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Area Forecast Discussion
Issued by NWS La Crosse, WI
Issued by NWS La Crosse, WI
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048 FXUS63 KARX 260732 AFDARX Area Forecast Discussion National Weather Service La Crosse WI 232 AM CDT Wed Jun 26 2024 .KEY MESSAGES... - Quieter Today & Thursday With Daytime Highs In The 70s to Low 80s - Storm Chances Return Early Friday, Sticking Around Into The Overnight Hours - Cooler Weekend On Tap, Temperatures 5 to 15 Degrees Below Normal For This Time Of Year && .DISCUSSION... Issued at 205 AM CDT Wed Jun 26 2024 Today & Thursday: Building upper level heights early this morning will usher in quieter weather for today and Thursday. Disagreement in specific timing of building heights is resulting in slight differences for daytime highs today, from low 70s to the low 80s. The slower the high pressure onset, the warmer the solution. Given overnight observations, have leaned into a slower solution, keeping higher temperatures aligned with bias corrected guidance. Eventually, the cooler northerly flow is expected to settle in for Thursday resulting in slightly below normal daytime highs in the 70s. Otherwise, have slightly backed off National Blend dewpoint temperatures given upstream observations. Short term model guidance shows a large spread (10+ degrees) between the HRRR (45 to 50) due to too much mixing the Fv3 (60 to 65) due to holding onto the departing moisture. Have gone in the middle by slightly backing off of National Blend. Rain & Storm Chances Return Friday: Rain and storm chances shift north-northeast through the Central into Northern Plains Thursday as a closed upper level low advects eastward. Best initial synoptic forcing lies off to our the west, meridionally advecting peak low level moisture into the Northern Plains. This gives the ridge a slightly longer residence time, delaying local precipitation and storm chances into Friday morning. Eventually, the synoptic closed low advects east, pushing precipitation and storm chances from west to east across the Upper Mississippi River Valley through the day Friday. Potential Impacts: Narrow southwest to northeast oriented corridors of higher precipitation take shape through Friday with breaks in peak low level moisture transport. Long term global ensembles suggest two main corridors of 1"+, north and south of the local forecast area. The EPS solution places the highest confidence along our south from northeast Iowa into far southwest Wisconsin while the GEFS solution remains to the north, along the International border. Best instability (>500 J/kg SBCAPE) pulses diurnally along our western periphery during the day Friday before shunting south with the best low level moisture transport. Deterministic (GFS/ECMWF) sounding solutions show long, skinny, and transient mixed layer CAPE with the quite variable shear/helicity most in unison with CAPE in the lowest levels. Much too early to discern severe threat at this time but will be subsequent timeframe to keep an eye on. Cooler Weekend On Tap: Another break in the recently active pattern expected through the weekend as upper level heights build and temperatures return to below normal. Long term global ensemble certainty suggests temperatures 5 to 15 degrees below normal through the weekend and into early next week with daytime highs in 70s and overnight lows in the 50s. && .AVIATION /06Z TAFS THROUGH 06Z THURSDAY/... Issued at 1038 PM CDT Tue Jun 25 2024 Weak front will push across the area Wednesday morning. The front could bring a few light rain showers into the RST/LSE taf sites. Have introduced VCSH at both taf sites at 12z Wednesday and the light rain showers should last for a few hours. Otherwise...VFR conditions will prevail across the region through the taf period. && .HYDROLOGY... Issued at 235 PM CDT Tue Jun 25 2024 Several rivers fell below flood stage over the last 12 to 24 hours, but most of this water is still on route to the Mississippi River. The Mississippi River is expected to keep rising through the next 5 to 7 days depending on location and which rivers route into that particular location. Minor to moderate flood stages are expected from Lake City through Guttenberg. While official forecasts from the River Forecast Center do take into consideration all of the water that has already fallen and is on its way into the Mississippi River, it only takes the next 24-48 hours of forecast precipitation. Since the next chance of precipitation for the local area is not until Friday, this will not be accounted for in the official forecasts. The forecast rain on Friday will likely keep the river elevated beyond the next 7 to 10 days and the river may initially fall some before beginning to rise again as the additional rainfall flows downstream this weekend into next week. && .ARX WATCHES/WARNINGS/ADVISORIES... WI...None. MN...None. IA...None. && $$ DISCUSSION...JAR AVIATION...DTJ HYDROLOGY...JAW