Area Forecast Discussion
Issued by NWS Gaylord, MI

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FXUS63 KAPX 170847
AFDAPX

Area Forecast Discussion
National Weather Service Gaylord MI
347 AM EST Fri Nov 17 2017

.NEAR TERM...(Today through Tonight)
Issued at 344 AM EST Fri Nov 17 2017

...More rain and snow arrive today...

High impact weather potential...Not much. Perhaps a bit of light
snow accumulation today and tonight across portions of eastern upper
Michigan.

Pattern synopsis/forecast...Pattern remains super progressive across
central NOAM, a result of an overly active Pacific regime. High
pressure, centered squarely across the state as of early this
morning, in the process of rapidly pushing off to the east as broad
troughing does the same across western NOAM. Lead wave within this
larger trough axis advancing across southern Canada/northern High
Plains, driving surface low development and broad/deepening warm air
advection along with it. Top-down saturation response already
beginning, with band of high and mid level clouds rotating into the
western Great Lakes. Some light precip returns to our west, although
noticeable lack of low level moisture preventing much of this
activity from reaching the surface...yet.

Features mentioned above just keep marching along, with that broad
upstream troughing rotating into the Plains later today and tonight.
Initial shortwave troughs will drive increasing and deepening warm
air advection into the region today and tonight as low level jet
organizes and strengthens. Primary wave rotating through base of
trough axis looks to drum up low pressure to our southwest tonight,
which is set to impact our weather Saturday. Combination of these
features will bring a prolonged period of inclement weather to our
region today into this weekend.

Primary forecast concerns/challenges: Timing and type of
precipitation today and tonight. Addressing potential for some light
snow accumulation across eastern upper Michigan.

Details: Initial focus for deepest moisture advection remains
centered west of our area this morning, waiting on arrival of that
low level jet to bring deeper moisture into our region later today.
Precipitable water values respond accordingly, increasing from less
than a quarter of an inch early this morning, to near/above three
quarters of an inch by later today and tonight. Despite this
progressive moisture advection, low levels look stubborn to
saturate, particularly for areas south of the Mighty Mac,
potentially taking to very late today into this evening to do so.
Have tailored chances for precip in such a fashion, delaying arrival
somewhat for northern lower and relegating best potential for
eastern upper, especially for this afternoon. Precip type across
eastern upper remains a formidable challenge, with development of
shallow surface rooted above freezing layer and potential for
evaporational cooling. Simple rain/snow wording will suffice for
now, with exact precip type potentially tied to intensity.
Definitely could see some minor snow accumulations, generally less
than an inch, by this evening. Warmer boundary and more pronounced
warm nose aloft expected to keep precip mainly rain (when it
eventually arrives) across northern lower.

Above trends continue into this evening and the first portion of the
overnight, with precipitation expanding across the region as dry low
levels is overcome. Rain the way to go across northern lower
(upwards of a quarter inch or more), only adding to an already
exceedingly wet fall season. Much tougher precip type call for
eastern upper remains, with a very shallow surface rooted above
freezing layer. Of bigger concern is elevated warm nose, with
guidance disagreeing on extent and elevation of such (Nam-wrf much
more pronounced and elevated). Once again gonna keep it simple for
now, using rain/snow mixture wording. Definitely do think some
additional snow accumulation is possible, especially if rates
increase enough to overcome those marginally warm surface
conditions. Best bet for this to occur will be for areas closer to
the SOO, where another inch or two of new snow is a definite
possibility by the early morning hours of Saturday. Precipitation
coverage and intensity expected to tail off some across the area
heading toward Saturday morning as best isentropic upglide pushes
off to the east.

&&

.SHORT TERM...(Saturday through Sunday)
Issued at 344 AM EST Fri Nov 17 2017

...Breezy and a bit wet Saturday transitioning to snow showers
Saturday night...

High Impact Weather Potential: Gusty winds Saturday afternoon/night.
Potential for flash freezing on area roads late Saturday
afternoon/night as wet roads from Saturday rain may freeze up as
temperatures fall Saturday evening.

Pattern Forecast: Progressive wave train extends from North America
back across much of the Pacific basin.  Short wave ridging was
advancing across the upper Midwest and Great Lakes...with troughing
across western Canada and the Pacific northwest.  Height falls will
be spreading quickly across central North America Saturday...and
into the eastern third of the CONUS Sunday.  Flat short wave ridging
expected to cross the upper Lakes quickly Monday.

Surface ridge axis anchored by a 1028mb high center over northern
Ontario runs north-south right across Michigan early this morning...
sandwiched between low pressure systems over New England/Quebec and
Saskatchewan. Will be watching lee cyclogenesis taking place over
the central High Plains later today...and gets kicked east as a
short wave trough moving across Kansas/Nebraska overnight and across
the Midwest Saturday.  Surface low is expected to reach Illinois by
Saturday morning and deepen as it gets caught beneath left exit
region of a 140kt jet streak associated with the Plains short wave
trough.  Low is expected to track into the lower Great Lakes by
Saturday evening...NAM-WRF is slower/weaker/farther south with this
feature...wonder if this is related to the fact that the NAM has a
broad area of low pressure from Michigan southwestward Saturday
morning while other guidance has a more consolidated system over
Illinois.  So forecast ideas will shy away from 17/00z NAM-WRF
solution.  Pressure gradient should tighten up and bring some gusty
north winds across the forecast area by Saturday evening...and begin
to pull cold air into the region as 850mb thermal trough axis edges
into Michigan.  Secondary short wave energy expected to dig
southeast across Wisconsin/Lower Michigan Sunday...though low level
cyclonic flow will relax its grip on Sunday.

Primary Forecast Concerns: Surface low expected to move from Illinois
and probably cross southeast Lower Michigan on its way into
southeast Ontario/Lake Ontario.  Deformation/frontogenetic
precipitation band will be the main threat during the day Saturday
along the northwest quadrant of the passing surface cyclone...
falling mostly as rain but higher elevations may see precip
transition over to snow with temperatures not straying far from the
mid 30s.  Synoptic precip shield expected to shift east of the state
at some point Saturday night...with perhaps a bit of a break during
the transition to lake induced convection as 850mb temperatures sink
at or below -10C overnight.  Northwest flow lake snow belts will be
under the gun for developing snow shower activity...not a great
signal for really heavy snow bands with inversion heights will
initially struggle to climb above 800mb...but will get a boost from
arrival of secondary short wave trough Sunday morning and associated
synoptic lift.  Overall though expect snow accumulations to be on
the light side.  But Saturday rains combined with temperatures
dropping below freezing could lead to icy roads developing Saturday
night.

Winds should start to ramp up as early as Saturday morning for areas
downwind of a north/northwest flow off Lake Michigan...where wind
gusts of 30-40mph anticipated by afternoon.  Gusty winds (20-30mph)
should impact the entire area by early Saturday evening. Winds will
start to diminish Sunday.

Snow showers are expected to continue into Sunday...diminishing with
time as winds begin to back with flow switching from cyclonic to
anticyclonic along with the onset of warm advection by Sunday night.

&&

.LONG TERM...(Sunday night through Thursday)
Issued at 344 AM EST Fri Nov 17 2017

High Impact Weather Potential: Minimal

Another short wave trough will quickly move in on the heels of this
weekend`s system by the time Tuesday rolls around...with some
indication of a splitting short wave trough with energy dropping
into the Gulf of Mexico for midweek.  But differences in evolution
of northern and southern branch energy leading to a lot of
uncertainty heading into Thanksgiving weekend.   Cold front looks to
pass through the state Tuesday...which will bring another push of
lake convection heading into midweek.  Beyond that tough call for
what we might see on Thanksgiving...but initially looks quiet though
there is some indication we could see some warm advection precip
during the afternoon/evening.  But a long way out yet.

&&

.AVIATION...(For the 06Z TAFS through 06Z Friday night)
Issued at 1134 PM EST Thu Nov 16 2017

Low clouds are still being very stubborn, with some breaks in the
Straits area and in sw lower MI. Eventually, high pressure over
our heads will move east, and southerly flow will kick in at low
levels. That will gradually dislodge the low clouds (temporarily)
overnight and Fri morning from south to north. However, the next
wx system will be approaching, and high/mid clouds will thicken
and lower. Light rain/snow mixed will get going at PLN in the
afternoon, with rain at all sites Fri evening (MVFR to IFR vsbys).

Light winds overnight, with gusty sse winds developing Friday.

&&

.MARINE...
Issued at 344 AM EST Fri Nov 17 2017

Increasingly gusty southeast to south winds expected across
the big waters today, with widespread small craft advisory
conditions the result. Still some support for a few low end gale
gusts along and south of Grand Traverse Light on northern Lake
Michigan today. Shouldn`t be widespread enough however to warrant an
upgrade to a gale warning. Winds decrease a bit tonight, only to
increase in speed out of the north Saturday as low pressure passes
by to our south and southeast. More widespread marine headlines
expected Saturday, with a few gale gusts again possible on northern
Lake Michigan.

&&

.APX WATCHES/WARNINGS/ADVISORIES...
MI...NONE.
LH...SMALL CRAFT ADVISORY until 4 AM EST Saturday for LHZ345>349.
LM...SMALL CRAFT ADVISORY until 4 AM EST Saturday for LMZ323-341-342-
     344>346.
LS...SMALL CRAFT ADVISORY until 4 AM EST Saturday for LSZ321-322.
&&

$$

NEAR TERM...MB
SHORT TERM...JPB
LONG TERM...JPB
AVIATION...JZ
MARINE...MB


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