397
FXUS63 KDTX 041809
AFDDTX

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
209 PM EDT Thu Jul 4 2024

.KEY MESSAGES...

- A stray shower or thunderstorm remains possible this afternoon and
evening, mainly north of I69 and toward the Ohio border.

- A Low pressure system in the Midwest brings a surge of showers and
thunderstorms across all of Lower Michigan Friday.

- The system lingers over the Great Lakes Saturday keeping a chance
of showers in the forecast.

- The holiday weekend closes out with dry weather Sunday under
partly sunny sky.

&&

.AVIATION...

Area of showers lifting into far southern Lower Michigan will need
to overcome an abundance of dry air in low-levels before rainfall
has any chance at reaching the surface. Forecast soundings continue
to advertise large dewpoint depressions below the 5 kft AGL level
which suggests an initial virga response. Overall convective picture
appears rather muted for this afternoon/evening, therefore only went
with a TEMPO for showers as lighting should be sparse in areal
coverage and frequency. Initial lake breezes are evident on radar
with limited inland penetration and a lack of parcel activation as
diurnal heating struggles beneath the cloud canopy. Upstream
observational trends, in conjunction with latest CAMs, favor column
moistening and subsequent rainfall lifting northeast by 20Z with
generally restriction-free ceilings and visibilities. Convective
trends will need to be monitored for any necessary amendments
related to updraft overachievement and potential isolated storm
development through the early evening hours once a vicinity trough
moves through the Lower Peninsula over the next several hours.
Conditional on evening rainfall/moistening and nearly SKC conditions,
some fog is possible early Friday morning, thus TEMPO-ed in a brief
MVFR mention. Dry start in-store Friday with increasing VFR clouds.

For DTW/D21 Convection...Showers and perhaps rumble of thunder
possible this afternoon and evening. Low confidence in thunderstorm
development from the current line of showers and with additional
activity from an inbound trough, therefore opted for a -SHRA
mention. Better chances for storms expected Friday afternoon/evening
with scattered activity. Did include a PROB30 for tomorrow.

DTW THRESHOLD PROBABILITIES...

* Low for thunderstorms today from 20-00Z, then medium for Friday
  from 22-00Z.

&&

.PREV DISCUSSION...
Issued at 1053 AM EDT Thu Jul 4 2024

UPDATE...

Mesoscale trends continue to be monitored for any update needs
related to showers and/or storms this afternoon and tonight. So far,
the slight chance/isolated POP in the going forecast is expected to
hold based on morning observational trends. High cloud debris moving
across Lower MI originates from the central Plains to Ohio valley
convective complex while the associated northern fringe of
stratiform rain remains south of the IN/OH border. The rain area
shows signs of diminishing with the nocturnal component of elevated
instability, but the parent MCV does maintain some organization and
will be capable of grinding out a light high based shower while
traversing Lower MI this afternoon. The mid level circulation also
has potential to interact with a larger scale surface trough/front
analyzed across the northern Great Lakes. This trough is projected
to settle into central Lower MI this afternoon while blending in
with some lake breeze augmentation. This is another favored area for
an isolated shower or thunderstorm, although inbound high clouds
will limit surface based instability through late afternoon and
early this evening.

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.....KGK
UPDATE.......BT
DISCUSSION...KDK
MARINE.......TF
HYDROLOGY....KDK


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