177
FXUS63 KDTX 220949
AFDDTX

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
549 AM EDT Sun Sep 22 2024

.KEY MESSAGES...

- Showers and thunderstorms late this afternoon through tonight.

- More seasonable temperatures Monday through Wednesday with highest
  chance of precipitation Tuesday.

&&

.AVIATION...

Initial conditions marked by VFR ceilings (high cirrus) and
unrestricted visibilities precede an approaching frontal boundary
this evening. Top-down saturation commences with the approach of the
front and it`s parent low pressure system. An eventual lowering to
MVFR ensues with the lead wave of resultant rainfall late this
afternoon and early evening (from west to east). Ceilings and
visibilities degrade overnight with increasing potential for IFR
restrictions (and perhaps LIFR). Did adjust the forecast to account
for a period of IFR cigs/vsbys after midnight. Winds generally hold
from the south with speeds around 10 knots today before veering
toward the west (post-front) and then northerly by Monday morning.
Ceiling improvement appears rather slow Monday, therefore opted to
include IFR restrictions through 12Z in the absence of notable
drying processes.

For DTW/D21 Convection...An embedded thunderstorm or two are
possible as rain overspreads the area late this evening with low
confidence in location or timing specifics.

 DTW THRESHOLD PROBABILITIES...

* Medium for ceilings at or below 5000 feet by 01Z Monday, then high
  through tonight and into Monday morning.

* Low for thunderstorms from 22-07Z this evening.

* Low for ceilings at or below 200 feet early Monday morning.

&&

.PREV DISCUSSION...
Issued at 313 AM EDT Sun Sep 22 2024

DISCUSSION...

Higher amplitude upper ridging still fixated over the great lakes
early this morning lends to one final day of well above average
warmth today, before shortwave energy impinging on the region within
general split flow affords a return to more seasonable conditions
heading into next week. Early day conditions marked by thickening
high based cloud as a deeper layer column stability holds firm under
lingering ridging. Cloud cover provides a lower ceiling for
prospective insolation potential relative to yesterday, but still
sufficient to push highs into the lower/mid 80s within the
background of a veering low level south to southwest flow. A lower
coverage of high based light showers/sprinkles plausible by early-
mid afternoon. Arrival of a higher magnitude theta-e plume attendant
to the inbound shortwave now over Iowa sets the stage for a steady
increase in rain potential from west to east between 20z and 00z late
today. High likelihood of rain exists through tonight as forced
ascent peaks with the passage of the surface reflection and cold
frontal boundary. Potential for some embedded thunderstorms given
quality of the moisture advection to diminish overall stability.

Frontal zone eases into the Ohio valley Monday, as high pressure
builds into the northern great lakes. This yields a cooler, yet
still moist low level northerly flow to begin the work week. This
maintains a high coverage of stratus, with a few spotty light
showers plausible particularly across the thumb with an added
moisture flux contribution off lake Huron. Resident thermal profile
suggests highs edged on the cooler side of average - upper 60s/lower
70s.

Attention midweek turns to behavior of a closed upper low currently
drifting across the four corners region and a trailing northern
stream wave/trough of north pacific origin. General consensus across
the collective ensemble guidance shows the lead height fall center
ejecting east-northeast with time, arriving locally Tuesday. Period
of meaningful isentropic ascent along the existing elevated frontal
zone offers an initial window for light rainfall production Monday
night into early Tuesday. Highest probability exists Tuesday
afternoon thru Tuesday night under strengthening convergence and cva
as the surface low and warm front arrive coincident with the
greatest height falls. NBM projected precip chances may ultimately
prove too conservative given the environment, but worth noting a
smaller subset of the ensemble suite, particularly within the GEFS
and GEPS, deflect some of the higher quality moisture and forcing to
the south. Potential for unsettled conditions to persist into
Wednesday as higher amplitude troughing takes residence and looks to
capitalize on continued moist low level conditions. Greater signal
for drier conditions to take hold starting Thursday, as the large
scale pattern again becomes high amplitude and blocked. This pattern
projects a stretch of dry and pleasant conditions Friday into next
weekend.

MARINE...

A strengthening inversion has and will continue to maintain some
areas of fog across portions of Lake Huron through this morning,
with improving visibilities expected by late this morning.

Otherwise, an approaching low pressure system which will travel east
across the northern Ohio River Valley into Lake Erie and Ontario
today which will allow a cold front to push across the Great Lakes
later tonight. Widespread showers with some embedded thunderstorms
are expected with the passage of low pressure and the front. Wind
direction will veer from the SSE to NNW/NNW in the wake of the
front, where wind gusts increase slightly to around 20 knots. These
slightly elevated wind gusts will persist through the day tomorrow.
A second low pressure system will target southern Michigan Tuesday
into Wednesday, bringing another round of showers and some elevated
winds.

HYDROLOGY...

Showers with embedded thunderstorms are expected along a cold front
from late this afternoon through tonight. Average rainfall will
range from a half inch to three quarters of an inch. Given PWATs
greater than 1.50 inches, locally higher amounts to 1.00 inch or
greater will be possible. No significant flooding is expected.

&&

.DTX WATCHES/WARNINGS/ADVISORIES...
MI...None.
Lake Huron...Dense Fog Advisory until 10 AM EDT this morning for LHZ361>363.

Lake St Clair...None.
Michigan waters of Lake Erie...None.
&&

$$

AVIATION.....KGK
DISCUSSION...MR
MARINE.......AM
HYDROLOGY....MR


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