Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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FXUS63 KDTX 132252
AFDDTX

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
652 PM EDT Thu Jul 13 2017


.AVIATION...

Expect a brief window for diminished cloud coverage this evening,
before the high moisture content translates into an expanding low
stratus tonight. Even with it being mid July, extensive stratus
cover to the north per GOES-16 Visible imagery support this idea.
IFR cigs will even be possible late tonight into Friday morning,
particularly from PTK northward.

For DTW...Expect VFR conditions to trend to MVFR overnight as status
gradually expands south into lower Michigan. These conditions will
most likely persist into Friday, but slowly improve during the day.


//DTW THRESHOLD PROBABILITIES...

* High in ceilings below 5000 feet late tonight into Friday.

&&

.PREV DISCUSSION...
Issued at 315 PM EDT Thu Jul 13 2017

DISCUSSION...

Temperatures have been slow to warm today as low clouds have held
through early afternoon, but temperatures still have reached to
around 80/lower 80s across most locations through 2 PM.

18Z SPC mesoscale analysis indicated 2000 J/kg of MLCapes across the
mid section of the CWA, but surface low already moving over
southern Lake Huron, coupled with impinging 700 MB dry slot and warm
air (10 C at 700 MB), convection having tough time getting past cap
or updrafts getting quickly sheared off with the strong mid level
flow. Still have surface cold front approaching the I-69 corridor at
the present time to work, but flow out ahead of it is not backed
enough to get really good convergence. None-the-less still expecting
scattered shower/thunderstorm activity (supported by latest
RAP/HRRR/12z ARW) with an isolated severe cell still not out of the
question across southern Thumb region where instability looks
maximized. Any outflow boundary that is generated could also help the
covergence.

700-500 MB lows over Lake Superior tracking east over northern Lake
Huron Tomorrow, with positive tilted trough axis swinging through
southern Lower Michigan during the day. Mid levels very dry above 5
kft, thus looking at a dry day, except perhaps toward the northern
half of the CWA, where steeper low level lapse rates may be able to
generate enough cape for a few showers. EQL levels likely not
reaching much past 10 kft, and and will have no mention of thunder.
Weak low level cold advection during the day, with 850 mb temps
lowering into the 10 to 12 C Range, should be good for maxes of
75-80 degrees, with urban heat island of Detroit slightly warmer with
modest downsloping low level northwest flow.

Big subsidence inversion Friday night may be able to trap low
level moisture/clouds, see 12z NAM 925 mb RH, before ridging at all
levels arrives for Saturday morning, allowing for mostly sunny skies
and normal highs in the 80-85 degree range. It will also feel
noticeably drier, as dew pts lower toward 60 degrees.

The next chance for showers and thunderstorms looks to return on
Sunday as a shortwave trough and weak cold front drop southeast
through the region. With CAPE up to 1000 J/kg during the afternoon
and weak to moderate bulk shear, a conditional severe threat will
exist depending on the timing of the aforementioned forcing
features. Surface high pressure then builds into the region early
next week bringing a period of dry conditions through Tuesday. With
a thermal trough overhead, slightly cooler, pleasant conditions are
expected on Monday with highs in the upper 70s. Ridging then builds
into the region on Tuesday allowing a warming trend to commence on
Tuesday with highs returning to the mid 80s through the middle of
next week. Showers and thunderstorms will return midweek as a
frontal boundary slowly pushes south through the region.

MARINE...

Moderate northeast flow stretching from Saginaw Bay into northern
Lake Huron will ease tonight as low pressure to the south gradually
broadens while weakening.  This low lingers near the region through
Friday, maintaining generally modest northerly winds.  High pressure
will then expand across the region over the weekend, sustaining
relatively light winds.

There remains the potential for thunderstorms across all marine
areas through the evening period.

HYDROLOGY...

There remains the potential for shower and thunderstorm development
through the evening hours.   The combination of moist low level
conditions and slow moving cells will bring the possibility of
localized heavy rainfall resulting in some minor flooding.  Average
rainfall will remain below a quarter of an inch, but with isolated
amounts reaching in excess of one inch possible.  Drier weather
returns for Friday and Saturday, with limited potential for
rainfall.

&&

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

$$

AVIATION.....DG
DISCUSSION...SF/JD
MARINE.......MR
HYDROLOGY....MR


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