Area Forecast Discussion
Issued by NWS Gaylord, MI

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678
FXUS63 KAPX 151421
AFDAPX

Area Forecast Discussion
National Weather Service Gaylord MI
921 AM EST Fri Dec 15 2017

.UPDATE...
Issued at 920 AM EST Fri Dec 15 2017

Low pressure continues to slowly organize over eastern
Lake Superior, with its attendant cold front/surface trough
(partially lake augmented) cutting into northwest lower Michigan.
Lake snows continue, at time fairly heavy, across northwest lower
Michigan. Low level shear ahead of the frontal boundary has
prevented much band organization, keeping heavier snow showers
rather transient and "blotchy". Best Superior snows remaining
offshore of Whitefish Point, at least for the time being. Cold front
will clear the area from west to east into early this afternoon as
low pressure pivots into/across northern Lake Huron. Lake snows will
transition to a more of a west to west/northwest regime, targeting
the traditional snowbelt locations. Gradual loss of synoptic
contribution and a slowly lowering convective cloud depth should
limit snow intensity. However, development of much more uniform flow
within the convective layer will likely support better band
organization, helping offset decreasing snow intensity some. Upshot
to the above, still expect a couple more inches in those favored
areas. Will leave inherited headlines untouched for now, but may be
able to drop areas south of M-72 this afternoon.

&&

.NEAR TERM...(Today through Tonight)
Issued at 338 AM EST Fri Dec 15 2017

...Another round of lake effect snow ramping up...

High impact weather potential...lake effect snow, locally heavy
over far northern lower MI.

And on and on and on it goes. (Though we will see a break after this
batch.) Shortwave will dig across northern MI this morning, in
advance of an upper low dropping into far ne Ontario. Lake effect
snow showers are already responding in w/wsw flow regimes, and will
remain vigorous over the next 9-12 hours. Snow trends are the main
concern.

Strongest returns on radar presently found from northern Leelanau Co
up to almost the Bridge, and are most impressive in Emmet Co.
This is as it should be with wsw 1000-850mb flow. There is likely
still a touch more backing expected in the pre-dawn hours, but
more substantial veering will occur after 12Z as a surface low
tracks from Superior to far northern Lk Huron. We will be wnw by
18z, and be a borderline wnw/nw thru this afternoon. By then
though, moisture will be rapidly stripping out as the system
departs. 850mb temps might wobble up as warm as -13C this morning
in the warm advection portion of the system, but will dip 1 to 4C
by early evening when cold advection inevitably returns.

Best snowfall will definitely be in the 1st half of the day, with
synoptic forcing for ascent and associated moisture acts on top of
lake processes. Should see inch/hour accums in spots this morning,
primarily in the tip of northern lower. The DGZ is nicely placed
within the max upward omega in the pre-dawn hours. But Nam Bufr
data at PLN suggests max omega drifts below the DGZ during the
morning. So snow-liquid should be above 20-1 now, but might drift
closer to 20-1 as we go thru the morning. Snow accums will be 4-9
inches in the 1am-1pm window today across Emmet/Charlevoix Cos and
the nw half of Cheboygan Co. Snowfall rates/amounts will be
considerably lighter as you head south into northern lower, where
the upstream Lake MI fetch is much shorter.

Headlines are mostly fine; the real question is whether the tip of
the mitt warrants an upgrade to warning. Forecast amounts at the
high end edge into warning criteria (8" in 12 hours), and precip
rates are already getting healthy at times will remain so. Not much
blowing/drifting today, it will get a touch breezier this afternoon
as the system departs, but not enough to warrant major concerns. I
think we can skirt by with an advisory headline, but this is a close
call for certain.

Max temps low/mid 20s.

Tonight...leftover baroclinic zone sharpens up to our s and w, with
moisture deepening downstate, over WI, and in northern MN. This does
not pose a substantial precip threat for us, but will contribute to
cloud cover in the nw half of the forecast area. As for lake effect:
high pressure will edge se-ward toward the north tip of Superior.
Winds will veer more nw and eventually n, while lightening up
considerably. The incoming airmass is becoming cooler (850mb temps
to -18c over upper MI), but also drier. Inversion heights dropping
from 6k ft in the evening, to 4k ft overnight. Still very healthy
coverage of (relatively light) lake effect snows in the evening, but
coverage will diminish to some degree overnight. Accums of 1-3"
expected over the high terrain of n central lower MI, and around an
inch in western Chip Co, less elsewhere.

Min temps in the teens in northern lower, single digits above zero
in eastern upper, around zero in the St Marys Valley.

&&

.SHORT TERM...(Saturday through Sunday)
Issued at 338 AM EST Fri Dec 15 2017

...Fairly quiet...

High Impact Weather Potential: None.

Primary Forecast Concerns/Challenges: Timing of the ending of lake
effect Saturday morning then whether or not to include pops Sunday.

Lake effect snow showers should quickly diminish Saturday morning as
a fairly strong area of high pressure ridges in from the north
(along with much drier air). We should remain under the influence of
this high through Saturday night resulting in precipitation free
conditions. As the high heads off to the east warmer and more moist
southerly winds kick in. Models vary on the extent/strength of an
associated ribbon of moisture. At this point will limit chances for
snow showers across the northern third of the forecast area for
Sunday afternoon. Chilly Saturday with highs ranging from the middle
teens north to the middle 20s southwest. Lows Saturday night in the
single digits and teens above zero. Milder Sunday with highs in the
middle 20s to the lower 30s.

.LONG TERM...(Sunday night through Thursday)
Issued at 338 AM EST Fri Dec 15 2017

...Lake effect Tuesday then perhaps a bigger system Thursday...

Lingering small chances for snow showers Sunday night then mainly
dry Monday as we await the arrival of the next short wave and
associated cold front Monday night. This system will lead to a
chance for snow showers...perhaps even mixed with rain near the lake
shores. Another shot of colder air and resultant lake effect snow
showers (west northwest flow?) arrive Tuesday into Tuesday
night...perhaps lingering into Wednesday. Extended models then vary
on the track of a potential deepening area of low pressure emerging
out of the central states which looks like it will head toward the
western Great Lakes. This system has the potential to produce
widespread accumulating snowfall Wednesday night into Thursday
across northern Michigan...and depending upon the track maybe even a
mix with or changeover to rain or freezing rain at some point just
beyond the scope of this forecast Thursday night or Friday morning.
Another shot of much colder air is then shown to move in behind this
system just in time for Christmas.

&&

.AVIATION...(For the 12Z TAFS through 12Z Saturday morning)
Issued at 642 AM EST Fri Dec 15 2017

IFR this morning, then improving.

Low pressure over eastern Lake Superior producing lake effect and
lake enhanced snow across northern MI this morning. IFR conditions
expected, with LIFR vsbys at PLN at times. Conditions will improve
after the system departs, beginning this afternoon, with snow
showers becoming less widespread and intense. That trend really
kicks into gear tonight. All sites expected to become MVFR and
then VFR with time.

Southerly winds in most spots this morning, will becoming westerly
during the morning, and will be a bit gusty at times thru early
evening.


&&

.MARINE...
Issued at 338 AM EST Fri Dec 15 2017

Westerly winds will increase as low pressure passes just north of
the area today. Advisory-level conditions expected on most waters.
Lighter winds by Sat morning as high pressure noses toward the
northern tip of Superior.


&&

.APX WATCHES/WARNINGS/ADVISORIES...
MI...WINTER WEATHER ADVISORY until midnight EST tonight for MIZ008-
     016-017-019>022-025>028-031-032.
LH...SMALL CRAFT ADVISORY until 5 AM EST Saturday for LHZ347>349.
LM...SMALL CRAFT ADVISORY until 5 AM EST Saturday for LMZ323-342-
     344>346.
LS...SMALL CRAFT ADVISORY until 5 AM EST Saturday for LSZ321.
&&

$$

UPDATE...MSB
NEAR TERM...JZ
SHORT TERM...AS
LONG TERM...AS
AVIATION...JZ
MARINE...JZ



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