703
FXUS63 KDTX 040512
AFDDTX

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

.KEY MESSAGES...

- 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.

&&

.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 353 PM EDT Wed Jul 3 2024

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.

&&

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

$$

AVIATION.....MR
DISCUSSION...BT
MARINE.......TF

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