Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI
Issued by NWS Detroit/Pontiac, MI
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976 FXUS63 KDTX 191733 AFDDTX Area Forecast Discussion National Weather Service Detroit/Pontiac MI 133 PM EDT Thu Sep 19 2024 .KEY MESSAGES... - Warm weather continues through this weekend with a slight increase in humidity each day. - Scattered showers and storms are possible Friday afternoon into Friday night. Another round of rain is likely Sunday night into Monday. - Additional chances for rain through next week with temperatures settling to more seasonable values. && .AVIATION... Daytime heating has once again mixed out the morning fog and resulted in an expanding cu field across the region. Conditions should remain VFR through the rest of the day with the 2-4kft cu field scattering out over time. Persistence forecasting will lead to expectations for another round of fog, possibly dense in spots, Friday morning as easterly low level flow persists. The difference this time will be the potential for high cloud debris shedding off a cold front to the west. The thicker clouds could reach MBS and FNT by morning helping to reduce their chances for fog, while the Detroit area terminals (and PTK) likely not seeing thick enough clouds to affect their fog chances. So will again start a tempo group for fog in the late morning hours. For DTW/D21 Convection...Some scattered light showers may develop later in the afternoon or evening as an elevated cold front works into the area. There is the possibility of an isolated thunderstorms embedded in these showers but confidence is low at this time and coverage would be isolated so will not include in the tafs with this forecast. DTW THRESHOLD PROBABILITIES... * Low for ceilings and visibilities to drop below 200ft or 1/2SM Friday morning. * Medium for ceilings below 5kft Friday morning as fog mixes out. * Low for thunderstorm chances late Friday. && .PREV DISCUSSION... Issued at 341 AM EDT Thu Sep 19 2024 DISCUSSION... Broad troughing over the Mid-Atlantic opens up and slowly drifts northeast today. Meanwhile, a potent upper low tracks from the northern Plains into Manitoba and sends an expanding trough into the western Great Lakes. These features continue to squeeze a shortwave ridge over the central Great Lakes through the day, maintaining the dry and warm streak. Another round of patchy fog this morning, with some areas of dense fog at times, gives way to partly cloudy skies as there should be enough boundary layer moisture for another healthy cu up through the afternoon. High temps again reach the lower to mid 80s. We may start to see some high cloud move in from the west this evening but thinking this will do little to affect the otherwise favorable radiating conditions overnight, and another round of fog looks likely Friday morning. Latest guidance shows the ridge giving way to the inbound height falls associated with the aforementioned trough moving in from the Midwest. The parent low will be displaced over northern Manitoba but a coherent lobe of PV will spread over the northern Lakes within the left exit region of the upper jet and looks to bring a corridor of deep moisture into the region. Daytime Friday will be mostly dry but spotty showers may start to move in from the west by the afternoon and evening as elevated moisture ahead of the front moves in. The front and attendant moisture depth do shows signs of substantial weakening as they encounter the resident ridge and dry air mass, but trends in the latest ensemble guidance continue to support at least a chance of showers in the Friday night to early Saturday time frame. Some thunderstorms will also be possible as mid-level lapse rates should be sufficient for several hundred J/kg of MUCAPE. A weak pressure pattern follows through the weekend with the trough sinking southeast and eventually merging with the Mid-Atlantic trough. This places us under another short lived mid-level ridge which should maintain dry and warm conditions Saturday and most of Sunday. During this period a closed low will release from the 4 Corners region and track northeast into the Mid-Mississippi Valley by late Sunday. This system looks to sweep up the moist Gulf air mass over the southern Plains and direct it toward the Great Lakes. LREF grand ensemble data shows around 50% probability for PWAT to reach 1.50 inches within this moisture plume - the highest we`ve seen locally since late August. Likely PoPs are warranted for Sunday night into Monday as the lead moisture surge works in from the south along the system`s warm advective wing. This will mark the beginning of a substantial pattern shift in which various flavors of troughing are depicted over the Great Lakes and eastern CONUS for the first time in weeks. Additional rain chances will exist Tuesday through the rest of the week in this pattern, with high temperatures likely to be more seasonable in the upper 60s or 70s. MARINE... High pressure remains in control through the end of the week which will maintain lighter wind speeds. The next chance for rain showers or a thunderstorm will enter tomorrow afternoon into early Saturday morning as a weak cold front and upper-level disturbance moves over the Great Lakes. Otherwise, dry weather will persist today. && .DTX WATCHES/WARNINGS/ADVISORIES... MI...None. Lake Huron...None. Lake St Clair...None. Michigan waters of Lake Erie...None. && $$ AVIATION.....DRK DISCUSSION...TF MARINE.......AM You can obtain your latest National Weather Service forecasts online at www.weather.gov/detroit.