314
FXUS63 KDTX 201929
AFDDTX

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
329 PM EDT Fri Sep 20 2024

.KEY MESSAGES...

- Warm weather continues through this weekend with a slight increase
in humidity each day.

- Scattered showers and storms are possible this afternoon and early
tonight with additional rainfall Sunday night into Monday.

- Lower confidence in rain chances for the middle of next week while
temperatures cool off to seasonable values.

&&

.DISCUSSION...

Anticyclonically curved left exit region dynamics and dampening
absolute vorticity lobe will push into the central Great Lakes by
this evening. A fair amount of synoptic support for ascent is
expected with 1000-500mb geopotential height falls sliding through
Southeast Michigan between 21-06Z this evening. Model consensus has
been consistent in convection initiating/expanding this afternoon in
the lee of Lake Michigan before trying to push eastward. Regional
Reflectivity mosaic has supported this. Most recent CAM UVV signal
suggests activity pushing up to the western edge of the cwa prior to
00Z, but significantly weakening and dissipating before it tracks
into the area. Survey of forecast soundings and HREF data suggests
MUCAPES increasing to <1000 J/kg for the western cwa, but with a
significant amount of dry air in the near surface environment. Thus,
the atmosphere is expected to remain statically stable in the lowest
5 kft agl. No strong or severe thunderstorms are anticipated. The
latest Swody1 keeps the forecast area under a General Thunderstorm
designation.

Low chances for a shower and an isolated thunderstorms will exist
throughout the evening hours with the best low-mid convergence,
cyclonic flow, and height falls will be in place over the area.
Difficult to provide much detail with a sparse QPF footprint in the
solutions. Did introduce areas of fog mention into the zone forecast
daybreak Saturday. Low confidence exists given cloud cover,
particularly over Metro Detroit, but the potential exists with light
flow and possibly some recent rainfall this evening.

After morning clouds, shortwave ridging and a renewed bout of warm
advection will yield warm and humid weather again Saturday
afternoon. Highs are expected to reach the lower 80s which is
approximately 10 degrees.

A complex evolution to split upper level flow is expected to take
place in vicinity of the Great Lakes late this upcoming weekend.
Models are generally in agreement that a cold frontal boundary will
push into the area before slowing and stalling out for the beginning
of next week. Given the progressive behavior of the northern stream
trough the feeling is the quicker timing trend of the precipitation
for Sunday is preferred. Plan view perspective of moisture/thetae
fields show a significant wave of thetae/moisture advection across
the forecast area late Sunday.  Still some uncertainty regarding
whether or not categorical rain/thunderstorm activity will arrive
before 00Z Sunday. Pops are now categorical for Sunday evening with
a chance for rainfall amounts to exceed 0.5 inch. There is a lot of
question regarding how far south the frontal boundary will clear for
the beginning of next week. Reasonable confidence exists that
Southeast Michigan will reside on the cool side of the boundary.
Fairly high precipitation chances do exist for next week accounting
for the possibility of stretching deformation forcing. Highs next
week are expected to reside around normal with daytime readings in
the lower 70s.

&&

.MARINE...

Scattered to numerous showers with a low chance for an isolated
thunderstorm will continue through the evening hours as an upper-
level disturbance and cold front move through the Great Lakes. Some
isolated gusts nearing 20 knots continue to be possible across
northern Lake Huron through tonight, but otherwise, a weak pressure
gradient will maintain lighter winds through the day. High pressure
holds through Sunday afternoon, before a cold front/low pressure
system then brings the likely chance for rain and some thunderstorms
Sunday into Monday.

&&

.PREV DISCUSSION...
Issued at 103 PM EDT Fri Sep 20 2024

AVIATION...

Weak south-southeast winds with mid to high clouds around this
afternoon ahead of a weak cold front. Lower VFR clouds will arrive
early this evening, as the weak convergence long the front slowly
crosses southeast Michigan. Enough instability around to support
scattered coverage of showers late this afternoon into the evening,
with isolated thunderstorms not out of the question, but too limited
in potential to highlight attm. Border line MVFR/VFR cigs will be
possible where showers develop. Clouds decrease late tonight behind
the front, which could lead to a period of low stratus or fog by
sunrise Saturday as winds will be nearly calm. Held the visibility
in the tafs in MVFR for now, as confidence is low in dense fog, as
there may be just enough wind around.

For DTW/D21 Convection...Scattered showers around this evening with
a slight chance of thunderstorm as a weak frontal boundary tracks
through. Will continue with the prob30 mention of showers.
Confidence in thunderstorms is too low to include at this time.

 DTW THRESHOLD PROBABILITIES...

* Low for ceilings at or below 5000 ft this evening and tonight.

* Low for thunderstorm chances this evening.


&&

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

$$

DISCUSSION...CB
MARINE.......AM
AVIATION.....SF


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