Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI
Issued by NWS Detroit/Pontiac, MI
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657 FXUS63 KDTX 190441 AFDDTX Area Forecast Discussion National Weather Service Detroit/Pontiac MI 1241 AM EDT Wed Jun 19 2024 .KEY MESSAGES... - Hot and humid conditions will persist across most of the area through the week. - Chances of thunderstorms will continue each day of the week. Some of these storms may be strong to severe with locally heavy downpours. && .AVIATION... VFR ceilings and vsbys are expected tonight and into Wednesday. Mid/high clouds will gradually fill in overnight, introducing some uncertainty in regards to how thunderstorms chances will play out on Wednesday. Thunderstorms remain possible, especially after 21Z on Wednesday, with both individual storms and clusters of storms possible. Winds will maintain a southerly component tonight, becoming southwesterly by Wednesday morning. A backdoor cold front begins to move in from the north late Wednesday night, with north to northeast winds overspreading southeast Michigan. For DTW/D21 Convection...Attention turns to Wednesday, mainly during the afternoon and evening hours for our next chance for thunderstorm activity. There will be a bit more deep layer wind shear to work with tomorrow, so we may see both individual pulse-type thunderstorms and clusters of storms move through the area. While there are a few high-rest models that bring thunderstorms in during the late morning hours, the best time period for convective activity will take shape after 21Z. The potential for wet microbursts will be a concern once again, should stronger storms develop over/near D21 airspace. DTW THRESHOLD PROBABILITIES... * Low to Moderate risk for thunderstorms Wednesday between 21Z and 03Z. * Low risk for ceiling at or below 5000 ft, conditional with thunderstorms. && .PREV DISCUSSION... Issued at 353 PM EDT Tue Jun 18 2024 DISCUSSION... Opaque mid cloud altostratus and haze associated with the shortwave lifting into western Lower Michigan has been very effective in dampening insolation through the noon hour. Have observed very little boundary layer cumulus growth into the early afternoon hours across Southeast Michigan. The real forecast challenge now heading forward is what sort of low-midlevel convective inhibition will hold on as forecast soundings were advertising the greatest projected instability would exist at midday just prior to the deepest boundary layer mixing. The most recent ACARS soundings do show a pronounced stable layer residing in the 850-775mb layer that does match with the forecast soundings (3.0 to 6.0 kft agl). Signal of the 18.12Z CAMS was decidedly leaner with convective coverage over all of the forecast area, although the MPAS runs and a couple of the WRF ARW runs continue to show some development after 20Z. Small scale of the modeled updrafts in the CAMS suggest a more muted UVV response and for this reason the potential for strong to severe storms (if they were to develop) is probably less than yesterday. Will leave PoPs in the high chance category this afternoon given the convergence that is expected to develop. Strong wind gusts from water loading/wet downbursts are the main threat with heavy rainfall from any training another possibility. A ribbon of sheared absolute vorticity is expected to lift northward along the periphery of the upper level ridging into the Great Lakes region during the daytime Wednesday. Model data shows the strongest shortwave center then impinging directly into the area during the late afternoon. More transparency to the cloud and modest cooling in the 850-700mb layer is expected to result in less low-mid CIN over the area. Surface based CAPEs of over 1500 J/kg with 0-6 km bulk shear increasing to 30 knots will support a strong to severe thunderstorm threat. The current Day 2 for SPC has Southeast Michigan in a General Thunderstorm Outlook. A dynamic behavior and evolution of the upper level ridge is expected this week with a pseudo rex block taking shape over the eastern United States tonight and Wednesday before the centroid retrogrades back to the Tennessee Valley by Saturday. Latest indications are that ridging will hold just north of Southeast Michigan with H5 heights of 592-596 dam. Projected 850mb temperatures during this timeframe are expected to range between 18- 19C with high temperatures rising into the lower 90s. The uncertainty for the week regarding heat indices is on two items. 1. Favorable setup for inertial instability-and backdoor cold front flipping flow northerly in the Thumb for Thursday. Current high temperatures along the Lake Huron shoreline are in the 70s. 2. Guidance and forecasted surface dewpoints running higher than what has been verifying. The current gridded forecast has values reaching/exceeding 70 degrees each of the days. The cumulative effects of consecutive days of heat and humidity will cause stress on vulnerable individuals and populations. The heat headlines will remain in effect. MARINE... Southwest winds will maintain the hot and humid conditions into tomorrow. A high degree of surface stability with the cooler waters should keep wind speeds under 25 knots. 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. A cold front is now progged to move south Wednesday night, even faster than indicated yesterday. This will allow for northerly winds over Lake Huron on Thursday and Friday as seasonably strong high pressure tracks through Ontario. Even so, airmass remains warm, which should help limit wind speeds to around 15 knots. Thus, any wave build up with the longer fetch is expected to remain below 4 feet. A stronger cold front looks to be on track for the second half of the weekend however, and wind speeds then could reach or exceed 25 knots with waves building to around 4 feet. Small craft advisories may be needed. && .DTX WATCHES/WARNINGS/ADVISORIES... MI...Heat Advisory until 8 PM EDT Friday for MIZ047-053-060-068-075-082- 083. Heat Advisory until 8 PM EDT Thursday for MIZ048-049-054-055-062- 063. 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.....JA DISCUSSION...CB MARINE.......SF You can obtain your latest National Weather Service forecasts online at www.weather.gov/detroit.