683
FXUS63 KDTX 212003
AFDDTX

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
403 PM EDT Sat Sep 21 2024

.KEY MESSAGES...

- Showers and thunderstorms tomorrow afternoon into tomorrow night.

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

&&

.DISCUSSION...

Quick passing ridge builds in behind this mornings front will result
in dry and stable conditions through the remainder of the day. Lack
of strong cold air advection with the quickly arriving thermal ridge
carrying 850mb temperatures to 15C and greater has allowed afternoon
high temperatures to climb back into the 80s. Mixing down of the dry
air aloft will also keep humidity in check. There is some potential
for fog development tonight, but expecting coverage of high clouds
to increase. This should limit the degree of fog that is able to
develop as overnight as temperatures cool. Will continue to leave
any fog mention out given the low probability, but the best chance
at seeing some fog will be from light southeast winds advecting
fog/moisture off the lakes.

Increasing clouds tonight are associated with strong southwest flow
extending from the desert southwest into Ontario and the base of the
central Canadian trough. This is improved moisture transport will
usher in PWATs greater than 1.50 inches by early Sunday afternoon,
which is the highest we have seen since late last month. This
moisture will be drawn northward ahead of an advancing cold front
tied to the central Canadian trough and surface low lifting into
northern Ontario/Hudson Bay. This will support widespread rainfall
spreading across Michigan tomorrow. Initial shower activity will
begin spreading into southeast Michigan during the afternoon, more
than likely after 2 pm. Timing of higher QPF amounts likely arrives
more towards the evening and through the first half of the night.
Average QPF amounts will average a half inch to three quarters of an
inch from Sunday afternoon through Monday morning. Stronger forcing
along the front and the larger scale ascent in the left exit region
of the upper jet will be capable of pushing some rainfall totals
towards 1.00 inch or greater. This is especially true for areas north
of I-69 across the northern Thumb and Tri-Cities. There will be a
slight chance of thunderstorms along the front, but should be more
isolated to scattered. The limited surface instability, weak mid-
level instability with MUCAPE of a few hundred j/kg and weak mid-
level lapse rates will limit the thunderstorm potential.

Frontal passage Monday morning will bring winds out of the northwest
that will also usher in a cooler airmass to the region. Much more
seasonable high temperatures around the low 70s are expected Monday
through Wednesday. Monday also appears to be mostly dry for a lot of
the area, though cannot rule out a few stray showers developing
within the north-northeast flow off Lake Huron. Tuesday holds the
higher likelihood of rainfall as a northern stream wave interacts
with the inbound shortwave trough originating from the Four Corners
region.

&&

.MARINE...

A ridge of high pressure will maintain dry weather and light winds
for the remainder of the day. Starting late tonight and into the
overnight hours, a subsidence inversion will strengthen and will
trap near surface moisture across portions of Lake Huron. The
development of marine fog to or under one mile will be possible
overnight (about a 50% chance of going under one mile), and will
continue to monitor observations for the possible issuance of a
marine dense fog advisory. Any fog development will clear out
through the morning hours, ahead of an approaching low pressure
system and cold front, which will bring widespread rain and embedded
thunderstorms across the region.

Precipitation will initially start across northern Lake Huron
tomorrow afternoon, with an expansion across the remaining Great
Lakes through the evening hours. Wind direction will back from south-
southeast to more northerly after the passage of the front, with
improved mixing depths bringing wind gusts up to 20 knots, late
tomorrow through Monday.

&&

.HYDROLOGY...

Showers with embedded thunderstorms are expected along a cold front
from Sunday afternoon into Monday morning. 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. This is especially true for areas north of
I-69 and associated with any embedded thunderstorms. No significant
flooding is expected.

&&

.PREV DISCUSSION...
Issued at 1234 PM EDT Sat Sep 21 2024

AVIATION...

Clear-mostly clear skies around the rest of the day with light west-
northwest flow. The surface moisture/higher dew pts will be
attempting to diminish as the boundary layer mixing depths increase.
This makes for a challenging forecast tonight with the fog
potential, as high clouds spilling over tonight also attempts to
mitigate fog potential as well. Confidence is low in avoiding fog
altogether, as there looks to be a light easterly trajectory setting
up late, which puts the moisture source of Lake Huron/Lake ST. Clair
into play. Ultimately, will carry just a MVFR visibility for now and
monitor the progress of the high clouds this evening. Increasing
southerly flow on Sunday, with gusts expected to top out around 20
knots.

For DTW/D21 Convection...No thunderstorms are expected through
Sunday morning.

 DTW THRESHOLD PROBABILITIES...

* None


&&

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

$$

DISCUSSION...AA
MARINE.......AM
HYDROLOGY....AA
AVIATION.....SF


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