Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI
Issued by NWS Detroit/Pontiac, MI
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470 FXUS63 KDTX 171937 AFDDTX Area Forecast Discussion National Weather Service Detroit/Pontiac MI 337 PM EDT Mon Jun 17 2024 .KEY MESSAGES... - A prolonged period of heat and humidity will continue through the week. Excessive heat warnings and heat advisories are in effect. - There will be periodic chances for thunderstorms throughout the week. Locally heavy rainfall will be primary driver of impacts. && .DISCUSSION... Amplifying upper-level ridge episode over eastern North America and correlated building heat dome is well underway. Surface dewpoints are surging into the lower 70s with temperatures climbing to around 90 - pushing heat index values into the upper 90s. Furthermore, low temperatures will only settle back to around 70 with higher readings in the urban settings (mid-70s). These conditions will be the norm for the balance of the work week and will take its toll on exposed populations - hence the long duration heat advisory and excessive heat warning. Subsidence in the wake of the morning mesoscale convective vortex and associated thunderstorms is starting to lose influence across southern Lower Michigan. There is still evidence of a ribbon of anti- cyclonic enhanced flow aloft over Southeast Michigan in the GOES-WV imagery. Consequently, expect the suppression of deeper cumulus development to continue over the next few hours. The scattered activity along the periphery over the Saginaw Valley will continue to bubble northeast across the thumb. While there is plenty of instability to tap (MLCAPE > 2.5-kJ/kg) with adequate depth (>2-km), there is very little flow and/or shear to support scaled growth. Therefore, heavy rainfall is the primary outcome with some wet microburst potential with hydrometeor loading in deeper cells. The quality of instability on Tuesday will not be as good, but a north-south oriented buoyancy gradient in the 1-2-km layer will linger over Southeast Michigan. This in combination with better jet level forcing rolling north into the region will help initiate scattered thunderstorms once again. Precipitable water values will increase to well over 1.75-inches - supporting intense downpours once again. If the buoyancy gradient maintains integrity along the mean flow vector, convective training and resultant flash flood potential will be more likely. Still some variance in guidance offerings, but a small cluster of heavy rainfall outcomes is very evident. The mid-levels do not get dramatically warm with this heat dome; therefore, afternoon convection is possible each day through this heat spell. Medium range guidance is now suggesting that the current heat will grab another day on Saturday with the timing of the next shortwave and cold front remaining questionable. && .MARINE... Southwest winds will continue to advect hot and humid air into the Central Great Lakes through the mid week period. High degree of surface stability with the cooler waters should keep wind speeds under 25 knots through the rest of the work week. The exception will be in and near and strong thunderstorms which develop. Timing and location will be highly uncertain, but the typical peak heating of the day into early evening hours will be favored. Indications are the surface frontal boundary will be sinking south Thursday and Friday as seasonably strong high pressure tracks through Ontario. This will allow for light northeast/northerly flow (~15 knots) over Lake Huron. Airmass will remain warm, thus any wave build up with the longer fetch remains below 4 feet. && .HYDROLOGY... A moist and unstable airmass will be in place across the region through Tuesday. Scattered thunderstorms are expected this afternoon and again Tuesday afternoon. The most intense thunderstorms have the potential to produce rainfall amounts in excess of 2 inches over a short period of time, resulting in urban and low lying area flooding. Uncertainty in specifics for both timing and potential for flooding precludes issuance of a flood watch, at this time. && .PREV DISCUSSION... Issued at 157 PM EDT Mon Jun 17 2024 AVIATION... VFR conditions will prevail the much of this TAF period with daytime heating and the increased moisture supporting a cumulus field at around 6kft this afternoon. There remains potential for afternoon/early evening isolated/scattered thunderstorm development supported mainly by the diurnal instability. The overall uncertainty and anticipated pop up nature of activity will preclude mention in TAFs at this time, but may require an amendment if confidence increases for any terminal to be affected. Low VFR to possible MVFR conditions would be possible with any heavier shower/thunderstorm. Winds will be out of the southwest through this afternoon while deep mixing is yielding gusts to around 20 knots. Winds back towards the south for tonight before veering back towards the southwest tomorrow. For DTW/D21 Convection... There remains a chance for isolated to scattered showers and thunderstorms to develop this afternoon. Confidence is not high enough that any D21 terminal will be impacted, so will not include a tempo group at this time. The favored time frame for activity is towards 22-00Z. Will continue to monitor and amend if needed. DTW THRESHOLD PROBABILITIES... * Low for thunderstorms this afternoon and evening. * Low for ceiling at or below 5000 ft, conditional with convective development. && .DTX WATCHES/WARNINGS/ADVISORIES... MI...Heat Advisory until 8 PM EDT Friday for MIZ047>049-053>055-060-062- 063-068-075-082-083. Excessive Heat Warning until 8 PM EDT Friday for MIZ061-069-070-076. Lake Huron...None. Lake St Clair...None. Michigan waters of Lake Erie...None. && $$ DISCUSSION...Mann MARINE.......SF HYDROLOGY....Mann AVIATION.....AA You can obtain your latest National Weather Service forecasts online at www.weather.gov/detroit.