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000
FXUS63 KMQT 182037
AFDMQT

Area Forecast Discussion
National Weather Service Marquette MI
437 PM EDT Sun Apr 18 2021

.SHORT TERM...(This evening through Monday)
Issued at 437 PM EDT SUN APR 18 2021

The short term will bring another return back to winter. Water vapor
imagery and RAP analysis show a shortwave trof extending from Hudson
Bay to ND. Associated sfc cold front runs from James Bay across ne
MN to SD. Shra are occurring along/just behind front with shra
switching to shsn within about 3hrs of fropa. Closer to home, it`s
been a warm/dry day and generally partly to mostly sunny skies.
Temps in the interior are in the mid 50s to around 60F. Lake breezes
are keeping lakeside locations cool in the low/mid 40s. With dwpts
as low as the upper teens/lwr 20s F, RH has fallen to 20-30pct in
the interior.

Approaching shortwave will amplify as it swings se across the Upper
Great Lakes. Much of the model guidance indicates a weakly closed
mid-level low will form over the fcst area with the center passing
across northern Lake Superior. With 12hr 500mb height falls around
100m tonight and a nice upper diffluence signature within left exit
of upper jet surging into the western Great Lakes, stage should be
set for a band of shra mixing with/changing to shsn moving across
the fcst area tonight. Of concern is the lower level cyclonic flow
that develops under postfrontal caa regime dropping 850mb temps
around -11C and the amplifying trof/falling heights. Further aided
by brisk upsloping NW winds, expect an upslope/lake enhanced snow
scenario to develop overnight into Mon morning. High terrain of the
w and nw fcst area will be favored for this event. DGZ ends up
mostly above the best upward motion so SLRs will be on the low side,
probably around 10 to 1. 12hr snow amounts over the high terrain
from around KIWD ne up the spine of the Keweenaw overnight/Mon
morning may push low SLR winter wx advy criteria of 3 or more
inches. For now, given the greatest amounts pinned locally to the
high terrain, will issue an SPS for the western counties to
highlight the potential of hazardous travel conditions due to some
roads likely becoming slushy/snow covered, at least in spots, for
the Mon morning commute. Winds will also ramp up behind the front as
sfc low pres wave develops on the front over Lake Superior and
briefly deepens. Wind gusts of 25-35mph should be common, developing
nw late tonight then spreading across the area thru Mon morning.
Gusts up to around 45mph are expected at lakeside locations exposed
to a nw wind from the Keweenaw eastward.

So, a blustery, much colder day is on the way for Mon. During the
day, expect temps generally in the upper 20s/lwr 30s F across the w
and n. Temps may sneak up to 40F across the s central, but given the
expectation of abundant cloud cover, that may be optimistic. Loss of
deeper moisture/relaxing cyclonic curvature of the low-level winds
will lead to diminishing snow over the w and nw fcst area during the
aftn. To the e, conditions for lake enhanced snow never become
nearly as favorable as over the w. Minor snow accumulations under 1
inch are expected. Limited daytime heating and moisture off the lake
may support some development of isold -shsn/flurries well inland
during the day.

.LONG TERM...(Monday night through Sunday)
Issued at 327 PM EDT SUN APR 18 2021

A active early long term period with the tail end of a lake effect
snow event followed by a quiet period thanks to a 1027mb surface
high shifting southeastward into the northern Plains. Expecting
below normal temps initially before warming up Thursday and Friday,
with a weekend finish near normal following the passage of a cold
front this weekend.

Starting off Monday night, lingering troughing over the region with
the mid-level low just east of our forecast area will help maintain
the unseasonable colder temperatures. Overnight 850mb temps are
progged to remain about -12 to -14 over the region under
northwesterly flow off Lake Superior. With Lake Superior hovering
near +3C resulting in a delta T of 15 to 18, lake effect snow
showers are expected across the northwest wind snow belts. While
there is decent lift through the DGZ, model soundings show an
inverted V at the lower levels, indicating any snow will have to
overcome the dry air near the surface. If earlier showers are able
to erode the dry layer some, that could add to the snow
accumulations. Generally, expecting an inch or two being possible,
mainly across the Hurons and in the northwest wind belts east of
Marquette. The northern half of the Keweenaw could also see another
half inch or so on top of their daytime accumulations. Overnight
lows are expected to bottom out in the low 20s, but if cloud cover
breaks away from the lakeshores, particularly in the interior west,
some mid to high teens can`t be ruled out.

As the upstream high pressure sinks into southern Saskatchewan
Tuesday, anticyclonic flow and increased subsidence should bring an
end to any early lake effect snow showers. With temps hovering
around -10C during the day Tuesday, expecting day time highs to
remain largely in the 30s. Some low 40s across the south-central
can`t be ruled out. A weak shortwave is expected to migrate south
through the region late Tuesday night into Wednesday. This
enhancement may help develop some flurries or light snow showers,
but with drier low levels, notable accumulations are not expected.
Daytime highs in the upper 30s across the north half and near 40
south half are expected.

Height rises resulting from the upstream high building southeastward
into the central and eastern Plains should help clear out the skies
Wednesday night. With the colder air aloft lingering, winds becoming
light and PWATS near 0.25", expecting an opportunity for some good
radiational cooling. Lows right now look to be in the low 20s with
mid teens in the colder interior west, but I wouldn`t be surprised if
guidance trends colder, especially in the interior central and east.
With the ridge persisting over the region Thursday and Friday,
sunshine and WAA will help temps rebound back into the 50s. The next
precip chances look to be Friday night or Saturday, but there are
noticeable timing differences among the 12z guidance. The GFS looks
to be the fastest solution with the cold front moving into the
region Friday night. This contrasts well with the slower Canadian
and Euro solutions, whom delay the system until Saturday afternoon
or evening. Given there is still plenty of time for things to change
and for the guidance to reach a better consensus, ran with NBM pops
for now.
&&

.AVIATION...(For the 18Z TAFS through 18Z Monday afternoon)
Issued at 143 PM EDT SUN APR 18 2021

VFR conditions will prevail thru the aftn at KIWD/KCMX/KSAW. A cold
front just nw of Lake Superior will then sweep across the area
tonight. Expect a period of -shra changing to -shsn as the front
passes. While these -shsn will end at KSAW late tonight/early Mon
morning, -shsn should continue thru Mon morning at KIWD/KCMX. With
the pcpn, expect conditions at all terminals to fall to at least
MVFR. Upsloping postfrontal winds at KIWD/KCMX may result in IFR
conditions at times, especially at KIWD. Postfrontal nw winds will
also be gusty to 20-30kt, strongest at KCMX where some gusts to 30-
35kt appear likely.
&&

.MARINE...(For the 4 PM Lake Superior forecast issuance)
Issued at 437 PM EDT SUN APR 18 2021

Strong cold front will sweep across Lake Superior tonight. Along the
front, a low pres wave will also develop and briefly deepen. Thus,
after fropa, nw winds will ramp up, especially from central to
eastern Lake Superior overnight thru Mon. Increasingly colder air
and 3-4mb/3hr pres rises on the backside of the low pres wave will
further boost winds. Thus, expect high end nw gales of 40-45kt to
develop from central into eastern Lake Superior overnight thru Mon
morning. Not out of the question that there could be an hr or two
where wind gusts reach storm force in a corridor from n of the
Keweenaw Peninsula se toward Grand Marais. Winds will diminish from
w to e Mon aftn thru Mon night. While winds will fall blo 20kt over
the w by sunrise Tue, winds may still be gusting to around 25kt over
the e. Winds generally blo 20kt are then expected thru the midweek
period.
&&

.MQT WATCHES/WARNINGS/ADVISORIES...
Upper Michigan...
None.
Lake Superior...
  Gale Warning from 8 AM to 11 PM EDT Monday for LSZ251-267.

  Gale Warning from 5 AM to 11 PM EDT Monday for LSZ249-250-266.

  Gale Warning from 5 AM to 8 PM EDT Monday for LSZ265.

  Gale Warning from 2 AM to 8 PM EDT Monday for LSZ244-245-264.

  Gale Warning from 2 AM to 2 PM EDT Monday for LSZ243-263.

  Gale Warning from 8 AM to 8 PM EDT Monday for LSZ248.

Lake Michigan...
None.
&&

$$

SHORT TERM...Rolfson
LONG TERM...JP
AVIATION...Rolfson
MARINE...Rolfson