Area Forecast Discussion
Issued by NWS La Crosse, WI
Issued by NWS La Crosse, WI
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303 FXUS63 KARX 032337 AFDARX Area Forecast Discussion National Weather Service La Crosse WI 637 PM CDT Mon Jun 3 2024 .KEY MESSAGES... - Showers and storms continue through the evening across portions of northeast Iowa and southwestern Wisconsin. Small hail and locally heavy rainfall are the primary threats with these storms. - Additional showers and storms will progress through the region Tuesday evening bringing rainfall amounts of 0.5 to 1" with locally higher amounts possible. An isolated severe storm or two are possible across portions of southeast Minnesota and northeast Iowa. - Below normal temperatures with shower chances are expected into the latter half of the week with highs holding in the 70s for much of the region. Gusty winds to 30-40 mph are possible during the afternoon Wednesday and Thursday. && .DISCUSSION... Issued at 253 PM CDT Mon Jun 3 2024 * REST OF THIS AFTERNOON/EVENING: Showers and Storms across Northeast Iowa, Southwest Wisconsin Currently, showers and storms have developed across portions of northeast Iowa along a residual boundary resulting from clearing skies further west allowing for differential heating to take place. MLCAPE values in this region are around 1500-2000 J/kg certainly plenty of fuel to keep storms going into southwestern Wisconsin. However, with shear profiles being fairly unfavorable (20-30 kts of bulk shear), resulting in fairly messy convective development with storms struggling to maintain any organized updraft. As a result, primary threats with storms moving through will be locally heavy rain and hail (up to quarter sized) with initial updraft development. Storms will progress eastbound and should push east of the local area by 7-8pm at the latest. With prior rainfall across portions of northeast Iowa and southwest Wisconsin, may have to watch for some localized flooding concerns with already saturated soils. * TUESDAY/TUESDAY NIGHT: Showers and Storms, Additional Robust Rainfall Amounts With Some Severe Potential Tuesday will feature an amplified upper-level trough progressing through the region with an accompanying surface cold front. Earlier in the day, moisture advection will work its way into the region with southerly surface flow allowing dewpoints to reach well into the 60s for the afternoon with precipitable waters reaching to around 1.5" to 1.75" shown in the 03.00z HREF by late afternoon. With the increased moisture expecting fairly respectable instability with values of MLCAPE of around 1500 J/kg into the evening in the 03.15z. While the morning and much of the afternoon should remain mostly dry, cannot rule out a shower or two ahead of a subtle warm front that will push its way north into the region ahead of the aforementioned cold front. Getting into the evening hours, the recent CAMS push convection into our region from west to east along the incoming cold front. Currently, the 03.09z RAP really diminishes instability as the cold front pushes eastbound with only around 750-1000 J/kg of MLCAPE for the linear convection to work with as it pushes east of the Mississippi River. This combined with fairly marginal shear to work with as much of it is behind the boundary. This is reflected fairly well in the 03.00z joint CAPE/shear probs in the HREF which has very low probabilities (5-15% chance) for both 500 J/kg and 30 kts of bulk shear or greater. As a result, expecting minimal severe potential with low-mid level in model soundings only reaching to around 35-40 kts. So would be the kind of setup where a few gusts approach 50-55 mph or a quarter sized hail stone are possible and would be isolated in nature. This would be more likely to occur at onset of convection moving into the local area across portions southeast Minnesota and northeast Iowa where SPC has a slight risk (Threat level 2 of 5). Otherwise, with the aforementioned ample moisture and warm cloud depths of around 3500m shown in the 03.12z NAM/GFS. Expecting there could be some fairly efficient rainfall with the line of showers and storms that pushes through. Currently, 03.12z GEFS/EC ensemble show very good agreement (70-90% chance) on rainfall amounts of 0.5" or greater, with amounts of 1" or greater certainly possible (20-40% chance). The 03.12z HREF is in fairly similar agreement with roughly similar probabilities for 1" or greater. Consequently, river locations may want to be alert to potential rises in light of some of the prior rainfall that has fallen this week. * WEDNESDAY INTO THE WEEKEND: Mild Temperatures and Breezy Late Week With Shower Chances As we get through Tuesday, a broad scale upper-level trough will entrench itself over the eastern half of the CONUS with a broad ridge situated over the west subjecting our region to northwest cyclonic flow on the western periphery of the trough. As a result, expecting temperatures to trend below normal through the end of the week which essentially means highs persisting in the upper 60s to upper 70s this time of year. Current deterministic soundings show weak instability in the low levels each afternoon suggesting some cyclonic cumulus and spotty showers, particularly the further northeast you get. Additionally, with increasing low/mid-level wind fields increasing on the western flank of the synoptic trough and diurnal mixing to aid momentum transfer to the surface, would expect to see some increase in wind gusts late week. This would primarily be during the afternoon with the 03.06z EC ensemble showing respectable probabilities (40-70% chance) for wind gusts approaching 40 mph, particularly in more open areas across southeast Minnesota and northeast Iowa. Some subtle ridging Friday into Saturday may help moderate temperatures closer to normal ahead of a potential secondary trough ejection where guidance still tends to deviate in its position and timing. && .AVIATION /00Z TAFS THROUGH 00Z WEDNESDAY/... Issued at 637 PM CDT Mon Jun 3 2024 The showers and storms over southwest Wisconsin will move east of the area by 04.01z. With these already east of the TAF sites, kept them dry. With a deep layer of light winds and low level moisture enhanced by rain earlier in the day, included a broken IFR deck and BCFG for KLSE between 04.10z and 04.13z. With the CAMs keeping the next round or showers and storms west of the TAF sites until Tuesday evening, kept them dry for now and just increased the mid clouds in the afternoon. && .ARX WATCHES/WARNINGS/ADVISORIES... WI...None. MN...None. IA...None. && $$ DISCUSSION...Naylor AVIATION...Boyne