Area Forecast Discussion
Issued by NWS Marquette, MI

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FXUS63 KMQT 150536
AFDMQT

Area Forecast Discussion
National Weather Service Marquette MI
1236 AM EST Mon Jan 15 2018

.SHORT TERM...(This evening through Monday)
Issued at 259 PM EST SUN JAN 14 2018

...Moderate to heavy lake effect/enhanced snowfall expected tonight
downwind of Lake Michigan...

Upstream of Upper Michigan, water vapor imagery showed shortwave
energy digging south across the northern Plains this afternoon with
its associated low pressure trough tracking just ahead across the
Upper Mississippi Valley. As a sharp axis of 850mb warm air
advection continued to nose into the surface through this afternoon,
widespread snow developed across the northern Plains and stretched
into northern portions of Minnesota. Immediately downstream of the
area, a band of lake effect snow has developed across eastern Lake
Michigan. Elsewhere, conditions were mostly sunny across Upper
Michigan this afternoon with mid and high clouds beginning to stream
eastward. The main forecast concerns during this time period are
widespread light system snow tonight through Monday, moderate to
heavy lake enhanced snow expected off of Lake Michigan tonight into
Monday, and then the return of lake effect/enhanced snow across the
far west and north central on Monday.

Widespread system snow tonight through Monday transitioning to lake
enhanced snow on Monday: As the above mentioned shortwave continues
to dig south across north central portions of the CONUS, widespread
snow will move across much of Upper Michigan. The stronger warm air
advection and moisture is expected to remain south of the area;
therefore, system snow over the next 24 hours is expected to remain
fairly light. As the shortwave becomes cutoff across the region
tonight into Monday and slows down, weak warm air advection will
continue to linger across the area allowing the widespread light snow
to linger. Overall, the system snow should only amount to around 1
to 3 inches across the area, except downwind of Lake Michigan where
lake enhanced snow is expected (see the below discussion). As the
surface low slowly tracks across southern Lake Michigan into Lower
Michigan, flow will back east-northeast on Monday, so expect lake
enhanced snow to impact the Keweenaw and north central portions of
Upper Michigan. Models are not highlighting much QPF across these
areas, outside of the high-res ARW/NMM, likely due to the lack of
saturation through the DGZ advertised by forecast soundings. If the
airmass can modify more than what is shown in current guidance,
headlines may be needed across the Keweenaw Monday. Further west,
medium and high-res guidance have slowed the arrival of lake effect
snow on the back side of the exiting surface trough, with the
potential for meso-lows coming onshore shifting a bit further west
across far northwest Wisconsin.

Moderate to heavy lake enhanced snow downwind of Lake Michigan
tonight into Monday: The main concern during this time period is the
band of moderate to heavy lake effect/enhanced snow expected to push
onshore tonight through mid/late Monday morning downwind of Lake
Michigan and its impacts on travel. With the surface low progged to
track across Wisconsin/Iowa/Illinois, southwesterly flow across
northern Lake Michigan will back southeasterly and allow this strong
band of lake effect snow to push onshore across Schoolcraft and
Delta counties late tonight into Monday morning, and become enhanced
by lingering synoptic-scale lift. With 850mb temperatures around -15
to -18C initially and the leading edge of the PV anomaly tracking
across the region, inversion heights will lift upwards of 8-10kft,
with decent lake induced instability. Therefore, expect a deep
convective layer in which forecast soundings continue to show strong
lift and saturation through the DGZ. This will result in SLRs of at
least 20-30:1. Initially as this band comes onshore, the 1000-850mb
convergence signature remains fairly transient across Schoolcraft
county, but based on the strong lift through the DGZ, wouldn`t be
surprised if locations across southern portions of the area pick up
a quick 4 to 6 inches of snow as the band moves overhead. It is
conceivable that a few locations across far southwest Schoolcraft
county may see warning criteria snowfall, but based on how transient
the band is expected to be opted to hold off on upgrading their
advisory for now.

As winds continue to back Monday morning expect the strong band of
lake enhanced snow to push into Delta, Menominee, and possibly
portions of Dickinson Counties. This will result in slippery to
difficult travel Monday morning, including along US-2 and US-41.
Delta County looks like it will take the brunt of the accumulating
snow, especially the Garden and Stonington Peninsulas where the lake
effect snow is expected to be more persistent. By the end of Monday,
far southeast portions of Delta County may see upwards of 10 to 12
inches of new snow. Elsewhere, across Delta County, 6 to 8 inches
are expected with much of this snow falling from the early to late
morning hours on Monday. Confidence is not as high in regards to how
things will play out across Menominee and Dickinson Counties as the
low-level moisture gets reduced significantly due to ice cover on
the Bay of Green Bay. However, there should still be enough
lingering modified moisture and lift to foster an additional 2 to 4
inches Monday morning west of the Bay of Green Bay. Therefore, did
opt to expand the winter weather advisory further west to include
Dickinson and Menominee Counties to draw attention for potential for
travel impacts during the Monday morning commute.

.LONG TERM...(Monday night through Sunday)
Issued at 346 PM EST SUN JAN 14 2018

Building ridge over the western CONUS will reach peak amplitude
tonight/Mon with 500mb heights upwards of 400m above normal over nw
toward n central Canada. This will force a shortwave se and
reinforce/maintain current cold conditions over the Upper Lakes thru
Tue. Advertised warmup for the last half of the week is still on
track as the ridge deamplifies and shifts to the E Coast by Sat in
in response to a trof swinging from the ne Pacific into the western
CONUS. As a result, Pacific air will push across the CONUS this
week. 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 will likely be more variable btwn above
and blo normal temps with warmer conditions more frequently
occurring. As for pcpn, pcpn will be largely lake effect driven thru
Tue under cold air mass. Shortwave reinforcing the cold for the next
few days will provide a period of widespread light snow for the fcst
area into Mon along with mdt to hvy lake enhanced snow off Lake MI
and also off Lake Superior into Tue morning. LES will end midweek as
much warmer air arrives, then there may be some light mixed pcpn
late week. With Pacific energy moving across the CONUS in the
overall 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.

As deepening trof over the western Great Lakes on Mon begins to
shift e Mon night/Tue, e to ne low-level flow across the Upper Lakes
to start Mon evening will back to the n and then nw. Much of the
light synoptic snow from Mon should be out of the area by evening,
and any lingering/diminishing lake enhanced snow off Lake MI into
Menominee county will end early. The backing winds will shift
attention to lake enhanced/lake effect snow off Lake Superior. This
snow (potentially mdt to hvy) will already be ongoing into the
Keweenaw under easterly flow to start the evening. Under backing
winds, mdt/hvy snow will swing into the rest of western Upper MI and
also n central Upper MI Mon night into Tue morning. Deep layer
forcing for upward motion will be diminishing and slipping s and e
during this time, but deep moisture and well positioned DGZ in the
lake induced convective layer will likely support a period of hvy
snow Mon night/Tue morning. Temp/moisture profiles look favorable
for amounts to exceed warning criteria locally in high terrain where
upsloping is maximized. Otherwise, the steady backing of winds will
work as a limiting factor. With blsn not likely to be much of an
issue since winds aren`t strong and since snow-to-water ratios are
likely to be quite high given the well positioned DGZ (lower impact
snowfall), a watch or warning issuance at this time is not
warranted. Advys will likely be needed at a later time. The morning
commute on Tue will be impacted. With loss of deep layer forcing and
eventually deep moisture from w to e Tue/Tue evening, lake enhanced
snow off Lake Superior will diminish and transition to lighter pure
LES from w to e Tue aftn/night. Backing wind from n to w will also
shift the lingering snow showers which will continue to diminish
under the start of waa Tue night.

Strong waa will already be underway by Wed morning, and this will
raise 850mb temps sufficiently to end LES. The strong waa/isentropic
ascent could generate some -sn on Wed over the far eastern fcst
area, but that looks doubtful. Better potenital of -sn will be
farther ne, 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 chill. Temps will then
push above normal Thu thru the weekend. There may be some spotty
light mixed pcpn at times Thu night thru Sat under continued waa
pattern with the potential of a couple of shortwaves to pass across
the area. Any pcpn would be 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
lifting ne from the Southern Plains toward the western Great Lakes.
GEM/GFS ensembles show quite a bit of spread in low track and
intensity as would be expected at this time range, but there is a
decent signal for a deepening sfc low lifting ne from the Southern
Plains, a rare occurrence for this cold season. At this point, it
looks like this system will spread pcpn into Upper MI on Sun, and
pcpn could be a variety of ptypes.
&&

.AVIATION...(For the 06Z TAFS through 06Z Monday night)
Issued at 1235 AM EST MON JAN 15 2018

Conditions at all the TAF sites will alternate between MVFR and IFR
in light snow through Monday morning. LIFR visibilities will be
possible at KCMX Monday afternoon into Monday evening when winds
become easterly bringing lake enhanced snow into the terminal. When
winds turn northeast late Monday evening persistent IFR conditions
in lake enhanced snow will be likely at KIWD into early Tuesday
morning.
&&

.MARINE...(For the 4 PM Lake Superior forecast issuance)
Issued at 259 PM EST SUN JAN 14 2018

As low pressure tracks south of the area across Wisconsin and
Illinois tonight, an inverted surface trough will linger across Lake
Superior and bring winds of 20 to 30 knots. Cannot rule out a few
gale force gusts to 35 knots tonight out ahead of the low pressure
system across the eastern half and then again Monday night night
behind the exiting low across the west half. Periodic heavy
freezing spray is possible behind the exiting system, otherwise only
moderate freezing spray is expected through the first half of the
week. Tuesday through the end of the week, expect winds to remain
between 20 to 30 knots with a chance for gales Wednesday.
&&

.MQT WATCHES/WARNINGS/ADVISORIES...
Upper Michigan...
  Winter Weather Advisory until 1 PM EST this afternoon for MIZ006-
     014-085.

  Winter Weather Advisory until 6 PM CST Monday for MIZ011-012.

  Winter Storm Warning until 7 PM EST this evening for MIZ013.

Lake Superior...
None.
Lake Michigan...
None.
&&

$$

SHORT TERM...Ritzman
LONG TERM...Rolfson
AVIATION...Voss
MARINE...Ritzman



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