Area Forecast Discussion
Issued by NWS Marquette, MI

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FXUS63 KMQT 181009

Area Forecast Discussion
National Weather Service Marquette MI
509 AM EST Mon Dec 18 2017

.SHORT TERM...(Today and tonight)
Issued at 508 AM EST MON DEC 18 2017

WV imagery and RAP analysis indicated mainly a zonal flow through
the northern CONUS and southern Canada into the Upper Great Lakes
with an upstream shortwave trough from Manitoba into the Northern
Plains. At the surface, a sw flow prevails between high pres to the
south and east and a low pressure trough approaching from the
Plains. 09z radar imagery shows a weakening snow band sliding south
and east of Upper Mi. Otherwise no pcpn was reported early this
morning. Moist low-levels however have contributed to the formation
of stratus and patchy fog across much of the area.

Today, southwest winds will increase as a deep low moves from
northern Manitoba into far nw Ontario. WAA will help push temps
above seasonal averages with highs in the lower to mid 30s. A few
upper 30s readings may even be possible for a few downsloping
locations along Lake Superior. A shortwave moving toward northern
MN, with upper level divergence in the left exit region of the 250-
300 mb jet, may help to spread some light snow into western Lake
Superior and possibly into the far western cwa late.

Tonight, A series of embedded trough axes rounding a broad mid-level
low over Hudson Bay will brush the CWA tonight. A strong surface
pressure gradient combined with a favorable isallobaric wind
component will promote gusty W/WNW winds late tonight across the
Keweenaw Peninsula with mixing off NAM fcst soundings suggesting
gusts over 40 mph and perhaps as high as 45 mph possible. Deep
moisture and q-vector convergence ahead of the initial shortwave
will spread 1 to possible 3 inches of snow into mainly the western
and and eastern counties of the cwa tonight. 850 mb temps near -5C
this evening probably only marginally cold enough for lake
enhancement with initial shortwave. By the time colder 850 mb temps
of around -8C advect into the area between 09-12z Tue associated
with secondary shortwave, best forcing will have passed east and mid-
level drying is occurring. Thus, only expecting mininal potential
for lake enhancement tonight to add to pcpn totals so have sided on
lower end of qpf guidance and thus more conservative on snow
amounts. Rain mixing with snow especially along Lake Superior could
also cut into snow accumulation.

.LONG TERM...(Tuesday through Sunday)
Issued at 430 AM EST MON DEC 18 2017

With colder air moving in Tue into Tue night, LES will be on the
increase Tue and will peak Tue night into Wed morning with light to
moderate intensities. Have 3-5" in the forecast Tue and Tue night
for the Keweenaw and E of Munising. Meanwhile, W-NW winds will gust
to 45mph into the Keweenaw Peninsula and shoreline areas of Alger
and Luce counties Tue afternoon into early Tue night. Blowing snow
will be an issue in these areas, especially late Tue into Tue night
after some fresh snow can accumulate. Large waves will lead to
concerns of minor lakeshore flooding and beach erosion Tue and Tue

There could be some light snow Wed night into Thu morning ahead of
the next system, but confidence is pretty low from Wed night on due
to model disagreement/change and complexities. Greater potential
impacts will be later on Thu through Fri (or possibly later) as
models show a low ejecting out of the central Plains and moving SE
of here. There is a typical amount of model disagreement and
forecast uncertainty in the track/timing/strength of the system,
which makes discussing details not useful feasible at this time.
Potential exists for significant winter impacts if everything lines
up, so those with related concerns should continue to monitor the
forecast over the coming days.

.AVIATION...(For the 06Z TAFS through 06Z Monday night)
Issued at 1130 PM EST SUN DEC 17 2017

There is enough low level moisture that conditions will continue to
be in the IFR/LIFR range for overnight. More substantial dry
advection with improving conditions is expected by Monday afternoon
with improving conditions. Conditions will fall back to IFR late in
the forecast period.

.MARINE...(For the 4 AM Lake Superior forecast issuance)
Issued at 508 AM EST MON DEC 18 2017

Southwesterly winds will increase to 20 to 30 knots today over the
west and north central portions of Lake Superior possibly reaching
gale force gusts late this afternoon and evening before veering to
northwesterly gales to 35-40 knots late tonight into Tue night. With
increasing wave heights and colder air temperatures, freezing spray
is possible Tuesday night into Wednesday.

Upper Michigan...
Lake Superior...
  Gale Warning from 1 AM Tuesday to 4 AM EST Wednesday for

  Gale Warning from 10 AM EST /9 AM CST/ to 11 PM EST /10 PM CST/
     Tuesday for LSZ162-241-242-263.

Lake Michigan...


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