Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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FXUS63 KDTX 232021
AFDDTX

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
321 PM EST Mon Jan 23 2017

.DISCUSSION...

Moist airmass in place, as 12z dtx sounding came in with a 4 C dew
pt at 850 MB, and 5 C at 925 MB. Inverted surface trough/moisture
axis drifting west through the day has been sufficient to generate
widespread light showers. South-North ribbon of moisture, PW values
near 0.75 inches, will attempt to hold on tonight before the
moisture axis quickly decays/falls apart as Mid Atlantic System
pushes off the Coast Tomorrow. Before this occurs, the weakening 700
mb circulation/low over West Virginia early this evening should
still be able to help generate additional light showers through much
of the night, or at the very least drizzle and fog. Airmass will
slowly cool as the column drys out, with 850 mb temps progged to
slip below 0 C on Tuesday. With low clouds expected to remain locked
in Tomorrow, don`t see maxes getting much past lower 40s.

Powerful West Coast trough tracking through the Rockies into Central
Plains for Mid Week. Fortunately, the deep low/cold pool (-32 to -34
C at 500 mb) off the Northern California coast looks to be slow to
round the bend and track through the four corners region Tuesday
Night/Wednesday, and thus the surface low tracking through the
Midwest into southern Lower Michigan does not look to be very strong
(993-994 mb). Warm frontal FGEN precipitation expected to be mostly
north of M-59 during Wednesday, with rather sharp temp gradient
setting up. There are plenty of thermal profile differences between
EURO/NAM/CANADIAN/GFS solutions, with average 925-850 mb temps
looking to range from -2 C north (Saginaw Bay) to +5 C south (right
near the Ohio Border). Even so, the colder 12z Euro indicating
surface temps remaining above freezing across the FAR north through
at least early Thursday evening, and expecting mainly a rain event.
The warmer NAM even generates decent instability with showalter
index dropping below zero, along with very steep mid level lapse
rates (8 C/KM), so would not rule out thunderstorms, but other
models are not as unstable. Colder air filtering in on the backside
of the low, as 850 mb temps fall into the -5 C to -6 C range by
Thursday morning, with the low level convergence/cyclonic flow
providing a good chance for snow showers by Thursday morning.

Active weather pattern will continue through the extended time
period as longwave troughing persists over the Great Lakes region.
The surface and upper level lows will be in the process of moving
eastward over Ontario on Thursday.  Not far behind will be more
shortwaves that come in and keep a chance for unsettled weather over
the area into the weekend.  Even cooler air will be allowed to
filter down bringing an end to the milder airmass that has been
around these past few days.  Above normal temps will fall back to
seasonable through the end of the week before dropping below
normal for the upcoming weekend.

&&

.MARINE...

The ongoing easterly winds should continue to diminish lingering
marine fog this evening. There will be a slow decrease in these
easterly winds during the course of the night as the gradient slowly
relaxes. Light southeasterly winds will then develop on Wednesday
morning as weak low pressure moves into the western Great Lakes. The
passage of the low across Lake Huron Wed evening will allow winds to
again become light and variable. Colder air will funnel into the
region late Wednesday night through Thursday under strengthening
northwesterly winds. Peak wind gusts should primarily remain under
30 knots.

&&

.PREV DISCUSSION...
Issued at 1203 PM EST Mon Jan 23 2017

AVIATION...

With the exception of MBS, there has been a marked improvement in
visibilities over the last six hours under slight sfc drying within
light northeast flow. The sfc temp/dewpoint spreads are still lower
than most guidance. This and given the observed cloud trends across
the region, IFR with some LIFR cigs should persist into the evening.
The forcing now contributing to the region of light rain across Se
Mi is expected to weaken a bit this afternoon, likely causing some
weakening in intensity and decrease in coverage. This will be before
some strengthening of the large scale forcing supports an increase
in rainfall coverage this evening. Slight low level cooling during
the evening with a weakening sfc gradient may again promote
redevelopment of fog and possible lowering of conditions back to
VLIFR.

For DTW... Generally light northeast winds will persist into the
evening while gradually weakening. Radar indications suggest the
rain will either end or diminish to drizzle over the next couple of
hours. Slight low level cooling this evening should result in cigs
lowering and fog redevelopment. There is a chance for some dense fog
redevelopment during the evening.

//DTW Threshold Probabilities...

* High for ceiling 5000 ft or less today through Tues afternoon.

* Low for ceiling below 200 feet/visibility below 1/2 sm during the
  evening and overnight.


&&

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

$$

DISCUSSION...SF/SS
MARINE.......SC
AVIATION.....SC


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at www.weather.gov/detroit.



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