Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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FXUS63 KDTX 202027
AFDDTX

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
327 PM EST Sat Jan 20 2018

.DISCUSSION...

Weak surface gradient flow under nearly zonal flow aloft will lead
to pleasant conditions with light winds and a few high clouds
streaming over Michigan today. High pressure across the southeastern
US will keep the warmer southwesterly flow across southeast
Michigan, though not much of a change compared to yesterday from a
thermal advection standpoint. This will only allow the diurnal
response to increase high temperatures slightly from yesterday into
the low 40s for most of the area with a few locations remaining in
the upper 30s.

Low stratus clouds associated with a plume of moisture pushing
northward in the 925-850 mb layer has been slow to reach Michigan,
but anticipate that it will eventually enter the area tonight. The
eastern edge of this moisture can be see on satellite moving over
IL/IN this afternoon. This push of moisture will bring with it some
fog potential. How dense the fog becomes remains uncertain, at least
for the early part of tonight, with the higher dewpoints lagging a
bit. Though, conditions will be favorable for some patchy fog to
develop. This warm air advection and surge of theta-e may allow for
some areas of light rain/drizzle to develop by tomorrow morning
across the lower half of Michigan. The warmer guidance with
temperatures remaining at or slightly above freezing overnight into
the early morning hours. This suggests only a small window of
opportunity with little impact expected if any light precipitation
were to occur at locations hovering around the freezing mark before
the diurnal response squashes any lasting frozen precipitation
chances.

Tomorrow will likely be a gloomy day with cloudy and moist
conditions and the potential for fog to stick around as snow melt
continues throughout the day. An increase in rain chances for Sunday
into Sunday night look possible given the weak isentropic ascent and
presence of a frontal boundary stretching eastward from the
developing surface low in the Central Plains. Will need to monitor
precip and temperature trends heading into tomorrow night, mainly in
the northern Thumb and northern parts of the Tri-Cities. Current
forecast lows overnight will be below freezing in the low 30s and
upper 20s. With increased precipitation chances, a small window of
light freezing rain/drizzle will be possible.

A dynamic system will bring categorical PoPs for Monday as a low-mid
level cyclone ejects out of the Central Plains and into the western
Great Lakes by Monday afternoon. The zonal flow will shift to strong
south/southwesterly flow with southeast Michigan residing on the
eastern end of the surface low and in the warm sector. Uncertainty
with the position and timing of the surface cyclone remain with the
GFS a little faster and the ECMWF a little slower. However, rain
chances still remain good Monday afternoon and into the Monday
evening time frame. Transition for rain to a rain/snow mix enters
the forecast late Monday night into Tuesday morning as temps drop
overnight.

Low pressure is expected to be positioned across Lake Huron by 12Z
Tuesday, and will continue to push northeast into Ontario throughout
the afternoon, bringing lingering precipitation chances to southeast
Michigan. The chance for light scattered showers will hold on
throughout the morning hours before cold Canadian air wraps around
the northwest side of the low, bringing the slight chance for a
wintry mix to snow transition throughout the afternoon. Minimal snow
accumulations are expected at this time for the rain that does
transition to snow.

Otherwise, an amplified long-wave trough and associated broad
surface high pressure system will fill in across the eastern U.S.
through the mid to late-week period, bringing an extended period of
dry conditions Wednesday - Friday. Cloud cover is expected to start
to scour out throughout Thursday, bringing periods of sunshine for
both Thursday and Friday as temperatures remain seasonal to slightly
above seasonal. WAA is expected to continue to ramp up into
Saturday, allowing temperatures to potentially peak in the mid to
upper-40s for a high. Saturday, however, will also mark next chance
for likely widespread rain chances as southwesterly brings a warm
front and a surge of moist air to the region, providing enough
forcing and moisture for widespread rain chances.

&&

.MARINE...

A weak cold front will settle over the north third of Lake Huron
tonight and stall there during Sunday. This will allow a warm front
to bring mild air in from the Ohio valley over all other marine
areas. The boundaries will merge into a stronger warm front by
Monday as low pressure strengthens over the central Plains and
Midwest. This system will produce widespread coverage of
precipitation, primarily rain from Saginaw Bay southward and a
wintry mix to the north. Increased easterly gradient flow will
result over the north half of Lake Huron, which will be enhanced by
cold air moving in from high pressure centered over Hudson Bay.
Easterly gales will be possible Monday afternoon through Monday
evening and a gale watch is now in effect for this time period. The
wind will weaken and then shift northwest as the low moves across
the lake Tuesday. Northwest wind trailing the system could approach
gales briefly Tuesday night into Wednesday.

&&

.PREV DISCUSSION...
Issued at 1240 PM EST Sat Jan 20 2018

AVIATION...

Observations so far today indicate VFR over Lower Michigan that is
expected to hold through afternoon. A plume of MVFR stratus is shown
developing from the central Plains on pace to reach Lower Michigan
during the evening. The clouds will be the first stage of
deterioration in aviation conditions through tonight as mild air
moves into the region. A downward trend into IFR in stratus and fog
is expected as this air moves in over the snow cover that extends
down through at least the Ohio River valley. These conditions will
be augmented during Sunday by even milder air already producing IFR
over east Texas and Arkansas today which could lead to LIFR over SE
Michigan. The bulk of this moisture and associated drizzle/rain
potential will arrive after sunrise as temperatures warm steadily
above freezing from the Ohio border northward, if not already above
freezing by then. This will be monitored but the potential for icing
remains low at this time. LIFR/IFR will however continue through
Sunday along with increasing chance of rain showers through the day.

For DTW... VFR will lower to MVFR in stratus during the evening, and
then down to IFR/LIFR in stratus and fog overnight. Temperatures are
expected to be above freezing before the greatest potential for
drizzle or light rain develops Sunday morning.

/DTW THRESHOLD PROBABILITIES...

* Low for ceiling 5000 ft or less today. High tonight through
  Sunday.

* Moderate for rain as precipitation type Sunday morning.


&&

.DTX WATCHES/WARNINGS/ADVISORIES...
MI...NONE.
Lake Huron...Gale Watch from Monday morning through Monday evening for
     LHZ361>363.

Lake St Clair...NONE.
Michigan waters of Lake Erie...NONE.
&&

$$

DISCUSSION...AA/AM
MARINE.......BT
AVIATION.....BT


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