Area Forecast Discussion
Issued by NWS Duluth, MN

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FXUS63 KDLH 121741
AFDDLH

Area Forecast Discussion
National Weather Service Duluth MN
1241 PM CDT Thu Apr 12 2018

.UPDATE...
Issued at 1032 AM CDT Thu Apr 12 2018

Latest short term hires models are indicating lower QPF amounts
from 06-12Z tonight. Current NAM12 is also onboard with that
approach. Have lowered those amounts into a more representative
range favoring these latest runs. This led to much lower snow
amounts for this same time. Have made some adjustments based on
these trends.

&&

.SHORT TERM...(Today through Tonight)
Issued at 350 AM CDT Thu Apr 12 2018

Rain and snow, heavy at times, will quickly move through the
Northland this morning. Road surfaces largely deflecting
accumulation probably due to the warm April suns` residual
heating effect and surface temperatures hovering around freezing.
So little impact this morning despite the snow falling steadily.

Precipitation moves to the east later this morning, leading to
dry conditions for the afternoon under mostly cloudy skies.

More chances for precipitation tonight through the weekend
as a powerful early spring storm impacts the Midwest.

.LONG TERM...(Friday night through Wednesday)
Issued at 350 AM CDT Thu Apr 12 2018

The focus continues to be on how the Northland will be affected
by a powerful storm system set to move through the Central US
during the end of the week. Please read on for more details.

A strong area of low pressure is expected to move through the
Central Plains tonight and Friday, and slowly drift and lift to
the south of the Great Lakes Friday night through early Sunday,
before more quickly lifting into eastern Canada late in the
weekend. This storm track puts the Northland on the northern and
colder edge of precipitation with the system, and puts the
Northland at risk of significant snow, sleet, freezing rain, and
rain. Over the past several days, we have seen a trend of shifting
the precipitation south, not only affecting less of our forecast
area, but also suggesting more snow and sleet than rain and
freezing rain. This trend is not surprising for a few reasons.
First of all, the parent upper-level trough/low that will cause
this storm has been over the Pacific Ocean, making it difficult to
get adequate measurements of the storm. Second, this is overall a
tricky time of the year for the models in general. Third, there
will be a strong area of high pressure in Canada to our north,
which will feed drier air into the Northland from the north, and
as we have seen in so many of these scenarios, the models shift
and tighten-up the precipitation south as we get closer in time to
the storm. Therefore, coming from a cautious perspective of how
this storm will affect the Northland and wish to avoid conveying
confidence in the forecast of snowfall and icing.

This storm could bring a couple rounds of precipitation to our
southern forecast area. There is greater confidence in the first
round. A band of snow will likely develop over or near the southern
forecast area late tonight due to moderate large-scale forcing for
ascent from the storm system and an west-east orientated mid-level
frontogenetical band. Temperatures aloft could be warm enough in our
far south to melt the snow as it falls and result in sloppy, wet
snow and freezing rain (provided road/surface temperatures are cold
enough, which is questionable) late tonight and Friday. At this
time, it looks like the areas from northwest Wisconsin into east-
central Minnesota can anticipate up to a few inches of wet snow,
rain, and maybe light icing from from freezing rain.

There will be a push of colder and drier air from the north later
into the day Friday when the storm nears Iowa and slows down as it
becomes a vertically-stacked low. This may bring a break in the
precipitation Friday night, or even completely stave off the
precipitation to our south for the remainder of the storm. While the
GFS, and to some degree the European, have another round of
precipitation lifting into our south late Friday night and Saturday,
the Canadian shifts the precipitation south and keeps it south
through Saturday. Think the Canadian may be headed in the right
track, and we may see the GFS and European trend this way.
However, if the GFS pans out, our south could get up to several
inches of snow Friday and Saturday, with the greatest amounts near
and south and southwest of Pine County. Beyond Saturday, there
could be some lake effect snow downwind of Lake Superior Saturday
night and Sunday when the wind direction becomes more northerly,
but think snowfall will be quite light given how relatively dry
and mild the air will be from the north.

Another concern with this storm system, regardless of our
precipitation, will be winds. Strong northeast flow will develop
Friday into Saturday. The GFS and NAM soundings and analysis of
winds in the mixing layer suggest the Northland could get widespread
15 to 25 mph winds with frequent gusts of 25 to 35 mph. Even
stronger winds are likely over Lake Superior, which will translate
downwind inland. The Lake could have sustained winds of 30 to 40 mph
and gusts approaching 50 mph. The South Shore and Twin Ports area
could see these 50 mph gusts and also get large wave buildup. The
winds could be a hazard for high profile vehicles on the elevated
Blatnik and Bong Bridges. Isolated tree damage and power outages are
possible. Concerned about infrastructure to the south shore. The
last time the western side of Lake Superior saw winds approach this
kind of caliber, when the waters were mostly free of ice, was with
the storm before last Halloween that damaged the shoreline. That
storm had stronger winds than we are currently forecasting, and
there was no ice at the time. However, we may see our wind forecast
increase and become more extreme as we get closer in time.

Held off on any headlines at this time given the lack of confidence
in the snow and wintry precipitation affecting the Northland. The
parent upper-level storm will soon be on the west coast, so the 12Z
model runs should be of higher quality and should give us greater
confidence on how this storm will affect us.

High pressure will move into the Northland early next week, bringing
sunnier and drier weather. While the unseasonably cool weather will
likely continue next week, it at least looks more mild by the middle
of the week with return flow with 850 hpa temperatures above zero
degrees Celsius.

&&

.AVIATION...(For the 18Z TAFS through 18Z Friday afternoon)
Issued at 1241 PM CDT Thu Apr 12 2018

A cold front was dropping south through northern Minnesota at the
start of the forecast. This resulted in VFR at INL. South of the
front, MVFR cigs were common with a stripe of IFR from BRD to DLH
to HYR. Expect the MVFR and IFR cigs to improve near VFR before
00Z. Look for gusty winds to develop at all sites except INL
through the early morning. Not expecting gusty winds at INL.

&&

.PRELIMINARY POINT TEMPS/POPS...
DLH  41  28  33  21 /  50  10  40  30
INL  39  20  35  16 /  20   0   0   0
BRD  43  32  37  24 /  10  30  60  30
HYR  42  31  36  24 /  20  30  70  50
ASX  41  28  34  22 /  70  10  50  40

&&

.DLH WATCHES/WARNINGS/ADVISORIES...
WI...None.
MN...None.
LS...Gale Watch from Friday evening through late Saturday night for
     LSZ121-140>148.

     Small Craft Advisory from 4 AM to 10 PM CDT Friday for LSZ121-
     140>148.

&&

$$

UPDATE...GSF
SHORT TERM...Wolfe
LONG TERM...Grochocinski
AVIATION...GSF



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