911 FXUS63 KARX 092342 AFDARX Area Forecast Discussion National Weather Service La Crosse WI 542 PM CST Thu Nov 9 2023 .DISCUSSION...(This evening through Thursday) Issued at 134 PM CST Thu Nov 9 2023 Key Messages: - Scattered Light Mix of Snow/Flurries/Sprinkle Chance Tonight and Friday Primarily North of Interstate 94, Little to no Accumulation Expected - Colder With Decreasing Winds Friday As Clouds Increase - Anomalous Warmth Builds Through The New Week Overview: Water vapor satellite imagery/heights/lightning show a closed low over the U.P. of Michigan trailing westward into the Upper Mississippi Valley and Northern Plains within a broader trough that extends toward the Four Corners and Southwest U.S. Another closed low was over Saskatchewan and ridge over parts of the Northwest U.S. Lightning was noted across parts of the Southern Plains. The WSR-88D mosaic has light snow and flurries from the Dakotas into northern MN with light rain being reported across parts of far northern WI. A strong pressure gradient was noted across the region with a 1001mb surface low over just north of the U.P. and a 1030mb surface high over eastern Wyoming. Westerly surface winds were gusting 20 to 40 mph. Cooler and less windy tonight into Friday. Spotty light snow/rain mix possible north of I94: The mid-tropospheric trough will continue to move through this afternoon with continued cold air advection. The pressure gradient relaxes as surface high pressure builds in tonight, however a reinforcing cold front may increase gusts for a brief time early Friday with gusts to 25 mph, otherwise wind gusts should be 10 to 20 mph during the day. Forecast soundings show increasing moisture from the north and steepening lapse rates with with potential saturation in the dendritic growth zone. The models vary on the temperatures and degree of saturation, but show some potential for light snow/flurries/mix, but little to no accumulation. The prob WSSI is also null for any winter weather related impacts. Have kept low pops/flurries in the forecast north I94 to account for any patchy precipitation that may develop. Lowering 850mb temperatures - 4 to -8 and 1000-850mb thicknesses 530 to 534dm and clouds will hold temperatures down Friday. The HREF probability of getting above 40 Friday is 0 to 20% for southeast MN and parts of west central WI. Highs are currently forecast only in the 30s to lower 40s. Non-Zero Rain Chances Saturday Night: A progressive upper level pattern provides diffluent flow for Saturday followed by building heights for Sunday. Before heights can build, they temporarily decrease as an upper level trough lifts through the Central Plains Saturday night. A thin filament of increased theta e accompanies this lifting trough with an overall synoptic weakening trend. Select high resolution models (NAM12 09.12;NAM 4km 09.12; Fv3 09.12Z) advect scattered precipitation from southwest to northeast with this theta e lobe. Southwest neighboring offices have elected to increase PoPs for this time over National Blend. Locally, have continued with 0-10% PoPs given the overall weakening trend, limited ensemble consensus (<20%; HREF 09.15Z), and dry high resolution soundings. Anomalous Warmth Through The New Week: This aforementioned ridge reinforces through the new week, pushing 95th percentile compared to climatology by midweek. Resultant low level (850mb) temperatures near 15C above normal, centered over the Northern Plains. Highest confidence (70-100%) within long term global ensembles (GEFS 09.12Z; EPS 09.06Z) for greater than 10 degree surface temperature anomalies reach the local area in southeast Minnesota as early as Monday night, lasting into Friday. Both intermodel and intramodel trends have wavered exact location and strength of low level temperature anomalies. GEFS dProg/dT of 850mb temperature anomalies pushed 18C in the previous two runs (09.00&06Z) and have decreased to near 12C in the most recent run (09.12Z). While less wavering in the most recent EPS (09.06Z) runs, similar scenario when compared to Thursday morning's run. Temporally, EPS is slightly quicker than the GEFS for the anomalous temperatures, building into the Northern Plains through Tuesday. The resultant ensemble confidence for 10 degree or greater surface temperature anomalies reaches definite (100%), on Tuesday. All in all, irregardless of aforementioned variances potentially influencing timing and magnitude of maximum daytime temperatures through the new week, there is an overall minimal intramodel variance for surface temperatures through the week. Model interquartile ranges remain in the single digits. NBM IQR (25th-75th) is 3-5 degrees through midweek. In summary, have continued with National Blend for temperatures, keeping 50s for much of the forecast period, outside of Wednesday with low 60s. Anomalous temperatures are a few degrees from being record breaking, yet, with warm lows closest to records, only a few degrees below at the current forecast hour. && .AVIATION...(For the 00Z TAFS through 00Z Friday evening) Issued at 540 PM CST Thu Nov 9 2023 MVFR stratus spreads southward overnight and lingers through much of the day on Friday. There is some variability in the guidance for how soon the stratus arrives overnight (some have the leading edge decaying as it arrives and delaying the ceilings by 2-4 hours), but given the fast overall upstream motion and cohesive shield in satellite, leaned towards the more progressive end of the guidance envelope. Stratus may clear by the end of the TAF period, but confidence in timing is not high. Winds will be from the NW at 5-10 kts. && .ARX WATCHES/WARNINGS/ADVISORIES... WI...NONE. MN...NONE. IA...NONE. && $$ DISCUSSION...Zapotocny/JAR AVIATION...Skow