Area Forecast Discussion
Issued by NWS Marquette, MI

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FXUS63 KMQT 222326

Area Forecast Discussion
National Weather Service Marquette MI
626 PM EST Thu Feb 22 2024


- A cold front will bring in a round of lake effect snow showers
  beginning late tonight, as well as blustery conditions. Snow
  accumulations will be light, generally 1-3 inches at most in
  the north snow belts.
- A brief bout of colder weather (below normal temperatures)
  Friday, then back to well above normal early next week.
- A more active period is likely next week with one or two low
  pressure systems lifting northeast through the Mid and Upper
  Mississippi Valley/Great Lakes region.


Issued at 251 PM EST Thu Feb 22 2024

Skies are clearing out across much of the UP this afternoon as a
weak shortwave exits eastward, with fairly dry midlevel air apparent
across the Great Lakes on water vapor imagery. Temperatures have been
able to quickly climb into the 40s where skies have turned sunny,
and areas closer to the WI border are even reaching into the lower

A surface low is currently analyzed just south of Hudson Bay, and
will continue to track eastward into Quebec tonight. As this
happens, a sharp cold front currently extending from western Ontario
into Manitoba will drop southward across Lake Superior the second
half of the night and through the UP Friday morning. Increasing
clouds and chances for flurries and snow showers (initially mixing
in with rain) spread across the area, then a transition entirely
over to lake effect snow is expected after 06Z, behind the cold
front. 850mb temperatures fall to as low as -20C by 12Z Friday, and
soundings are showing decent saturation through the DGZ. Towards
daybreak, however, drier air works in and inversion heights lower.
Unsurprisingly, then, href guidance shows our best snowfall rates of
around a quarter inch/hr across the NNW snowbelts, immediately
following FROPA. With blustery northerly flow developing behind the
front and a long fetch off of Superior, snow bands may extend
farther inland than usual. Thus, light snow totals below an inch are
possible across much of the UP, save the south-central areas, with
higher totals closer to Superior. Locally higher amounts of 1-2in
are possible by sunrise across the upslope enhanced areas of the
north-central and western UP.

Otherwise, expect temperatures to drop rapidly with the passing
front. Most of the area should be starting off in the teens by
Friday morning, though some of our typically cooler spots may flirt
with the single digits behind the cold front. Blustery NNW winds
will contribute to wind chills in the single digits across most of
the UP, and perhaps below 0F in the Keweenaw and the highlands of
Marquette and Baraga counties.


Issued at 449 PM EST Thu Feb 22 2024

Beginning Fri, a vigorous northern stream shortwave now diving se
through northern Ontario today will support an associated sfc low
pres moving from northern Ontario today into Quebec tonight. The
associated cold front with the low will sweep s across Lake
Superior/Upper MI late tonight and ongoing CAA into Friday, will
send 850mb temps dropping rapidly from around -7C this evening to
near -20C by late morning Fri, leading to rapid LES development
under post-frontal low-level nnw flow. Despite the strong
instability, the rapidly lowering inversion to 4-5kft, sharp
transition to anticyclonic flow and quick influx of drier air will
hold LES in check. Only expect snow accumulations of 1-2 inches
tonight/Fri with maybe a few local amounts near 3 inches. The LES
will quickly diminish w to e on Fri, likely ending over the w by
late afternoon, and will end e around sunrise Sat. Weather on Fri
will be a huge change from today`s warmth as the surge of much
colder air results in daytime temps in the 10-15F range n and around
20F across the s central. Gusty north winds, especially in the
morning, will drive wind chills down the single digits above and blo
zero on Fri. So, it will feel 40-50 degrees colder on Fri compared
this afternoon. Passing sfc high pres ridge and a dry air mass Fri
night should allow temps to fall to a few degrees above and blo 0F
interior w half.

Over the weekend, the mid-upper level trough lifts into eastern
Canada and the eastern U.S. as ridging expands across the Upper
Great Lakes. In this transitioning flow, another fairly vigorous
shortwave will track ese from Saskatchewan/Manitoba Sat to northern
Ontario late Sat night/Sun. Strong waa in response to this wave
pushes into the area Sat aftn/night and may support a period of -sn
into the eastern fcst area late Sat night or Sun morning (only 20pct
chc for now), but better chc of pcpn will certainly pass by to the n
and ne, closer to track of shortwave and deeper into the retreating
cold air where saturation for pcpn production is more likely. As
this wave continues eastward, another push of caa occurs Sun, but
probably not quite cold enough to generate any LES except for
maybe some flurries into the Keweenaw and eastern fcst area.

On Mon, deepening mid-level trough over western N America will
quickly back flow to the sw into the Great Lakes, leading to
unseasonable warmth spreading out of the Plains to the Great Lakes
Mon/Tue. Strong waa/isentropic ascent lifting into the area late Sun
night/Mon morning suggests some potential of a light wintry mix
(less than 20pct maybe over the tip of the Keweenaw), but again,
better chc of pcpn will be n and ne of the area, deeper into the
retreating cold air. Ensembles, particularly the EPS and GEPS, show
increasing probability of max temps exceeding 50F Mon into Tue over
the west half, especially on Tue where probabilities rise into the
60-80 percent range.

As for pcpn Tue-Thu, models seem to moving toward some agreement on
how things will play out. Southern stream energy originating off of
CA seems unlikely to phase with the shortwave in the amplifying
northern stream. These lead waves would support some shra across
Upper MI as they lift thru the Upper Mississippi Valley/Great Lakes
on Tue. Might even be some thunder with indications of elevated
instability lifting into the area. The main shortwave will then
swing into our area Tue into Wed, leading to an organizing sfc low
along cold front that moves into the western Great Lakes Tue in
association with the lead energy. That low then deepens as it lifts
ne. Whether this low deepens rapidly to support a significant snow
for portions of Upper MI remains to be seen, but based on
deterministic runs and ensembles, that still seems unlikely.
However, the ensembles have increased the potential of at least some
accumulating snow across Upper MI for Wed into early Thu.


Issued at 624 PM EST Thu Feb 22 2024

VFR conditions early this evening give way to MVFR cigs and
occasionally IFR vis from time-to-time as a cold front brings
blustery northerly winds and lake-effect snow showers across the TAF
sites late tonight into Friday (KIWD and possibly KSAW are more
likely to see IFR vis reductions last longer than KCMX). Also, NBM
guidance is bringing some LLWS over KSAW this evening for a couple
hours, with the gusty winds associated with the cold front making
its way over the terminal after midnight tonight. As the lake-effect
snow dissipates Friday, expect there to be a slow improvement across
the TAF sites, with KIWD improving to VFR by early afternoon and
KCMX and KSAW improving to VFR by late afternoon.


Issued at 449 PM EST Thu Feb 22 2024

Low pres tracking se into northern Ontario today will drive
associated cold front s across Lake Superior tonight. West winds
shift north and increase further tonight/early Fri after cold front
passes. Much colder air surging s into the area, leading to strong
overlake instability, combined with an incoming 4mb/3hr pres rise
will support 35-40kt nnw gales late this evening to early Fri
morning over central and eastern Lake Superior. Given how quickly
the cold air moves into the area and how strong the resulting
instability becomes over the water, winds may exceed all model
guidance. Although there are no indications for winds to exceed 40kt
in the model guidance, peak gusts to 40-45kt are a possibility in a
corridor from north of Copper Harbor down toward Marquette.
Combination of the much colder air and building waves/strong gusty
winds will lead to heavy freezing spray over all but western Lake
Superior late tonight thru Fri morning. Winds will then diminish as
high pres ridge arrives Fri night. Gusts will drop to blo 20kt from
w to e Fri aftn thru Fri night. As the ridge departs and the next
low pres tracks e toward far northern Ontario on Sat, sw winds will
increase, reaching 25-30kt late Sat aftn thru Sat night.
Probabilistic guidance indicates a 30-50pct chc of reaching low end
gales at this time. Winds will shift w to nw on Sun and diminish
just a little. After winds briefly fall off to under 20kt Sun night,
they will increase to 20-25kt on Mon.


Upper Michigan...
Lake Superior...
  Small Craft Advisory until 5 PM EST /4 PM CST/ Friday for

  Heavy Freezing Spray Warning from 1 AM EST /midnight CST/ to 1
    PM EST /noon CST/ Friday for LSZ240>251-263>267.

  Gale Warning from 1 AM to 8 AM EST Friday for LSZ243>251-

  Small Craft Advisory from 8 AM to 5 PM EST Friday for LSZ243-

  Small Craft Advisory from 8 AM to 1 PM EST Friday for

Lake Michigan...



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