Area Forecast Discussion
Issued by NWS Duluth, MN

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FXUS63 KDLH 182206
AFDDLH

Area Forecast Discussion
National Weather Service Duluth MN
406 PM CST Sat Feb 18 2017

.SHORT TERM...(This evening through Sunday)
Issued at 405 PM CST Sat Feb 18 2017

There is minimal change to the overall forecast philosophy or
sensible weather from this morning for the tonight and Sunday time
periods. Winds will decrease this evening as a surface high
pressure ridge slowly moves eastward, and eventually overhead by
after midnight. A large shield of rather dense alto/cirrostratus
clouds will also traverse most of the region through the first
half of the night, so despite the diminishing winds, temps will
likely be somewhat slow to cool. However, with the large amounts
of water vapor that have been injected into the boundary layer by
melting snow the past couple of days, we expected areas of fog to
develop overnight, which could become dense in some areas -
especially over locations where the mean snowpack temp is still
somewhat cooler - namely over interior northeast Minnesota and
many of the favored areas in northwest Wisconsin.

Winds will eventually turn to the east/southeast on Sunday as the
ridge moves to the east, and onshore flow and increasingly long
across-lake trajectories should keep temps in check in areas near
Lake Superior - especially later in the day. However, it will be a
push-pull between increasing clouds and moisture during the
afternoon, and mixing of a very warm low level airmass that will
remain in place across the southern/western CWA. Temp forecasts
for Sunday in those areas may eventually need to be raised from
current forecast values.

With the warm temps persisting for the next several days, we will
be sending an updated Public Information Statement summarizing our
record high temps and record warmest minimum temps for both Duluth
and International Falls for the next several days shortly.

.LONG TERM...(Sunday night through Saturday)
Issued at 405 PM CST Sat Feb 18 2017

Summary: Mild temperatures continue into next week. A storm system
will move through the area Monday and Monday night bringing
widespread rainfall, a chance of thunderstorms, ending as light
snow, to the Northland. Another storm system will move through the
Midwest Thursday, Friday, and early Saturday, and has the potential
for significant snow accumulation.

A mid-level ridge will be centered over the Upper Midwest Sunday
evening with a shortwave trough over the Rockies. The trough/ridge
pattern will advance eastward overnight with lee cyclogenesis taking
place over northern Colorado and southern Wyoming. As the ridge axis
slides east of the region, southerly return flow will bring a surge
of warmer air and Gulf moisture northward into Minnesota and
Wisconsin ahead of the developing system. The trough will amplify as
it moves across the Plains Monday with the surface low strengthening
and lifting northeastward into Manitoba and northwest Ontario by
Monday evening. The low will occlude and gradually drift toward
Hudson Bay overnight and Tuesday, pulling a cool front eastward
across the Northland.

Rain, with embedded thunderstorms, will spread northeastward across
central and northern Minnesota on Monday morning and into northwest
Wisconsin Monday afternoon and evening. Rainfall amounts of one-
third to one-half inch are expected, and a few locales could receive
around an inch of rain. With the mild temperatures and melting snow
pack, the rainfall will lead to rises on area streams and rivers.
There is a potential for minor flooding of low-lying areas and urban
locations where storm drains remain frozen. Hydrologic models only
include the first few hours of the rain event as of this afternoon,
and therefore any forecast rises are due to pure snowmelt.
Additional information will be available tomorrow afternoon
regarding the potential for minor flooding.

Behind the cool front Monday evening and Tuesday morning,
temperatures will cool sufficiently for rain to change to snow. With
the warm temperatures this week, and continued warmth through
Monday, less than one-half inch of accumulation is expected. Even
with the light accumulation, it may be enough to create slippery
spots on roads in north-central and northeast Minnesota for the
Tuesday morning commute.

A fast-moving clipper will graze the Northland Tuesday night and
Wednesday bringing another round of rain and snow to the area.
Accumulations should be low and focused mainly over the northern
half of our forecast area.

Attention then shifts to the Thursday through Saturday period. A
significant trough of low pressure is forecast to move into the
western CONUS Wednesday morning and emerge over the High Plains on
Thursday. Lee cyclogenesis is forecast to take place over central
Colorado Wednesday night and early Thursday morning. Ahead of the
trough, a quasi-zonal pattern is expected, with southwesterly winds
in the low-levels. This setup will pump ample moisture from the Baja
Pacific and the Gulf of Mexico into the Central Plains and Upper
Midwest. While the deterministic models have diverged in handling
this system, the ensemble members continue to bring a potential for
significant snow accumulation to portions of Minnesota and
Wisconsin. The 12Z consensus blends have trended drier over the
Northland than previous runs, but considering the ensemble member
solutions, raise POPs above consensus. This change yields
"categorical" POPs over interior northwest Wisconsin, and "likelies"
from near the Brainerd Lakes through the Twin Ports and points east.
A rain/snow mix is expected for Thursday afternoon into Thursday
evening, changing to all snow overnight. Even with the southerly
shift and differences in the deterministic models, there is still a
potential for significant snow accumulation somewhere in the
Northland late next week. Anyone with travel plans Thursday through
Saturday is encouraged to keep up with the latest forecast during
the week.

&&

.AVIATION...(For the 18Z TAFS through 18Z Sunday afternoon)
Issued at 1241 PM CST Sat Feb 18 2017

VFR conditions will continue this afternoon into tonight as
surface high pressure builds across the Upper Midwest. Meanwhile,
a compact and vertically stacked area of low pressure will move
across far northern Ontario. Sunshine and warming temperatures
this morning have deepened the boundary layer, allowing higher
momentum air aloft to mix to the surface. RAP model guidance and
KDLH VWP continue to indicate a low-level jet stream associated
with the tight pressure gradient aloft and downward transport of
stratospheric air on the southwest side of the Ontario low. The
axis of strongest winds stretched from central Manitoba across
northwest Ontario and across northern Lake Superior. Maintained
the LLWS at HYR for another hour, but expect wind speeds and gusts
to increase as boundary layer continues to deepen over northwest
Wisconsin.

A warm front aloft will move northeastward into Minnesota tonight
with a subsequent increase in mid- and high-cloud cover. The warm
temperatures across the region and melting snow will yield
additional low-level moisture at the terminals overnight.
Continued the visibility reductions overnight as fog develops.
Given how poorly models have been handling the low stratus and fog
potential, confidence in the lower visibilities is not high.
Since this is the third day of very mild temperatures, there may
be enough moisture flux and snowmelt to support fog and low
stratus and so opted to leave visibility forecast largely
unchanged overnight.

&&

.PRELIMINARY POINT TEMPS/POPS...
DLH  30  44  37  49 /   0   0  10  90
INL  27  45  37  49 /   0  10  10  90
BRD  30  52  43  53 /   0  10  20  90
HYR  30  50  40  53 /   0   0   0  90
ASX  31  47  36  56 /   0   0   0  80

&&

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

$$

SHORT TERM...Miller
LONG TERM...Huyck
AVIATION...Huyck



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