FXUS63 KDTX 242315 AFDDTX Area Forecast Discussion National Weather Service Detroit/Pontiac MI 715 PM EDT Thu Apr 24 2025 .KEY MESSAGES... - Showers and scattered thunderstorms developing tomorrow. Isolated thunderstorms may be marginally severe in the afternoon. - High pressure this weekend brings dry conditions. Cool Saturday before returning to near normal Sunday. - Temperatures back into the 70s on Monday before another cold front arrives on Tuesday. && .AVIATION... Diurnal, high based boundary layer cumulus will fade with the loss of daytime heating. VFR conditions are anticipated tonight with wind directions becoming easterly behind a backdoor cold front. VFR conditions throughout much of Friday. Absolute vorticity advection and height falls ahead of amplifying northern stream trough will bring the potential for thunderstorms Friday afternoon. Did include a prevailing group for -TSRA between 21-00Z. For DTW...Most likely timeframe for -TSRA between 21-00Z Friday. .DTW THRESHOLD PROBABILITIES... * Low for ceiling at or below 5000 ft Friday. * Moderate for thunder late Friday afternoon/evening. && .PREV DISCUSSION... Issued at 258 PM EDT Thu Apr 24 2025 DISCUSSION... Another warm day today with an expanded coverage of high temperatures reaching 80+ degrees (most locations along/south of I- 69). With weak flow in place and differential heating, marine influences will be a significant cooling influence, with lake breezes pushing farther inland through early evening. Positive tilted progressive upper level trough approaching southern Manitoba border this afternoon, swinging through the Central Great Lakes on Saturday morning. Out ahead of this trough, some upper level energy/weak height falls ejects out of the Midwest on Friday, supporting cyclogensis over southeast Michigan tomorrow. Increasing large scale ascent and destabilization will support blossoming coverage of showers and thunderstorms in the afternoon. ML/1000-850 MB capes increasing aoa 1000 J/kg draws some concern for severe storms. There are some lower 60 dew pts noted over southern Indiana this afternoon which will make a run at or just north of the southern Michigan border tomorrow. However, the surface low pressure is broad and the low level winds are weak, coupled with modest mid level lapse rates (~6 C/KM from 700-500 MB). 0-6 KM bulk shear also borderline south of the surface low, running around 30 knots. On the flip side, the system is ramping up as it tracks through, with phasing occuring as the low pressure system tracks into the Eastern Great Lakes Friday night. With downdraft capes around 1000 J/kg Friday afternoon, a marginal/isolated severe threat seems valid with precip loaded downdraft. Marginal hail not out of the question as well if any cell rotates and sustains the updraft, as machine learning outlook indicating a 5% probability for both wind and hail. Good shot of cold advection to follow for Friday night, as 850 MB temps progged to reach around zero Saturday morning. With rather tight pressure gradient, local probabilistic guidance suggests northwest winds gusting around 30 mph, supported by Euro ensembles. Sprawling high pressure builds into the Central Great Lakes through Sunday and then slides east, with an active warm front developing over the Western Great Lakes to close out the weekend. All/bulk of elevated showers expected to stay west of the CWA through Sunday night, as the 700 MB jet core is back across Iowa, per 12z Euro. Pronounced upper level ridge axis building over southeast on Monday with 850 MB temps reaching 13 C, supportive of highs well into the 70s to near 80 degrees once again with southwest flow ramping up, ahead of a cold front on track to move through on Tuesday. Strong wind fields with the amplified northern stream upper level trough could present a severe threat, but timing is uncertain. Morning timing would mitigate any severe threat. MARINE... A weak cold front stalls over the region today into tonight with wind 15 kt or below for most of the area. The exception will be Saginaw Bay where northeast flow will quickly ramp up to 20 to 25 kt this afternoon and a Small Craft Advisory has been issued. Low pressure lifts into the region on Friday, bringing scattered to numerous showers and embedded thunderstorms across the central Great Lakes. Moderate easterly flow across northern Lake Huron backs to northerly and spreads southward across the lake as the low departs late Friday. N to NNE wind then peaks late Friday night into midday Saturday with gusts to around 30 knots over central Lake Huron. Small Craft Advisories will likely be needed as waves build along the nearshore areas in the southern basin. North flow persists through Saturday but gradually weakens as strong high pressure builds in from the west. This high promotes lighter winds and waves through Sunday. HYDROLOGY... Increasing daytime instability and surface low pressure arriving tomorrow will support showers and scattered thunderstorms developing during the afternoon, as PW values rise aoa 1.25 inches. Although basin average rainfall is generally expected to be a half an inch or less, any strong to marginally severe thunderstorms will produce localized rainfall of 1.0-1.25 inches in a short period which could cause minor urban and small stream flooding. && .DTX WATCHES/WARNINGS/ADVISORIES... MI...None. Lake Huron...Small Craft Advisory until midnight EDT tonight for LHZ421-422. Lake St Clair...None. Michigan waters of Lake Erie...None. && $$ AVIATION.....CB DISCUSSION...SF MARINE.......TF HYDROLOGY....SF You can obtain your latest National Weather Service forecasts online at www.weather.gov/detroit.