Area Forecast Discussion
Issued by NWS Gaylord, MI

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FXUS63 KAPX 050112
AFDAPX

Area Forecast Discussion
National Weather Service Gaylord MI
812 PM EST Mon Dec 4 2017

.NEAR TERM...(Tonight through Tuesday)
Issued at 322 PM EST Mon Dec 4 2017

...Big changes a`coming...

High impact weather potential...Plenty! High wind potential tonight
and Tuesday , especially along Lake Michigan. Few non-severe
thunderstorms possible this evening. Lake snow threat on the
increase later Tuesday. Long duration widespread gale event across
the Great Lakes.

Pattern synopsis/forecast: Pattern amplification and a what is soon
to be a change to much colder weather well underway as deep trough
axis and embedded strong shortwave rotate into the northern Plains.
Developing intense thermal gradient on the leading edge of this
trough axis drumming up quite the early season winter storm, with
low pressure rapidly deepening near the Twin Cities of Minnesota.
Deep layer moisture feed and intense low level jet dynamics ahead of
this system bringing soaking rains to the northwoods today, although
the steadiest and heaviest rains have centered further north with
time early this afternoon.

Minnesota low will continue to rapidly deepen, easily falling to sub
980mb levels as it passes along the northwest coast of Lake Superior
tonight, pivoting further northeast into central Ontario Tuesday.
Attendant cold front will propel east through northern Michigan
tonight, ushering in the start of the now much talked about
transition to a much colder weather regime.

Primary forecast concerns/challenges: Addressing thunder threat this
evening. Potential need for a wind advisory for some areas tonight
and Tuesday. Addressing developing lake snows Tuesday and possible
winter weather headline concerns.

Details: Strong cold front tied to that deepening low races east
across the region later tonight, pushing into Lake Huron and Ontario
near or shortly after sunrise Tuesday. Strong forcing will generate
additional showers along and ahead of this front. Plume of decent
mid level lapse rates along primary forcing axis continues to
support some isolated thunderstorms. No severe weather expected as
storms will remain rooted well above stable low levels, preventing
them from bringing strongest winds to the surface. Post-frontal dry
air punch should bring an end to most shower activity right after
fropa. Coldest air is partially delayed, and when combined with that
dry air/subsidence, will likely keep any early morning lake
processes somewhat muted. Perhaps biggest issue tonight remains
those very gusty winds. Simple intensity of low pressure and tight
pressure gradient supports a continuation of gusty southerly winds,
which should only increase as the cold front approaches. Development
of post-frontal cold air advection will help destabilize the low
level environment during the early morning hours, allowing more
potential to tap into 50+ knot low level jet core. This will be
especially true along the Lake Michigan coast where instability will
be maximized and with limited friction. See little reason widespread
wind gusts nearing 45 mph will not be realized along and just inland
of the coast, which will continue through much of Tuesday as
instability only further deepens with time. Will issue a wind
advisory for those Lake Michigan bordering counties. Elsewhere,
winds will increase, but look to remain just below headline criteria.

Transition to a much colder weather regime kicks into overdrive
Tuesday. Lake parameters only increase through the day as system
backside moisture returns and thermal profiles continue to cool.
Long fetch and excellent speed shear through the growing convective
boundary layer should only help lake effect organize as we head
through the afternoon. Initial rain/snow mixture expected to
transition to all snow during the afternoon, with the primary target
area focusing on the Tip of the Mitt counties, as well as up into
far southeast Chippewa County. Late start to better organization
should keep snow totals in check, but still expect 1 to 3 inches by
Tuesday evening in those favored areas...with much more yet to come
Tuesday night into Wednesday. Gusty southwest winds will create some
blowing and drifting snow, only adding to the developing hazardous
driving conditions. Winter weather headlines have been issued
starting Tuesday afternoon to account for such. Please see the short
term section to follow for more of these wintry details. Expect lake
induced cloud cover and lighter snow showers elsewhere, especially
closer to Lake Michigan. Temperatures free-fall through the day,
with morning readings in the 30s and 40s dipping into the 20s to
lower 30s by late afternoon. Add in those gusty winds, and wind
chill readings by later in the day will be down into the teens.

&&

.SHORT TERM...(Tuesday night through Thursday)
Issued at 322 PM EST Mon Dec 4 2017

...Lake effect snow, gusty winds and hazardous travel...

High Impact Weather Potential: Accumulating lake effect snow is
expected across sections of northwest lower and eastern upper
through the forecast period. Gusty winds through Wednesday will
raise concern for areas of blowing snow and reduced visibility.

Pattern Forecast: By Tuesday evening, well-advertised strong area of
low pressure is expected to be centered across north-central
Ontario/near James Bay with anomalously deep troughing becoming
draped across the midsection of the country. Several subtle
perturbations are expected to pinwheel through the base of said
troughing, ultimately providing synoptic support and deeper moisture
for occasional upticks in lake effect snow intensity through the
middle of the week.

Primary Forecast Concerns/Challenges: Lake effect snow primary
threat areas/amounts, gusty winds and potential impacts.

Little change from yesterday`s thinking regarding Tuesday night`s
lake effect snow setup. Snow showers ramp up Tuesday afternoon with
LES parameters becoming more favorable Tuesday evening through
Tuesday night. Initial west-southwesterly flow ever so slowly veers
more westerly throughout the overnight hours targeting areas
primarily north of M-32 with the heaviest snowfall. H8 temperatures
throughout the night vary from -12 to -15 C across northwest lower
and eastern upper leading to plenty of over-lake instability with
resultant delta Ts ~20 C and modeled lake induced CAPE near 500
J/kg. Plenty of instability will be combined with open water on
Green Bay providing a longer fetch, sufficient moisture through the
column with no threat for dry air entrainment above the progged 7-8
kft inversion, omega pegged squarely in the DGZ, sufficient speed
shear within the lake induced convective boundary layer for banded
structures, and subtle synoptic support from mid level perturbations
pinwheeling through the deepening trough overhead. All this gives
credence to increased likelihood of 1-2"+/hr snowfall rates and
accumulation of 5-10", locally higher, Tuesday night in locations
under well organized banding (most likely to occur in the Emmet,
Cheboygan, Charlevoix county area... extending northeastward into
the Drummond Island area). Lighter snows remain likely further south
toward the Grand Traverse Bay region with accumulation under an inch.

Winds continue to gradually veer throughout the day Wednesday
becoming west-northwesterly during the afternoon and shifting
greatest intensity snow showers to portions of southern Charlevoix,
Antrim, Otsego and eventually Kalkaska County. Once again, model
soundings suggest fairly impressive LES parameters heading into
Wednesday afternoon and evening with several inches of snow falling
under the steadiest bands in the aforementioned areas. Deep layer
moisture gradually strips out during the day Thursday; however,
northwest flow lake effect should continue through much of the day
before winds gradually begin to back more westerly Thursday
afternoon and eventually southwesterly ahead of a clipper set to
dive into the region late this week.

Only to add to the impact of heavy snow will be continued gusty
winds Tuesday night through Wednesday morning before gradually
diminishing Wednesday afternoon. Highest wind gusts upwards of
40-45 mph, most notable near the Lake Michigan shoreline, will
result in areas of blowing snow for locations across the Tip of
the Mitt that experience steadier snowfall. Travel could get quite
nasty for a handful of locations Tuesday night into the Wednesday
morning commute with snow covered roads and falling/blowing snow
significantly reducing visibilities - likely worst on north-south
oriented roadways including US-31 and I-75. Have opted to hoist a
Winter Storm Watch for Emmet, Charlevoix, Cheboygan Counties and
Chippewa County (primarily for the Drummond Island area) from 21z
Tuesday through the day Wednesday.

.LONG TERM...(Thursday night through Monday)
Issued at 322 PM EST Mon Dec 4 2017

High impact weather potential: Active surface and upper level
pattern will continue wintry weather across northern Michigan
through the forecast period.

Upper trough which settled into the Great Lakes earlier in the week,
will linger over the entire region through the weekend while a
couple of quick moving canadian sfc features sweep over the state.
This pattern will continue snow showers over much of northern
Michigan Friday through the weekend. Highest snowfall will be
confined to westerly flow snowbelts. 850mb temps in this pattern
will be largely between -16c and -20c, generating below normal
afternoon highs in the mid and upper 20s.

&&

.AVIATION...(For the 00Z TAFS through 00Z Tuesday evening)
Issued at 812 PM EST Mon Dec 4 2017

Gusty winds will be the biggest impact at the terminal sites over
the next 24 hours. Deep low pressure system is over western
Wisconsin this evening with a potent cold front sweeping into the
Midwest/Great Lakes region. Front will bring another round of
showers and MVFR conditions through northern lower Michigan over
the next several hours...and there may be some thunderstorms
rolling through as well (have not included TSTM in any TAF
forecast given the low probabilities). After FROPA...winds veer
westerly with gusts of 25 to 35 knots common at the terminal sites
through Tuesday.

Showers diminish after FROPA with much colder air arriving on
Tuesday. Lake effect snow shower will increase across parts of NW
lower Michigan through the day...primarily impacting PLN at
first.

&&

.MARINE...
Issued at 322 PM EST Mon Dec 4 2017

Deepening low pressure to our west will pivot up into Ontario
Tuesday, propelling a strong cold front across the area tonight.
Pre-frontal south to southeast winds will be very gusty, with
these winds only increasing in speed as they turn southwest behind
the front with increasing low level instability. Very strong
southwest winds continue right through Tuesday. Winds slowly veer
more westerly Tuesday night and Wednesday, decreasing in speed
some in the process (although still very gusty). Gale warnings
remain in effect through Tuesday night across all nearshore
waters. Very possible some isolated storm force wind gusts will be
realized across portions of northern Lake Michigan very late
tonight into Tuesday morning.


&&

.APX WATCHES/WARNINGS/ADVISORIES...
MI...WIND ADVISORY until 4 PM EST Tuesday for MIZ015-016-019>021-025-
     031.
     WINTER STORM WATCH from Tuesday afternoon through Wednesday
     evening for MIZ008-016-017-019.
LH...GALE WARNING until 4 AM EST Wednesday for LHZ345>349.
LM...GALE WARNING until 4 AM EST Wednesday for LMZ323-341-342-344>346.
LS...GALE WARNING until 4 AM EST Wednesday for LSZ321-322.
&&

$$

NEAR TERM...MB
SHORT TERM...MG
LONG TERM...SR
AVIATION...BA
MARINE...MB



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