Area Forecast Discussion
Issued by NWS Marquette, MI

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FXUS63 KMQT 202335
AFDMQT

Area Forecast Discussion
National Weather Service Marquette MI
735 PM EDT Mon Mar 20 2017

.SHORT TERM...(This evening through Tuesday)
Issued at 409 PM EDT MON MAR 20 2017

Broad upper trough has settled across cntrl Canada. Strong upper jet
along base of trough and ribbon of mid level moisture supported mid
clouds and a patchy light rain/snow along WI border today, but
clouds have cleared out quickly this aftn leading to plenty of
sunshine for all areas except far scntrl to east cwa. After temps in
the 30s lingering til around midday, readings have risen well into
the 40s this aftn with even a 50 degree reading at fire wx site near
Kenton. Also quite dry with dwpnts in the lower teens leading to RH
as low as 20 pct over interior west. Clouds over scntrl and east cwa
will continue to diminish per satellite trends leading to clear
skies for the evening. Temps over interior west may fall off quickly
this evening given how dry it is. Lowered mins into the low teens
for those areas.

Later this evening and overnight, strong shortwave over cntrl
Manitoba this aftn will slide toward Lk Superior. This system will
be what propels sfc cold front to the northwest of Lk Superior this
aftn across the cwa after midnight. Limited moisture with the system
upstream and the dry ambient airmass overhead will result in minimal
precip chances with the front as it moves through. Have the highest
pops across Keweenaw and ncntrl for a few snow showers to develop as
the front arrives. Cold air charging in behind the front (h95 temps
falling from +5c over western Upper Michigan at midnight to near
-10c by 12z Tue) on gusty NW winds and increasing h85 moisture and
cold air advection at h85 (temps down to -18c by midday Tue) should
eventually lead to lake effect snow showers late tonight and more so
into Tue morning closer to Lk Superior. Even with extent of cold air
advection, it is still springtime and expect snow showers to spread
farther inland late Tue morning into Tue aftn. Moisture will be
provided by ongoing lake moistening/fluxes and instability will be
from daytime heating as sfc-850mb lapse rates climb above 9c/km and
forecast soundings show 30-50j/kg at inland locations like IMT and
ESC.

Where the lake effect sets up Tue morning and more or less persists
through the day, increasing SLRs toward 20:1 will lead to fluffier
snow and at least isolated 2" snow amounts are not of question. Most
areas will see less than 1 inch through the day though. Will certainly
be blustery and colder for all areas. May even see some blsn near
Lk Superior where NNW winds gust over 25 mph. Temps will stay
steady in the lower 20s for northwest higher terrain areas and
will be mainly in the mid-upper 20s otherwise. Downslope areas in
scntrtl may reach well into the 30s so if there is precip that far
south, could end up being a rain/snow mix.

.LONG TERM...(Tuesday night through Monday)
Issued at 401 PM EDT MON MAR 20 2017

A cold nly flow ahead of Cndn hi pres bldg toward the Upr Lks wl
cause some les over mainly the e half on Tue ngt, but the dryness of
the incoming airmass/lowering subsidence invrn base wl limit the
intensity of this pcpn, which wl end on Wed with the arrival of the
sfc hi. After some dry and milder wx on Wed and Thu, another chc for
some mixed pcpn wl arrive on Thu ngt ahead of a warm fnt associated
with a srn branch closed lo lifting enewd out of the srn Rockies.
How long this pcpn lingers wl then depend on how quickly/far to the
s a sfc hi pres under a nrn branch flow in scentral Canada expands
into the Upr Lks on Sat.

Tue night...Upr MI wl be under the influence a confluent nw flow alf
btwn shrtwv sliding to the se and progressive upr rdg axis moving e
thru the nrn Plains. The cold n flow ahead of a Cndn hi pres center
that is progged to move fm near Lk Winnipeg to the MN arrowhead by
12Z Wed is fcst to drop h85 temps as lo as about -19C over the ern
cwa during the ngt, allowing for a transition to pure les in the
absence of daytime heating. But the dry nature of the incoming
airmass that leads to an inverted-v T/Td profile on the fcst
sdngs/fcst lo invrn base near 4-5k ft agl and trend toward a more
acyc llvl flow especially over the w under the large scale
dnva/subsidence wl hold down the les intensity/coverage. The best
chc for a few inches of fluffy sn wl be over the ncentral and e, an
area closer to the h85 thermal trof and impacted by a longer
fetch/more modification acrs Lk Sup that is fcst to allow some lk
induced troffing and more near sfc cnvgc possibly enhanced by a land
breeze wind component. With diminishing winds, pwat falling toward
0.10 inch, and at least partial clrg closer to the incoming hi pres,
temps over the interior w half wl fall into the single numbers and
perhaps near zero. Tended toward the lower end of guidance for temps
in this area.

Wed/Wed ngt...Lingering les over the e half wl end Wed mrng as the
sprawling sfc hi pres builds over Upr MI during the day ahead of the
incoming upr rdg axis. Under mosunny skies/incrsg early spring sun
angle, expect temps to rebound sharply well into the 30s over at
least the interior w half. The combination of incrsg hi clds
sprilling over the aprchg upr rdg axis and an incrsg sly flow on the
wrn flank of the sfc hi pres retreating to the e wl limit the
diurnal temp fall, which wl be sharpest over the interior e closer
to the departing hi/core of drier air.

Thu...The gusty sly flow on the western flank of the departing sfc
hi pres is fcst to lift h85 temps as hi as about 4C by late in the
day. Despite some incrsg waa mid/hi clds, max temps wl recover into
the 40s away fm the cooling influence of mainly Lk MI. Although some
of the medium range guidance indicates there could be some light
pcpn under the waa/incrsg mid lvl mstr, the dryness shown in the
llvls of the fcst sdngs suggest the day wl be dry.

Thu ngt into Sat...The fcst for Upr MI during this time wl depend on
the evolution of an incrsgly split upr flow that wl feature a closed
srn branch lo moving fm the srn Rockies on Thu ngt toward the OH
River Valley/Lower Great Lks on Sat and sfc hi pres under upr rdging
in the nrn branch flow that wl prevail over scentral Canada.
Although the guidance differs on the details, the medium range
models show some mixed pcpn, with ptype impacted by near sfc
evaporate cooling of the very dry llvl antecedent airmass that would
favor at least a period of freezing ra during fvrbl period of
nocturnal cooling, wl dvlp on Thu ngt but change to mainly ra into
Fri ahead of the warm fnt extending enewd fm the srn branch lo
emerging into the srn Plains toward the Lower Lks and under some upr
dvgc in the rrq of an h3 jet core within the confluence zn btwn the
branches located to the s of James Bay. Following the passage of a
cold fnt attendant to a nrn branch disturbance tracking thru
Ontario, the Cndn hi pres is fcst to follow into nw Ontario on Sat.
Exactly how quickly and far to the s this hi blds into Ontario and
how much cold/dry air flows into the Upr Lks wl determine the
evolution/placement of the waa pcpn band. The trend exhibited by the
12Z GFS/Cndn models shows a sfc hi pres bldg faster/farther to the
s, suppressing the waa pcpn band to the s by 12Z Sat, with only some
lgt pcpn persistening over the ncentral on Sat under an upslope ene
flow on the srn flank of the Ontario hi pres. Considering the
uncertainty with the expected split flow pattern, maintained the
model consensus fcst.

Sun/Mon...Uncertainly lingers in the longer term as to whether some
pcpn on the nrn flank of the slow moving srn branch closed lo wl
expand back toward the Upr Lks later in the weekend/early next week
following the passage of the sfc hi pres center into Quebec. Any
associated mixed pcpn would impact mainly the se cwa closer to the
closed lo. If the hi pres is more expansive, this period could be
dry.
&&

.AVIATION...(For the 00Z TAFS through 00Z Tuesday evening)
Issued at 735 PM EDT MON MAR 20 2017

Ahead of an approaching cold front, a dry air mass will persist in
the low to mid levels, allowing VFR conditions to continue at
KIWD/KCMX/KSAW until fropa. With passage of the cold front late
tonight/early Tue morning, sct -shsn will arrive with winds becoming
gusty to 20-30kt from nw to n, continuing thru the day Tue. Colder
air surging into the area on Tue combined with moisture off Lake
Superior and daytime heating should result in sct -shsn on Tue
though the -shsn should occur mostly during the morning at
KIWD/KCMX. Cigs should drop to around 3kft Tue morning, but
otherwise will end up in the lower VFR range around 4kft. Vis within
heavier shsn could drop to IFR at 1-2sm, but for the most part
should be MVFR to VFR.
&&

.MARINE...(For the 4 PM Lake Superior forecast issuance)
Issued at 409 PM EDT MON MAR 20 2017

Winds 25 kts or less into the evening then SW winds could increse to
around 30 kts before shifting NW overnight as cold front crosses Lk
Superior. May see brief gales to 35 kts immediately behind the front
over much of the lake as cold air charges in, but more persistent
gales are expected late tonight into late Tuesday aftn over the east
two thirds of the lake. There will also be freezing spray as well
late tonight through Tuesday, especially over the east half of Lk
Superior.

Nnw winds as hi as 25-30kts/freezing spray over the e half of the
Lake on Tue night will diminish on Wed as a sprawling hi pres builds
over the Upper Lakes. After this hi pres shifts to the e on Wed
night, s winds up to 30 kts will be possible on Thu under the
tightening pres gradient on the western flank of the departing hi
pres. Expect winds to diminish on Thu night thru Fri as a flatter
pres gradient dominates. Stronger ne winds up to 25-30 kts may
return on Sat under the tightening pres gradient on the southern
flank of hi pres building into Ontario.
&&

.MQT WATCHES/WARNINGS/ADVISORIES...
Upper Michigan...
None.
Lake Superior...
  Gale Warning from 5 AM Tuesday to 2 AM EDT Wednesday for
     LSZ249>251-266-267.

  Gale Warning from 2 AM to 4 PM EDT Tuesday for LSZ243>248-264-
     265.

Lake Michigan...
None.
&&

$$

SHORT TERM...JLA
LONG TERM...KC
AVIATION...Rolfson
MARINE...JLA/KC



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