Area Forecast Discussion
Issued by NWS Marquette, MI

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FXUS63 KMQT 180506
AFDMQT

Area Forecast Discussion
National Weather Service Marquette MI
1206 AM EST Sat Nov 18 2017

.SHORT TERM...(This evening through Saturday)
Issued at 335 PM EST FRI NOV 17 2017

...Heavy snow possible through early evening on the Keweenaw...
...Wintry mix will lead to slippery travel into Sat...

Large scale trough expands across Great Lakes through Sat. Stronger
shortwave and jet streak in base of trough will support stronger sfc
low spinning up from mid Mississippi River Valley late tonight to
the lower Great Lakes by late Sat aftn. Widespread precipitation
that moved in this aftn will diminish from west to east tonight as
sfc trough tied to low over northern Ontario continues to cross
Upper Michigan. Warm layer aloft 850-800mb or 3-4kft AGL led to
wintry mix of ra/fzra/sleet and snow earlier today but that mostly
has changed to rain now for central and east. Out west, already
seeing signs that cold air is slipping back into the region as rain
has changed back to snow at KCMX and has mixed with mixed with snow
at KIWD.

Attn is on h8-h7 fgen band in right entrance of jet streak causing
moderate to heavy precip over northeast MN and over western Lk
Superior. This forcing/precip slides across Keweenaw this evening.
RAP and HRRR are locked on to period of heavy precip, all snow,
through 00z with tapering to dz/fzdz afterwards. Will put out a
short duration winter wx advy for evening across Keweenaw Peninsula
for a brief period of moderate to heavy snow occurring right during
the evening commute.

Elsewhere, expect rain/snow mix over mostly scntrl and east forecast
area to gradually change to mainly dz or fzdz late evening into the
overnight hours. Will have to watch out for potential for some more
rain/snow scntrl and east as late as a bit after midnight as one
last push of precip tied to left exit of jet streak over central
Plains moves through. N to NW winds in wake of the sfc trough will
lead to best chance of dz/fzdz later tonight over higher terrain of
west, northwest and ncntrl Upper Michigan.

Other than the winter weather advy for evening on the Keweenaw
Peninsula, another SPS will be issued for the west half of Upper
Michigan to cover continual wintry mix and possible icy roads
tonight into Sat morning. Already hearing of icy roads in the
interior west U.P. as temps are just above freezing. Would expect
more of the same this evening and overnight as temps fall below
freezing.

Into Sat, precip for most of the day will be dz/fzdz, mainly west
and ncntrl higher terrain. Approaching shortwave from Manitoba and
northern Ontario that eventually helps carve out deeper troughing
and brings in colder air aloft on Sat night could also lead to
enough ice introduced aloft to lead to ptype becoming mostly snow in
the afternoon for the west half. Any ice and snow amounts on Sat
will be light.

.LONG TERM...(Saturday night through Friday)
Issued at 334 PM EST FRI NOV 17 2017

Main issues in the extended will be lake effect snow potential for
northwest wind snow belts Saturday night into Sunday and again
Tuesday into Wednesday. Travel weather into Thanksgiving looks to be
fairly quiet across much of the eastern CONUS outside of some light
lake effect snow potential.

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 1 to 3 inches with
up to 5 inches possible in the northwest wind favored snow belts.
The greatest totals are 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
through at least early Wednesday afternoon. 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. At this point, late Wednesday afternoon through
Thanksgiving looks to be fairly quiet with dry high pressure
building across much of the eastern CONUS.
&&

.AVIATION...(For the 06Z TAFS through 06Z Saturday night)
Issued at 1206 AM EST SAT NOV 18 2017

Upslope flow off Lake Superior combined with moisture trapped under
inversion will lead to prevailing IFR conditions at KCMX/KSAW
overnight with LIFR conditions more likely at KIWD. In addition,
there may be some -dz or -fzdz at times with temps hovering around
the freezing mark. As gradually colder air arrives during the day
today, cigs will lift to MVFR at all terminals. Late in the aftn and
into the evening hrs, some lake effect -shsn may develop off Lake
Superior.
&&

.MARINE...(For the 4 PM Lake Superior forecast issuance)
Issued at 335 PM EST FRI NOV 17 2017

Gales will diminish this evening as cold front to the south of low
over northern Ontario moves through. However, northwest winds
increase to gales again late Sat into Sat night. Not quite sure if
we`ll see prevailing gales though so will keep just gusts for now
and not issue a Gale warning. Winds diminish to 30 kts Sun into Mon
but more gales are possible late Mon night through Tue night as
active pattern continues.
&&

.MQT WATCHES/WARNINGS/ADVISORIES...
Upper Michigan...
None.
Lake Superior...
None.
Lake Michigan...
None.
&&

$$

SHORT TERM...JLA
LONG TERM...KEC
AVIATION...Rolfson
MARINE...JLA



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