Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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FXUS63 KDTX 171728
AFDDTX

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
1228 PM EST Wed Jan 17 2018


.AVIATION...

Drier low level air has scoured out much of the morning stratus as
increasingly anticyclonic gradient flow moves into the region
courtesy of high pressure moving eastward across the Tennessee
Valley. The increasing pressure gradient will cause southwest winds
to increase through the afternoon into the evening with 20+ knot
gusts expected by early evening before dissipating gradually late
tonight.

/DTW THRESHOLD PROBABILITIES...

* Medium for cigs aob 5kft this afternoon and low on Thursday
  morning.

&&

.PREV DISCUSSION...
Issued at 240 AM EST Wed Jan 17 2018

DISCUSSION...

NEAR TERM / TODAY THROUGH TONIGHT

As of 240 AM EST...Upper-level trough continues to open up and
become more progressive with time as it continues its exit east of
the region early this morning. Increasing subsidence has allowed for
a few patches of clearing in the cloud cover, with temperatures
plummeting into the lower single digits to a few degrees below zero
in these areas due to the fresh snowpack. Where clouds have lingered
through the night, temperatures have been a few degrees warmer
solidly in the single digits. Would not be surprised if low
temperatures bottom out near or slightly below zero for most areas
around daybreak, so will go on the colder side of guidance.

Behind the departing trough, upper-level heights will continue to
build through today and into tonight as surface high pressure ridges
in from the southwest. This pattern will result in mainly dry
conditions through the near term period. The exception will be
sporadic brief flurries as a release of lake moisture downstream of
Lake Michigan plagues the region with mostly cloudy stratus/stratocu
throughout the day. The low-level flow will back to the
west/southwest and become increasingly gusty as the day progresses
due to a tightening pressure gradient between the high to the south
and low pressure tracking up near Hudson`s Bay. Wind gusts of 20-30
mph will be common especially during the afternoon and evening, with
occasional gusts of 30-40 mph in the Saginaw Valley and northern
Thumb regions. High temperatures will reach into the mid 20s. With
the gusty winds in place, it will feel much colder with wind chills
in the single digits.

Drier air will filter in tonight allowing for gradually clearing
skies. Continued gusty winds will limit low temperatures tonight,
with lows only falling into the mid and upper teens with a few
readings near 20.

SHORT TERM / THURSDAY THROUGH FRIDAY NIGHT

Quiet and dry weather continues through the short term period with
dry northwest flow aloft and flat upper-level ridging. Lake
aggregate moisture in the low-levels will continue to lead to
periods of mostly cloudy skies, especially north of the Detroit
metro. Surface high pressure settling across the southeast states
will result in southwesterly breezy return flow setting up across
the region, advecting in a moderating airmass with time as
temperatures rise into the mid and upper 30s. Northern stream
shortwave energy will dive southeast across the northern Great Lakes
Thursday into Thursday night with little fanfare as this system will
be quite moisture-starved.

LONG TERM / SATURDAY THROUGH TUESDAY

Long range guidance continues to be in fairly good agreement with an
increasingly unsettled weather pattern taking shape for the weekend
and into early next week. Vigorous Pacific energy moving into the
Intermountain West will carve out a deepening longwave trough that
will induce lee cyclogenesis over the central Plains Friday into
Saturday. This low pressure system will deepen as it tracks
northeastward into the Great Lakes region, with good consensus that
the low will track northwest of southeast Michigan. This track will
result in the region being placed in the warm sector ahead of the
system, which will feature southwesterly flow advecting in milder
and more moist air as temperatures rise into the 40s. A tightening
pressure gradient between the approaching low and lingering high
pressure anchored over the southeast CONUS will also lead to a
period of gusty winds as well.

There remains some timing differences in the long range guidance as
to the beginning of increasing rain chances, so will take a
consensus blend which favors increasing chances for drizzle/light
rain showers late Saturday night and into Sunday, with more steady
rain Sunday night and into Monday. Timing will be refined as we get
closer to the event, but the weekend and into early next week will
generally feature cloudy, mild, but damp conditions.

MARINE...

The Gale Warning will continue for Wednesday and Wednesday evening
as strong and unstable southwest flow develops within strengthening
pressure gradient between arctic high pressure to the south and low
pressure traversing the southern shores of Hudson Bay. Gusts to at
least marginal gales are probable over a good portion of Lake Huron,
including Saginaw Bay and the northern nearshore waters. Gusts to 40
knot gales are anticipated over the central open waters. Episodes of
fresh to strong southwest flow will be common for the remainder of
the week, but gust potential will diminish due to an increasingly
warm stable fetch.

&&

.DTX WATCHES/WARNINGS/ADVISORIES...
MI...NONE.
Lake Huron...Gale Warning until 4 AM EST Thursday for LHZ363-441-462.

     Gale Warning until 10 PM EST this evening for LHZ362-421.

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

$$

AVIATION.....JD
DISCUSSION...IRL
MARINE.......DG


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