 inches near the Illinois border, to less than 0.05 inches in the far northern counties. Not expecting this to have much of an effect on the main Stem river flooding across the area. Long term... Monday through Tuesday...forecast confidence is high. Models are showing northwest flow at 500 mb Monday and Tuesday becoming more zonal or southwesterly Wednesday into Thursday. Canadian high pressure is expected to move southeast through the region Monday into Tuesday, bringing dry conditions with slowly warming temperatures. Northeast winds will remain rather brisk Monday, before becoming light on Tuesday. Tuesday night through Thursday...forecast confidence is medium. The GFS is trying to develop quantitative precipitation forecast within a fairly dry warm air advection setup Tuesday night into Wednesday across the area. The European model (ecmwf) and Canadian models are dry during this time, which seems more reasonable given the setup and lack of good moisture advection. For now, will leave the low pops going for Tuesday night into Wednesday in parts of the area, but this may need to be removed in later forecasts. More robust warm air advection then develops for Wednesday night into Thursday. The European model (ecmwf)/GFS generally show some warm air advection/low level jet driven precipitation across the area during this time. Things beyond Thursday get murky, with the models differing greatly with the timing of a fairly potent surface low moving northeast through or near southern Wisconsin. Left pops in this period as is for now. Mild temperatures should return by Wednesday into Thursday. Aviation(21z taf updates)... MVFR ceilings are continuing to push southeast and will be out of the area over the next few hours. Expect clear skies the rest of the afternoon, before clouds move back in with the cold front tonight. Most areas remain VFR, but areas near the Lake May see a brief period of MVFR ceilings between 8z to 12z Friday. Skies will then clear for the afternoon. Marine... As the cold front pushes through this evening, expect an increase in winds from the northwest. Gale force winds are likely over open waters Friday morning and afternoon, therefore a Gale Warning is in effect from 4 am to 4 PM Friday. Additionally, a Small Craft Advisory is in effect for late tonight through the daytime Friday. High pressure then will move in Friday night into Saturday, bringing calm winds and sunny skies. && Mkx watches/warnings/advisories... WI...none. Lm...Gale Warning from 4 am to 4 PM CDT Friday for lmz080-261-362-364- 366-563-565-567-669-671-673-675-777-779-868-870-872-874-876- 878. Small Craft Advisory from 1 am to 7 PM CDT Friday for lmz643>646. && $$

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