Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI
Issued by NWS Detroit/Pontiac, MI
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579 FXUS63 KDTX 170741 AFDDTX Area Forecast Discussion National Weather Service Detroit/Pontiac MI 341 AM EDT Mon Jun 17 2024 .KEY MESSAGES... - Heat and humidity will affect the area through the week. Excessive heat warnings and heat advisories are in effect. - There will be periodic chances for thunderstorms throughout the week. && .DISCUSSION... A compact mid level MCV will traverse Se Mi during the early morning hours. This wave has been responsible for clusters of strong to severe convection upstream, with the more robust convective response occuring closer to the sfc warm front. The passage of this wave and influx of deep layer moisture and elevated instability will sustain some degree of convection across Se Mi this morning, particularly across the southern portions of the forecast area. Elevated instability will be advecting into Se Mi from the west during the course of the early morning, which may be enough support isolated strong to marginally severe convection. Some building of the mid level height field in the wake of this mornings MCV will allow respectable diurnal heating to occur. High temps upstream yesterday were in the lower to mid 90s, which look reasonable across Se Mi this afternoon. Diurnal mixing will likely hold sfc dewpoints in the 60s this afternoon which will cap heat indices in the mid to upper 90s. Forecast soundings across Se Mi this afternoon/evening are uncapped. Late day convective development can therefore not be ruled out, especially considering lingering sfc boundaries expected across Se Mi. A building mid level ridge across the East Coast over the next couple days will be responsible for the heat across the southern lakes. Models have been very consistent showing 500mb heights rising to 598-600dm as the mid level high becomes centered over the Mid Atlantic Wednesday into Thursday, while the ridge axis builds westward across the Ohio Valley and eastern Great Lakes. Thermal profiles (with 850mb temps of +19 to +21C) across southern Michigan will be supportive of high temps into the 90s. There does remain considerable uncertainty as to the timing and strength of numerous short wave impulses that will be circulating around the large mid level ridge, especially Tuesday and Wednesday. These short waves are likely to impact portions or all of Se Mi at times and will continue to support a chance of showers and thunderstorms. Moderate to possibly high instability with a little bit of mid level flow along the northwestern side of the ridge will support a chance for a few strong to severe storms both Tuesday and Wednesday. Timing/coverage however remains highly uncertain. Medium range model ensemble members show increasing spread in the Friday to Sunday time frame with respect to the breakdown of the mid level ridge across the Great Lakes resulting from northern stream energy. This and the increasing potential for convection to bleed into portions of Se Mi lead to some degree of uncertainty as to temps late week into next weekend. The excessive heat watch was issued due to multiple consecutive days of hot weather as opposed to just one day of possibly breaking a heat index of 100. This is due to the fact that heat stress worsens with number of consecutive hot days. Per coordination with surrounding offices, the heat watch is being replaced with a long fused head advisory. The exception to this is the urban Detroit and Flint areas (Wayne, Oakland, Macomb, Genesee Counties) where a warning is being issued given the more adverse affects of heat on these urban areas. && .MARINE... A warm and humid airmass will hold over the Great Lakes through the week, which will support relatively stable near surface lake conditions. The earlier passage of a warm front has reinforced south to southwest flow, which will hold through at least the early week period. Otherwise, there will be a couple of chances for showers and thunderstorms today. The first through this morning, pending the evolution of an upstream storm complex, with renewed chances possible later this afternoon and evening. Additional development is possible tomorrow, but this is more favored over land or along the nearshore. Localized stronger wind speeds and gusts around 20 to 25 knots will be possible through the Saginaw Bay into central Lake Huron with the favorable southwest fetch tomorrow. && .HYDROLOGY... A moist and unstable airmass will be in place across the region through Tuesday. This will bring the potential of a few rounds of showers and thunderstorms this morning through at least Wednesday. Locations which experience strong thunderstorms will have the potential for rainfall amounts to exceed 2 inches in a short period of time, leading to urban/low lying flooding. There is too much uncertainty both the timing and potential for localized heavy flooding to issue any type of flood watch products at this time. && .PREV DISCUSSION... Issued at 1207 AM EDT Mon Jun 17 2024 AVIATION... A large cluster of thunderstorms now represents both earlier surface based activity plus new development farther west fed more by nocturnal mechanisms. The parent MCV still makes storms possible farther north toward MBS although radar trends at forecast issuance clearly favor PTK and the DTW corridor for several hours of borderline MVFR/IFR conditions depending on rainfall intensity. Other observational trends will be monitored for signs of greater coverage of ceiling or visibility restriction within the frontal zone. The shower/storm pattern then moves eastward by late morning and VFR cumulus follows within the inbound heat and humidity for the afternoon. A stray pop-up shower or storm is possible in this air mass but with predictability too low for a mention at this point in the forecast. For DTW/D21 Convection... The leading edge of thunderstorms inbound from LAN to JXN weaken to lighter showers in favor of new storms farther west. It is possible the later activity holds together for scattered storm coverage across D21 and at DTW after 08Z until about 12Z. Localized heavy rainfall is the primary hazard with this activity until moving east of D21 by late morning. DTW THRESHOLD PROBABILITIES... * Moderate for thunderstorms at the terminal late tonight into early morning. * Moderate for ceiling 5000 ft or less mainly with convection late tonight and early morning. && .DTX WATCHES/WARNINGS/ADVISORIES... MI...Heat Advisory from noon today to 8 PM EDT Friday for MIZ047>049- 053>055-060-062-063-068-075-082-083. Excessive Heat Warning from noon today to 8 PM EDT Friday for MIZ061-069-070-076. Lake Huron...None. Lake St Clair...None. Michigan waters of Lake Erie...None. && $$ DISCUSSION...SC MARINE.......AM HYDROLOGY....SC AVIATION.....BT You can obtain your latest National Weather Service forecasts online at www.weather.gov/detroit.