Area Forecast Discussion
Issued by NWS La Crosse, WI
Issued by NWS La Crosse, WI
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205 FXUS63 KARX 171157 AFDARX Area Forecast Discussion National Weather Service La Crosse WI 657 AM CDT Fri May 17 2024 .KEY MESSAGES... - Shower and storm chances (20-30%) remain in the forecast for Saturday afternoon and evening. An isolated strong to severe thunderstorm cannot be ruled out if storms do develop. - Additional shower and thunderstorm chances remain for the end of the weekend and into next week. Keep up to date with the latest forecast, especially if you have outdoor plans next week. && .DISCUSSION... Issued at 425 AM CDT Fri May 17 2024 Precipitation Chances Through Saturday Night: A fairly quiet night so far as clouds have cleared over much of the local area. Surface observations and GOES Nighttime Microphysics reveal some patchy fog has developed over parts of the area and along some river valleys this early morning. A subtle wave was also noted in GOES satellite imagery generally moving from the Dakotas towards Minnesota this morning, with ongoing and developing showers/ storms advancing across Minnesota. Latest hi-res models try to develop a few echos during the day today locally as this system continues eastward. Model forecast soundings show some mid level moisture and elevated instability, but there is some concern with quite a bit of dry air shown in the lower levels into the day. For now have added in some low sprinkle/shower chances (mainly SE MN into NC WI) to account for any precip that may be able to develop. Otherwise, warm air advection will spread across the region today, with high temperatures rising into the upper 70s to low/mid 80s. As we head into Saturday an upper level shortwave trough is forecast to move eastward across southern Canada and the Northern Plains towards the region on Saturday. An associated surface boundary will move through the region bringing some chances for some showers and isolated storms to develop. Model guidance suggests increasing instability building through the afternoon along with steepening low level lapse rates as high temperatures rise into the 80s. Have noted model soundings do show some capping in place across the area, though a few models show this cap eroding in the north by the early evening. Will need to monitor conditions especially as more hi-res guidance continues to come in. For now, SPC has placed portions of north-central WI in a marginal risk (1 out of 5) for severe weather. Additional Showers & Storms Into Next Week: As we head into the end of the weekend and into early next week, flow aloft becomes southwesterly as an upper level trough develops in the western U.S. A series of shortwave energy looks to eject out from the trough and lift through the region, bringing a more active period of shower and storm chances. Ensembles do appear to be coming together on increasing shower and storm chances late Sunday night into Monday and again on Tuesday. With that said, there is still plenty of variability in details (i.e. timing, amounts) among GEFS and ECMWF ens solutions. This variability continues to result in broad precipitation chances in blended model guidance. However, in reality there will be shorter more focused windows for shower and storm chances which will be better reflected as details are refined. Do not want to jump ahead too much, but it will be a period to watch as WPC has highlighted a day 4-5 marginal for excessive rainfall and CSU severe progs are beginning to highlight some probabilities across the region. Keep an eye on the forecast for continued updates over the coming days, especially if you have outdoor plans next week. && .AVIATION /12Z TAFS THROUGH 12Z SATURDAY/... Issued at 650 AM CDT Fri May 17 2024 VLIFR/MVFR conditions have developed at KLSE/RST due to the recent rains, light winds, and clear skies this morning. A low level jet over parts of MN combined with a mide-level trough moving through is kicking off a few showers and isolated thunderstorms. The low level jet is forecast to weaken as it moves into the local area, however clouds should continue to push east and the winds aloft should begin to increase enough to keep KRST from dropping below MVFR. Generally kept the fog in through 14Z with improvement 14 to 15Z at both sites. Unsure if the spotty showers will reach RST/LSE due to low confidence in converage. Did include a VCSH at KRST for 1 hr. Depending on the heating today, could see additional showers early this afternoon with convective temperatures being met with highs in the 80s. After the morning fog, kept conditions VFR-sct-bkn100-150. Light southeast to south winds increase today. Mentioned stronger wind gusts at KRST 20-30kt knts this afternoon. The winds remain elevated tonight but drop off after 01Z. && .ARX WATCHES/WARNINGS/ADVISORIES... WI...None. MN...None. IA...None. && $$ DISCUSSION...EMS AVIATION...DTJ/Zapotocny