Area Forecast Discussion
Issued by NWS Duluth, MN

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FXUS63 KDLH 181811
AFDDLH

Area Forecast Discussion
National Weather Service Duluth MN
1211 PM CST Sun Feb 18 2018

.UPDATE...
Issued at 1211 PM CST Sun Feb 18 2018

Please see the 18Z Aviation discussion below.

UPDATE Issued at 1118 AM CST Sun Feb 18 2018

Very impressive low amplitude/progressive S/W trof is currently
traversing the northern Plains/western Great Lakes region, with
very strong forced ascent. In addition, a very deep/strong frontal
circulation has set up along/north of the highway 2 corridor. The
heavy snow band associated with this frontal circulation has one
of the more impressive radar presentations in recent memory, with
some reflectivities approaching 35 dBz, and a very strong
reflectivity gradient on the southern side of the band. As this
gradient moved over the WFO in the past 30 mins, we went from 1-2
inch per hour snow rates and visibility of a few hundred feet to
just flurries.

Underneath the primary FGEN band of snow from the Brainerd Lakes
region/Walker, to the Iron Range Cities, to the Arrowhead, 1-2
inch per hour snow will continue into mid/late afternoon. We may
need to up snowfall amounts by a few inches in a few areas, and we
may also need to expand the advisory and/or warning a tad farther
south in the Brainerd/Aitkin areas. A deeper quasi-isothermal layer
of temps in the -12C to -18C range over northern MN will also aid
in enhancing snowfall rates in this area.

Meanwhile, along the southern edge of this band, the frontal
circulation appears to be sufficiently intense to cause a small
area of enhanced subsidence just before parcels are rapidly
accelerated upward and to the north in the ascending branch of the
frontal circulation. This is not uncommon in very intense
frontogenesis events, and is likely the cause of the intense
reflectivity gradient on the southern side of the main band
(flurries in Duluth and 2 inch per hour snow at Island Lake
currently for instance) At any rate, snow should eventually fill
back in across the Duluth-Cloquet-I35 corridor, but the 2-3 hour
period of flurries from now until that occurs will cut down on
amounts significantly in areas where the heavy rates have
currently abated. Thus, areas from Moose Lake/Cloquet to Duluth,
may end up on the lower end of the forecasted 2 to 5 inch range.

&&

.SHORT TERM...(Today through Monday)
Issued at 315 AM CST Sun Feb 18 2018

An active pattern will develop across the Northland today, and
persist through tonight and Monday. A potent mid-level shortwave
trough, with strong large-scale lift will move across the region.
A band of 850-700 mb frontogenetical forcing is progged to make
its way through mainly the northern portions of the Northland
later this morning and afternoon, which will bring accumulating
snow. The latest suite of guidance has shown the axis of the
heaviest snow shifting slightly to the north, with the models
coming into better agreement. The SREF and HREF ensembles both
indicate the heaviest precipitation falling from northern Cass
county east-northeast towards the Arrowhead/North Shore region. An
associated surface low pressure center will advance eastward,
which will turn winds more easterly over Lake Superior, so we`re
expecting some lake enhancement/orographic lift along the North
Shore. The latest WPC snowfall accumulation amounts indicate a
swath of 4 to 8" across the aforementioned areas, which matches up
well with our snowfall forecast. Some adjustments were made to
the Winter Storm Warning and Winter Weather Advisory, including
expanding the Winter Storm Warning to include northern St. Louis
and all of Itasca counties, and the advisory is now in effect for
Douglas and Bayfield counties. There was some thought as to
including northern Cass county in the Winter Storm Warning, but
decided against it as only a small portion of the zone was
reaching warning criteria. Confidence is much higher for Itasca to
reach warning criteria. The main hazards with this FGEN band will
include reduced visibilities and slick road conditions. Winds may
gust to 25 to 35 mph over northwest Wisconsin where a strong low-
level jet will develop for a time, so some blowing snow will be
possible as well. A tight baroclinic zone will accompany this
system, which should bring some warmer air to portions of
northwest Wisconsin, and the potential for a wintry mix for a time
this afternoon and early evening. Highs today will range from the
upper teens along the International Border to the lower to middle
30s over northwest Wisconsin.

Snow will end from west to east this afternoon and evening as the
lift weakens, although some lingering low-level FGEN will keep
chances of light snow over northwest Wisconsin. The latest
HRRR/RAP guidance both shows some higher reflectivities
developing downwind from Lake Superior as winds turn more
northeasterly, so some lake enhancement will be possible. The
baroclinic zone mentioned earlier will linger over northwest
Wisconsin, lending to the validity of the model output from the
HRRR/RAP guidance, so chances of snow could linger over northwest
Wisconsin through the overnight hours. There is the possibility
of some light ice accretion through Monday afternoon mainly over
Price county as well. There was some thought of issuing more
winter weather headlines for Monday, especially for northwest
Wisconsin, but considering the current headlines already in
effect, decided to wait on issuing additional headlines for this
time period. Another 1 to 4 inches of snow could fall over
northwest Wisconsin Monday morning and afternoon.

.LONG TERM...(Monday night through Saturday)
Issued at 315 AM CST Sun Feb 18 2018

Southwest upper level flow will continue to impact the Northland
through the early to middle part of the upcoming work week. Another
wave of precipitation should spread northeast across the area on
Monday night and continue into Tuesday, before diminishing Tuesday
night. While the various model solutions indicate lower confidence
in some of the details, they are consistent in bringing widespread
snow across the area during that time. Some wintry mix will be
possible across the far eastern portions of northwest Wisconsin.
Another area we will need to watch carefully is the area around Lake
Superior, as northeast winds bring the potential for lake enhanced
snowfall amounts. At this point, it appears the potential exists for
several inches of new snow from Monday night into Tuesday, and we
may again need to issue winter weather advisories for much of the
area after a bit of a break on Monday evening. High pressure will
build into the Northland Tuesday night and Wednesday, with dry
weather expected to continue through Thursday. Long term models
start to show extreme differences toward the end of the week and
into the weekend, with GFS bringing the potential for several inches
of snow, and ECMWF indicating only limited precipitation. Highs will
be in the teens on Tuesday and Wednesday, with highs in the 20s on
Thursday. By Friday, Saturday and Sunday, highs will range from the
upper 20s to middle 30s.

&&

.AVIATION...(For the 18Z TAFS through 18Z Monday afternoon)
Issued at 1211 PM CST Sun Feb 18 2018

Low pressure will lift eastward from northeast South Dakota into
Minnesota, and eventually into western Wisconsin tonight. This
will bring anywhere from LIFR to VFR conditions over the next six
hours, with conditions gradually improving. The lowest ceilings
and visibilities will be confined to HIB and INL terminals due to
a heavy snow band moving through. Expect this band to lift
northeastward, which will gradually lighten snowfall, improve
visibilities and lift ceilings. Leaned on a combination of the
GFS and RAP guidance as they are handling the current situation
the best. After snow ends this evening HIB and INL will see VFR
conditions through the end of the TAF period.

Below average confidence in the forecast late tonight through
Monday morning for DLH/HYR and BRD. The latest GFS/ECMWF and GEM
spread snow back in, bringing MVFR/IFR conditions. However, higher
resolution guidance (NAM/ARW/NMM/RAP and HRRR) keep a relatively
dry forecast. Opted to keep snow in the forecast as a stationary
front will be close by with some forcing aloft. Kept VFR/MVFR
ceilings for now, but may need to lower in future updates.

&&

.PRELIMINARY POINT TEMPS/POPS...
DLH  23   7  16   5 /  90  50  50  80
INL  15  -8  11  -5 / 100   0   0  50
BRD  29   6  16   5 /  70  40  50  80
HYR  35  12  18  10 /  60  60  70  60
ASX  30  13  17  10 /  90  90  70  70

&&

.DLH WATCHES/WARNINGS/ADVISORIES...
WI...Winter Weather Advisory until 6 PM CST this evening for WIZ001-
     002.

MN...Winter Storm Warning until 6 PM CST this evening for MNZ011-012-
     018>021-025-026.

     Winter Weather Advisory until 6 PM CST this evening for MNZ010-
     033>035-037.

LS...None.
&&

$$

UPDATE...WL
AVIATION...WL



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