263
FXUS63 KDTX 191949
AFDDTX

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
349 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 late tomorrow afternoon
  into tomorrow night. Dry Saturday then likely rainfall Sunday
  night into Monday.

- Additional chances for rain through next week with temperatures
  settling to more seasonable values.

&&

.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.

&&

.PREV DISCUSSION...
Issued at 133 PM EDT Thu Sep 19 2024

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.


&&

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

$$

DISCUSSION...AA
MARINE.......AM
AVIATION.....DRK


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