Area Forecast Discussion
Issued by NWS La Crosse, WI
Issued by NWS La Crosse, WI
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935 FXUS63 KARX 081052 AFDARX Area Forecast Discussion National Weather Service La Crosse WI 550 AM CDT Mon Jul 8 2024 .KEY MESSAGES... - Hit or miss showers and storms (20-40% chance) from now through the middle of the week. More likely you will remain dry than not. - Temperatures holding steady for much of the week with highs in the upper 70s and lower 80s. A warming trend is expected late week and this weekend where highs could reach into the 90s for some areas. - Locations along the Mississippi River from Guttenberg, IA on northward are observing falling river stages that are expected to continue through this week. && .DISCUSSION... Issued at 329 AM CDT Mon Jul 8 2024 Today - Wednesday: Periods of Showers and Storms The overall synoptic pattern over the next couple days revolves around a broad 500mb trough that be seen clearly in the GOES-16 water vapor imagery and RAP 500mb heights. Embedded within this, there are multiple weak areas of vorticity within this pattern with one swinging through east/northeastern IA early this morning and weakening with limited instability currently in place. As we progress through the early morning, this MCV will make its way northeast bound with a broad area of weak showers and isolated storms with it. Additional, weak pieces of energy behind it through the first half of the week can be noted in the 500mb flow as well. Consequently, expecting scattered showers and storms to pop up with increasing diurnal instability (500-1500 J/kg) during the afternoon/evening on Monday. Expecting fairly limited coverage with these during afternoon/evening so would anticipate that any given location is more likely to be dry than wet. Additionally, with limited shear profiles (much of your stronger synoptic winds are above 400mb in the 08.04z RAP), would expect very low potential for any severe threat with these having overall light rainfall amounts with maybe some pockets of heavier rainfall if storms are slow moving. As diurnal instability wanes later into the evening, expect convective coverage to diminish. Tuesday will likely feature a similar type of setup with marginally lower instability (500-1000 J/kg) so have trended precipitation chances ever so slightly lower (15-25% chance) for Tuesday but similar idea with scattered showers/storms but most locations remaining dry. As we turn to Tuesday night and Wednesday, the remnants of Hurricane Beryl will track well southeast of the region with the current NHC forecast have the system as an post-tropical cyclone moving through portions of southern MO/IL/IN and into the Ohio valley. Guidance has generally shifted much of the heavier precipitation further south east with virtually no probabilities (under 10% chance) in the 07.00z GEFS of seeing 0.5" or greater in southwestern WI. Regardless, could see some wrap around showers and isolated storms with the combination of cyclonic flow around the system and a descending shortwave from southern Canada. Overall the heavy rain threat from now through Wednesday seems minimal with precipitable waters in the 1.3" to 1.6" range and marginal warm cloud depths to around 3.5km. As a result, probablistic guidance paints light amounts for our local area from now through Wednesday with the 07.00z GEFS/EC ensemble showing lower probabilities (20-50% chance) for total QPF of 0.5" during this time. Therefore, would need slow moving or repeating thunderstorms to get any flooding issues. Thursday - Sunday: Warming, Drier Trend Going into late week, a building ridge out west tries to nudge slightly eastward and with the synoptic trough pushing towards the eastern US will subject our region to northwesterly flow. Consequently, expecting a drier but warmer pattern to ensue with high temperatures beginning to trend warmer than normal by late week and into the week with the 07.00z grand ensemble (GEFS/EC ensemble/Canadian ensemble) wants to show an inter-quartile range for high temperatures at La Crosse of 86 to 93 degrees with a median of 89 on Sunday. With probabilities for highs of 90 degrees or greater of around 20-60% across the region by Sunday. Shower/storm chances right now trend lower with the NBM in the quasi-zonal to northwest flow. However, will want to monitor for any pieces of shortwave energy that can pivot into our region during this period. So overall would say this is more a reflection of lower confidence in any specific features that can increase our precipitation chances at this time. && .AVIATION /12Z TAFS THROUGH 12Z TUESDAY/... Issued at 550 AM CDT Mon Jul 8 2024 CIGS: mostly looking at SCT-BKN VFR clouds through the period. WX/vsby: instability/upper level shortwave also look to trigger isold/scattered -shra/ts later this afternoon with latest CAMS favoring 21-02z. Opting to not add a VCSH given the more miss than hit nature of the convection. Will monitor trends through the day and adjust forecast is needed. Potential for the river valleys to fog up tonight with light near sfc wind field. More likely if extended period of SKC/SCT is realized - less so if more BKN. Will add BCFG to KLSE for now. WINDS: southerly becoming more westerly moving through the afternoon. Going to stay relatively light. && .HYDROLOGY... Issued at 329 AM CDT Mon Jul 8 2024 Falling river stages can be noted from Guttenberg, IA on northward along on the Mississippi River. Falling river stages are expected to continue through this week from southwest WI/northeast IA on northward. Currently, locations at La Crosse, WI, McGregor, IA and Guttenberg, IA remain at Moderate flood stage with several other locations at minor flood stage. As we head through this week, expecting scattered showers and storms during the afternoon/evening hours on Monday and Tuesday to produce generally light rainfall amounts. Locally heavier rainfall will be possible with slow moving storms or if storms repeat over the same locations. Overall though these showers/storms are not expected to have much impact on the Mississippi River basin. && .ARX WATCHES/WARNINGS/ADVISORIES... WI...None. MN...None. IA...None. && $$ DISCUSSION...Naylor AVIATION.....Rieck HYDROLOGY...Naylor