Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI
Issued by NWS Detroit/Pontiac, MI
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464 FXUS63 KDTX 202306 AFDDTX Area Forecast Discussion National Weather Service Detroit/Pontiac MI 706 PM EDT Fri Sep 20 2024 .KEY MESSAGES... - Warm weather continues through this weekend with a slight increase in humidity each day. - Scattered showers and storms are possible this afternoon and early tonight with additional rainfall Sunday night into Monday. - Lower confidence in rain chances for the middle of next week while temperatures cool off to seasonable values. && .AVIATION... Lower VFR clouds will arrive early this evening as weak convergence along an encroaching front. There will be enough instability around to support scattered coverage of showers early/mid evening with an isolated thunderstorm or two not out of the question (particularly KFNT north). Border line MVFR/VFR cigs will be possible where these showers develop. Clouds decrease overnight in the wake of this front with a period of low stratus or fog possible by sunrise Saturday as winds become calm. With maintain MVFR visibility in the tafs, but will monitor for the potential of dense fog in upcoming forecasts. For DTW/D21 Convection...Scattered showers this evening with the slight chance of a thunderstorm as a weak frontal boundary tracks through the area. Will continue with the prob30 mention of showers. Confidence in thunderstorms is too low to include at this time. DTW THRESHOLD PROBABILITIES... * Low for ceilings at or below 5000 ft this evening and tonight. * Low for thunderstorm chances this evening. && .PREV DISCUSSION... Issued at 329 PM EDT Fri Sep 20 2024 DISCUSSION... Anticyclonically curved left exit region dynamics and dampening absolute vorticity lobe will push into the central Great Lakes by this evening. A fair amount of synoptic support for ascent is expected with 1000-500mb geopotential height falls sliding through Southeast Michigan between 21-06Z this evening. Model consensus has been consistent in convection initiating/expanding this afternoon in the lee of Lake Michigan before trying to push eastward. Regional Reflectivity mosaic has supported this. Most recent CAM UVV signal suggests activity pushing up to the western edge of the cwa prior to 00Z, but significantly weakening and dissipating before it tracks into the area. Survey of forecast soundings and HREF data suggests MUCAPES increasing to <1000 J/kg for the western cwa, but with a significant amount of dry air in the near surface environment. Thus, the atmosphere is expected to remain statically stable in the lowest 5 kft agl. No strong or severe thunderstorms are anticipated. The latest Swody1 keeps the forecast area under a General Thunderstorm designation. Low chances for a shower and an isolated thunderstorms will exist throughout the evening hours with the best low-mid convergence, cyclonic flow, and height falls will be in place over the area. Difficult to provide much detail with a sparse QPF footprint in the solutions. Did introduce areas of fog mention into the zone forecast daybreak Saturday. Low confidence exists given cloud cover, particularly over Metro Detroit, but the potential exists with light flow and possibly some recent rainfall this evening. After morning clouds, shortwave ridging and a renewed bout of warm advection will yield warm and humid weather again Saturday afternoon. Highs are expected to reach the lower 80s which is approximately 10 degrees. A complex evolution to split upper level flow is expected to take place in vicinity of the Great Lakes late this upcoming weekend. Models are generally in agreement that a cold frontal boundary will push into the area before slowing and stalling out for the beginning of next week. Given the progressive behavior of the northern stream trough the feeling is the quicker timing trend of the precipitation for Sunday is preferred. Plan view perspective of moisture/thetae fields show a significant wave of thetae/moisture advection across the forecast area late Sunday. Still some uncertainty regarding whether or not categorical rain/thunderstorm activity will arrive before 00Z Sunday. Pops are now categorical for Sunday evening with a chance for rainfall amounts to exceed 0.5 inch. There is a lot of question regarding how far south the frontal boundary will clear for the beginning of next week. Reasonable confidence exists that Southeast Michigan will reside on the cool side of the boundary. Fairly high precipitation chances do exist for next week accounting for the possibility of stretching deformation forcing. Highs next week are expected to reside around normal with daytime readings in the lower 70s. MARINE... Scattered to numerous showers with a low chance for an isolated thunderstorm will continue through the evening hours as an upper- level disturbance and cold front move through the Great Lakes. Some isolated gusts nearing 20 knots continue to be possible across northern Lake Huron through tonight, but otherwise, a weak pressure gradient will maintain lighter winds through the day. High pressure holds through Sunday afternoon, before a cold front/low pressure system then brings the likely chance for rain and some thunderstorms Sunday into Monday. && .DTX WATCHES/WARNINGS/ADVISORIES... MI...None. Lake Huron...None. Lake St Clair...None. Michigan waters of Lake Erie...None. && $$ AVIATION.....DG DISCUSSION...CB MARINE.......AM You can obtain your latest National Weather Service forecasts online at www.weather.gov/detroit.