996
FXUS63 KDTX 031953
AFDDTX

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
353 PM EDT Wed Jul 3 2024

.KEY MESSAGES...

- A stray shower or rumble of thunder remain possible toward the
  Canadian and Ohio borders as a weak cold front exits eastward by
  this evening.

- Today`s front ushers in a typical summer air mass for the July 4th
  holiday. Partly sunny sky helps lift temperature to highs in the
  mid to upper 80s with moderate humidity.

- Showers and thunderstorms spread back across Lower MI Friday as the
  next low pressure system sets up in the Midwest.

&&

.DISCUSSION...

Observational trends continue to frame a rather benign passage of
the cold front through SE MI during late afternoon. Surface analyses
indicate a mostly diffuse pressure trough with minimal contrast in
air mass across the boundary helping explain the lack of shower
coverage so far today. Better mid and upper level forcing is also
reflected in greater shower/storm coverage in radar composite now
well to the north and east across Ontario and Quebec. There is some
extra instability being created between mid and high cloud breaks
which hourly mesoanalysis hints may help surface based CAPE approach
1000 J/kg in a narrow corridor toward the Canadian/Ohio border. It`s
therefore prudent to keep the forecast open to a stray shower or
rumble of thunder until the front exits the area toward 00Z this
evening.

The front stalls across the Ohio valley tonight and is followed by
equally diffuse high pressure late tonight and Thursday. The high
pressure weakness raises doubts regarding cloud evolution, however
upstream satellite trends this afternoon do support a clearing trend
other than patchy cirrus. A fog signal is also absent from model
soundings despite surface dewpoint projected to remain above 60
during the night and Thursday morning. Other than a stray lake breeze
shower, the front holds far enough south for a dry July 4th around
the area while temperatures warm into a typical mid 80s range under
partly sunny sky.

The next low pressure system scheduled to affect the Great Lakes has
a respectable satellite presentation centered roughly over Montana
this afternoon. Consensus of regional/global models brings the mid
level circulation into the northern Plains Thursday and into the
Midwest by Friday morning. The associated surface low then connects
with the stalled Ohio valley front to set up a well organized warm
front and low to mid level moisture transport into Lower MI. Model
850-700 mb theta-e and lapse rate projections show a mature moisture
and instability axis centered over Lower MI by 12Z Friday which is
alone capable of numerous to widespread showers and scattered
thunderstorms but also boosted by seasonably strong mid and upper
level dynamic forcing. The mid level circulation is positively
tilted but still exhibiting more than adequate DCVA across the
central Great Lakes under a SW to NE oriented upper level jet max.
Good model consensus on a strong occlusion process sweeps the
rainfall pattern into and across SE MI from about late morning
through late afternoon followed by the mid level dry slot Friday
night.

Heading into the holiday weekend, today`s 12Z models are trending
toward a farther south position on moisture wrapping around the mid
level wave late Friday night while also shrinking the pattern from
south to north during Saturday. Model moisture/QPF fields support
entry level chance POPs in blended guidance both of which suggest
nuisance coverage of showers until early afternoon when the mid
level ridge between low pressure systems builds into the central
Great Lakes. This gives weak high pressure a chance to close out the
weekend with dry and warm weather Sunday.

&&

.MARINE...

A cold front continues crossing the central Great Lakes this
afternoon and evening with southwest wind around 10 to 20 knots
preceding it. Winds will weaken tonight post-front, remaining
predominantly southwest. Weak high pressure builds into the region
Thursday promoting benign marine weather with light winds. An
isolated pop-up shower or storm will be possible near the shoreline
in the afternoon. Otherwise, quiet weather continues Thursday night
before winds organize out of the east on Friday ahead of a low
pressure system moving in from the Midwest. Its warm front will lift
across the region during the day Friday, bringing scattered to
numerous showers with embedded thunderstorms. The cold front will
follow with winds veering around to southwest by Saturday morning at
around 10 to 20 knots.

&&

.PREV DISCUSSION...
Issued at 127 PM EDT Wed Jul 3 2024

AVIATION...

Frontal zone is noted on satellite extending SW-NE from KMGC to KMBS
at TAF issuance. Ceiling observations within the frontal band range
from MVFR to low VFR alongside isolated showers. Larger degree of
solar insolation compared to upstream observations favors the
optimistic VFR forecast locally until the front clears to our east by
00z. Decreasing cloud cover to follow overnight. Modest instability
will struggle to generate deep convection this afternoon with dry
subsident air working in aloft, so convective initiation will be
limited. Still, there is a low (~20%) chance for a pulse- type
thunderstorm to impact one of the Detroit terminal sites between
20z-00z. Southwest winds subside below 7 knots tonight with a 30-60
degree shift to the west-northwest post-front. Just some mid- high
cloud lingers for daytime Thursday along with light west- southwest
winds.

For DTW/D21 Convection...There is a low (~20%) chance of a pulse-
type thunderstorm to impact the airspace between 20z and 00z. Storm
motion will be to the east-northeast at around 30 knots.

DTW THRESHOLD PROBABILITIES...

* Moderate for intervals of 5000 foot or less ceilings before 00z.
  Low tonight and Thursday.

* Low for a pulse thunderstorm between 20z and 00z.


&&

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

$$

DISCUSSION...BT
MARINE.......TF
AVIATION.....MV


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