Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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FXUS63 KDTX 040101
AFDDTX

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

.UPDATE...

Stratus continues to blanket the forecast area under a deep
inversion. Clearing of the low clouds have nudged into NW Indiana.
Given the weak flow across srn Mi, it is likely to take into Sun
morning before the stratus clears, if at all. By this time, mid
and high clouds will be on the increase. Given the current temps
across the area and taking into consideration the persistent
stratus deck, an update will be issued simply to nudge nighttime
temps up a couple degrees.

&&

.PREV DISCUSSION...
Issued at 603 PM EST Sat Dec 3 2016

AVIATION...

The depth of the low level inversion overhead and extensive stratus
across the region argues for the clouds to persist through the night
even as sfc high pressure drifts overhead. While bases are primarily
in the 3500 to 4k ft range, there are pockets of MVFR clouds around.
These may influence the terminals off an on this evening. A push of
a little warmer air Sun morning may dislodge some of the stratus
briefly. Confidence on this overall scenario does however remain low.

For DTW...

Observations are suggesting that the MVFR cigs in place over metro
Detroit will be short lived as cigs upstream in nrn IN/OH have
jumped above 3k ft. Otherwise, a wet snow is expected to move into
metro in the 21 to 23Z time frame on Sunday.

//DTW Threshold Probabilities...

* High in ceilings below 5000 ft tonight. Medium Sunday morning,
  then high Sunday afternoon and evening.

* Medium in precip type being mostly wet snow late Sunday afternoon
  and evening.

PREV DISCUSSION...
Issued at 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.

&&

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

$$

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


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