Area Forecast Discussion
Issued by NWS La Crosse, WI
Issued by NWS La Crosse, WI
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206 FXUS63 KARX 160345 AFDARX Area Forecast Discussion National Weather Service La Crosse WI 1045 PM CDT Sun Sep 15 2024 .KEY MESSAGES... - Summer warmth through much of the new week with highs in the 80s. - Dry start to the week with increasing rain chances from west to east moving into the weekend. && .DISCUSSION... Issued at 110 PM CDT Sun Sep 15 2024 OVERVIEW: models remain steadfast with reestablishing the upper level ridge axis across the region as we kick off the new week. There have been various interpretations of what will happen to the ridge as west coast troughs dig and spin shortwaves into the ridge`s western flanks and/or across its "top". While there have been some differences in the GEFS and EPS, one trend has been standing out - holding the ridge influence longer into the week, and keeping rain chances at bay (to the west). Comparing previous runs of the WPC cluster analysis of the 500 mb pattern show this trend with all clusters favoring it. Somewhat subtle, but definite impacts on the local forecast area`s sensible weather. Looking at the EPS and GEFS suites of members also portrays this, keeping the area essentially "dry" until the weekend. Further, the grand ensemble doesn`t start to press in small measurable rain chances (10-30%) until early Fri morning. The NBM has pushed back rain chances to Thu night, through the weekend. This looks more reasonable, although still might be a bit early depending on ridge strength. Meanwhile, there are some hints in the GEFS and EPS that the ridge could hold even longer through the weekend. A Canadian trough that looked to drop southeast for the weekend, kicking the ridge east and/or taking the top off of it, could hold across southern Canada - essentially skirting north of the ridge axis. Whether that shortwave would interact with others originating from the CONUS west coast and give that ridge a firm push is uncertain - lowering confidence in how the weekend will shape up. That said, confidence is high on the summer warmth through the work week and moderate/high that the local area will stay dry through mid week. PCPN: as mentioned in the overview section above, pcpn chances this week are going to hinge on the stoutness of the upper level ridge and the ability of west coast troughs/shortwaves to work into it. Recent model trends have the ridge winning out for most of the work week, spreading pcpn chances in from west to east for the weekend. This looks reasonable given some of the model uncertainties. And again, there is the possiblity the ridge influence wins out over the weekend - although these chances are likely less than 30%. Will continue to hold with the NBM for rain chances. TEMPS: no change in the summery forecast with the long range guidance holding fast to an upper level ridge and the pooling of warm air under it. The grand ensemble continues to paint 80-100% chances for 80+ degree highs Mon-Wed, trending a bit lower moving into the latter half of the week due to model uncertainties with ridge/shortwave placement (rain or no rain). GEFS and EPS ensembles also continue to show very little variance between its 10-90%, generally under 10 degrees with 75% of their members lying in the 80s. Dewpoints will be dropping as the ridge works in however, so humidity will be a bit more comfortable compared to this weekend. && .AVIATION /06Z TAFS THROUGH 06Z TUESDAY/... Issued at 1045 PM CDT Sun Sep 15 2024 VFR conditions are forecast through the period with current satellite showing mid to high level clouds moving into the area. No significant change in thoughts from the previous forecast as increased flow aloft/increase in clouds may work to limit fog development at KLSE. Otherwise, winds remain south/southeast through the period with some diurnal cumulus through the afternoon. && .ARX WATCHES/WARNINGS/ADVISORIES... WI...None. MN...None. IA...None. && $$ DISCUSSION...Naylor AVIATION...EMS