657
FXUS63 KDTX 190441
AFDDTX

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
1241 AM EDT Wed Jun 19 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.

&&

.AVIATION...

VFR ceilings and vsbys are expected tonight and into Wednesday.
Mid/high clouds will gradually fill in overnight, introducing some
uncertainty in regards to how thunderstorms chances will play out on
Wednesday. Thunderstorms remain possible, especially after 21Z on
Wednesday, with both individual storms and clusters of storms
possible. Winds will maintain a southerly component tonight,
becoming southwesterly by Wednesday morning. A backdoor cold front
begins to move in from the north late Wednesday night, with north to
northeast winds overspreading southeast Michigan.

For DTW/D21 Convection...Attention turns to Wednesday, mainly during
the afternoon and evening hours for our next chance for thunderstorm
activity. There will be a bit more deep layer wind shear to work
with tomorrow, so we may see both individual pulse-type
thunderstorms and clusters of storms move through the area. While
there are a few high-rest models that bring thunderstorms in during
the late morning hours, the best time period for convective activity
will take shape after 21Z. The potential for wet microbursts will be
a concern once again, should stronger storms develop over/near D21
airspace.

DTW THRESHOLD PROBABILITIES...

* Low to Moderate risk for thunderstorms Wednesday between 21Z and
  03Z.

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

&&

.PREV DISCUSSION...
Issued at 353 PM EDT Tue Jun 18 2024

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.

&&

.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.
&&

$$

AVIATION.....JA
DISCUSSION...CB
MARINE.......SF


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