Area Forecast Discussion
Issued by NWS Marquette, MI

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FXUS63 KMQT 252234

Area Forecast Discussion
National Weather Service Marquette MI
634 PM EDT Sun Oct 25 2020

.SHORT TERM...(This evening through Monday)
Issued at 352 PM EDT SUN OCT 25 2020

Lake-effect snow continues this afternoon, with decent snowfall
rates seen across Marquette County and out west near Ironwood to
Bergland as a mesolow could be seen moving onshore via GOES imagery.
IWD observations have been down near 1/2 mile to 1/4 at times, which
usually suggests 1 inch an hour rates. The caveat to all this is
with sfc temperatures near freezing and with an abv freezing ground,
accumulations and roadways don`t seem to be as much and bad as we`d
normally see if it was say late November into December. MDOT camera
on M64 near Merriweather, shows decent snowfall rates and
accumulation on trees, but the roadway is open. The same can be seen
near the Marquette welcome center off US41 in Harvey, with minor
slushy accumulations on the shoulder. Due to this, felt comfortable
leaving the SPS across the west, and the advisory across the central
for now. The question heading into tonight then is how long do these
snowbands remain with the weak boundary layer flow and then if they
do remain, how much snow accumulates as temperatures fall?

This morning`s CAMs didn`t handle this afternoon`s lake-effect well,
and this afternoon`s CAMs for tonight are, well...all over the
place. Weak boundary layer flow is making this lake-effect snow a
little tough to predict, especially when guidance is so all over the
place. I started with a persistence approach and adjusted PoPs based
on sfc wind direction. Since I don`t think any one location will
have a more dominant band over another, I spread the QPF out more
evenly bringing 2 to 4 more inches across Marquette and Alger
counties, with of course locally higher amounts possible. Across the
west, weak westerly flow is moving in which should start to create
diminishing PoPs and I have 1 to 3 inches out that way. If PoPs hang
on a little longer into tonight, could see some local 4 inch reports
as well. Latest HRRR and ESRL HRRR do suggest a mesolow develops
tonight, remaining over Lake SUperior, but following parallel to
Marquette County. If part of this makes it on to shore, could see a
quick accumulation from it. Roads could get a little slick tonight
as temperatures fall in the 20s.

By tomorrow, winds continue to back a bit more to the west, with
weak flow prevailing. Lake-effect bands should follow this wind
shift, with most showers ending by 18Z tomorrow. As a ridge of high
pressure shifts in from the west, model soundings suggest subsidence
to dry the column out, with some clearing skies from west to east in
the afternoon looking possible. Look for highs to still be below
normal in the low to mid 30s west and mid to upper 30s east.

.LONG TERM...(Monday night through Sunday)
Issued at 341 PM EDT SUN OCT 25 2020

Models finally advertise a break in the cold, wet pattern for the
extended as the persistent broad mid-upper level trough across much
of the continent will be replaced by zonal flow and a milder,
Pacific air mass late week into next weekend.

Beginning Monday night, as a sfc high pres ridge moves overhead, the
attendant dry air mass and light winds should result in an
unseasonably cold night. Fresh snowfall and PWATs of .25 inch or
less will only enhance radiational cooling. Siding on the low-end of
model guidance, expect overnight lows over the west half in the
teens with maybe even some single digits possible over the typical
interior west cold spots. In the east and by the lakeshores,
expecting lows to bottom out in the low 20s to high teens.

A series of shortwaves moving through south central Canada will
bring a surface trough/cold front through the Upper Great Lakes late
Wed/Wed night. Tue still looks dry, but then later Tue night into
Wed weak forcing from passing shortwaves could support some light
rain/snow showers brushing northern and eastern portions of the cwa.

CAA behind Wed night`s cold fropa will support some scattered light
lake effect snow showers for the north wind snowbelts on Thu.

Friday-Saturday, a broad mid-upper level ridge from the Plains will
be building over the region resulting to dry conditions and a
warming trend. Expect highs in the lower to mid 40s on Friday. WAA
in a southwest flow really kicks in on Sat as model consensus shows
850 mb temps climbing as high as 10C, perhaps even higher, under
sunny skies. Should be one of the warmest Halloweens in recent
memory with highs likely well into the 50s, perhaps even reaching
the lower 60s at a few locations under a breezy southwest flow.

Sunday, a Pacific-based shortwave moving in from the west will bring
in increasing clouds and maybe some isolated rain showers as high
temps fall back into the lower to mid 40s.

.AVIATION...(For the 00Z TAFS through 00Z Monday evening)
Issued at 633 PM EDT SUN OCT 25 2020

Continuous lake-effect snow will continue into the overnight with
light winds allowing the snow to be persistent. IFR/LIFR conditions
will continue this evening at all sites before drier air works in
and starts to slowly diminish the intensity of the snow. All sites
will go to MVFR later tonight.

.MARINE...(For the 4 PM Lake Superior forecast issuance)
Issued at 352 PM EDT SUN OCT 25 2020

Light winds will prevail through Monday as high pressure moves over
Lake Superior. This high pressure drifts south and east Monday night
as a clipper low pressure system moves over Lake Winnipeg and skirts
by Lake Superior to the north. With Lake Superior caught between
these two systems, the pressure gradient tightens and SW winds
increase to gales up to 35 knots across the west half and north
central portions of the lake Tuesday night into Wednesday. Winds
diminish Wednesday evening as high pressure moves back over Lake
Superior, which will persist into the weekend.

Upper Michigan...
  Winter Weather Advisory until 6 AM EDT Monday for MIZ005-006.

Lake Superior...
Lake Michigan...


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