077
FXUS63 KDTX 221532
AFDDTX

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
1132 AM EDT Sat Jun 22 2024

.KEY MESSAGES...

- Flood watch this afternoon-tonight for Midland/Bay/Saginaw
  counties.

- Slight risk of severe thunderstorms this afternoon into tonight
  over much of southeast Michigan, with damaging winds being the main
  hazard, but isolated tornadoes also possible.

- Hot and humid today with high temperatures in the 90-95 range
  south of I-69 with heat indices peaking out just under 100 degrees
  this afternoon.

&&

.UPDATE...

Severe weather chances once again today, with SPC placing the area
north of Pontiac and Port Huron in a Slight Risk for severe weather
and outlining that all severe threats are possible. This area
includes Flint, the Thumb, and the Tri-City area. While there is
still a decent amount of uncertainty, the best chances for severe
storms looks to be between 2pm and 8pm today. Wind damage is the
greatest threat from this system, and DCAPE values range from 500-
1000 J/kg in the northern region where storms are expected. Values
over 1000 J/kg will be in place to the south, and could provide
greater potential for wind damage if either advected northward or a
storm develops in the southern part of the CWA. A main limiting
factor for this system will be CAPE. Values peak over 1000 J/kg of
SBCAPE in the thumb, but the available instability is very narrow
and will hug Saginaw Bay/Lake Huron. As such, initiation will be an
issue in this environment, and anything that does get going will
struggle to develop severe hail. Shear will be the key factor this
afternoon that will support any developing storms. 30 knot bulk
shear is expected across the northern part of the CWA, where chances
for severe storms to develop are the greatest. Hodograph lengths at
the 0-1km level are long, and the presence of low level shear means
that an isolated tornado cannot be ruled out. 0-1km shear starts at
around 20 knots in the Tri-Cities and Thumb, increasing this evening
to upwards of 30 knots. Further south, models agree that CAPE is
much lower, with much of the area not reaching 500 J/kg.

A Flood Watch is currently in effect for Bay, Midland, and Saginaw
counties from noon today through 6am tomorrow, which covers both the
severe event outlined above and the passage of the cold front
tonight. Flood watch is in place due to the potential for excessive
rainfall, and the Tri-Cities are currently under a Marginal Risk of
excessive rainfall from the WPC. Ensemble means give around a half
an inch with the exception of the GFS, which has sustained means
over an inch for the past few runs. Expected northward progression
of the stationary front this evening may keep some of the evening
showers originally expected to move over the Tri-Cities to the
north. Model progression has shown increasing tendencies to break
apart the line of storms along the front, leaving only scattered
showers over the CWA overnight. These two factors in combination
could reduce rainfall totals as far as 0.5-0.75" through both
events. HREF guidance tends to agree, giving a sharp precipitation
total gradient near that area between 0.5-1". Have kept some
slightly higher precipitation totals in the official forecast, as a
direct hit from a storm this afternoon could cause a significant
local increase in precipitation and produce much spatial
variability.

&&

.PREV DISCUSSION...
Issued at 715 AM EDT Sat Jun 22 2024

AVIATION...

Low clouds and fog are focused along a surface front stalled in the
MBS area early this morning. ImprovEment is seen there as the front
drifts northward and as a wave of low pressure moves in with showers
and thunderstorms that graze the area. Additional rounds of activity
are expected through the day mainly north of FNT, along the edge of
the cloud field during peak daytime instability. Farther south it is
VFR above 5000 ft under scattered to broken cumulus coverage and a
mix of high clouds where hot and humid air caps off thunderstorm
activity through the afternoon. Low pressure then moves farther
north into Lake Huron and Ontario while pulling a cold front through
Lower MI tonight. Showers and thunderstorms become focused in the
moisture axis ahead of the front and sweep through the region from
MBS by late evening to DTW late tonight. MVFR ceiling follows with
passage of the cold front also NW to SE early Sunday morning.

For DTW/D21 Convection... Showers and thunderstorms track north of
D21 this afternoon and this evening. A cold front then remains on
schedule to generate storms as it sweeps NW to SE across Lower MI
late tonight into Sunday morning.

DTW THRESHOLD PROBABILITIES...

* Moderate for thunderstorms late tonight and early Sunday.

PREV DISCUSSION...
Issued at 300 AM EDT Sat Jun 22 2024

DISCUSSION...

Jet forcing tracking through Central Lower Michigan yesterday
afternoon allowed for convection to keep re-firing and track across
the Tri-Cities region, resulting in localized rainfall amounts of 4+
inches. There remains potential training of storms today as the deep
moisture plume hangs around Saginaw Bay (PW values aoa 2 inches) area
and a surface wave then tracks through Central Lower Michigan this
evening. Expecting MLcapes to build to around 1500 J/kg , which will
lead to efficient rain producers, and easily could see 2-4 inches of
rainfall, with isolated higher totals not out the question. Now,
there is some uncertainty if the bulk of the storms will reside just
north of the Tri-Cities, but this set up is worthy of a flood watch
for this afternoon through tonight.

Still looks like locations south of M-59 will be capped during the
day as the mid level dry slot with 700 MB temps of 11 C tracks
through, persisting into the early evening hours. This should allow
the Detroit Metro area and points south to climb into the low to mid
90s with the favorable southwest flow, pushing heat indices to near
100 degrees.

Deep moisture plume coming out the Plains will track through the
rest of the CWA tonight. Significant differences amongst the models
with the strength and placement of the low over northern Lower
Michigan this evening/tonight, but there does appear to be a
consensus with a strengthening low pressure system as it moves
through northern Lake Huron/Georgian Bay. This is concerning, as low
wind shear, both 0-6 km and 0-1 KM will be ramping up with low level
jet in excess of 50 knots developing. Instability/capes may prove
sufficient with 1000-850 MB cape progged to reside in the 500-1000
J/kg range, per NAM. If storms arrive earlier in the evening,
organized severe storms with rotation are in play. SPC day 1 has
upgraded much of southeast Michigan into slight chance. Hopefully, as
the night wears on, the near surface layer will be just stable
enough to keep stronger winds and any rotation above the surface, or
instability could also end up being even more modest and we fail to
generate thunderstorms all together as line approaches the Detroit
Metro Area. Several solutions indicating the line dissipating, with
just some leftover scattered activity along the cold frontal passage
late tonight. However, preference will continue to skew the forecast
toward a broken or solid line of showers/thunderstorms (see RRFS A)
with the good large scale forcing/heights falls/PV advection for
summer standards.

Modest cold advection to follow for Sunday, with 850 MB temps
progged to lowering into the lower teens by Monday morning per 00z
Euro. None-the-less, the 500 MB trough axis swinging through the
Central Great Lakes may still touch off a few showers, mainly over
the Thumb region, as 500 MB cold pool (-15 C) tracks through Lake
Huron.

Warming back up early next week, as shortwave ridging arrives by
Tuesday morning, ahead of a strong northern stream upper level
wave/trough expected to sweep through on Wednesday, triggering storms
and leading to modest cool down for end of the work week.

MARINE...

Stalled front that has been hovering around southern MI the last
couple days will get pulled back north today generally across Mid MI
which should result in more shower and thunderstorm activity lifting
north today as well. This will also allow southwesterly winds to
spread back across the southern Lakes ushering in another hot
airmass keeping stable conditions across the waters. A stronger,
more organized low pressure system will then track east across
northern MI tonight which will pull a cold front through the region
on Sunday. Increased winds ahead of the front have been topping out
near 25 knots for a couple days now, and continue to do so but
stable conditions and possibly short duration may limit the need for
a small craft advisory but will continue to monitor.

HYDROLOGY...

Flood watch in effect for Midland/Bay/Saginaw this afternoon into
tonight. The potential exists for repeated rounds of showers and
thunderstorms. Total rainfall amounts of 2 to 4 inches possible with
locally higher amounts not out of the question. With yesterday`s
locally heavy rainfall, flooding would be likely if those totals
verify.

A line of showers and thunderstorms is then expected to spread east
into the rest of southeast Michigan this evening and tonight, and if
these storms hold together, rainfall amounts of half an inch to two
inches can be expected, which may cause minor urban/low lying
flooding. However, the activity may weaken significantly through the
night, and lower rainfall totals under half an inch are not out of
the question by the time the storms arrive over Detroit Metro Area.

&&

.DTX WATCHES/WARNINGS/ADVISORIES...
MI...Flood Watch through late tonight for MIZ047-048-053.

Lake Huron...Small Craft Advisory from midnight tonight to 10 AM EDT Sunday for
     LHZ421-422.

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

$$

UPDATE.......BC
AVIATION.....BT
DISCUSSION...SF
MARINE.......DRK
HYDROLOGY....SF


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