Area Forecast Discussion
Issued by NWS La Crosse, WI
Issued by NWS La Crosse, WI
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269 FXUS63 KARX 080340 AFDARX Area Forecast Discussion National Weather Service La Crosse WI 1040 PM CDT Fri Jun 7 2024 .KEY MESSAGES... - Rain likely across much of the area (50-90% chance) overnight and into Saturday morning. Rain chances (50-70%) have increased across portions of northeast IA and southwestern WI. - Below normal temperatures expected this weekend and early next week. An isolated shower or two are possible late Saturday and Sunday (10-20% chance). - Warming trend is expected with temperatures trending above normal by the second half of next week. Highs will reach well into the 80s for much of the local area. && .DISCUSSION... Issued at 240 PM CDT Fri Jun 7 2024 Tonight - Saturday: Rain Likely Overnight, Isolated Thunder Possible Current surface analysis shows low pressure centered over the pan handle of Nebraska with southerly flow advecting moisture north in a somewhat narrow ribbon 3/4ers the width of the state. The 60F dewpoint line has rapidly shot north to near I-80 with radar showing elevated /10ft/ showers and storms across SD into nwrn IA early this afternoon. This area is associated with a strong area of 600-700mb frontogenesis within the MuCAPE gradient of 250-750 J/Kg per SPC, with the heart of the MUCAPE pool further southwest over wrn NE/CO. Per latest RAP guidance, this elevated forcing /fgen/ translates east today in swift zonal flow, grazing northeast IA closer to I-35 early this evening, however without the elevated instability /which spreads in late tonight/. With the low-level ridging and dry air mass holding firm across the Upper Miss Valley, would think this will translate into thick clouds at 10kft and scattered very light showers or sprinkles. GOES water vapor showing a well-formed shortwave trough in northwest flow dropping southeast through srn Saska/Alberta at 18Z. Short term model consensus has moderate 300-500mb QVector convergence along and north of I-90 Saturday morning with moderate isentropic lift through the low-levels as well with this wave. As the low-level southwest flow increases late tonight as the ridge axis pushes east, low MUCAPE instability /100-300 J/Kg/ does shift in near and south of I- 90, and is speed convergent, isentropically upgliding. Have a hard time believing showers would not be present south of I-90 with isolated thunder too after about 3 am. At that same time, a cold front with the northwest flow trough is heading through MN, moving through the area Saturday morning into very early Saturday afternoon. This will act to prolong the period of showers Saturday and there is some timing spread among the CAMS. So, forecast will paint a little bit bigger window than may actually occur and hopefully timing can be refined in the next 12 hours. So, continued very high rain chances near and I-90 and north late tonight into Saturday, and increased them southward into northeast IA and southwest WI /60%/...with clearing trying to work in post-frontal in the afternoon from NW->SE. Saturday Night - Monday: Cool, Slight Shower Chances Heading through the rest of the weekend, temperatures will continue to remain on the cooler side of average with highs consistently shown in guidance to remain in the upper 60s and lower 70s areawide, roughly around 5-10 degrees below normal. Monday will likely be the coolest day with the 07.00z grand ensemble (GEFS/EC ens/Canadian ens) showing an inter-quartile range of 66 to 72 degrees for highs at La Crosse with a median of 70 degrees. A few showers and storms are possible late Saturday and Sunday with continued cyclonic flow in place allowing for cooler air aloft enabling some diurnal instability. However, this is fairly inconsistent between different CAMs runs so will hold with lower precipitation chances (10-20%) for now. Tuesday - Friday: Warming Trend, Shower/Storm Chances As we approach the middle of next week, deterministic guidance shows a weak shortwave trough progressing towards our region. While deterministic guidance has come into some more agreement on how this trough will manifest, still lots of questions with available moisture and any instability associated with it. Consequently, confidence still remains not the highest with the 07.06z GEFS showing around 50-70% chance for measurable precipitation with this wave. As a result, have some increase in precipitation chances (20-40% chance) with the recent NBM for Tuesday but will still need to assess, either way would likely be very light amounts and have minimal thunder chances. Otherwise, the other story for next week, mainly into Wednesday is an upper-level ridge will progress east and flatten as it inches its way into our region. While this will help warm temperatures some, northwest flow appears to maintain through the period which should keep temperatures from trending well above normal when also considering the 07.00z EFI shows minimal signal for significantly above normal temperatures. Consequently, expecting highs to get as warm as the middle to upper 80s, perhaps a 90 in a few spots. Thursday currently appears to be the warmest day next work week with the NBM percentiles showing an inter- quartile range of 84 to 91 degrees with a median of 87 degrees. && .AVIATION /06Z TAFS THROUGH 06Z SUNDAY/... Issued at 1023 PM CDT Fri Jun 7 2024 Scattered showers moving west to east at 08.04Z ushering in VFR cloud deck. Widespread precipitation chances will be slow to usher east as low level dry air sustains for a short time locally. Eventually, widespread precipitation chances reach the local area overnight into early Saturday morning, ushering in MVFR clouds. No visibility restrictions expected as intensity expected to remain light. Model guidance is optimistic to lift as the precipitation forcing quickly moves east into central Wisconsin into Saturday afternoon. && .ARX WATCHES/WARNINGS/ADVISORIES... WI...None. MN...None. IA...None. && $$ DISCUSSION...Baumgardt/Naylor AVIATION...JAR