911
FXUS63 KDTX 231953
AFDDTX

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
353 PM EDT Mon Sep 23 2024

.KEY MESSAGES...

- Seasonable temperatures through the early and mid week period.

- Showers are likely Tuesday and Tuesday night, with a chance of non-
  severe thunderstorms.

- Most areas will receive around a half inch of rain or less, but
  localized totals in excess of 1 inch will be possible.

- Drier conditions through the rest of the week with temperatures
  trending back above normal.

&&

.DISCUSSION...

Relatively quiet conditions hold in place through the evening hours
as high pressure over Wisconsin slides across the northern Great
Lakes. Some breaks in the low stratus are occurring as the boundary
layer mixes into drier air aloft, but satellite imagery shows plenty
of additional mid-level and high clouds that will fill in from the
south through the evening. So cloudy conditions will prevail, with
mild temperatures in the 60s and lower 70s this afternoon settling
into the 50s and 60s through the evening.

Upstream MSLP analysis shows a surface low beginning to take shape
over Missouri in response to a mid-level wave tracking into the area
from the west. This wave will be kicked northeast tonight as a 100+
kt upper jet dives equatorward across the northern Plains. The
surface low will continue to deepen overnight into Tuesday morning
as it lifts toward lower MI, bringing with it a surge of deeper
moisture characterized by PWAT near 1.50 inches. The elevated warm
front will work in across the state line around midnight, continuing
north through the morning hours. This may bring spotty showers at
times during the early morning before more numerous showers fill in
by the mid-morning as saturation is achieved through the column. Off
and on showers will continue through the daytime and evening hours
with a chance of non-severe thunderstorms.

An item of interest will be the track/speed of the surface low and
the subsequent placement of the warm front by the evening hours. The
higher instability and attendant marginal severe threat will be held
south of this front, but there are several recent model runs that
carry the low a bit more quickly into SW lower MI by late afternoon.
This would place the warm front and localized larger low-level
hodographs in the vicinity of the I-94 and Metro Detroit corridor.
If the trend continues, will need to keep an eye on this area as
there would be potential for isolated strong or severe storms in the
evening along the front/triple point. The track of the low will also
have implications on any potential localized heavier rainfall axes
as there is signal for slow-moving/training storms with enhanced
deformation setting up just north of the surface low track during
the late evening. Most areas are likely to see a half inch or less
through the 24 to 36 hour period of showers, but if a heavier axis
does set up totals in excess of 1 inch will certainly be possible
along a localized swath.

The low reaches Lake Huron by Wednesday morning before getting
absorbed into a larger scale trough descending from Hudson Bay. This
trough, tied to the aforementioned jet, will send additional PV
energy over the region and may be enough to touch off isolated light
showers on Wednesday. Otherwise, seasonable temps hold with some
peeks of sun possible by late in the day. Dry northeast flow looks
to dominate the area through the late week as we sit north of a deep
cutoff upper low over MO/AR and within an induced blocking ridge.
The late Friday and Saturday periods carry a bit more uncertainty as
this upper low looks to slingshot a tropical system north into the
Ohio Valley before absorbing it. The northward extent of the
moisture transport will need to be monitored for future forecast
adjustments, but for now will continue to carry a chance for showers.

&&

.MARINE...

Will allow the small craft advisory to expire late this afternoon,
as wind speeds will be dropping just below 20 knots shortly, and
wind direction will trend more easterly tonight, and then southeast
Tuesday morning as an area of low pressure tracks through the
Central Great Lakes Tuesday and Tuesday night. Numerous showers with
a slight chance of thunderstorms will accompany the low. Large area
of high pressure building in Wednesday night-Thursday will lead to
light northwest winds, becoming northeast to end the work week as
the high moves off into Eastern Canada and low pressure lifts north
out of the Southeastern United States. The pressure gradient will be
tightest over Lake Erie, and gusts reaching at or above 25 knots
appear likely Friday-Saturday morning.

&&

.HYDROLOGY...

Low pressure brings scattered to numerous showers and a chance of
thunderstorms Tuesday and Tuesday night. Basin average rainfall is
forecast to be between one quarter and one half inch, but totals in
excess of 1 inch will be possible where any training storms develop.
Flooding is not likely but there is the potential if any heavier
rainfall axis does develop over the urban corridor.

&&

.PREV DISCUSSION...
Issued at 1253 PM EDT Mon Sep 23 2024

AVIATION...

Cool northerly low level wind supports a Lake Huron boosted plume of
borderline IFR/MVFR stratus and stratocu across SE Mi this
afternoon. Ceiling struggles into low end VFR during peak heating
while coverage becomes more broken as high pressure only grazes the
area this afternoon and this evening. It is displaced northward by MO
low pressure moving into the IL/IN area by Tuesday morning while
spreading another round of showers and a rumble of thunder along a
northward extending warm front. Low clouds and fog also solidify into
IFR within the frontal zone and along the track of the surface low
that is expected to move slowly across Lower Mi during the day.

For DTW/D21 Convection...A stray rumble of thunder remains possible
late tonight and Tuesday morning as the next low pressure system
arrives from the MO valley.

 DTW THRESHOLD PROBABILITIES...

* High for ceiling at or below 5000 feet this afternoon through
  Tuesday.

* Low for thunder after 11Z Tuesday.


&&

.DTX WATCHES/WARNINGS/ADVISORIES...
MI...None.
Lake Huron...Small Craft Advisory until 10 PM EDT this evening for LHZ421-
     441>443.

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

$$

DISCUSSION...TF
MARINE.......SF
HYDROLOGY....TF
AVIATION.....BT


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at www.weather.gov/detroit.