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Area Forecast Discussion
Issued by NWS Twin Cities, MN
Issued by NWS Twin Cities, MN
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078 FXUS63 KMPX 240830 AFDMPX Area Forecast Discussion National Weather Service Twin Cities/Chanhassen MN 330 AM CDT Mon Jun 24 2024 .KEY MESSAGES... - Slight Risk (Level 2/5) of severe thunderstorms this evening. Uncertainty remains due to a conditional setup, but if storms develop they`d likely have significant severe weather given the environment. - Active pattern continues with another round of widespread rainfall Thursday afternoon through Friday night and another system for the start of July. - Local river levels remain on the rise following the recent rainfall. River flooding remains a concern, as several sites have yet to crest in moderate or major flood stage. && .DISCUSSION... Issued at 329 AM CDT Mon Jun 24 2024 All eyes are on today and the potential for a high-end severe weather event across MN/WI. Water vapor imagery shows a series of shortwaves this morning from Montana up into Saskatchewan. In response to these features, we`ve seen both a very warm EML and Gulf moisture getting pulled north up into the Dakotas. Within this environment, we`ve seen a severe cluster of storms drop out of Saskatchewan into north central NoDak. These storms have not been handled well by guidance (including CAMs) and represents the first bit of uncertainty for this forecast. The CAPE gradient and 850- 300mb thickness pattern would say this cluster of storms will make a run toward Fargo the rest of the night, with the big question being how deep into MN does this cluster make it as it encounters an environment with less instability and increasingly stronger capping (as h7 temps push to upwards of 14+ C). Given the increasingly hostile environment for convection, this activity is expected to be not much more than some disorganized showers (if they`re even still producing rain) into central MN by late this morning. However, how this activity modifies our environment in terms of what the northward extent of the capping h7 thermal ridge and surface warm front end up being are still uncertain for our potential severe event late in the day. For later today/tonight, the warm front is expected to at the very least clear the upper MN River. Dewpoints behind this warm front will increase into the mid and possibly even upper 70s, this combined with air temperatures in the upper 80s to lower 90s sends forecast heat index values into the 100 to 105 range from Fairmont and Mankato up along the MN River to the SoDak border, so have issued a Heat Advisory along the upper MN River Valley for today. h7 temperatures will be increasing to between 14C and 16C. These warm h7 temps will allow for dry adiabatic mid-level lapse rates to develop above a surface environment with observations in the ballpark of 90/75. This combination will create a thermodynamic environment with extreme instability, with mlCAPE values likely to exceed 5000 j/kg in the warm sector. This instability is the reason for the "boom" or "bust" messaging we`ve had. If updrafts form in this environment, they will be strong to violent (boom), but those toasty h7 temps also mean we have the bust in play given the capping. When looking at the HREF the non-HRRR members all produce a forward propagating MCS, but differ on where that develops. The northern outlier is the Fv3, which keeps its MCS north of the Arrowhead. At the other end of the spectrum, you have the ARW/NSSL WRFS which bring the MCS through central MN and western WI (including the Twin Cities). Given the convective debris we`ll have today, we favor that more southern solution, with storms developing in west central MN in the late afternoon, quickly growing upscale and racing southeast along the CAPE gradient. This is a high end severe environment given the degree of instability with the curved hodographs and 40-50 kts of deep layer shear. There`s still enough uncertainty on convective initiation that the SPC maintained a slight risk, but the hatched wind area they have is a pretty good indication for where the most likely region to see a significant wind event evolve resides. For Tuesday, some instability lingers across southern MN, but the main surface front by the afternoon will reside from roughly Des Moines to Milwaukee, so other than some lingering showers in southern MN Tuesday morning, Tuesday continues to look like a day to dry out with mostly sunny skies and highs in the low to mid 80s, very similar to what we just saw on Sunday (minus the isolated showers in western WI!). Wednesday will be dry as well as high pressure moves through, but as we`ve seen going back to the second half of March, dry stretches tend to not last all that long! The next period of active weather continues to be Thursday through Friday, with Thursday night/Friday morning looking to be the most likely window for seeing more showers/storms. If you`re looking for some good news, models overnight started backing down some on the heavy rain signal as this system is looking a bit more organized. The 00z guidance has started trending toward the idea that we see a double warm front structure develop with this system. One down in Iowa will have the tropical airmass (and dewpoints in the 70s, with another up along the international border (with dewpoints in the 60s). We`re kind of stuck between the two, with lesser QPF resulting for the MPX area (with heavier precip focused to the north and south). Still, we will have favorable upper diffluence with a LLJ moving through, so the likely PoPs we have Thursday night are still warranted, we`ll just hopefully be able to avoid the worst of the heavy rain with this one. Behind this system, the last weekend of June looks to be absolutely spectacular, good news for once if you have any outdoor plans. However, in a growing theme for this warm season, the nice/dry weather will be short lived with the ensembles and deterministic models showing another seasonably strong cyclone impacting the upper MS Valley in the July 1-2 period, but this looks to be another opportunity for severe weather and excessive rainfall. When it rains it pours... && .AVIATION /06Z TAFS THROUGH 06Z TUESDAY/... Issued at 1107 PM CDT Sun Jun 23 2024 Clear skies, light winds will continue tonight. Some patchy fog is possible in WI, especially EAU. Otherwise, gusty southeast winds by Monday afternoon with SCT low level CU and BKN mid level clouds. Potential is increasing for a cluster of thunderstorms to develop late Monday afternoon over eastern ND or northwest MN, then become a fast moving line of severe thunderstorms along and north of I-94 Monday evening. A PROB30 has been introduced for all TAFs except RWF and MKT for now. KMSP...No significant concerns tonight. Light winds will shift southeast overnight then increase and gust 25-30 kts late morning and afternoon. A PROB30 has been introduced for the potential for a line of severe storms Monday evening. /OUTLOOK FOR KMSP/ TUE...VFR. Wind NW 10-15 kts. WED...VFR. Wind NW 5-10 kts. THU...VFR. MVFR/-TSRA likely Thursday night. Wind S 5-10 kts. && .MPX WATCHES/WARNINGS/ADVISORIES... MN...Heat Advisory from 1 PM this afternoon to 8 PM CDT this evening for Blue Earth-Brown-Chippewa-Faribault-Lac Qui Parle-Martin-Nicollet-Redwood-Renville-Watonwan-Yellow Medicine. WI...None. && $$ DISCUSSION...MPG AVIATION...Borghoff