Area Forecast Discussion
Issued by NWS Marquette, MI

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784
FXUS63 KMQT 210921
AFDMQT

Area Forecast Discussion
National Weather Service Marquette MI
421 AM EST Sat Jan 21 2017

.SHORT TERM...(This evening through Saturday)
Issued at 310 PM EST FRI JAN 20 2017

Murky conditions over much of Upper Michigan today with moist
easterly low-level flow to the north of weakening sfc low pressure
system over Ohio Valley. Shearing out shortwave trough and area of
isentropic lift is leading to slow northward push of light rain into
southern Upper Michigan. Despite temps at or blo freezing this
morning as the rain moved in, there were not many icing issues
reported as main roads were mostly wet. Cold ground temps likely led
to slippery non treated surfaces as was occurring over northern WI.
As weakening shortwave continues to drift north expect the shield of
steady light rain to do so as well. Should be pretty rainy evening
for northern Upper Michigan but the rain should taper off by late
evening or after midnight. Due to the moisture from the rain that
will have occurred and/or potential light drizzle at times, temps
falling into the low to middle 30s could lead to icy conditions on
untreated surfaces tonight. Plan to cover this with special weather
statement and mention in the hazardous weather outlook.

On Sat, the damp and murky conditions will continue. Temps will rise
into the upper 30s or near 40 by the aftn. At this point, with
minimal insolation, thinking 40 will be a stretch. Low level flow
remains weak as weakening area of low pressure lifts toward Upper
Mississippi river valley and warm front slides to the western Great
Lakes. Another shortwave currently over the central Plains lifting
in along with the low-level forcing/lift should enhance light rain
especially in the aftn. May see drizzle at times before the next
surge of rain on Sat. Since sfc temps will be around freezing could
still see icy conditions at times on untreated sfcs at least during
the morning hours.

Other larger issue is fog. Fog was very widespread near Lk Michigan
and the Bay of Green Bay into early aftn with widespread reports of
vsby less than 1/4sm. Fog has lifted this aftn though with vsby now
more in the 1-3sm range as the more widespread rain moved in,
scouring out the tiny fog droplets. However, weak east to southeast
low-level flow and sfc temps/dwpnts above freezing flowing across
ice on Bay and sfc temps in the mid 30s over the open waters of Lk
Michigan should result in more dense fog forming again near Lk
Michigan by this evening as the steadier rain lets up. Moist ESE
flow and an ongoing melting snowpack will likely allow this fog
to expand over much of cntrl Upper Michigan and across the
Keweenaw later tonight (especially once the rain ends) and similar
wind trajectories and dwpnts on Sat indicate the fog could
persist through much of the day. Went with dense fog advy for all
but far western cwa (since downslope E-SE flow not as favorable
there) through midday Sat. Widespread dense fog probably will not
develop until after the steady rain lifts out later this evening.
Later shifts can extend or cancel the advy as needed.

.LONG TERM...(Sunday through Friday)
Issued at 401 AM EST SAT JAN 21 2017

The unseasonably warm and dreary conditions are expected to
linger through the first part of next week as the cold arctic air
remains well north of the area. Afternoon high temperatures are
expected to climb into the mid to upper 30s through Wednesday.
Overnight lows will start off around freezing before gradually
cooling through the week. However, the medium range models are
consistent with the pattern finally changing in favor of cooler
temperatures, albeit still above normal, by mid to late next week
as longwave troughing is progged to dominate the central and
eastern CONUS.

On Sunday as shortwave energy lifts north across the area, expect
rain to diminish from south to north. However, cannot rule out
some lingering drizzle during the day with lingering stratus. Forecast
soundings across the area show cloud ice diminishing Sunday night
into Monday morning. This coupled with cooling temperatures at
night may lead to freezing drizzle concerns. However, right now
cloud top temperatures look to be right around the threshold of
supporting ice. Therefore, not too confident that freezing drizzle
will develop at this time, but have at least included mentions of
it. Also, Given the recent warm temperatures and rainfall, with
ample moisture at the surface would not be surprised if areas of
patchy fog continue to impact the area.

The attention that turns to cutoff energy that will lift north
across the Appalachian Mountains pushing deeper moisture towards
the area on Monday. Along with this deeper moisture, comes warmer
air aloft. The big question is where the 850mb freezing line will
set up, as that will bisect areas that see predominately rain and
snow. Right now most of the models push this line back across
central Upper Michigan. Given the uncertainty right now have opted
to run with a rain/snow mix for now. Highest chances of
precipitation remaining all snow will be across far western
portions of the area and then all rain across the east. A few
pockets of freezing rain/sleet mixture may develop Monday night
into Tuesday, but this will be highly depending upon how far west
the nose of warm air aloft can get. Lingering upper-level energy
on Tuesday will allow for light rain/snow chances to remain
primarily in the east and downwind of lake superior.

The attention then turns to a storm system progged to develop in
the lee of the rockies and lift northeast across the Great Lakes
region Tuesday night through Wednesday. There is quite a bit of
uncertainty with this system, with the GFS being the quickest and
the Canadian being the slowest of the medium range models. The
ECMWF and GFS Ensemble mean seem to be the middle of the road at
this point, and would suggest the bulk of the precipitation with
this storm would track across much of Wisconsin and southern
portions of Upper Michigan. With the storm expected to track well
south of the area at this point, with relatively mild air still in
place we could still be dealing with a rain/snow mix in many
locations. However, after this system lifts out of the region
large-scale troughing will dominate the central and eastern CONUS
allowing for multiple waves of colder air to drop south. This will
knock temperatures down to at least more seasonable and allow for
LES to return to the region, with perhaps a few chances to see
area-wide system snows as shortwaves periodically dig south across
the area.

&&

.AVIATION...(For the 06Z TAFS through 06Z Saturday night)
Issued at 1121 PM EST FRI JAN 20 2017

Low cigs and low visibility will result in IFR to LIFR conditions
into Sat night. Upslope flow will result in potential for VLIFR
conditions at SAW and possibly CMX.
&&

.MARINE...(For the 4 PM Lake Superior forecast issuance)
Issued at 310 PM EST FRI JAN 20 2017

A relatively weak pressure gradient over the Upper Great Lakes in
the absence of any strong weather systems will result in winds under
20 kts over Lake Superior most of the time into early next week.
Abundant low-level moisture will result in fog over northern Lk
Michigan.
&&

.MQT WATCHES/WARNINGS/ADVISORIES...
Upper Michigan...
  Dense Fog Advisory until 1 PM EST /noon CST/ this afternoon for
     MIZ001-003>007-010>014-084-085.

Lake Superior...
None.
Lake Michigan...
  Dense Fog Advisory until 1 PM EST this afternoon for LMZ221-248-
     250.

&&

$$

SHORT TERM...JLA
LONG TERM...Ritzman
AVIATION...07
MARINE...JLA



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