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


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