AVIATION

Persistence forecasting suggests that another round of early morning fog, some locally dense, will occur Friday morning. A period of low stratus may accompany some of the fog as well. A greater degree of high level cloudiness may impede this somewhat, especially KFNT north. Otherwise, VFR conditions continue with east to southeast flow under 10 knots as a ridge of high pressure remains positioned off to the east of the region. An approaching cold front will bring an increase in mid/upper level clouds late in the day with spotty light showers/virga. Will leave this period dry for now.

For DTW/D21 Convection...Some scattered light showers may develop late day Friday as an elevated cold front works into the area. There is the possibility of an isolated thunderstorm embedded with these showers, but confidence is low at this time and coverage would be minimal so will forgo a mention in the forecast at this time.

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 349 PM EDT Thu Sep 19 2024

DISCUSSION...

Michigan will reside between troughing through the Mid-Atlantic and troughing with mid level closed low across south central Canada and the northern plains. This will maintain shortwave ridging over the central Great Lakes for the rest of today. The lower level moisture noted by the morning low stratus and fog has helped support the daytime cumulus field with daytime heating. Highs are on track this afternoon under the partly cloudy skies. Cumulus field will decrease this evening with mainly lower coverage of inbound high clouds tonight. The southeasterly flow maintains the boundary layer moisture from Lake Erie and mostly favorable radiational cooling conditions tonight will result in patchy to locally dense fog development tomorrow morning.

A shortwave will release out of the Dakotas from the parent trough and into the Great Lakes tomorrow. These height falls will help flatten the ridge as the axis shifts to the east while drawing a cold front in from the west. The weak front will move through western WI/IL early tomorrow morning and weaken as it moves across Lake Michigan later in the day allowing for dry conditions for most of the day. The shallow front with extra upper level support from the left exit region of the southern stream jet bring at least a chance of precipitation. Activity may arrive across western portions of the CWA by late afternoon which gradually spreads eastward into early Saturday morning. A corridor of instability (MLCAPE 500-1000 j/kg) ahead of the front will encroach into western portions of the CWA helping support the late afternoon activity with a decrease in instability through the evening. Bulk shear will be weak as better shear is displaced across southwest MI and northern IN, but steep enough mid level lapse rates (6.5-7.0 C/km) will support a slight chance of general thunderstorms. The lack of overall moisture should yield more scattered coverage of precipitation with this front as it pushes into the resident dry airmass and weakens while pushing east towards daybreak.

A brief period of shortwave ridging will follow the this trough as it merges with the Atlantic coast trough. Expect dry conditions beyond 12Z Saturday under a light northwest wind. Weak post frontal cold advection will quickly be replaced by the low level thermal ridge and 850mb temps of greater than 15C. This will support daytime highs still in the 80s for Saturday. Meanwhile, vorticity advection ahead of a mid-level low ejecting out of the Four Corners region will move atop another frontal zone extending across the Midwest/Great Lakes. This brings the next chance of showers and thunderstorms starting Sunday afternoon with likely rainfall Sunday night as system rolls through. This system is forecast to bring a decent slug of moisture compared to what we have seen of late with PWATs to 1.50 inches or greater. It is looking increasingly likely that much of southeast Michigan could see up to a half inch of rainfall or more Sunday into Monday. Precipitation chances continue into mid-week period as troughing lingers over the region. There will be an opportunity to better hone the timing of PoPs with upcoming forecasts given the broad brush of PoPs offered by the extended guidance. The higher confidence in the extended will be the cool down to more seasonable temperatures with high temperatures returning to the 70s.

MARINE...

The long stretch of dry weather and light winds will continue today through tomorrow morning as high pressure remains in control.
Tomorrow afternoon into Saturday morning will then likely put an end to dry conditions for portions of the Great Lakes, as a cold front and upper-level disturbance brings the chance for scattered to numerous rain showers and isolated thunderstorms. The best coverage of precipitation is expected across Lake Huron, tied to the stronger upper-level disturbance, but all locations across the Great Lakes will have a chance to see rain. Some elevated gusts nearing 20 knots will be possible with the front within northern Lake Huron, but otherwise, a weak pressure gradient will maintain lighter winds through the weekend.

DTX WATCHES/WARNINGS/ADVISORIES
MI...None.
Lake Huron...None.
Lake St Clair...None.
Michigan waters of Lake Erie...None.