171 FXUS63 KMPX 230648 AFDMPX Area Forecast Discussion National Weather Service Twin Cities/Chanhassen MN 148 AM CDT Mon Jun 23 2025 .KEY MESSAGES... - Extreme Heat Warning expired last evening but high heat/humidity continues through the overnight hours. - Conditional threat for severe thunderstorms tonight. Slight Risk (Level 2/5) in place across central and western Minnesota. - Active weather pattern resumes Tuesday. Multiple rounds of showers and thunderstorms will produce heavy rain this week. && .DISCUSSION... Issued at 306 PM CDT Sun Jun 22 2025 The ongoing round of record setting heat and humidity continues across the Upper Midwest this afternoon. Afternoon highs are on track to reach the mid-90s for most locations, with even warmer temperatures near 100 degrees across western Minnesota. Combine the heat with dew points in the low to mid 70s and you get another afternoon of triple digit heat indices. An Extreme Heat Warning continues through this evening, before heat indices fall below headline criteria. At this point, we are not planning on extending the Warning past 9 PM, however, the duration of fatigue from heat and humidity may persist across far eastern MN/western WI tonight as minimum temperatures aim to stay above 75 degrees prior to a cold frontal passage early Monday. The forecast focus will shift from dangerous heat to the potential for strong to severe thunderstorms tonight. The setup for strong convection is tied to the large scale relationship between the heat dome over the Great Lakes (characterized by a 594dm ridge) and a longwave trough over the Pacific Northwest. Afternoon surface analysis depicts ~998mb surface low over eastern SD, located in the exit region of the aforementioned upper trough. The low is forecast to slide northeast over the coming hours, which will drag a cold front from west to east across the area tonight into tomorrow morning. The prefrontal environment is volatile, owing the ongoing moisture advection of lower 70s Td`s. This is illustrated by RAP mesoanalysis capturing 2500+ J/kg of CAPE, steep lapse rates between 8-9 deg C/km, and 30-40kts of effective shear. That being said, we continue to refer to this setup as conditional, given the presence of anomalously warm mid-level temperatures (700mb T`s ~16C/850mb T`s ~22C) acting as a stout cap aloft. With this in mind, we feel fairly confident that the coverage area will remain storm free through at least ~1-2z, prior to what will be more successful attempts at convective initiation as the front draws near. As previously stated, the best chance for severe thunderstorms will be across western MN, which is in closest proximity to the front while also working in tandem with the eroding cap/pool of strong instability. Large hail and damaging winds are the greatest concern, however an isolated tornado or two cannot be ruled out across west-central MN closer to the surface low. SPC recently issued a Tornado Watch across eastern ND/northwest MN to reflect this potential. HREF tends to show the low to mid level wind fields displaced well to the east of the surface front tonight, which may limit the overall forcing available for a more widespread threat (especially when factoring in the thermo scenario). CAMs show an uptick in scattered shower/storms as the upper level forcing shifts east over the region heading into Monday morning, which is reflected by 20-40% PoPs. Given the conditional nature of this setup, SPC has maintained a Day 1 Slight Risk (2/5) for central/western MN. A Marginal Risk (1/5) is in place across SE MN/western WI. The front will continue to move to the east/southeast Monday. This feature will serve as the focus for renewed shower and thunderstorm activity as early as late Monday morning, though more likely into the early afternoon. Slight differences in the frontal position by mid to late morning across the guidance suite have prompted a Marginal Risk (1/5) to be extended across eastern/southern MN, however the greater chance for stronger convection is SE of a line from Rochester to Eau Claire where a Slight Risk (2/5) is in place. Once again looking at damaging winds and hail as the primary threats, though a brief spin-up cannot be ruled out in the expected prefrontal environment. The eastward movement of renewed convection will signal the end of active weather for tomorrow. Northwesterly winds will bring a "cooler" day with highs in the 70s across western MN and the lower 80s along and east of I-35. The aforementioned front will sag south of the MN/IA border heading into Tuesday and is forecast to stall in this general area through midweek. Guidance displays a zonal pattern aloft taking shape this week, which will result in multiple waves sliding east across the flow/the surface boundary. We anticipate several rounds of showers and thunderstorms driven by moisture transport into the boundary in combination with the passing waves aloft. With PWATs forecast to be near/in excess of 2", each round of convection will likely produce heavy rain and training of thunderstorms will become a concern from a hydro perspective. WPC`s latest QPF forecast features 2-3" of QPF across southern MN/western WI from Tuesday morning through Friday morning. Given the frontal position, lower amounts between 1-2" are forecast across central MN. Training of thunderstorms and enhanced rainfall rates tied to stronger convection may produce more substantial localized amounts, though will lean on CAM solutions in the coming days to better define the corridors of highest rainfall. WPC continues to display Slight Risk ERO`s across the southern half of the area Tuesday-Thursday. On the flip side, the active wet pattern will keep temperatures in check, so look for a more comfortable stretch of air with highs in the 70s midweek. Guidance teases height rises within the zonal flow heading into next weekend, which supports highs climbing back into the 80s. && .AVIATION /06Z TAFS THROUGH 06Z TUESDAY/... Issued at 1249 AM CDT Mon Jun 23 2025 Showers/thunderstorms developing over western MN will drift NE, potentially impacting a number of TAF sites through the overnight hours with brief MVFR-worthy conditions. Higher confidence in the TSRA impacting TAF sites as allowed several PROB30s to be converted to TEMPOs for the first 6-9 hrs of some TAFs. Otherwise, confidence remains fairly low on the occurrence of TSRA at sites during the afternoon-evening hours, so have been more judicious on that side. Otherwise, as the cold front responsible for the storms shifts east, ceilings will likely drop to MVFR range for much of the morning into mid-afternoon hours before clearing prevails. Some storms may impact EAU late in the period but confidence too low to include at this point. Winds will remain generally NW, with sustained speeds in the 10-15kt range with higher gusts. KMSP...VFR with LLWS conditions to start, but LLWS conditions abate shortly after initialization. Only concern for precipitation comes during the middle-to-late portions of the morning push as some storms over western MN may make a run for eastern MN after sunrise. With the frontal passage, ceilings are likely to drop to MVFR range late morning followed by ceilings lifting/clearing going into the afternoon hours. /OUTLOOK FOR KMSP/ WED...SHRA/MVFR. Chc TSRA. Wind E 5-15kts. THU...SHRA/MVFR. Chc TSRA. Wind E 5-15kts. FRI...VFR. Wind variable 5 kts. && .MPX WATCHES/WARNINGS/ADVISORIES... MN...None. WI...None. && $$ DISCUSSION...Strus AVIATION...JPC