Area Forecast Discussion
Issued by NWS Gaylord, MI

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FXUS63 KAPX 150258

Area Forecast Discussion
National Weather Service Gaylord MI
958 PM EST Tue Nov 14 2017

Issued at 946 PM EST Tue Nov 14 2017

Broad, moist southwest flow with increasing isentropic ascent
across the western Great Lakes this evening in advance of
approaching shortwave/surface front. This was resulting in
increasing coverage of showers. This trend will continue
overnight, with airmass finally completely saturating as mid
level dry air erodes and showers become more widespread. Backed
off slightly on bringing the highest POPS into the area (given a
bit slower saturation), but otherwise kept most aspects of the
current forecast. Lows tonight generally ranging from the middle
30s to around 40.


.NEAR TERM...(Tonight through Wednesday)
Issued at 307 PM EST Tue Nov 14 2017

High impact weather potential: Minimal. Just rain moving in tonight
and Wednesday.

Pattern synopsis and forecast:

Shallow mid level ridging was overhead this afternoon with a
shortwave trough pushing eastward toward southern Manitoba. This
feature was working on a dry air mass, but moisture can already be
seen advecting northward via an open Gulf and increasing southerly
winds within a tightening pressure gradient from the Plains through
the western Great Lakes. In nrn Michigan, stratus had engulfed most
all of the region, except the far eastern edge of NE lower, where
it`s battling downslope of the interior higher terrain. WAA from the
southerly winds was racing north however, and has begun eroding out
all the low clouds. A different scenario is playing out over Lake
Michigan into far NW lower and into eastern upper. Overlake
instability and those increasing southerly winds were increasing the
moisture flux off Lake Michigan and actually deepening the low level
moisture. It`s not deep enough to tap -10C, so we are seeing some
reduced visibilities due to fog and a light mist.

The aforementioned shortwave trough sharpens through tonight, before
moving in over nrn Michigan Wednesday. The deeper moisture advects
up into nrn Michigan overnight and into Wednesday morning when
forcing is greatest with a 40kt H8 LLJ, left exit region upper
divergence and of course DPVA. Rain will develop over this time,
with no snow anticipated, as the air mass continues to warm with sfc
based temperatures no colder than the upper 30s and a deepening
above freezing low level warm layer. The forcing departs east in the
afternoon as the cold front is crossing the region, and wrap around
deeper moisture is dropping into eastern upper. Could possibly see a
late day mix of snow and rain across eastern upper, while lake
effect will just about be wanting get started everywhere. However,
that will mainly be Wednesday night.


.SHORT TERM...(Wednesday night through Friday)
Issued at 307 PM EST Tue Nov 14 2017

...Turning colder with a couple precip events...

High Impact Weather Potential...Minimal.

Pattern Synopsis/Forecast...A one-two punch of shortwaves will cross
northern Michigan Wednesday night as larger-scale parent trough
migrates across the Great Lakes. Under the influence of strong cold
air advection, a drier, colder 850mb airmass will progressively wrap
into the region behind the departing low, leading to a period of
northwest flow lake effect snow showers through Thursday morning.
Heights aloft will rise through the day Thursday as a ridge and
associated surface high slide across the region with much drier air.
That pattern will quickly change heading into Friday as warm air
advection ramps up thanks to a robust low level jet ahead of a
developing storm system.

Primary Forecast Concerns...Lake effect showers through Thursday
morning. Another round of precipitation arriving on Friday.

Colder, drier air will quickly settle in Wednesday night behind the
departing system. Temperatures at 850mb are progged to fall to
roughly -8 to -10C by daybreak Thursday. Despite the cold air
advection, Wednesday`s relatively mild temperatures in the 40s will
likely delay the transition to snow until closer to midnight when
the low levels look to cool sufficiently. Brisk NW to NNW winds
should carry the lake effect showers well inland across northern
Michigan, with upsloping adding some additional lift to that
provided by the shortwaves. However, not overly impressed by the
over-lake instability that comes into play with inversion heights
gradually dropping beneath 850mb. Additionally, the influx of drier
air with the incoming Canadian surface high will gradually strip out
moisture in the column from top down Thursday morning. This should
lead to an eventual end to the lake effect showers around midday
Thursday. All told, expecting around an inch within the favored
snowbelts, maybe closer to 2 in the higher elevations. Should see
some sunshine Thursday afternoon with highs in the 30s.

Next round of precip moves in late Friday morning into the afternoon
as developing low level jet quickly transports higher moisture
content into the region. PWATs will climb into the 0.75 to 0.9"
range with isentropic showers spreading in from the west. Models
remain somewhat split on the time of arrival, with the NAM and
Canadian keeping most of northern Michigan dry until late afternoon,
whereas the GFS and ECMWF bring the showers in earlier for eastern
Upper and northwest Lower. Steadier, more widespread precip will
arrive Friday night. Predominantly rain near the lakes with a
rain/snow mix during the day in the higher elevations.

.LONG TERM...(Friday night through Tuesday)
Issued at 307 PM EST Tue Nov 14 2017

Models continue to show a storm system impacting the forecast area
Friday night through the weekend...although there are still
discrepancies among them on exact location and how long any lake
effect will last behind the departing storm with a northwesterly
flow regime. Regardless, northern Michigan will see some system snow
and some lake effect through at least Sunday morning. Too many
uncertainties to begin to guess at snow amounts. High pressure and
drier air will then return during the time frame of later
Sunday/early Monday...diminishing any lingering lake effect snows.
Models then hint at another lower pressure system developing over
the northern Great Lakes region Tuesday. Highs will be generally be
in the 30s while lows will be in the 20s, except for Saturday
morning with WAA still ongoing at the time...lows will only reach
into the low 30s.


.AVIATION...(For the 00Z TAFS through 00Z Wednesday evening)
Issued at 631 PM EST Tue Nov 14 2017

Widespread rain developing from west-east across northern Michigan
tonight and continuing into at least the first half of Wednesday.
Cigs dropping to MVFR with pockets of IFR possible on Wednesday as
a cold front pushes through the area. LLWS at all terminals
tonight into early tomorrow with increasing winds aloft. Those
winds aloft will eventually translate to gusty surface winds on
Wednesday, shifting to the west during the afternoon.


Issued at 955 PM EST Tue Nov 14 2017

Added one additional marine zone to the gale warning (Seul Choix
Point to 5 NM west of the Mackinac Bridge) given persistent
south/southwest flow and increasing wave heights in that zone
(particularly western parts).

No marine concerns through tonight in weak wind regime while sfc
high pressure departs east. Winds have been increasing through the
day today in tightening pressure gradient, and are starting to reach
advisory levels speeds in Lake Michigan. Gale force will develop
tonight across Lake Michigan and possibly Whitefish Bay, and maybe
as early as Wednesday over as early as Wednesday for Lake Huron Lake
Huron. However, coordination with surrounding offices has led to
Gales over Whitefish Bay and Lake Huron Wednesday night into
Thursday as strong cold advection develops behind a passing cold
front. Low pressure crossing srn Ontario later tonight through
Wednesday night will result in decent rains across the Lakes.


LH...SMALL CRAFT ADVISORY until 6 PM EST Thursday for LHZ345-346.
     GALE WARNING from 6 PM Wednesday to 6 PM EST Thursday for
LM...GALE WARNING until noon EST Thursday for LMZ323-341-342-344>346.
LS...SMALL CRAFT ADVISORY until 6 PM EST Thursday for LSZ322.
     GALE WARNING from 6 PM Wednesday to 6 PM EST Thursday for LSZ321.


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