Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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FXUS63 KDTX 172256
AFDDTX

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
656 PM EDT Fri Mar 17 2017


.AVIATION...

The band of heavy snow will be east of the terminals by TAF
issuance. There has also been some sleet and freezing rain on the
back edge of this precip shield. Satellite data show an aggressive
push of mid level dry air in the wake of this band of snow. However,
plenty of low level moisture will remain in place. Upstream sfc obs
show fairly widespread IFR cigs in stratus. Reduction in visibility
and weak radar returns are suggestive of some decent coverage of
drizzle. While temps have dropped to 32 deg over much of Se Mi with
the snow, upstream temps have largely rebounded to 33 deg. Suspect
this will be the case at the terminals shortly (except for PTK in
the higher terrain where temps may hold at 31 or 32 for a prolonged
period, supporting some freezing drizzle).

While there is clearing pushing into Chicago attm, the sfc front
will stall over lower Mi tonight as low pressure slides into the
area from the northwest. This should pool low level moisture across
Se Mi and thus hold low clouds in place through the night. Mid level
cooling late tonight through Sat morning associated with an upper low
rotating overhead will offer a chance at lifting cigs into the VFR
category Sat morning. The timing of which does however carry a good
deal of uncertainty.

For DTW...The trends upstream support the idea that temps will hold
above freezing tonight. Model soundings actually suggest the
boundary layer will remain warm enough to support liquid precip
types through the day Saturday.

//DTW THRESHOLD PROBABILITIES...

*  High in ceilings below 5000 ft tonight and Saturday.

*  Moderate in precip type being all liquid the remainder of tonight
   through the day Saturday.

&&

.PREV DISCUSSION...
Issued at 302 PM EDT Fri Mar 17 2017

DISCUSSION...

Lead band of precipitation along elevated warm front in advance of
approaching low pressure and parent shortwave has pretty much gone
completely to slowly saturating the lowest 10-15kft atmospheric
column (12z KDTX sounding depicts the dry airmass in place below 500
mb this morning).

Expect rain and snow shower activity to increase to some extent
along this first frontal boundary early to mid afternoon. That said,
no accumulations are expected initially as this moisture continues
to dry up and surface temperatures hold in the 35 to 40 degree range
for most locations.

Secondary frontal boundary lower in the atmosphere will progress
steadily eastward into the forecast area in behind this lead front.
Shower activity being forced by this feature has been on the uptick
over southern Lake Michigan late this morning and expect this trend
to continue as this front moves into the area mid to late afternoon.
With some degree of instability along this frontal band, a number of
the convective elements have become rather vigorous midday (even a
few in cloud lightning strikes noted in cell over southern Lake
Michigan) and see no reason for this trend not to persist into peak
heating late this afternoon.

Precipitation chances will increase notably with this second front
after 18z-20z, and given the convective nature, snow accumulations
will still be possible despite the relatively mild boundary layer
conditions. The caviot(s) in this scenario will be that the snow
accumulations on the order of an inch or a bit more will be limited
in areal coverage and also limited mainly to grassy and/or elevated
surfaces given the degree of solar insolation that has occurred
today in advance of the precipitation/thickening clouds.

The main shortwave/low pressure digs southeast over area late
tonight into Saturday morning, maintaining a chance of rain/snow
shower activity or perhaps periods of drizzly weather tonight into
Saturday as this system basically pivots down frontal boundary as it
settles over area. Even with this system moving into the area from
Canada, very little cold air is tapped with temperatures only
settling down to around freezing tonight before climbing back into
the 40s Saturday as mid March sunshine overcomes shallow cold pool
of air to a large degree.

Dry and relatively mild conditions persist through Sunday as the
temperatures again climb into the 40s after bottoming out in the 25
to 30 degree range Saturday night.

Next week will begin and end with the potential for precipitation,
however the majority of the week will feature dry conditions.  A
cold front will push across the region on Monday bringing a chance
for mainly rain showers as temperatures remain above freezing.
Arctic high pressure then fills in behind the cold front Monday
night and holds through Thursday, keeping the area dry. Temperatures
will start off a little warmer at the front end of the week before
cooling off slightly by the middle of the week.

MARINE...

A low pressure system will track across southern Michigan on
Saturday. Increased southerly flow ahead of the system will be
tempered by stable warm air aloft which should cap any gusts to
around 25 knots through tonight. Winds will then back over Lake
Huron while veering over Lake St Clair and Lake Erie due to the
track of the low. Wind speeds should decrease under the low pressure
center which should minimize the impacts of the changing wind
directions while becoming light and northerly across the region by
Saturday night.

&&

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

$$

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


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