Area Forecast Discussion
Issued by NWS Duluth, MN

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351
FXUS63 KDLH 221755
AFDDLH

Area Forecast Discussion
National Weather Service Duluth MN
1155 AM CST Thu Feb 22 2018

.UPDATE...
Issued at 1155 AM CST Thu Feb 22 2018

Updated for the 18z Aviation Discussion below.

&&

.SHORT TERM...(Today through Friday)
Issued at 445 AM CST Thu Feb 22 2018

After yesterdays quiet, the weather gets active once again. Our
upper level pattern shows a deep trough over the western CONUS
with ridging to the east, producing deep southwest flow over the
Upper Midwest that continues through the end of the work week and
into the weekend. Satellite imagery shows a potent, fast moving
shortwave ejecting out of the base of this trough across New
Mexico, beginning to form into a baroclinic leaf. This shortwave
will sweep our direction today, interacting with the mid level
baroclinic zone and intensifying. An surface level inverted trough
with 850mb low will move across the forecast area late this
evening and overnight before moving out Friday morning. The
surface low will move from Missouri this evening northeast to
eastern Lake Superior by Friday morning. This system will bring a
period of moderate to heavy snow to the forecast area, beginning
late this afternoon, and tonight before moving out Friday morning.
The models have been slowing this feature down over the past few
runs, and this trend has continued, and as a result it appears to
move in later, but also lingers a little longer and is able to
produce more precipitation, as shown by the steadily increasing
snowfall forecast. Have increased forecast pops, but delayed them
by a few hours over the previous forecast. The NAM12 is a high end
outlier in having the most QPF produced by a fair amount, but it
is not unreasonable given the total PW values that will be coming
our direction with the shortwave, so have bumped up the consensus
QPF a little to lean that direction some. With all this going on,
it appears we are looking at getting another 6 inch plus snowfall
event along the north shore, mostly falling within a 12 hour
period. Have decided to replace the watch with a Winter Storm
Warning for the zones immediately along the North Shore, with
advisories for all other counties but Koochiching county. Have
kept the original watch counties separated as they may need to be
upgraded to a warning, depending on what information we get on the
day shift.

.LONG TERM...(Friday night through Wednesday)
Issued at 445 AM CST Thu Feb 22 2018

The main area of focus of the extended forecast period will be on
the Saturday evening/Sunday morning time frame due to the potential
for another winter storm to impact the Northland. Otherwise, mostly
dry conditions and slightly above normal temperatures will be the
more dominant weather pattern through the extended period.

Initially, Friday night/Saturday morning will be quiet but chilly as
high pressure will advance over the region. I decreased the morning
low by a degree or so from the consensus blends to better capture
the radiational cooling expected to occur. Then, clouds will
increase gradually in the late morning hours ahead of the next
system to impact the Northland. Synoptically, a large amplitude
longwave trough will be in place over the Intermountain West states,
which will make its way across the central Great Plains states, and
move poleward towards the region. An associated surface low will
undergo lee cyclogenesis in the southern Colorado/northern New
Mexico region and advance eastward over Iowa and central Wisconsin
by Saturday evening/Sunday morning. The large scale lift with this
system looks quite impressive, with both the 22.00z GFS and NAM
indicating 850-300 mb layer omega values in excess of -45 ubar/s, so
quite strong. QPF amounts are also looking quite impressive for this
time of the year, with 6-hour QPF amounts from the GFS and NAM
models between 00z-06z Sunday in excess of one-half inch each over
northwest Wisconsin, and likely more on top of that from 06-12z
Sunday. However, much uncertainty exists with this forecast as the
models disagree somewhat on the path the surface low track takes,
with the GFS coming the closest of all of the guidance. Also, if you
take the 22.00z ECMWF into account, the QPF amounts drop quite a bit
over the GFS and NAM for the same time frame. Moreover, there may be
some wintry mix over northwest Wisconsin given the thermal profile,
so some freezing drizzle/freezing rain may mix in with the snow,
which will decrease snowfall amounts. My thoughts are that
confidence is high in precipitation occurring across a large portion
of the Northland Saturday evening/Sunday morning, but confidence is
much lower for QPF and timing of the onset of precipitation. This
will need to be monitored closely in later forecast updates. Right
now, the swath of the heaviest snowfall amounts is most likely
across northwest Wisconsin and adjacent areas of northeast Minnesota
and along the North Shore, where 6+ inches of snow will be possible.
Snowfall should begin to taper off by Sunday afternoon when the
system moves out to eastern Ontario Canada.

From Monday through the end of the period, the only other chance of
snow, which should be much lighter in nature, will be Tuesday
afternoon and evening, but the guidance doesn`t have much in the way
of QPF, so this looks to be a very small chance. High temperatures
Saturday through Thursday look rather stagnant, with highs ranging
from the upper 20s to near 30 over north-central Minnesota to the
lower to middle 30s over northwest Wisconsin. Lows will fluctuate
between the single digits and teens above zero.

&&

.AVIATION...(For the 18Z TAFS through 18Z Friday afternoon)
Issued at 1155 AM CST Thu Feb 22 2018

High pressure will shift off to the east this afternoon as low
pressure begins to approach from the southwest. VFR conditions
will prevail for the first part of the period, but clouds will be
on the increase for the afternoon and evening hours. CIGS are
expected to drop to MVFR and IFR during the early morning hours as
heavier snowfall moves in. Light snow will begin this evening and
spread across the terminals from south to north. VSBYs will also
drop to MVFR/IFR with the heaviest snow. Snowfall may be heavy
enough at times to drop VSBYs to LIFR at times. The system will
move out Friday morning and conditions will quickly return to
MVFR/VFR after sunrise.

&&

.PRELIMINARY POINT TEMPS/POPS...
DLH  24  18  29   7 /  30 100  60   0
INL  26  13  26   0 /   0  80  70   0
BRD  24  17  28   5 /  70 100  30   0
HYR  30  22  33   8 /  30 100  50   0
ASX  30  21  34  11 /  20 100  70  10

&&

.DLH WATCHES/WARNINGS/ADVISORIES...
WI...Winter Weather Advisory from 9 PM this evening to noon CST
     Friday for WIZ001>004.

     Winter Weather Advisory from 6 PM this evening to noon CST
     Friday for WIZ006>009.

MN...Winter Weather Advisory from 9 PM this evening to noon CST
     Friday for MNZ011-012-018-019-026-037.

     Winter Weather Advisory from 6 PM this evening to noon CST
     Friday for MNZ025-033>036-038.

     Winter Storm Warning from 9 PM this evening to noon CST Friday
     for MNZ020-021.

LS...None.
&&

$$

UPDATE...BJH
SHORT TERM...LE
LONG TERM...JTS
AVIATION...BJH



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