Area Forecast Discussion
Issued by NWS Gaylord, MI

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105
FXUS63 KAPX 111509
AFDAPX

Area Forecast Discussion
National Weather Service Gaylord MI
1009 AM EST Mon Dec 11 2017

.UPDATE...
Issued at 1009 AM EST Mon Dec 11 2017

Low pressure continues to swing SE out of Central Canada and into
the Upper Mississippi Valley late this morning. Southerly low
level flow is strengthening across the Western Great Lakes region
ahead of this system...pumping moisture into Michigan as lift
increases. Area of mainly light synoptic snow continues to spread
eastward into our CWA as a result. This area of light snow will
impact most of our CWA thru the balance of the day and into this
evening as the surface low center continues to dive SE into
Indiana by 00Z Tuesday. Expected QPF is rather light and only
expect new snow amounts of an inch or two with this system. The
exception will be Mackinac county where S/SW low level flow lake
enhancement will boost new snow amounts to 2 to 4 inches today.
Will certainly maintain the Advisory currently in effect for
Mackinac county thru 23Z this evening. High temps will be mainly
in the 20s this afternoon.

&&

.NEAR TERM...(Today through Tonight)
Issued at 347 AM EST Mon Dec 11 2017

...Another round of snow/lake effect snow...

High Impact Weather Potential...prolonged period of lake effect
snow for some areas through Tuesday night.

Pattern Synopsis/Forecast...Highly amplified pattern remains
intact of course with a sharp blocking ridge up through the
western CONUS and downstream troughing encompassing much of
central and eastern NOAM. We do have just a hint of low amplitude
short wave ridging sliding through the western lakes region
currently...and attending surface high pressure sliding through
the region. Thus...we have caught at least a little bit of a
break...although there remains some lighter NW flow lake snow
showers impacting some areas.

Upstream...a rather well defined short wave and attending surface
low is dropping quickly southeastward into the upper Midwest...with
a secondary piece of energy is noted over western Hudson Bay.
Warm advection "synoptic" snowfall ahead of the lead wave is
already sliding into Wisconsin and will be reaching us this
morning. This system will slip quickly southeast through the
western Great Lakes region into the Ohio Valley through this
evening before pivoting and substantially deepening heading into
the New England region on Tuesday. This will bring all areas some
light accumulating snow today. But...lake effect snow is another
matter.

Primary Forecast Concerns...SW flow lake enhanced snowfall on the
front end of this system...prolonged NNW flow lake effect snow and
gusty winds on the back.

As mentioned...short wave trough and attending surface low will
drop quickly southeastward through the western Great Lakes through
the course of the day. Upstream swath of warm advection forced
snowfall will overspread the region through the morning before
peeling off to the east through the afternoon. Shouldn`t be a big
deal overall with much of the CWA picking up and inch or two of
snow. However...S/SW flow ahead of wave coupled with increasing
forcing/synoptic moisture will bring several hours of enhanced
lake effect banding into the western portions of Mackinac county
and potential for 3, 4, 5 inches of snow. With that in mind...plan
on hoisting a winter weather advisory for Mackinac county for
today...focusing on the western/central part of the county.

Gets much more interesting tonight (and beyond). Clipper will be
pivoted through the Ohio Valley this evening before heading
northeastward toward New England...while secondary northernmost
short wave dives down through the western Great Lakes and brings
along a big plunge of arctic air. Fairly sharp low level trough
axis/cold front will be passing through the CWA this evening
ahead of the arctic plunge...likely accompanied by a period of
enhanced snowfall. Behind the trough...winds still looking to
turn sharply NNW and set the stage for a prolonged period of
healthy lake effect snows later tonight through Tuesday night.
Extreme instability (Bufkit forecast sounds at MBL/TVC give over
1000 J/KG lake induced CAPE) persistent NNW flow all suggest some
rather healthy snow totals along the Lake Michigan coastline from
Leelanau county southward...assuming the flow does lock in as
forecast. Coupled with gusty winds/blowing snow potential...plan
on issuing a winter storm warning for Leelanau through Manistee
counties as well as Grand Traverse county...bordered by an
advisory.

&&

.SHORT TERM...(Tuesday through Wednesday)
Issued at 347 AM EST Mon Dec 11 2017

...Frigid Arctic air and significant lake effect snow...

High Impact Weather Potential...Significant lake effect snow on
Tuesday around and south of Grand Traverse Bay. Blustery winds
will result in blowing snow and very frigid wind chills at times.

Pattern Synopsis/Forecast...Deep troughing overhead (2 to 3
standard deviations below the mean) will be reinforced by another
lobe of energy dropping south from western Ontario Tuesday morning.
Arctic air will surge southward with this trough on the backside of
an intense departing surface low, with 850mb temperatures dropping
to around -20C over northern Michigan. Surface ridge will drift
across the region Tuesday night into Wednesday, but lake aggregate
troughing will hold fast. Another incoming shortwave will
become sheared out as it passes through the region on Wednesday.

Primary Forecast Concerns...Cold temperatures, significant lake
effect snow, and Wednesday`s clipper system.

The coldest surge of Arctic air thus far this season will arrive on
Tuesday, though the airmass will moderate slightly as it plunges
south into the Upper Great Lakes. Not looking at any strong
temperature anomalies (only around 1 to 2 standard deviations below
the mean at 925 and 850mb), but this airmass will be significant
just because of it being the coldest thus far. Highs will be in the
teens both Tuesday and Wednesday for most. Lows Tuesday night (the
coldest period) will be in the single digits on either side of zero
everywhere except west of M-37. Factor in the blustery winds Tuesday
morning and somewhat brisk winds Wednesday morning, and wind chills
will plunge well below zero across much of northern MI both mornings.
If skies manage to clear out more than currently expected Tuesday
night, temperatures could drop even lower than the current forecast
east of I-75, but don`t expect the boundary layer will completely
decouple to allow for an ideal radiational cooling setup.

As for snow, forecast soundings show a very ideal lake effect setup
for areas south of Grand Traverse Bay on Tuesday. Steep low level
lapse rates and strong lake-induced instability. Inversion heights
at MBL approach 8 kft, and strong unidirectional NNW winds from the
surface through the upper levels will provide strong low level
convergence along the coast. Very impressive low level omega
coincident with the dendritic growth zone and pretty high RH from
the surface up through ~750mb. Thus, expecting some very impressive
snow bands to develop by daybreak Tuesday, and the hi-res ARW/NMM
show just that with banding focused from Leelanau County south to
Manistee throughout the day. Relied heavily on ARW/NMM QPF. This
would yield daytime snow accumulations of around 4-8 inches across
our southwestern counties, likely highest over Benzie and Manistee
counties. And, of course, this snowfall would be on top of what
falls in that area tonight. Hence the headline decisions
mentioned above. Do expect some NW flow lake effect off Lakes Huron
and Superior as well, but not of the same magnitude. Upstream
surface ridge sliding in Tuesday night will cause lake effect to
diminish in coverage and intensity with only light additional
accumulation expected through Wednesday morning. Next clipper system
will dive in from the NW late morning into the afternoon, but models
still don`t have its precise track pinned down. Only looking like
light snow accumulation potential from this system, however.

.LONG TERM...(Wednesday night through Sunday)
Issued at 347 AM EST Mon Dec 11 2017

High impact weather potential...Ongoing lake effect snow with
additional enhancement from a clipper system or two.

A slow moderation in temperatures expected the remainder of the
week...even signals of temperatures climbing /above/ freezing this
weekend! But still an active wintry pattern to deal with in the
meantime with lake effect snow and an occasional clipper system.

Deep longwave troughing over the eastern CONUS is progged to
gradually lift NE heading into Thursday with upper flow turning
zonal for a brief time as the strong ridge out west begins to
flatten. Additional energy drops south from Canada on Friday,
yielding a sharp but quick moving trough over the region. Flow
then turns largely zonal again towards next weekend.

&&

.AVIATION...(For the 12Z TAFS through 12Z Tuesday morning)
Issued at 643 AM EST Mon Dec 11 2017

...Overall MVFR conditions continue...

Low pressure system will move through the region today and bring a
period of mainly light snowfall to the region...and continued MVFR
conditions at the terminal sites. System exits east this evening
with winds turning sharply NW...pulling arctic air into the region
and setting the stage for heavy lake effect snows impacting
portions of NW lower MI. TVC/MBL will see the biggest
impact...with MVFR and periodic IFR conditions tonight into
Tuesday.

In addition to the snow...gusty NW winds develop tonight and
persist through Tuesday.

&&

.MARINE...
Issued at 643 AM EST Mon Dec 11 2017

Clipper system will pass through the region today and exit east of
the state tonight. Behind this system...winds turn sharply NW and
gusty...with gale force gusts anticipated for much of the western
Great Lakes region tonight through Tuesday.

&&

.APX WATCHES/WARNINGS/ADVISORIES...
MI...WINTER STORM WARNING from 10 PM this evening to midnight EST
     Tuesday night for MIZ020-025-026-031.
     WINTER WEATHER ADVISORY from 10 PM this evening to midnight EST
     Tuesday night for MIZ021-027-032-033.
     WINTER WEATHER ADVISORY until 6 PM EST this evening for MIZ015.
LH...GALE WARNING from midnight tonight to 6 PM EST Tuesday for
     LHZ347>349.
     SMALL CRAFT ADVISORY from 6 PM this evening to 6 AM EST
     Wednesday for LHZ345-346.
LM...GALE WARNING from midnight tonight to 6 PM EST Tuesday for
     LMZ323-342-344>346.
     SMALL CRAFT ADVISORY from 6 PM this evening to 6 AM EST
     Wednesday for LMZ341.
LS...GALE WARNING from midnight tonight to 6 PM EST Tuesday for
     LSZ321-322.
&&

$$

UPDATE...MR
NEAR TERM...BA
SHORT TERM...MK
LONG TERM...MK
AVIATION...BA
MARINE...BA



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