220
FXUS63 KDTX 230358
AFDDTX

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
1158 PM EDT Sat Jun 22 2024

.KEY MESSAGES...

- Flood watch through tonight for Midland/Bay/Saginaw counties.

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

- Return to more seasonable conditions Sunday. A few widely scattered
  showers possible to finish the weekend.

&&

.AVIATION...

Complex of showers and thunderstorms will track across southeast
Michigan through the early morning hours. While a steady decline in
coverage of thunderstorms will occur with time as instability wanes,
radar trends warrant an inclusion to highlight the potential at all
locations. Trailing area of MVFR stratus with some lingering showers
to accompany the fropa mid-late morning. Enough instability may
exist to allow for an isolated thunderstorm, but coverage to limited
too highlight attm. Daytime heating leaves a broad lower VFR diurnal
cu field, with some widely scattered showers/thunderstorms for
Sunday afternoon. Pre-frontal winds from the south to southwest,
becoming northwesterly and turning modest gusty Sunday afternoon.

For DTW/D21 Convection...Main window for thunderstorm development
centered 07z-09z early Sunday morning. An isolated thunderstorm
possible mid-late morning Sunday with the cold frontal passage and
again with daytime heating late Sunday afternoon, but likelihood of
occurrence remains very low.

DTW THRESHOLD PROBABILITIES...

* Moderate for thunderstorms late tonight. Low Sunday.

* High for ceilings aob 5kft Sunday.

&&

.PREV DISCUSSION...
Issued at 932 PM EDT Sat Jun 22 2024

UPDATE...

Attention for the overnight period remains upstream, as convective
trends continue to evolve across southern Wisconsin with forced
ascent along an ESE propagating surface wave and frontal zone
engaging the existing deeper instability reservoir residing to the
west. East-southeast propagating linear convective cluster marking
the lead edge of this activity now translating across south-central
WI. Maintenance and possible upscale growth of this activity does
remain a possibility given projected trajectory of the governing
wave, but with a noted decrease in available instability evident
with eastward extent looming as a definitive deterrent in
prospective convective coverage/vigor. This remains evident within
the CAM solution space, with some members carrying some remnant
activity across most or all of SE MI while others extinguish
activity on arrival. Marginal Risk designation remains for the
overnight period to acknowledge an isolated risk of strong wind
gusts. Otherwise, heavy rainfall the focus with any activity that
arrives, noting the PW of 1.87 on the 00z DTX upper air sounding.
Ongoing radar trends suggest the Tri-cities remain best positioned
for episodic shower/embedded thunder production overnight, so plan
to hold tight with the flood watch with this update.

PREV DISCUSSION...
Issued at 342 PM EDT Sat Jun 22 2024

DISCUSSION...

Severe potential has yet to be realized so far today, but showers
and storms still on the way. Hi-res guidance now suggests that the
best chances for storms are this evening from 22-02Z. Limited
availability of instability continues to be a problem for updraft
development, and peak available SBCAPE reaches just over 1000 J/kg
in the Thumb. Wind damage is the main threat with this system, and
DCAPE values range from 500-1000 J/kg where rain is expected. Bulk
shear values of 30-40 knots are currently in place, so if an updraft
can develop, it is possible to see a severe storm develop still.
Severe hail looks unlikely, but given the combination of 0-1km shear
of 20 knots, LCL heights below 1000 mAGL, and long hodograph lengths
at the lower levels mean that an isolated tornado cannot be ruled
out. Further showers may develop along the stationary front beyond
02Z, which looks to impact Midland and Bay counties but will
dependent on how far north the front propagates. Frontal passage
brings chances for showers to the entire CWA, but there has been an
increasing signal for banding along the front to break apart after
sunset.

Flood watch remains in effect through 6am tomorrow for Midland, Bay,
and Saginaw counties. MRMS analysis has suggested that ~0.25" or
less has fallen so far over Midland and Bay counties. PWATs over 2
inches still suggest potential, and if isolated showers still
develop, localized downpours can still produce flooding. Ensemble
means suggest 0.5" of rain will fall in total, while the latest HREF
guidance suggests 0.75-1". Forecasted storm total QPF remains
between 1-1.5" in the flood watch due to the aforementioned isolated
shower potential and that these totals can occur in a short amount of
time. WPC has issued a Marginal Risk for excessive rainfall for this
area.

As the low pressure moves out early this morning, colder air
advection allows overnight temperatures to dip down into the low
60s. Trough axis passes overhead on Monday and weak ridge builds in
behind. Setup allows for warm, moist air to return to the region and
produce similar 90 over 70 temperature and dew points to toady`s
current conditions. Shortwave disturbance is set to move into the
region on Tuesday evening ahead of a larger trough on Wednesday.
Chances for showers and storms return with this system Wednesday,
and a cold front is set to track across the region. High pressure
and cool, dry air fills in behind the front and brings high
temperatures back down into the low to mid 80s on Thursday and
Friday. ThetaE gradient across the front is around 20 degrees K,
helping drop dew points down into the 50s. Zonal flow aloft keeps
calm conditions before the next system is set to move in over the
weekend.

MARINE...

A stalled front will linger across northern Lake Huron the rest of
today into tonight with a developing low pressure system over the
Midwest tracking along it tonight. This will keep a showers and
thunderstorms going across that area through that time as well. This
low will then pull a cold front through the region Sunday morning
into the afternoon with a secondary low possibly developing along it
Sunday afternoon which would track across southern Lake Huron.
Increased southwest winds ahead of the front will increase to around
25 knots later tonight thus a Small Craft Advisory has been issued.
Winds will become more northwesterly Monday behind the passing
system and possible secondary cold front early Monday morning. After
that high pressure will quickly build back into the region keeping
winds minimized to start the new week.

&&

.DTX WATCHES/WARNINGS/ADVISORIES...
MI...Flood Watch until 6 AM EDT Sunday for MIZ047-048-053.

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

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

$$

AVIATION.....MR
UPDATE.......MR
DISCUSSION...BC
MARINE.......DRK


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