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Area Forecast Discussion
Issued by NWS La Crosse, WI
Issued by NWS La Crosse, WI
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975 FXUS63 KARX 120746 AFDARX Area Forecast Discussion National Weather Service La Crosse WI 246 AM CDT Mon Aug 12 2024 .KEY MESSAGES... - Although a few showers could occur in spots today, chances for more widespread showers/storms continue to increase later this week, highest (60-80%) Wednesday night and Thursday. - Temps will be warmer, near seasonable values, for most of this week. && .DISCUSSION... Issued at 246 AM CDT Mon Aug 12 2024 Today-Tuesday: A few ripples in the flow were evident in GOES water vapor imagery early today across the Dakotas into Iowa/Minnesota. Regional radar mosaics showed scattered weak returns across southern Minnesota and northern Iowa with a few surface reports of light rain. However, the bulk of showers/storms should pass farther south across central/southern Iowa into Missouri today where the warm advection/moisture transport signal is focused. A few showers or sprinkles could graze southeast Minnesota and northeast Iowa. Otherwise, much like the past few days, isolated to scattered showers/storms are possible diurnally across northern into central Wisconsin this afternoon where weak destabilization is expected to occur. Although the airmass remains dry, a favorably deep light wind layer, relatively clear skies, and surface ridge axis crossing the region may lead to some fog development tonight, especially in valleys, but patchy fog could not be ruled out area-wide in the scenario. Gradual warming will continue into Tuesday as mid-level ridging spreads eastward from the plains. Wednesday-Friday: Surface ridging will slide east into the Great Lakes on Wednesday with return southerly flow developing and deep layer moisture beginning to increase. Some showers/storms could develop (20-40%) through the day with the increase in moisture transport/warm advection, especially with any weak lead shortwaves. However, the higher shower/storm potential is expected for Wednesday night and Thursday as a broad mid-level trough crosses the region. NAEFS precipitable water values increase above the 90th percentile relative to climatology during this time and among all GEFS/EPS/CMC ensemble members, probabilities for at least 1/2 inch of rain through Thursday are generally 40-60% with 20-40% chances for 1" or more. Thus, although there is uncertainty how this system will evolve, especially with convection involved, confidence in a more widespread precipitation event continues to grow, with NBM rain chances continuing to increase (60-80% chance). Global model spread in temps is larger on Thursday, likely owing uncertainty in storm track and impacts of clouds/rain. No strong signal for severe weather is evident given the greater uncertainty in details of the trough/surface pattern evolution and potential for clouds/showers to limit destabilization. The trough may linger across the area on Friday with some continued shower chances, but spread in potential outcomes for the trough increases in time. Next Weekend: Heading into next weekend, guidance generally suggests ridging expanding across the southern Rockies/plains downstream from a larger trough across the Pacific Northwest. Our late week trough will move east across the Great Lakes. Lower end rain chances (10-30%) linger due to potential proximity to the larger trough, although this evolution remains unclear. Overall, seasonable temps are favored with global ensemble interquartile ranges for high temps in the 70s to mid 80s. && .AVIATION /06Z TAFS THROUGH 06Z TUESDAY/... Issued at 1119 PM CDT Sun Aug 11 2024 Light winds with mainly VFR ceilings through the TAF period. Variable mid and high level clouds with ripples in the northwest flow and some spotty showers passing mainly to the southwest. The latest satellite imagery shows some reduction in the high clouds at KLSE, so will want to monitor this as the forecast is for high relative humidity at the 300-400mb level. In house research shows due to the large sfc dewpoint depressions the probability for dense fog is low at KLSE. The mid clouds and spotty showers are a little farther east as well west of KRST. Some potential for spotty showers Monday, but due to low confidence did not mention VCSH at this time. && .ARX WATCHES/WARNINGS/ADVISORIES... WI...None. MN...None. IA...None. && $$ DISCUSSION...JM AVIATION...Zapotocny