Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI
Issued by NWS Detroit/Pontiac, MI
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714 FXUS63 KDTX 131120 AFDDTX Area Forecast Discussion National Weather Service Detroit/Pontiac MI 720 AM EDT Thu Jun 13 2024 .KEY MESSAGES... - Scattered showers and isolated thunderstorms arrive from the west this morning. Severe weather is not anticipated with this activity. - Warmer than normal today with high temperatures in the mid to upper 80s and noticeably higher humidity. - Scattered showers and thunderstorms develop this afternoon and evening with potential for severe weather. Damaging wind gusts to 60 mph will be the main threat between 3pm and 10pm. Southeast MI is outlined in a Marginal to Slight Risk from SPC. - Higher than usual confidence in hot and humid conditions much of next week. Temperatures well into the 90s Monday and beyond with relatively high humidity will likely bring the highest heat indices we have seen so far this year. && .AVIATION... Scattered VFR showers are moving across southeast Michigan this morning and worthy of a tempo across YIP/DTW within the first 1 to 2 hours of this TAF period. A pop of wind to 25 knots or greater will be possible with these showers. A secondary complex is moving across Lake Michigan, which is expected to weaken as it approaches southeast Michigan with the lack of instability. Confidence is not high that it holds together well as it approaches. Scattered showers will remain would be possible up to about 15-16Z if it maintains some integrity with MBS and possibly FNT most likely to be affected. Attention turns to the afternoon and evening as better instability will support a greater thunderstorm threat when an upper trough and cold front move through the Upper Midwest. Thunderstorms should impact all TAF sites starting at KMBS at around 20-21Z and spreading southeast to KDTW by around 23Z. Strong to severe thunderstorms will be possible. For DTW/D21 Convection... An approaching low pressure system and cold front bring a line or broken line of thunderstorms that will be moving west to east at 25 to 35 knots through southeast Michigan this afternoon/evening. The primary window to affect DTW is expected to arrive by around 23Z and move east by around 02Z. DTW THRESHOLD PROBABILITIES... * Moderate for thunderstorms impacting the terminal by around 23z today. && .PREV DISCUSSION... Issued at 411 AM EDT Thu Jun 13 2024 DISCUSSION... Conditions this morning characterized by weak warm/moist advection within southwest flow ahead of a cold front tracking across NW Wisconsin at press time. A west-southwesterly LLJ is directing a theta-e ridge across WI into northern lower MI, causing nocturnal convection to fire all along western lower MI within the gradient of elevated instability. As the LLJ progresses eastward and veers westerly, this convection will arrive across the Saginaw Valley over the next few hours, with a slight boost in forcing arriving after sunrise as a remnant MCV currently over northern Lake Michigan tracks in. With very little elevated instability in place this far east, expectation is for scattered showers with a few rumbles of thunder, mainly in the Tri-Cities and Thumb, this morning. Most of the activity should move out and/or dissipate by late morning as the LLJ steers the better moisture north and east. Weak subsidence looks to work into the area through early afternoon in the wake of the morning convective disturbance aloft. This will bring increasing amounts of sunshine and should help boost temps into the mid to upper 80s. We are still on track for a round of showers and thunderstorms to develop this afternoon and evening as instability builds in along a SW to NE oriented corridor of moisture convergence. Dew points within this area from SW lower MI to the Thumb are forecast to reach the mid to upper 60s. A plume of higher mid-level lapse rates (6.5 to 7 C/km) will arrive from the west simultaneously, resulting in MLCAPE on the order of 1000 to 2000 J/kg. Respectable height falls ahead of a potent shortwave moving into the northern Great Lakes will time favorably with cold frontal positioned over southern WI early this afternoon, providing the most likely scenario for convective initiation with support among much of the latest hi-res guidance. This convection then tracks east across Lake MI into southern lower MI and may be strong to severe by the time it arrives locally. Wind shear will initially be lacking but will increase as the upper jet works in the from the west, increasing 0-6km bulk shear to 40 to 50 kt and supporting organized updrafts. Damaging wind gusts will be the main threat with timing most likely between 3pm and 10pm. Secondary threats will be large hail and an isolated tornado. SPC has designated areas west of I-75 within a Slight Risk (2/5) while eastern areas are in a Marginal Risk (1/5) for severe weather. The cold front then sinks across the area late tonight and ushers precipitation south and east. The mid-level trough axis passes overhead Friday morning with an accompanying surge of lower 850mb temps around 10 C within drier northwest flow. This brings cooler, more comfortable weather for Friday and Saturday with seasonable highs in the 70s and lower 80s. There will be a low chance for an isolated shower within the diurnal cumulus field Friday afternoon as weak instability develops with a boost from the cooling mid-levels. Otherwise, inbound high pressure maintains dry and tranquil weather through Saturday. Uncertainty remains with shower/storm chances by Sunday when a shortwave rides across the ridge axis in place. Most model solutions carry the better moisture and attendant precipitation chances to our north, so will hold on to the inherited slight chance PoPs on Sunday and Sunday night. Significantly warmer and muggier weather remains in the forecast for next week as a 594 dam 500mb ridge develops over the SE CONUS on Sunday then expands north and east through the mid-week. This directs a plume of 850mb temps of around 20 C (near the 99th climatological percentile per NAEFS) into the Great Lakes and favors high temps in the 90s as well as a humid air stream tied to the Gulf of Mexico. This pattern will prove to be stubborn with ensemble mean 500mb height fields showing strong positive anomalies through the week. Differing ensemble systems do begin to vary in handling the ridge by late week however with the GEFS and CMCE steering the ridge axis over New England before having it begin to break down. Meanwhile, the EPS holds on to the ridge directly overhead through the bulk of the week and thus advertises hotter late week temps. Will note that 500mb vorticity progs do show several shortwaves riding into the ridge from the west which would bring potential for periods of showers and storms which, depending on diurnal timing, could short circuit the current temperature forecast. MARINE... A cluster of showers and storms is expected to wane through the morning across Lake Huron. Southwest flow will then become reinforced over the lake through the day today as a warm airmass sets up across the Great Lakes. This will continue to promote stable over-lake conditions considering the cooler waters, however, gusts 20-25 knots will be possible immediately along the nearshore, given well mixed southwest flow coming right off the land. These localized higher gusts will be most likely across the inner Saginaw Bay with the southwest fetch funneling into the Bay. At this time, will continue to preclude the issuance of any Small Craft Advisories, taking into account the stable marine layer, noting the chance to reach isolated 25 knot gusts immediately along the shoreline. The issuance of a short-fused Small Craft Advisory will be considered this afternoon and evening if surface observations support stronger wind gusts having a farther reach into the open waters relative to current projections. Otherwise, redeveloping showers and thunderstorms, some strong, will be possible this afternoon and evening, south of the central portion of Lake Huron. Wind gusts to or in excess of 34 knots and small hail will be the main threats with any strong to severe thunderstorm development. The passage of a cold front late tonight into Friday morning will veer wind direction from southwest to northwest as high pressure builds in behind the front. This will bring lighter winds to the Great Lakes by Friday. && .DTX WATCHES/WARNINGS/ADVISORIES... MI...None. Lake Huron...None. Lake St Clair...None. Michigan waters of Lake Erie...None. && $$ AVIATION.....AA DISCUSSION...TF MARINE.......AM You can obtain your latest National Weather Service forecasts online at www.weather.gov/detroit.