Area Forecast Discussion
Issued by NWS Marquette, MI

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FXUS63 KMQT 162353

Area Forecast Discussion
National Weather Service Marquette MI
653 PM EST Thu Nov 16 2017

.SHORT TERM...(This evening through Friday)
Issued at 255 PM EST THU NOV 16 2017

...Wintry mix leads to slippery travel at times through Fri...

WV loop and 12z ROABS indicate deep trough over Pacific Northwest
with 130-140kt jet rounding base of trough from CA to northern U.S.
Rockies. As trough shifts east through Fri toward central Conus, jet
splits with northern branch surging toward northern Ontario while
southern branch jet moves toward Middle Mississippi River Valley and
eventually the Ohio River Valley. As stronger shortwave in the
trough over southern Alberta and Saskatchewan moves to northern
Ontario on Fri morning, a 992-996mb sfc low will track over Manitoba
and Hudson Bay/northern Ontario. Thus late tonight through Fri
morning expect heavier precip to remain to north of Lk Superior.
Model soundings indicate increase in mid level moisture tied to warm
air advection aloft with the shortwave to the north. Any precip
tonight that occurs due to this moisture advection would be light
the form of snow. However we will also have a continued risk of
freezing drizzle/flurries over higher terrain of central due to
upslope flow, this evening from northeast winds and overnight from
south to southeast winds as return flow develops.

Later Fri morning, diffluence from upper jet streaks along with
increasing moisture advection ahead of sfc trough tied to low over
northern Ontario will spread light to moderate precip over much of
Upper Michigan. Still could see risk of freezing precipitation late
morning or even into early aftn as temps stay near freezing over
inland west. Most areas by early to mid aftn should see precip
change to rain as temps warm into the mid 30s with warmer air moving
in behind the warm front. There may be enough cold air for snow to
mix with the rain over far west in the aftn and also in the far east
forecast area.

Overall it looks like we`ll be dealing with a messy mix of wintry
precip late tonight through much of Fri. At this point since the
heavier precip is expected to fall during the aftn when most areas
will see only rain will handle light wintry precip in the morning
with an SPS. Evening or mid shift can issue winter weather advisory
if it appears there will be more precip around late tonight into Fri
morning when ptype will be bigger issue. The SPS will mention the
possible slippery travel and also strong/gusty south winds expected
as the warm front moves through.

.LONG TERM...(Friday night through Thursday)
Issued at 332 PM EST THU NOV 16 2017

Main issues in the extended will be rain potential for Friday night,
then focus shifts to freezing drizzle potential late Friday night
through Saturday.

Friday night into Saturday: Low pressure is progged to lift from
Missouri, Friday night, to near Lake Erie/Lake Ontario by Saturday
afternoon. At the same time, a shortwave is progged to slide across
the area Friday night with another/stronger wave expected to move
through by Saturday afternoon. The deeper moisture is progged to
slide into at least the eastern half of the U.P. This will be the
main area of focus for heavier precipitation, especially for Friday
night. As the low moves closer to Lake Erie/Lake Ontario on
Saturday, the deeper moisture will continue to slide of to the east.
The increased forcing associated with the surface low and first
shortwave will allow for widespread, mainly rain to continue through
much of Friday night over the eastern U.P. Overall, not expecting
much more than a tenth to a quarter inch of QPF, again, due to the
deepest moisture staying off to the east of the U.P. The best chance
of seeing closer to a quarter of an inch would be over the far
eastern U.P. The western half of the U.P., seeing mainly shallow
moisture, would be primed for more of a drizzle/freezing drizzle
setup for Friday night. This would likely fall as drizzle through
much of the evening before colder air moves in overnight, allowing
for freezing drizzle to occur. Temperatures aloft are not expected
to be cold enough and moisture is not expected to be sufficiently
deep to see snow for this time period, the only exception may be a
brief change over to snow as the deeper moisture departs. Forecast
soundings continue to indicate lack of moisture in the mid levels,
with most of the moisture being warmer than than the -10C isotherm
from late Friday night through Saturday.  While the freezing drizzle
will be light, it doesn`t take much to make travel very slippery,
especially on untreated surfaces.

Saturday night through Sunday: As the aforementioned stronger second
wave slides into the Upper Great Lakes Saturday night, expect colder
air to slide into the Upper Peninsula. This will act to lower the
DGZ enough to take away the freezing drizzle potential and keep
precipitation in the form of lake effect snow for mainly northwest
wind favored locations. Yet another wave is progged to slide across
the area late Saturday night into Sunday morning, which will help to
increase lake effect snow coverage. 850mb temperatures are expected
drop to the -14C to -17C range through this time period, giving
delta-t values in the 19C to 22C range.  More than enough for lake
effect snow potential. Inversion heights are progged to be around
5kft to around 8kft when accounting for lake surface temperatures;
however, the sounding is lacking moisture in the 6kft to 8kft layer.
This points to mainly a light to possibly a moderate lake effect
event for this time period. The best chance of seeing the moderate
snow would be as  the aforementioned waves move overhead Saturday
night into Sunday morning. Generally looks like 3 to 5 inches
possible in the northwest wind favored snow belts, with the greatest
totals expected over the higher terrain.

sunday night through Monday night: As weak ridging slides into the
Upper Great Lakes and low pressure begins to approach form the
Northern Plains, winds will become westerly Sunday night and then
southerly for Monday into Monday night. This will effectivly push
the lake effect snow over Lake Superior before ending as warmer air
pushes in both at the surface and aloft.

Tuesday through the extended: Models are in good agreement that a
low pressure system will slide just north of Lake Superior early
Tuesday morning and into Quebec by Wednesday morning. This will drag
a cold front through the area during this time period and shift
winds to the northwest. 850mb temperatures are progged to drop into
the low to mid teens below zero, which would again be a good setup
for some lake effect snow for northwest wind favored snow belts.
Details will have to be ironed out as the system gets closer. At
this point will stick with a consensus of the models as this systems
looks to be handled well with the consensus.

.AVIATION...(For the 00Z TAFS through 00Z Friday evening)
Issued at 652 PM EST THU NOV 16 2017

Expect MVFR conditions initially at KIWD/KCMX/KSAW. As high pres
ridge departs and winds become s to se, downsloping should allow
KIWD to improve to VFR toward 06z. KCMX may also improve to VFR
overnight as winds downslope off the Huron Mtns. KSAW will likely
remain MVFR as winds will still be upsloping. In addition, as pres
gradient tightens and winds above inversion strengthen, LLWS will
develop overnight at KIWD and late tonight/Fri morning at KCMX. Some
light wintry mixed pcpn may develop late tonight, but more likely on
Fri, and there may be a little light icing before sfc temps rise
above freezing. Increase in low-level moisture will lead to
conditions falling to IFR at all terminals during Fri. Also,
southerly winds will be gusty to around 30kt.

.MARINE...(For the 4 PM Lake Superior forecast issuance)
Issued at 255 PM EST THU NOV 16 2017

Brief lull in winds into this evening then south to southeast winds
increase late tonight into Fri as low pressure crosses northern
Ontario. Gales are expected over central and eastern Lk Superior and
a gale warning has been posted. Cold front to the south of the low
moves through Fri night with winds diminishing blo gales. However,
northwest winds increase to gales again late Sat into Sat night.
Winds diminish to 30 kts Sun-Mon but more gales are possible Tue
into Wed as active pattern continues.

Upper Michigan...
Lake Superior...
  Gale Warning from 5 AM to 4 PM EST Friday for LSZ244-245-248>251-

Lake Michigan...
  Gale Warning from 6 AM to 7 PM EST Friday for LMZ221-248-250.



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