261
FXUS63 KMQT 222109
AFDMQT

Area Forecast Discussion
National Weather Service Marquette MI
409 PM EST Wed Jan 22 2025

.KEY MESSAGES...

- Lake effect snow into Thursday morning to bring generally 1-4
  inches of fluffy snow to the north-northwest wind snow belts,
  but locally 4 to 6 inches in the vicinity of the
  Marquette/Alger county line.

- Moderating airmass will see temperatures trending more or
  less towards normal values from midweek onwards.

- Passing clipper systems will bring in rounds of light lake
  effect/enhanced snow through the extended period, but
  widespread significant snowfall is not expected.

&&

.SHORT TERM /THROUGH TONIGHT/...
Issued at 408 PM EST Wed Jan 22 2025

Water vapor imagery and RAP analysis show mid-level troffing
dominating central and eastern N America. Within the trof, a
shortwave over ne MN and adjacent Ontario is beginning to move out
over Lake Superior. At the sfc, associated ill-defined low pres is
located btwn Isle Royale and the Keweenaw along cold front extending
from near the Slate Islands in northern Lake Superior to near Saxon
Harbor. Canadian radar near Thunder Bay has been showing a band of
hvy lake effect snow along the cold front to the se and e of Isle
Royale. Ahead of the shortwave, areas of -sn have been spreading
across Upper MI today. A mid-lake convergent LES band in the sw flow
up Lake MI early today just brushed the se corner of Luce County.
That hvy snow band has moved eastward and is now streaming onshore
btwn Naubinway and the Mackinac Bridge. Current temps across the
area range mostly btwn 10 and 15F.

As aforementioned shortwave continues to drop se tonight, cold front
will do the same. The ill-defined sfc low along the front is likely
to become much better defined over the water given the heat/moisture
fluxes off the lake due to the cold air moving overhead (850mb temps
of -15 to -20C). The exact evolution of the the low/circulation is
uncertain. While consensus is for the low to track down toward
somewhere btwn Grand Marais and Whitefish Pt, some of the guidance,
HRRR/WRF-ARW in particular, trail a sharpening sfc trof westward and
almost a secondary circulation that moves onshore in western Alger
County. This results in winds veering more northerly in that area,
even well w into Marquette County per ARW. There is very low
confidence in that playing out, but the consensus overall is for a
NNW wind to develop as the sfc low moves onshore to the e, ideal for
heavier LES to develop vcnty of the Marquette County/Alger County
line. This occurs due to slightly backed winds off of Marquette
County enhancing a convergence zone offshore that streams into that
area. NAM fcst soundings indicate inversion on the lower side around
5kft, but the HRRR is up to 6 to maybe 8kft. Even with the lower
inversion height, the DGZ will be well positioned in the convective
layer to fluff up snow accumulations with a high SLR. Opted to issue
winter wx advy for Marquette/Alger counties, but that`s largely for
the area btwn Marquette and Au Train southward in the vcnty of the
Marquette/Alger County line for the potential of 4-6 inches of snow
late tonight thru Thu morning, impacting the morning commute. A
period of hvy snow will occur closer to where the sfc low moves
onshore farther e, but it is anticipated to be short-lived since the
convergence owing to the low is short-lived around the time of
landfall. Nonetheless, will be something to monitor for potential
inclusion of Luce County/northern Schoolcraft County in advy. Winds
will be gusty to 30 mph or so near the shore late tonight and early
Thu morning, so there will blsn as well.

To the w, inversion is lower than to the e and it gradually lowers
thru the night. DGZ does slowly fall blo the ideal position in the
convective layer, so SLRs should gradually decrease during the
night. Still, it will be fluffy snow, leading to less impacts for
travel. From late this aftn to sunrise on Thu, expect 1-3 inches in
general, except 2-4 to isold 5 inches in the high terrain.

Temps will fall to 0 to 10F above by sunrise, coldest interior w. In
those coldest areas, wind chills will fall to -10 to -15.

&&

.LONG TERM /THURSDAY THROUGH TUESDAY/...
Issued at 224 PM EST Wed Jan 22 2025

Anomalously strong ridging setting up over the northeast
Pacific/Gulf of Alaska on Friday with 500 mb height rises of 360 m
or more will gradually weaken through the weekend into early next
week as the ridge moves ever slowly toward western Canada. This mid-
upper level ridging will promote downstream troughing across the
northeast portion of North America through most of next week. The
end result will be a nw flow into the Upper Great Lakes between
these large scale features with a series of mainly weak Clipper
shortwaves moving through the region from late this week into next
week. Any system snow with these shortwaves looks to be light until
at least maybe mid to late next week. However, forcing from these
shortwaves along with associated shots of cold advection will
support bouts of light to at times moderate lake effect snow over
mainly the NW to W snow belts through the extended forecast period.
Temperatures will gradually trend warmer for the most part, from
below normal late this week, to near normal this weekend into early
next week, to above normal by the middle of next week.

Beginning Thursday, cold advection in the wake of this
afternoon/tonight`s Clipper system will support NW flow LES through
Thursday night. Although model soundings have inversion heights
abruptly lowering to near 3 kft west and 4-5 kft east as sfc ridging
quickly advances from the Northern Plains, much of the cloud layer
beneath the inversion is within the DGZ which should yield another
fluffy 1-2in of snow, locally higher up to 2-4in in the eastern UP
with a longer fetch off of Superior. Clearing skies and light winds
Thu night under the sfc ridge will promote ideal radiational cooling
conditions and min temps on the lower end of forecast guidance.
Decided to lean a bit toward the cooler and usually better
performing biased-corrected Canadian guidance which suggest the
potential for min temps of -10 to -15F over the western interior and
a few -10F or colder readings over the typical cold interior central
locations as well.

After a dry, cool and breezy Friday, the next round of clipper
shortwaves arrive Friday night into Saturday bringing light snow to
mainly northern portions of the cwa with maybe some weak lake
enhancement from the shortwaves bringing perhaps a period of
moderate snow into the Keweenaw on Saturday. CAA with 850 mb temps
dipping near -20F will support a brief period of light to at times
moderate NW flow behind the Clipper on Sat night.

A brief period of weak ridging should result in drier conditions
Sunday, before the next series of clipper shortwaves move through
early to middle of next week. Guidance continues to keep the
strongest shortwave energy mainly northeast of Lake Superior, so
have continue to limit PoPs to the northern UP, greatest in the
northeast UP where NW flow may lead to some lake enhancement.

Operational GFS and Euro continue to show stronger shortwave action
dropping through sometime in the Wed-Thurs time period, with below
normal temps and NW flow LES behind it for the end of next week.
There are significant timing differences, however, and these
solutions run somewhat counter to the current GFS and ECMWF ensemble
means which aren`t quite as strong, and also have mid-upper level
ridging moving into the Upper Great Lakes for the end of the week.
This would suggest warmer than normal temps and drier conditions at
that time.

&&

.AVIATION /18Z TAFS THROUGH 18Z THURSDAY/...
Issued at 1252 PM EST Wed Jan 22 2025

Low pres currently just s of Isle Royale will track ese this aftn
and tonight. Ongoing areas of -sn will transition to lake effect
-shsn under gusty nw to nnw low-level winds to 20-25kt after passage
of the associated cold front. At IWD, expect a mix of IFR and MVFR
this aftn and prevailing IFR tonight, though some periods of MVFR
will still occur. Around the time of fropa at around 20z, a period
of LIFR vis is possible. MVFR should prevail Thu morning at IWD. At
CMX, expect VFR to fall to IFR in the next couple of hrs as heavier
shsn associated with fropa arrive. A brief period of LIFR vis is
possible at around the time of fropa. IFR will then prevail tonight
at CMX due to -shsn and blsn under winds gusting to around 25kt.
Expect MVFR to prevail Thu morning. At SAW, VFR will largely prevail
this aftn, though periods of -sn may drop conditions to MVFR. Expect
MVFR to prevail tonight. There is some uncertainty on how much winds
will veer during the night into Thu morning as some models veer
winds enough to bring frequent lake effect -shsn and probable IFR
vis to SAW. For now, opted for MVFR conditions with a prob30 for
IFR.

&&

.MARINE...
Issued at 224 PM EST Wed Jan 22 2025

A clipper low is tracking across northern Lake Superior this
afternoon, with SW winds out ahead of it across eastern Lake
Superior veering to the NW across the western half of the lake. Wind
gusts up to 20-30kts continue this afternoon, but a few NW gale-
force gusts to 35kts will be possible across the central portions of
the lake tonight. Confidence remains too low to warrant a headline.
As high pressure influences the forecast for Thursday, winds slowly
backing westerly around 20-25 kt are expected. For Friday into the
weekend, primarily southwest to west winds of 25-30 kts are expected
but there could be brief periods of gale gusts to 35 knots at times,
especially late Saturday into early Sunday (around 40-70% chance) as
winds shift to the NW again behind a passing clipper system. W-NW
winds remain elevated at around 20-30kts into early next week with
again a potential for gale gusts to 35 kts at times behind yet
another clipper.

&&

.MQT WATCHES/WARNINGS/ADVISORIES...
Upper Michigan...
  Winter Weather Advisory from midnight tonight to noon EST
     Thursday for MIZ005-006.

Lake Superior...
  Heavy Freezing Spray Warning until 7 AM EST Thursday for
     LSZ243>245-248-264-265.

Lake Michigan...
None.

&&

$$

SHORT TERM...Rolfson
LONG TERM...LC
AVIATION...Rolfson
MARINE...LC