Area Forecast Discussion
Issued by NWS Gaylord, MI

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FXUS63 KAPX 150004
AFDAPX

Area Forecast Discussion
National Weather Service Gaylord MI
704 PM EST Thu Dec 14 2017

.NEAR TERM...(Tonight through Friday)
Issued at 328 PM EST Thu Dec 14 2017

...Significant lake snow accumulations through Friday evening...

High impact weather potential...Lake effect snow, at times heavy,
expected across the traditional snow belts overnight through Friday
evening.

Pattern synopsis/forecast: Talk about stating the obvious, but area
remains firmly entrenched in broad eastern NOAM centered trough axis.
Well below normal temperatures the result, with current readings
once again struggling through the teens and lower 20s. Simple
magnitude of the over-water thermal gradient continues to kick off
scattered light lake effect snow showers, fanning out across the
snowbelts as winds steadily back more westerly. Plenty of lower
amplitude waves within the larger trough, the most prominent of
which shows up nicely on water vapor diving southeast across western
Ontario. One has to look just a bit further upstream to see the next
wave in the wave train, it to diving southeast across northern
Manitoba. Both of these waves will dig across the northern Lakes,
the first arriving later tonight, with that Manitoba wave arriving
later Friday. Attendant dynamics/moisture working on a still very
favorable and intense over-water thermal gradient sets the stage for
a round of rather robust lake effect snows to end this work week.

Primary forecast concerns/challenges: Lake effect snow placement,
amounts, and attendant headline decisions through Friday night.

Details: Synoptic scale moisture (already well evident just
upstream) steadily increases tonight as that lead wave digs into the
northern Lakes. Lake effect parameters ramp up accordingly, with
inversion heights spiking north of 10kft by morning, with said
moisture preventing any dry air entrainment into the increasing
convective cloud depth. Figuring the exact flow regime a much more
formidable forecast challenge. Pattern recognition strongly supports
Lake Superior low pressure development overnight, with a sharpening
surface trough extending down the length of Lake Michigan. These
should force a more backed low level wind response, likely taking on
a full southwest direction during the early morning hours. This
would of course target better Lake Michigan producing accumulating
snows into the Tip of the Mitt counties, while punting Lake Superior
convection offshore of Whitefish Point (but not perhaps until an
enhanced convergence band impacts areas near Whitefish Point with
accumulating snow this evening). Lake Michigan surface trough pivots
into the northwest lower coast toward sunrise, likely with an
attendant band of enhanced snowfall. All told, looking like several
inches of new snow tonight north of the M-32 corridor in northern
lower, with a bit lesser amounts in the other snowbelts (although
much of that may come quickly with that surface trough early in the
morning).

Surface trough races across the area during the morning as Lake
Superior low pressure follows tightest thermal gradient into
northern Lake Huron. Convective boundary layer flow veers to
northwest after its passage, targeting lake snows into the
traditional snowbelt locations. Guidance not quite as impressive with
regards to inversion heights and deep layer synoptic moisture
contribution as that secondary wave passes by a bit further north
than earlier projected. Still, lake parameters remain quite robust,
with lake induced convective depths up near 10kft and omega pegged
in-cloud and within the favored dendritic growth layer. Some hints
of enhanced convergence along lake aggregate trough axes, one
focused near or just west of northwest Chippewa County with the
other near the M-32 corridor of northwest lower Michigan. Upshot to
the above, expect several more inches of snow, especially so along
that M-32 corridor and in far northwest Chippewa County.

Headlines: Winter weather advisories will be issued for a handful of
favored lake effect counties tonight through at least the first half
of Friday evening across northwest lower and eastern upper Michigan.
While no doubt some isolated areas with near/exceed warning level
snow amounts by later Friday night, lack of blowing and drifting
snow and expected isolated nature of those higher end totals
precludes issuing warnings at this time.

&&

.SHORT TERM...(Friday night through Sunday)
Issued at 328 PM EST Thu Dec 14 2017

...Diminishing snow Saturday...

High Impact Weather Potential...Freezing drizzle potential Sunday.

Pattern Synopsis/Forecast...A clipper will continue to drop south
from James Bay through the day Saturday, providing more of a
glancing blow for us as it moves through southern Ontario and into
Quebec. High pressure will follow close behind, with the center
passing just south of James Bay through the weekend. Throughout the
week, a larger synoptic system from early in the week and the
clipper system that just moved over us will work their way
northeast, helping to weaken the downstream blocking that has been
keeping this prolonged period of cold air drainage going.

Primary Forecast Concerns...With snow diminishing through the day
Saturday, the primary concern turns to the potential for freezing
drizzle.

A brief period of lake effect will linger into early Saturday
morning as cold high pressure moves into the region. The combination
of large scale subsidence and a drying airmass should suppress precip
chances as the day goes on. Sunday poses a bit of a challenge at
this point. As deep moisture strips out and ice nucleation could be
lost, there is a potential for some freezing drizzle. Always
precarious this far out as minor fluctuations can make a large
difference, but it is worth at least a mention and will be left in
the inherited grids. With the pattern getting more zonal,
temperatures will begin to moderate Sunday, with highs getting above
freezing early next week.

.LONG TERM...(Sunday night through Thursday)
Issued at 328 PM EST Thu Dec 14 2017

High Impact Weather Potential: Potential for accumulating lake
effect snow Tuesday/Wednesday...maybe some synoptic snow Thursday?

Breakdown of strong +PNA ridge along the west coast underway...
overall evolution of the large scale pattern by the start of next
week is a trend to something a little less amplified with more of a
split trough over the Rockies spilling into a quasi-zonal pattern
over the eastern half of the CONUS.  Eventually...expect northern
branch height falls to spread across the Plains/Midwest and into the
Great Lakes by midweek...although troughing looks to be short-lived
as heights rise over the eastern states with renewed troughing into
the intermountain west Thursday as pattern adjusts to a sharply
negative trend in the EPO (almost like a discontinuous retrogression
current pattern with upper ridge axis setting up over the eastern
Pacific/Alaska) (and probably opens the door for another cold push
by the weekend before Christmas).

Biggest potential impacts next week will deal with a return of cold
air with a short wave trough/frontal passage Tuesday and a decent
shot of accumulating lake effect snow Tuesday night into
Wednesday...then with next trough moving into the west potential for
cyclogenesis along associated baroclinic zone Thursday.  While there
is agreement on this idea even this far out...lots of room for
change going forward.  But at the very least would bring another
chance for widespread synoptic snow to the region heading into the
latter half of the week.

&&

.AVIATION...(For the 00Z TAFS through 00Z Friday evening)
Issued at 651 PM EST Thu Dec 14 2017

Currently in a transition between systems, as the previous system
moves out, and its lake effect snow diminishes, and the next
system is on our door step, about to reinvigorate the lake effect
from a different direction (SW). The sfc trough will move through
the forecast area by Friday morning (~12z), producing NW flow lake
effect again. So over the next 24 hours, Cigs and Vsbys will
bounce around from VFR currently to MVFR/IFR as the lake bands put
snow into TVC, MBL, and PLN. APN, being on the east side of the
state will be the least affected as the mainly system snow will
remain light and keep things VFR and MVFR.

&&

.MARINE...
Issued at 328 PM EST Thu Dec 14 2017

Small craft advisory conditions return very late tonight
through Friday night as gusty west to northwest winds develop.
Current trends support winds and waves remaining below advisory
levels for the upcoming weekend.


&&

.APX WATCHES/WARNINGS/ADVISORIES...
MI...WINTER WEATHER ADVISORY from midnight tonight to midnight EST
     Friday night for MIZ016-017-019>022-025>028-031-032.
     WINTER WEATHER ADVISORY from 10 PM this evening to midnight EST
     Friday night for MIZ008.
LH...SMALL CRAFT ADVISORY from 5 AM Friday to 5 AM EST Saturday for
     LHZ347>349.
LM...SMALL CRAFT ADVISORY from 5 AM Friday to 5 AM EST Saturday for
     LMZ323-342-344>346.
LS...SMALL CRAFT ADVISORY from 11 AM Friday to 5 AM EST Saturday for
     LSZ321.
&&

$$

NEAR TERM...MB
SHORT TERM...AM
LONG TERM...JPB
AVIATION...JL
MARINE...MB



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