Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI
Issued by NWS Detroit/Pontiac, MI
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117 FXUS63 KDTX 181953 AFDDTX Area Forecast Discussion National Weather Service Detroit/Pontiac MI 353 PM EDT Tue Jun 18 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. && .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. && .PREV DISCUSSION... Issued at 153 PM EDT Tue Jun 18 2024 AVIATION... Complex aviation setup today with current cloud cover and possible thunderstorms this afternoon. Extensive cloud cover due to mid level wave passing over lower MI this afternoon has prevented temperatures from rising as rapidly as previously thought which in turn will likely cause storms to be delayed. Storms have already initiated over CLE and north of MBS, both of which had less cloud cover and cu`ed up already. With lake breezes already forming, and the back edge of the denser clouds exiting in a couple hours, will hold onto thunderstorm chances for now in a 20-23Z window. Winds will generally be out of the south/southwest around 12 knots with a few gusts to near 20 possible. Strong gusty winds and microburst potential exists with the deepest convective storms. Otherwise VFR conditions should hold the rest of the evening and overnight. For DTW/D21 Convection...Storms currently going up east and southeast of DTW in the areas where skies have remained mostly clear. Looks like clouds could thin on the backside of the passing wave allowing temps to peak and storms to be possible. Lake breezes are already forming which should help any storms to develop later. Bumped the timing of the storms back an hour to account for the increased clouds, so looking around 20-23Z for best chance. Potential for wet microbursts should stronger storms develop over/near D21 airspace. DTW THRESHOLD PROBABILITIES... * Low to Moderate for thunderstorms from 20 to 23Z. * Moderate for ceiling at or below 5000 ft, conditional with thunderstorms. && .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. && $$ DISCUSSION...CB MARINE.......SF AVIATION.....DRK You can obtain your latest National Weather Service forecasts online at www.weather.gov/detroit.