Area Forecast Discussion
Issued by NWS Duluth, MN

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FXUS63 KDLH 220117
AFDDLH

Area Forecast Discussion
National Weather Service Duluth MN
717 PM CST Thu Feb 21 2019

.UPDATE...
Issued at 717 PM CST Thu Feb 21 2019

Added some fog to portions of northwest Wisconsin as Siren/RZN
visibility has already lowered due to fog. Made some other minor
changes.

&&

.SHORT TERM...(This evening through Friday night)
Issued at 404 PM CST Thu Feb 21 2019

The focus remains on a round of snow expected to move through the
Northland Friday afternoon through Friday night. In general, the
latest 12Z model runs appear to bring in the snow and precipitation
slower than earlier model runs and our previous forecast, but there
also seems to be greater model disagreement than before. What
earlier looked like one wave of snow from a passing shortwave, could
be two or more areas/bands of snow from two or more passing
shortwaves. There is also less agreement on the location of where
these waves will bring the snow. Considering the model disagreement,
leaned on a consensus of the models, which overall keeps the
precipitation chances and snowfall lower and more dispersed than
what we might otherwise forecast getting this close to a round of
snow. We will need to ramp up the precipitation chances and narrow
down and focus the snowfall when hopefully the models come into
better agreement with subsequent model runs.

A weak mid-level ridge is over the Northland this afternoon with
light westerly winds and scattered to broken cumulus. Light
southwest winds will develop tonight in the wake of the passing
ridge. Clouds will likely linger and redevelop, keeping cloudy to
mostly cloudy skies overnight into Friday morning. Overnight lows
should be about 8 to 14 degrees, but it could be up to several
degrees colder under any breaks in the cloud cover.

Friday looks mostly cloudy with highs near seasonal normal in
the upper 20s. One, two, or maybe more shortwaves will lift into the
Northland and surrounding region Friday afternoon through Friday
night from the southwest. These waves will bring weak to moderate
forcing for ascent and resulting snow. An initial wave will likely
bring snow into central and north-central Minnesota beginning in the
afternoon and into the Minnesota Arrowhead by the evening. That snow
would likely continue and expand east overnight before diminishing
around or after sunrise Saturday. However, there could be another
wave farther south that brings additional snow in northwest
Wisconsin, or areas farther south and east in Wisconsin, later in
the night. In general, this looks like a longer duration light snow
system that begins Friday afternoon, continues overnight, but slowly
diminishes through Saturday morning, likely bringing 2 to 3 inches
of snow to areas of central, north-central, and northeast Minnesota
through early Saturday. We may need a Winter Weather Advisory for
areas forecast to get around 3 inches, but given some uncertainty in
the snowfall forecast, the snow primarily falling overnight, and the
snowfall barely meeting Advisory criteria, will hold off on
Advisory for the time being.

.LONG TERM...(Saturday through Thursday)
Issued at 404 PM CST Thu Feb 21 2019

A very active period of weather is expected this weekend into
early next week.

A major winter storm will eject northeastward from the central
Plains into the Great Lakes Saturday and Sunday, bringing another
bout of significant precip and heavy snow to parts of the
Northland. Ongoing weak forcing for ascent ahead of the main wave
on Saturday will likely lead to a persistence of light snow or
light wintry mixed precip from the Friday night system.

Forcing for ascent will continue to increase later
Saturday/Saturday night as the main dynamics and wave lift
northeastward while amplifying. Forced ascent will be about as
strong as it gets for a synoptic scale system with 300+ meter/12
hour height falls, and the atmospheric response will also be
aided by weak stability within a rapidly northward advancing warm
sector with a 50+ knot low level jet in the warm sector.

Model guidance currently taken at face value would suggest a band
of heavy snow starting in Iowa and tracking northeastward across
Wisconsin into the U.P. of Michigan, with a potential for at least
8-12 inches over our eastern-most northwest Wisconsin counties. We
are concerned, however, that with a rapidly deepening system and
at least a bit of phasing potential with the wave dropping
southeastward from Manitoba, that there is the potential for the
track to shift a bit westward in future model runs, similar to the
past couple of storm systems. There are some hints of this today,
with the ECMWF and NAM runs shifting westward a tad and also being
a bit slower - both of which make sense. Given the uncertainty and
that we still have plenty of time, we have opted to hold off on a
winter storm watch issuance until we see at least a couple of
additional model cycles. That said, it seems a near certainty that
we will need a watch, and eventual warning somewhere in the
eastern third to half of our CWA at some point.

In the wake of the storm, considerably colder air will once again
take up residence over the region, with overnight lows dipping
well into the teens and 20s below zero in many locations for the
early to mid part of next week. We have undercut consensus
guidance on overnight lows be a few degrees, but conversely, with
any sunshine, the lower forest albedo effect should be able to
warm daytime temps up rather nicely with 40+ degree diurnal
swings, and we have nudged daytime highs upward from consensus
guidance over interior northeast Minnesota and northwest
Wisconsin Monday-Thursday accordingly.

&&

.AVIATION...(For the 00Z TAFS through 00Z Friday evening)
Issued at 539 PM CST Thu Feb 21 2019

High pressure will be in the neighborhood through much of the
forecast. MVFR cigs are expected however, as low stratus will be
near all terminals. HYR may briefly go to VFR thanks to some
clearing from the south. But, confidence is low and will keep the
MVFR cigs. Some BR/HZ is also possible at HYR, especially if the
sky clears and have MVFR vsbys if the BR/HZ prevails. Again,
confidence is low on the BR. Some improvement in the cigs to VFR
is possible by mid day, before the arrival of some snow late in
the forecast. Have added a VCSH mention for the onset of the light
snow toward the end of the forecast, but timing differences
preclude a predominate mention.


&&

.PRELIMINARY POINT TEMPS/POPS...
DLH  13  28  21  31 /   0  20  70  60
INL  11  26  20  32 /   0  40  70  70
BRD   7  26  22  30 /   0  50  70  60
HYR  10  31  23  35 /   0  10  60  40
ASX  13  31  21  35 /   0  10  60  50

&&

.DLH WATCHES/WARNINGS/ADVISORIES...
WI...None.
MN...None.
LS...None.
&&

$$

UPDATE...GSF
SHORT TERM...GRG
LONG TERM...Miller
AVIATION...GSF


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