386 FXUS63 KARX 161953 AFDARX Area Forecast Discussion National Weather Service La Crosse WI 253 PM CDT Sun Oct 16 2022 .DISCUSSION...(This evening through Sunday) Issued at 250 PM CDT Sun Oct 16 2022 Key Messages: - Anomalously cold air mass moving in with wind chills in the teens by morning. Prepare for these unusual cold temperatures. - A tale of extremes this week...Well below normal temperatures to start the week and well above normal temperatures to end the week - Still mainly dry through Saturday...some potential for rain by Sunday Through Monday: Numerous showers today in WI, giving way to near-record cold temperatures and wind chills by morning. The dominance of the deep large scale trough over Great Lakes will increase through Monday with the heart of the coldest air coming in. Cold advection is ongoing with temperatures not warming much from morning lows (~3F). GOES water vapor with RAP tropopause mapping shows a vigorous shortwave trough near Minneapolis with moderate lift now over the area. Showers have blossomed and continue to develop and increase in coverage as steep lapse rates and minor MUCape (~100 J/Kg) is released. More stability and shallower moisture westward is causing a sharp cutoff to the showers on about the Miss River. As the trop fold passes overhead and shifts east, and with nightfall, showers are expected to decrease in coverage but still be around this evening. These may change to snow as well but no accumulation is expected. The steep lapse rates will continue to harvest a moderately strong wind field for gusts overnight in the 20-30 mph range in the mixed layer. Overnight lows are tricky with consensus in the CAMs and national blend suggesting dewpoints will crash into the teens for most of the area. Recently, observations are showing dewpoints falling into the 18-22F range in the eastern Dakotas and western MN making this scenario a bit more plausible. Highest confidence is in WI remaining cloudy overnight and latest GOES visible imagery suggests a cellular nature to the clouds in MN/IA, suggesting some clearing is quite possible overnight on the western flank. This will aid in getting colder. Have warmed the WI areas a few degrees from previous forecast for overnight lows. The main impact weather of the week is the combination of winds and temperatures Mon/Tue mornings...VERY unusual to have wind chills in the teens...and that is without the wind gusts factored in. Have already hit this in social media but will continue to increase the message for preparedness for those mornings. Extended Overview: The broad trough of 500mb low pressure covers much of the Upper Mississippi Valley/Great Lakes south to the South Atlantic States eastward. Anomalously cold temperatures continue through mid-week as the low gradually migrates eastward. Wednesday through Sunday...a ridge over the Rockies and a more westerly flow aloft allows warmer temperatures to return across the Plains. The next potential weather-maker moves into the Pacific Northwest Saturday. There is a spread in if the 500mb heights will amplify or remain more zonal affecting temperatures for the weekend and the strength of moisture return Sunday. Monday Night through Wednesday Morning: The NAEFs anomalies continue to show that 850mb temperatures are 2 standard deviations below normal with winds 2 to 3 standard deviations above normal and specific humidity 1 to 2 standard deviations above normal. This leads to blustery conditions Tuesday with cold wind chills in the single digits and teens Tuesday and teens Wednesday mornings. Still dry with highs in the upper 30s to mid 40s Tuesday with 40s for Wednesday. The record low at Rochester Tuesday the 18th is 17, and we have a near record low of 20 forecast. Precipitable water values remain very low...only 0.2" to 0.4". Wednesday Afternoon Through Sunday: The winds will not be quite as strong Wednesday, however look for west winds to gust at times 10 to 20 mph. Moderating highs in the 40s are on tap for Wednesday with highs in the 50s Thursday. Southwest winds increase for Friday, thus we have much warmer...above normal temperatures in the 60s expected. These warmer temperatures continue for Saturday/Sunday, where 60s and a few 70s return. Depending on how the storm system evolves for Sunday, we could see the chance for showers/thunderstorms. Some of the GEFs ensembles return precipitable water values back to above 1" by then. && .AVIATION...(For the 18Z TAFS through 18Z Monday afternoon) Issued at 1206 AM CDT Sun Oct 16 2022 Northerly flow continues over the airfields with mainly VFR conditions. Ceilings should remain around 3-4kft, but could slip occasionally into the MVFR BKN025-030 range. Instability rain showers will be around during the afternoon for KLSE with a temporary MVFR CIG/VSBY possible should a vigorous shower directly hit the airfield. These should largely be circum-navigable and brief. Showers will be on the decrease tonight. During the morning hours Monday, there is an alternate scenario where clouds may clear from the west at KRST (30% probability). Gusty northwest winds will be persistent through the TAF period. && .ARX WATCHES/WARNINGS/ADVISORIES... WI...NONE. MN...NONE. IA...NONE. && $$ DISCUSSION...Baumgardt/Zapotocny AVIATION...Baumgardt