004
FXUS63 KDTX 100006
AFDDTX

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
806 PM EDT Tue Jul 9 2024

.KEY MESSAGES...

- A Flood Watch remains in effect for much of the area from the I-94
  corridor north from this evening through Wednesday as the remnants
  of TD Beryl bring widespread moderate to heavy rainfall to the
  region.

- Heaviest rainfall expected to fall after midnight into Wednesday
  morning.

- Rain bands pivot daytime Wednesday as the center of Beryl crosses
  into Ontario. Pivot axis is expected to be roughly a
  Lexington-Flint-Kalamazoo line which will lead to areas under/near
  this line likely seeing the highest storm total rainfall.

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

&&

.AVIATION...

The clusters of heavier showers have waned throughout the evening
with predominately VFR in place to start this TAF period. Widespread
rainfall will increase into tonight as the remnants of the tropical
system Beryl bring deteriorating conditions by early tomorrow
morning. Expect ceilings to fall down into MVFR and then to IFR
before sunrise with visibilities under areas of heavier rainfall
down to 2SM or less. Heavy rainfall will be the prevailing condition
with a chance for thunderstorms. Targeting a window for
thunderstorms comes with low predictability and will introduce TSRA
when observations give a more clear time frame. Northeast winds will
be gusting to 25-30 knots throughout tomorrow morning and part of
the afternoon as the main surface low arrives over Lake Erie by late
afternoon. Expect conditions to improve slightly during the afternoon
with lingering shower activity into the evening.

For DTW/D21 Convection... Remnants of tropical system Beryl will
dominate the conditions late tonight and tomorrow. There will be
chances for thunderstorms, but confidence in timing and duration is
low. Will adjust the forecast accordingly based on observations
throughout the night and tomorrow morning.

DTW THRESHOLD PROBABILITIES...

* Low for thunderstorms late tonight and tomorrow.

* High for cigs aob 5kft late tonight through tomorrow morning.

&&

.PREV DISCUSSION...
Issued at 325 PM EDT Tue Jul 9 2024

DISCUSSION...

Remnant diffuse frontal boundary that crossed the area overnight
becomes the focal point for the lead arm of deformation from post-
tropical cyclone Beryl this afternoon-evening. While initial
afternoon showers are confined to areas near the state line to
Detroit, this boundary is lifting north toward the M-59 corridor at
time of discussion. This region also coincided with the gradient
between stratocu/cirrus offering a modest differential heating setup
to support a diurnal flareup in (thunder)shower intensities. With PW
values ranging between 1.5-1.8" at this point, a quick accumulation
of an inch or so would be possible within this band. Said
enhancement wanes by ~01Z with the loss of diurnal heating. Broader
synoptic ascent, and associated rain, from Beryl then begins to
expand south to north over all of SE MI through early tonight. Main
surge of attendant tropical moisture arrives after midnight as
PWAT`s exceed 2" (which would be near/tying the daily climo max)
resulting moderate to heavy rain into Wednesday morning. This period
is expected to result in the window greatest accumulations where 1-
2" are possible, with some areas potentially approaching 3"
dependent on any embedded convection and overall storm speed.

By late Wednesday morning, Beryl`s center will reach the southern
Great Lakes resulting in a pivoting of dominant rain banding over
southern lower MI from more W-E to SW-NE. This carries the main
point of lingering uncertainty which is tied to the exact track the
center takes as this will directly influence the pivot axis and
subsequent axis of heaviest storm total rainfall. Based on morning
model suite, the most favored around for this pivot to occur over is
the I-69 corridor, roughly from Lexington-Flint-Kalamazoo line.
Locales under and along this line (within a county) have the
greatest chance to see near persistent rain, or least the fewest
potential breaks. To the south- Ohio border to Detroit, dry slotting
around the low center likely works in late morning-early afternoon;
which while not offering a full end to rain, will result in more
frequent breaks in between showers. This drying does support however
the generation of several hundred J/kg of MLCAPE which could be
sufficient for a few thunderstorms Wednesday afternoon. Ample
directional shear on the edge of low center, including near 20kts 0-
1km shear, makes this scenario something to monitor as we get
closer. Also worth noting that winds likely increase latter half of
the day Wednesday as Beryl`s center slides across the region into
southern Ontario. Gusts up to 25-30mph will be possible mainly north
of I-69, given current favored low track between Detroit-Toledo,
which could result in some power outages due to the wetter soils by
that time.

Low pushes east into Ontario by Wednesday evening though interaction
with a northern stream trough digging out of the Plains still looks
to slow Beryl`s departure speed. Expectation is for the NW/rear
flank deformation to linger over most of SE MI (north of roughly I-
94) through Wednesday night. Showers linger over the Thumb the
longest with shower activity not fully winding down until late
morning-early afternoon Thursday.

Overall between this afternoon and Thursday morning, 1 to 3 inches
still are possible across the region with the higher end of that
range most favored towards the Lexington-Flint-Kalamazoo line- these
locales also carry the greatest chance at higher amounts around or
in excess of 4 inches. Flood Watch remains in effect for all
counties, save for Monroe-Lenawee, 11PM tonight through 8PM
Wednesday.

Upper troughing settles over the central Great Lakes Thursday into
Friday keeping highs slightly below normal in the upper 70s to lower
80s. Hotter, humid weather returns by the start of next week as
upper flow turns more zonal allowing the airmass over the Plains to
squeeze eastward into southern MI.

MARINE...

Remnants of hurricane Beryl are bearing down on the region and are
set to produce heavy rainfall through Wednesday. Flow will
strengthen overnight tonight and veer to the northeast. As the low
pressure center tracks northeast into the Great Lakes, it is
expected to strengthen and create a tighter pressure gradient.
Therefore, strong onshore flow up to 25 knots has become a concern.
Gusts to 30 knots will have the ability to mix down as well. Small
Craft Advisories have been issued for all of the nearshore areas for
Lake Huron. Harbor Beach to Port Huron will see the longest duration
for criteria winds, and the advisory is in effect from 8AM Wednesday
through 4PM Thursday. Port Austin to Harbor Beach will have the
advisory from 2PM Wednesday through 4PM Thursday, and Saginaw Bay
will have the advisory run 2PM Wednesday through 10AM Thursday. The
center of the low is set to track over southeast Michigan Wednesday
and strong winds are expected to drop off on Thursday afternoon as
high pressure takes control.

HYDROLOGY...

A Flood Watch remains in for all of southeast Michigan, except for
Monroe and Lenawee counties, from this evening through Wednesday.

Remnants of Beryl work into the area this evening with rain
continuing through the day Wednesday. Band of showers has developed
in advance of said remnants near the I-94 corridor and is lifting
toward the M-59 corridor for this evening. These (thunder)showers
will be capable of a quick inch or so of accumulation.

Heaviest area-wide rainfall expected after midnight tonight into
Wednesday morning. 1 to 2 inches of accumulation is likely with more
localized ares around 3 inches. Center of Beryl is forecast to track
between Detroit-Toledo resulting in a pivot of the more west-east
orientated rain bands to southwest-northeast. Pivot axis looks to be
roughly a Lexington-Flint-Kalamazoo line resulting in these areas,
and areas near (within roughly a county) likely seeing the greatest
storm total accumulations.

Overall between Tuesday afternoon and Thursday morning, all of
southeastern Michigan is expected to receive between 1 to 3 inches
of rain. Higher totals, near or in excess of 4 inches most probable
near that aforementioned L-F-K line.

&&

.DTX WATCHES/WARNINGS/ADVISORIES...
MI...Flood Watch through Wednesday evening for MIZ047>049-053>055-
     060>063-068>070-075-076.

Lake Huron...Small Craft Advisory from 2 PM Wednesday to 10 AM EDT Thursday for
     LHZ421-422.

     Small Craft Advisory from 2 PM Wednesday to 4 PM EDT Thursday for
     LHZ441.

     Small Craft Advisory from 8 AM Wednesday to 4 PM EDT Thursday for
     LHZ442-443.

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

$$

AVIATION.....AA
DISCUSSION...KDK
MARINE.......BC
HYDROLOGY....KDK


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at www.weather.gov/detroit.