Area Forecast Discussion Issued by NWS Detroit/Pontiac, MI
000
FXUS63 KDTX 130904
AFDDTX
Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
504 AM EDT Wed Mar 13 2024
.KEY MESSAGES...
-Mild conditions continue today with above average highs mainly in
the 60s.
-Low-end rain chances exist this afternoon and overnight before
broader coverage of showers arrives Thursday.
-Thunderstorms are possible Thursday afternoon and early evening
while an isolated severe storm or two cannot be ruled out.
-Colder temperatures arrive Sunday and linger into early next week.
&&
.AVIATION...
A weak cold front on pace to ooze across the region today.
Maintenance of a dry and stable low level environment ensures VFR
conditions hold as this fropa occurs. Some pockets of high based
cloud will continue to mark conditions throughout the day, as winds
turn from southwest to northwest. Increasing mid level moisture atop
the elevated frontal zone will result in some lower of cloud base
tonight, but with expectation for ceiling height to remain at VFR.
Low chance for a few showers to develop overnight and Thursday
morning in this environment.
.DTW THRESHOLD PROBABILITIES...
* Low for ceiling heights at or below 5000 ft late tonight and
early Thursday.
&&
.PREV DISCUSSION...
Issued at 421 AM EDT Wed Mar 13 2024
DISCUSSION...
Enhanced southwesterly LLJ clipping far southern Lower Michigan
weakens after 12Z today before getting displaced by a drier (and
cooler) airmass bleeding south as a backdoor cold front within the
wake of a northern stream wave. Earlier nocturnal ThetaE advection
via Gulf-interfacing low-level trajectories appears limited, but a
lingering ribbon of marginally higher specific humidity stretches
longitudinally across southern Lower today. PWATs of 0.6-0.8 inches
only extend up to I-96/696, coinciding with a convergence boundary
that will serve as a focus for isolated to scattered afternoon
shower activity. 00Z model signals remain mixed in converting weak
ascent to actual rainfall within an otherwise subsaturated column.
This warrants the continuation of low-end (Slight Chance) PoPs for
the afternoon period near the dewpoint gradient while split-flow
arises in the lower troposphere atop zonal mid-upper level flow.
Overall, expectation is for more virga than shower activity.
Afternoon temperatures vary as the front oozes south flipping winds
northeasterly. This caps highs around 60F north of M-46 while
readings approach 70F across Metro Detroit.
The aforementioned boundary retreats northward late this evening
with renewed southwesterly LLJ tracking up the Mid-Mississippi
Valley which begins the northward migration of a potent warm front.
Aggressive uptick noted in the magnitude of moisture transport just
to the west while a more modest increase occurs over Lower Michigan
by midnight. This plume then moves in throughout the mid levels with
minimal adjustments in thermodynamic profiles while a shallow cold
air feed wraps in along easterly flow near the surface yielding
separation from the elevated dynamic ascent. Solutions indicate some
uniformity to a line of light showers developing overhead from 05-
10Z, orthogonal to the mean wind vector, but QPF is forecast to
remain rather light (if any).
A pronounced polar jet streak ejects across the Plains Thursday and
elongates into the Great Lakes region as the parent upper low
retrogrades further into the Desert Southwest. Left exit region of
the speed max lifts through the southern half of the Lower Peninsula
Thursday while 850 mb temps spike to near 10C, at least south of I-
69. Continuous ThetaE advection anticipated Thursday morning with an
initial burst of showers spilling in from the west. A fair amount of
model spread remains regarding the exact arrival time and spatial
coverage of showers during the morning timeframe. There will likely
be several waves of elevated light to moderate intensity showers
that generate overhead, anchored in cyclonically perturbed energetic
flow aloft. Main window for more organized thunderstorm potential
arrives Thursday afternoon, conditional on the vertical distribution
of instability. A plume of higher MUCAPE spills northeastward into
the CWA after 15Z with forecast soundings revealing the bulk of this
instability originates around the 900 mb level, just above the
capping inversion. Some potential exists for a transition to surface-
based instability during the late afternoon period which could lead
to marginally severe wind gusts should any organized linear
multicell convective activity arise. The surface low also tracks
across the area during this time when dewpoints peak offering a
brief window for strong 0-1 km shear. Cannot rule out a brief weak
spin-up tornado as flow backs INVOF the triple point before the warm
sector exits. Trailing shower activity will be brief Thursday night
as northerly flow spills in and the column stabilizes via isentropic
downglide.
Drier and colder environment in-place Friday with low-level
anticyclonic flow building out of the High Plains. Could see some
stratus linger throughout the day while 925 mb temps drop to around
0C. Northerly gradient wind draws even cooler air into The Thumb
region off Lake Huron where temperatures hold in the 40s while the
rest of the area attempts to break 50F. Clearing skies help send
overnight lows near the freezing mark Friday night. A positively
tilted longwave trough extends across the Upper Midwest over the
weekend and into Monday, buttressed by a Rex Block along the West
Coast. This maintains a much more seasonable airmass locally while
the compressed geopotential height center tracks along the northern
coast of Lake Superior. Main axis of CVA carves through the region
Saturday evening into Sunday with periodic chances for showers. Some
snow could mix in briefly, especially for the Tri-Cities and Thumb
regions Sunday as temperatures trend below climatological normals.
MARINE...
A weak, dry cold front will continue to pass through the Central
Great Lakes this morning, with modest northwest winds following for
Wednesday afternoon over Lake Huron. A series of low pressure
systems then look to be tracking through the southern Great
Lakes/northern Ohio Valley in the Thursday-Friday time frame. Rain
showers are expected across southern Lake Huron and locations south.
A period of moderate east-northeast winds (~25 knots) are also
expected to develop over central Lake Huron as high pressure
translates east through Ontario/Quebec during the same period. Waves
likely building at or above 4 feet across parts of the southern Lake
Huron Basin/Saginaw Bay by Friday.
&&
.DTX WATCHES/WARNINGS/ADVISORIES...
MI...None.
Lake Huron...None.
Lake St Clair...None.
Michigan waters of Lake Erie...None.
&&
$$
AVIATION.....MR
DISCUSSION...KGK
MARINE.......SF
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