735
FXUS63 KDTX 101809 CCA
AFDDTX

Area Forecast Discussion...CORRECTED National Weather Service
Detroit/Pontiac MI 144 PM EDT Wed Jul 10 2024

.KEY MESSAGES...

- A Flood Watch and Flood Advisories remain in effect for much of
the  area from the I-94 corridor northward this afternoon and
evening as  the remnants of post-tropical storm Beryl produce heavy
rain across  the region.

- Rains diminishes tonight with just scattered showers and storms
possible during the late week.

- A period of above average temperatures is expected to begin this
weekend into early next week.

&&

.AVIATION...

Beryl remnants are continuing to track through the region today
bringing heavy rainfall. MVFR cigs are in place across the CWA, with
showers dropping cigs and visibilities to IFR conditions. Northerly
winds of 20 knots gusting to 30 also remain in place this afternoon.
Winds will back to become more northeasterly through the evening
hours and overnight and begin to drop off in strength as the low
pressure center moves out. MVFR ceilings are set to remain in place
overnight until sunrise tomorrow. Guidance remains muddled on the
post-storm environment tomorrow in terms of clouds. Models are split
as some show viability for a broken MVFR deck while others trend
instead towards a high cloud deck. Have included both in the TAFs
for now but expecting guidance to resolve the situation within the
next couple of cycles to provide a more coherent answer.

For DTW/D21 Convection... Lightning has not been observed in the
showers associated with this system, and it is expected to remain
that way through the evening. Strong cloud cover has significantly
limited instability available for storms to develop further.
However, a stray storm or rumble of thunder is still a possibility,
and trends will be monitored and updates will be provided if
anything more significant does materialize.

DTW THRESHOLD PROBABILITIES...

* Low for thunderstorms today and this evening.

* High for ceiling aob 5kft today and tonight.

&&

.PREV DISCUSSION...
Issued at 1113 AM EDT Wed Jul 10 2024

UPDATE...

Leading moisture transport ahead of Beryl surged south to north
across Lower MI during the early morning. Rainfall amounts since
midnight generally fell in the 1-2 inch range with a few higher
totals near 3 inches reported north of metro Detroit and south of
the Tri Cities. This was followed by a dry slot supported pause
around sunrise, especially from metro Detroit south to the Ohio
border, until the second phase of deformation forcing brought a new
band in from Indiana/SW Lower MI. The Flood Watch remains in effect
for the Tri Cities and northern Thumb, and Flood Advisories are
extended into this afternoon for the I69 corridor south to I94.
There is good model consensus on projections that pivot the
deformation band northward while producing another 1 to 2 inches of
rain on average with locally higher totals possible, mainly north of
I69 and east of I75. The afternoon peak in this phase starts a
diminishing trend as we head into the afternoon commute followed by
additional decrease this evening while exiting the Thumb into
Ontario.

PREV DISCUSSION... Issued at 351 AM EDT Wed Jul 10 2024

DISCUSSION...

Post tropical cyclone Beryl has now arrived over the Ohio River
Valley, and will bring extended periods of moderate to heavy
rainfall to SE MI through the day as the system progresses northeast
into southern Michigan and eventually Lake Erie and Lake Ontario.
MIMIC-TPW satellite imagery showcase PW values around 2", which is
in-line with model derived projected values around 2.10-2.20". These
near record values (99.5th percentile w.r.t climatology) are a
direct result of a massive amount of Gulf derived moisture that has
accompanied Beryl.

Ongoing rainfall is a result of this initial surplus of near record
moisture values along the nose of the downstream jet (now pinching
into the Metro region), coupled with increased low level
frontogenetic forcing that is aligning north of the low pressure
system, which at present is maximized from roughly southern Lake
Michigan to Alma. Additional difluent flow aloft along the nose of
an upper-level jet is also providing lift through the upper-reaches
of the atmosphere, directly over SE MI. From now through roughly 12Z
(8 AM), this frontogenetic forcing/deformation zone will start to
increase in strength in the lower levels and will pivot deeper into
SE MI, generally north of I-94 but south of Midland/Bay Counties.
This will bring rainfall rates on the order of .25"-.50" per hour
through the mid to late morning hours. Concurrently as the center of
this system starts to encroach into southern Michigan, a deep mid-
level dry slot will briefly pinch into the Metro region. This will
not outright end rain chances, but can act to decrease coverage and
intensity across the Metro region and possibly for locations north,
through the late morning hours. Several hundred joules of MUCAPE do
build in during this time frame, so some isolated thunderstorms are
not out of the question.

The dry slot will quickly pivot east out of Michigan during the
early afternoon as the system centers over Lake Erie, where wrap
around moisture will continue to interact with the strong
deformation zone, maintaining or reinvigorating the production of
moderate to heavy rain showers into the afternoon and early evening.
The deformation axis is expected to again hold over SE MI, along or
just north of I-94, to just south of Midland/Bay counties. The
deformation axis is expected to wane after 21Z (5 PM), but lingering
rain will hold in through the late evening, especially closer to the
Thumb, tied to the better moisture axis. All rain associated with
this system is expected to move out early Thursday morning.

Last, low-level modeled soundings show neutral to slightly unstable
profiles. Sporadic gusts of 25-35 mph will be possible today,
especially with any thunderstorm activity. Ensemble guidance shows a
few outliers of 40 mph gusts in a higher-end scenario.

Rainfall totals of 2-4" are expected across the greater portion of
SE MI, particularly where the aforementioned deformation axis sets
up and holds. ECMWF Shift of Tails, a measure of extremities
comparing of the ensemble QPF output from the top ten percent of M-
Climate, is showing extreme values over SE MI -- not a major
surprise with a post-tropical system directed over us, but it does
highlight SE MI (and SW MI) as the locations most susceptible to
higher-end precipitation totals for today. A Flood Watch remains in
effect for all counties outside of Monroe and Lenawee. An upgrade to
portions of the Flood Watch to a Flood Warning will be possible,
pending presentation of radar/satellite imagery combined with
monitoring of in-situ observations.

High pressure will fill in behind the system, but will maintain a
20% chance for an isolated shower as an upper-level trough swings
over the state tomorrow. Low end PoPs hold on Friday as well with
the trough axis clearing by Friday evening, before a shortwave ridge
builds in by Saturday. Temperatures return back into the mid-80s
through the weekend.

MARINE...

Remnants of Beryl continue to move into the region today and bring
heavy rainfall. Flow strengthens overnight as low pressure center
nears and brings a tighter pressure gradient overhead. Strong
onshore flow will develop as a result, with wind speeds of 20-25
knots over Lake Huron, gusting up to 30 knots. As a result, Small
Craft Advisories have been issued for the nearshore zones of Lake
Huron and the Michigan waters of Lake Erie. Lake Erie will see Small
Craft Criteria earlier than Lake Huron with more southeasterly flow
closer to the center of the low, and the advisory is in effect until
10 AM today. For Saginaw Bay to Port Huron, the advisory is in
effect starting 8 AM this morning.

The low pressure center will move over Southeast Michigan/Western
Lake Erie this afternoon, veering winds to the west over Lake Erie
while maintaining northeast flow over Lake Huron. This may
reinvigorate breezy conditions across Lake Erie and possible Lake
St. Clair. Strong winds are expected to die down Thursday with the
departure of the low. Winds will back to the northwest as high
pressure takes over.

HYDROLOGY...

A Flood Watch remains in for all of southeast Michigan through
tonight, except for Monroe and Lenawee counties.

Widespread moderate to heavy rainfall will continue through the
morning and afternoon hours. As the center of post-tropical storm
Beryl moves into Lake Erie this afternoon, the band of heaviest
precipitation is expected to pivot to a more southwest to northeast
orientation, aligning the heaviest rainfall potential north of I-94
but south of Midland/Bay counties and northern Thumb (Huron County).
All locations across SE MI will still be susceptible to periods of
intense rainfall, however, the longer staying power of this wider
band of rainfall brings increasing chances to see 2-4 inches of
total accumulation by early tomorrow morning. There is also a chance
for isolated to scattered thunderstorms during the late morning and
early afternoon, favored across the Metro region and south towards
the Ohio border, which can produce highly localized elevated
rainfall totals.

Flooding concerns are elevated through today, especially for small
streams, creeks, and flood prone locations. Flooding may also occur
in poor drainage and urban areas

&&

.DTX WATCHES/WARNINGS/ADVISORIES...
MI...Flood Watch until 8 PM EDT this evening for MIZ047>049-053>055-
    060>063-068>070-075-076.

     Beach Hazards Statement until 10 PM EDT this evening for MIZ049-
055-     063.

Lake Huron...Small Craft Advisory until 10 AM EDT Thursday for
LHZ421-422.

     Small Craft Advisory until 4 PM EDT Thursday for LHZ441>443.

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

$$

AVIATION.....BC
UPDATE.......BT
DISCUSSION...AM
MARINE.......BC
HYDROLOGY....AM


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