Area Forecast Discussion
Issued by NWS Marquette, MI

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FXUS63 KMQT 152038

Area Forecast Discussion
National Weather Service Marquette MI
338 PM EST Mon Jan 15 2018

.SHORT TERM...(This evening through Tuesday)
Issued at 336 PM EST MON JAN 15 2018

...Light to moderate lake effect snow off of Lake Superior to impact
the northeast to north wind snow belts and the morning commute on

Low pressure slowly continued to rotate across far southwest
Wisconsin and northeast Illinois this afternoon allowing winds
across Upper Michigan to become primarily easterly. This has allowed
the dominant, heavy band of lake effect snow that impacted areas
across Alger and Delta county to push well south of the area into
east-central Wisconsin this afternoon. Lingering snow continued to
impact much of Upper Michigan today as the main upper-level low
continued to slowly rotate across the region this afternoon.

The light widespread snow is expected to linger through the rest of
the evening hours before the above mentioned low pressure system and
its main synoptic-scale forcing continue to dig southeast of the
region. The attention then turns towards the approaching lake effect
snow off of Lake Superior tonight through Tuesday.

Locations out west will see the lake effect snow kick in and/or
intensify later tonight and linger through early/mid Tuesday
morning. Initially as the lake effect comes on shore, these snow
showers should bring a quick burst of 2 to 3 inches, perhaps locally
up to 4 or 5 inches across the higher terrain. However, the low-
level flow is progged to progressively back, so it will be
challenging to maintain steady orientation of the low-level flow and
the resulting focus for lift. Due to the backing progressive flow
expected, this lake effect snow will move into the northeast, north
and then west wind snow belts with the most intense snow expected
immediately after the bands push onshore tonight into early Tuesday
morning. Due to the timing of this snow and narrow window of
moderate lake effect snow, opted to issue an SPS for the Keweenaw
and far west instead of an advisory for now. By the Tuesday morning
commute, light lake effect snow is expected to linger. However, as
we progress through the afternoon and evening hours on Tuesday the
flow will continue to back west-southwest and will allow any
lingering focus for lake effect snow to shift across the Keweenaw

Across the north central, from Baraga to Alger county, low-level
flow will remain northeast to northerly throughout the time period
allowing for better organization of lake effect snow and focus for
lift, especially across the higher terrain in Baraga and Marquette
counties later tonight through Tuesday. Forecast soundings show the
strongest lift through the DGZ, so have increased snow ratios closer
to 30:1 resulting in snow accumulations of 2 to 4, perhaps 5 inches
near the Lake Superior shoreline by Tuesday evening, with higher
totals closer to 8 to 10 inches across the higher terrain in
Marquette and Baraga counties by Tuesday evening. Further east
across Alger county snowfall totals will be a bit less, but still
expecting 2 to 4 inches, perhaps locally higher across the western
half of the county where the better, more persistent focus for lake
effect snow will set up Tuesday morning and afternoon. It is not out
of the question that we may see some of this lake effect make it
down towards the northern edge of the Bay of Green Bay, so do also
have light snow accumulations down into Delta and northern Menominee
counties during the day on Tuesday. Right now, we`re looking at a
high-end advisory, perhaps low-end warning criteria based on
snowfall amounts, but given the fluffy nature of the snow expected
did opt to hold onto the advisory with higher-end wording. It is
possible that if higher snowfall rates occuring during the morning
commute, a bump up in headlines may be justifiable based on impacts
to the morning commute, especially across Marquette County. The lake
effect snow across the north central will transition from the
northeast to north wind snow belts through the afternoon hours while
diminishing in intensity.

.LONG TERM...(Tuesday night through Monday)
Issued at 336 PM EST MON JAN 15 2018

Ridge over western N America is currently at peak amplitude with
500mb heights upwards of 400m above normal over nw toward n central
Canada. This ridge is forcing a trof downstream over the Upper
Mississippi Valley/western Great Lakes, which is maintaining the
current cold weather/blo normal temps over the fcst area. The ridge
will deamplify and shift to the E Coast by Sat in response to a trof
swinging from the ne Pacific into the western CONUS. In turn, this
will lead to the long advertised warmup for the last half of this
week as Pacific air is driven across the CONUS downstream from the
trof. This pattern change is consistent with the signal from the
current active MJO over the Indian Ocean, in phase 3, which favors
western N America troffing and eastern N America ridging. Unless the
MJO weakens, it will be a forcing mechanism for mild
conditions/above normal temps over the Upper Lakes for the next few
weeks, suggesting cold spells thru the end of Jan will be short-
lived. In the end, pattern still looks like it will be more variable
btwn above and blo normal temps with warmer conditions more
frequently occurring than cold. As for pcpn, LES will end midweek as
much warmer air arrives, then there may be some spotty light mixed
pcpn late week. With Pacific energy moving across the CONUS in the
developing mild pattern during the last half of the month, there
should be more frequent opportunities for storm systems/pcpn to
affect the area, but unfortunately, that may include mixed ptypes.
The first of these systems should impact the Upper Lakes late this
weekend/early next week, and there are increasing indications that
this first stystem could become a significant winter storm as it
lifts from the southern Plains to the western Great Lakes. More on
that later.

Beginning Tue evening, deep moisture will be out of the area by
evening. With onset of waa and with lowering inversion and backing
winds to the wsw, LES will steadily diminish Tue night as it shifts
with the backing winds. In fact, LES will end over the w as 850mb
temps rise to around -8C by 12Z Wed, and it may be out of the ne
fcst area by 12z as winds become wsw, pushing whatever -shsn are
left out over the lake. Strong waa will be underway by Wed morning.
The strong waa/isentropic ascent could generate some -sn on Wed over
the far eastern fcst area, but that still looks doubtful. Better
potential of -sn will be farther ne and e, deeper into retreating
cold air where it`s easier to erode antecedant dry low levels.
Although the upward temp trend begins Wed, gusty w to sw winds will
add a notable chill. Temps will then push above normal Thu thru the
weekend. There may be some spotty light mixed pcpn at times Thu thru
Sat under continued waa pattern with the potential of a couple of
shortwaves to pass across the area. Any pcpn would be very light if
it occurs.

Over the weekend, trof that moves into the western CONUS late week
will shift out over the Plains on Sun with an associated sfc low
organizing as it lifts ne from the Southern Plains. Operational
GFS/GEM/ECMWF have strongly converged toward a solution that has the
mid/upper trof spinning up a fairly strong winter storm as it moves
to the western Great Lakes. Exact track, critical for ptypes as well
as zone of heaviest snowfall, will be a detail that won`t be more
certain for several days. GFS ensembles show quite a bit of spread
with track/intensity, but in general, lean toward the e side of the
envelop, a colder solution favoring more snow as ptype. The 00z GEM
ensembles leaned toward the w side, a warmer solution that would
result in more mixed ptypes, including rain. The 12z GEM ensembles
overall shifted slightly s and e for a colder solution. For what
it`s worth at this time range, the last 2 runs of the operational
ECMWF favor a more western track/mixed ptype scenario for at least
parts of the fcst area while the GFS is the eastern cold/snow
solution. The 12z GEM shifted to a colder solution from its 00z
warmer mixed ptype scenario. In any event, the Sun/Mon time frame
will be a period to monitor as there is a decent signal for a
potentially significant winter storm to impact the Upper Mississippi
Valley/western Great Lakes, a rare event for this cold season.
Western trof will reload behind this system, so there could be
another system tracking across the central/eastern CONUS next week.

.AVIATION...(For the 18Z TAFS through 18Z Tuesday afternoon)
Issued at 1251 PM EST MON JAN 15 2018

KIWD and KCMX: -SHSN will continue with MVFR ceilings and generally
IFR visibility into this evening, through high-end IFR ceilings will
be possible at times at KCMX. Backing winds will then allow a
potentially heavy lake effect snow band shift southward across KCMX
from 03-06Z and KIWD from 07-10Z. A brief period of 1/4SM vis will
be possible during these times. By Tuesday morning, -SHSN will

KSAW: Generally MVFR ceilings and vis expected through this
afternoon before gradually backing winds bring pronounced LES and
IFR vis tonight. A potentially heavy lake effect snow band will then
shift southward across the terminal from 12-15Z Tuesday. Moderate
LES bands will follow through the remainder of the forecast period.
A brief period or two of 1/4SM vis will be possible during the
morning, especially between 12-15Z.

.MARINE...(For the 4 PM Lake Superior forecast issuance)
Issued at 336 PM EST MON JAN 15 2018

As the pressure gradient increases across western Lake Superior
behind the exiting surface low, a brief period of gale force gusts
to 35 knots will be possible. However, this window looks like it
will be very narrow, perhaps 2 or 3 hours. On Tuesday winds will
diminish to around 15 to 25 knots, but then will quickly ramp up to
gales of 35 to 40 knots late Tuesday night through early Wednesday
night across much of Lake Superior, see the latest Marine Weather
Statement for further details. Otherwise, winds will drop back down
to between 20 and 20 knots Thursday through the beginning of the
weekend. Freezing spray will continue across much of the lake,
especially the west half through Tuesday morning. As the winds
increase on Wednesday, heavy freezing spray looks possible mainly
over the western half.

Upper Michigan...
  Winter Storm Warning until 4 PM EST this afternoon for MIZ013.

  Winter Weather Advisory until 6 PM CST this evening for MIZ011-

  Winter Weather Advisory from 7 PM this evening to 5 PM EST
     Tuesday for MIZ004-005.

  Winter Weather Advisory from 5 AM to 7 PM EST Tuesday for MIZ006.

Lake Superior...
  Gale Watch from Wednesday morning through Wednesday evening for

  Gale Watch from late Tuesday night through Wednesday evening for

  Gale Watch from late Tuesday night through late Wednesday night
     for LSZ263-264.

Lake Michigan...


SHORT TERM...Ritzman
LONG TERM...Rolfson
MARINE...Ritzman is the U.S. government's official web portal to all federal, state and local government web resources and services.