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Area Forecast Discussion
Issued by NWS La Crosse, WI
Issued by NWS La Crosse, WI
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242 FXUS63 KARX 112323 AFDARX Area Forecast Discussion National Weather Service La Crosse WI 623 PM CDT Thu Jul 11 2024 .KEY MESSAGES... - Some fog potential overnight, otherwise a quieter day expected for Friday. - Temperatures increasing into the weekend with highs in the upper 80s to low 90s and heat indices nearing 100 by Sunday. - Monitoring how the risk for severe weather unfolds for Saturday evening through Tuesday. The forecast remains complex and of lower confidence. && .DISCUSSION... Issued at 318 PM CDT Thu Jul 11 2024 Rest of Today - Tomorrow: Currently, GOES-16 water vapor imagery and 11.14z RAP 500mb heights shows a synoptic trough slowly pushing eastbound with a shortwave ridge positioned to our northwest. As we head through the afternoon, increasing instability (1000-1500 J/kg of MLCAPE) and some weak cyclonic flow may help develop showers, maybe an isolated storm. However with very weak shear profiles in the 11.14z RAP, would not expect any convective development to maintain in any organized fashion. However, with the 11.12z HREF showing ensemble max values for 3-hr QPF of up to around 1", could not completely rule out extremely localized areas receiving some higher totals. As we head into tonight, subsidence builds in with the aforementioned ridge allowing for more clearing in sky cover and calming winds. As a result, expecting some fog formation overnight, primarily in river valley locations and in central Wisconsin. Still some questions for coverage and density for fog with the 11.12z NAM trying to hold onto some saturation at 850mb in addition to some increased low-level winds at 925mb to around 10 kts. Regardless, with the aforementioned subsidence in place, should be a drier forecast for Friday outside of a few possible sprinkles across north- central WI with temperatures reaching into the middle 80s for most. Saturday - Sunday: A challenging forecast remains for the weekend as we monitor the potential for storms. The ridge that has persisted over the West is forecast to build towards the region on Saturday with a series of upper level shortwaves riding around it. With increasing moisture and warm air advection beneath an EML, strong instability looks to build across the region. Some indication in model guidance for elevated convection to develop early as one of the aforementioned waves moves through. However, as we continue to move into the day there remains some concern revolving around capping. Latest ensemble guidance, as an example/proxy, keeps us right on the eastern edge of the 700 mb temperature probabilities for 12C+ with model forecast soundings showing a bit less of a capped environment in the east. With a weak moisture transport convergence signal into southern Wisconsin along with the warm front, guidance suggests this could be enough to get showers and thunderstorms to develop. However, there seems to still be plenty of variability on how that evolves. Will need to continue to monitor trends over the next day or so, especially as we remain in a slight risk for severe weather from SPC. The story remains the same as with previous forecasts for Sunday, which will be dependent on Saturday`s convection as well as the strength of the cap building across the area. Model guidance again diverges quite a bit on how exactly this unfolds and where storms track. Overall though, current thinking would be that storms will track along the gradient of the instability pool and weaker capping (potentially favoring more north/northeast). With the strong instability and better shear to work with will be closely monitoring over the next couple days for the potential for severe weather. Of higher confidence is for increasing temperatures into the weekend. Sunday still looks to be the warmest day coming up, with current forecast high temperatures in the upper 80s to low 90s. This is supported by quite low spread (~2-3 degrees) between the 25th and 75th percentiles of the blended model guidance. There does not look to be much relief for the overnight as temperatures only drop into the 60s to low 70s. With the addition of increased dewpoint temperatures, heat indices may rise into the 90s to near 100 for some especially Sunday. Now, will note that one wrench in this would be any impacts from potential convective systems Saturday night into Sunday morning. Something to monitor as these details become more clear, but for now will continue to message the heat. Into Early Next Week: Some signal for an upper level trough to move across the region with additional showers and storms possible. However, it is uncertain how any convection on Sunday will impact storms on Monday. Otherwise, the heat does not look to last long as temperatures drop back to the 70s by mid-week. && .AVIATION /00Z TAFS THROUGH 00Z FRIDAY/... Issued at 623 PM CDT Thu Jul 11 2024 Isolated to scattered showers and storms will continue through 12.02z and then dissipate with the loss of diurnal heating. Still seeing mixed signals on valley fog. While the wind profile is favorable, the low level moisture is rather shallow and time of year is not as favorable. Due to this uncertainty, just went BCFG for KLSE. Some of the CAMs indicate that as diurnal warming occurs on Friday, there will be scattered 4-7K clouds and isolated to scattered showers and storms. The confidence ins the clouds was enough to include them, but not high enough to include the precipitation. && .ARX WATCHES/WARNINGS/ADVISORIES... WI...None. MN...None. IA...None. && $$ DISCUSSION...EMS AVIATION...Boyne