Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI
Issued by NWS Detroit/Pontiac, MI
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314 FXUS63 KDTX 051748 AFDDTX Area Forecast Discussion National Weather Service Detroit/Pontiac MI 148 PM EDT Wed Jun 5 2024 .KEY MESSAGES... - Widespread showers and thunderstorms this afternoon, ending early this evening. Some of these storms may be strong to marginally severe. - Localized rainfall totals of 1 to 2 inches are possible for areas that see multiple storms this afternoon. - Pattern shift for the latter half of the week brings below normal temperatures through at least the end of the week along with periodic chances of rain. && .AVIATION... Convection has begun to perk up this afternoon ahead of the approaching cold front. Will include a VCTS for the scattered activity from 18-20Z before a convection cluster over northern Indiana brings a more solid line of storms which a tempo will cover for now. Biggest risk with these storms will be heavy rainfall, wind gusts to 50-60 mph and large hail. Some question as to whether there could be redevelopment behind the leading storms or not. Will keep a couple hours of showers lingering and adjust as needed. An additional period of showers will be possible from about 06-10Z overnight as a secondary cold front drops through. For DTW/D21 Convection...Scattered showers and thunderstorms are ongoing as of 18Z around the area but the better coverage remains off to the west and southwest. A cluster of storms currently lifting into MI will impact DTW generally 20-23Z. Storms will be moving NE at 30 mph while the cold front pushes everything east over time. Storms will be capable of brief heavy downpours reducing visibilities, strong winds to 50-60 mph and some large hail. DTW THRESHOLD PROBABILITIES... * Moderate in thunderstorms this afternoon/evening. && .PREV DISCUSSION... Issued at 1023 AM EDT Wed Jun 5 2024 UPDATE... Moist airmass in place, as 12z DTX sounding indicated a PW value of 1.5 inches, with further moisture pooling today ahead of cold front expected to produce PW value of 1.75 inches. With a negative tilted shortwave trough lifting through the Central Great Lakes, seems reasonable widespread showers and scattered thunderstorms will develop this afternoon, despite the less than stellar instability/capes/mid level lapse rates. Surface dew pts generally in the 67-72 degree range across southern Lower Michigan/Indiana this morning. In the upper range, surface capes will reach 2000 J/kg with highs in the lower 80s, but lower dew pt range will result in capes more in the 500-1000 J/kg range. Adequate shear 0-6 KM bulk shear of 35-40 knots if the higher instability is realized to support a few marginally severe storms (mainly wet micro-burst), favored mostly in the 3-7 PM window. Overall, accounting for some modest mixing out of dew pts, preference is to hold dew pts in the 68-70 degree range. Zone update was mainly cosmetic, and do not anticipate any change with SPC Day 1 outlook. PREV DISCUSSION... Issued at 411 AM EDT Wed Jun 5 2024 DISCUSSION... Main forecast concern for today is several opportunities for showers and thunderstorms across SE Michigan, including strong to severe potential as a line of storms tracks through this afternoon-evening. Leading the way is the warm front, which will lift into the cwa through the early morning hours. The fropa so far has just been producing virga locally, as better forcing and moisture transport are to our west invof a 35-40 knot nocturnal low level jet. This low level jet will eventually reach the western edge of the forecast area between 12-15z (8am-11am), driven primarily by eastward progress of an expansive surface trough and mid-level wave that arc from low pressure near central Saskatchewan-Manitoba to Texas. Diurnal weakening of the jet should lead to a decaying convective complex by the time it reaches SE Michigan, but some degree of remnant elevated showers/storms is likely. PoPs are highest near the Tri Cities and decrease with southeastward extent away from the LLJ forcing, although presence of elevated instability (500-1000 J/kg) does keep a chance for scattered convective potential through the morning for all of SE Michigan. Trends in radar mosaic over the past 3 hours have shown significant dissipation of radar returns along the upstream surface front, which is currently over western Wisconsin/Illinois. Meanwhile, GOES-16 WV loop depicts the lead edge of the mid-level wave catching up to the surface feature, and will be the mechanism to watch heading into the afternoon for redevelopment of linear convection. With the warm front already well into the cwa and 00z KDTX RAOB observing 750 J/kg MUCAPE ahead of the warm sector last night, should be able to realize model forecast instability this afternoon even if we get clipped by elevated convection this morning. With temperatures reaching into the low 80s and dewpoints in the mid to upper 60s, this equates to MLCAPE up to 1000-1500 J/kg by the time the mid- level forcing arrives with minimal capping. Timing of the wave and phased surface troughing continue to align well with CAM output in bringing a line of thunderstorms west to east across SE Michigan between roughly 1pm-9pm tonight. Environmental parameter space will be favorable both from a thermodynamic (discussed above) and kinematic perspective, with mid- level flow increasing to 35-40 knots this afternoon for a Marginal Risk of severe weather (SPC SWODY1). Linear mode suggests damaging wind gusts in excess of 60 mph will be the main severe weather threat, although heavy rainfall is also a concern considering the seasonably high moisture content of this airmass (PWAT to 1.75") and depth of the warm layer. Heavy downpours owing to very good precipitation effiency could lead to localized rainfall totals of 1 to 2 inches should training storms develop ahead of the main line. The speed and orientation of the line however are fairly progressive, bringing an end to heavy rainfall potential late this evening as a dry slot moves in aloft. A notable pattern transition occurs for the late week period as the parent closed upper low spreads southeast toward the Great Lakes. H8 temperatures drop into the single digits, corresponding to daytime highs generally in the 70s with coolest temperatures on Friday capped in the upper 60s. Several additional shortwaves ripple through the flow, including a pair of waves Thursday that keep low chances for showers and thunderstorms in the forecast. MARINE... A ridge of high pressure now resides across Lake Ontario, with attention now turning to the cold front which currently resides just west of Lake Michigan. This front is projected to move across the eastern Great Lakes through the afternoon and evening hours, which will likely bring numerous to widespread rain showers along with embedded thunderstorms. There will be a marginal risk for severe weather across all of the eastern Great Lakes given the building instability, where wind gusts in excess of 30 knots and hail to an inch will be possible with the strongest storms. While much less likely, an isolated waterspout cannot be ruled out with the thunderstorms. Passage of the front will veer wind direction from the southeast to the southwest this evening. A cooler air mass will then gradually setup over the Great Lakes through at least the end of the week. The enhanced mixing depths will bring some breezy conditions, particularly for the nearshore zones. Small Craft Advisories may be needed tomorrow, with the Saginaw Bay having higher probabilities to reach criteria given the southwest flow. The favorable fetch will allow wave heights to near the three ft threshold while wind gusts near 25 knots. HYDROLOGY... A line of showers and thunderstorms is expected to track west to east across SE Michigan between 1 PM and 9 PM today ahead of a cold front. The airmass will seasonably warm and moist, helping this storms become efficient rain makers with widespread rainfall amounts up to a half inch expected. Localized higher amounts are possible if several storms pass over any single location, in which amounts will be closer to 1 to 2 inches. Minor flooding of prone urban and low- lying areas, ponding of water on roadways, and rises in area rivers will all be possible. && .DTX WATCHES/WARNINGS/ADVISORIES... MI...None. Lake Huron...None. Lake St Clair...None. Michigan waters of Lake Erie...None. && $$ AVIATION.....DRK UPDATE.......SF DISCUSSION...MV MARINE.......AM HYDROLOGY....MV You can obtain your latest National Weather Service forecasts online at www.weather.gov/detroit.