Area Forecast Discussion
Issued by NWS Gaylord, MI

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FXUS63 KAPX 211708

Area Forecast Discussion
National Weather Service Gaylord MI
1208 PM EST Sun Jan 21 2018

Issued at 1107 AM EST Sun Jan 21 2018

Feeling more and more comfortable with just issuing advisories
over the next few hours, due to projected snowfall amounts in
eastern upper and snow/ice combination in nrn lower. In nrn lower,
snow first then icing will at least likely limit ice impacts.
Refined snowfall and icing totals will be coming out over the next
few hours as well.

UPDATE Issued at 1034 AM EST Sun Jan 21 2018

Updated the forecast this morning for stratus and fog very slowly
creeping north this morning with dense fog impacting the M-55
corridor as well as portions of eastern upper. Meanwhile more of
the same with mid and upper level cloud streaming over nrn
Michigan, in fast upper level zonal flow, with moisture being
primarily fed by developing low pressure in the central plains.
This will be the feature of prime interest, which will bring
increasing chances for precipitation late tonight into Monday
night. Nrn Michigan will be getting accumulating snows north with
a wintry mix and possible significant icing south of M-68 and
generally east of US 131. Will likely issue a quick watch here
soon, with more definitive snow/ice advisories or warnings later
this afternoon. Whatever it may be, nrn lower Michigan should
prepare for at least some ice, and snow along and north of M-72.
Mainly just snow in eastern upper.


.NEAR TERM...(Today through Tonight)
Issued at 335 AM EST Sun Jan 21 2018

...Mild again today with increasing chances of precip tonight...

High Impact Weather Potential...Areas of light freezing precip
tonight possibly causing some slippery travel.

Pattern Synopsis/Forecast...Low pressure continues to develop to the
lee of the Rockies over the Central Plains early this morning.
Associated warm front extends eastward from the developing low thru
Kansas and Missouri into the Ohio Valley. Increasing moisture
continues to gradually advect northward along and north of this
boundary thru Illinois and Indiana into Wisconsin and Michigan...
resulting in increasing clouds...lowering cigs and widespread fog.
Closer to home...patchy fog is beginning to develop across southern
sections of our CWA along the northern periphery of this increasing
moisture shield...but low clouds remain south of our area for now.
Temps remain relatively mild this morning (for late January
anyway)...with most locations in the upper 20s to lower 30s.

As we head into today and tonight...deepening surface low center
will begin to lift NE out of the Central Plains...reaching the
Iowa/Missouri border by 12Z Monday. The deep/closed upper low will
be close in tow right behind the surface low center. Associated warm
front will lift northward into southern Lower Michigan by evening
and will stall there for the remainder of the night. Some
strengthening in WAA today will boost temps back into the upper 30s
and lower 40s today despite increasing/thickening low cloud cover as
low level moisture advects into the region from south to north.
Still appears any precip chances will hold off until tonight...
increasing from south to north as moist isentropic ascent (I295)
increases along and north of the warm front. All precip will be
rather light...mainly of the patchy drizzle/freezing drizzle/light
snow variety...due to limited depth of moisture during the onset. At
this point...precip intensity should be sufficiently light enough to
preclude the necessity of any headline for now. Will certainly keep
a close eye on how the onset of this event evolves. Low temps
tonight will range from the lower 20s in eastern Upper Michigan to
the lower 30s in southern sections of our CWA.


.SHORT TERM...(Monday through Tuesday)
Issued at 335 AM EST Sun Jan 21 2018

...Messy wintry mix will impact travel...

High Impact Weather Potential...Significant snow and ice
accumulations possible, which will make for difficult, if not
hazardous, travel.

Pattern Synopsis/Forecast...Well-advertised storm system will slowly
travel from NW Missouri Monday morning through northern Lower
Michigan by Tuesday morning, departing into Quebec by Tuesday
evening. The system will interact with a very moist environment to
produce widespread precipitation as it crosses the Upper Great
Lakes, with PWATs over northern Michigan ranging from 0.5" to
greater than 0.75" (2 to 4 standard deviations above the mean for
late January). Strong low level thermal gradient across northern
Michigan will lead to a variety of precip types until colder air
arriving behind the departing system brings a change to all snow
early Tuesday. This will be followed by a transition to lake effect
processes by Tuesday afternoon.

Primary Forecast Concerns...Precipitation types and amounts and
potential headline decisions.

Over the last 24 hours, models have come into better consensus
regarding the track of this system, roughly taking it just south of
a line from Ludington to Alpena as it crosses northern Lower late
Monday night. However, there remain some subtle variances in how far
north the warm air will progress, which will have a huge impact on
low level thermal profiles and resultant ptypes. Among the 21.00Z
suite of deterministic models, the GFS and GEM take the surface 32F
isotherm nearly all the way north to Straits Monday evening, while
the NAM and ECMWF take it only to about M-32. Have leaned more
toward the slightly warmer end of guidance with this forecast.

Very favorable forcing will move into the area on Monday, consisting
of strong upper divergence, PVA, warm air advection, low level jet
nosing into the area, and impressive f-gen banding. Generally the
strongest forcing won`t arrive until afternoon, when the steadier,
heavier precipitation is expected to begin. As the core of this
wound up system enters northern Michigan Monday evening/night, a
somewhat muddled dry slot will strip out moisture from top down.
Moisture will increase again within the column towards daybreak
Tuesday on the backside of this departing system. Impressive QPF for
this event, ranging from around 0.60" over western Chippewa/Mackinac
counties to around an inch near Lake Huron.

Precip type...Still looking like mainly snow across eastern Upper,
but as the column dries out from top down Monday evening/night, that
may lead to a loss of ice crystals in the clouds and hence a period
of freezing drizzle/rain. Northern Lower ptype forecast remains a
challenge given models` continued variances in low level thermal
profiles. A wintry mix is still expected with snow, freezing rain,
and sleet overspreading the area Monday morning. As surface
temperatures slowly warm through the day from south to north, will
see a corresponding gradual transition to rain migrating north
towards the Straits. Colder air filtering in on the backside of this
system Tuesday morning will bring a rather quick transition to all
snow across the forecast area, with synoptic snow giving way to
some lake effect snow showers Tuesday afternoon.

Precip amounts...Given the impressive amount of QPF with this
system, a significant amount of snowfall is expected across eastern
Upper and Tip of the Mitt from Monday morning through Tuesday
morning. Within that 24-hour period, the current forecast calls for
potentially 4-7" between M-32 and the Bridge and around 7-9" across
eastern Upper. This will be a wetter, heavier snow with SLR
averaging around 10:1 across the area. Much lower confidence in
potential ice amounts. Certainly plausible that some northern Lower
locales see 0.1 to 0.2" of ice accumulation, but there`s still too
much model variance at this point with regard to thermal profiles to
pin down which locations will be most impacted. So, expect
additional adjustments to snow/ice forecasts today following later
model runs.

Potential headlines...Potential snowfall across eastern Upper and
Tip of the Mitt look to fall short of winter storm watch criteria
but would definitely warrant an advisory later on. Potential ice
accumulations across northern Lower also look to fall short of watch
criteria but would warrant an advisory later on. Given we`re still a
few periods out and confidence remains low in potential snow/ice
amounts, will hold off on any headlines for now.

.LONG TERM...(Tuesday night through Saturday)
Issued at 335 AM EST Sun Jan 21 2018

High Impact Weather Potential...Minimal.

Lake effect snow showers will continue around and south of the Grand
Traverse Bay region through Wednesday, when a considerably drier
airmass settles into the region with a large surface high. Generally
quiet weather then expected through Friday when temperatures will
warm back into the low 40s for much of northern Lower. Another
synoptic system is progged to track through the Upper Midwest on
Saturday, passing well to our north and bringing mainly rain to
northern Michigan.


.AVIATION...(For the 18Z TAFS through 18Z Monday afternoon)
Issued at 1200 PM EST Sun Jan 21 2018

Low clouds and fog have stopped advancing northward due to mixing
out, but will likely continue to impact MBL for at least a couple
more hours. All other airports still to see some higher level
cloud passing overhead. Heading through tonight, lowered VSBYS and
CIGS will be the theme with perhaps some drizzle/freezing drizzle
developing late and into Monday. Precipitation turns more rain for
TVC/MBL while more significant snow and freezing rain will impact
PLN/APN. Icing potential through the day of around a tenth of an
inch and snow of 1-3 inches. The light wind regime will turn more
easterly with winds increasing Monday and some gustiness, but the
low levels will be rather stable for any significant gusts. Maybe
some low end LLWS to occur, but confidence is not too high in that
scenario right now.




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