117
FXUS63 KDTX 181953
AFDDTX

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
353 PM EDT Tue Jun 18 2024

.KEY MESSAGES...

- Hot and humid conditions will persist across most of the area
through the week.

- Chances of thunderstorms will continue each day of the week. Some
of these storms may be strong to severe with locally heavy
downpours.

&&

.DISCUSSION...

Opaque mid cloud altostratus and haze associated with the shortwave
lifting into western Lower Michigan has been very effective in
dampening insolation through the noon hour. Have observed very
little boundary layer cumulus growth into the early afternoon hours
across Southeast Michigan. The real forecast challenge now heading
forward is what sort of low-midlevel convective inhibition will hold
on as forecast soundings were advertising the greatest projected
instability would exist at midday just prior to the deepest boundary
layer mixing. The most recent ACARS soundings do show a pronounced
stable layer residing in the 850-775mb layer that does match with
the forecast soundings (3.0 to 6.0 kft agl). Signal of the 18.12Z
CAMS was decidedly leaner with convective coverage over all of the
forecast area, although the MPAS runs and a couple of the WRF ARW
runs continue to show some development after 20Z. Small scale of the
modeled updrafts in the CAMS suggest a more muted UVV response and
for this reason the potential for strong to severe storms (if they
were to develop) is probably less than yesterday. Will leave PoPs in
the high chance category this afternoon given the convergence that
is expected to develop. Strong wind gusts from water loading/wet
downbursts are the main threat with heavy rainfall from any training
another possibility.

A ribbon of sheared absolute vorticity is expected to lift northward
along the periphery of the upper level ridging into the Great Lakes
region during the daytime Wednesday. Model data shows the strongest
shortwave center then impinging directly into the area during the
late afternoon. More transparency to the cloud and modest cooling in
the 850-700mb layer is expected to result in less low-mid CIN over
the area. Surface based CAPEs of over 1500 J/kg with 0-6 km bulk
shear increasing to 30 knots will support a strong to severe
thunderstorm threat. The current Day 2 for SPC has Southeast
Michigan in a General Thunderstorm Outlook.

A dynamic behavior and evolution of the upper level ridge is
expected this week with a pseudo rex block taking shape over the
eastern United States tonight and Wednesday before the centroid
retrogrades back to the Tennessee Valley by Saturday. Latest
indications are that ridging will hold just north of Southeast
Michigan with H5 heights of 592-596 dam. Projected 850mb
temperatures during this timeframe are expected to range between 18-
19C with high temperatures rising into the lower 90s. The
uncertainty for the week regarding heat indices is on two items. 1.
Favorable setup for inertial instability-and backdoor cold front
flipping flow northerly in the Thumb for Thursday. Current high
temperatures along the Lake Huron shoreline are in the 70s. 2.
Guidance and forecasted surface dewpoints running higher than what
has been verifying. The current gridded forecast has values
reaching/exceeding 70 degrees each of the days. The cumulative
effects of consecutive days of heat and humidity will cause stress
on vulnerable individuals and populations. The heat headlines will
remain in effect.

&&

.MARINE...

Southwest winds will maintain the hot and humid conditions into
tomorrow. A high degree of surface stability with the cooler waters
should keep wind speeds under 25 knots. The exception will be in and
near and strong thunderstorms which develop. Timing and location
will be highly uncertain, but the typical peak heating of the day
into early evening hours will be favored. A cold front is now
progged to move south Wednesday night, even faster than indicated
yesterday. This will allow for northerly winds over Lake Huron on
Thursday and Friday as seasonably strong high pressure tracks
through Ontario. Even so, airmass remains warm, which should help
limit wind speeds to around 15 knots. Thus, any wave build up with
the longer fetch is expected to remain below 4 feet. A stronger cold
front looks to be on track for the second half of the weekend
however, and wind speeds then could reach or exceed 25 knots with
waves building to around 4 feet. Small craft advisories may be
needed.

&&

.PREV DISCUSSION...
Issued at 153 PM EDT Tue Jun 18 2024

AVIATION...

Complex aviation setup today with current cloud cover and possible
thunderstorms this afternoon. Extensive cloud cover due to mid level
wave passing over lower MI this afternoon has prevented temperatures
from rising as rapidly as previously thought which in turn will
likely cause storms to be delayed. Storms have already initiated
over CLE and north of MBS, both of which had less cloud cover and
cu`ed up already. With lake breezes already forming, and the back
edge of the denser clouds exiting in a couple hours, will hold onto
thunderstorm chances for now in a 20-23Z window. Winds will
generally be out of the south/southwest around 12 knots with a few
gusts to near 20 possible. Strong gusty winds and microburst
potential exists with the deepest convective storms. Otherwise VFR
conditions should hold the rest of the evening and overnight.

For DTW/D21 Convection...Storms currently going up east and
southeast of DTW in the areas where skies have remained mostly
clear. Looks like clouds could thin on the backside of the passing
wave allowing temps to peak and storms to be possible. Lake breezes
are already forming which should help any storms to develop later.
Bumped the timing of the storms back an hour to account for the
increased clouds, so looking around 20-23Z for best chance.
Potential for wet microbursts should stronger storms develop
over/near D21 airspace.

DTW THRESHOLD PROBABILITIES...

* Low to Moderate for thunderstorms from 20 to 23Z.

* Moderate for ceiling at or below 5000 ft, conditional with
  thunderstorms.


&&

.DTX WATCHES/WARNINGS/ADVISORIES...
MI...Heat Advisory until 8 PM EDT Friday for MIZ047-053-060-068-075-082-
     083.

     Heat Advisory until 8 PM EDT Thursday for MIZ048-049-054-055-062-
     063.

     Excessive Heat Warning until 8 PM EDT Friday for MIZ061-069-070-076.

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

$$

DISCUSSION...CB
MARINE.......SF
AVIATION.....DRK


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