Area Forecast Discussion
Issued by NWS Twin Cities, MN
Issued by NWS Twin Cities, MN
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599 FXUS63 KMPX 232339 AFDMPX Area Forecast Discussion National Weather Service Twin Cities/Chanhassen MN 639 PM CDT Sun Jun 23 2024 .KEY MESSAGES... - Slight Risk (Level 2/5) of severe thunderstorms Monday evening. Uncertainty remains due to a conditional setup but if storms develop they`d likely be severe given the environment. - Active pattern continues with another round of widespread rainfall Thursday afternoon through Friday night. - 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 353 PM CDT Sun Jun 23 2024 Isolated thunderstorms have developed across northeast Minnesota and may track through portions of eastern MN and western WI this afternoon. These showers miss the majority of us, but the unlucky few will see brief downpours and a few flashes of lightning. Elsewhere, temperatures have warmed in the upper 70s and lower 80s with scattered CU and dry conditions. Northwest winds have produced a few gusts up to 20 mph and winds will taper off this evening. For tonight, the forecast remains dry with lows in the 60s for most of us. Some patchy fog cannot be ruled out in W WI given the recent stretch of wet weather and light winds forecast tonight. By daybreak, a warm front will lift through the region with southeasterly winds ramping up by Monday morning. Some guidance tracks elevated convection into west central MN that dissipates by mid-morning. There isn`t enough confidence to reflect this in the PoPs, but if this does happen it`ll add additional complexity to Monday`s severe weather setup. On Monday, a complex conditional (boom or bust) severe weather setup Monday evening across MN and NW WI. SPC`s mid-day update to the Day 2 severe weather outlook has maintained a Slight Risk (level 2 out of 5)across most of Minnesota and all of northwest Wisconsin after collaboration with the SPC. However, there was an addition of sig wind hatching over central Minnesota & western Wisconsin that I`ll expand on later. Aloft, a shortwave trough over the Canadian prairies will trek east during the day. It`ll bring a cold front through the Dakotas and into Minnesota Monday afternoon. In the warm sector, warm air advection increases across the Upper Midwest Monday morning, resulting in a very warm and humid day on tap with highs in the mid 80s to low 90s out in W MN. Moisture transport will push surface dewpoint temperatures level moisture to the warm sector res in the the upper 60s to mid 70s by mid-afternoon. Guidance continues to advertise an impressive thermodynamic environment in the warm sector. 12Z HREF develops strong to high-end instability with MLCAPE values pushing 4000-5000+ J/kg. This high-end instability would favor a severe risk should thunderstorms develop, but will they? CAMs offer a few different scenarios for Monday afternoon into Monday night. Global models offer additional solutions that we can infer the outcome from. So I`ll do my best to break down the potential scenarios similarly to what the previous shift did. Forecast soundings highlight an impressive EML building across much of south central Minnesota during the daytime, effectively capping the extreme instability and limiting convection across the MPX CWA. Looking at the 700hPa layer offers support to this with temperatures between 14 to 16c by 21Z Monday. The capping is present in all of the models I`ve looked at so why are we concerned about potential severe? Let`s dive into the potential outcomes for Monday`s severe threat below: 1) Scenario #1 is the most likely scenario given the environment in place, but it doens`t guarantee severe wx in the MPX cwa. In this scenario, Monday is very quiet across south central Minnesota and western Wisconsin under the cap. Most of us have to combat the heat and humidity while instability builds in beneath the cap. Further northwest, the approach of a cold front in northwest Minnesota will be the focus for convection during the mid-afternoon/evening hours, likely developing along the northern edge of the instability axis. Differences exist in where this axis will setup will could have big implications for where the convection tracks Monday evening. Once storms develop over NW MN, they will be able to intensify quickly into a MCS that would be capable of producing potentially significant damaging winds as it tracks along the CAPE gradient across central MN into NW WI. However, if it`s further north, it would keep the severe storms in FGF/DLHs forecast areas. Regardless of where storms develop, the track of said complex of storms would likely move southeast along the CAPE gradient, with an expected growth along the MCS as the nocturnal low-level jet strengthens into the evening. This solution would mean a threat for severe weather would be Monday evening, but the threat would persist well into the night if the storm complex can maintain it`s cold pool. 2) This is the slightly less favored, but still possible. Some models maintain elevated convection across the Dakotas into western Minnesota Monday morning. There is some possibility that convection makes it into W MN and continue east along the instability axis lifting north Monday morning. If this were to happen, we could be in for a round of storms, possibly strong, before they taper out by late morning. This would impact the location of the warm front and recovery potential across the area. This would further throw a wrench into the setup for the remainder of the day and add additional complexity. This scenario would likely see development of isolated to scattered elevated thunderstorms on the nose of the nocturnal LLJ Monday late evening into Tuesday morning across central and southern MN. These could post a severe hail threat but little to no wind concern given the stable nocturnal boundary layer. The continued Slight Risk from the SPC represents some of the uncertainty expressed above with the overall setup, however given the extreme instability, steep lapse rates, and adequate shear would support any convection becoming severe if a convective event may unfold. The SPC did add an area of sig wind hatching across central MN and NW WI. This represents the potential for a higher end MCS solution with damaging winds, but other threats such as large hail and a few tornadoes will also be in play. It was hinted at in the SWODY2 update that tonight`s SPC update could begin to ramp up the severe risk if confidence increases. The pattern does support the potential for a long-lived MCS wind producer across the region IF storms can develop and organize before sunset. Finally, storms may produce heavy rain given the ample moisture forecast to be present, however the progressive nature of the storm motion should limit the flash flood threat. Additional rises in area rivers would also delay crests. Tuesday and Wednesday offer a break from the active pattern as high pressure builds in for the middle of the week. Temperatures remain warm on Tuesday, in the 80s, but we`ll see highs in the upper 70s on Wednesday. Thursday and Friday, a large system will move into the Plains on Thursday. Large scale warm advection sets up on the return flow Thursday afternoon. A low pressure will move into the Dakotas late Thursday, setting the table for another round of thunderstorms Thursday night into Friday. This system may threaten to produce additional rounds of heavy rain given favorable moisture transport & forcing aloft. The WPC`s Day 5 Excessive Rainfall Outlook supports this potential with a Marginal Risk across most of Minnesota and western Wisconsin, along with a Slight Risk across southern Minnesota/northern Iowa. Unfortunately, the concern for additional flash flooding and river flooding remains with us for the foreseeable future. && .AVIATION /00Z TAFS THROUGH 00Z TUESDAY/... Issued at 639 PM CDT Sun Jun 23 2024 VFR and light winds tonight. Some patchy fog could develop in WI, but confidence is low in RNH or EAU experiencing it directly. Winds become south and gusty Monday with storms possible, primarily north of I-94 Monday night. KMSP...No significant concerns tonight. Northwest winds will ease and become light later this evening, then become SSE and gust 25-30 kts late Monday morning and afternoon. TS potential Monday evening is too uncertain to include in this TAF set, but a PROB30 may be considered for the next issuance. /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...None. WI...None. && $$ DISCUSSION...BPH AVIATION...Borghoff