FXUS63 KARX 212238 AFDARX Area Forecast Discussion National Weather Service La Crosse WI 540 PM CDT Sat Jun 21 2025 .KEY MESSAGES... - Dangerous heat continues through Sunday with heat indices reaching 100F to 105F, potentially climbing above 105F. - New week brings persistent potential for heavy rain but low forecast confidence overall in amounts and locations most impacted. Monday through Friday warrant close monitoring for potential flooding impacts. && .DISCUSSION... Issued at 208 PM CDT Sat Jun 21 2025 Dangerous heat through Sunday Well advertised heat event is unfolding this afternoon as an upper high over the low to mid Mississippi Valley has brought very warm temperatures aloft to the region while also bringing low level moist advection. Additionally, 45/35 knot 850/925mb winds and sunny skies in most locations are leading to surface winds mainly in the 15 to 25 mph and concomitant efficient mixing. Surface heating has occurred quickly today with temperatures as of 18z are around 90 with dewpoints in the low to mid 70s, yielding heat indices in the upper 90s. Expect these to reach the triple digits areawide over the next few hours as insolation is maximized. Tonight, with lee cyclogenesis occurring to our west, resulting surface gradient should help a light breeze continue into the nighttime hours. While mostly clear skies are expected, have leaned temperatures upward a bit in line with the expected breeze. Record warm lows appear to be a good bet as temperatures only fall to the upper 70s. Sunday, dangerous heat continues as, while the ridge starts shifting to the east, low level moist advection refuses to yield as flow through the column becomes south-southwestwerly. Thus, while air temperatures may be a touch lower than today, 21.12z HREF suggests a good chance (50-90%) for heat indices to reach or exceed 100 once again. Multiple rounds of heavy rain potential Aforementioned moist advection should lead to anomalously moist conditions with 21.00z NAEFS PWAT values near the 99.5th percentile Monday through Wednesday. With the ridge shifting to the east, cooler temperatures aloft should allow for deep lift to occur ahead of numerous disturbances progged to eject downstream. That said, as time goes on, lapse rates will moderate and best forcing for ascent looks to increasingly focus along an E-W oriented quasi-stationary front, introducing the potential for heavy rain to focus on the same areas depending on how mesoscale processes shake out with respect to exact frontal position. Given the high amount of moisture available through the column, should heavy rain in the same location occur during 1-2 consecutive rounds of precip, flash flooding would be a concern. Should heavy rain occur within a basin across a few different rounds, river flooding would easily become a concern. In any case, 21.00z LREF mean QPF values are in the 2-3.5" range across most of the CWA and even LREF minimums are around an inch, suggesting getting appreciable rain at some point next week is a near certainty. As for severe convection, with the move toward a more moist adiabatic profile occurring over time, focus is on Monday when steeper lapse rates are still present, yielding MLCAPE values of around 1500 J/kg in the presence of sfc-6km shear of 25-35 knots. Near-surface shear profiles appear unsupportive of tornadoes but mid- level lapse rates and aforementioned shear would support potential for a bit of severe hail and, given modeled DCAPE of around 1000 J/kg, severe wind gusts. && .AVIATION /00Z TAFS THROUGH 00Z MONDAY/... Issued at 540 PM CDT Sat Jun 21 2025 CIGS: SKC/FEW conditions through Sunday evening. Trends don't favor an increase in clouds/cigs until Monday afternoon when a sfc front and bits of shortwave energy bring the promise of showers/storms. WX/vsby: no impacts through Sunday night. Next shot for shra/ts will come Monday as a sfc front eases in from the west. This boundary is likely to wobble across the region, in a northeast-southwest running orientation, providing a focus for periods of shra and a few ts through the new work week. WINDS: relatively strong/gusty from the south will continue tonight through Sunday night. If the winds do decouple this evening (don't stay gusty), some threat for LLWS as RAP/HRRR have winds blowing 50+ kts by 2kft through 06z. && .CLIMATE... Issued at 238 AM CDT Sat Jun 21 2025 Daily record high and warm lows this weekend (record / forecast): Maximum Warm Low June 21 La Crosse: 102 (1988) / 96 74 (1943) / 77 Rochester: 99 (1988) / 95 72 (1943) / 76 June 22 La Crosse: 97 (1995) / 96 75 (1983) / 80 Rochester: 94 (1911) / 94 71 (1983) / 77 Warmest June Lows: La Crosse: 80F on June 29, 1931 Rochester: 77F on June 26, 1943 and June 19, 1953 Warmest All-Time Low Temperatures: La Crosse: 81F on July 21, 1901, July 13, 1995, and July 4, 2012 Rochester: 85F on July 3, 1911 && .ARX WATCHES/WARNINGS/ADVISORIES... WI...Heat Advisory until 9 PM CDT Sunday for WIZ017-029-032>034- 041>044-053>055-061. MN...Heat Advisory until 9 PM CDT Sunday for MNZ079-086>088-094>096. IA...Heat Advisory until 9 PM CDT Sunday for IAZ008>011-018-019-029- 030. && $$ DISCUSSION...Ferguson AVIATION.....Rieck CLIMATE...Boyne