Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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FXUS63 KDTX 221739
AFDDTX

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
139 PM EDT Tue May 22 2018

.AVIATION...

Plume of deep low level moisture will remain entrenched across the
southeast MI airspace through the latter half of the day as a broad
area of low pressure slowly transits the region. This will maintain
a high coverage of low stratus. Daytime heating will slowly lift
cloud bases with time, with recent observational trends suggesting
predominant IFR level restrictions for the afternoon period. Narrow
window this afternoon under modest instability for a few showers to
emerge, mainly PTK south into the Detroit corridor. Greater
thunderstorm potential will reside across northwest Ohio. Drier air
will slowly infiltrate the region this evening in the wake of the
exiting low. This will bring a gradual clearing trend early tonight.
This environment may support some degree of fog development
Wednesday morning, given residual moist near surface conditions
and a light wind field.

For DTW...Low stratus remains prevalent through the early evening
period. Slow improvement in cigs with time, but with bases holding
below 5000 ft. Greater TSRA potential expected to hold along/south
of the Ohio border through the afternoon, precluding any defined
mention at the terminal. Clearing skies early tonight, supporting
possible vsby restrictions in fog as winds remain light Wednesday
morning.

.DTW THRESHOLD PROBABILITIES...

* High for ceiling 5000 ft or less today.

* Very low in thunderstorms through late afternoon.

&&

.PREV DISCUSSION...
Issued at 1133 AM EDT Tue May 22 2018

UPDATE...

Minor adjustments to POPs through the afternoon to time the possible
showers and thunderstorms. Things are lining up pretty much as
expected so far. The circulation in the base of the upper level
trough can be seen now on satellite spinning over southern Lake MI
with the mid level jet max surging eastward just to the south.
Surface cold front now taking shape as the surface low drifts into
southern Ontario. RAP continues to advertise 500-1000 J/kg of MLCAPE
lifting north into extreme southern MI supported by most recent SPC
mesoanalysis. Visible satellite shows clouds thinning in the
developing dry slot/warm sector just ahead of the mid level trough.
This will add some destabilization to the low levels adding to low
level wind shear and moisture pooling. Most model soundings show a
CAP around 700mb which will try to suppress convection so will have
to see how fast we can warm up with thinning clouds and southerly
warm air advection. Best chance of storms remains south of M59, with
a slight chance farther north. Do not expect storms to be severe but
could see heavy rain as PWATS are around 1.25".

PREV DISCUSSION...
Issued at 315 AM EDT Tue May 22 2018

DISCUSSION...

Latest water vapor imagery shows upper level wave/circulation
tracking over northern Lake Michigan, with corresponding mid level
jet (500 MB) of 45 knots tracking through southeast Michigan around
noon. A pool of low level moisture seen coming out of northern
Indiana (see NAM 850-700 MB Theta-E/surface dew pts) looks like it
will be sufficient to generate at least scattered showers and
isolated thunderstorms as MLCapes reach and exceed 500 J/KG toward
the Ohio border (per local probabilistic guidance), as surface winds
flip around to light southwest and surface dew pts climb above 60
degrees south of M-59. The low levels (925 MB) look to remain fairly
saturated/low clouds, but with the surface boundary straddling the
heart of the cwa, and differences in wind direction, probably looking
at highs ranging from 65 (north) to 75 (south). If instability does
ramp up a little more than expected, there is concern for locally
heavy rain as inland inverted surface trough arches back and
hovers/persists this afternoon over central sections of the State, as
good push of dry air does not look to occur until/toward 00z.
However, preference is toward a more muted response such as 00z HIres
ARW/Rap.

Surface ridging building in tonight could set the stage for fog
development, but there is some uncertainty whether low clouds
are going to fully dissipate in a timely fashion.

A significant warmup will occur over the end of the work week, as
pronounced 500 MB upper level ridge over the Mississippi River
Valley slowly advances east, with the ridge axis arriving Friday
morning in a slightly flattened/weakened mode. None-the-less,
strengthening low level southwest winds will advect a lot of warmth
into Lower Michigan, and 850 mb temps of 16+ C will supports temps
well into the 80s on Friday, as frontal boundary looks to be
sufficiently north over the northern Great Lakes.

Height falls over the weekend as upper level low coming out of the
northern Rockies gradually slides into the Western Great Lakes. Bulk
of 12z Euro ensembles keep CWA within the warm sector on Saturday,
supporting temps still in the 80s with good chance of showers and
thunderstorms. Obviously, timing of any thunderstorm complex during
the mid day hours could easily short circuit temps.

MARINE...

Weak low pressure will track across southern Lower Michigan and Lake
Erie today, leading to generally light and variable winds across
Lakes St Clair and Erie. On Lake Huron, light east-northeast winds
will back to the north-northwest during the afternoon and evening as
the low advances into the eastern Great Lakes. High pressure will
expand into the region from the west tonight into Wednesday. This
high will reside over the region through Thursday, providing
generally light and variable winds.

&&

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

$$

AVIATION.....MR
UPDATE.......DRK
DISCUSSION...SF
MARINE.......SC

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at www.weather.gov/detroit.


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