Area Forecast Discussion
Issued by NWS Twin Cities, MN
Issued by NWS Twin Cities, MN
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887 FXUS63 KMPX 121750 AFDMPX Area Forecast Discussion National Weather Service Twin Cities/Chanhassen MN 1250 PM CDT Wed Jun 12 2024 .KEY MESSAGES... - Warm and muggy today with strong to severe thunderstorms expected. Large hail, damaging winds and a few tornadoes are possible. - Seasonable temperatures and dry weather are expected to end the week with rain returning Saturday through early Sunday. - Chances for precipitation along with warmer temperatures will persist through early next week. && .DISCUSSION... Issued at 235 AM CDT Wed Jun 12 2024 Surface analysis early this morning shows a departed cold front over central WI snaking SW over southern IA, high pressure briefly sitting behind the front over northwest IA and southeast SD, and a second cold front emanating from a low pressure center over southern Saskatchewan province and extending SW over MT/IA. It is this second cold front that will be the focus for anticipated convection across portions of the WFO MPX coverage area today and tonight. Aloft, a rather lengthy zonal pattern, and a fast one at that, is present from the Dakotas all the way to the Great Lakes over the northern tier states. While there are some minor buckles in the flow from H85 all the way up to H5, the prevailing west-to-east flow will aid in producing speed shear across a broad area of the Upper Midwest. To be specific, H5 flow is nearly 60kt over MN, while low level flow is generally from the S and SSW, aiding in advecting higher moisture content into the region As the front approaches from the west, lapse rates will become much steeper, ranging 7-8 C/km per model soundings. In addition, a highly unstable airmass will also be present in advance of the front with MLCAPE values likely around 2000 J/kg, potentially as high as 3000 J/kg. Model soundings, particularly for this afternoon, show strong winds veering with height, which is a good indicator of supercell potential. These factors with the steep lapse rates indicate a strong potential for large hail. So, with multiple severe weather indices showing the strong potential for severe weather, the questions now are: when and where. And this is where different CAMs have different ideas for such. The main consensus this morning looks to be a pre-dawn cluster of storms over southeastern ND that will move into west-central MN around 12z then continue spreading SE over southern MN through midday. Models had previously shown a second round of convection not too far behind the initial, but that idea looks to have less support at this time. Once the morning Cc pushes through, residual cloud cover with plenty of convective energy having been used, there may not be enough time for recovery to occur later in the day in southern MN due to sufficient mid-to-late day capping. However, northern MN looks to have less such capping and is also in closer proximity to the low pressure center. Thus, with the better prolonged period of convection expected, the addition of an Enhanced Risk over northern MN makes sense, as is the greater possibility of any tornadic storms. As the storms develop, the hazard mode will transition from one of hail to one of wind gusts, especially the more they can propagate east and maintain themselves. Of course, there are outliers to this which diminish the incoming cluster and instead focus on a cluster near-north of I-94 in MN which drives SE mid to- late afternoon. This complication in timing/location is the main reason of holding back the severe risk to a Slight while points north have been upgraded to Enhanced. The cold front will sweep across MN/WI tonight through sunrise Thursday, followed by a broad area of high pressure from southwest Canada spreading ESE into the Upper Midwest. This will promote cooler, drier and clearing conditions for Thursday- Friday. The focus then turns to the weekend as a conglomerate areas of small low pressure centers over WY/CO undergoes cyclogenesis into a primary low over the Northern Plains. Impressive moisture advection is again expected across the Upper Midwest in advance of this next system, such that PWATs exceed 1.50", possibly near 1.75". The slow progress of the frontal system across the area along with only modest instability will make for plenty of rainfall across the region Saturday into Saturday night. QPF for much of the WFO MPX coverage area will exceed 1", with south- central MN possibly looking at over 2". The warm front of this system is expected to snap northeast, placing central-southern MN and western WI within its warm sector. Thus, another warm/humid day is expected on Sunday but with lower precipitation chances. The weak frontal boundary is expected to stall out over the Northern Plains and Upper Midwest while several weak shortwaves drift across the region, keeping chances for rain in the forecast through early next week. && .AVIATION /18Z TAFS THROUGH 18Z THURSDAY/... Issued at 1228 PM CDT Wed Jun 12 2024 The first round of showers and storms is moving through south central Minnesota early this afternoon. The big question remains what will happen this afternoon. Confidence is low in widespread coverage of TSRA and MVFR conditions, so kept TEMPOs and PROB30s through this evening. Winds have been quite breezy behind the line of showers from this morning, but things should settle back to 20-25kts out of the south/southwest in the next hour or so. After any storms that manage to develop this evening, we will clear out with light northwest winds. KMSP...As mentioned above, there`s still plenty of uncertainty regarding the coverage of any evening storms. The window for storms looks to be between 00-04z. These storms will likely lead to MVFR/IFR conditions and could be severe. /OUTLOOK FOR KMSP/ FRI...VFR. Wind VRBL at 5 kts. SAT...RA/TSRA/MVFR likely, IFR possible. Wind SE 10-15 kts. SUN...Mainly VFR. Slight chc TSRA/MVFR. Wind SW 10-15 kts. && .MPX WATCHES/WARNINGS/ADVISORIES... MN...None. WI...None. && $$ DISCUSSION...JPC AVIATION...Dye