Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI
Issued by NWS Detroit/Pontiac, MI
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632 FXUS63 KDTX 172308 AFDDTX Area Forecast Discussion National Weather Service Detroit/Pontiac MI 708 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. && .AVIATION... Hot, humid, and unstable air is now rooted across the central Great Lakes tonight and Tuesday. Daytime instability set off a cluster of thunderstorms that brushed MBS on the way into the Thumb region. The latest radar and satellite trends favor a corridor extending back into SW Lower MI for additional development that could approach MBS and FNT this evening, however observations will be monitored for location and intensity trends with sunset. There is little else of concern outside of convective trends under VFR clear to scattered sky condition. A brief period of haze is possible around sunrise, however there is not much signal evident in the data for this forecast issuance. Tuesday then brings more of the same with hot, humid, and unstable conditions developing for the afternoon making a random thunderstorm possible into Tuesday evening. For DTW/D21 Convection... An isolated thunderstorm remains possible across D21 this evening, mainly in the northern reaches of the area where outflow from earlier storms resides. The Erie lake breeze is also just north of DTW this evening but which shows less potential for new development before daytime instability fades with sunset. DTW THRESHOLD PROBABILITIES... * Low for thunderstorms this evening and again Tuesday afternoon. * Low for ceiling at or below 5000 ft, conditional with convective development. && .PREV DISCUSSION... Issued at 337 PM EDT Mon Jun 17 2024 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. && .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. && $$ AVIATION.....BT DISCUSSION...Mann MARINE.......SF HYDROLOGY....Mann You can obtain your latest National Weather Service forecasts online at www.weather.gov/detroit.