Area Forecast Discussion
Issued by NWS Duluth, MN

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985
FXUS63 KDLH 182355
AFDDLH

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

.SHORT TERM...(This evening through Monday)
Issued at 412 PM CST Sun Feb 18 2018

Very impressive low amplitude wave and associated intense frontal
circulation continues to result in intense snowfall rates across
much of the Minnesota Arrowhead late this afternoon. This is one
of the more impressive FGEN events in recent memory, with snowfall
rates of 2-3 inches per hour common across the north shore areas
of Lake Superior for the past 3-6 hours. One location hear Tofte
has received over a foot of new snow in only the past 6 hours
since it started around 10 AM.

While intense snowfall rates will persist across Lake and Cook
Counties into this evening, the primary wave responsible for all
of the snow will move into Ontario by mid evening, which should
signal a cessation of the really strong snow rates by 7-8 PM -
even over the Arrowhead - as the back edge of the main forcing
area and radar echoes appears to lie from roughly Hibbing to
Brainerd as of 4 PM per KDLH radar. However, we have extended the
warning for Lake/Cook Counties through 9 PM in anticipation of
snow lasting well into the evening. All other winter headlines
will be allowed to expire at 6 PM as scheduled as snow should have
tapered off to flurries by that time in most areas west/south of
the Arrowhead.

Some scattered light snow/flurries and perhaps some mixed precip
may continue during the overnight hours along the primary frontal
boundary across the south/east portions of the CWA as cold air
deepens and weak low level ascent continues in the vicinity of the
front. However, the next organized period of precip should begin
in earnest Monday afternoon as the next disturbance moves
northeastward along the front and spreads another prolonged
period of ascent across the area. We held off on issuing any
advisories or watch at this point simply to simplify the
messaging. We wanted to postpone issuing any new headlines until
after the major ongoing snow event was completed. With that said,
it seems likely that we will need additional headlines of some
kind (likely advisories) for the Monday-Tuesday time frame with
additional accumulating snow and mixed precip over the far
southeast part of the Duluth CWA. Either the evening shift or the
night shift tonight can address that after the current heavy snow
abates later this evening.

.LONG TERM...(Monday night through Sunday)
Issued at 412 PM CST Sun Feb 18 2018

Fairly complex scenario at the beginning of the extended with a
quasi-stationary front draped from the Central Great Lakes,
southwest to the Central Plains Monday evening. While this is going
on, a positively tilted longwave trough extends to the
southwestern United States. The trough will lift northeastward
into the Intermountain West and Central Plains by Tuesday evening.
An embedded shortwave will lift into the Northern Plains and
Upper Midwest through Tuesday. At the surface along the stationary
front a broad area of low pressure will develop somewhere in the
Mid to Upper Mississippi River Valley, while an inverted trough
extends northwest into Wisconsin and Minnesota. Confidence is
still lower than normal for this time range for QPF and snowfall
amounts, as there still is a lot of spread between guidance.
Suspect the difference is largely due to thunderstorm development
across the Lower and Middle Mississippi River Valley. This will
impact the strength, location, and track of the developing low,
which in turn will impact the intensity of the inverted trough.

As of right now there are two camps, the GFS/GEM which have a
weaker low - in turn a weaker inverted trough and tighter
precipitation gradient. The other camp is the ECWMF/NAM which have
a deeper low - which ultimately results in a broader
precipitation field and more precipitation across the region.
Stuck with a compromise between solutions at this point in time
due to the differences, but if things trend toward the ECMWF/NAM
will need to increase precipitation totals. Warmer air aloft will
advect into portions of northwest Wisconsin, which will bring a
period of a wintry mix of freezing rain and snow across southeast
portions of northwest Wisconsin. The combination of accumulating
snow and ice accumulation from Monday evening through Tuesday will
likely result in a Winter Weather Advisory being needed for
portions of the CWA, however due to Winter Weather concerns in the
short term, have held off from issuing a Winter Weather Advisory
for the next system. The latest snowfall accumulations from Monday
through Tuesday generally range from 3 to 6 inches across the
region.

Low pressure will lift northeastward from the Central Great Lakes
Tuesday evening into Ontario by early Wednesday morning. Behind this
system, high pressure will build into the Northern Plains and Upper
Midwest on Wednesday through Thursday. This will bring partly to
mostly sunny skies with warming temperatures as 850 hPa
westerly/southwesterly flow advects in warmer air. Highs on
Wednesday will be in the upper teens and low 20s. Highs on Thursday
will be in the mid to upper 20s. After Thursday confidence in the
forecast is low as guidance splits on the timing, strength and
evolution of a trough digging into the Pacific
Northwest/Intermountain West. Forecast high temperatures for Friday
through the weekend are in the upper 20s and low 30s.

&&

.AVIATION...(For the 00Z TAFS through 00Z Monday evening)
Issued at 555 PM CST Sun Feb 18 2018

A potent snow band still affecting KBRD and KDLH with IFR to LIFR
visibilities and MVFR ceilings will slowly diminish over the area
over the next 2-4 hours, returning conditions at those sites at least
MVFR if not VFR by 06z tonight. The snow band will sag into KHYR,
reducing conditions there to at least MVFR if not IFR from 04z
through 09z, even as the band weakens. A new band is expected to
develop and intensify around 15z Monday, bringing snow and MVFR to
KHYR, KBRD and even KDLH by 18z and continuing through the end of
the TAF period.

&&

.PRELIMINARY POINT TEMPS/POPS...
DLH   7  16   7  18 /  50  60  80  70
INL  -8  11  -3  13 /   0  10  50  60
BRD   6  16   6  17 /  30  60  80  60
HYR  14  18  11  22 /  60  70  70  60
ASX  13  17  12  20 /  90  70  80  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 MNZ011-018-
     019-025-026.

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

     Winter Storm Warning until 9 PM CST this evening for MNZ012-020-
     021.

LS...None.
&&

$$

SHORT TERM...Miller
LONG TERM...WL
AVIATION...LE



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