Area Forecast Discussion
Issued by NWS Gaylord, MI

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FXUS63 KAPX 101707
AFDAPX

Area Forecast Discussion
National Weather Service Gaylord MI
1207 PM EST Sun Dec 10 2017

.UPDATE...
Issued at 949 AM EST Sun Dec 10 2017

Sharp lake-enhanced trough axis remains locked along the southern
shore of Lake Superior this morning...aiding in the production of
a persistent heavy lake snow band running along this shoreline
area right into far Northern Chippewa county around Whitefish
Point and Paradise. Latest KMQT base ref loop shows this
persistent band has dislodged from the shoreline and has pushed
south into Upper Michigan in response to the sharp trough
beginning to drop southward. Low level convergence has begun to
strengthen further southward into Northern Lower Michigan. As a
result...reflectivities within our westerly flow lake snow bands
have increased over the past couple of hours. Will need to monitor
this evolution for the possibly necessity of headlines across this
area. Will also monitor snowfall/vsbys across Northern Chippewa
county to see if the advisory that expires at 18Z will need to be
extended.

&&

.NEAR TERM...(Today through Tonight)
Issued at 335 AM EST Sun Dec 10 2017

...Accumulating lake snows continue...

High Impact Weather Potential...Heavier snow amounts in a few
locations.

Pattern Synopsis/Forecast...Midnight water vapor imagery and
surface analysis reveals another piece of short wave energy
rotating down the upper Midwest/western Great Lakes region.
Associated surface reflection stretches across Lake Superior into
northern Minnesota. Low level mean flow has been backing westerly
through the night shoving lake convection back eastward across
northern lower Michigan. Best defined lake banding and heavier
snow is on eastern Lake Superior including a well defined band of
heavy snowfall just off shore of the U.P. slowly inching down
into far norther Chippewa county around the Whitefish Point area.

Primary Forecast Concerns...snow accumulations and ongoing
headlines.

Short wave energy and attending surface low will pass down through
northern Michigan during the course of the day with winds veering
northwesterly followed by another reinforcing push of cold air
into the region by tonight. Broad area of lighter snow will pass
through the region today giving most areas a little bit of
snowfall. But...there will be a window of decent lake effect
snow showers through mid to late afternoon as axis of decent QG-
forcing for ascent/deeper moisture and increased inversion heights
move through. West flow lake effect snowbelt areas will be the
main target early on before winds veer northwesterly through the
afternoon hours. Think parts of NW lower Michigan through Antrim/
Charlevoix/Otsego counties will likely see 2-3 inches of snow
(perhaps more?) through today...just a bit shy of advisory
criteria amounts.

But potential still exists for a period of heavy lake snowfall
across northern Chippewa county this morning as sharp low level
convergence axis and that intense band of lake effect snow just
offshore passes down through the region. Easy potential there for
a quick 3-5 inches this morning...although only for a relatively
smaller portion of the county. But I will of course maintain
current winter weather advisory through 18Z today.

Lake effect conditions become increasing hostile for better snow
showers late this afternoon and tonight as we lose synoptic
support/inversion heights inch back down and low level flow
weakens substantially as surface high pressure builds overhead.
But...this is lake effect and we will likely continue to see some
light snow showers with minor accumulations through tonight...
primarily along the immediate Lake Michigan shoreline areas as
well as parts of eastern upper Michigan.

&&

.SHORT TERM...(Monday through Tuesday)
Issued at 335 AM EST Sun Dec 10 2017

...Clipper system on Monday followed by more lake effect and
colder temperatures...

High Impact Weather Potential...Widespread light snow event on
Monday, followed by more lake effect snow on Tuesday. Gusty winds
Monday night into Tuesday will result in some blowing snow.

Pattern Synopsis/Forecast...Split upper flow pattern will be over
northern Michigan on Monday with two shortwave troughs dropping
through the region, embedded within the larger longwave ridge-trough
pattern dividing the West from the eastern 2/3 of the CONUS. The
southern shortwave will be associated with a clipper system dropping
in from the Dakotas. A rapid intensification of this surface low
will occur Monday evening as the northern shortwave sharpens and
digs into the Upper Great Lakes. This resultant deeper trough will
be reinforced by another piece of energy dropping out of western
Ontario on Tuesday, pulling in a blast of Arctic air.

Primary Forecast Concerns...Snowfall amounts through the period,
particularly with Monday`s system. Also gusty winds behind the
departing clipper system late Monday night into Tuesday.

Band of isentropic ascent over Wisconsin early Monday morning will
slide into Lower Michigan. Meanwhile, low level moisture will
increase across the region, leading to a nearly saturated column up
through 300mb. This will allow for widespread (mainly light)
snowfall through the day. The more challenging forecast aspect will
be lake enhancement, complicated by varying low level wind
direction. Largely southeasterly low level flow over land for much
of the day, with southwest winds over Lake Michigan and southerly
winds over Lake Huron providing decent convergence over the open
waters. This will favor lake enhancement for portions of eastern
Upper, likely coming off both lakes. Once the surface low pushes
through Monday evening, wind direction will become more uniform out
of the NW to NNW, bringing the convergent band over Lake Michigan
ashore, with continued NW to NNW flow lake effect thereafter
affecting eastern Upper and northwest Lower all the way through
Tuesday as 850mb temperatures progressively plunge even farther.

In terms of snowfall amounts, Monday`s widespread snow looks to
bring around 2 to 3 inches to much of the forecast area, potentially
higher in lake enhancement areas. The additional lake effect Monday
night into Tuesday could add an additional 1 to 3 inches, highest
south of Grand Traverse Bay.

Although the main clipper system looks to miss us as it dives into
the Ohio Valley, the sharp digging northern shortwave is progged to
induce its own smaller-scale surface cyclogenesis Monday evening.
Regardless, the two surface lows will quickly merge overnight into
a single intensifying departing low over the eastern Great Lakes.
This will result in a rapid tightening of the pressure gradient over
northern Michigan and the surrounding lakes late Monday night into
Tuesday. Gales are looking increasingly likely over Lakes Michigan
and Huron...not so much Whitefish Bay at this time, but that could
change. These winds combined with the dry lake effect snow will lead
to areas of blowing snow and reduced visibility, especially near the
coasts. A very cold day on Tuesday with highs in the teens for most
of the area.

.LONG TERM...(Tuesday night through Saturday)
Issued at 335 AM EST Sun Dec 10 2017

High impact weather potential...Ongoing lake effect snow with
additional enhancement from periodic clipper systems. This could
yield some significant snow totals for some areas.

A continued active wintry pattern for the long term period, starting
off very cold with an Arctic airmass overhead Tuesday night. Lake
effect will be ongoing in NW to N flow snowbelts, but there could be
some partial clearing that develops east of I-75 as a surface ridge
slides overhead. Temperatures could plunge below zero across
portions of eastern Upper and interior northern Lower with wind
chills late Tuesday night dropping into the minus teens to -20F.
Highs only in the teens for most once again on Wednesday, but a slow
moderation in temperatures expected the remainder of the week...even
climbing into the low 30s by Saturday. Still some lake effect on
Wednesday, followed by another clipper system on Thursday, more lake
effect on Friday, and potentially another clipper system on
Saturday. Old man winter is in full swing.

&&

.AVIATION...(For the 18Z TAFS through 18Z Monday afternoon)
Issued at 1207 PM EST Sun Dec 10 2017

A sharp lake-enhanced trough axis will drop thru Northern Lower
Michigan this afternoon/early evening. This feature will enhanced
ongoing lake effect snow shower activity...especially across far NW
Lower Michigan (PLN). This trough will reach the Thumb area of
Lower Michigan by 00Z...but light lake effect snow showers will
continue...targeting NW Lower Michigan for the most persistent
snow showers. Overall conditions will remain MVFR...but vsbys will
occasionally drop to IFR within heavier snow showers. Widespread
synoptic snow will develop from west to east on Monday ahead of
low pressure diving SE out of South Central Canada...reaching
Illinois and Indiana by 00Z Tuesday. Widespread IFR conditions are
expected with this area of mainly light snowfall. West winds
around 10 kts will shift to the N/NW behind the trough axis this
evening...but will switch around to the S/SE on Monday ahead of
the approaching low pressure system.

&&

.MARINE...
Issued at 335 AM EST Sun Dec 10 2017

A period of gustier westerly winds...veering northwest this
afternoon...will impact the nearshore areas today leading to small
craft advisory conditions. Winds/waves diminish quickly heading
into tonight as high pressure builds overhead. But...gusty winds
and possible gale force gusts return again Monday night into
Tuesday.

&&

.APX WATCHES/WARNINGS/ADVISORIES...
MI...WINTER WEATHER ADVISORY until 7 PM EST this evening for MIZ019-
     021-022-027-028.
     WINTER WEATHER ADVISORY until 1 PM EST this afternoon for MIZ008.
LH...SMALL CRAFT ADVISORY until 5 PM EST this afternoon for LHZ345-
     346.
     SMALL CRAFT ADVISORY until 11 PM EST this evening for LHZ347>349.
LM...SMALL CRAFT ADVISORY until 5 PM EST this afternoon for LMZ341.
     SMALL CRAFT ADVISORY until 11 PM EST this evening for LMZ323-342-
     344>346.
LS...SMALL CRAFT ADVISORY until 5 PM EST this afternoon for LSZ321-
     322.
&&

$$

UPDATE...MR
NEAR TERM...BA
SHORT TERM...MK
LONG TERM...MK
AVIATION...MR
MARINE...BA


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