Area Forecast Discussion
Issued by NWS Gaylord, MI

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856
FXUS63 KAPX 201712
AFDAPX

Area Forecast Discussion
National Weather Service Gaylord MI
1212 PM EST Sat Jan 20 2018

.UPDATE...
Issued at 942 AM EST Sat Jan 20 2018

See very little need for updates. Subtle hints of a weak frontal
boundary draped down across nrn lower, with another more defined
boundary from south central Canada through Lake Superior and back
up into low pressure in Quebec. Flow in the mid levels was rather
convergent with a srn branch coming out of the Rockies and the nrn
branch coming out central Canada. There was a weak shortwave in
Manitoba that was working it`s way ESE within a relatively higher
moisture regime, tracking along the aforementioned more defined
frontal zone. The shortwave dampens with time, but as it passes
late this afternoon and tonight and there is another subtle hint
that FGEN comes into play, and the front/deeper moisture sags
toward Chippewa county. Doubt forcing will be strong enough for
any light precip, but it would be there. Otherwise, it`s still a
nearly continuous feed of higher level moisture with the sub 650mb
layer remaining dry. No precipitation anticipated.

&&

.NEAR TERM...(Today through Tonight)
Issued at 307 AM EST Sat Jan 20 2018

...Well above normal temperatures to continue...

High impact weather potential: Minimal.

Pattern synopsis/forecast: Fast zonal flow across the northern Conus
has engulfed the area with much modified Pacific originated air.
Nocturnal influences doing little on this modified airmass, with
current reading still mostly in the 30s. Plenty of high level clouds
streaming overhead, a typical by-product of these fast zonal
regimes. Weak (and I mean...weak) cold front crossing the northern
Lakes at this early hour, coming through practically unnoticed,
other than a slight wind shift to a more westerly direction and
slight off-the-deck cooling.

Really, not a whole lot of change expected through tonight as area
will remain squarely under the zonal and significant wave lacking
regime.

Primary forecast concerns/challenges: Cloud and temperatures trends
throughout and possibility for a bit of fog tonight.

Details: Despite slow cooling aloft, low level airmass has no source
of cold air, resulting in high temperatures today very similar to
those experienced yesterday (upper 30s and lower 40s). Plenty of
high clouds yet to stream overhead, keeping skies partly to mostly
cloudy. Pressure gradient really relaxes with time today, with
mostly light west to southwest winds the result.

And, not a whole lot of change heading through tonight. Some
indication of a growing elevated fgen response within tightening
thermal gradient, bringing a more robust mid level cloud deck along
with it. Dry wedge centered below H7 level should prevent any
precipitation from reaching the surface. Only other issue is some
expected fog development, with increased surface based moisture from
snow-melting processes. Don`t think this will get too out of hand,
but may see isolated areas of low visibility. Lows tonight look to
be a degree or two colder than current readings, but still well
above normal for this time of year.

&&

.SHORT TERM...(Sunday through Monday)
Issued at 307 AM EST Sat Jan 20 2018

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

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

Pattern Synopsis/Forecast...A cyclone developing lee of the Rockies
on Sunday will eject towards the Great Lakes on Monday. The system
will be negatively tilted as it approaches, carving out a decent
trowal as it occludes over the middle Mississippi Valley on Monday.
Though this system`s exact path has yet to be pinned down (which
will have all-important ramifications on low level thermal profiles
and resultant precipitation types - see below for details), models
do seem to be coming into reasonable agreement with a track across
northern Lower. Plenty of moisture will come into play with PWATs
climbing to around 0.5 to 0.75 inches. Easterly low level flow
courtesy of a strong Canadian surface high over James Bay will
supply a feed of cooler, subfreezing air near the surface for much
of the area.

Primary Forecast Concerns...Precipitation types and amounts.

Not a whole lot of significant changes with this winter storm in the
overall scheme of things in the last 24 hours. Its precise track is
still a little uncertain, but most model guidance finally seems to
be coming into better consensus. As mentioned above, a track across
northern Lower appears likely, probably somewhere in the vicinity of
M-55 or M-72. The NAM remains the colder solution with a more
southward shifted track over Saginaw Bay, but the latest ECMWF has
shifted north a bit, coming into better agreement with the GFS.

As for precip onset timing, there seems to be some general consensus
to delay its arrival until late Sunday night as the precip shield
gradually lifts northeast across the area. But the steadier, heavier
precip won`t arrive until during the day Monday as the better
forcing pushes into northern Michigan.

Precip type remains the bane of the forecast for this system and
will continue to be tweaked over the next couple days. Very tricky
with the path of this system heading right through the APX forecast
area and highly dependent on any subtle shifts in the storm`s track.
The overall conceptual model does not scream a classic freezing rain
setup, though the ingredients do point to a good possibility of
freezing rain. There is a strong surface high centered to our north
which will provide cooler ENE flow near the surface. There is also
somewhat of a warm nose that develops aloft as warm air advection
overspreads the area. However, it`s looking rather subtle with max
layer wet bulb temperatures struggling to climb above 2C for the
majority of our forecast area, except south of M-72. This would
suggest more partial melting and an increased likelihood of some
sleet. Regardless, looking like it will generally be cold enough
near and north of the Straits to support mainly snow (though a
period of freezing drizzle/rain may be possible). For the rest of
northern Lower, a wintry mix of snow, freezing rain, and sleet will
be likely before surface temperatures /slowly/ creep above freezing
from south to north during the day, bringing a gradual transition to
rain. How far north this rain transition will progress still remains
in question, but perhaps as far north as M-32.

Snow and ice amounts still far from certain this far out, but
confidence is increasing in the potential for significant (several
inches) snow across eastern Upper and the Tip of the Mitt, as well
as significant ice accumulations across much of northern Lower,
perhaps in excess of 0.1" for some areas. Stay tuned over the next
couple days as details become clearer. But for now, the takeaway
message should be a high likelihood of an impactful winter storm
that will likely make travel across northern Michigan very difficult
if not hazardous.

.LONG TERM...(Monday night through Friday)
Issued at 307 AM EST Sat Jan 20 2018

High Impact Weather Potential...Some accumulating lake effect snow
expected through midweek.

Widespread precipitation from the winter storm is expected to
continue into Tuesday as the low slowly passes overhead. Snow will
become less widespread as lake effect processes develop heading into
Tuesday night behind the departing system. Northwest lower and
western Chippewa/Mackinac counties will be most impacted by the lake
effect activity. Drier air arriving midweek will bring an end to the
lake effect activity, with a weak disturbance possibly bringing some
snow showers to our north on Friday. Temperatures look to warm again
by the end of next week.

&&

.AVIATION...(For the 18Z TAFS through 18Z Sunday afternoon)
Issued at 1205 PM EST Sat Jan 20 2018

Thinner higher level clouds out there thus far, but mid and upper
clouds will increase again later today through tonight. Through
Sunday, IFR CIGS expected to develop from south to north through
the NW lower airports during the day as winds turn light
southerly, drawing up current stratus over Illinois. Still VFR
CIGS expected for now at APN. This light winds tonight and into
Sunday will also likely result in the development of at least some
light fog across nrn Michigan. Still no precipitation expected
this TAF period, and likely not until late Sunday night into
Monday morning.

&&

.APX WATCHES/WARNINGS/ADVISORIES...
MI...NONE.
&&

$$

UPDATE...SMD
NEAR TERM...MB
SHORT TERM...MK
LONG TERM...MK
AVIATION...SMD



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