Area Forecast Discussion
Issued by NWS Gaylord, MI

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FXUS63 KAPX 121733
AFDAPX

Area Forecast Discussion
National Weather Service Gaylord MI
1233 PM EST Tue Dec 12 2017

.UPDATE...
Issued at 936 AM EST Tue Dec 12 2017

Mature north-northwest flow lake effect event unfolding as
planned, with the most intense/well organized banding structures
impacting areas west and southwest of Traverse City where best Lake
Superior connection is estabilished. Less intense bands further
east, but definitely still enough to result in some hazardous travel
conditions. Lake parameters change little until later today, with
excellent instability within a lake induced near 10kft convective
boundary layer, and omega pegged in the favored dendritic growth
layer under the most intense banding structures. Wind direction also
does not vary, suggesting current banding locking in place through
early this evening. The result, several more inches of snow
expected, especially in those areas southwest and west of Grand
Traverse Bay. Warnings/advisories will be trimmed further northeast
as most persistent activity will remain along and west of US-131.

Temperatures expected to only go up a few degrees from current
readings in the single digits and teens, and when combined with
gusty winds, will result in wind chill readings staying several
degrees below zero.

&&

.NEAR TERM...(Today through Tonight)
Issued at 338 AM EST Tue Dec 12 2017

...Heavy snow showers/blowing snow through the day...

High Impact Weather Potential...Heavy lake effect snows along the
Lake Michigan shoreline. Blowing snow and reduced vsbys elsewhere.

Pattern Synopsis/Forecast...Early overnight water vapor imagery and
surface maps reveal a couple strong short waves traversing the
region...one rotating through the Ohio Valley into Pennsylvania and
second wave on it`s heels diving southward through the state. Drawn
out surface low pressure extends through the central Great Lakes
region with one low center over Ohio and second low over Lake Huron
with a trailing arctic cold front swinging down through southern lower
Michigan. Gusty NW winds/strong cold advection now well underway...
poised to pull core of -24C H8 air sitting over Ontario last evening
into the northern lakes region.

As expected...well developed multi-banded lake convection/snow
showers also underway off Lakes Superior and Michigan. Most
persistent banding thus far have cutting down across Grand
Traverse Bay and points SE. But low level mean flow remains a bit
more northwesterly at this point and there are some Lake Superior
connected bands cutting across eastern upper and down into parts
of north central and northeast lower Michigan. A bit more
transient...but heavy at times. Very gusty winds also with quite
a bit of BLSN out there this morning.

Surface lows will aggregate and deepen while heading through the
eastern lakes region into New England through the course of the
day. This should veer the low level mean flow more NNW this morning
and persist through the day with the heaviest/most persistent
snow showers continuing to target the SW quarter of the CWA. More
transient snow showers will continue farther east/south downwind
from the lakes of course. Eventually...surface high pressure
builds across the western Great Lakes tonight and brings a
diminishing trend to the snow and gusty winds.

Primary Forecast Concerns...snow accumulations/headline
management. As mentioned above...still anticipate predominate NNW
mean low level flow to set up through today with the most
persistent snow showers impacting areas around Grand Traverse Bay
and points south. Bufkit forecast soundings at TVC/MBL/and over
Lake Michigan suggest "extreme" lake effect conditions with lake
induced CAPE values over 1000 J/KG...Bufkit lake induced
equilibrium levels over 11K feet...although lake induced CAPE and
EQL`s do begin to drop off through the day and especially tonight
as high pressure builds in and inversion heights slowly lower.
Until then...pretty typical to see one to two inch per hour
snowfall rates (possibly higher) given those conditions. That
said...snow->liquid ratios will begin to lower as we go through
the day owing to an increasingly cold atmosphere and lake
convection migrating out of the DGZ layer (-12C to -18C). Of
course...that will just make for smaller flakes/blowing snow
issues as well.

Lake effect snow accumulations are tough and...let`s face it...
difficult to measure anyway with all the blowing/drifting going
on. Focusing on impacts...certainly periodic heavy snow showers
along with blowing snow/low visibilities will be the rule through
the day...before diminishing tonight. Potential remains for 5 to
10 inches of accumulation through tonight where snow showers are
expected to be most persistent (Leelanau to Manistee counties)...
and there is still the possibility of a few places reporting a
foot.

Now...headlines. Given the high impact and where the most
persistent snow showers are anticipated...winter storm warnings
will remain as-is. Current advisories will also remain intact. In
addition...given the decent transient banding that is still
impacting a good part of eastern upper and northern lower Michigan
this morning...and the gusty winds/blowing snow issues through
the day...I will add in several more counties to the advisory
despite relatively lower forecast snow amounts.

&&

.SHORT TERM...(Wednesday through Thursday)
Issued at 338 AM EST Tue Dec 12 2017

...Continued cold with some areas seeing a bit of light snow...

High Impact Weather Potential...Continued cold conditions with light
snowfall amounts.

Pattern Synopsis/Forecast...A clipper system diving southeast across
the Upper Midwest on Wednesday will deepen as it crosses into the
the Ohio Valley where it is progged to merge with a potent incoming
shortwave. Warm air advection and a band of isentropic lift will
pivot into Lower Michigan as the clipper passes by, impacting mainly
our southwestern counties. Wind back NW behind the departing system
as cold air advection brings in a reinforcing shot of cold air,
leading to some lake effect on Thursday, though activity looks to be
rather light.

Primary Forecast Concerns...Continued cold temperatures and snow
amounts through the period.

A frigid airmass will linger over northern Michigan through the
period with 850mb temperatures generally around -15 to -18C.
However, low level temperatures will moderate ever so slightly as
winds from back from the northeast on Wednesday to the west on
Thursday. We`re looking at highs generally in the teens on
Wednesday, dropping into the single digits again for most Wednesday
night, and then a few degrees or so warmer on Thursday. No strong
winds through the period, but even a light wind at those
temperatures will send wind chills for most of the area below zero
Wednesday morning and again Wednesday night. Coldest wind chills
generally single digits below zero east of US-131 but as cold as -15
degrees up near the Soo. Any patches of clear sky Wednesday night
would favor potentially colder temperatures than currently forecast.

Only some light snow activity through the period from the clipper
brushing our southwest counties on Wednesday and some returning NW
flow lake effect on Thursday. Nothing looking particularly menacing
given the light wind fields overhead. Band of isentropic lift will
struggle to make significant inroads into northern Michigan, and
models are in good agreement with keeping the northern edge of the
QPF from around Grand Traverse Bay down to Standish. Up to an inch
or so of snow possible south of this line, perhaps up to 2 inches
for Benzie and Manistee counties. Influx of colder 850mb air
Wednesday night into Thursday and winds progressively backing to the
NW will favor additional lake effect snow for portions of eastern
Upper and northwest Lower. Rather light winds will limit the inland
progression of these bands, though, and inversion heights will be
around 5 kft with a little bit of drier air to overcome near the
surface. Nothing too impressive, but perhaps sufficient for up to an
inch or so of accumulation in the favored snowbelts.

.LONG TERM...(Thursday night through Monday)
Issued at 338 AM EST Tue Dec 12 2017

High impact weather potential...Continued occasional chances for
light snow and lake effect snow.

Still looking like a busy winter weather pattern over the long term
period. However, it appears that after Friday the stubborn longwave
troughing pattern that`s been stuck overhead will finally lift out
of the region with only shorter-lived, smaller-scale troughs
occasionally passing through thereafter. As a consequence,
temperatures will likely moderate a bit over the weekend and into
early next week.

A digging trough on Friday will bring one more shot of colder air
into the region for a brief time, allowing for renewed NW flow lake
effect chances along with a weak clipper system passing through.
Weather pattern forecast for the weekend into Monday is currently
rather muddled given model differences with timing/placement of
another potential clipper system, but it loo

&&

.AVIATION...(For the 18Z TAFS through 18Z Wednesday afternoon)
Issued at 1228 PM EST Tue Dec 12 2017

Lake effect snow showers, some quite intense, will continue to
bring rapidly varying conditions to the taf locations into this
evening. This will be especially true at KTVC and KMBL as locally
heavy snow bands traverse overhead. Current lake snows impacting
KAPN should rotate out of that area later this afternoon. Gusty
winds will only exacerbate the conditions, producing areas of
blowing and drifting snow. Snow to liquid ratios will remain high,
on the order of 20 to 1.

Improving conditions expected overnight as lake snows lighten and
focus closer to the Lake Michigan coast. Band of snow tied to low
pressure passing off to our southwest will likely bring
deteriorating conditions once again to KTVC and KMBL during the
morning hours of Wednesday.

&&

.MARINE...
Issued at 338 AM EST Tue Dec 12 2017

Gale force wind gusts will persist on most nearshore areas through
the day...before diminishing tonight. Winds/waves will diminish to
below headline criteria heading into Wednesday and we should be
headline free for the next few days.


&&

.APX WATCHES/WARNINGS/ADVISORIES...
MI...WINTER WEATHER ADVISORY until midnight EST tonight for MIZ019-
     021-027-032-033.
     WINTER STORM WARNING until midnight EST tonight for MIZ020-025-
     026-031.
LH...GALE WARNING until 6 PM EST this evening for LHZ345-347>349.
     SMALL CRAFT ADVISORY until 6 AM EST Wednesday for LHZ346.
LM...GALE WARNING until 6 PM EST this evening for LMZ323-342-344>346.
     SMALL CRAFT ADVISORY until 6 AM EST Wednesday for LMZ341.
LS...GALE WARNING until 6 PM EST this evening for LSZ321-322.
&&

$$

UPDATE...MB
NEAR TERM...BA
SHORT TERM...MK
LONG TERM...MK
AVIATION...MB
MARINE...BA



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