443
FXUS63 KDTX 021931
AFDDTX

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
331 PM EDT Tue Jul 2 2024

.KEY MESSAGES...

- Chance of light showers tonight, mainly across the Saginaw Valley
  and Thumb region. An isolated non-severe thunderstorm is also
  possible early Wednesday morning.

- Warm and humid on Wednesday with a continued chance of showers and
  thunderstorms. An isolated strong to severe storm will be possible
  during the afternoon, capable of producing strong wind gusts and
  heavy downpours.

- Typical heat and humidity for the 4th of July holiday. Isolated
  showers and thunderstorms will be possible late in the day south of
  M-59.

&&

.DISCUSSION...

A mid-level trough and associated surface low moving from Manitoba
into northwestern Ontario will have increasing influence over local
conditions tonight into Wednesday. The system is currently directing
a shortwave and plume of 700-500mb moisture advection over west and
mid MI, producing pockets of light to moderate showers. The SW upper
jet will steer most of this moist flow north of the forecast area,
but trends in radar presentation and surface obs bring at least a
chance for a few late afternoon sprinkles mainly north of I-69.
Otherwise, we continue to be governed by dry SSE flow below 700mb
which should hold overall dry conditions through tonight. Another
shortwave follows a similar track into northern Lower MI overnight
into early Wednesday morning, bringing a renewed chance for showers
and an isolated elevated thunderstorm mainly for the Tri-Cities and
Thumb. Instability will be minimal and severe weather is not
anticipated.

Low pressure developing today along the trailing cold front over the
Midwest tracks northeast across northern Lower MI Wednesday morning,
sending a surge of higher low-level theta-e across the state to
start the day. Much warmer and muggier conditions will be in store
with HREF mean dew points rising to around 70 degrees. This will be
paired with highs in the mid to upper 80s. With mean flow parallel
to the SW-NE oriented cold front and neutral PV advection and height
fields providing little organized forcing, expectation is for just
widely scattered showers through the day as the front eases eastward
across the state.

A window emerges late in the day southeast of a line from Jackson to
Sandusky where daytime heating and resultant instability (MLCAPE
near 1000 J/kg) may be enough to induce better convective
development as the front moves through. Should this play out, a
conditional marginal severe threat exists as bulk 0-6km shear of 30
kt may support an isolated stronger cell with damaging wind gusts
and heavy downpours the most likely threats. There remains a sizable
camp of hi-res guidance that pushes the front through before
convection gains much traction, with 30 to 50% of 12z HREF
membership showing <500 J/kg of SBCAPE by 6pm. This faction of
solutions suggests little to no severe threat. The front then
departs to our south and east Wednesday night with slightly lower
dew points settling in and dry conditions likely thereafter.

Weak cool advection behind the front keeps a seasonably warm and
humid air mass around for the 4th of July holiday. Highs again will
be in the mid to upper 80s with dew points in the upper 60s and weak
winds keeping a muggy feel to the air. Model soundings show a
respectable cap in place much of the day, but weak height falls
associated with a low amplitude shortwave arriving during the
evening may be sufficient to allow for isolated convection late in
the day. Given the relatively warm mid-levels, any instability would
be lean and do not expect an organized severe threat at this time.

Friday presents a higher probability for showers and thunderstorms
as a higher amplitude upper low tracks in from the Midwest, bringing
a corridor of more focused height falls and associated ascent during
the latter half of the day. Blended guidance advertises a 60-70% PoP
peaking during the mid afternoon to early evening. Wind shear will
be favorable for organized severe weather with a 50 kt jet streak
passing overhead, but instability progs remain modest with only 15%
of LREF members showing >1000 J/kg SBCAPE. The most likely outcome
at this stage looks to be numerous showers with scattered
thunderstorms.

Slightly cooler weather for Saturday as the upper trough sinks
across the Great Lakes. At least scattered light shower activity
appears likely as moist cyclonic flow wraps around the low across
the state. Medium range progs show a strong ridge developing over
the SW CONUS this weekend and persisting into the early part of next
week. This favors a troughy, active summertime pattern over the
local area with periodic chances for showers and thunderstorms.

&&

.MARINE...

Return flow from the departing high pressure that is now centered
over New England has reinforced southeast flow over the Great Lakes,
which will hold through tomorrow morning. A weak surface low will
move across Lake Michigan later this evening, strengthening the
pressure gradient across the lakes which will support gusts on the
order of 20 to 25 knots across Lake Huron today. Rain showers with
possible embedded thunderstorms will continue mainly across Lake
Huron through tonight as low pressure approaches.

A cold front is then expected to move over the Great Lakes tomorrow
morning and afternoon which will veer wind direction to the west-
southwest. There will be a window between 4AM-4PM tomorrow where
gust potential will near 25 knots across the Saginaw Bay with the
southwest flow, but will preclude the issuance of a Small Craft
Advisory as model soundings exhibit a stable profile, lowering
confidence of 25 knot gust potential for any 3+ hour window. There
will be a low chance for a shower or storm along the front tomorrow.
Otherwise, high pressure fills back in Thursday, relaxing wind
speeds and gust potential.

&&

.PREV DISCUSSION...
Issued at 1258 PM EDT Tue Jul 2 2024

AVIATION...

Central Plains to Midwest low pressure draws warmer air with
elevated humidity into Lower MI tonight and Wednesday. The air mass
change is preceded by greater coverage of mid and high clouds this
afternoon while higher based showers are directed west and north of
the terminal corridor. The MBS area could be an exception, although
with just a sprinkle of light rain possible there through this
evening. Conditions are otherwise VFR above 5000 ft until the
trailing cold front moves in from the west during Wednesday.
Borderline MVFR/VFR stratus and light rain showers are likely in the
warm sector/moisture axis prior to the frontal passage. Thunderstorm
potential also returns but mainly during daytime peak instability
and as the front moves west to east across Lower MI Wednesday
afternoon.

For DTW/D21 Convection... Thunderstorms are not expected this
afternoon and tonight. Storm potential returns with the passage of a
cold front Wednesday afternoon.

DTW THRESHOLD PROBABILITIES...

* Low for ceiling 5000 ft or less in the morning, moderate Wednesday
  afternoon.

* Low for thunderstorms Wednesday afternoon.


&&

.DTX WATCHES/WARNINGS/ADVISORIES...
MI...None.
Lake Huron...None.
Lake St Clair...None.
Michigan waters of Lake Erie...None.
&&

$$

DISCUSSION...TF
MARINE.......AM
AVIATION.....BT


You can obtain your latest National Weather Service forecasts online
at www.weather.gov/detroit.