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Area Forecast Discussion
Issued by NWS Marquette, MI
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FXUS63 KMQT 200526
AFDMQT

Area Forecast Discussion
National Weather Service Marquette MI
1226 AM EST Tue Nov 20 2018

.SHORT TERM...(This evening through Tuesday)
Issued at 246 PM EST MON NOV 19 2018

The main story for the rest of this afternoon into tonight will be
lingering lake-effect/upslope snow for much of Marquette County as
well as western Alger and the highlands of Baraga. Surface winds
remain NE`ly, but convergence has weakened now that the surface
trough has cleared our area to the south. The result is that the
strong band from Superior into Marquette that dropped several inches
of snow this morning has devolved into a broader region of lighter
snow that is mostly upslope-forced. Still, visibilities remain low
in spots and a few inches of additional snow accumulation is
expected, so have kept the Winter Weather Advisory in effect until 7
PM. Declined to extend it past that point even though snow will
likely persist into the night as the intensity and additional
accumulations after that time would not otherwise warrant a headline.

As a surface high slides by to our south tonight, winds will veer
from northerly to westerly by sunrise tomorrow. Drier air aloft with
also filter in, which will further weaken any lingering north-wind
lake-effect snow showers. However, both the NAM and RGEM hint at
enhanced convergence along the Marquette County shoreline late this
evening, generally between about 03z and 09z, likely driven by the
lake breeze circulation enhancing as the interior cools. Along with
the NW wind, this could set up a shoreline LES band into Marquette
and farther south and east into western Alger, with a renewed bout
of snow. That said, the aforementioned dry air aloft will remain a
limiting factor and should keep amounts in check; only an inch or
two of additional snowfall is expected in the overnight period.

As for temperatures... with most of the U.P. having a fresh snow
cover and with light winds expected because of surface ridging, have
leaned toward the statistical guidance for lows tonight which are
more likely to drop off accordingly. Countering these signals for
rapid cooling will be lingering cloud cover which will probably keep
temps from just absolutely plummeting. But some guidance does have
clearing right before or around sunrise tomorrow. If that verifies a
few hours earlier than expected, these lows could bust high. As is,
lows tonight are forecast to be in the teens along the shorelines
and low single digits in the western interior. Highs on Tuesday will
only rebound into the low to mid 20s, despite some filtered sunshine.

Those partly clear skies do not last long in this progressive flow.
The next system approaches from the northwest Tuesday afternoon,
bringing with it more light snow of about an inch, expect perhaps on
the Keweenaw and the higher elevations of western Ontonagon where
one or more SW wind LES bands may set up and enhance snowfall in the
afternoon before transitioning to multiple NW wind bands in the
evening.

.LONG TERM...(Tuesday night through Monday)
Issued at 342 PM EST MON NOV 19 2018

Persistent, strong ridge that has been in the vcnty of the w coast
of N America is still fcst to shift steadily downstream during the
week, but in a much weakened state. Ridge/positive height anomaly
will reach the Great Lakes Thu night and se Canada/New England by
Sat. This pattern change will bring about a warmer period for the
Upper Lakes late this week, something longer range models had
indicated for a long time, but kept being delayed by more persistent
western ridging. Meanwhile, a massive mid-level anticyclone/positive
height anomaly (around 400m at 500mb) that formed vcnty of
Scandinavia over the weekend is fcst to retrograde across Greenland
to vcnty of Baffin Island/ne Canada over the next 10 days, though it
will be weakening as it does so. The resulting negative NAO will
support eastern CONUS troffing, and that`s what the GFS/CMC/EMCWF
ensemble means all develop again for early next week. Strongly
negative AO also normally supports a cold pattern for the Upper
Lakes. So, while there will be a warmup late this week to normal,
even above normal for a day or two, looks like temps will likely
fall back some early next week. However, despite the negative
AO/NAO, lack of strong ridging over western N America should
probably keep cooling early next week weaker/more moderate than
might otherwise be expected, but we`ll see how that plays out. As
for pcpn, after one last shortwave dives se in the departing central
to eastern N America trof, bringing a period of -sn/lake enhanced
snow and then LES Tue night/Wed, dry weather/warming should prevail
for Thanksgiving Day and Fri. Shortwave crossing the W Coast late
Wed will reach the Upper Lakes early this weekend, providing a chc
of -ra/-sn. Trailing shortwave will then spin up a low pres system
early next week in the Ohio Valley/Great Lakes. Given the
retrograding positive height anomaly toward ne Canada, seems that
this system would probably stay far enough s and e to keep any
significant weather s and e of Upper MI.

Beginning Tue night/Wed, final shortwave dropping into the departing
central/eastern N America trof will brush ne Lake Superior Tue night
with associated arctic cold front sweeping across Upper MI during
the evening. As is typical for arctic fropa, expect a brief burst of
hvy shsn with fropa. Quick arrival of subsidence, drying and
lowering inversion to 5kft w half and 7kft e half will largely keep
snow amounts in check Tue night. However, with the DGZ falling
squarely in the convective layer under CAA driving 850mb temps down
to around -18C, snow-to-water ratios will increase to fluff up
accumulations. Longer fetch and higher inversions suggest advy may
be required for parts of n central Upper MI, Marquette/Alger
counties in particular as a dominate band connected to Lake Nipigon
preconditioning will stream onshore btwn Marquette and Munising as
the night progresses. This band may impact the tip of the Keweenaw
around Copper Harbor as well. Increasingly anticyclonic low-level
flow as arctic high pres builds over northern Ontario on Wed will
cause LES to diminish steadily Wed. It will end over the w as winds
veer ese during the aftn. The veering winds will focus decent LES
connected to Lake Nipigon over Marquette county thru the morning hrs
as DGZ will be ideally positioned in the convective layer. For this
time of year, it will be a very cold day Wed under 850mb temps of
-17C to -22C from w to e across the fcst area at midday. Highs will
only range from the low/mid teens nw/n central high terrain to the
lwr 20s s central. Record low max temp of 15F here at NWS Marquette
could certainly fall.

As the high shifts e Wed night and winds continue to veer, will
probably see some flurries/-shsn into s central Upper MI Wed night
into Thu morning under shallow se flow across Lake MI. Elsewhere, it
will be a very cold night if skies can clear anywhere for a few hrs.
However, right now, it appears there will be little/no gap btwn the
loss of lake stratocu and arrival of high/mid clouds under
developing waa regime. Eastern fcst area would likely have best
opportunity for temps to tank.

Thanksgiving Day...waa will strengthen thru the day. Despite decent
isentropic ascent, sharply anticyclonic mid-level flow should keep
pcpn from being a concern. NAM indicates significant low-level
moistening, supporting potential of flurries/-fzdz. For now, this is
viewed as a very low probability given the over moistening that the
NAM can exhibit at times. Will be on the breezy side. Temps will
rebound into the mid 20s to lwr 30s.

Shortwave trof will move across the Mississippi Valley on Fri and
reach the western Great Lakes Fri night/Sat. While models show
differences in the structure/timing of trof, there is good agreement
for pcpn to occur at some point Fri night/Sat. GFS remains on the
fast side of guidance with pcpn arriving Fri aftn. Little weight
will be placed on its solution for now. Expect pcpn to arrive Fri
evening and continue Sat. Looks like column may cool sufficiently
for at least a mix of rain/snow and potential change to all snow.
Doesn`t look like a headline event, but if pcpn ends up as mainly
snow, the wet snow will make for sloppy travel at times.

Should see a break in pcpn for most areas on Sun. 12z models still
show next shortwave spinning up an Ohio Valley/Great Lakes low pres
system Sun night/Mon. While movement of high latitude anomalies
should keep this low far enough s and e to prevent any notable
weather impacts here, that remains to be seen given the number of
GFS/CMC ensembles that show a fairly strong low on a farther
nw track.
&&

.AVIATION...(For the 06Z TAFS through 06Z Tuesday night)
Issued at 1225 AM EST TUE NOV 20 2018

Lake-effect snow is winding down, but snow bands will likely persist
through much of the overnight hours before finally allowing for a
brief reprieve early Tuesday. SW winds will take over at this point
before returning to out of the W-NW. Once the winds shift back
around, look for snow showers to return to the terminals,
anticipated to reappear by Tuesday evening.
&&

.MARINE...(For the 4 PM Lake Superior forecast issuance)
Issued at 246 PM EST MON NOV 19 2018

Winds shift from northerly to westerly and relax to 10 to 15 knots
tonight across the lake as a surface ridge passes to the south. They
become southwesterly and increase back to about 25 knots Tuesday
afternoon ahead of an approaching surface trough. Behind that trough,
winds will veer to northwesterly and then northerly for Tuesday
night and Wednesday morning but remain at about 25 knots over the
western lake and 30 to 35 knots over the eastern lake. A few widely
scattered gale-force gusts are possible over eastern Superior early
Wednesday morning, but will not be worthy of a headline. Winds
across the lake weaken below 20 knots Wednesday afternoon. Winds
stay light through Thursday morning as a high pressure ridge drops
south out of Canada across the lake. As the high departs to the
southeast Thursday afternoon, winds become southerly and increase
back to 25 to 30 knots for Thursday night into Friday.
&&

.MQT WATCHES/WARNINGS/ADVISORIES...
Upper Michigan...
None.
Lake Superior...
None.
Lake Michigan...
None.
&&

$$

SHORT TERM...RJC
LONG TERM...Rolfson
AVIATION...JLB
MARINE...RJC
National Weather Service Regional Headquarters
