873
FXUS63 KDTX 190833
AFDDTX

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
433 AM EDT Wed Jun 19 2024

.KEY MESSAGES...

- Hot and humid conditions will persist across most of the area
today as a Heat Advisory is in-place for all of Southeast Michigan.

- Chances of thunderstorms continue each day of the week, some of
which may be strong to severe with locally heavy downpours and
isolated damaging wind gusts.

&&

.DISCUSSION...

Resident eastern CONUS ridge sampled by KLWX 19.00Z RAOB (Sterling,
VA) revealed a H5 geopotential height center of 597 dam. The
anticyclone is expected compress along the y-axis and broaden
significantly along the x-axis today in response to the slight
retrograde of a coastal California trough, a deepening progressive
longwave over central Canada and a developing tropical cyclone over
The Gulf. Early morning GOES vapor imagery highlights confluent
southwesterly flow aloft driving a cloud street up into Lower
Michigan, hampering nocturnal cooling. Deterministic H9 and H8 progs
suggest minimal thermal advection processes today as significant
level temps hover near 25C and 20C, respectively. Mixing capacity
lends highs only near 90F (a 3-5F downward revision), but given the
very warm starting point this morning (08Z readings in the mid 70s
to near 80F) and the summer solstice being only a day away,
insolation should sufficiently filter through the mid-high cloud
deck offering MaxTs in the low 90s (up to 93F for Detroit heat
island). As for heat indices, the slightly cooler shift with
dewpoints generally AOB 70F holds peak index values AOB 100F today.
Opted to downgrade the Excessive Heat Warning to a Heat Advisory
given the lower expected HIs and a shorter expected duration to the
cumulative high heat days.

Other controlling factor that could further cut high temperatures
(and max heat indices) is the potential for diurnal convection.
Consensus of CAMs, ensembles, and deterministic solutions suggest a
more robust thunderstorm response today. Instability pool build
across Southeast Michigan with HREF SBCAPEs in the 1250-1750 J/kg
range. The bulk of the activity should develop during the afternoon
timeframe with a mix of pulse storms and multicell clusters. Given
only 25 knots of surface to H5 shear, severe storms are unlikely,
but the threat of damaging wind gusts from isolated wet microbursts
exists. SPC`s SWODY1 did include most of the region in a Marginal
Risk.

Pattern unlock begins Thursday as a backdoor cold front washes
across Lake Huron providing cooler air with northeast flow. Did
shorten the Heat Advisory by a day for the northeast segment as heat
indices should remain well below criteria Thursday behind the FROPA.
The main question becomes, how far south(west) will the front get
before stalling out. Latest forecast foreshadows some potential
adjustments for the Tri-Cities and possibly further south.
Additionally, yet another shortwave feature moving along the
northern periphery of the ridge is expected to force more
showers/storms Thursday afternoon with a better defined baroclinic
zone. Some revisions to PoPs should be expected as the ridge adjusts
over the next 24 hours.

Thermal gradient stays entrenched across Southeast Michigan Friday
with northeast flow holding on over The Thumb  while the stalled
front retreats northward as a reinvigorated warm front. Familiar
dewpoints near 70F and southwest winds creep northeast with a return
to highs in the lower 90s for the roughly the southern half of the
forecast area. This scenario unfolds all while the ridge axis rolls
southeastward across Appalachia and into the Mid-Mississippi Valley.
By Saturday the system centers over The Southeast and could interact
with another ridge over The Southwest. While the NAM, GFS, and ECMWF
are in decent agreement with a more zonal upper level pattern and a
draw-down in heights, another warm advection push out of The Plains
could bring a more widespread return of heat/humidity. Note that a
lot of spread still exists, even amongst the different ensemble
groups. For reference, KDTW`s mean high temperature per the 19.00Z
GEFS is 87F while the EPS has a high of 94F. NBM/extended highs
currently reflect values more analogous to the latter ensemble.

&&

.MARINE...

Southwest winds will maintain the hot and humid condition today. 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 tonight. 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.

&&

.HYDROLOGY...

A moist and unstable airmass remains in place today. Isolated
showers and thunderstorms are possible south of I-96/696 this
morning followed by broader coverage (with a northward expansion)
this afternoon and evening. The most intense thunderstorms and
repeated rounds have the potential to produce rainfall amounts in
excess of an inch over a short period of time which could lead to
possible flooding for urban and low lying areas. Uncertainty in
specifics of location and exact timing for any flooding precludes
the issuance of an flood watches. Additional storms are possible
Thursday with low confidence in flood potential.

&&

.PREV DISCUSSION...
Issued at 1241 AM EDT Wed Jun 19 2024

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.


&&

.DTX WATCHES/WARNINGS/ADVISORIES...
MI...Heat Advisory until 10 PM EDT Thursday for MIZ047-053-060-061-
     068>070-075-076-082-083.

     Heat Advisory until 10 PM EDT this evening for MIZ048-049-054-055-
     062-063.

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

$$

DISCUSSION...KGK
MARINE.......SF
HYDROLOGY....KGK
AVIATION.....JA


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