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Area forecast discussion
National Weather Service Duluth Minnesota
1257 PM CDT sun Apr 30 2017

issued at 1133 am CDT sun Apr 30 2017

Updated minimum relative humidity forecasts and hourly trends through tonight.
Even with high cirrus over north-central Minnesota, efficient
mixing was observed once again with relative humidity values dipping below 25% by
10 am. Have also made minor adjustments to precipitation type and
amounts through 12z Tuesday. Adjusted the snow/mix temperature
threshold up to 35 degrees from 34 yielding slightly more snow in
central through northeast Minnesota.


Short term...(today through monday)
issued at 412 am CDT sun Apr 30 2017

The focus remains on the potential for snow tonight and Monday
associated with an area of low pressure that will lift into the
upper Midwest. It still appears much of the northeast Minnesota
will get accumulating snow, but there is increasing confidence the
snowfall will remain below 6 inches, enough so to warrant dropping
the Winter Storm Watch in favor of a Winter Weather Advisory.
Please read on for more details.

A potent area of low pressure over the Southern Plains, as of
early this morning, will lift into the Central Plains today and
become well organized and vertically stacked. Meanwhile, an area
of high pressure near James Bay in Canada will maintain dry and
cool easterly flow across the Northland today. Strong northeast
flow will develop over Western Lake Superior, translating into
gusty and cool flow downwind of the lake across portions of
northwest Wisconsin, the twin ports area, and into east-central
Minnesota. Cirrus will continue to spread into the Northland
today because of the upper- level flow from the low, maintaining
scattered to broken cloud cover for much of the day and limiting
our heating potential. There was a general trend in warmer trend
in the latest model runs for today's temperatures compared to the
previous model runs, so increased today's high temperature
forecast a bit, despite leaning with the cooler models. Highs
should range from the upper 30s to low 40s near Lake Superior, to
the middle 40s farther inland from the lake, and to as high as the
upper 40s to low 50s for areas of central into north-central
Minnesota out of the way from the Lake Superior flow.

The low will move into the Central Plains this afternoon and will
lift into the upper Midwest tonight and Monday, reaching southeast
Minnesota and west-central Wisconsin by late Monday morning. This
low will spread abundant moisture into the Northland tonight and
early Monday, with precipitable water values of about 0.75 inches.
Widespread synoptic lift from the approaching low, as well as from
embedded shortwaves in the flow, will bring increasing chances of
rain from the south late this afternoon into tonight with this
surge of moisture. The latest models slowed down the timing of the
precipitation lifting into the Northland. This is not a surprising
trend for well-entrenched dry air across the Northland, so leaned
on the slowest models, including the NAM and regional Canadian,
for the onset of the precipitation because the rain will more
likely be virga until the moisture can modify the dry air.

The moderate rain will move into central and northeast Minnesota
by the wee hours of Monday morning. While temperatures aloft, in
the low and mid-levels, will initially support primarily rain,
there will be a transition to snow overnight into Monday morning
because of dynamic cooling from the falling snow from the
upper/mid-levels, which will cool the low-levels and near the
surface near the surface. While some of that snow may melt at
first, it should not take long for the snow to accumulate given
the decent snowfall rates. Plus, there will likely be a period of
good dendritic growth from good lift and saturation near the -15
degree celsius areas aloft to enhance the snowfall rates. Despite
the favorable environment for snow, there has been some backing
off in the latest model runs in the potential for heavy snow
(greater than 6 inches). The slower trend of the models in
bringing in the precipitation, though, is perhaps one reason the
threat of heavy snow looks less likely than it did yesterday
afternoon, since more of the snow may fall well into the morning
hours, with melting cutting down on total snowfall accumulation.
The previously faster model runs would have brought more of the
snow overnight when temperatures could remain cold and support
snow accumulation. The latest forecast is now for widespread
snowfall of 2 to 5 inches across much of northeast Minnesota, but
would not be surprised if isolated locations approach 6 inches.
Some parts of northwest Wisconsin, from the Superior area into the
Bayfield peninsula, could also get up to a couple inches of snow.
Snow or snow, this low will bring widespread rainfall of 0.50 to
1.25 inches across much of the Northland, with the heaviest rain
in northwest Wisconsin. Many rivers in the Northland will likely
respond with significant rises into the middle of the week as the
rain works its way into the rivers.

The snow should transition back to rain or wintry mixture, with
little additional snow accumulation, by Monday afternoon when the
deeper moisture and synoptic lift moves out of the Northland.
Cool and gusty north to northeast flow and rain and light snow
will continue through the day. Highs will only range from the
middle 30s to low 40s, with the warmest of those temperatures
limited to the fringes of the far southeast and far northwest
forecast area.

Long term...(monday night through saturday)
issued at 412 am CDT sun Apr 30 2017

The vertically stacked system moves from northeast Wisconsin to
Quebec Monday night. Will have highest pops in the evening,
trending downward overnight. Will see a mix of rain and snow in
the evening, becoming all snow in some locations as colder air
allows for a change over. Forecast soundings no longer support any
freezing rain Monday night and have removed. Some light snow
accumulation is possible over The Arrowhead. The aforementioned
system no longer affects the region on Tuesday. However, a
positively tilted short wave trof moves over the area. Will carry
pops over the eastern third of the forecast area Tuesday as the
trof passes and where best forcing is found. Will see a transition
from snow early, to a rain/snow mix by mid morning, then all rain
in the afternoon. Max temps will return to near normal. The
shortwave departs by Tuesday evening. This allows some ridging to
build over the area for Tuesday night late and Wednesday morning.
Precipitation returns Wednesday afternoon through Thursday. There
are differences amongst the models on the handling of a long wave
trof on the region. This includes timing, location, strength and
quantitative precipitation forecast. Used a blended approach for pops and ptypes. The long wave
trof departs Thursday night. A cold front follows behind and with
just enough moisture, may wring out a few showers over north
central Wisconsin in the evening. The cold front falls apart
overnight as upper level and surface ridging build into the
region. This ridging remains over the area through Saturday. Max
temps return to the 50s and 60s during this time.


Aviation...(for the 18z tafs through 18z Monday afternoon)
issued at 1250 PM CDT sun Apr 30 2017

A strong late winter storm will take aim on the Northland over the
duration of the taf period. VFR conditions will gradually give way
to MVFR and eventually IFR from south to north tonight. Kinl
should see VFR conditions continue. Rain will spread into the
region fairly quickly this evening, and then gradually move north
and west as the night wears on. The rain will switch to snow,
fairly quickly as it moves northward. The snow, or a mix of rain
and snow will continue on Monday as well.


Preliminary point temps/pops...
dlh 44 33 36 32 / 10 100 100 60
inl 54 34 41 33 / 0 30 60 50
brd 50 33 39 33 / 20 100 100 50
hyr 46 35 39 33 / 30 100 80 60
asx 43 34 38 33 / 20 100 90 70


Dlh watches/warnings/advisories...
Minnesota...Winter Weather Advisory from midnight tonight to noon CDT Monday
for mnz011-012-018-019-025-026-033>037.

Ls...Small Craft Advisory until 4 am CDT Tuesday for lsz121-140>148.



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