Area Forecast Discussion
Issued by NWS Marquette, MI

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FXUS63 KMQT 232037

Area Forecast Discussion
National Weather Service Marquette MI
337 PM EST Fri Feb 23 2018

.SHORT TERM...(This evening through Saturday)
Issued at 333 PM EST FRI FEB 23 2018

Moderate to heavy snow that impacted the morning commute earlier
today quickly pushed offshore and dissipated through the mid/late
morning hours as the main surface low continued to track northeast
into Ontario. Lingering cloud cover did keep temperatures down a
bit, but many locations saw temperatures still climb into the upper
20s to mid/upper 30s.

Over the next 24 hours, we will be in between systems with fairly
quiet weather. Isolated light lake effect snow showers will be
possible this evening across the Keweenaw as westerly flow comes in
off of Lake Superior, but any lingering precipitation should come to
an end tonight as surface ridging begins to build into the region.
Forecast soundings do show some lingering low-level moisture, this
coupled with a decoupling boundary layer due to light winds, should
favor the development of some patchy fog overnight.

Cloud cover will impact temperatures over the next 24 hours. Overall
overnight lows should drop into the teens to lower 20s, with the
coldest temperatures expected across the interior west. However,
temperatures will be highly dependent on how cloud cover and any fog
that does develop evolves. Warm air advection ahead of the next
system expected to impact the region later this weekend will begin
to return northward Saturday afternoon. This will support another
day will slightly above normal temperatures and thickening cloud
cover. For details pertaining to upcoming system expected to bring
another round of winter weather to Upper Michigan Saturday night
into Sunday, see the long term forecast discussion.

.LONG TERM...(Saturday night through Friday)
Issued at 333 PM EST FRI FEB 23 2018

...Winter storm to impact Upper Michigan Saturday night into

Bottom Line: The much anticipated winter storm still looks on track
for much of the western Great Lakes beginning Saturday evening
and lasting into Sunday morning. At this time, the heaviest snow
is expected to fall across the western tier of counties in the
U.P. with a wintry mix generally east of a line from Deerton to
Iron Mountain. The heaviest snow is expected to fall late Saturday
night through Sunday morning. A winter storm watch is in effect
for the western tier of counties along Lake Superior from Saturday
evening to Sunday morning, with a special weather statement
across the rest of the cwa.

Now for the details...The overall picture of the storm hasn`t
changed much over the past few days, with lee cyclogenesis expected
to occur early Saturday beneath a positively-tilted trough located
over the western US. The low will then intensify fairly rapidly
(aided by coupled jets), reaching 990mb or so by early Sunday over
the Upper Peninsula of Michigan. Aided by a "kicker" shortwave
trough surging southeast across the Four Corners region early
Sunday, the low will continue moving quickly northeast reaching
western Quebec Sunday evening. The exact track of the system is
still somewhat uncertain as the GFS and ECMWF have started
shifting ever so slightly southeast with each new run. Regardless
of each wiggle in forecast track, the actual path of the low will
likely cross over the central or south central U.P. early Sunday.
Such a track favors the heaviest snowfall across western Upper
Michigan through the Keweenaw Peninsula. It is worth noting the
NAM continues to show a model track much further west across the
western U.P., which, if it were to verify, blow up our current

In terms of snowfall amounts, there`s actually a bit more
uncertainty now than there was, say, 24 hours ago. For one, we`re
becoming increasingly concerned about an 8-12 hour period of very
heavy and wet snowfall--specifically 06-15Z Sunday--across the
western parts of our CWA. Without getting too into the weeds, it
looks quite possible snowfall rates may approach 2"/hr in the
heaviest snow bands owing to impressive moisture flux into the
region (e.g. easterly 850 mb jet coupled with anomalously strong
southerly flow/moisture transport toward the Upper Great Lakes).
Yet, as hinted by the D2 SPC Severe Weather Outlook, quite a bit
of convection is expected across mid Mississippi River valley
Saturday, which traditionally would disrupt moisture flow into the
upper Great Lakes. Perhaps unsurprisingly, QPF has been on the
downward trend with just about all models. Considering the recent
heavy rainfall across northern Illinois through lower Michigan,
I`m inclined to believe that moisture transport won`t be a
problem. So, even though the low will be tracking northeastward
fairly fast, we are still thinking warning-criteria snowfall (6-8"
or so/12 hours) will occur across the western tier of counties in
Upper Michigan. More of a wintry mix is expected across eastern
Upper Michigan//east of the center of low pressure//with a period
of snow followed by a switch to freezing rain/freezing drizzle
early Sunday morning. generally 1- 3" with up to 0.10" of ice is
forecasted for these areas.

As for central Upper Michigan, there is somewhat lower confidence in
precipitation type as it is highly dependent on the eventual
track of the surface low. As of now, it looks like primarily snow
can be expected but a mix with sleet is certainly possible toward
sunrise Sunday. Amounts are not expected to be as high as toward
the west owing to slightly less favorable dynamics for banding.
Regardless, a general 3-6" seems fair across the central U.P. with
perhaps a light glaze of ice.

Finally, it`s worth mentioning that winds may be quite gusty both
ahead of the low (e.g. east to southeast winds) across the east and
as the low departs (e.g. northwesterly to westerly in the CAA region
) across the west. Gusts > 40 MPH certainly look possible across the
west on Sunday, but there is low confidence on just how much this
will be of an impact given the expected very heavy and wet nature of
the snow. This is still something to keep an eye on.

Beyond Sunday, a period of light lake effect snow is possible late
Sunday and into Monday mainly across the west wind snow belts.
Somewhat marginal (and becoming less favorable) thermodynamic
profiles behind the departing storm system should keep things in
check. There looks to be another chance of light snow Wednesday
night and into thursday, but it certainly doesn`t look too exciting
at this point.  Seasonable temperatures will prevail through the
rest of the extended period.

.AVIATION...(For the 18Z TAFS through 18Z Saturday afternoon)
Issued at 1159 AM EST FRI FEB 23 2018

Ceilings will gradually improve from west to east across all
terminals into at least the MVFR category by tonight, if not
scattering out. Models continue to keep lingering low-level moisture
in place overnight, but with drier air working into the region from
the west, confidence is not high in regards to any stratus build
down tonight. However, if any lingering moisture is hanging around,
it may be possible to achieve lower ceilings given the light winds
progged to be in place. Precipitation wise, KCMX may see some light
wintry precipitation off of Lake Superior. Otherwise, KSAW/KIWD
should remain dry for the rest of this TAF period.

.MARINE...(For the 4 PM Lake Superior forecast issuance)
Issued at 333 PM EST FRI FEB 23 2018

Winds between 15 and 25 knots are expected though the rest of the
afternoon and evening hours before gradually subsiding to less than
15 knots tonight. On Saturday, winds will remain below 15 knots, but
will quickly ramp up to gales of 35 to 40 knots Saturday night
through Sunday as a deepening low pressure system lifts across the
Upper Great Lakes region. Depending on the track of the system, high-
end gales are possible especially Sunday behind the exiting system.
Winds will fall below 30 knots by Monday morning and remain
so through the first half of next week.

Upper Michigan...
  Winter Storm Watch from Saturday evening through Sunday
     afternoon for MIZ001>003-009.

Lake Superior...
  Gale Watch from late Saturday night through late Sunday night
     for LSZ264>267.

  Gale Watch from Sunday morning through Sunday evening for LSZ162-

Lake Michigan...
  Gale Watch from Sunday morning through Sunday evening for LMZ248-



SHORT TERM...Ritzman
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