Harsens Island, Michigan Weather Forecast Discussion

142
FXUS63 KDTX 231603
AFDDTX
Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
1203 PM EDT Tue Sep 23 2025
.KEY MESSAGES...
- Potential exists for scattered to numerous showers and
thunderstorms to develop throughout the mid week period. Localized
heavy rainfall may be possible.
- Temperatures in the 70s through the remainder of the week, which
will generally be at to slightly above normal.
&&
.AVIATION...
Stubborn fog and LIFR cigs across the southern tafs finally
dissipating as daytime heating and approaching line of showers and
thunderstorms help with the boundary layer mixing process. This
first wave of storms tracks through this afternoon, but
scattered renewed activity/development is possible for rest of the
day into evening hours. With the high degree of low level moisture
around and weak surface convergence/boundary in place tonight,
should see another round of LIFR cigs/fog once again, and likely
more extensive, getting into the northern tafs as well.
Developing showers Wednesday morning should help improve
visibility`s/cigs, but likely only reaching into MVFR by noon
Wednesday.
For DTW/D21 Convection...Line of showers and thunderstorms
over south central Lower Michigan still holding together at the
present time and should arrive around or just after 18z. After this
activity clears around 20z, a continued low chance of showers and
thunderstorms into the evening hours exists.
DTW THRESHOLD PROBABILITIES...
* Meduim for cigs at or below 5,000 feet this afternoon. Low this
  evening, then becoming high tonight into Wednesday morning.
* Medium for cigs/vsby to 200ft and/or 1/2sm late tonight/early
  Wednesday morning.
* Medium for thunderstorms at start of the taf period, then low
  through this evening.
&&
.PREV DISCUSSION...
Issued at 346 AM EDT Tue Sep 23 2025
DISCUSSION...
The main influence on weather over the next few days will be a
thermodynamic environment that includes a moist troposphere below
8.0 kft agl and little to no stability in the column. In fact, model
soundings support unstable conditions continuing during the Tuesday
and Wednesday overnight periods with midlevel lapse rates steeper
than moist adiabatic. PWAT values are projected to hold at around
1.30 inches during the coming days. As a result, the primary concern
through Thursday will be the potential for heavy rainfall with
shower and thunderstorm activity and the possibility of flash
flooding.
For this morning, a lack of surface wind with moist near surface
conditions has led to fog development for the lower elevation areas
south of the Irish Hills. Some HRRR condensation pressure deficit
data suggests this will continue through daybreak or 13Z. Unsure and
uncertain how much fog will really develop or fill in over the urban
heat island but the potential does exist for some fog in Detroit.
Added areas of fog into the forecast and will monitor trends this
morning. If it becomes widespread could issue a Dense Fog Advisory.
Very subtle forcing mechanisms at play today with weak quasi
stationary baroclinic zone hanging out around Saginaw Bay and the
warm sector to the south. Models show closed upper low circulation
meandering very slowly/drifting southward from the U.P. and Lake
Superior likely only accentuating the boundary. A weak upper level
jetlet is shown to eject eastward along the southern periphery of
the closed low directly into Lower Michigan. Plan view of thetae
shows moisture ribbon/higher thetae content advecting into the area
timed with the jet streak. This is forecasted to slide across the
northern cwa invof the aforementioned baroclinic zone this
afternoon. So while precipitation/shower thunderstorm chances will
exist across all of the cwa, the most likely location for activity
is north of the M59 and I 69 corridors. Slow storm movement of west
to east brings the potential for heavy rainfall at any one
location. Difficult to really message rainfall amounts given the
convective setup, but the modeled interquartile ranges of QPF is not
outright concerning.
For tonight, a persistence in elevated instability brings the
potential for additional shower and thunderstorm activity tonight.
Stalled out activity and/or training along boundaries may result in
heavy rainfall.
One big model trend in the latest guidance is for an increase or
convergence in model solutions for vertical velocities late
Wednesday afternoon particularly across the south half of the cwa.
This is in response to upper level low pressure and prior MCV
remnants  phasing into and ejecting northward across the Ohio River
Valley. The trend has been to move timing of this low pressure up
prior to Wednesday night. Latest guidance including the NAM and EPS
membership suggest bulk of the frontogenesis and strong isentropic
lift associated with the near surface circulation will just miss the
area to the south and east. Control run of ECMWF still brings a
direct hit. Obviously, this is something that will need to be
monitored, possibly even a Flood Watch, as any northward jog could
bring heavy rainfall axis into the forecast area under a SHARS type
scenario.
Mainly dry conditions are possible for the end of the week and and
next weekend as models are suggesting midlevel and surface ridging
in place. Despite northwest flow, not seeing any signal for cold air
so above normal temperatures of upper 70s and near 80 degrees is a
real possibility. Humidity values are more uncertain and could be
running a little high in the latest forecast.
MARINE...
An upper level trough is draped over the Great Lakes and will linger
through mid week while slowly dropping southeast. Low pressure
system currently spinning over the northern lakes will help force a
stalled front southward today while additional weak wave may ripple
along the front. This will lead to an extended period of unsettled
weather with multiple rounds of showers with occasional embedded
thunderstorms. Pressure gradient is weak and winds aloft are also
weak so chances of any stronger winds or gusts with storms are
lower. Winds will become northeasterly today behind the front and
remain northeasterly through midweek.
&&
.DTX WATCHES/WARNINGS/ADVISORIES...
MI...None.
Lake Huron...None.
Lake St Clair...None.
Michigan waters of Lake Erie...None.
&&
$$
AVIATION.....SF
DISCUSSION...CB
MARINE.......DRK
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at www.weather.gov/detroit.

NWS DTX Office Area Forecast Discussion