462 FXUS63 KDTX 292308 AFDDTX Area Forecast Discussion National Weather Service Detroit/Pontiac MI 708 PM EDT Sun Aug 29 2021 .AVIATION... Showers and thunderstorms will continue to work through the area early this forecast as a cold front driven by shortwave energy to the north pushes into the area. KMBS should remain dry, but KFNT south should see an hour or two of scattered convection before this activity works off to the east and southeast. Thereafter, expect VFR conditions with the exception of a period of minor MVFR for early Monday morning. For DTW...Scattered to numerous showers/thunderstorms will be ongoing at the beginning of the forecast with this activity shifting east/southeast in the 00z-02z time frame. Will maintain minor MVFR fog late tonight/early Monday morning will VFR conditions on Monday. .DTW THRESHOLD PROBABILITIES... * Moderate for ceilings at or below 5 kft at times into tonight. * Moderate for thunderstorms early in the forecast (00z-01z). && .PREV DISCUSSION... Issued at 412 PM EDT Sun Aug 29 2021 DISCUSSION... Severe Thunderstorm Watch 473 is in effect until 7 PM EDT. Surface based CAPE values approaching 3000 J/kg, DCAPE exceeding 1100 J/kg, and a well mixed boundary layer brings the potential for efficient damaging wind gust production this afternoon and evening. The main limiting factor remains weak deep layer shear that will increase up to 20 knots after 20Z. Multicellular storm organization with embedded line segments brings damaging wind gusts of potentially greater than 60 mph into play. The wind threat is expected to be fairly scattershot and pulselike with no signal for strong cold pool generation. Hail and tornado threats appear to be minimized for this event. Low confidence exists in any short duration training this evening as convective activity pushes south of the I 96 corridor. Model signal continues to suggest that a better potential for a multiple hour duration would be across portions of Southwest or South Central Lower Michigan. The deep 925-600mb cold front is forecasted to sag southward and clear the Michigan/Ohio state line between 15-18Z Monday. A big drop in surface dewpoints are expected with readings lowering down into the low 60s areawide. Heat indices will reside in the lower to mid 80s which will be some 10 to 15 degrees lower than recent days. Diurnal cumulus is anticipated at/around 5.0 kft agl but differential cold advection in the low levels will lead to very stable conditions. Modest upper level confluence will become increasingly more organized over the central Great Lakes region Monday and Tuesday. Dynamic forcing aloft will then be bolstered by differential geopotential height increases to result in strong surface ridge axis expanding down into Lower Michigan. The surface ridging will be non- trivial as high confidence exists that Ida remnants will be blocked and turned sharply to the east on Wednesday. Expectations are for the precipitation to miss Southeast Michigan with increase in northerly geostrophic flow Wednesday afternoon and Wednesday night. A secondary cold front is expected to release through the area Tuesday night. The biggest effect will be on low temperatures with morning readings in the 50s and perhaps the upper 40s Thursday morning. Models do show an upper level jet arriving for the end of the week. Lower confidence exists on how exactly the sensible weather effects could play out because of possible anticyclonic shear dominating the region. MARINE... One more day of unsettled weather will exist across the local waters as a very warm and humid airmass promotes another round of thunderstorms through this evening ahead of a passing cold front. Any thunderstorm will have the potential to produce strong winds in excess of 34 knots and locally erratic waves. Outside of thunderstorms, moderate southwesterly winds gusting 20-25 knots at times will eventually veer northwesterly behind the cold front passage as drier air begins to filter into the central Great Lakes. Moderate north to northwesterly flow will then prevail through midweek as broad high pressure settles over the region. HYDROLOGY... Scattered to numerous thunderstorms develop this afternoon and continue into the evening as a cold front moves in from the Midwest. Locally heavy rainfall remains possible with this activity although flooding potential is reduced slightly by fast motion of the line. Conditions will be monitored for any west to east positioning of storms which would be more capable of flooding. Basin-average rainfall totals are expected to range from 0.25 to 0.50 inches, but localized areas could receive upwards of 1 to 2 inches as rainfall rates will likely exceed 1 inch per hour. This may result in flooding of susceptible areas, particularly if repeated storms occur over urban areas before the line moves south and east of the region toward midnight. && .DTX WATCHES/WARNINGS/ADVISORIES... MI...NONE. Lake Huron...NONE. Lake St Clair...NONE. Michigan waters of Lake Erie...NONE. && $$ AVIATION.....DG DISCUSSION...CB MARINE.......IRL HYDROLOGY....BT You can obtain your latest National Weather Service forecasts online at www.weather.gov/detroit.