Area Forecast Discussion
Issued by NWS Gaylord, MI

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FXUS63 KAPX 211727

Area Forecast Discussion
National Weather Service Gaylord MI
1227 PM EST Tue Nov 21 2017

Issued at 1030 AM EST Tue Nov 21 2017

Not too much of an update. The air mass ahead of a cold front
which has crossed eastern upper and moving through the NW lower
coast, was very dry. No synoptic precipitation can develop in this
air mass, despite DPVA and upper divergence ahead of a shortwave
pushing through the western Great Lakes. Rather, as temperatures
fall through the day in strong CAA with gusty westerly flow, lake
effect rain and snow showers will develop, which will changeover
to only snow for everyone pretty quickly. Forecast soundings leave
much to be desired, with inversion height tipping 4500 to 5500
feet with an "inverted V" look in the lowest layer of the BL,
suggesting things will not be all that moist.

Total snowfall through the night in the favored NW flow snowbelts,
around an inch or two, maybe up to 3 inches in eastern upper.


.NEAR TERM...(Today through Tonight)
Issued at 231 AM EST Tue Nov 21 2017

...Windy and turning colder today and tonight with lake effect
precipitation developing...

High Impact Weather Potential...Mix of rain and snow changing to all
snow with minor accumulations and gusty winds.

Pattern Synopsis/Forecast...Deep low pressure is centered just north
of Lake Superior early this morning...with a trailing cold front
extending thru Central Lake Superior thru Eastern Wisconsin into
Iowa and Kansas. Strong low level southerly flow/WAA continues
across our entire CWA at this hour ahead of this cold front. S/SW
winds are gusting to 25 to 35 kts ...especially along our Lake
Michigan shore areas...keeping temps in the 40s even at this early
morning hour. Local and upstream radars remain echo-free thanks to
plenty of dry low/mid level air still in place.

Wx will change substantially as we head thru today and tonight. Cold
front will sweep thru our CWA this morning...reaching the Thumb area
by around 18Z...with the upper level trough axis clearing our CWA by
mid to late evening. Strong CAA will quickly commence in the wake of
the cold front this morning...with the heart of the cold air
arriving with the upper level trough axis this afternoon and
tonight. Thus...our high temps for the day will occur during the
morning before temps begin to fall this afternoon as CAA begins.
Initial push of colder air this morning should begin to activate the
lakes...but low level temp profile suggests any precip that develops
will be mainly rain...with some snow mixing in across Eastern Upper
Michigan and within the higher elevations of Northern Lower
Michigan. Arrival of significantly colder air with the upper trough
axis during the afternoon along with the arrival of a large area of
wrap-around low level moisture will enhance ongoing lake effect
precip and will gradually switch precip to all snow from NW to SE.

Still expect only minor snow accumulations (less than an inch) for
the afternoon for areas targeted by NW flow as low level winds shift
to a NW trajectory behind the upper trough axis. Portions of Eastern
Upper Michigan will see an additional inch or two tonight...with
less than an inch expected across NW Lower Michigan tonight.
Overnight lows will drop into the low to mid 20s tonight thanks to
ongoing CAA.


.SHORT TERM...(Wednesday through Thursday)
Issued at 231 AM EST Tue Nov 21 2017

...Lingering light lake effect diminishes Wednesday...

High Impact Weather Potential: Minimal.

Pattern Forecast: By early Wednesday morning, weak warm air
advection is expected to be underway across northern Michigan.
Combined with limited lingering synoptic support and expansive
surface high pressure nosing in from the south, any lingering light
lake effect snow showers are expected to diminish. The next system
of interest approaches the region on Thursday in the form of a cold
front tied to low pressure over Hudson Bay skirting the far northern
reaches of the forecast area. By and large, it does not like
anything of high impact and may struggle to produce much more than
flurries before exiting Thursday evening.

Primary Forecast Concerns/Challenges: Diminishing lake effect
Wednesday morning. Limited snow shower threat Thursday.

As was alluded to above, a significant diminishing trend to
lingering lake effect snow showers is anticipated Wednesday morning
as anemic moisture and synoptic support, along with lowering
inversion heights and weak warm advection all suggest scattered snow
showers end across northern lower by mid-late morning and across
eastern upper around midday. Perhaps another couple of tenths of new
snow prior to midday; otherwise, little in the way of consequence.

Quiet weather is expected Wednesday afternoon through Thursday
morning before another cold front approaches the region from the
north. Current trends suggest the greatest pre-frontal moisture and
support will remain over southern Ontario with only a few snow
showers developing as far south as eastern upper diminishing to
perhaps a few flurries across sections of northeast lower (have
opted to exclude the 21/00z NAM as it appears overly agressive with
precip development, but remains a trend to monitor with busy holiday
travel in full swing). Otherwise, Thanksgiving is shaping up to be a
dry and seasonable day across the bulk of northern Michigan with
highs topping out in the mid-upper 30s area-wide.

.LONG TERM...(Thursday night through Monday)
Issued at 231 AM EST Tue Nov 21 2017

High impact weather potential: Accumulating lake effect snow chances
increase later Saturday through Sunday.

Attention in the extended portion of the forecast revolves around
the Friday through Sunday timeframe as active weather returns to the
heart of the country.

Warm air advection is expected to ramp up in earnest across the
region late Thursday night into Friday morning ahead of a potent
clipper system set to trek across southern Canada late this week
into the upcoming weekend. While a small threat for a rain/snow mix
exists across far northern locales during a brief window of
isentropically driven precip on Friday, the bigger story will be
widespread rainfall late Friday afternoon through Friday night
before much cooler air wraps into northern Michigan behind the
departing system. Lake effect snow chances ramp up downwind of Lakes
Superior and Michigan as early as Saturday afternoon...potentially
continuing through Sunday night. Plenty of time for the details to
fall into place regarding the exact threat areas and snow
accumulation, but worth following later outlooks through the
upcoming holiday weekend.


.AVIATION...(For the 18Z TAFS through 18Z Wednesday afternoon)
Issued at 1218 PM EST Tue Nov 21 2017

A cold front has crossed all nrn lower airports with winds now
shifted more westerly and were quite gusty. Cold air was pouring
into the region and temperatures were falling. The air will get
cold enough through the afternoon for lake effect rain and snow
showers to develop, and then quickly change to just snow. CIGS
will be low end VFR for the most part, maybe going MVFR at times.
The snows are not expected to be heavy, with low snowfall rates
being dominant. Vsbys will still likely be able to fall to around
1-2sm at times, briefly sub 1sm. The snows will likely trend less
intense going through the overnight hours and into Wednesday
morning. Total snowfall around an inch, maybe two if in a stronger
snow band.


Issued at 231 AM EST Tue Nov 21 2017

Winds and waves will continue to reach gale warning/SCA criteria
thanks to strong southerly flow and WAA ahead of the approaching
cold front early this morning and then the beginning of CAA in the
wake of the front today and tonight. Lake effect precip will begin
to develop this morning as CAA begins...and will become further
enhanced this afternoon and tonight as the heart of the cold air
along with an area of low level moisture arrive with the upper
trough axis. Winds and chances of precip will diminish on Wednesday
as high pressure begins to build into the region.


LH...SMALL CRAFT ADVISORY until 6 AM EST Wednesday for LHZ345-346-349.
     GALE WARNING until 11 PM EST this evening for LHZ347-348.
LM...SMALL CRAFT ADVISORY until 6 AM EST Wednesday for LMZ345-346.
     GALE WARNING until 5 PM EST this afternoon for LMZ323-341-342-
LS...SMALL CRAFT ADVISORY until 6 AM EST Wednesday for LSZ322.
     GALE WARNING until 11 PM EST this evening for LSZ321.


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