Area Forecast Discussion
Issued by NWS Gaylord, MI

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189
FXUS63 KAPX 101107
AFDAPX

Area Forecast Discussion
National Weather Service Gaylord MI
607 AM EST Sat Dec 10 2016

.NEAR TERM...(Today and Tonight)
Issued at 255 AM EST Sat Dec 10 2016

...Accumulating lake effect snow continues...

High Impact Weather Potential...More accumulating lake effect snow
today...transitioning to lake enhanced snow tonight with the
approach of our next low pressure system.

Pattern Synopsis/Forecast...NW low level flow lake effect snow event
continues across Northern Michigan early this morning. Persistent
deep cyclonic flow remains over the entire Great Lakes region...
further enhanced at low levels by a rather sharp lake aggregate
trough currently located across Eastern Upper Michigan into far NE
Lower Michigan. Presence of this trough has resulted in some minor
disruptions to lake band organization throughout the night...but
dominant (albeit broken) snow band continues to target Antrim county
for heaviest snowfall attm. Recent snowfall rates across southern
Antrim county have been 1 to 2 inches per hour overall...with a few
isolated spots of up to 3 inches per hour. Upstream KMQT base ref
loop has shown a slight shift in the dominant snow band toward a
more westerly trajectory...but it is slight. High res models suggest
a very slow break down of the lake aggregate trough throughout the
day as surface high pressure builds into the region. This process
should result in a gradual transition to a more straight westerly
lake effect snow band trajectory throughout the day...as well as a
diminish in overall intensity as inversion heights drop from 8-9 kft
early this morning to around 4 kft by this evening. Prolonged lake
effect snow event then begins to transition to a SW flow lake
enhanced snow and synoptic snow event tonight as mid/upper level
moisture begins to increase from SW to NE in advance of developing
low pressure heading NE out of the Central Plains toward the Western
Great Lakes region. Temps will remain more the sufficient to
maintain over-lake instability and thus lake snow production thru
tonight. Focus of this lake convection will shift northward toward
the Straits and far NW Lower Michigan as low level winds shift to
the SW ahead of this system. Increasing mid level moisture may also
provide some enhancement thru seeder-feeder processes later
tonight...but certainly better chances of synoptic enhancement will
hold off until Sunday as deep moisture arrives.

Primary Forecast Concerns...Additional snowfall potential remains
the primary focus thru tonight...with shifting wind direction
playing a large role in the evolution of snowfall amounts and POPS.
Recent frames from KAPX base ref loop has also shown the beginning
of a slight westerly shift in the dominant lake snow band
trajectory...which mirrors the shift in the dominant band over
southern Lake Superior. Regardless...the transition to a more
westerly low level wind trajectory will likely take some time today
given the persistent lake aggregate trough battling building high
pressure into Michigan. Will maintain currently headlines thru the
morning hours as focus for highest POPs and greatest additional snow
amounts will remain within these counties. The expected shift
northward in snow band focus may require an extension and/or
adjustment to headlines for the afternoon.

&&

.SHORT TERM...(Sunday through Monday)
Issued at 255 AM EST Sat Dec 10 2016

...Warm advection snow ahead of the next system....

High Impact Weather Potential...warm advection snow may get enhanced
on SE winds into NE Lower and portions of E Upper for a time. This
could produce moderate snow amounts during Sunday/Sunday night.
Monday LES will be limited as the wind directions will change
through out the 24 hour period.

Pattern Synopsis/Forecast...Fast 500 mb flow over the region with
periodic shortwave troughs in the flow will continue to spin up
small sfc lows and push them across the Upper Great Lakes. This
general pattern looks to continue into next and not just for the
next two days.

On Sunday, the sfc low looks to be in C Iowa with warm advection
precipitation expected from N Indiana to Upper Michigan by 18z at
the latest. Winds in the 1000-850 mb layer, look to be SE from 18z
to about 03z/Mon. This has a little potential for some lake
enhancement, but the wind directions don`t look steady enough to
enhance any particular area. So the main precipitation concern will
be with the warm advection ahead of the low. The low itself will be
moving through N Michigan during Sunday night (after 06z/Mon) so
that it will be exiting the region by 12z/Mon.

Winds Monday, start north and northwest, but quickly turn west by
18z, and SW by 00z/Tue. Overnight Monday/Tuesday morning may have
been the real concern if the winds didn`t shift so much by 12z. With
W an wnw winds, the snow bands will shift around quite a bit. 850 mb
temperatures are expected to be around -20c so significant amounts
may be held down as the colder temperatures should yield smaller
flake sizes, not to mention that the synoptic moisture in the 850-
700 mb layer is < 40% which will limit the amount of cloud over the
region.

.LONG TERM...(Monday night through Friday)
Issued at 255 AM EST Sat Dec 10 2016

Despite the relatively flat flow over the region, the 500 mb
vortex to the north sinks into the Upper Great Lakes so that the
colder air continues to sink into the region as well and keeps us
that way though most of the week until end of the week when the
temperatures begin to moderate a bit as another possible system
begins to build north again. So a combination of system and lake
snow will continue through Friday.

&&

.AVIATION...(For the 12Z TAFS through 12Z Sunday morning)
Issued at 607 AM EST Sat Dec 10 2016

Lake effect snow showers will continue to impact far Northern and
NW Lower Michigan thru Sunday morning. Focus of heaviest snow
bands will slowly shift toward the Straits (PLN) as low level
winds shift to the west and eventually to the SW ahead of low
pressure developing in the Central Plains. Intensity of lake
effect snow will diminish as high pressure builds into the region
this afternoon and evening...but will likely ramp up again late
tonight and Sunday as increasing synoptic moisture serves to
enhance SW flow lake effect snow showers.

&&

.MARINE...
Issued at 255 AM EST Sat Dec 10 2016

SCA winds and high waves will continue to impact our nearshore areas
from Manistee to Grand Traverse Light thru this morning. Winds and
waves should drop below SCA criteria this afternoon as high pressure
builds into the region. NW low level flow lake effect snow showers
will continue to target the typical snowbelt areas this morning...
but will begin to shift northward toward the Straits this afternoon
and tonight as low level winds shift to the west and eventually to
the SW ahead of developing low pressure over the Central Plains.

&&

.APX WATCHES/WARNINGS/ADVISORIES...
MI...WINTER WEATHER ADVISORY until noon EST today for MIZ016-017-020-
     022-028.
     WINTER STORM WARNING until noon EST today for MIZ019-021-027.
     LAKE EFFECT SNOW ADVISORY until noon EST today for MIZ008.
LH...NONE.
LM...SMALL CRAFT ADVISORY until noon EST today for LMZ345-346.
LS...NONE.
&&

$$

NEAR TERM...MLR
SHORT TERM...JSL
LONG TERM...JSL
AVIATION...MLR
MARINE...MLR



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