989
FXUS63 KDTX 182008
AFDDTX

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
408 PM EDT Sat May 18 2024

.KEY MESSAGES...

- Patchy fog, locally dense at times, will be possible tonight.

- An Air Quality Advisory is in effect for portions of Southeast
  Michigan, including Metro Detroit through this evening.

- Warm and muggy conditions continue through early next week with
  daytime highs in the 80s.

- Chance for showers and thunderstorms tomorrow afternoon and
  evening favored toward the lakeshores. Locally heavy rainfall and
  strong thunderstorm winds will be possible.

&&

.DISCUSSION...

Lower clouds supported by lake moisture under the strong inversion
this morning has mixed out this afternoon bringing mostly clear
skies. Warm and muggy airmass in place today. The 12Z DTX RAOB came
in with 925mb temperatures in the mid teens (C). This is supporting
the temperatures into the 80s this afternoon. Daytime heating and
low level moisture has brought a scattered field cumulus, but high
pressure and ridging should largely limit any shower activity with
instability lacking and very weak forcing. Higher dewpoints,
southeast flow off Lake Erie, and mostly clear skies will bring
potential for patchy fog development again tonight.

An unstable airmass residing across Michigan tomorrow will set the
stage for scattered shower and thunderstorm potential. The RAP
offers 1000-1500 J/kg of MLCAPE developing by 18Z tomorrow across
much of southeast Michigan with increased mid level lapse rates of
6.5-7.0 C/km and low level lapse rates to around 9 C/km. A northern
stream shortwave will drive a weakening cold front into southeast
Michigan tomorrow. Shear over much of the area will be weak though
with best flow off to the north. Bulk shear from 0-6 km is mostly
below 20 knots with the exception across portions of the Tri-Cities
and Thumb. The northern stream shortwave will push a weakening cold
front into southeast Michigan during the late morning/early
afternoon while stronger surface heating will likely lead to the
development of multiple lake breezes during the afternoon. This
brings several opportunities for surface convergence to force
convection initiation, especially if the front tracks further into
southeast Michigan and meets up with any lake breeze. The weaker
flow leads to mainly a pulse type thunderstorm mode that form
initially on either of the aforementioned boundaries with
thunderstorm outflow also driving additional updrafts. Current Hi-
res model suite wants to place greater probability for initiation
across Port Huron to the Detroit Metro area and down to Monroe
County along the lake breezes. Though, some capping in the forecast
soundings could also put a damper on some thunderstorm development.
Will maintain the chance PoPs in the forecast here. Main threats
with activity will be strong downburst winds and brief heavy
rainfall with the PWATs of 1.25" to 1.35". Heavy rainfall and slow
storm motions bring some potential for localized flooding of prone
spots, especially in the urban footprint in and around Detroit for
any areas that experience a longer duration of thunderstorm
activity. Shower and thunderstorm activity will weaken and
eventually come to an end in the evening with the loss of
instability.

The next shortwave lifts out of the central plains and through the
southwest flow between the Canadian troughing and the ridging
through the Appalachian Mountains. A weak surface reflection is
forecast to travel across WI and northern Lake Michigan. A plume of
theta-e will support scattered showers and thunderstorms with a
boost in larger scale ascent from the shortwave. Greater forcing and
placement of the higher moisture axis puts higher PoPs towards the
Tri-Cities. Active stretch of weather remains as the above normal
temperatures and moist airmass remain over Michigan into the middle
of the week helping field additional showers and thunderstorms. Long
range models are mostly in agreement with a Tuesday night into
Wednesday system as shortwave energy originating off the Baja Coast
shoots northeast within the flow of the southern and northern stream
jets. Frontal timing will ultimately decide severe weather potential
mid-week. The well above normal temperatures with daytime highs in
the 80s will carry continue Sunday through Tuesday with overnight
lows in the upper 50s to mid 60s. Cooler temperatures will arrive
behind frontal system mid-week bringing highs back down into the 70
degree range for the late week period.

&&

.MARINE...

High pressure dominates local conditions this weekend with light
southeasterly winds generally 10 knots or below through the rest of
today, veering south tonight. Very warm and humid air in place keeps
areas of fog across marine areas, with potential for dense fog to
redevelop tonight. Will continue to monitor observations and reissue
a marine Dense Fog Advisory if/where conditions warrant. Models do
show a slightly stronger gradient picking up overnight which may
disperse any more dense fog before sunrise Sunday. A weak cold front
moves into the region on Sunday with a few showers and storms
possible, mainly in the nearshore waters. An area of low pressure
then tracks in from the Midwest late Monday into Tuesday, bringing
the next likelihood for showers and storms. Winds and waves are
expected to remain below Small Craft Advisory criteria outside of
any localized higher winds within any thunderstorms.

&&

.HYDROLOGY...

Scattered to numerous showers and thunderstorms are possible, mainly
tomorrow afternoon and evening with favored areas along the lake
breezes across Port Huron through Metro Detroit to Monroe County.
Locally intense rainfall rates are possible with any thunderstorms
that can develop with the high moisture environment. Forecast
average rainfall amounts are a quarter to half inch with locally
higher amounts of 1 inch or more possible. Several areas may remain
dry, but the slow moving nature of the scattered thunderstorms will
bring potential for these localized higher rainfall totals. Main
concern would be for localized flooding of prone urban areas across
the Detroit Metro if any of these thunderstorms develop and linger
over parts of the metro region.

&&

.PREV DISCUSSION...
Issued at 1251 PM EDT Sat May 18 2024

AVIATION...

Morning fog and LIFR/IFR low clouds have dissipated (outside of
DET), and looking at just a bit of diurnal CU development this
afternoon, mainly in the 5000-6000 foot level. The rest of the mid
levels look very dry, and not anticipating convective development.
Enough low level drying during the day and a subtle southerly wind
tonight to help limit fog potential compared to this morning.
However, leaning toward fog/moisture from Lake Erie to make inroads
into the southern TAFS late tonight, and have put tempo LIFR cigs in
for DTW/YIP/DET. A weak surface cold front should allow for light
winds to flip to southwest, helping to accelerate the mixing out of
the low clouds and fog with diurnal CU (around 5000 feet) likely in
the afternoon. Lake breeze convergence and instability will bring
the potential for scattered thunderstorms during the late afternoon.

For DTW/D21 Convection...Potential for FEW-SCT clouds flirting with
the 5000 foot level much of the period. Fog/LIFR low cloud concerns
late tonight as light southeast flow off Lake Erie exists.

Thunderstorms are not expected this afternoon, but there is a chance
of thunderstorms Sunday afternoon, with lake breezes serving as the
focus.

DTW THRESHOLD PROBABILITIES...

*  Low for ceilings aob 5kft.

*  Low for ceilings and visibilities to drop below 200ft or 1/2SM
   8-14Z Sunday.

*  Low for thunderstorms Sunday afternoon.


&&

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

$$

DISCUSSION...AA
MARINE.......TF
HYDROLOGY....AA
AVIATION.....SF


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