Area Forecast Discussion
Issued by NWS Gaylord, MI

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FXUS63 KAPX 060236

Area Forecast Discussion
National Weather Service Gaylord MI
936 PM EST Tue Dec 5 2017

Issued at 936 PM EST Tue Dec 5 2017

Evening surface analysis reveals broad/deep cyclonic flow across
the Great Lakes along the southern edge of stacked/deep departing
low pressure over northern Ontario. Lead short wave trough axis
just exiting east out of the state...which did bring a brief
uptick in lake enhanced snows a few hours back with the better
snowfall across the tip of the mitt. We`ve settled back into a
more banded SW flow lake effect regime with modest snow showers
impacting NW lower Michigan up through the tip of the mitt.

Lake snow shower intensities have been a bit underwhelming so
far...the product of subsidence and a wedge of drier air working
out of eastern Wisconsin into lower Michigan behind the lead short
wave trough. Dry air evidenced by surface dewpoints in the single
digits in eastern Wisconsin to the teens across northern lower
Michigan...and inverted V signature seen on this evenings APX
sounding. That said...snow shower intensities have picked up a
little bit in the last hour or so.

Light to moderate snow showers will persist through the overnight
hours with the focus remaining across the tip of the mitt...and
mainly light snows further south. Another short wave/deeper
moisture is rotating into NW Wisconsin this evening and will bring
a further uptick in snow shower intensities early Wednesday
morning. Despite the modest start...still think some areas in the
headline counties (Charlevoix/Emmet/Cheboygan) could see 3-4
inches of snow by morning where lake banding is most persistent...and
a bit more for Wednesday before winds veer more westerly. Not
quite the 5 to 10 inches as originally thought...but coupled with
the gusty winds/blowing snow aspect...still high impact. So I
won`t touch those headlines at this point.

Chippewa/Mackinac counties are a bit more problematic. Overall
flow appears to be more WSW than anticipated with some of the
better banding really not impacting those counties much. Chippewa
county is further complicated due to anticipated heavier NW lake
snows developing off Superior on Wednesday. I may remove Mackinac
county from the headlines completely but extend Chippewa and
start focusing on lake effect for Wednesday/Wednesday night.


.NEAR TERM...(Tonight through Wednesday)
Issued at 245 PM EST Tue Dec 5 2017

...Lake snows on the increase...

High impact weather potential...Spread the wealth lake snows through
the near term (and more than likely well beyond). Lingering very
gusty winds.

Pattern synopsis/forecast: NOAM pattern amplification going full
bore, featuring a sharp western ridge and ever deepening Great Lakes
centered troughing. Exceedingly deep low pressure driven by this
pattern reversal has reached maturity over northern Quebec, with a
sub 975mb center. Pretty impressive indeed. Strong pressure gradient
lingers overhead, and when combined with steepening low level lapse
rates via continued cold advection, continues to result in very
gusty southwest winds. Now despite this onslaught of cold air, as is
often the case, increasing over-water delta t`s simply are not
enough to drive organized lake processes, needing some background
moisture to help the precip-generating cause. One such area of
moisture currently overspreading the region, driving an expected
uptick in southwest flow snow showers this afternoon. This initial
round of moisture will be fleeting, with aggressive drying to our
southwest quickly punching northeast into our area early this
evening. Secondary subtle shortwave trough rotating within mean
trough axis brings deeper moisture back overhead later tonight and
Wednesday, reinvigorating the lake machine and bringing some pretty
substantial snow accumulations to the favored lake belts in the

Primary forecast concerns/challenges: Placement of better lake
snows, attendant snow amounts, and associated headline management.

Details: First things first...still very gusty winds requires an
extension of the wind advisory through the remainder of this
afternoon. Really challenging forecast with regards to snow
accumulations tonight. Upstream dry air poses a big problem with
regards to lake effect intensity, especially this evening. Hi-res
guidance, which is usually a bit too robust with lake effect,
remains disconcerting with their very low qpf values until very late
tonight. Perusal of guidance derived soundings shows plenty of
negatives, most noticeably that incoming dry air and a sharp and
lowering subsidence inversion. That trend reverses late tonight with
arrival of that secondary shortwave and its attendant moisture
field. While inversion heights remain limited (about 5kft), solid
moisture profiles above this level (no dry air entrainment into the
cloud tops), delta t`s up around 20c, and good speed shear through a
uniform west/southwest flow in the convective boundary layer all
supports good band organization and an increase in snow intensity
heading toward Wednesday morning. Favored areas for heaviest snows
remain in the Tip of the Mitt counties and along the Lake Huron
shoreline of eastern upper Michigan. Given much later start to band
organization, have scaled back on overnight snow accumulations by a
few inches. Gusty winds will result in blowing and drifting snow,
especially on those north/south oriented roadways. So, despite less
snow than earlier advertised, inherited headlines remain warranted
(a bit later start time) given increasingly difficult travel
conditions. Away from these favored areas, expecting generally light
snow showers and flurries, with limited accumulation.

Lake parameters continue to increase Wednesday as deep moisture
spreads overhead. Relatively shallow inversion levels (still up
around 5kft) about the only negative. Will also need to watch for
some potential afternoon diurnal disruption, although maintenance of
good speed shear should help negate this some. Winds do slowly veer
through the day, with west/southwest flow during the morning become
west/northwest by evening. This will help spread snows around a bit,
preventing any one area from remaining under a dominate band. All
told, expecting several more inches, centered on the
Otsego/Antrim/Charlevoix corridor. Additional accumulating snows
across this same region expected to continue right into Thursday
(see that information in the short term section below). And, to
further complicate maters, those veering winds eventually bring
accumulating snow into the more traditional snowbelts of Chippewa
county, with several inches expected through Thursday. Additional
headlines will likely be needed for Chippewa, but going to let
current ones expire before heading that direction. Winds remain
gusty, with more blowing and drifting snow expected...just
exacerbating the hazardous travel conditions.


.SHORT TERM...(Wednesday night through Friday)
Issued at 245 PM EST Tue Dec 5 2017

...Lake effect snow continues through the forecast period...

High Impact Weather Potential: Accumulating lake effect snow is
expected across sections of northwest lower and eastern upper
through the forecast period with hazardous travel likely.

Pattern Forecast: Little change in yesterday`s thinking regarding
the overall pattern evolution with anomalously deep troughing
anchored across the midsection of the country through the remainder
of the week. As a result, cold temperatures aloft will continue lake
effect snow chances with occasional mid level perturbations
providing an uptick in lake effect snow intensity and coverage at
various times.

Primary Forecast Concerns/Challenges: Lake effect snow threat areas
and amounts through the entire forecast period.

By Wednesday evening, low level flow is expected to have veered from
westerly to west-northwesterly, continuing a reorientation of the
heaviest lake effect snow bands to focus across Charlevoix, Antrim
Otsego, Kalkaska and northern Crawford counties in northern lower
and across northern Chippewa County in eastern upper. H8
temperatures through Thursday in the -13 to -15 C range will result
in plenty of over-lake instability (delta Ts around 20 C). Model
soundings prog an uptick in LES parameters as we head into the
Wednesday evening hours with 450-500 J/kg of lake induced CAPE,
sufficient moisture above a ~6kft inversion and omega pegged
squarely in the DGZ. Gradual veering of the winds continues
throughout the night, becoming more northwesterly by Thursday
morning. This may be the main inhibiting factor, but should by no
means inhibit heavy snowfall under the better structured bands.
Additional snowfall Wednesday night through midday Thursday on the
order of 4-7 inches across the aforementioned locations with a few
inches possible across the far southwestern counties, including the
GTV Bay region.

Confidence decreases to an extent during the day Thursday. By all
means, it will continue to snow (most frequently in NW flow
locales), but a lack of guidance consistency with respect to how
quickly mid level moisture strips out above a sinking subsidence
inversion precludes much confidence in snowfall amounts Thursday
afternoon and Thursday night. Winds begin to back more westerly once
again Thursday night before turning west-southwesterly during the
day Friday ahead of a clipper set to drop into the northern/western
Great Lakes late Friday afternoon/Friday night. As a result,
steadiest snow showers should become reoriented across the Tip of
the Mitt for a period of time late Thursday night into Friday.

With respect to headlines, in collaboration with GRR, will go ahead
and issue Winter Weather Advisories for the remaining counties along
the Lake Michigan shoreline to as far east as Crawford and Missaukee
from Wednesday afternoon through Thursday afternoon. It`s likely
that a new headline will be needed for Chippewa County once the
ongoing advisory ends...likely to be done late tonight or during the
day tomorrow.

.LONG TERM...(Friday night through Tuesday)
Issued at 245 PM EST Tue Dec 5 2017

High impact weather potential: Active pattern will continue the cold
wintry weather across much of northern Michigan through the weekend.

Deep upper trough which settled over the Great Lakes earlier in the
week, will remain over the region through the forecast period. 850mb
temps in this pattern will be around -16c/-18c this weekend, while a
second shot or reinforcing cold air drops mid level temps to around
-21c by Tuesdsay. A couple of clippers sweeping across the
 northern Great Lakes Friday night and Monday, will enhance
 westerly flow lake effects, generating several rounds of snow
 over northern Michigan through the forecast period.


.AVIATION...(For the 00Z TAFS through 00Z Wednesday evening)
Issued at 728 PM EST Tue Dec 5 2017

Cold air continues to stream into the region on very gusty
southwest winds. Lake induced clouds and snow showers cover a good
portion of northern lower Michigan although with largely VFR
cigs. Snow showers are most persistent and robust through the PLN
terminal site where CIGS are MVFR with some heavier snows
occurring. That will pretty much remain the case through tonight
with the most persistent snows impacting PLN.

Better moisture rotates into the region on Wednesday and should
bring an uptick to lake effect snow showers to the snowbelts of
northern lower Michigan. Still anticipate overall MVFR conditions
at MBL/TVC/PLN through the day.

Winds...have backed off some. But SW gusts of 25 to 35 knots will
remain common through tonight...with gusts slowly diminishing
through the day Wednesday while winds veer more westerly.


Issued at 245 PM EST Tue Dec 5 2017

While winds are slowing subsiding, gale producing west winds
are still expected across all nearshore waters through at least
Wednesday morning. Winds further decrease in speed Wednesday night
and Thursday as they become northwest. A brief period of sub-
headline winds looks reasonably by later Thursday, with winds once
again becoming quite gusty to end the work week.


MI...WINTER WEATHER ADVISORY from 4 PM Wednesday to 4 PM EST Thursday
     for MIZ020-025-026-028-031>033.
     WINTER STORM WARNING from noon Wednesday to 4 PM EST Thursday
     for MIZ021-022-027.
     WINTER WEATHER ADVISORY until 7 AM EST Wednesday for MIZ008-015.
     WINTER STORM WARNING until 5 PM EST Wednesday for MIZ016-017.
     WINTER STORM WARNING until 4 PM EST Thursday for MIZ019.
LH...GALE WARNING until 11 AM EST Wednesday for LHZ345>349.
LM...GALE WARNING until 11 AM EST Wednesday for LMZ323-341-342-
LS...GALE WARNING until 11 AM EST Wednesday for LSZ321-322.


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