Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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FXUS63 KDTX 242007
AFDDTX

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
307 PM EST Tue Jan 24 2017

.DISCUSSION...

The mild southerly weather pattern will be shifting to the more
typical colder northwest winter flow over the next several days,
with temperatures falling back to near normal values over the
weekend.

Sheared out upper wave/pv lifting north into the Northern Great
Lakes this afternoon, with subsidence/drying ending residual morning
showers over southeast Michigan, with further amplification off
shortwave riding this evening into Tonight expected to maintain a
dry forecast through the night.

Longwave trough axis still anchored across the Rockies Wednesday
morning. The highly positive tilted axis pinching off the mild and
moist air in the mid levels from reaching into Lower Michigan, as
average temps in the 850-700 mb layer reside in the zero to -4 C
range. None-the-less, still sufficient warm layer in the sfc-925 mb
layers to support all rain as 993-995 mb low pressure remains on
track to slide east through southern Lower Michigan, but slower
timing, Wednesday Evening/Night. Mid level dry slot seen at 700 mb
level draws in question on much rain will fall south of M-59 during
Wednesday, and could be looking at mainly drizzle if anything. With
the warmer air at 850 mb getting pinched off, NAM has backed off on
the instability, as showalter index remains solidly positive, but
still good mid level lapse rates (700-500 MB) to support a remote
thunderstorm chance, but not worthy of inclusion in zones due to the
lack of available moisture at that level.

Slower timing of the surface low will delay transition to snow
showers as well, but still would expect a good coverage (numerous)
of snow shower activity Thursday morning, with 850 mb temps falling
to at least -4 C and some lingering deformation and low level
cyclonic flow. Steep low level lapse rates and middle section of the
cloud deck also intersecting DGZ support continued mention of snow
showers into the afternoon hours.

Per 12z Euro, Upper wave/shortwave trough seen dropping south from
Ontario through the Central Great Lakes on Friday, worthy of chance
of snow showers with favorable 850 mb temps in the -11 to -13 C
range.

Additional upper waves/re-enforcing shots of cold air over the
weekend will continue to bring a chance of snow showers, with
potential clipper system for early next week.

&&

.MARINE...

Weak high pressure building into the central Great Lakes will
maintain light northwest flow late today into tonight. Low pressure
over the Central Plains will lift up across the area Wednesday. This
will keep winds light though the day, but bring a good chance for
rain and snow showers. Southerly winds will increase Wednesday
evening south of Harbor Beach as a warm front lifts into the area,
but the main impact on marine interests from this next low pressure
system will be gusty winds that develop behind a cold front early
Thursday morning and persist into Saturday. Gusts to 30 knots look
possible for all areas. Colder air rushing into the region will also
bring a chance for lake effect snow showers through the end of the
week.

&&

.PREV DISCUSSION...
Issued at 1259 PM EST Tue Jan 24 2017

AVIATION...

The slow improvement to MVFR ceilings will continue through the
early afternoon as a ridge of high pressure slowly builds into
Michigan and northwest winds increase to 7-10 knots. The ridge will
become centered overhead this evening, favoring a lowering of
ceilings/vis once again as it also becomes more diurnally favorable.
Some question as to how low visibility will go (LIFR versus VLIFR)
as weak southeast gradient starts to tighten around 12Z near the
Detroit-area terminals due to an approaching low pressure system.
Persistence and questionable performance of forecast models in
recent days favors a more pessimistic forecast at this time. Showers
associated with the area of low pressure may begin to affect the
area with rain/snow showers between 15-18Z, however most rain
showers look to hold off until after 18Z.

For DTW...Improving trend is expected to continue through the
afternoon, with low potential for a brief period of low-end VFR
conditions in the very early evening. Conditions are expected to
deteriorate again by late evening as conditions become calm under
the influence of high pressure. This should promote the
redevelopment of LIFR to VLIFR ceilings during the early morning
hours. There is some question as to how long those conditions will
hold at DTW however as approaching low pressure begins to increase
the surface pressure gradient around 12Z.

favors a more pessimistic

//DTW Threshold Probabilities...

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

* Moderate for ceiling aob 200 feet/visibility aob 1/4SM at times
  through mid morning.


&&

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

$$

DISCUSSION...SF
MARINE.......HLO
AVIATION.....HLO


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