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228
FXUS63 KDTX 302315
AFDDTX

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
715 PM EDT Tue Apr 30 2024

.KEY MESSAGES...

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- Gusty southwest winds Wednesday.

- Well above normal temperatures remain through the week.

- Likely a dry frontal passage on Wednesday with the next chance
  of precipitation arriving early Friday morning.
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&&

.AVIATION...

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Clouds are rapidly dissipating across the Saginaw Valley and Thumb
regions - while elsewhere the residual limited diurnal cumulus are
also vanishing. The reduction in boundary layer mixing will also
temper winds quickly early this evening. A steady southerly flow
will emerge post-sunrise Wednesday and will mix to southwesterly
along and behind a warm front by noon with a notable increase in
gusts once again. Gusts are expected to approach 30kt at MBS with
more around 25kt for the Detroit terminals.

There will be some remnant mid-cloud Wednesday morning from the
ongoing convection upstream over Iowa. Additionally, the increase in
near surface moisture along the warm front will support a window of
high based (VFR) cumulus development during the midday.

For DTW/D21 Convection...Thunderstorms are not expected through the
TAF period. West-southwest gusts are expected to be around 25kts mid-
afternoon Wednesday. If gusts closer to 30kt are realized,
crosswinds may become a minor concern.

DTW THRESHOLD PROBABILITIES...

* Low for crosswinds late Wednesday afternoon.

* Low for ceilings at or below 5kft Wednesday midday.
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&&

.PREV DISCUSSION...
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Issued at 352 PM EDT Tue Apr 30 2024

DISCUSSION...

The dense stratocumulus cloud line this afternoon is generally west
to east along or just south of the M 46 corridor. There could be
some slight additional development along the southern edge, but
current observation trends suggest a persistence forecast throughout
the remainder of the afternoon for the majority of the area. Did try
to hand edit some temperature grids to account for temperatures that
are cooler under the opaque overcast. Favorable radiative cooling
conditions tonight and low dewpoint airmass will support lows down
into the 40s, a few colder spots in the outlying low drainage areas.

Strong synoptic support for ascent and a reasonably dynamic low
pressure system is forecasted to push across northern Wisconsin/U.P.
and Lake Superior early Wednesday. The main narrative will be dry
conditions for Southeast Michigan as a large amount of static
stability will hold between 3.0 and 12.0 kft agl. A notable
disconnect in moisture between the mid to low levels with surface
moisture will be well lagged and late in the day. From a sensible
weather perspective on the ground, warmer and more humid conditions
are expected during the afternoon. Surface dewpoints are expected to
rise from 40s early Wednesday to the middle 50s between 18-21Z. A
rare, dry warm advection/cold front system for Southeast Michigan

Longer wavelength ridging is forecasted to develop over the central
Great Lakes Thursday before amplifying over the eastern United
States on Friday. Strong static stability is expected to hold while
lowering on Thursday leading to very comfortable weather. The
exception will be areas adjacent to Lake Huron on Thursday with
highs in the 50s to lower 60s.

The next chance for precipitation will come Friday as a deamplifying
shortwave is forecasted to lift out of the Mississippi River Valley.
Large scale forcing for ascent will be well to the northwest of
Lower Michigan with the forecast area solidly in anticyclonic flow
trajectories. There is some potential for elevated showers/rumble of
thunder late Thursday night with nocturnal moisture transport/LLJ
forcing but higher chance should reside north of Saginaw Bay. Model
consensus brings the best potential along and ahead of the surface
cold Front Friday afternoon. Surface temperatures are forecasted to
warm in the upper 70s with surface dewpoints making a run at 60
degrees. From this vantage point, quality of lower tropospheric
moisture is expected to remain compromised as background large scale
forcing favors ridging which will try to perpetuate a veered wind
profile. Model differences to exist and some adjustment to
forecasted thunderstorm expectations are still anticipated.

Differential cold/dry air advection with rising geopotential heights
will result in building high pressure for next weekend. Comfortable
conditions are expected with conditions some 10 degrees above normal.

MARINE...

Surface ridge in place this evening will provide light and variable
winds tonight before south-southwest winds increase tomorrow, ahead
of the next low pressure system which will track through Lake
Superior.

Wind gusts Wednesday afternoon do look to reach 20-25 knots over the
nearshore waters, especially over Saginaw Bay and along the
shoreline areas. However, banking on the warm air (925 mb temps up
to 17 C) ahead of the cold front to provide just enough stability to
keep gusts under 25 knots (outside of perhaps a brief stray one).
Winds veering to the west over Saginaw Bay by early evening will
also help to keep wind speeds in check, vs the more favorable
southwest wind.

Steady stream of cold advection behind the front Wednesday night
into Thursday, and outside of the north half of Lake Huron,
expecting wind speeds look to remain light, under 20 knots. Even
over northern Lake Huron, wind speeds look to peak at 25 knots to
perhaps up to 30 knots, centered around midnight per local
probabilistic guidance.

A return to light and variable winds for Thursday as surface high
builds over Lake Huron.
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&&

.DTX WATCHES/WARNINGS/ADVISORIES...
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MI...None.
Lake Huron...Small Craft Advisory from noon to 8 PM EDT Wednesday for LHZ421-422-
     441.

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

$$

AVIATION.....Mann
DISCUSSION...CB
MARINE.......SF


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at www.weather.gov/detroit.