145
FXUS63 KDTX 040954
AFDDTX

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
554 AM EDT Thu Jul 4 2024

.KEY MESSAGES...

- Typical summer airmass in place today. Widely scattered light
showers tied to convection over the northern Ohio Valley look to
work into the area this afternoon and evening.

- Low pressure arrives Friday bringing more numerous showers and
scattered embedded thunderstorms for much of the day.

- Additional scattered nuisance showers possible Saturday afternoon
as an upper trough drifts over the central Great Lakes.

- Drier, sunnier conditions return to close out the weekend Sunday.

&&

.AVIATION...

Predominant VFR conditions this taf period as a drier low level
environment holds firm. Some thickening of higher based cloud occurs
within a broader region of mid level moisture transport north of a
weakening region of convection transiting the Ohio valley today.
Plausible this process offers an initiation point for widely
scattered convective activity this afternoon and evening,
particularly as peak daytime heating engages lake breeze activity.
Confidence in occurrence at any one location carries too low of
predictability at this stage to offer a more definitive mention.
Otherwise, modest wind field from s southerly component into the
afternoon, with some acknowledgement for a direction shift this
evening with inland lake breeze penetration.

For DTW/D21 Convection...widely scattered convection is possible in
the airspace after 19z.

DTW THRESHOLD PROBABILITIES...

* Low for thunderstorms Thursday between 19z and 00z.

&&

.PREV DISCUSSION...
Issued at 331 AM EDT Thu Jul 4 2024

DISCUSSION...

Despite the "cold" frontal passage last evening, overall environment
remains largely the same over SE MI with dewpoints still holding in
the 60s and 850mb temps in the mid-upper teens (C). While past model
trends prior days suggested the frontal boundary would push far
enough south over Ohio to keep associated activity likewise south,
latest trends, particularly within the CAMs, suggest a much muddier
picture. Shortwave wave feature is progged to ride along this
boundary over northern Ohio supporting a complex of showers/storms
to our south. The northern periphery of the stratiform component of
this complex looks to partially shed north into southern lower MI
early afternoon, after ~19Z, resulting in high-based widely
scattered coverage of a light shower-drizzle-virga mix.
Additionally, some signal exists for an isolated convective
development chance along the edge this stratiform `shield`, focused
over areas north of I-69, where lesser cloud cover supports the
generation of a few hundred J/kg of MLCAPE combined with potential
lake breeze interaction increasing low level convergence and upper
jet divergence residing directly overhead. Overall, its a messy
setup that carries inherit low predictability for any one area
actually seeing rain, though aforementioned trends can`t be ignored
so have introduced slight chance PoPs (15-20%) across the region for
the latter half of the day.

Low pressure rapidly develops over the Plains Thursday before
reaching the western Great Lakes early Friday. Surface circulation
draws the staled frontal boundary over the Ohio Valley back north
into southern MI Friday afternoon while also beginning to undergo
the occlusion process. Result is a complex frontal setup over SE MI
as both the warm/occluded fronts work into the region. Areas under
the warm sector- most likely along/south of I-69, will see the
return of lower 70 dewpoints as a ribbon of enhanced theta-e is
wrapped in from the mid-Mississippi. While this moisture axis would
support a respectable instability axis (between 1000-1500 J/kg of
MLCAPE), ample cloud cover likely prevents this from being fully
realized. Regardless, moisture-rich environment beneath seasonably
strong synoptic forcing, both from the mature low/mid-level trough
as well as left exit region jet divergence, should support scattered
to numerous showers with embedded scattered thunderstorms through
the afternoon-evening hours before the arrival of the mid-level dry
slot late evening/overnight.

Upper trough tracks over the central Great Lakes Saturday allowing
thermal troughing to settle into the region and drop 850mb temps to
around 10C. Cooling aloft in concert with favorable synoptic
difluent flow aloft looking to support the diurnal steepening of
lapse rates as well as potentially generate at least of few hundred
J/kg of mixed-layer instability. This offers chances for isolated to
scattered showers across SE MI for the afternoon-early evening
hours. Low amplitude mid-level ridging and accompanying weak surface
high pressure then briefly work across southern lower MI for Sunday
bringing drier, sunnier conditions.

MARINE...

Weak high pressure builds into the central Great Lakes through the
day with light westerly winds early becoming light and variable.
Overall benign weather prevails, but may see an isolated pop-up
shower near the nearshore waters in the afternoon or evening. Wind
then organizes out of the east by Friday morning as the next low
pressure system moves into the western Great Lakes. This system
sends a warm front through during the day Friday with scattered to
numerous showers with embedded thunderstorms. The cold front will
follow late on Friday with winds veering around to southwest by
Saturday morning at around 10 to 20 knots. Unsettled weather with
light showers remains possible on Saturday as troughing is slow to
depart.

HYDROLOGY...

Low pressure arrives over the Great Lakes Friday generating numerous
showers with scattered embedded thunderstorms for much of the
daylight hours. Gulf moisture is looking to be wrapped into this
system pushing precipitable water values near 2 inches. Basin wide
average rainfall totals between 0.25-0.5 inches are most favored
given the progressive nature of rain expected. However given the
moisture rich environment, locally higher amounts around 1 inch
would be possible under any thunderstorms. Minimal flooding
potential expected outside the usual low lying areas.

&&

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

$$

AVIATION.....MR
DISCUSSION...KDK
MARINE.......TF
HYDROLOGY....KDK


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