Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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FXUS63 KDTX 120827
AFDDTX

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
327 AM EST Thu Jan 12 2017

.DISCUSSION...

Focus today will be on the upper wave that will track from the
Central Plains into Michigan by this afternoon, and what the
response will be as it rides over the frontal zone currently draped
over Lower Michigan. The north side of this front at 3AM was
characterized by light north winds and temperatures in the 30s,
while the south side was still enjoying temperatures as high as the
mid 50s. Latest surface observations place the front roughly along
the northern borders of Wayne and Washtenaw counties. Precipitation
meanwhile tapered off early this morning behind a wave that passed
through last night. Drier air at the mid-levels hinted at by IR
imagery has helped the drying process, but may allow for some
patches of freezing drizzle along/north of I-69 through the early
morning.

The front will slide southward this morning, allowing colder sub-
freezing temperatures on the north side to slide further down into
the area. Problem will arise as the upper wave approaching the area
from the Plains kicks up a surface wave that will ride along the
front as it draws close to the Michigan/Ohio border. This should
prompt an FGEN response in the low/mid levels along the frontal
boundary. Resurgence in low-level jet (60 knots) near the Ohio
border will boost theta-e advection again and maintain higher H850
dewpoints south of M-59 (above freezing). Expect to see a band of
precipitation slip across Southeast Michigan during the late morning
and early afternoon as a result of forcing, and have raised pops to
categorical south of I-69.

Precipitation type will again be an issue as colder air north of the
front is overrun by warmer temperatures aloft. There is some
uncertainty as to how far south freezing temps will extend by the
time precipitation arrives and as temperatures fall while precip is
occuring. This makes the location of potential freezing rain and
sleet accumulations on the northern edge of the precipitation shield
difficult to pinpoint. Highest potential to see ice will be from the
M-59 to I-69 corridor. Temperatures there could very well only be in
the low 30s, and in combination with wet and still warm pavement
from overnight rain and warmth that surged into the 40s and 50s, the
ice may end up having little impact on travel. With precipitation
expected to move through quickly, and given questions to location of
a fairly narrow band of freezing rain/sleet will not issue an
advisory at this time, but use other products (HWO, weather story,
social media) to highlight the threat. We still have several hours
to watch this event start to unfold. As mentioned, temperatures will
fall steadily through the day as the front slides south, with all of
Southeast Michigan back below freezing by mid-evening.

Frontal boundary slides south and east this evening, with west-
northwest winds becoming just a little gusty in its wake. Strong
surface high pressure will slowly build into the area tonight,
becoming centered over the area at close to 1045mb by Friday
evening. This will provide dry weather, but plenty of high clouds
streaming over the area will provide mostly cloudy skies late
tonight through Friday.

Surface troughing pushing across Ontario and weak return flow as the
surface high departs may bring some light snow or flurries to
Southeast Michigan late Friday night into early Saturday. Strong
ridging then looks to rebuild over the Central Great Lakes on
Sunday. The two strong surface highs over the Great Lakes Friday and
Sunday will be a key factor in keeping a baroclinic zone and
precipitation (some of it ice) developing along it to our south over
the Central Plains and Ohio Valley through the weekend. Temperatures
this side of the front will stay near to below freezing for high
temperatures, with lows falling back into the teens to low 20s.

&&

.MARINE...

Just a modest wind response over the central Great Lakes today with
north winds of 20 knots over Lake Huron. The organized northerly
flow will be in response to the surface wave of low pressure pushing
out of the region into Quebec. Winds will become westerly tonight
and pick up some steam in response to a compact pressure gradient
with high pressure ridge nosing into portions of the southern Great
Lakes. West winds of 35 knots or greater will be likely for the
northern Lake Huron basin. Gale are now in effect tonight for
northern Lake Huron between 00-09Z. Surface high pressure will then
rapidly build eastward into the region and allow winds to subside by
midday Friday. The large expanse of the high pressure system will
keep benign winds for January standards in place until possibly as
late as Monday.

&&

.PREV DISCUSSION...
Issued at 1205 AM EST Thu Jan 12 2017

AVIATION...

Ongoing showers and scattered thunderstorms remain on schedule to
exit SE Michigan 06-07Z. This will coincide with the passage of low
pressure which will allow the associated front to begin moving
toward the Ohio border through sunrise. Temperatures will not fall
significantly below freezing in the MBS area until the primary
rain pattern is gone. Instead, expect a very light freezing
drizzle to develop and spread toward FNT during the night.
Observations over Wisconsin and Illinois indicate icing will be
very minimal and will favor an optimistic approach until later in
the morning. Secondary low pressure on the front will spread
another round of rain showers possibly as far north as FNT by mid
morning. Temperatures are expected to be right around the freezing
mark from FNT to PTK and set up the best chance of wintry mix.
Otherwise, the colder northwest wind will lift ceiling into MVFR
which is expected to persist through at least mid afternoon
followed by a modest clearing trend into Thursday evening.

For DTW... MVFR in the warm sector of the system will return to IFR
with the frontal passage and the back to MVFR as the wind increases
from the northwest. Additional precipitation possible after sunrise
is expected to be a cold rain as temperatures remain above
freezing through the morning.

//DTW Threshold Probabilities...

* High for ceiling 5000 ft or less during the night through
  today.


&&

.DTX WATCHES/WARNINGS/ADVISORIES...
MI...NONE.
Lake Huron...Gale Warning from 7 PM this evening to 4 AM EST Friday FOR LHZ361-
     362.

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

$$

DISCUSSION...HLO
MARINE.......CB
AVIATION.....BT


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