Expert Forecast Opinion

611
FXUS63 KDTX 171135
AFDDTX

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
735 AM EDT Wed Jul 17 2024

.KEY MESSAGES...

* An upper level disturbance crosses through Lower Michigan today
providing scattered showers and perhaps a rumble of thunder or
two.

* High pressure brings cooler, drier, and less humid conditions
to the region through the end of the workweek.

* Temperatures moderate over the weekend as high pressure departs,
followed by an approaching boundary Sunday which offers low-end
precipitation chances.

&&

.AVIATION...

Colder midlevel temperatures associated with a deep upper level
trough will lead to diurnal VFR overcast across Southeast Michigan
today. A secondary cold front swinging through the region will
result in isolated to scattered rain showers from north to south
this afternoon. Did include a 2 hour TEMPO for rain showers at the
northern taf sites this afternoon. Confidence remains low at the
Detroit sites and left the mention in as a Prob30. MVFR stratus is
expected in cold advection late tonight.

For DTW/D21 Convection...An upper level trough will bring a chance
for scattered showers this afternoon. Included a Prob30 group
between 22-01Z.

DTW THRESHOLD PROBABILITIES...

* Low in thunderstorms Wednesday afternoon.

&&

.PREV DISCUSSION...
Issued at 358 AM EDT Wed Jul 17 2024

DISCUSSION...

Observations sampling the post-frontal airmass show a slow
improvement in dewpoints this morning while gradient winds prepare
to reorganize out of the northwest. A positively tilted mid-upper
level longwave trough axis extending from southern Hudson Bay to the
Upper Mississippi Valley is expected to pivot across the Great Lakes
with time today. While weak and disorganized ascent may trigger some
very isolated morning shower activity, height falls become more
prominent across Southeast Michigan after 12Z as an arc of CVA
descends on the region triggering an increase in precipitating rain
showers. Primary limiting factor relates to the lack of substantive
ThetaE advection as dry air dominates the mid-levels complicating
saturation depths. Nevertheless, surface-H5 shear of 45+ knots
combined with SBCAPE values up to 300 J/kg should suffice in
scattered showers with perhaps a few late afternoon rumbles of
thunder. Consensus QPF offers medium confidence with peak coverage
during the midday hours, particularly across The Thumb and vicinity
areas.

Temperature-wise, the lagged elevated portion of the frontal zone
has further southeastward progress to cover before H8 temps drop
from the lower teens to upper single digits (C). This supports highs
in the lower 80s for Metro Detroit and down toward the MI/OH border
while readings will be a bit cooler, in the upper 70s across the
northern half of the forecast area. More pronounced differential
temperature advection eventually sweeps through Lower Michigan
overnight. Skies are expected to trend toward clear late tonight as
isentropic downglide steepens, augmenting cold advection processes.
This yields a cooler start to Thursday with overnight lows dipping
to sub-60F readings, the first dose of 50s since the start of the
month.

A massive synoptic ridge will encompass the entirety of western
CONUS, from the Pacific Coast to the Mississippi River Thursday
while a surface reflection of high pressure maximizes near 1025 mb
over MN/IA. Cooler Canadian air filters in across the region along
anticyclonic flow trajectories offering a mainly dry and
climatologically cool forecast. One caveat attributed to a weak
inverted trough/convergence axis situates along the central
waterways Thursday afternoon. This may provide just enough forcing
to allow a few sprinkles to develop along the eastern edge of The
Thumb. No precipitation mention was made in the NDFD depiction of
the outgoing forecast. Elsewhere, dry conditions prevail with a
gentle northerly breeze. Diurnal temperatures maximize in the mid
70s with lows well into the 50s Thursday night.

Drier pattern persists Friday and throughout much of the weekend as
Lower Michigan situates within a split-flow configuration. Higher
energy systems relegated to the opposite ends of the continent with
a stalled, yet broad upper low over Quebec and an approaching
Pacific low near The Cascades. Surface high eventually drifts into
the Ohio Valley Saturday lending a return-flow setup which leads to
temperatures moderating to near-normal through Sunday. Gradual daily
increases in dewpoints present slightly more humid conditions into
the start of next week as a cold front descends on southern Lower.
The boundary likely stalls/washes out, bisecting the CWA and
presenting the first opportunity for precipitation.

MARINE...

Cold front is now well to our east over central Lake Erie, leaving
the Great Lakes under light northwest flow. The trailing upper
trough axis maintains a low chance for shower or thunderstorm
development this afternoon. Will need to monitor late tonight-
Thursday morning as flow veers slightly more northerly, offering a
brief window for nearshore waves to approach 5 feet. Otherwise,
Canadian high pressure builds in for the rest of the week and this
weekend affording dry and benign marine conditions.

&&

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

$$

AVIATION.....CB
DISCUSSION...KGK
MARINE.......MV


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