566
FXUS63 KDTX 181945
AFDDTX

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
345 PM EDT Wed Sep 18 2024

.KEY MESSAGES...

- Warm and dry weather prevails through the end of the week and
likely through the weekend.

- A weak cold front has a slight chance of reaching Lower MI with
spotty light rain possible late Friday into Saturday.

&&

.DISCUSSION...

Ridging continues across the Great Lakes as the dominate upper level
features remain stationary across the conus through at least
Thursday. The upper level trough over the west coast releases a
strong vort max while also reinforcing itself with a southward
diving jet down the coastline. Meanwhile, the weaker upper low over
the Carolinas continues to churn with little movement with the ridge
wedged between these two features. Airmass remains relatively
unchanged trapped under this ridge, but starting this morning there
has been an influx of low level moisture which resulted in an
enhanced cu field this afternoon. Continued easterly flow will keep
dewpoints up in the upper 50s to 60 tonight which should lead to
another round of fog in the morning.

Big question is whether or not we`ll see any precipitation Friday
into Saturday when the aforementioned upper level wave releases from
the west coast and tracks northeast through the Midwest. The main
vort max gets pulled northward into western Canada but the trough
swings through the Great Lakes while pivoting to a negative tilt.
The surface front looks to wash out moving into the dry and stable
air of the ridge still in place, but there is an arc of vorticity
and pretty good ribbon of theta e pushing across the area. We`ve
seen several times this summer where the 700mb forcing is enough to
squeeze out some showers even with deep dry layer several thousand
feet thick to work against. Model soundings show some elevated
instability (couple hundred J/kg) as well so a thunderstorm cannot
be ruled out but scattered light showers would be more likely. So
the NBM offers 20-30 POPs Friday and Friday night to account for
this which seems reasonable.

Weekend looks mostly dry once again but forecast does start getting
more interesting as models want to dislodge the cutoff west coast
low and release it across the conus. With the ridge still extending
up along the MS River, and the stronger flow aloft within the
dominate trough over Western Canada, expectations would be for this
low to eject northeastward into the Midwest as early as Sunday. GFS
and ECMWF differ on how connected the cutoff low is to the Canadian
trough and thus how progressive it is across the Plains. Regardless,
looks likes we can expect precipitation chances for the first half
of the new week as the trough slowly works through the region.

&&

.MARINE...

High pressure remains in control through the end of the week which
will continue to bring light winds. The next chance (30-40%) for
rain showers or a thunderstorm will enter Friday night into Saturday
morning as a weak cold front and upper-level disturbance moves over
the Great Lakes. Otherwise, dry weather persists.

&&

.PREV DISCUSSION...
Issued at 1259 PM EDT Wed Sep 18 2024

AVIATION...

Daytime heating has resulted in a scattered cumulus field early this
afternoon while the light easterly flow supplies the low level
moisture boost. Skies are expected to remain VFR, but cloud bases
will settle right around 3-4 kft and an occasional BKN observation
is possible. A return to mostly clear skies and light winds tonight
will bring another round of patchy to locally dense fog development.
Have tempo groups for MVFR VSBYs, but it will be possible to see
lower VSBY restrictions before lifting around 13-14Z. Winds remain
east-southeast and below 10 knots tomorrow with another round of
diurnal cumulus with the lake moisture boost.

For DTW/D21 Convection...No thunderstorms are forecast through this
week.

 DTW THRESHOLD PROBABILITIES...

* None.


&&

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

$$

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


You can obtain your latest National Weather Service forecasts online
at www.weather.gov/detroit.