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000
FXUS63 KDTX 210951
AFDDTX

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
551 AM EDT Sun Apr 21 2024

.KEY MESSAGES...

- Uncertainty exists in timing the clearing early today across
Southeast Michigan.

- Areas of frost are possible tonight. A Frost Advisory or Freeze
Warning may be needed for portions of Southeast Michigan.

- Warming trend continues Monday with dry and sunny conditions.

- Showers and possibly a thunderstorm arrive Tuesday with gustier
winds.

&&

.AVIATION...

The resident stratus deck based between 4000 and 5000 ft is
gradually clearing from northwest to southeast across Mid Michigan, a
trend expected to continue through the rest of the area this morning
as a subsident pattern takes hold. Timing of clearing still carries
a fair amount of uncertainty, especially with southeastward extent,
but latest data suggests the stratus should clear out of lower MI by
16Z. Prevailing VFR today with deep boundary layer mixing supporting
westerly wind gusting to 20 to 25 knots. FEW diurnal clouds around
6000 ft remain possible this afternoon before SKC becomes favored
this evening into tonight. Winds quickly taper off with the loss of
daytime heating and remain light and variable tonight.

DTW THRESHOLD PROBABILITIES...

* High in ceilings aob 5000 feet this morning. Low after 15Z.

&&

.PREV DISCUSSION...
Issued at 349 AM EDT Sun Apr 21 2024

DISCUSSION...

The heart of composite trough and lowered H85 geopotential heights
is located over Southeast Michigan this morning. The big uncertainty
for today is the exit timing of clouds as extensive 4.5 to 5.0 kft
agl stratus deck remains in place across all of the southern two
thirds of the Lower Peninsula. Models show midlevel differential
warm advection at the midlevels beginning in the 12-15Z timeframe
corresponding to a drop of saturation in the modeled RH fields. Flow
trajectories are decidedly anticyclonic today with a considerable
amount of warming shown in the sub inversion layer 3.5 - 6.0 kft agl
layer. Expectations still remain for sunshine during the afternoon,
but did raise sky cover percentage well into the mid to late morning
hours given the sluggish satellite trends. With insolation, boundary
layer mixing will result in west winds today of 15 to 25 mph.
Apparent temperatures should run some 15 degrees higher than
yesterday, resulting in a more pleasant day.

Building surface high pressure and Great Lakes mesohigh contribution
will lead to a backdooring of a weak, very shallow cold front
southward from the Thumb through Metro Detroit between 03-11Z
tonight. It is difficult to say exactly what this will do to the
temperature response as there should be a slight increase in mixing
and windspeed immediately behind the front. Regardless, surface high
pressure with clearing will lead to cold conditions tonight.
Guidance suggests a little bit of struggle to get into the lower 30s
in the urban heat island of Detroit, but confidence is high the
northern cwa will see some areas dip to 30 degrees or below. A Frost
Advisory or Freeze Warning may be issued later today for portions of
Southeast Michigan.

Models show a quick reemergence of southwesterly winds on Monday.
Deep high pressure center aloft is forecasted to pass through the
northern Ohio River Valley with pervasive anticyclonic flow across
Southeast Michigan. Plenty of early day sunshine with temperatures
climbing to around 60 degrees Monday.

Open trough with coherent upper level jet maximum is then forecasted
to release through Southeast Michigan on Tuesday. Abrupt increase in
moisture coinciding with lead edge of vorticity maximum will result
in widespread/categorical rain chances particularly Tuesday
afternoon. Model consensus has been strong in favor of a 6-9 hour
period in precipitation chances during the day Tuesday. The current
grids are way too broadbrushed and will need considerable
refinement. Forecast soundings point to a well defined frontal
inversion centered at 7-8 kft agl with very poor lapse rates from
the surface to approximately 700mb. A rumble of thunder will
certainly be possible with the projected UVV response and
conditionally unstable midlevels, however, any potential for strong
to severe storms appears to be extremely low. Cold air aloft will
then push down into Southeast Michigan Tuesday night. There will
again be PoP chances overnight as steepening lapse rates in the
lowest 7000 ft should result in some shower activity. This secondary
period for precipitation potential is likely stringing out the PoPs
for almost 24 hours. Again, there will be opportunities to refine the
PoPs.

Models support very stable conditions Wednesday, Thursday, and much
of the day Friday. Models show strong signal for deep subsidence
between 4.0 and 14.0 kft agl Wednesday then lowering to the surface
for Thursday. Very low RH conditions should be in place Thursday
afternoon. The next precipitation chances will come late in the day
Friday as warm air advection increases instantaneously as blocking
high retreats out of Southeast Michigan. Current indications suggest
a lagged response of warming and humidity at the surface, leading to
higher stability in the lowest 5000 ft Friday evening/Friday night.
Low confidence exists on Saturday as Southeast Michigan is progged
to be in the warm sector of central United States low pressure
system. The only problem here locally is that anticyclonic flow
trajectories will likely be favored through Saturday which casts
considerable doubt on track and timing of individual shortwaves.

MARINE...

Low pressure dropping southeast over far eastern Ontario draws a
cold front through the central Great Lakes late this afternoon-
evening. Result is a shift from westerly to northwesterly flow as
well as an uptick in strength particularly over the northern half of
Lake Huron as the gradient tightens. Gusts in this area expected to
reach 25-30kts this evening with 15-25kts more likely over the rest
of the region. A Small Craft Advisory is in effect for the Saginaw
Bay this late morning through the evening due to these stronger
winds. A broad region of high pressure stretching from northern
Ontario to the southern Plains briefly works over the area tonight
into the first half of Monday bringing a period of quieter marine
weather conditions. Active pattern then returns Tuesday as low
pressure ejects out of the northern Plains into the Great Lakes
bringing widespread showers, a chance for a few thunderstorms, and
stronger southwesterly winds.

&&

.DTX WATCHES/WARNINGS/ADVISORIES...
MI...None.
Lake Huron...Small Craft Advisory from 11 AM this morning to 10 PM EDT this
     evening for LHZ421-422.

Lake St Clair...None.
Michigan waters of Lake Erie...None.
&&

$$

AVIATION.....TF
DISCUSSION...CB
MARINE.......KDK


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