Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI
Issued by NWS Detroit/Pontiac, MI
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755 FXUS63 KDTX 131709 AFDDTX Area Forecast Discussion National Weather Service Detroit/Pontiac MI 109 PM EDT Thu Jun 13 2024 .KEY MESSAGES... - 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... Difficult convection forecast for late this afternoon into early evening hours. The 12z DTX sounding indicated a lot of dry air below 800 MB, and thus will be counting on the steepening mid level lapse rates/increasing cape to potentially trigger strong to severe thunderstorms late today. At this point, will continue with the inherited tempo group for TSRA at each taf site. Coverage and location is still uncertain, and bulk of storms could end up closer to the Michigan/Indiana border. Cold front/wind shift will track through southeast Michigan tonight, and low level convergence may be sufficient for a period of borderline MVFR/VFR clouds. Unfortunately, the amount of showers and thunderstorms that occur late this afternoon/this evening will be a factor in determing this scenario. It appears the southern TAFS stand the best chance and longest duration of low clouds, but should clear around sunrise Friday regardless. Light northerly flow tomorrow, with some sct-bkn mid cloud (5-10 kft) development expected with the cooler mid levels (zero at 700 MB) tracking through the Central Great Lakes. For DTW/D21 Convection... A scattered-broken line of thunderstorms looks to be developing/tracking through southeast Michigan late this afternoon/early this evening. The primary window to affect DTW is expected to arrive by 23Z and move east by around 02Z. DTW THRESHOLD PROBABILITIES... * Moderate for thunderstorms impacting the terminal by around 23z today. * Low for cigs aob 5000 ft this evening through tomorrow morning. && .PREV DISCUSSION... Issued at 1152 AM EDT Thu Jun 13 2024 UPDATE... Morning showers dying out as cloud cover continues to progress eastward allows for heating to take place and begin destabilizing the profile in advance of a cold front passing through overnight. Most of southeast Michigan is under a Slight risk for severe weather this evening, mainly due to threats of wind and hail. An isolated tornado has also not been ruled out for this evening. There remains a level of uncertainty with how things are going to play out for southeast Michigan, as hi-res models consistently shows a line of storms to the southwest, but still have not converged well on how this will evolve into southeast Michigan. The best chances for severe weather currently look to be in the southern part of the CWA, over Washtenaw, Wayne, Monroe, and Lenawee counties, but the potential does exist for something to pop up over the Thumb as well. Thermodynamics look favorable on paper, with SBCAPE reaching 1000- 1500 J/kg and lapse rates pushing 7 C/km. Shear will eventually reach 40-50 knots, but the stronger shear pushes in behind the storms overnight. Convergence along the front looks to be stronger to the southwest, while storms that do form may outrun a relatively narrow plume of instability. All this to say that should an updraft develop, the ingredients are in place to see storm organization, but confidence remains low on how widespread severe may be. 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.....SF UPDATE.......BC DISCUSSION...TF MARINE.......AM You can obtain your latest National Weather Service forecasts online at www.weather.gov/detroit.