Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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678
FXUS63 KDTX 240452
AFDDTX

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
1152 PM EST Mon Jan 23 2017


.AVIATION...

Band of more persistent fog has developed just east of fading area
of deformation rain. With vsbys once again dropping to 1/4SM at
times within this corridor, will maintain VLIFR conditions for a
number of terminals. Overall, moisture and wind conditions suggest
this fog will persist. However, slightly drier air to the east may
limit the extent somewhat as light east/northeast flow continues.
Cig/Vsby conditions will then edge back to IFR Tuesday morning and
MVFR by afternoon.

For DTW...Will maintain a least a tempo for 1/4SM fog and 200 foot
ceilings given trends this evening. With higher vsbys/cigs just to
the northeast of terminal, the VLIFR conditions may oscillate with
vsbys closer to 1/2-1SM overnight.

//DTW Threshold Probabilities...

* High for ceiling 5000 ft or less through the forecast.

* High for ceilings aob 200 feet/visibility aob 1/4SM at times
  overnight.

&&

.PREV DISCUSSION...
Issued at 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.

&&

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

$$

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


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