Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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861
FXUS63 KDTX 161723
AFDDTX

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
123 PM EDT Wed Aug 16 2017

.AVIATION...

Quiet condition through the balance of the day today. The early day
mid-cloud field continues to advance northeast and will clear the
terminals sites in the first few hours. Additional diurnal cumulus
development should fill in the wake as surface heating maximizes.
Winds will remain light easterly through the afternoon and slowly
veer to southeast overnight as a warm front approaches toward
daybreak. Scattered thunderstorm activity is expected to accompany
the warm front.

For DTW...Scattered to broken clouds with bases around 5kft are
expected this afternoon. Low level moisture increases substantially
overnight through Thursday with ceilings below 5kft on an off
through the balance of the forecast. Two possible waves of
thunderstorms are anticipated - one in the 12-16z window and the
other during the mid-late afternoon on Thursday. South winds will
become gusty Thursday afternoon.

//DTW THRESHOLD PROBABILITIES...

* Medium for ceilings at or below 5000 ft.

* Medium for thunderstorms affecting the airspace Thursday morning
  and late afternoon.

&&

.PREV DISCUSSION...
Issued at 346 AM EDT Wed Aug 16 2017

DISCUSSION...

Good model consistency through the last few cycle leading to
increasing confidence in the going forecast. Quiet weather today as
amplifying shortwave ridge aloft and high pressure centered over the
eastern Great Lakes result in strong subsidence inversion around
750mb and dry easterly flow. Airmass will modify only slightly
keeping temperatures in the low 80s.

Much attention remains on the potent mid level wave lifting out of
the four corners region into the Central Plains this morning.
Surface cyclogenesis will result in a rapidly organizing low, which
is forecast to lift northeast through the western lakes Thursday
morning and through the northern lakes by Friday morning. The
associated warm front will lift north/northeast through lower MI
Thursday afternoon ushering in a very moist airmass with the aide of
deep layer southwesterly flow and an 850mb low level jet around 40
knots. All guidance is advertising PWATs of 2 inches in the warm
sector with surface dewpoints rising to 70F which will lead to
moderate to heavy rainfall. Precipitation could arrive anytime after
06Z for locations along the Ohio border as elevated portions of the
front advect into the region but better chances will come after 12Z
as the surface front starts lifting into the area. The tight theta e
gradient at the lead edge of the moisture plume will lift through
between 12-18Z. Second enhanced area of precipitation, ribbon of
forcing along the prefrontal trough ahead of the cold front, will
then slide west to east across the area around 21-00Z. The actual
cold front will follow overnight around 06Z. Expect showers and
thunderstorms throughout the day Thursday and most of the overnight.
Some storms will be strong to possibly severe as most models support
CAPE values around 500J/kg with bulk shear of 30-40mph. The shear
will be plenty to support organization. CAPE is marginal as its
suppressed by the dearth of moisture in the column, which also leads
to weak lapse rates. Any storms that do gain strength will primarily
produce heavy downpours with strong wind gusts also possible.

The low will linger not far to our northeast on Friday keeping SE MI
in the vicinity of the wrap around moisture and trailing trough.
Broad troughing aloft will also be lingering over the region as the
next wave in the line is already diving into it. Stronger low level
lapse rates and the trailing trough should be able to produce at
least scattered coverage of showers into the afternoon hour before
it pulls away.

This next wave will be tracking across lower MI on Saturday over top
the broad surface high expanding across the region in the wake of
the strong low exiting. Strength of the wave in the mid levels
continues to warrant a slight chance pop as we continue to monitor
it. The longwave trough will break down as this wave exits allowing
longwave ridge to build back across the central and eastern conus.
Expect mostly dry conditions Sunday through Monday night.

MARINE...

High pressure to the east of the Great Lakes today will support
light easterly winds. These winds will begin increasing late in the
day across the warmer waters of Saginaw Bay and Lake Erie. A
strengthening southeast gradient will then develop tonight into
Thursday with the approach of low pressure and an associated warm
front. Despite rather stable conditions across the lakes, the
gradient alone will support gusts over 20 knots at times on
Thursday, especially across Lake Huron. The approach and eventual
passage of the warm front late Thursday will support showers and
thunderstorms. The surface low and warm front will move east of the
region late Thursday night through Friday, causing winds to veer to
the southwest. The resulting cold air advection will boost
instability across the lakes, leading to continued gusty winds.
There is a chance that some hazardous small craft conditions will
develop. Winds and waves will decrease on Saturday as high pressure
nudges in from the west.

HYDROLOGY...

Deepening low pressure will lift into the northern Great Lakes on
Thursday. Moist and unstable air will be driven into the area in
advance of this sfc low and associated warm Thursday, triggering
showers and thunderstorms. Rain will persist into Thursday night
with the passage of the associated occluded front. The tropical
moisture that will be driven into the area will support some locally
heavy rainfall. Widespread rainfall totals of a half inch to an inch
are expected. Locally higher totals are possible in regions that
experience more persistent thunderstorms.

&&

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

$$

AVIATION.....Mann
DISCUSSION...DRK
MARINE.......SC
HYDROLOGY....SC


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