939
FXUS63 KDTX 132338
AFDDTX

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
738 PM EDT Mon May 13 2024

.KEY MESSAGES...

- Scattered to numerous showers and thunderstorms are expected
tonight. Severe weather is not expected, just some brief heavy
rainfall and lightning.

- There is a chance for additional showers on Tuesday. The higher
chances are near the Ohio border.

- Dry weather is expected Tuesday and Wednesday.

&&

.AVIATION...

Quasi-stationary frontal boundary has now settled between FNT and
MBS and has been the focus for convective activity around the
airspace over the last several hours, but without a direct hit to
any terminals thus far. There is just a low (10-20%) chance of a
thunderstorm impacting MBS/FNT through roughly 03z tonight. The
front will very slowly drift south overnight, with the most recent
guidance holding shower potential along and north of PTK. Much lower
confidence exists across the DTW corridor for shower potential
tonight given poor low level moisture quality. Highly variable
guidance for cloud trends exists by Tuesday morning, although the
general message is that there will be increased moisture pooling
invof the front that will be favorable for either fog or low stratus
development between about 07z-11z. Lowest cigs/vsbys are expected
near PTK as the front will be right overhead during this timeframe.
Will note that forecast confidence is low and 18z guidance has
trended drier, so outgoing TAFs represent a more middle of the road
cig/vsby forecast for Tuesday morning-early afternoon. Once daytime
mixing ramps up, ceilings/vsbys should lift to at least MVFR if not
VFR by afternoon.

For DTW/D21 Convection...thunderstorm activity has remained north of
the terminal and will continue to stay well north through the
evening, thus no thunderstorms are expected at the terminal.

DTW THRESHOLD PROBABILITIES...

* Medium confidence in cigs aob 5000 feet late tonight and Tuesday.

* Very low confidence in cigs/vsby aob 200 ft and/or 1/2sm 08z-15z
  Tuesday.

&&

.PREV DISCUSSION...
Issued at 320 PM EDT Mon May 13 2024

DISCUSSION...

The latest meso analysis shows SB Cape near 1k J/kg across the
Saginaw Valley/thumb south of a sfc cold front where dewpoints are
in the low to mid 50s and temps are near 80. Ongoing development of
deep convection supports latest CAMS solutions which indicate
convection persisting through the early evening across the north,
aided by the influx of instability arriving from SW Lower MI.
Despite the sfc front forecast to push south of metro Detroit late
tonight, the loss in diurnal instability will limit nighttime
coverage of convection as the front sinks south. This will warrant
the better convective chances this evening along/north of the I-69
corridor, with decreasing chances to the south. With 0-1KM mixed
layer CAPE still below 1k J/kg and limited deep layer shear (0-6km
bulk shear values around 20 knots), strong to severe storm are not
favored. The thumb region will be along the edge of stronger shear
profiles and could see a marginal severe risk if late day
instability overachieves a bit. Otherwise, warm and breezy
conditions will last into the evening amidst robust late day mixing
depths.

The upper low and associated sfc reflection now over Kansas/Missouri
will track across the northern Ohio Valley Tues/Tues night. This
system will drive a plume of deep layer moisture into Se Mi Tues.
Overall, the 12Z model suite suggest the stronger deformation
forcing will remain closer to mid level circulation, generally south
of the I-94 corridor. Lingering mid level frontal forcing, albeit
weak, will remain over Se Mi into Tues night, which will at least
support a chance of showers across most of the forecast area.
Shallow post frontal cool air undercutting the moisture may also
support some areas of drizzle Tues morning. The post frontal cold
air advection and cloud cover will result in a notable cooler day
Tues (highs in the 50s near Lake Huron to 60s elsewhere). Mid level
ridging in the wake of the upper low will lead to a gradual
departure of the deep layer moisture on Wednesday.

The next chance of rain will be Friday resulting from deep layer
moist isentropic ascent along a fast moving short wave. At this stage
in the forecast, instability looks to be weak (under 1k J/kg) which
should limit any severe weather risk.

MARINE...

Satellite imagery shows increasing cloud depths located across the
Tri-Cities into the northern Thumb, pushing northeast into the
Saginaw Bay to southern Lake Huron. This will be the focal point for
shower and thunderstorm activity through the remainder of the
afternoon and evening hours. The strongest thunderstorms will be
capable of producing wind gusts to or just above 35 knots and small
hail. Special Marine Warnings may be needed with any vigorous
thunderstorms development. Showers and thunderstorms are expected to
last through tonight along a stationary front, sagging slightly
south into southern Lake Huron overnight into Tuesday morning. High
pressure will build in across the upper Great Lakes which will end
rain and thunderstorm chances through Tuesday afternoon and evening
as a cold front clears the state. Wind direction will veer and hold
from the north-northeast Tuesday and Wednesday in response to a low
pressure system which will fill in across the Ohio Valley. This will
increase wave heights into the Saginaw Bay and Lake Huron
shorelines, where Small Craft Advisories will be likely.

HYDROLOGY...

Scattered to numerous showers and thunderstorms will occur this
evening, primarily along and north of the Interstate 69 corridor.
Locally intense rainfall rates are possible in some of these
thunderstorms. Rainfall amount of a quarter to half inch are
possible locally. Basin average rainfall is expected to remain below
a half inch, so flooding (other than localized ponding of water on
the roads) is not expected.

&&

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

$$

AVIATION.....MV
DISCUSSION...SC
MARINE.......AM
HYDROLOGY....SC


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