Area Forecast Discussion


330 
FXUS63 KAPX 110447
AFDAPX
Area Forecast Discussion
National Weather Service Gaylord MI
1147 PM EST Sun Dec 10 2017
.UPDATE...
Issued at 926 PM EST Sun Dec 10 2017
A weak shortwave trough was overhead with a swath of added
moisture aloft pushing SE of nrn Michigan. This feature didn't
really have a chance to enhance any lake effect snows since the
banding hadn't really developed yet due to the disruption from the
earlier cold frontal snows. Banding has formed behind this
feature now however, but moisture was gradually thinning with time
and inversion heights were becoming shallower. High pressure will
work into the region over the next several hours before departing
east by Monday morning. This will weaken and back winds
significantly from NW to south by daybreak. As a result, lake 
effect will gradually work it's way closer to the shores or go 
offshore. No more than a half inch in any area across NW lower or
Chippewa county. In this fast/progressive synoptic pattern, the
next Alberta clipper will quickly be pressing SE into the mid
Mississippi valley. Warm advection and deepening moisture, mainly
aloft, will be increasing through Monday morning. Light synoptic
snows will start spreading through nrn Michigan from west to east.
This will bring some light amounts of snow, but despite a shallow
inversion, will also feed and energize light lake effect snows
which may be scraping portions of NW lower shoreline, as well as
into western Mackinac county. That increased snowfall intensity
doesn't really get going until later Monday morning.
&&
.NEAR TERM...(Tonight through Monday)
Issued at 325 PM EST Sun Dec 10 2017
...Lake effect snow tonight transitions to widespread synoptic 
snow Monday...
High Impact Weather Potential...Accumulating snow.
Pattern Synopsis/Forecast...Sharp lake-enhanced trough axis has 
dropped south into Northern Lower Michigan as expected this 
afternoon...helping to enhance ongoing westerly flow lake effect 
snow showers. Locations with the typical snowbelts have received the 
brunt of the snowfall this afternoon...although even portions of NE 
Lower Michigan are seeing brief bouts of heavy snowfall as a result 
of strong convergence along the trough axis. While Eastern Upper 
Michigan is still receiving lake effect snow showers...intensity has 
waned with the departure of the trough axis. Thus have let the 
Advisory expire as of 18Z for Chippewa county. Advisories still 
remain in effect for the big 5 counties in NW/North Central Lower 
Michigan where westerly flow combined with the trough axis continue 
to produce periods of heavy snowfall.
As we head into tonight...low level flow will shift to the N/NW in 
the wake of the departing trough axis. Lake snow bands will 
reorganize and will continue to target the current advisory areas... 
and will also begin to impact other areas around NW Lower Michigan 
such as TVC and MBL. However...with surface ridging and drier low 
level air building into our CWA tonight in the wake of the trough 
axis...overall snow band intensity will diminish. Thus...expect 
remaining snow bands at the time of Advisory expiration should have 
weakened enough to not need any extension of the Advisory...at last 
at this time.
Lake snow will continue to diminish overnight...and will begin to 
transition to a light synoptic snow event as we head toward early 
Monday morning. Low level winds will shift to a nearly straight 
south trajectory...which is one of the few directions that brings 
lake effect precip to a close across our CWA. Just as this 
happens...synoptic moisture and isentropic ascent will begin to 
increase from west to east across our CWA ahead of a fast-morning 
low pressure system dropping SE out of South Central Canada into 
Illinois and Indiana by 00Z Tuesday. QPF from this system will 
likely be relatively low...producing sub Advisory criteria snowfall 
for the day (i.e. an inch or two). 
&&
.SHORT TERM...(Monday night through Wednesday)
Issued at 325 PM EST Sun Dec 10 2017
...Lake Effect First, then Cold Air...
High Impact Weather Potential...Lake effect snow and the coldest air 
so far for Tuesday night/Wednesday morning. 
Pattern Synopsis/Forecast...We continue with the ridge/trough 500 mb 
pattern that has put the Upper Great Lakes into the cold air. This 
has put us into a pattern of a clipper every other day with the next 
two expected to be stronger than the previous. Monday night, the 
next clipper looks to deepen the 500 mb trough, and then lift out 
quickly on Tuesday, allowing for some clearing Tuesday night and 
temperatures falling into the single digits over the forecast area. 
Possibly below zero F in E Upper. Wednesday, the next clipper drops 
into the Upper Great Lakes can kicks off the process all over again. 
Primary Forecast concerns...Monday night into Tuesday, we transition 
from synoptic to LES as the system moves to the east. Again, with 
the cold air and relatively warmer water temperatures, we can get 
light to moderate snow fall rates. The issue will be the persistence 
of the bands. Winds turn to the north so most of the snow fall will 
be along and west of US-131. Tuesday, the 850-700 mb layer begins to 
dry out and the amounts begin to diminish to minor to light amounts, 
mainly near Lake Michigan, which continues into Tuesday night. 
Wednesday, the clipper begins to move into the Upper Great Lakes, so 
we will see snow showers begin to move into the region by the 
afternoon. 
.LONG TERM...(Wednesday night through Sunday)
Issued at 325 PM EST Sun Dec 10 2017
High impact weather: Periodic lake effect snows with additional snow 
possible from a couple clipper systems throughout the extended 
period.
The extended period will continue with below normal temperatures 
through Friday night. These cold temperatures will continue to 
produce periods of lake effect/enhanced snows and produce wind 
chills in the single digits below and above freezing through Friday 
morning...with Thursday morning seeing the coldest of the 
temperatures. Models are beginning to agree with yet another clipper 
system moving into the Great Lakes region Saturday...tracking 
through Lake Superior/Upper Peninsula. This track would provide us 
with more normal temperatures on southerly winds and possibly some 
rain mixing in at times with the snow both Saturday and Sunday 
afternoons over portions of northern lower. Too much uncertainty 
this far out in the forecast period to forecast any accumulations 
that may occur. Highs will be in the 20s Thursday and Friday, and 
then reach into the low to mid 30s for Saturday and Sunday. Lows 
will be mostly in the single digits Thursday morning, single digits 
to low 10s Friday morning, and then warming some each day of the 
remainder of the period...with Sunday morning only dropping into the 
low to mid 20s.
&&
.AVIATION...(For the 06Z TAFS through 06Z Monday night)
Issued at 1144 PM EST Sun Dec 10 2017
Light lake effect snow showers and flurries will gradually push
their way closer to the shorelines, or out over the Lakes through
the night as weak high pressure moves across the region and brings
weakening winds that back around to the south by daybreak. Little
to no accumulation for the remainder of the night. The next low 
pressure and cold front will bring deepening moisture and light
system snow to the region Monday into Monday evening with a 
general 1 to 2 inches of snow to all airports, maybe a shade 
higher around MBL. The cold front crosses Monday night, and winds 
shift and strengthen out of the NW/NNW and will be gusty. 
Accumulating lake effect snows will develop and lead to another 
general 1 to 3 inches, but amounts could be higher around MBL/TVC.
&&
.MARINE...
Issued at 325 PM EST Sun Dec 10 2017
Winds and waves will continue to reach SCA criteria into this 
evening but will drop below criteria overnight as high pressure 
builds into the Western Great Lakes region. Conditions will ramp up 
again to SCA and possibly gale warning criteria Monday night into 
Tuesday as northerly flow strengthens in the wake of a departing 
area of low pressure. Lake effect snow showers will continue to 
impact much of our nearshore areas tonight...but will transition to 
a light synoptic snow event on Monday as that next area of low 
pressure drops thru Michigan.
&&
.APX WATCHES/WARNINGS/ADVISORIES...
MI...NONE.
LH...NONE.
LM...NONE.
LS...NONE.
&&
$$
UPDATE...SMD
NEAR TERM...MR
SHORT TERM...JL
LONG TERM...TL
AVIATION...SMD
MARINE...MR