Area Forecast Discussion
Issued by NWS La Crosse, WI
Issued by NWS La Crosse, WI
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124 FXUS63 KARX 121547 AFDARX Area Forecast Discussion National Weather Service La Crosse WI 1047 AM CDT Wed Jun 12 2024 .KEY MESSAGES... - Scattered strong/severe storms possible between noon and 8 PM today. Primary threat is damaging winds with a secondary threat of hail. - Maybe a few strong to severe storms in north-central Wisconsin during the mid to late evening. - Additional strong to maybe severe storms are possible on Saturday night. - Near or record warm lows possible early next week. The highest chances at this time look to be Tuesday. Looking further out, CPC continues to have a slight (20-40%) risk for excessive heat for areas along and south of Interstate 90 from June 19 through June 25. && .MESOSCALE... Issued at 1045 AM CDT Wed Jun 12 2024 The 15Z surface analysis shows rapid heating taking place over northern Iowa south a secondary warm front lifting northward and arcing from Buffalo Ridge southeast to near Waterloo, Iowa with temperatures already in the low to mid 80s. Dewpoints to the south of the boundary area only hovering in the low to mid-60s, which is resulting in large inverted-V soundings and DCAPE values of 1000-1400 J/kg. A cluster of elevated storms developed the eastern flank of the 850-mb theta-e advection wing in western MN early this morning, with the storm clusters continuously outrunning the 500-1000 J/kg MUCAPE gradient and dissipating as they tracked eastward into central and eastern MN. However, this pool of higher 850-mb theta-e air is progressing eastward and will move over the region by midday. The last 30 minutes has already seen an uptick in lightning and storm organization along the western flank of the multi-cell cluster west of Mankato, MN, with bowing segments observed from KMPX. The HRRR has been suggesting this morphology over its last few runs, with this small MCS tracking along and just north of I-90 late this morning and early this afternoon. Winds of 60-70 mph would be the main threat given the environment in place, but hail cannot be ruled out as the 50 dBZ reflectivity heights have been touching the 1 inch hail heights periodically this morning and multiple 1-1.5 inch hail reports have occurred upstream. The organization of this upstream complex in south-central MN is occurring a little sooner than the HRRR depicted in its earlier runs, which may cause it to weaken sooner/farther west than was suggested given that the MUCAPE axis is still displaced to the west. However, this complex will present a narrow, focused window for damaging winds with the HRRR Neural Network progs depicting a 50% chance of winds in excess of 60 mph within this complex in southeast Minnesota early this afternoon. How soon this complex clears out will play an important role in the degree of destabilization that can take place in its wake ahead of the cold front sagging southeastward from western Minnesota. A second round of supercells/multi-cell clusters will work into the region along and ahead of this front after the 9pm timeframe, but the severe weather risk will hinge on how much airmass recovery takes place late this afternoon. && .DISCUSSION... Issued at 356 AM CDT Wed Jun 12 2024 Today... The CAMs have been gradually coming to some consensus early this morning. They are more in agreement that scattered showers and storms will develop north of Interstate 90 during the late morning and early afternoon as an area of 850 mb moisture transport moves into the region from the Central Plains. In the CAMs where convection develop earlier in the day, the storms are less intense than in the CAMS which develop convection more in the mid afternoon. This is simply due to the amount of instability that can develop ahead of storm initiation. With the area being in the right exit region of a 60-80 knot 250 mb jet, thinking that the convection will be more scattered. However, still cannot rule out some line segments in clusters of storms where cold pools can coalesce. With DCAPES climbing into the 1000 to 1500 J/kg and inverted Vs in the sub- cloud layer, damaging winds look to have highest probabilities (up to 25% in the HRRR neural network). In addition, with dry air aloft, hail looks to be a secondary threat. Tonight... A shortwave trough will move east through the area. This will result in an additional round of scattered showers and storms. With CAPE values decreasing, the threat for severe storms will be diminishing. However, there is some concern that HRRR is now showing a line of strong to potentially severe storms moving south into Taylor and Clark counties during the mid- to late evening. This is likely associated with southern extent of a shortwave moving through northern Minnesota and northern Wisconsin. Definitely something to watch in the CAMs today. Thursday... Another shortwave trough will move east through the region. As this occurs, a cold front will move south into Iowa and northern Illinois. During the mid- to late afternoon, the right exit of a 60 to 80 knot 250 mb jet will be moving into the region. This will enhance the lift across the southern half of the forecast area. At this time, it looks like the better instability and steeper lapse rates will be just south of the forecast area. However, there are a couple of CAMs suggest that Fayette and Clayton counties in northeast Iowa and Grant County in southwest Wisconsin could potentially see a few strong storms before they move south of the area. Fathers Day Weekend... A 500 mb ridge will build northward and eastward though the region. As this occurs, a warm front will lift northward into the region. 0-1 km mixed layer CAPES will range from 1000 to 2500 J/KG south of this front. As a 30-40 knot 850 mb jet focus moisture into the region, it continues to look like a mesoscale convective complex will develop ahead and approaching shortwave trough moving east out of the Northern Plains. Deep shear (0-6 km) of 25 to 35 knots in the ECMWF and 30 to 50 knots in the GFS will be potentially found for areas along and south of Interstate 90. With the soundings showing surface-based storms, there could be the potential for damaging winds. In the wake of the shortwave trough, a cold front will push south into northern Iowa, far southern Wisconsin, and northern Illinois on Fathers Day and then move back to the north as a warm front on Sunday night as the upper level ridge build across the region. The GFS continues to have much higher (2500-3500 J/kg) 0-1 km mixed-layer CAPES values than the ECMWF (1000-2000 J/kg). Unlike Saturday night, the 0-3 km and 0-6 km shear is rather light with values generally less than 20 knots. With a mean precipitable water value around 1.5 inches and warm cloud layer depths climbing to around 4 km, these showers and storms will be efficient rain producers from Saturday night into Sunday night. If these storms train over the same region, there could be some localized flooding. Monday through Tuesday... 500 mb heights will be climbing across the southern Great Lakes into the Mid-Atlantic Region. This will result in anomalous warmth (85th percentile or higher). Record highs and warm lows will be possible in this region. For our area, the highest chances will be on Tuesday when some warm low temperatures along and south of Interstate 90 could be tied or broken. && .AVIATION /12Z TAFS THROUGH 12Z THURSDAY/... Issued at 650 AM CDT Wed Jun 12 2024 Mid and high clouds increasing with convective debris and potential for VFR ceilings and MVFR visibilities with any storms. Satellite imagery and radar shows ACCAS developing across southern MN with thunderstorms from southwest MN into southeast SD. Initially, conditions are a bit dry, however as moisture transport increases across the Plains into the Upper Mississippi Valley, deep moisture returns the the area. Meanwhile, a strong upper level jet and a mid level shortwave move across the region as well. Scattered thunderstorms are forecast to increase across the region. Initially the storms will lift northeast across MN, however hi- res model show movement southeast toward RST/LSE this afternoon. Storms this morning with outflow and clouds could affect where the storms develop, but did include a prob30 along with gusty winds especially from 20-01Z. Additional storms may develop after 01Z, however confidence is low on timing and location, so did not include in the TAF. South winds 5 to 10kts increase 10 to 15kts with gusts 20 to 30kts, however stronger gusts with storms are possible. && .CLIMATE... Issued at 224 AM CDT Wed Jun 12 2024 A strong upper level ridge will build northward into the region for early next week. Both high and low temperatures will likely climb into the 85th or higher from at least Monday into Tuesday. While high temperatures (mid-80s to around 90) look to be too low for records to be tied or broken, the low temperatures (around 70 to the mid-70s) along and south of Interstate 90 will be warm enough for some potential warm low records to be tied or broken. At this time, the highest chances look be on Tuesday. Looking further out, CPC continues to have a slight (20-40%) risk (20-40%) for excessive heat for areas along and south of Interstate 90 from June 19 through June 25. && .ARX WATCHES/WARNINGS/ADVISORIES... WI...None. MN...None. IA...None. && $$ MESOSCALE... DISCUSSION...Boyne AVIATION...Zapotocny CLIMATE...Boyne