Area Forecast Discussion
Issued by NWS Marquette, MI

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FXUS63 KMQT 122331

Area Forecast Discussion
National Weather Service Marquette MI
731 PM EDT Mon Mar 12 2018

.SHORT TERM...(This evening through Tuesday)
Issued at 352 PM EDT MON MAR 12 2018

Water vapor imagery and RAP analysis show a weak shortwave moving
across the western fcst area this afternoon. Another well-defined
shortwave over nw Ontario is dropping south toward the Upper Great
Lakes. Forcing from these shortwaves, particularly the one over nw
Ontario will act to enhance lake effect snow tonight, especially
into north central Upper Michigan, where advisories are posted into
Tue afternoon for Marquette and Alger counties.

Tonight, models indicate Ontario shortwave will drop down across the
western fcst later this evening into the early overnight hours. Mid-
level q-vector convergence field indicate best forcing for lake
enhancement should occur this evening into the early overnight
hours. This enhancement potential combined with continued cooling at
850mb should lead to expansion/intensification of shsn this evening.
Then, thru the night, nocturnal cooling and 850mb temps falling to -
15 to -18C by 12z Tue will result in more traditional LES organizing
in the n wind favored snow belts. Have some concerns about analysis
of ice cover utilized in the mesoscale models and how it will affect
the QPF generated and thus LES amounts. The ice on the lake has
become more broken up in recent weeks and shouldn`t act as a solid
sheet that inhibits heat/moisture fluxes. As a result, LES
accumulations tonight could be greater than reflected by models,
especially with deep cold air under troughing leading to lake
induced equilibrium levels up to 8-10kft and DGZ well positioned in
the convective layer. For now expect, greatest accumulations over
the north central portions where upslope n wind and longer fetch
should easily support decent coverage of 3-5in/12hr snow
accumulations with locally higher amounts over higher terrain
locations. Thus advisory still looks good for Marquette/Alger
counties. To the w, n wind will favor the high terrain of Keweenaw
County and Gogebic/Ontonagon Counties. Ice cover is more substantial
off western Upper MI, but with the ice cover probably not as great
as modeled and not inhibiting heat/moisture fluxes as much as models
indicate, snow accumulations could be a surprise over the w tonight.
Bumped up accumulations more solidly into the 2-4 inch range for
starters with locally higher amounts up to 6 inches over the spine
of the Keweenaw.

Expect les to taper off by mid afternoon Tue as inversion heights
lower near 3 kft with ridging/subsidence building in from north and
west of Lake Superior.

.LONG TERM...(Tuesday night through Monday)
Issued at 247 PM EDT MON MAR 12 2018

Upper air pattern consists of a 500 mb trough on the west coast,
closed low in the lower Great Lakes and a ridge over the Rockies 00z
Wed. There is also a shortwave over northern Manitoba that drops
southward Tue night and moves into the lower Great Lakes Wed night
into Thu.

In the extended, GFS and ECMWF show a 500 mb trough over New England
and another over the western U.S. 12z Fri. The trough in the western
U.S. moves little through Sun while the ern U.S. begins to get into
some upper level ridging. Troughing moves into the Rockies on Mon.
Temperatures remain near normal for this forecast period and will be
fairly quiet.

.AVIATION...(For the 00Z TAFS through 00Z Tuesday evening)
Issued at 730 PM EDT MON MAR 12 2018

Lake effect snow showers will continue to impact KIWD/KCMX/KSAW
intermittently overnight leading to MVFR to IFR conditions,
especially at KIWD and KSAW. Conditions may occasionally dip to
LIFR at KSAW between 0500-1200 UTC as heavier snow showers pass
nearby, but confidence is a bit too low at this point in their
placement to include in the TAF. Conditions will increase to MVFR
and eventual VFR at all three airports from west to east tomorrow
as winds back and snow showers are pushed into eastern Upper


.MARINE...(For the 4 PM Lake Superior forecast issuance)
Issued at 352 PM EDT MON MAR 12 2018

Strongest winds across Lake Superior will be in the 20-30kt range
this afternoon through Tue morning, strongest across the east half
of the lake. Winds for the rest of the week will mostly be at or blo
20kt though a few periods of winds up to 25kt will occur. No gales
are expected.

Upper Michigan...
  Winter Weather Advisory until 5 PM EDT Tuesday for MIZ005-006.

Lake Superior...
Lake Michigan...


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