Area Forecast Discussion
Issued by NWS Twin Cities, MN
Issued by NWS Twin Cities, MN
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377 FXUS63 KMPX 190004 AFDMPX Area Forecast Discussion National Weather Service Twin Cities/Chanhassen MN 704 PM CDT Tue Jun 18 2024 .KEY MESSAGES... - Strong to severe thunderstorms are likely to develop this afternoon and evening. Primary hazards are damaging winds and a chance for a few tornadoes. Locally heavy rainfall is also possible this afternoon into tonight. - Additional rainfall of 0.50" to 1.00" through Wednesday morning. - Pleasant stretch with temperatures in the 70s Wednesday and Thursday. - Next chance for widespread rain arrives Friday into the weekend. && .MESOSCALE... Issued at 406 PM CDT Tue Jun 18 2024 Update on this evening`s severe threat and tornado watch. So far, the storms over western MN have been mostly struggling to sustain themselves, although there`s been a recent uptick in updraft growth. This is likely attributed to a lack of good upper level jet support, which is better over northern MN where storms are better organized and severe. The storms over our area should continue to get a bit better organized over the next hour or two as upper level support is forecast to improve somewhat, but the big question is how much. It will have to improve quite a bit in order to produce more organized/upscale storm growth, and the associated cold pools that would be needed for a more widespread wind and isolated tornado threat. Otherwise the storms will be more pulse in nature with mostly brief wind/hail threats and not much else. Latest runs of the HRRR prefer the pulse mode with a limited severe threat, however some other models are suggesting upper level support could improve just enough for a more organized storm mode with more widespread severe threats. If this were to occur, it appears most likely to occur in the 5pm to 7pm timeframe as the storms approach the I-35 corridor, and we will continue to monitor closely to see if this indeed looks to happen. && .DISCUSSION... Issued at 232 PM CDT Tue Jun 18 2024 Today and Tonight... A busy stretch of weather is on tap for this afternoon and evening. Current observations highlight the tropical-like airmass in place. Temperatures are in the low to mid 80s with dewpoint temperatures in the low 70s. Southerly winds with gusts up to 40 mph will turn northwesterly and decrease overnight behind the frontal passage. Our attention turns to this afternoon`s severe weather set up. A potent sfc low over the eastern Dakotas will lift northeast into northern Minnesota this afternoon. A trailing cold front moves into western Minnesota by early afternoon and will be the focus point for convective initiation. Strong southerly low-level flow will result in continued moisture advection through the afternoon hours. Ahead of the cold front, we`ve seen moderate instability 2500-3500 J/kg build into central and southern Minnesota. Effective shear remains around 30 knots with nearly unidirectional shear aloft, limited by weak flow aloft. Initial storm mode will be multicell with a supercell or two possible but storms will quickly congeal into a linear storm mode given the unidirectional shear profile aloft. Our primary concern will be the potential of damaging wind gusts convection moves through central and southern Minnesota and western Wisconsin. KMPX VAD profile highlights impressive low level SRH values between 200-300 m2/s2 and along with decent speed shear in the lower levels. Given the enhanced low level wind shear, a few tornadoes will be possible this afternoon. This matches up with the SPC SWO update added a 5% TOR area over our MN counties. Our 18z sounding highlights impressive moisture in the lower levels with PWAT of 1.91". The wind profile has some veering in the mid levels. Low level wind profile is impressive with nice curvature in the hodograph. Most importantly, the capping inversion has effectively eroded in the 18z ob. Initiation should when better upper level support arrives mid-afternoon, roughly 2-4PM, with a mixed convective mode before turning more linear. Storms impact the Twin Cities metro between 5 and 8pm. Heading into the evening hours, the front becomes more progressive and will shift the showers and storms into western Wisconsin with an overall diminishing trend by mid to late evening. Wednesday and Thursday... A brief break in the active weather pattern on tap for Wednesday and Thursday. Both days will be dry & pleasant with highs in the low to mid-70s, partly sunny skies, and light winds. Rain chances return Thursday night into Friday ahead of our next system. Friday through early next week...Southwest flow aloft will return and so will the moisture. This will support additional rain chances Friday and Saturday, with an additional 1-2" of rain likely for most locations, and 3"+ still possible where the strongest storms move through. Guidance hints at a slow moving system as it moves into the Upper Midwest on Friday. Placement of the surface boundaries will be important due to the potential for heavy rain. Any additional rain will contribute to additional rises in area rivers and streams for exacerbate flooding concerns into next weekend and early next week. Temperatures appear to warm back up during this period with highs in the 80s. && .AVIATION /00Z TAFS THROUGH 00Z THURSDAY/... Issued at 641 PM CDT Tue Jun 18 2024 Main issues for this TAF set are the timing of any TSRA into the terminals and how quickly ceilings drop into MVFR/IFR levels behind the storms. Western MN has already had the drop to IFR as evidenced by AXN. The trend is to have those lower ceilings spread east with the precipitation but confidence not quite high enough to go IFR at all terminals so have held ceilings at other sites in MVFR range, waiting to see how trends evolve. As for precip, have backed off the prevailing mention of TSRA in favor of a shorter-duration TEMPO wording as convection does not have the coverage as anticipated earlier. Still, certainly cannot rule out TSRA at any terminal over the first few hours of the 19/00z TAF. Behind the convection, winds will diminish and shift to W-NW with speeds around 10kts. MVFR ceilings will then hold in place overnight through most of tomorrow. If anything, VFR conditions may develop earlier than currently advertised. KMSP...Best window for having convection across the MSP area still looks to be 00z-03z as there are currently echoes near and around MSP that can easily develop into taller thunderstorms. The duration of any given storm will be relatively short, hence the TEMPO mention instead of prevailing. Once the main line, broken as it may be, moves through, wind speeds will diminish and directions will shift to westerly while ceilings drop into MVFR range. MVFR ceilings will then hold through late tomorrow afternoon if not tomorrow evening before conditions improve to VFR. /OUTLOOK FOR KMSP/ THU...VFR/MVFR, chc -TSRA/-SHRA. Wind E 5-10kts. FRI...VFR/MVFR, chc -TSRA/-SHRA. Wind S 10-15kts. SAT...VFR/MVFR, chc -TSRA/-SHRA. Wind SW 10-15kts. && .MPX WATCHES/WARNINGS/ADVISORIES... MN...None. WI...None. && $$ MESOSCALE...DPH DISCUSSION...BPH AVIATION...JPC