Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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FXUS63 KDTX 302255
AFDDTX

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
655 PM EDT TUE AUG 30 2016


.AVIATION...

Cold front will drop through terminals from north to south between
06z and 10z or so. A few shras or tsras will accompany the frontal
boundary and will include tempo/prob30 groups for a few hours during
the night to account for this expected activity. MVFR stratus with
minor fog will then settle into area in the wake of the front with
cigs then lifting and eventually scattering out Wednesday afternoon
with generally clear skies by the end of the forecast period as high
pressure begins to build into area.

For DTW...Fropa is expected around 09z, give or take an hour. Will
maintain prob30 group for tsras during this time frame. MVFR stratus
is then expected late tonight through Wednesday morning with NNW
flow behind front.

//DTW Threshold Probabilities...

* Moderate in ceilings below 5000 feet late night through Wednesday
  afternoon.

* Low in thunderstorms affecting terminal late tonight.

&&

.PREV DISCUSSION...
Issued at 348 PM EDT Tue AUG 30 2016

DISCUSSION...

Mid/upper level low pressure system working across northern Ontario
is sending a trough into the northwestern Great Lakes this afternoon
producing pop up showers and occasional thunderstorms. This system
will bring a weak cold front through the area later tonight with a
secondary trough settling southward early Wednesday. This secondary
trough will actually usher in the colder air with 850mb temps
falling from the mid/upper teens into the single digits with
northernly flow by Thursday morning. High temperatures will respond
by falling into the low 70s by Thursday which will be around 5
degrees below average for late August and early September.

Back to the convective potential for the remainder of today and
tonight. The nose of a deep mid level moisture plume lifted into SE
MI this morning with isolated to scattered showers popping up on the
lead edge within a lingering narrow band of negative showalter
values. With capping over most of the area the slightly cooler (1 or
2 degrees at 850mb per SPC mesoanalysis) this activity was short
lived and not widespread. As we progress through the afternoon,
surface based instability should increase for those locations not
socked in with cloud cover. In addition there is ML CAPE around 1000-
1500 J/kg over the northern CWA helping keep showers going there.
Activity remains fairly scattered/localized at the moment, but
expect slightly better coverage as we get into the peak diurnal
heating hours. With the abundance of moisture (dewpoints nearing 70,
strong theta e advection, and PWATs nearing 2 inches) and mid level
forcing, will keep a chance pop going through this evening.
Expectations are for mainly showers with some thunderstorms to
develop with main concern being heavy rainfall. Some gusts to 40 mph
may be possible but with a weak wind field, sub 20 knots through
500mb, even gusts within stronger cells will be limited.

The cold front will work through much of the area tonight from the
northwest. A narrow band of moisture convergence along it will aid
in shower/thunderstorm development through the overnight hours.
Though coverage currently along the front remains scattered, a
shearing axis of mid level vorticity and passage of the right
entrance region of the 250mb jet, should be enough support to keep a
chance pop going for the bulk of the area. With current radar
coverage showing a broken line convection along the front, find it
hard to target any one spot for likely pops.

The east to west orientation of the front will lead to a slow exit
to the south of the area Wednesday. Could see some lingering
precipitation over the Detroit Metro waning through the early
afternoon. The secondary trough axis will drop through the area
Wednesday evening bringing in the cooler air for Wednesday night.
The cool northerly flow over warm Lake Huron could result in some
lake induced light showers over the eastern Thumb. Will continue
the slight chance mention Wednesday night into Thursday.

High pressure will dominate the region on Friday and will continue
to sit over us throughout the weekend, bringing dry conditions and
plenty of sunshine. Temperatures will peak in the low to mid 70`s on
Friday and Saturday, before warming up into the lower 80s for a
daytime high on Sunday. The next chance for scattered showers and
thunderstorms will return on Monday through Wednesday, as a warm
front brings moist conditions to the area.

MARINE...

Fairly light southwest winds will turn to the northwest behind a
cold front over Northern Lake Huron this evening and then across the
remainder of the area overnight and early Wednesday. Speeds will not
initially be too strong, more in the 15 to 20 knot range over Lake
Huron late tonight and tomorrow, before a stronger surge of cold air
arrives Wednesday night and causes winds to increase. Small craft
advisories may be needed for the nearshore waters Wednesday night
and Thursday, particularly over Lake Huron as winds gust between 25
and 30 knots and the long fetch over the water allows wave heights
to build in excess of 4 feet. Winds will gradually decrease Thursday
night and become light by Friday as high pressure builds into the
area.

As the initial cold front drops through the Central Great Lakes, it
will continue to trigger scattered showers and thunderstorms in a
warm and humid airmass through tonight. Activity will linger over
Lake St Clair and Western Lake Erie Wednesday before the front drops
south and ushers in cooler and drier air.

&&

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

$$

AVIATION.....DG
DISCUSSION...DRK/AM/DE
MARINE.......HLO


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at www.weather.gov/detroit.



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