Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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122
FXUS63 KDTX 032024
AFDDTX

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
324 PM EST Sat Dec 3 2016

.DISCUSSION...

High pressure at the surface and aloft will encompass the region
this evening and tonight. Northwest flow this afternoon will turn
westerly this evening as the ridge axis glides across Lower
Michigan, then finally southwest overnight as the axis passes east.
Change in trajectory and lighter flow should allow for a few breaks
the stratus this evening and overnight, however high/mid clouds will
fill in tonight ahead of the next system ensuring an at least mostly
cloudy sky. Some cooling of the boundary layer and less wind tonight
will allow for cooler temperatures. Min temps in the mid 20s to near
30 offered by guidance and inherited forecast look reasonable.

Upper trough now pushing through the Rockies will take on a negative
tilt as it works up across the Great Lakes late tomorrow and
tomorrow night. Surface trough associated with this feature will
lift across during the evening, with a weak warm front preceding
during the day. Front looks more pronounced from a thermal
perspective in the 850-700mb layer. This boundary will be lifting
through a fairly dry atmosphere during the morning and afternoon,
with weak lift likely only enhancing lower clouds and helping the
atmosphere moisten in the mid-levels. Will keep the forecast dry
prior to 1PM at this time, but would not be surprised to see a few
sprinkles or flurries. Better moisture will be pulled northward
during the afternoon and evening ahead of the surface trough axis.
Deeper moisture will work with forcing ahead of the trough and strong
mid-level PVA to spread precipitation up into Southeast Michigan
during the afternoon and evening. Strongest lift and weaker
stability look to be better positioned in the mid-levels, mainly
above the dendritic growth zone. Precipitation type will be an issue
during the afternoon and into the evening. Surface temperatures are
expected to warm into mid 30s to near 40 in the late afternoon, but
should start to fall as precipitation begins due to web-bulb effect.
Temps/dewpoints should remain a few degrees either side of freezing
through much of the precipitation event, making both rain and snow
possible. NAM thermal profiles are warmer than other models and
support mostly rain, especially in the Detroit area. Other models
(GFS/Euro) are slightly cooler, but still warrant a rain mention
lingering into the evening for all but Bay and Midland counties.
Chances for precipitation to change to all snow will increase as you
move north and west of Detroit. Snow amounts will range from barely
anything from Detroit southward to 1-2 sloppy inches in the Saginaw
Valley.

Shortwave ridge building into the area Monday will bring a dry and
quiet day, although moisture below the subsidence inversion should
keep a stratus deck in place. Temperatures should rebound back to
near 40.

Low pressure centered over the Oklahoma/Arkansas border early
Tuesday morning will travel Northeastward towards the Ohio Valley by
late Tuesday evening. Uncertainty exists surrounding placement of
the low and type of precipitation to be seen. Latest 12Z GFS keeps
low pressure just south of Ohio, keeping most of the precipitation
south of the I-69 corridor starting in the late morning and early
afternoon, with the 12Z ECMWF pushing the low across central Ohio,
allowing precipitation to creep into most of our service area by the
afternoon and evening hour. Current thinking is any precipitation
seen in the late morning hours will be light snow or a wintry mix,
with a transition over to all rain by the afternoon and early
evening hours as daytime highs push in the lower 40s. Lingering
precipitation seen after sunset will have the chance to revert back
to a rain/snow mix as temperatures dip back down into the low to mid
30s. Changes to the precipitation type will be possible in the
forthcoming days...NAM model soundings keep us slightly cooler
through the day, with higher chances to see more of a wintry mix.
Otherwise, much cooler air is expected to enter the region mid-week,
keeping daytime highs capped in the mid 30s on Wednesday, and upper
20s Thursday - Friday. Slight chance for light snow showers for the
late part of the week.

&&

.MARINE...

Light winds and wave will persist into Sunday morning as high
pressure builds across the region. Southerly flow will then begin to
increase somewhat on Sunday in advance of approaching surface trough
with winds then veering to southwest with the passage of this trough
Sunday night. An area of light rain/snow will progress through the
region with this system, but winds will remain in check as gusts,
even in the southwest flow from Sunday night into Monday, remain
generally 20 knots or less.

&&

.PREV DISCUSSION...
Issued at 1209 PM EST Sat Dec 3 2016

AVIATION...

Very little low level mixing has occurred through 17z, which is no
surprise given model forecast soundings of taking decent inversion
already in place around H85 this morning and strengthening/lowering
it into this evening as high pressure builds east into area. Only
after 06z does some drier air work into the sub H85 layer which in
itself it a bit suspect as the low level inversion only weakens
slightly overnight. Will maintain MVFR to lower VFR stratus over the
whole area through 06z and will likely be slightly more pessimistic
after 06z as well given the extent of low level moisture over the
region. The next weather system to affect the area lies just beyond
the forecast period as a surface trough encroaches from the west and
bring snow or rain/snow mix after 21z Sunday.

For DTW...Ceilings will remain anchored around 3500 feet during the
afternoon with some chance of lower ceilings in the 2500-3000 foot
range as this lower layer of stratus just south attempts to spread
slowly northeast. It is difficult to ascertain the amount of low
level clearing to expect overnight, but given cloud trends so far
today will lean a bit more pessimistic. Further reductions in cigs
and vsbys will hold off until after 21z Sunday as rain/snow spreads
into area within region of isentropic lift in advance of trough.

//DTW Threshold Probabilities...

* High in ceilings below 5000 ft through this evening...medium
  overnight.


&&

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

$$

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


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at www.weather.gov/detroit.



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