Area Forecast Discussion
Issued by NWS Gaylord, MI

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FXUS63 KAPX 121532
AFDAPX

Area Forecast Discussion
National Weather Service Gaylord MI
1032 AM EST Fri Jan 12 2018

.UPDATE...
Issued at 1027 AM EST Fri Jan 12 2018

Synoptic snow across far southeast counties continues to progress
off to the east and will end shortly. Light lake effect snow
showers continue to slowly shift west as the flow goes from north
northwest to north. Cold today will low wind chills (mainly the
single digits above and below zero). Weak/light lake effect
continues, mainly in the Grand Traverse Bay region and up near
Whitefish (under a half inch of accumulation). Temperatures will
be steady to slowly falling...bundle up.

&&

.NEAR TERM...(Today through Tonight)
Issued at 320 AM EST Fri Jan 12 2018

...Temperatures running 30 to 40 degrees colder today...

High Impact Weather Potential...Icy road conditions this morning due
to rapid freezing of any standing water/slush. Much colder
temperatures today/tonight with very cold wind chills of -10 to -20
degrees by tonight.

Pattern Synopsis/Forecast...Arctic front now pushing through the
Thumb with strong cold air advection in its wake. Transition from
rain to snow has been fairly quick overnight with only a very brief
period of minor freezing rain and/or sleet in between. Expect the
few remaining pockets of rain down near Saginaw Bay (where
temperatures are barely hanging on above freezing) will turn to snow
very soon as temperatures continue to plummet. Will continue to
stress icy road conditions in HWO and SPS given the quick freeze up
of standing water/slush, which could make for a slick morning
commute.

Synoptic precipitation largely unimpressive across northern
Michigan early this morning with mostly weak forcing and a drier
airmass advecting into the region. Light synoptic snow showers
moving into eastern Upper are tied to PVA associated with an
elongated lobe of vorticity in the mid-level trough axis as well as
a right entrance region of an upper jet streak. Expect this activity
to slowly diminish over the next few hours as it gradually lifts NE.
More vigorous band of precipitation downstate continues to lift NE,
associated with frontogenesis along the cold front. This
precipitation (soon to be all snow) will stream over our
southeastern counties through the rest the early morning hours
before pushing out over Lake Huron mid to late morning. Up to an
inch or so of snow will be possible through this morning from
Gladwin to eastern Alcona counties.

During the day today, synoptic activity will exit northern Michigan
with lake effect activity becoming more of the focus as
progressively colder 850mb air filters into the region. Lake effect
snow showers are already well underway across the central UP where
850mb temperatures have dropped to -16 to -18C. By afternoon, 850mb
temperatures over our forecast area will drop to roughly around
-20C. Low level flow will generally be northerly, perhaps a little
more NNW this afternoon over eastern Upper. This will confine lake
effect activity to western Chippewa/Mackinac counties and mainly
west of M-37 through the day. Forecast soundings show largely
unimpressive low level RH, however, with a dry inverted-V
temperature and dewpoint profile in the boundary layer. This
combined with inversion heights only up to 3-4 kft will really limit
lake effect activity overall with minimal snowfall accumulations
expected by daybreak Saturday...perhaps up to an inch west of M-37
and western Chip/Mack counties, though a little more in the northern
tip of Chippewa County.

Drier air filtering into the region will lead to a decent amount of
sunshine by this afternoon, especially along and east of I-75.
Nevertheless, a MUCH colder airmass overhead and brisk northerly
winds gusting 20-30 mph will make it feel bitterly cold in
comparison to yesterday, with highs running about 30-40 degrees
colder today, generally in the teens to low 20s. Clouds will expand
across northern Michigan tonight, but temperatures will still drop
into the single digits below zero across much of eastern Upper and 0
to 12 degrees for northern Lower. Very cold wind chills today,
dipping to -10 to -20 degrees by tonight across much of the area.

&&

.SHORT TERM...(Saturday through Sunday)
Issued at 320 AM EST Fri Jan 12 2018

...Weak Lake Effect Snow...

High Impact Weather Potential...Very cold wind chills in E Upper (-
25F) and at this time -15F in NE Lower. The moderate amounts of LES
in western Mackinac County Sunday night into Monday morning.

Pattern Synopsis/Forecast...500 mb longwave trough is over the Upper
Great Lakes for Saturday with another shortwave trough rotating into
it on Sunday. This keeps us in the cold air through the 48 hours of
the weekend from Saturday morning to 12z/Mon. 850 mb temperatures
stay sub -20C 12z/Sat to 12z/Sun. This brings us plenty of
instability, but the moisture is on the low side as the rh in the
850-700 mb layer varies from about 40% to about 60%  with NNW winds
and with the ice coverage, the fetches will be limited, to will
minor to light lake effect snow amounts. Sunday morning as the next
shortwave trough begins to dig into the longwave trough, the
shortwave spins up a sfc low during the day on Sunday, which turns
the winds SW, warms the 850 mb temperatures to -17c by 00z/Mon. There
is still good instability, and the temperatures allow for better
dendrite growth. Not to mention that the SW to SSW flow through the
day brings better fetches. The all of the models start pegging
moderate amounts of snow in western Mackinac county.

Primary Forecast concerns...The sfc high trying to nose into the
Upper Great Lakes look to produce some clearing and subsequent land
breeze off of the hills north of CYAM. This will produce the -5F to
-10F temperatures and with the wind speeds, will expect near -25F
wind chills. the main concern with this is whether the lake
aggregate trough to the west of the high nosing into Ontario can be
shifted a little more west. If so, then the issues spread farther to
the west in E Upper, with little lake effect in the western parts of
the county.

The other thing will be the SW to S flow pattern on Sunday night.
trusting the models to have  this figured out 48 hours out is
tricky. However, it looks likely that there will be light to
moderate snow near this area. The question is does the bands set up
longer east like near Brevort, or does it set up farther west closer
to ISQ? For now, the models have it between the two, which puts the
best snow near Engadine.

.LONG TERM...(Sunday night through Thursday)
Issued at 320 AM EST Fri Jan 12 2018

...Below Normal Temperatures then Uncertainty...

Extended (Monday through Thursday)...500 mb shortwave looks to move
the pattern out of the longwave that is over the Upper Great Lakes
on Monday to lifting it out by Wednesday and allowing the 500 mb
ridging to begin Wednesday night into Thursday. However, confidence
is low for the forecast as the models converge with the solutions
Thursday night. The GFS has more of a flat ridge/zonal flow that
will bring in more precipitation and based on the 850 mb
temperatures, that precipitation will be snow. The ECMWF has an
amplified ridge that keeps the weather Clear, and possibly mild.

So expect various amounts of synoptic and Lake Effect snow through
Tuesday/Wednesday, then some sort of uncertain moderating trend for
the end of the week.

&&

.AVIATION...(For the 12Z TAFS through 12Z Saturday morning)
Issued at 637 AM EST Fri Jan 12 2018

Widespread snow showers affecting APN will continue to gradually
push east over the next couple hours. Otherwise the pattern is
transitioning to lake effect, with NNW flow bands showing an
uptick over the last couple hours. Expecting winds will eventually
become more northerly later this morning, which would confine the
snow bands to mainly TVC and MBL through the day into tonight.
Activity should generally be light with minimal accumulations,
though some visibility restrictions will be possible in the
heavier bands. Winds will be fairly strong through the day with
gusts of 25-30 knots, slowly diminishing later tonight. Ceilings
generally MVFR, though some scattering is expected at APN and PLN
this afternoon.


&&

.MARINE...
Issued at 320 AM EST Fri Jan 12 2018

Gusty northerly winds will continue today with gale force gusts this
morning on portions of Lake Michigan and Lake Huron. Winds will
gradually decrease from this afternoon through Saturday, backing a
little more to the NW as cold high pressure over the Dakotas slowly
builds east. A much colder airmass will be in place through the
weekend with some lake effect snow showers.


&&

.APX WATCHES/WARNINGS/ADVISORIES...
MI...NONE.
LH...GALE WARNING until 1 PM EST this afternoon for LHZ347>349.
LM...GALE WARNING until 1 PM EST this afternoon for LMZ323-342-
     344>346.
LS...NONE.
&&

$$

UPDATE...AS
NEAR TERM...MK
SHORT TERM...JL
LONG TERM...JL
AVIATION...MK
MARINE...MK



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