Area Forecast Discussion
Issued by NWS La Crosse, WI
Issued by NWS La Crosse, WI
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394 FXUS63 KARX 110902 AFDARX Area Forecast Discussion National Weather Service La Crosse WI 402 AM CDT Thu Jul 11 2024 .KEY MESSAGES... - Generally quiet and seasonal weather for today and Friday. A stray shower or rumble of thunder possible for some today. - Temperature warm for the weekend with highs around 90 and heat indices nearing 100 by Sunday. - Still assessing how the severe weather risk for Saturday evening through Tuesday will unfold. The forecast remains complex and of a lower confidence. && .DISCUSSION... Issued at 400 AM CDT Thu Jul 11 2024 Today - Friday: Seasonal Temperatures, Mostly Dry Mid to high clouds attendant with a persistent MCV centered over eastern Iowa have lingered for longer than forecast across much of the region overnight, tempering the risk for fog for most locales. Still cannot rule out fog with visibilities under a mile forming west of Highway 52/63 where heavier rain fell yesterday, burning off shortly after sunrise. For today, the energy lobe with this final shortwave wrapping through the longwave trough stays east of the forecast area, though there may be just enough cyclonic flow in place to pop a few showers along a corridor near I-90 between drier air to the north and stronger 700-600-mb capping to the south. However, forcing and shear are weak and SBCAPE values are <750 J/kg. The steering flow remains light and storms are not expected to move much, therefore any areas under these cells could pick up a quick 1/2 to 1 inch of rain as shown in the max QPF fields from the 11.00Z HREF--but these areas will be VERY localized in nature. With general height rises occurring through the day on Friday ahead of shortwave ridging and deeper moisture still lingering to the south, have stayed with a dry forecast for Friday but did increase sky cover above the NBM "clear" grids as we look to at least reach convective temperatures for the afternoon on Friday. The stagnant airmass lingers for one more day before southerly flow sets in for Friday, thus have forecast highs very similar to yesterday and started nudging highs a few degrees warmer for Friday. Saturday - Sunday: Slowly Warming, Severe Weather Details As surface high pressure slides further to the east, a warm front surges northeastward Friday night and Saturday morning. With a weak upper level shortwave moving through at this same time, cannot rule out elevated convection developing along this corridor of theta-e advection, but these storms should be weaker in nature with the stronger jet displaced to the west. However as we go through the afternoon and evening, SBCAPE values increase to over 3000 J/kg under a deepening EML and shear profiles becomes more conducive for organized storms. That being said, there is concern that we could remain capped over the forecast area and differences exist in the timing of the instigating upper level wave, with some solutions lingering the impulse more into Sunday morning. The Slight Risk from the SPC for Saturday afternoon/night is quite conditional in nature and will require further assessment over the next few days, especially as we move into the range of the CAMs. For Sunday, the zonal +21 to +24 C thermal ridge axis builds into the region, which is shaping up to be the hottest of the stretch with highs around 90 and dewpoints in the low to mid-70s pushing heat indices into the upper 90s to near 100. There exists minimal spread (2-3 degrees) in the inter-quartile range of the NBM inputs for max temperatures on Sunday, thus forecast confidence is on the high side. That being said, if we somehow have an MCS that comes through late Saturday night into Sunday morning, highs on Sunday may need to be adjusted downward in areas affected by convective debris or the cold pool. The severe weather threat on Sunday hinges on what transpires on Saturday night. The northwesterly flow during the day on Sunday is rather laminar in nature and there isn`t much of a signal to latch onto for determining how the convective threat will evolve. There is a possibility that we find ourselves between systems with the next MCS arriving Monday morning. Monday - Wednesday: Storms and Warmer Temps Shifting South The global models diverge quickly on the timing of Monday`s shortwave and subsequent waves on Tuesday/Wednesday. The thermal ridge should be shunted southward with the passage of Sunday`s or Monday`s storms, but confidence is low on any further details. The warmer air and storm threat pushes south of the area by Tuesday, resulting in a very pleasant and dry forecast for midweek as highs fall back into the upper 70s. && .AVIATION /06Z TAFS THROUGH 06Z FRIDAY/... Issued at 1031 PM CDT Wed Jul 10 2024 The main question overnight is how fast will the mid and high clouds linger overnight. This will likely impact fog development in the river valleys overnight. With low confidence on this, kept the valley fog in for KLSE. As we reach convective temperatures during the late morning and early afternoon, a scattered to broken 4-7K deck of clouds will develop. Some of the CAMs even suggest that there will be some isolated to scattered showers and storms. Confidence was low on whether any of the TAF sites would see them, so kept them out of the forecast for now. && .ARX WATCHES/WARNINGS/ADVISORIES... WI...None. MN...None. IA...None. && $$ DISCUSSION...Skow AVIATION...Boyne