Area Forecast Discussion
Issued by NWS Marquette, MI

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FXUS63 KMQT 161138

Area Forecast Discussion
National Weather Service Marquette MI
638 AM EST Mon Dec 16 2019

.SHORT TERM...(Today and tonight)
Issued at 235 AM EST MON DEC 16 2019

Bottom line up front: snow showers are expected for the Keweenaw
Peninsula today through tonight, portions of the east this
evening, and the west tonight. Temps will remain below normal for

Flurries and light snow ongoing across a good chunk of the U.P.
early this morning will taper off with little to no accumulation
expected. Snow chances will persist though in the Keweenaw
Peninsula through this forecast period as it sits on the periphery
of a surface high centered near the MN/WI border, aided by a
subtle disturbance dropping down across Lake Superior. As an upper
trough axis approaches the Upper Great Lakes this evening, vort
max will intensify a bit, with snow showers popping up in the east
as well, primarily for locations close to the Lake Superior
shoreline in eastern Alger into Luce County. Although these
eastern showers look to be fairly short-lived, a quick inch or two
could easily be accumulated this evening. As the night continues,
the attention shifts back to the west as this aforementioned
trough kicks off some cyclogenesis over northern Lake Superior.
Expect the lake to assist in providing some lower-level moisture,
along with aiding in the trajectory of said snow showers, as 850mb
to 700mb winds remain nearly westerly today into tonight. Surface
winds will be a bit more erratic, rocking back and forth between
the WNW to SW, before becoming northwesterly across the west half
of the lake by sunrise tomorrow. Accumulations today into tonight
will generally range from 2" to nearly 4" in the Keweenaw, with
those higher amounts likely confined to the higher terrain
locations along the spine.

As alluded to, highs today will remain on the chilly side, topping
out in the teens and 20s. This will translate into tonight as
well, although a non-diurnal temp curve for at least the west half
is anticipated to play out. Temperatures in the west are looking
to bottom out relatively quickly initially, moderating as
additional cloud cover traverses into the area. In the east, have
followed a bit more of a traditionally seen diurnal curve as the
clouds briefly part after the snow showers this evening taper off.
Single digits on either side of the zero degree mark is expected,
with teens along the lakeshores and the Keweenaw.

.LONG TERM...(Tuesday through Sunday)
Issued at 325 AM EST MON DEC 16 2019

A polar cold front will be right on our doorstep Tuesday morning,
pushing into western Upper Michigan with the beginnings of snow
shower activity that will transition to LES, strengthen through the
evening and overnight, then diminish from west to east Wednesday
into Wednesday night as flow aloft becomes anticyclonic and a sfc
high quickly pushes through the region. Winds turn to southerly
behind this high and after a cold Wednesday temperatures will
gradually warm through the weekend with highs back into the low to
mid 30s by Sunday thanks to large scale ridging building over the
CONUS. The latter half of next week will also feature a few
shortwaves interrupting the ridge and bringing intermittent light
precip to the region as well as the potential for a weak split flow
low pressure system to traverse the region Friday into Saturday.
After it exits it will leave Upper Michigan on the western periphery
of an ECONUS trough to end the weekend but it will quickly be
replaced by large scale ridging into early next week after perhaps
one last clipper shortwave Sunday night.

Tuesday morning, snow will mainly be relegated to the northwestern
UP but colder air and modest northwesterly winds will overspread the
region behind the cold front. Snow will pick up over the east half
through the afternoon and evening and LES will really get going in
earnest overnight. Inversion heights will build to near 7kft over
the east and 6kft over the west before subsidence moves in from west
to east during the daytime Wednesday and begins to cut off snow.
SLRs likely maximize 18Z Tue-00Z Wed and could end up similar to
last night with areas seeing values north of 50:1 for a time.
However, after this 850 mb temps will plummet to -24 to -27C and the
column will exit the DGZ leading to smaller, non-dendritic
snowflake growth. Thus, late Tuesday night into Wednesday
visibility will become a concern. Some blowing and drifting will
also be possible at times near Lake Superior.

In total over the 36 hour period Tuesday morning through Wednesday
evening, snow accumulations will be in the 2-6" range west with the
better chances for the higher end over the spine of the Keweenaw.
For Alger, northern Schoolcraft, and northern Luce, it`s looking
like a 4-7" event with lower totals as you head south towards Lake
Michigan. Given the NW wind direction dominating, probably only an
inch or two for the more heavily populated Harvey to Ishpeming
corridor and of course the south-central will remain mainly dry.
Again, heaviest snowfall rates probably come Tuesday evening through
the overnight, but travel may be impacted by snow-covered roads and
visibility restrictions Wednesday morning, especially from Munising

Wednesday night the LES ends and winds turn to the south. A quick-
moving clipper may bring light snow to the Keweenaw and eastern UP
into Thursday morning, then models hint at some additional LES
developing off of Lake Michigan before the colder airmass pulls out.
This would impact primarily Schoolcraft and Luce Counties through
the day. Model spread increases after this as split flow develops
over the region. GFS continues to develop a closed low and
associated sfc circulation that would bring sustained
south/southeasterly flow off the lake and some weak synoptic lift
for additional UP-wide snow showers later Friday. The ECMWF,
however, never closes off at 500 mb and remains dry Friday and
Friday night.

Pretty good agreement, however, in a Saturday clipper shortwave
bringing some light snow primarily to the north half and opted to
increase POPs to chance from the blends slight chance accordingly.
May be another similar clipper shortwave later in the weekend,
however this feature is not included in the deterministic GFS
solution. Broad ridging will build into the central CONUS for Monday
and should lead to a drier day, but at 7 days out this may change
so stay tuned...

.AVIATION...(For the 12Z TAFS through 12Z Tuesday morning)
Issued at 628 AM EST MON DEC 16 2019

KCMX`s ceilings have dipped down into the IFR category, but is not
anticipated to last much longer, and have reflected the ceilings
teetering right on the edge through midday. KSAW`s ceilings also
dropped a category, into MVFR, with a similar setup anticipated,
teetering right on the edge. Generally speaking, MVFR ceilings are
anticipated to prevail for much of this TAF period at all three
terminals, although some partial clearing could occur at KSAW
later in the period. On and off snow showers are expected at KCMX
through the period, with snow chances dropping off at KIWD today
before re-emerging later tonight. Winds will become westerly
today through tonight, with gusts over 20 knots possible at KCMX.


.MARINE...(For the 4 AM Lake Superior forecast issuance)
Issued at 316 AM EST MON DEC 16 2019

A few near gale-force west to southwesterly wind gusts will
persist today into this evening, briefly diminishing early tonight
before re-energizing by early tomorrow. Widespread near gale-
force northwesterly wind gusts are expected tomorrow into tomorrow
night, hanging on in the east until early Wednesday. Surface high
pressure moving in Wednesday through early Thursday will allow
for sustained winds to remain less than 20 knots, with this trend
continuing into the weekend, thanks to ridging taking hold.

Moderate freezing spray will be a concern today into tomorrow,
with heavy freezing spray becoming increasingly concerning by
tomorrow night. Moderate freezing spray potential continues into
Wednesday, subsiding Wednesday night, with sporadic icing
potential through week`s end.

Upper Michigan...
Lake Superior...
Lake Michigan...


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