National Weather Service - Area Forecast Discussion

917
FXUS63 KAPX 120440
AFDAPX

Area Forecast Discussion
National Weather Service Gaylord MI
1140 PM EST Wed Dec 11 2019

.UPDATE...
Issued at 1043 PM EST Wed Dec 11 2019

Evening composite analysis reveals larger scale trough axis now
progressing through the eastern lakes region with the coldest air
(aloft anyway) already starting to move out of the area. Large
expanse of surface high pressure...centered over Ohio...spans
much of the eastern third of the CONUS. But, lake aggregate
troughing is still evident over eastern Lake Superior down into
northern Michigan, maintaining our overall west-southwesterly flow
and some lingering gustiness.

Substantially drier air has also spread into the region. seen on
this evenings APX sounding. Westerly flow lake effect snow showers
continue in NW Lower Michigan but have dwindled substantially
especially in the last few hours. More substantial lake snows are
ongoing in eastern Lake Superior and just clipping the Whitefish
Point area.

Upstream, weak-ish warm advection forcing is underway through the
Upper Midwest, evidenced by a developing corridor of radar returns
from the Dakotas into western Wisconsin. Low pressure is
stretched out along the front range of the Rockies with another
short-wave trough axis moving eastward through that region.
Short-wave trough and surface low will eject into the Midwest
overnight into Thursday before sliding up through northern
Michigan Thursday/Thursday night bringing us another round of
accumulating snow.

Rest of tonight: Remaining lake effect snow showers will further
diminish as temperatures warm aloft and low level mean flow backs
southwest. Only remaining headlines were in western Chippewa
county and expired at 10 pm. There are still some snow showers
grazing the Whitefish Point area, but should be pushing out of
there in the next few hours.

Thursday`s system: Early peek at the 00Z (NAM/NAMNEST) guidance
tracks the low level circulation up through the Straits
region...perhaps just a tad further northward than previous
guidance. Tight thermal gradient and a very strong pulse of
f-gen/deformation forcing is still looking to take aim across the
U.P., Straits and just into the tip of the mitt from around mid
morning into mid afternoon and should bring ~6 hour window of
heavier snowfall through that region. Some SW flow lake
enhancement is also possible. All told, it still appears that a
good 5 to 8 inch snowfall is a good bet through Thursday evening
with much lesser amounts further south. Contemplated hoisting
winter weather headlines with the evening update. But heavier
snowfall will not really get going until mid-late morning onward
and I may let the midnight shift to make the final adjustments
and headline determination.

&&

.NEAR TERM...(Through Tonight)
Issued at 359 PM EST Wed Dec 11 2019

...Very cold with lake effect snow showers transitioning to synoptic
snow tonight...

High Impact Weather Potential...Cold temperatures...gusty winds and
ongoing snow showers will continue to produce low vsbys...very cold
wind chills and hazardous travel conditions thru tonight.

Pattern Synopsis/Forecast...Weak wave has reached the Ontario/Quebec
border this afternoon. Reinforcing shot of even colder air has
pushed into our entire CWA behind the associated surface
reflection...with our entire CWA holding in the teens at what is
usually diurnal peak heating. GLR has barely warmed out of the
single digits all day. Very cold airmass continues to produce
westerly flow lake effect snow showers despite an increasingly
hostile airmass for lake precip production as subsidence and drier
air continue to edge into the Western Great Lakes. We have seen some
diminish in coverage and intensity...but the combination of small
flake size due to the very cold airmass and winds gusting to 30 kt
is resulting in diminished vsbys to 1/4SM or less under any of the
more enhanced snow shower bands. Will need to maintain all headlines
into the evening hours given the continued threat of poor vsbys due
to falling and blowing snow...not to mention very low wind chills.
Additional snow amounts will be rather light due to small flake
size...but ongoing hazards into the evening hours certainly warrants
the continuation of headlines.

Low level flow will begin to back to the SW overnight as the narrow
surface ridge slides east of Michigan and our next low pressure
system begins to approach the Western Great Lakes. Residual lake
effect snow showers will transition to a more lake enhanced and
eventually widespread synoptic snow very late tonight into Thursday
as deep moisture surges into the region in advance of this system.
Vast majority of accumulating snow from this system will happen
during the day on Thursday. Expect another bitterly cold night
across the Northwoods as overnight lows dive mainly into the single
digits above zero.

&&

.SHORT TERM...(Thursday through Saturday)
Issued at 359 PM EST Wed Dec 11 2019

High Impact Weather: Several inches of accumulating snow possible
for northern lower and eastern upper MI by Friday morning

A longwave trough will depart off of the New England coast to begin
the period as surface high pressure also vacates the Great Lakes to
the east. A subtle shortwave moving across the northern Great Plains
will provide upper-level ascent to support a cyclone in lee of the
Rockies to move northeast into the region by Thursday evening.
Although this cyclone won`t be particularly deep by any measure, the
surface response with strong high pressure just to the east along
with strong low to mid-level winds could lead to somewhat gusty
conditions into Thursday night.

The aforementioned surface systems will funnel relatively warmer air
into the Great Lakes with enhanced southerly flow. Warm air
advection/isentropic ascent in the lower-levels accompanied by
synoptic lift aloft provided in the exit region of the advancing
shortwave will be ample forcing to support snow production. This
forcing within a relatively deep, moist dendritic growth layer along
with potential lake enhancement with warm lake temps and mean
southwest low-level flow could lead to heavy snowfall in the tip of
the mitten/eastern upper MI. Accumulations in this area are expected
to be in the 6-8" range by Friday morning with locally higher
amounts possible. Otherwise, a more widespread 2-4" is expected,
mainly along M-32 and north. The previously mentioned warm air
advection will help temps reach into the upper 20s/low 30s on
Thursday and level off overnight. High temps on Friday could get
into the mid 30s before cooling off late ahead of the next round of
precipitation chances Friday night.

.LONG TERM...(Saturday night through Wednesday)
Issued at 359 PM EST Wed Dec 11 2019

High Impact Weather Potential: Minimal

A large, positive-tilt trough will be moving across the southeast
CONUS at the beginning of the weekend, providing favorable upper-
level support to develop a surface cyclone that will move up the
Atlantic coast over the weekend. Surface high pressure builds
underneath subsidence across the northern Great Plains, helping to
funnel cold air back into the Great Lakes by the start of next week.
High temps hovering near freezing will likely drop overnight lows
into the teens and high temps into the low to mid 20s by Monday. The
potential exists for a system to impact the forecast area towards
the end of this period, but considerable uncertainty exists at this
time given large discrepancies in models this far out.

&&

.AVIATION...(For the 06Z TAFS through 06Z Thursday night)
Issued at 1140 PM EST Wed Dec 11 2019

Westerly flow light lake effect snow continues in the snowbelts of
northern Lower Michigan, although they have weakened substantially
this evening and will continue to do so overnight. MVFR lake
cloud cover is still impacting the NW Lower Michigan coast but
will also thin out overnight as winds back to south by morning.

But after a brief respite, more snowfall is on the way for
Thursday. Low pressure over the front range of the Rockies will
eject into the Midwest tonight and slide up through northern Lower
Michigan Thursday. This system will spread another round of
snowfall across northern Michigan with the heaviest snow
anticipated north of M-32 into the U.P. Conditions will gradually
trend to MVFR and possibly IFR through the day...with the worst
conditions at PLN.

&&

.MARINE...
Issued at 359 PM EST Wed Dec 11 2019

Winds and waves will continue to reach SCA criteria tonight thru
Thursday in the wake of one departing upper level short wave and in
advance of our next low pressure system moving into the Western
Great Lakes region. Residual lake effect snow showers tonight will
transition into widespread synoptic snow on Thursday as this next
system approaches.


&&

.APX WATCHES/WARNINGS/ADVISORIES...
MI...WINTER WEATHER ADVISORY from 6 AM Thursday to 1 AM EST Friday
     for MIZ016>018-086>088-095>099.
LH...SMALL CRAFT ADVISORY until 6 AM EST Friday for LHZ348-349.
     SMALL CRAFT ADVISORY until midnight EST Thursday night for
     LHZ345>347.
LM...SMALL CRAFT ADVISORY until 7 PM EST Thursday for LMZ341-342.
     SMALL CRAFT ADVISORY until 6 AM EST Friday for LMZ323-344>346.
LS...SMALL CRAFT ADVISORY until 7 PM EST Thursday for LSZ321-322.
&&

$$

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

NWS APX Office Area Forecast Discussion