Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI
Issued by NWS Detroit/Pontiac, MI
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683 FXUS63 KDTX 212003 AFDDTX Area Forecast Discussion National Weather Service Detroit/Pontiac MI 403 PM EDT Sat Sep 21 2024 .KEY MESSAGES... - Showers and thunderstorms tomorrow afternoon into tomorrow night. - More seasonable temperatures Monday through Wednesday with highest chance of precipitation Tuesday. && .DISCUSSION... Quick passing ridge builds in behind this mornings front will result in dry and stable conditions through the remainder of the day. Lack of strong cold air advection with the quickly arriving thermal ridge carrying 850mb temperatures to 15C and greater has allowed afternoon high temperatures to climb back into the 80s. Mixing down of the dry air aloft will also keep humidity in check. There is some potential for fog development tonight, but expecting coverage of high clouds to increase. This should limit the degree of fog that is able to develop as overnight as temperatures cool. Will continue to leave any fog mention out given the low probability, but the best chance at seeing some fog will be from light southeast winds advecting fog/moisture off the lakes. Increasing clouds tonight are associated with strong southwest flow extending from the desert southwest into Ontario and the base of the central Canadian trough. This is improved moisture transport will usher in PWATs greater than 1.50 inches by early Sunday afternoon, which is the highest we have seen since late last month. This moisture will be drawn northward ahead of an advancing cold front tied to the central Canadian trough and surface low lifting into northern Ontario/Hudson Bay. This will support widespread rainfall spreading across Michigan tomorrow. Initial shower activity will begin spreading into southeast Michigan during the afternoon, more than likely after 2 pm. Timing of higher QPF amounts likely arrives more towards the evening and through the first half of the night. Average QPF amounts will average a half inch to three quarters of an inch from Sunday afternoon through Monday morning. Stronger forcing along the front and the larger scale ascent in the left exit region of the upper jet will be capable of pushing some rainfall totals towards 1.00 inch or greater. This is especially true for areas north of I-69 across the northern Thumb and Tri-Cities. There will be a slight chance of thunderstorms along the front, but should be more isolated to scattered. The limited surface instability, weak mid- level instability with MUCAPE of a few hundred j/kg and weak mid- level lapse rates will limit the thunderstorm potential. Frontal passage Monday morning will bring winds out of the northwest that will also usher in a cooler airmass to the region. Much more seasonable high temperatures around the low 70s are expected Monday through Wednesday. Monday also appears to be mostly dry for a lot of the area, though cannot rule out a few stray showers developing within the north-northeast flow off Lake Huron. Tuesday holds the higher likelihood of rainfall as a northern stream wave interacts with the inbound shortwave trough originating from the Four Corners region. && .MARINE... A ridge of high pressure will maintain dry weather and light winds for the remainder of the day. Starting late tonight and into the overnight hours, a subsidence inversion will strengthen and will trap near surface moisture across portions of Lake Huron. The development of marine fog to or under one mile will be possible overnight (about a 50% chance of going under one mile), and will continue to monitor observations for the possible issuance of a marine dense fog advisory. Any fog development will clear out through the morning hours, ahead of an approaching low pressure system and cold front, which will bring widespread rain and embedded thunderstorms across the region. Precipitation will initially start across northern Lake Huron tomorrow afternoon, with an expansion across the remaining Great Lakes through the evening hours. Wind direction will back from south- southeast to more northerly after the passage of the front, with improved mixing depths bringing wind gusts up to 20 knots, late tomorrow through Monday. && .HYDROLOGY... Showers with embedded thunderstorms are expected along a cold front from Sunday afternoon into Monday morning. Average rainfall will range from a half inch to three quarters of an inch. Given PWATs greater than 1.50 inches, locally higher amounts to 1.00 inch or greater will be possible. This is especially true for areas north of I-69 and associated with any embedded thunderstorms. No significant flooding is expected. && .PREV DISCUSSION... Issued at 1234 PM EDT Sat Sep 21 2024 AVIATION... Clear-mostly clear skies around the rest of the day with light west- northwest flow. The surface moisture/higher dew pts will be attempting to diminish as the boundary layer mixing depths increase. This makes for a challenging forecast tonight with the fog potential, as high clouds spilling over tonight also attempts to mitigate fog potential as well. Confidence is low in avoiding fog altogether, as there looks to be a light easterly trajectory setting up late, which puts the moisture source of Lake Huron/Lake ST. Clair into play. Ultimately, will carry just a MVFR visibility for now and monitor the progress of the high clouds this evening. Increasing southerly flow on Sunday, with gusts expected to top out around 20 knots. For DTW/D21 Convection...No thunderstorms are expected through Sunday morning. DTW THRESHOLD PROBABILITIES... * None && .DTX WATCHES/WARNINGS/ADVISORIES... MI...None. Lake Huron...None. Lake St Clair...None. Michigan waters of Lake Erie...None. && $$ DISCUSSION...AA MARINE.......AM HYDROLOGY....AA AVIATION.....SF You can obtain your latest National Weather Service forecasts online at www.weather.gov/detroit.