Area Forecast Discussion
Issued by NWS Gaylord, MI

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FXUS63 KAPX 120442
AFDAPX

Area Forecast Discussion
National Weather Service Gaylord MI
1142 PM EST Mon Dec 11 2017

.UPDATE...
Issued at 1039 PM EST Mon Dec 11 2017

A cold front is bisecting nrn Michigan late this evening while
pushing eastward, out ahead of incoming shortwave across the
western Great Lakes. One more expanding area of snow was
developing with this forcing, especially in the higher terrain of
nrn lower due to upslope. Lake effect banding was quickly
exploding behind this area of snow and NNW/NW winds were rapidly
increasing with gusts already up to 35 mph coming off Lake
Michigan. The parent mid level trough to the shortwave gradually
builds in over nrn Michigan through the night, with inversion
heights increasing to 6500-7000 feet. Despite the lowest levels of
the convective boundary layer looking a shade dry, we do have some
slight cyclonic convergence and a good tap on Lake Superior. Plus,
this flow regime still looking to hold pretty steady through
Tuesday night. If one area can continue to get frequently hit with
snow showers (still most likely around the Frankfort and Manistee
areas), then amounts could reach a foot over the next 24 hrs.
Generally though, lowered amounts to a general 5-10 inches. Gusty
winds will create blowing snow into Tuesday before winds start
weakening into Tuesday night.

&&

.NEAR TERM...(Tonight through Tuesday)
Issued at 407 PM EST Mon Dec 11 2017

...Synoptic snow transitions to lake effect snow and windy
conditions...

High Impact Weather Potential...Accumulating snow combined with wind
and very cold temperatures resulting in hazardous travel conditions.

Pattern Synopsis/Forecast...Low pressure continues to swing SE out
of the Upper Mississippi Valley into Illinois this afternoon. Area
of mainly light synoptic snow that developed ahead of this low is
impacting much of our CWA attm...generally dropping vsbys to 1 to 2
miles. Low level winds have just shifted to the S/SW across far
Northern Lake Michigan and Mackinac county...which should begin to
push lake effect snow bands into the current Advisory area.

Still expect overall synoptic snowfall should produce a total of an
inch or two across most of our CWA for today into early evening.
Certainly Mackinac county will receive more snow (a total of 2 to 4
inches) given increasing lake enhancement potential as low level
winds shift to a more SW trajectory. Will maintain the Advisory for
Mackinac county thru 23Z this evening...at which time low level
winds will have begun to shift to the NW cutting off further Lake
Michigan enhancement.

Rest of our CWA will see low level winds shift to the N/NW by around
06Z tonight and gradually strengthen as strong low level CAA
commences in the wake of the departing low. 850 mb temps will drop
from around -9C across Northern Lake Michigan this afternoon to -19C
by 12Z Tuesday. Synoptic snow event will quickly transition to a
N/NW flow lake effect snow event late this evening and overnight...
with moderate to heavy lake snow bands continuing to fall across
mainly locations along and west of US-131 thru Tuesday. Areas under
the Advisory late tonight thru Tuesday evening will receive 4 to 6
inches of new snow during this time...with localized amounts up to 8
inches. Areas under the Warning for this same time will receive 5 to
8 inches with local amounts up to 14 inches. North winds gusting to
25 to 35 mph will produce plenty of blowing/drifting snow...and will
certainly aid in drastic drops in vsbys within these areas.

With CAA beginning late tonight...low temps will drop into the
single digits above zero across Upper Michigan and into the teens
for Northern Lower Michigan. Temps on Tuesday will only "warm" a few
degrees above the overnight lows. Stay warm and safe everyone!

&&

.SHORT TERM...(Tuesday night through Thursday)
Issued at 407 PM EST Mon Dec 11 2017

...End of a Clipper, then Cold Temperatures and Wind Chills ...

High Impact Weather Potential...The Lake effect from Tuesday will be
continuing into the evening, but with drier air moving in, will
expect a down turn. So will expect a low impact.

Pattern Synopsis/Forecast...It looks like the ridge/trough idea at
500 mb will continue through Thursday. Again, everyday or so will
have energy topping the ridge in Alberta and dropping into the
trough that is in the Great Lakes. Some of the energy will help to
dig the trough and retrograde it into the Upper Great Lakes and
Midwest, keeping the forecast area in the cold air through the rest
of the week.

Primary Forecast concerns...As always with these clippers, the
precipitation that they do bring will be enhanced by the lakes. With
the 850 mb temperatures expected to remain below -10c from Tuesday
night through Thursday, there will be enough instability (delta
T~15C) to continue the LES production. So the main concerns will be
layer RH (850-700 mb) to help the seeder/feeder process, the wind
direction and the persistence of the wind direction to get moderate
to heavy amounts. The current warnings and advisories look good as
the winds will still be out of the NNW direction and based on the
HiResW-ARW model (which seems to do well in these situations), there
should still be some great bands going over the warning and advisory
areas into the evening. However, will expect that as the dry air and
the wind directions change as the clipper approaches the state, will
the bands diminish. This clipper on Wednesday will drop a little
more to the south and will be to the west, so will expect the south
winds out ahead of the clipper to remain out of N Lake Michigan and
producing any enhancement. Models are showing different versions of
850-700 mb moisture Wednesday night and Thursday, The ECMWF is the
fastest with the moisture moving into the region the GFS, is a
little slower, but has the same wind directions as the ECMWF.

.LONG TERM...(Thursday night through Monday)
Issued at 407 PM EST Mon Dec 11 2017

High Impact Weather Potential: Varying snow chances through the
weekend.

Door will still be open for cold air to spread southward into the
Midwest/Great Lakes as deep full-latitude long wave trough will
persist into Friday...but overall strong +PNA pattern will weaken as
long wave trough over the eastern Pacific splits and leaves a cut
off low behind over Hawaii.  This allows flow over the eastern
Pacific to become more zonal and as a result weakens the anomalous
western North American ridge and allows upper level winds to back as
height falls dig into the Rockies Saturday.  This trough should be
progressive...sweeping across the nation`s midsection Sunday and
into the eastern states Monday.

Combination of weak short wave energy and cold air over the region
will bring a continued threat for snow Friday...but the weekend
forecast is a bit more muddled with North American guidance pushing
a more strung out area of low pressure across the Great Lakes...
while ECMWF is more consolidated single low track through the Ohio
Valley and resulting in a swath of snow across much of Lower
Michigan.  This pattern difference also manifests itself in a new
push of colder air across the Lakes Sunday in the North American
guidance...while the ECMWF has a strong push of warm air advection
into Michigan for Monday.  Between either synoptic or lake forcing
not sure that model differences make a huge difference in the
general forecast...with varying precip chances through the weekend.
Not planning on making many changes to the consensus forecast.

&&

.AVIATION...(For the 06Z TAFS through 06Z Tuesday night)
Issued at 1139 PM EST Mon Dec 11 2017

Strong and gusty NNW/NW winds and lake effect snow showers
continue to develop eastward, and will firmly be in place through
the TAF period, although winds will start to subside into Tuesday
night. The snow showers will primarily impact TVC/MBL with
periodic moderate snow showers and possible significant snowfall
amounts through Tuesday night. More sporadic and lighter snow
showers around PLN/APN. MVFR and periodic IFR conditions expected
through the TAF period. Snow ratios 20:1 to 25:1 and snowfall
potential of 5 to 10 inches around the GTV Bay region. Certainly
possible to see more than that through Tuesday night.

&&

.MARINE...
Issued at 407 PM EST Mon Dec 11 2017

Winds and waves will ramp up again to mainly gale warning criteria
tonight thru Tuesday as northerly flow strengthens in the wake of a
departing area of low pressure. Light synoptic snow will continue to
impact much of our area into this evening before winds shift to the
north in the wake of the departing low and strengthen to 30 to 40 kt
gusts. Strong CAA will produce N/NW flow heavy lake effect snow
showers...impacting mainly our Lake Michigan nearshore areas. Expect
periods of heavy snow...strong northerly winds and poor vsbys.


&&

.APX WATCHES/WARNINGS/ADVISORIES...
MI...WINTER STORM WARNING until midnight EST Tuesday night for MIZ020-
     025-026-031.
     WINTER WEATHER ADVISORY until midnight EST Tuesday night for
     MIZ021-027-032-033.
LH...GALE WARNING until 6 PM EST Tuesday for LHZ347>349.
     SMALL CRAFT ADVISORY until 6 AM EST Wednesday for LHZ345-346.
LM...GALE WARNING until 6 PM EST Tuesday for LMZ323-342-344>346.
     SMALL CRAFT ADVISORY until 6 AM EST Wednesday for LMZ341.
LS...GALE WARNING until 6 PM EST Tuesday for LSZ321-322.
&&

$$

UPDATE...SMD
NEAR TERM...MR
SHORT TERM...JL
LONG TERM...JPB
AVIATION...SMD
MARINE...MR


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