Area Forecast Discussion
Issued by NWS Gaylord, MI

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FXUS63 KAPX 171800
AFDAPX

Area Forecast Discussion
National Weather Service Gaylord MI
100 PM EST Fri Jan 17 2020

.UPDATE...
Issued at 1044 AM EST Fri Jan 17 2020

Large area of high pressure sliding across the Great Lakes this
morning. Resultant squashing of the convective boundary layer and
weak wind fields finally putting an end to the persistent lake
snows. Even seeing a slow scattering out of the low level
overcast, with this trend expected to continue as we head into the
afternoon. Unfortunately, still not expecting a ton of sunshine
as cirrus spreads overhead within early stages of top-down
saturation tied to developing central Plains low pressure. Deep
enough saturation to generate snow still looks to hold off until
tonight. Regarding that upcoming storm, overall forecast remains
on track, with mostly light snow accumulations tonight, followed
by heavier snow heading through Saturday. Definitely no changes
required to inherited winter weather advisory.

&&

.NEAR TERM...(Today through Tonight)
Issued at 327 AM EST Fri Jan 17 2020

Impactful weather: System accumulating snow starting tonight.

Pattern synopsis and forecast:

A fairly high amplitude upper air pattern out there early this
morning, with troughing over both coasts, and ridging in the central
conus. On the forward flank of the ridging, strong sfc high pressure
continues to work it`s way into nrn Michigan, with much drier air
and lowering inversion heights via increased subsidence. This has
been creating an increasingly harsher environment for sustaining
lake effect snow showers, which were weakening/diminishing with time
in the NW flow snowbelts. There was still enough low level moisture
stuck underneath the lowering inversion, for widespread stratus, but
breaks in the clouds were developing, in part due to weakening winds
resulting in less inland transport of moisture flux off the Great
Lakes. Well upstream in western MT, low pressure has developed just
ahead of the upper troughing, resulting in areas of snow.

A pretty quiet day, with the strong sfc high pressure swinging
across nrn Michigan. Winds will continue to weaken, with less and
less moisture flux off the Great Lakes. Lake effect light snow and
flurries will initially work closer and closer to the shoreline,
before 1000-850mb winds shift more southerly, and perhaps move the
flurries into upper Michigan (if the dry air and subsidence hasn`t
squashed all Lake convection). Either way, there will be little to
no accumulation. Outside of the lake effect, low clouds are expected
to scattered out, or even go clear, due to the subsidence and
drying.

The western MT sfc low pressure and associated upper troughing will
have moved into the central Plains by late in the day, which will
then track through the mid and upper Mississippi valley by daybreak
Saturday. Skies will start clouding back up as top down moistening
ensues via gradually increasing theta-e advection, DPVA and 100+kt
upper jet dynamics. The atmosphere completely saturates for most all
of nrn Michigan through the overnight hours, with light to moderate
snow breaking out while the max forcing arrives. Expecting smaller
flake size, as the max lift is well below the DGZ. The heavier snow
will come Saturday (see below), but 1-3 inches is possible by
daybreak Saturday, the most snow in the SW CWA and the least to the
NE CWA.

Highs today will be in the lower half of the 20s with lows tonight
early this evening, in the teens to low 20s, before temperatures
very slowly climb through the night via WAA/thickening clouds.

&&

.SHORT TERM...(Saturday through Sunday)
Issued at 327 AM EST Fri Jan 17 2020

...A Moderate Ending, and then Moderate Lake Effect...

High Impact Weather Potential...Moderate to possibly heavy snow from
a storm that will move through the Upper Great Lakes Saturday. Then
lake effect snow Saturday night into Sunday.

Pattern Synopsis/Forecast...Saturday morning, the system moves from
the Upper Mississippi Valley and into Lower Michigan by 18z. The
GFS, NAM and ECWMF/00z have a very similar track with the low moving
through C Lower during the day and to be in eastern Lake
Huron/Georgian Bay by 00z/Sun. The moisture looks good on the
models, but there is some warm air near the sfc (SFC Temp near mid
30s) near Saginaw Bay that may get a mix of rain and snow. However
the rest of the region remains cold enough for snow so will. Model
QPF is suggesting that the snow could be moderate to heavy at times.
It continues to look like the 12 and 24 hour amounts will be in the
advisory range.

Saturday evening, the system is east of the region, and we quickly
transition to LES mode. The 850 mb temperatures remain between -10c
and -18c. With the moisture in the layer around 80 to 90%. The
concern then turns to the wind directions to see if the bands can
amount residence time to get heavy snow to continue. As we go into
Sunday, the winds in the 1000-850 mb layer are north on the models.
This will limit some of the fetches, as the winds in lake Superior
are more NE. This produces little LES from the north and the shorter
fetch over Lake Michigan may not produce much. The snow amounts on
the GFS and ECMWF diminish from the limited fetch over the lakes.
The 850 mb temperatures are around -14c and the water temperatures
are around +3c +4c, Lake Superior, and Michigan respectively. so
enough delta T for the instability. Just the wind direction and the
dry air in the 850-700 mb layer by Monday morning on the ECMWF and
the NAM. The GFS still maintains moisture until 12z/Mon.

Primary Forecast Concerns...The system could produce some higher
amounts, and wouldn`t be surprised that somewhere a 10"/24 hour
amounts are possible, especially near eastern Chippewa county as the
initial winds are SE off of Lake Huron. However, all in all, the
expectation is that this will produce moderate amounts of snow  with
gusty winds. Winter Weather Advisory is the expectation.

The start of the LES is still a concern, as we debated how to align
the headlines. The problem is that some counties in NW Lower will be
still snowing due to LES, after 00z/Sun when the low moves out. This
could cause some confusion with the public, so we tried to put
headlines up that will cover the event.

.LONG TERM...(Sunday night through Thursday)
Issued at 327 AM EST Fri Jan 17 2020

High Impact Weather Potential...lake effect snow for Monday through
about Tuesday.

Extended (Monday through Thursday)...The winds remain favorable
through Tuesday morning with a favorable temperature profile on the
GFS. The ECMWF is slightly warming lowering the delta TS to around
13C. Also on both models, there is drier air that will inhibit the
moderate snow amounts. So will expect minor to light snow amounts
through Wednesday morning

The models are in much better agreement Wednesday as that system
moves up out of the S Plains with a sfc trough in the Upper
Mississippi Valley and a weak warm front. This looks to kick off
some light precipitation (looks like rain or a mix Wednesday night).
Thursday, the models then are in disagreement with the potency of
the system and the resultant temperature profiles, and thus p-type.
The ECMWF would suggest light snow, the GFS some rain showers,
before a stronger system will push into the region Friday morning.

&&

.AVIATION...(For the 18Z TAFS through 18Z Saturday afternoon)
Issued at 1255 PM EST Fri Jan 17 2020

Low pressure cutting up into and through the area later tonight
and Saturday will bring lowering clouds and widespread snow from
southwest to northeast overnight. Expect primarily IFR conditions
by late tonight through Saturday morning. Expect several inches of
snow by later Saturday afternoon, with increasingly gusty
southeast winds bringing blowing and drifting concerns. Snow to
liquid ratios will not be particularly high, suggesting the snow
will be a bit wetter than usual.

&&

.MARINE...
Issued at 327 AM EST Fri Jan 17 2020

Winds continue to weaken as high pressure moves more into the western
Great Lakes. This high pressure works across the region today, while
the next low pressure system crosses nrn Michigan Saturday. Winds
will ramp up substantially out of the SE tonight ahead of the low
pressure, resulting in advisory and many gale force speeds. After
the low passes Saturday night, additional advisory winds are
anticipated, and potentially additional gales for over srn sections
of Lake Michigan. This storm will bring widespread snow to the
region, with lake effect snow into early next work week.


&&

.APX WATCHES/WARNINGS/ADVISORIES...
MI...WINTER WEATHER ADVISORY from midnight tonight to 7 PM EST Sunday
     for MIZ020-021-025>027-031>033.
     WINTER WEATHER ADVISORY from 5 AM Saturday to 1 PM EST Sunday
     for MIZ086>088-095-096.
     WINTER WEATHER ADVISORY from 3 AM Saturday to 1 PM EST Sunday
     for MIZ016-022-028-098-099.
     WINTER WEATHER ADVISORY from 3 AM Saturday to 7 AM EST Sunday
     for MIZ017-018-023-024-029-030-097.
     WINTER WEATHER ADVISORY from midnight tonight to 1 AM EST Sunday
     for MIZ034>036-041-042.
LH...GALE WATCH from midnight EST tonight through Saturday afternoon
     for LHZ345>349.
LM...GALE WATCH from midnight EST tonight through Saturday afternoon
     for LMZ323-341-342-344>346.
LS...GALE WATCH from midnight EST tonight through Saturday afternoon
     for LSZ321-322.
&&

$$

UPDATE...MB
NEAR TERM...SMD
SHORT TERM...JL
LONG TERM...JL
AVIATION...MB
MARINE...SMD


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