Area Forecast Discussion
Issued by NWS Marquette, MI

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FXUS63 KMQT 172048

Area Forecast Discussion
National Weather Service Marquette MI
348 PM EST Sun Dec 17 2017

.SHORT TERM...(Today and tonight)
Issued at 417 AM EST SUN DEC 17 2017

WV imagery and RAP analysis indicated a wnw wind flow across the
northern CONUS into the Upper Great Lakes with a shortwave trough
upstream from southern Manitoba into the Northern Plains. At the sfc
ridging from high pressure centered over eastern Ontario was keeping
conditions dry over Upper Michigan into the early morning hours.
Much cooler air advecting in from sfc high centered over Ontario has
resulted in sub-zero min temps over eastern Upper Mi early this
morning. Across the rest of the U.P weak warm advection and cloud
cover has kept readings more generally in the teens to lower 20s.

Today into Tonight, with marginal moisture to -10C for ice nuclei,
and weak isentropic ascent, freezing drizzle could mix with snow
over south central counties this morning and then spread into north
central and eastern counties this afternoon and evening as
isentropic ascent increases ahead of the approaching shortwave from
the Northern Plains. Given how light pcpn is expected to be, impacts
if any should be minimal. Even with considerable cloud cover, WAA
will push high temps into the mid 20s to lower 30s today.

As the shortwave passes east later this evening, weakening
isentropic ascent will allow any lingering light mixed pcpn to
dissipate. There could be some breaks in cloud cover into west and
north central Upper Mi later tonight with subsidence behind the
shortwave.  Expect min temps to generally range from the teens
inland to the lower 20s closer to the Great Lakes shorelines.

.LONG TERM...(Monday night through Sunday)
Issued at 347 PM EST SUN DEC 17 2017

Monday night through Wednesday: A series of embedded trough axes
rounding a broad mid-level low over Hudson Bay will brush the CWA
the during this time. A strong surface pressure gradient juxtapose
with a favorable isallobaric wind will promote gusty W/WNW winds
late Monday night into Tuesday evening. 925-850hPA winds of 40-45kts
should allow for surface gusts to 40mph across the Keweenaw
Peninsula late Monday night through much of Tuesday. Though 850hPa
temps of just -10 to -12C and reduced residence time from the
stronger winds will limit LES intensity, intermittent white out
conditions will be possible given the added component of blowing
snow from the current snowpack. This concern will also translate to
the immediate shore of Lake Superior from Munising eastward Tuesday

As noted, LES should be limited early on Tuesday, but a secondary
trough axis will bring more favorable thermodynamic conditions for
LES Tuesday evening. A period of moderate LES will be possible for
the W to NW wind snow belts Tuesday night into Wednesday before
lowering inversion heights subdue the LES into Wednesday evening.

Wednesday night through Sunday: As can be expected this time of
year, model guidance continues to show decent run-to-run differences
with the evolution of the large scale pattern and associated period
of active weather across the western Great Lakes. The main message
is that high-impact weather may affect early holiday travel
somewhere across the region during this time.

Light WAA snow should spread across the CWA late Wednesday evening
into Thursday morning, producing sub-advisory accumulations across
the SW half of Upper Michigan. Guidance begins to diverge after this
as notable disagreement develops with the handling of lee
cyclogenesis in the central and southern Plains as a mid-level
trough ejects from the four corners region. Contrary to yesterday,
the GFS has become the strongest and northern most solution with
this low, bringing a period of high-impact snowfall to Upper MI late
Thursday morning into Friday night. The ECMWF and CMC model bring a
broader swath of moderate snow across Upper MI Thursday evening into
Friday, keeping more significant precipitation well south of the
region. Again, given the highly varying solutions, providing any
detailed forecast is nearly impossible at this point. However, those
who could be affected by moderate to heavy snow accumulations in the
western Great Lakes Wednesday night into Saturday should continue to
monitor forecast updates through the upcoming week.

.AVIATION...(For the 18Z TAFS through 18Z Monday afternoon)
Issued at 1240 PM EST SUN DEC 17 2017

IFR to lower end MVFR cigs may give way to some improvement as winds
veer to the sw this evening. However, there is enough low level
moisture upstream so that confidence in rising cigs is low. More
substantial dry advection with improving conditions is expected

.MARINE...(For the 4 AM Lake Superior forecast issuance)
Issued at 417 AM EST SUN DEC 17 2017

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

Upper Michigan...
Lake Superior...
  Gale Watch from late Monday night through late Tuesday night for

  Gale Watch from Tuesday morning through Tuesday evening for

  Gale Watch from Tuesday morning through late Tuesday night for

Lake Michigan...


LONG TERM...Kluber
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