Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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FXUS63 KDTX 161921 CCA
AFDDTX

Area Forecast Discussion...CORRECTED
National Weather Service Detroit/Pontiac MI
221 PM EST Thu Nov 16 2017


.AVIATION...

MVFR with some low end VFR CIGS continue to stream across the region
and will last through the at least 00Z. Gusty winds ouf of the west
continue this afternoon with gusts to around 25 knots at all TAF
sites. Winds will subside throughout the evening as high pressure
begins to drift through the region. Winds will become light or calm
and veer more towards a northerly direction. As cold and dry air
advection takes over tonight, there should be a clearing out into
VFR CIGS. Some uncertainty still exists with how quickly this lower
stratus deck clears out, but feel the dry air will take over and low
clouds will be gone the overnight hours. Once these clouds clear
out, potential exists as temperatures drop to get some radiational
cooling that could promote some fog development. Do not anticipate
dense fog development at this time, so will just leave mention of
BR.

For DTW...Gusty W/NW winds will persist through the early part of
the afternoon. Gusts will be at or slightly above 20 knots from a
290-310 direction. As the winds ease up, the cross wind threshold
will be less likely to be reached, but cannot rule out an occasional
gust to 25 knots or slightly more. Low stratus will continue through
the daylight period with a potential to clear out after 00Z.

//DTW THRESHOLD PROBABILITIES...

* High for ceilings below 5kft through early evening...then low
  after 00z.

* Low in westerly wind gusts exceeding crosswind thresholds for
  the early part of this afternoon.

&&

.PREV DISCUSSION...
Issued at 250 AM EST Thu Nov 16 2017

DISCUSSION...

Strong westerly winds gusting between 30 to 35 mph slowly advecting
colder air into the State. Strong upper wave tracking through
southeast Michigan early this morning, with good subsidence to
follow for today, keeping conditions dry (exception perhaps being
the Thumb region). However, moisture/clouds will be trapped
underneath the subsidence inversion, with temperatures fairly steady
(around 40 degrees) with continued cold advection into the early
afternoon. With yesterday`s rainfall in the .25 to 0.5 inches, cloud
cover will not allow ground to fully dry out, and with surface ridge
building into southeast Michigan tonight, assuming skies clear out,
it appears we could be set up for fog, potentially dense, as
temperatures crash into the 20s. Still, there is light northerly
flow coming off Lake Huron through at least Midnight, so it is no
guarantee low stratus will clear out. Also, increasing high clouds
late tonight may help level off the temps, and may be enough to
suppress fog development. Will all the uncertainty, just went with
patchy fog to highlight the potential.

Upper level trough now slowly moving onshore of the West Coast, and
bulk of the upper level energy/PV to track across the Ohio Valley on
Saturday. Impressive moisture axis to surge north toward the southern
Michigan border, with 850 mb dew pts rising into the high single
numbers. Still some significant model differences between 00Z
Euro...GFS...and Canadian. Euro/GFS indicating the deepening low
track through southeast Michigan on Saturday. While, the Canadian
places southeast Michigan on the cold/northwest side of the strong
low pressure system. Even so, it still appears the northern stream
cold infusion will come in just a touch to late to support
accumulating snow, but will allow for possible changeover across the
Tri-Cities region Saturday evening translating southeast before
precipitation tapers off. 00z NAM maintains two distant low pressure
centers on Saturday, consolidating into one for Sunday. Rainfall
potential in excess of 1 inch, along with possible thunderstorms,
ultimately dependent on final low track/frontal zone, with
temperatures on Saturday still subject to significant revisions.

Cold cyclonic northwest flow for the second half of the weekend
still looks to present an opportunity for snow shower/flurries as
850 mb temps bottom out between -10 C to -12 C.

Temperatures rebounding back into the 40s early next week with
strong southwest flow developing and 925/850 mb temps rising into
the mid single numbers.

MARINE...

Rough boating conditions will exist today as overlake instability
increases under cold northwest flow. The strongest northwest winds
will exist this morning, where winds of 25 to 30 knots will gust up
to 40 knots at times across the lake Huron open waters.  This will
result in a period of maximum wave heights in excess of 10 feet over
the central and southern lake Huron basin. A prolonged period of
small craft conditions for the near shore waters as higher wave
action continues through tonight. Diminishing winds late today and
tonight as high pressure builds into the region with bring a
corresponding drop in wave heights by Friday.  Winds then become
southerly and strengthen late Friday and Friday night in advance of
an approaching low pressure system.  A modest degree of stability
under this pattern will restrict peak wind gusts to around 30 knots
during this time.  A period of weaker winds on Saturday as the low
tracks through, before rapidly strengthening Saturday night as
colder air returns.  An increasing potential for gales exists
Saturday night and Sunday, possibly reaching high end with gusts
near 45 knots.

HYDROLOGY...

A low pressure system will lift across southeast Michigan early this
weekend. A deeper plume of moisture will accompany this system,
resulting in an extended period of precipitation between Friday
night and Saturday night. The bulk of this precipitation will fall
as rain through Saturday evening, with a period of moderate to
briefly heavy rainfall expected. The latest forecast indicates total
rainfall amounts ranging between .75" and 1.5 inches will be
possible.

&&

.DTX WATCHES/WARNINGS/ADVISORIES...
MI...NONE.
Lake Huron...Gale Warning until 5 PM EST this afternoon for LHZ361>363-462>464.

     Small Craft Advisory until 5 PM EST this afternoon for LHZ422.

     Small Craft Advisory until 4 AM EST Friday for LHZ421-441>443.

Lake St Clair...Small Craft Advisory until 5 PM EST this afternoon for LCZ460.

Michigan waters of Lake Erie...Small Craft Advisory until 5 PM EST this afternoon for LEZ444.

&&

$$

AVIATION.....AA
DISCUSSION...SF
MARINE.......MR
HYDROLOGY....MR


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