Area Forecast Discussion
Issued by NWS La Crosse, WI
Issued by NWS La Crosse, WI
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337 FXUS63 KARX 291136 AFDARX Area Forecast Discussion National Weather Service La Crosse WI 636 AM CDT Sat Jun 29 2024 .KEY MESSAGES... - A few sprinkles are possible Saturday followed by cooler, drier conditions into Monday. - More rounds of showers/storms are expected Monday night into Tuesday which bring a threat for heavy rain. Should details come together, some severe storms could occur Tuesday afternoon and evening. - Additional rainfall could occur Thursday and Friday but, at this time, heavy rain and severe chances appear to be lower during this period. && .DISCUSSION... Issued at 402 AM CDT Sat Jun 29 2024 * TODAY INTO MONDAY: Sprinkles, then Cooler and Drier Today, a few sprinkles may occur as an upper shortwave dives southeastward out of ND. While the overall pattern is reminiscent of a setup where scattered thunderstorms may occur despite a recent cold frontal passage, progged soundings from most guidance show warm temperatures at 700mb keeping a lid on things. Therefore, while have kept sprinkle mentions in the forecast, have opted to limit mentions of thunder this afternoon. Tonight and Sunday night, as surface high pressure builds eastward, light winds and mostly clear skies should result in efficient radiational cooling. Have therefore moved forecast lows toward the cool side of consensus blends, with the Black River Falls/Tomah area favored to see temperatures below 45 Sunday night. * MONDAY NIGHT INTO TUESDAY: Heavy Rain Threat, Potential Severe Monday, as the aforementioned surface high shifts eastward, next upper trough advances over the central/northern Rockies. Expect 850mb moist fetch from the Gulf of Mexico to resume in earnest as a result. With plenty of moisture returning to the CWA, as lead shortwaves eject downstream Monday night into Tuesday and the main body of the upper trough arrives Tuesday evening, expect multiple rounds of convection to develop. The primary threat during this period will be heavy rain. Both NAEFS and ENS PWATs approach and even exceed 2", approaching the 99.5 percentile of their respective model climatologies. NBM probabilities indicate most areas will receive around 0.5" to 2" of rain from Monday night through Tuesday night but with a long tail on the high side of the distribution, suggesting the potential for localized areas to receive higher amounts around 4". Needless to say, given the high amount of antecedent rainfall, flash flooding and additional river flooding look to be possible given this setup. As for severe thunderstorm potential, focus is largely on Tuesday as winds aloft increase ahead of the main upper trough. Accordingly, progged hodographs should a good deal of wind shear with plenty of turning in both the low and mid levels. With potential instability building as heights aloft fall and low level moist advection continues in earnest, severe storms capable of all hazards would be possible if sufficient destabilization occurs. Given the likelihood of abundant cloud cover following Monday night`s round of convection, it remains far too early to lock this one in. * THURSDAY/FRIDAY: Next Chance for Rain The wave train rolls on Thursday into Friday when guidance is in good agreement that an upper low will bring potential for additional precipitation. While ensembles continue to differ in details, resulting in an extended time period with precipitation mentions, good news is that best moisture transport is still largely displaced to our south across much of the 29.00z guidance suite. && .AVIATION /12Z TAFS THROUGH 12Z SUNDAY/... Issued at 627 AM CDT Sat Jun 29 2024 VFR expected through the 29.12Z forecast period. Difficult forecast detail will potential scattered precipitation this afternoon/evening. Only impacts will be temporary reduction in ceilings. Responsible incoming low level cold air also ushers in dry air. Have kept BKN as low as 050 but if saturation increases, may warrant slightly lower ceilings. Otherwise, increased northwest winds gusting 25kts are expected from late morning into tonight. && .HYDROLOGY... Issued at 452 AM CDT Sat Jun 29 2024 While additional rain should take a break through at least Monday morning, expect continued minor to moderate flooding at most locations along the Mississippi River in our CWA as large amounts of water continue to flow downstream from the Minnesota River into the Upper Mississippi. Latest HEFS guidance suggests all sites except Alma will very likely (95%) remain in at least minor flood for the next 7 days. Monday night into Tuesday night continue to remain of high interest as most areas look to receive around 0.5" to 2" of rainfall with the potential for localized amounts to around 4". Smaller basins may return to flood as a result, with flashier basins showing a good deal of variation in HEFS projections due to the expected localized nature of those higher end amounts. Thus, interests along all water courses in the CWA will need to remain vigilant as Monday night approaches. && .ARX WATCHES/WARNINGS/ADVISORIES... WI...None. MN...None. IA...None. && $$ DISCUSSION...Ferguson AVIATION...JAR HYDROLOGY...Ferguson