Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI
Issued by NWS Detroit/Pontiac, MI
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666 FXUS63 KDTX 202040 AFDDTX Area Forecast Discussion National Weather Service Detroit/Pontiac MI 440 PM EDT Mon May 20 2024 .KEY MESSAGES... - Another round of showers and thunderstorms is expected this evening as activity develops and moves in from western Lower Mi. - An isolated thunderstorm could approach severe intensity with damaging wind the primary hazard. Large hail is also possible but tornado potential is low. - Additional storms are possible Tuesday afternoon followed by a line of strong to severe storms late Tuesday night. Damaging wind is the greatest threat Tuesday night. - Warm and muggy conditions with high temperatures in the mid to upper 80s continue through mid week until a cold front moves through the region Wednesday. - There is one more chance for showers/storms Wednesday before a cooler and less humid air mass follows the front for the late week period && .DISCUSSION... The early afternoon convective cluster followed the warm front supported instability gradient along and north of the I-69 corridor this afternoon. Hourly mesoanalysis showed 0-6 km bulk shear sneaking up to around 30 knots as the storms increased coverage, just enough for some forward propagation and sporadic wind damage as the storms matured. The southward moving outflow then became the focus of a secondary development capable of its own sporadic wind damage and large hail before exiting into Ontario at press time. Yet another round of storms is on schedule to affect Lower/SE Mi this evening as upstream activity develops eastward. Mid afternoon satellite imagery clearly shows the outflow reinforced warm front beginning to recover northward or at least hold a position near the M-59 to I-96 corridors for the late afternoon. Surface pressure falls associated with the inbound MCV will be sufficient to draw instability northward into SW Lower Mi late in the diurnal cycle while the mid level circulation further supports organized convection. Maintenance of instability then becomes more questionable after midnight as the surface low slips through central Lower Mi. The surface low is a tracer for MCV support that carries the remaining convective clusters into Lake Huron before sunrise. The MCV subsidence wake appears as a substantial short wave ridge in model data to start off Tuesday. The effective frontal boundary sinks back south as well to leave conditions dry for the morning before a transition to return flow moisture transport occurs in the afternoon. Scattered showers and a stray thunderstorm are possible through the evening as the surface warm front sharpens up ahead of the next Midwest low pressure system. The southern stream circulation in today`s Pacific coast trough has good model agreement on a track into the Midwest where it deepens substantially by Tuesday night. The leading cold front becomes the subject of the next round of severe thunderstorm potential for our area, although the latest model trends exhibit a strong nocturnal limiting factor for eastward longevity. The 12Z HREF hi-res members show good agreement on a convincing weakening trend across Lower Mi late Tuesday night. This is a surprising solution given how strongly forced the pattern is on the background of the larger scale low pressure system. The SPC Slight/Marginal risk combo nicely depicts the decreasing potential for severe intensity into Wednesday morning. && .MARINE... A stalled boundary extends from southern Lake Huron to southern Lake Michigan with a mid level system rippling along it. This helped touch off a afternoon round of storms. Additional mid level support this evening will lead to another round of storms reaching the eastern lakes around midnight. The front will linger Tuesday which could help another round of storms in the afternoon. A stronger surface low will then lift northeast through northern Michigan Tuesday night into Wednesday, pulling a cold front through the region leading to yet another round of storms Wednesday. Conditions are expected to remain below Small Craft Advisory criteria tonight through Tuesday, though locally higher winds and waves will be possible within any thunderstorms. Winds increase out of the south to 20 to 30 knots ahead of the associated cold front Wednesday, then veer to the west Wednesday night into Thursday while remaining gusty to around 25 knots. Less humid air settles in for the late week as high pressure builds in. && .CLIMATE... Here are the record high temperatures for May 20th through May 22nd: May 20th: Detroit 91 (set in 1977) Flint 92 (set in 1934) Saginaw/Tri-Cities 93 (set in 1977) May 21st: Detroit 92 (set in 1977) Flint 93 (set in 1921) Saginaw/Tri-Cities 94 (set in 1977) May 22nd: Detroit 90 (set in 1994) Flint 91 (set in 1934) Saginaw/Tri-Cities 89 (set in 1992) Here are the record high low temperatures for May 20th through May 22nd: May 20th: Detroit 68 (set in 1934) Flint 65 (set in 1939) Saginaw/Tri-Cities 70 (set in 1975) May 21st: Detroit 71 (set in 2013) Flint 67 (set in 1934) Saginaw/Tri-Cities 66 (set in 2021) May 22nd: Detroit 67 (set in 1941) Flint 65 (set in 1977) Saginaw/Tri-Cities 68 (set in 1977) && .PREV DISCUSSION... Issued at 1204 PM EDT Mon May 20 2024 AVIATION... High based (6-10 kft), mostly scattered CU field developing with diurnal heating/instability, with potential for scattered strong thunderstorm development. Much higher confidence across Tri-Cities region (MBS) and Flint vicinity as circulation/shortwave trough tracking out of the Midwest lifts through northern Lower Michigan this evening. Still, warm advection arm/instability gradient lifting through southeast Michigan still presents a low chance for southern areas, especially as activity becomes more surface based later today. The 500 MB trough axis will be slow to move through the Central Great Lakes, and with strong low level jet, scattered rain showers/thunderstorms tonight, which will also tend to help lower cloud bases more in the 2-6 kft range, mainly northern taf sites, closest to the departing circulation. Southwest winds today around 10 knots becoming weak westerly or variable tonight. For DTW/D21 Convection... Low chance of thunderstorms this afternoon into tonight, with the bulk of storms expected to be north of the terminal. With timing very difficult to pin down and the low chances of the airport being directly impacted, preference is to leave out of the taf and monitor trends for possible inclusion if confidence increases. Otherwise, cloud ceilings look hard to come by, and any bkn-ovc layers above 5000 feet. Best chance for cloud bases aob 5000 feet looks to be Tuesday morning. DTW THRESHOLD PROBABILITIES... * Low for thunderstorms this afternoon through tonight. * Low for aob 5000 feet Tuesday morning. && .DTX WATCHES/WARNINGS/ADVISORIES... MI...None. Lake Huron...None. Lake St Clair...None. Michigan waters of Lake Erie...None. && $$ DISCUSSION...BT MARINE.......DRK CLIMATE......BT AVIATION.....SF You can obtain your latest National Weather Service forecasts online at www.weather.gov/detroit.