Area Forecast Discussion
Issued by NWS Duluth, MN

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FXUS63 KDLH 141453
AFDDLH

Area Forecast Discussion
National Weather Service Duluth MN
953 AM CDT Sat Apr 14 2018

.UPDATE...
Issued at 953 AM CDT Sat Apr 14 2018

Minor updates to the forecast to incorporate some of the early
short-range guidance this morning, but overall messaging remains
the same. The worst of the wind is going on this morning with a
gradual decrease in intensity expected through the evening.
Lakeshore flooding is ongoing in Duluth`s Canal Park and a few
trees have been downed due to the strong winds in northwest
Wisconsin this morning. Snowfall timing and amounts remain on
track. A tough forecast for the Twin Ports and the north shore as
the 00z a strong outlier compared to the rest of the guidance
suite. As 12z data rolls in this morning the high-res convection-
allowing guidance keeps the bulk of the precip further east, but
just a slight just westward plus lake-enhancement from the very
strong northeast winds leads to below average confidence for this
area. Will keep current messaging as-is with around 3 to 6+ inches
expected, but this could end up being higher or lower. Elsewhere
in northwest Wisconsin confidence is VERY high that there will be
significant and high-impact snow and wind on Sunday that could
produce a prolonged period of time where travel is dangerous if
not impossible at times due to heavy snowfall rates and strong
winds. It is conceivable blizzard conditions could develop, and
this will be something we will evaluate this afternoon. For now we
do NOT plan to upgrade to a blizzard warning for any locations in
northwest Wisconsin but conditions could be blizzard-like at
times. (For reference, blizzard criteria is wind gusts 35+ mph and
visibility below a quarter mile for 3+ hours.)

&&

.SHORT TERM...(Today through Sunday)
Issued at 500 AM CDT Sat Apr 14 2018

The main focus for the short-term period continues to be on the
impending early spring storm system that will impact northwest
Wisconsin and adjacent areas of northeast Minnesota today and
Sunday. This system continues to have some uncertainty appended
to it due to a large surface high pressure system lingering over
northern Ontario Canada, with a large area of dry air over our
northern counties. This system is driven by surface low pressure
currently situated over northern Missouri, placing us under the
inverted trough region. Strong large scale lift is associated with
this system, characterized by upper-level diffluence and a potent
mid-level shortwave with a low-level deformation zone as well.
Current regional radar mosaic shows a large area of precipitation
on-going from South Dakota to southern Minnesota and east towards
central Wisconsin. However, this precip is struggling to maintain
itself over our area due to the aforementioned dry air. RAP/NAM
model soundings at HYR both indicate very dry air up to 700 mb, so
very little moisture for this system to work with. The biggest
concern through this afternoon will be persistent strong
northeast winds, especially over Lake Superior and adjoining
areas. Very tight and strong pressure gradient will continue,
along with some blocked flow due to the higher terrain of the
North Shore, will lead to these very strong winds. Sustained
winds of 20 to 30 mph, with gusts of 35 to 45 mph possible over
adjacent areas of Lake Superior, due to the long fetch flow. Kept
the Lakeshore Flood Warning as is. Also issued a Wind Advisory for
areas downstream of the northeast flow, including Two Harbors,
the Twin Ports, Bayfield, and Ashland. The Wind Advisory goes to
7 PM tonight.

Then, attention turns to increasingly high chances of snow over
northwest Wisconsin and much of northeast Minnesota. The 850-700
mb layer deformation zone lifts northward, bringing the strongest
lift of this event over northwest Wisconsin tonight. Increased
moisture advection will overtake the dry air, and lead to a period
of moderate to heavy snow through Sunday afternoon. The northeast
fetch, and cooling 850 mb temperatures, will lead to some lake
enhancement of the synoptic scale stratiform snow. Snowfall rates
of up to one inch per hour will be possible. Gusty northeast winds
will remain over the region overnight and Sunday, so some areas
of blowing and drifting snow will also be possible. In total,
snowfall accumulations will generally range between 8 to 14
inches, with some locally higher amounts in areas downstream of
Lake Superior in northwest Wisconsin. Due to increased confidence
in snowfall amounts, decided to upgrade the Winter Storm Watch to
warnings. Adjacent areas of northeast Minnesota have been placed
in a Winter Weather Advisory, from southern Aitkin to southern St.
Louis to southern Lake counties, where between 4 to 7 inches of
snow will be possible through Sunday. Chances of snow will
eventually diminish late in the day Sunday, with some lingering
lake effect snow possible over the Lake Superior snowbelt region.

.LONG TERM...(Sunday night through Friday)
Issued at 507 AM CDT Sat Apr 14 2018

The main concern in this time range is the snow continuing on Sunday
night and Monday, adding to our snow totals for this event. The
surface low will be moving north through Michigan at this time, and
depending on the model we will have an inverted trough extending up
across the forecast area, generating snow that continues through
Sunday night and early Monday before tapering off.  With the
uncertainties that exist in the near term, do not have a huge amount
of confidence in this part of the forecast, with model differences
in QPF being quite significant. Have gone with a blend in between
models for now, but expect that as convective trends farther south
earlier in the forecast are clarified this will improve.  We are
still looking at another 1-3 inches overnight Sunday night, so
having the winter headlines continue until 12z Monday remains
reasonable.  We may have to extend some areas if lake effects
develop, but am concerned that the shear will be too great for the
somewhat marginal lake-850 T difference we will have. Lake effect
potential continues Monday night into early Tuesday, but we will be
losing moisture and the trajectory is not as long, so the best
potential may shift east of the forecast area.  Have kept pops going
along the south shore, but only in the chance category and with
light snowfall amounts.  Otherwise, Tuesday is a lull in the
forecast, with high temperatures rising into the upper 30s and low
40s.

The upper level pattern continues to produce large cut off lows
during the extended, with strongly amplified features, as is fairly
typical of spring, even if it doesn`t look like it outside.  The
models agree on bringing another strong upper low across the central
CONUS mid week, but vary in strength and track.  These differences
result in a dry and warm forecast for us from one, to a snowy and
windy from the other. Unfortunately, the snowy and windy one
looks more realistic, and have kept the higher pops and
temperatures going for Wednesday into Thursday.

After another lull day on Friday, we are looking at yet another
storm that may affect us next weekend but model differences are
quite large and have poor confidence in it for now.

&&

.AVIATION...(For the 12Z TAFS through 12Z Sunday morning)
Issued at 653 AM CDT Sat Apr 14 2018

A strong early spring storm will move across the region today,
with a surface low moving slowly from northern Missouri east
across Illinois tonight. Initially the main concern is for winds,
with northeast winds in the 25-30kts with gusts in the 35-40 knot
range for KDLH, with lighter northeast winds elsewhere. Winds to
remain strong through at least 00z this evening before diminishing
after 00z. Snow will move in after 21z, affecting mainly KBRD and
KHYR up through 06z with MVFR ceilings and IFR visibilities, then
moving into KDLH after 06z. KHIB and KINL to remain VFR through
the TAF period, though KHIB may get to MVFR after 12z Sunday.


&&

.PRELIMINARY POINT TEMPS/POPS...
DLH  27  21  27  19 /  30  90  90  50
INL  33  18  32  19 /   0  10  20  40
BRD  32  22  31  18 /  30  70  60  30
HYR  30  22  29  21 /  70 100 100  50
ASX  28  23  28  22 /  30 100 100  80

&&

.DLH WATCHES/WARNINGS/ADVISORIES...
WI...Lakeshore Flood Warning until 10 AM CDT Sunday for WIZ001>004.

     Wind Advisory until 7 PM CDT this evening for WIZ001>003.

     Winter Storm Warning from 1 PM this afternoon to 7 PM CDT Sunday
     for WIZ006>009.

     Winter Storm Warning from 7 PM this evening to 7 AM CDT Monday
     for WIZ001>004.

MN...Lakeshore Flood Warning until 10 AM CDT Sunday for MNZ020-037.

     Winter Weather Advisory from 7 PM this evening to 7 PM CDT
     Sunday for MNZ020-036-037.

     Wind Advisory until 7 PM CDT this evening for MNZ020-037.

     Winter Storm Warning from 1 PM this afternoon to 7 PM CDT Sunday
     for MNZ038.

LS...Gale Warning until 10 PM CDT Sunday for LSZ121-140>148.

&&

$$

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



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