Area Forecast Discussion
Issued by NWS Marquette, MI

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FXUS63 KMQT 130839

Area Forecast Discussion
National Weather Service Marquette MI
439 AM EDT Tue Mar 13 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...(Wednesday through Monday)
Issued at 438 AM EDT TUE MAR 13 2018

Fairly quiet weather expected through much of the extended forecast
with only a couple chance of light lake effect snow Wednesday night
through Thursday night.

Wednesday through Thursday night: A couple quick moving shortwaves
will slide through the area Wednesday night into Thursday morning
and then again late Thursday afternoon into Thursday night. This
will give a couple periods of increased lake effect snow showers
across the north central and eastern U.P. on a quick shift back to
north to northwest winds. 850mb temperature are progged to drop into
the 14C to -18C range as the shortwaves rotate through the U.P.,
which will create favorable delta-T values to support lake effect
snow. Moisture profiles do not look overly impressive, with only a
small portion of the moisture nosing into the DGZ; therefore,
overall snowfall totals are expected to remain light to moderate as
SLRs remain in check. For locations outside of the north to
northwest wind snowbelts, little to no snow is expected, and many of
those locations will likely see sunshine. Temperatures will
generally be near to slightly above normal for this time period.

Friday and Saturday: A surface ridge and weak upper level ridge are
progged to slide across the Upper Great Lakes through this time
period. This will bring mostly clear skies to the area under light
winds. As temperatures warm aloft and ample sunshine is in place,
look for high temperatures to warm above normal Friday into Saturday
with most locations seeing highs in the upper 30s to possibly even
low to mid 40s by Saturday afternoon.

Sunday through Tuesday: There are no indications of any major
weather impacts during this time period. Its possible that a couple
weak systems could brush to the south of the area during this time;
however, there is little agreement among the models at this point.
Will stick with a consensus of the models keeps most of the area
dry, with only a small chance of precipitation Sunday into Sunday
night. Otherwise, near to slightly above normal temperatures can be

.AVIATION...(For the 06Z TAFS through 06Z Tuesday night)
Issued at 123 AM EDT TUE MAR 13 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 also fall to LIFR at
KSAW overnight, but confidence is too low to include in the TAF.
Conditions will increase to MVFR and eventual VFR at all three
airports from west to east today as winds back and snow showers are
pushed into eastern Upper Michigan.

.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 this afternoon for MIZ005-

Lake Superior...
Lake Michigan...


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