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Area forecast discussion
National Weather Service Duluth Minnesota
838 PM CST Sat Nov 16 2019

Update...
issued at 838 PM CST Sat Nov 16 2019

Threat for a period of freezing drizzle leading to a glaze of ice
in northeast Minnesota continues, with up to an inch or so of snow
expected across parts of northeast Minnesota and most of northwest
Wisconsin overnight into Sunday morning.

Light rain/drizzle is finally beginning to fall across north-
central Minnesota, slowly saturating the very dry air in the low
to mid levels of the atmosphere. Inl 00z sounding indicated this
dry layer still extending from the surface through about 700mb,
with the wetbulb profile all below freezing at the time of the
sounding. While the 00z sounding did show a throughly saturated
snow growth zone, the west-southwest flow aloft could cause drier
air to advect in - something most of the short-range guidance is
showing - and thus may lead to a loss of ice aloft and thus a
period of freezing drizzle as temperatures slowly fall. Surface
temps are still very warm, though, with surface wetbulb values
still well above freezing. Made some adjustments to the hourly
temperatures and dewpoints through tonight, warming them both a
bit to match current observations and trends in the hrrr.

The window for freezing drizzle seems to be smaller than
previously forecast because of the warmer temps, but have no plans
to get rid of the advisory since where the advisory is out still
has the greatest risk for freezing drizzle and a glaze of ice.
Currently the Road temperature measured by a mndot weather station
near Ely is 32 degrees, and given the snow cover in northern St
Louis County and the Minnesota arrowhead, most other Road surface temps
are likely to the same or cooler ahead of the precipitation.

Snow/ice amounts were not significantly changed, with just the
area for ice accretion just reduced in area a bit.

&&

Short term...(this evening through sunday)
issued at 400 PM CST Sat Nov 16 2019

A shortwave trough and cold front will move through the Northland
tonight and Sunday morning. A wintry mix of rain, snow, and
freezing drizzle is expected. Roads and sidewalks may become
slippery overnight due to ice accumulation. A Winter Weather
Advisory was issued for the northern 2/3 of St. Louis County and
all of lake and Cook counties from 10 PM tonight until 10 am
Sunday morning.

Warm southerly breezes across the Northland today have boosted
temperatures into the low and middle 40s for much of the
Northland. A few exceptions were noted near Phillips and over
portions of The Arrowhead where temperatures have remained in the
30s. The warm temperatures will continue this evening as clouds
thicken, helping to trap the warmth near the surface. By late
evening or early Sunday morning frontogenetic forcing for ascent,
along the front along with isentropic forcing in a trough of warm
air aloft, will lead to precipitation development over north-
central and central Minnesota. The initial precipitation type will
be rain for some areas, and snow for other locations. The rain
will eventually change to snow overnight as the front pushes
eastward. In the wake of the front, model soundings suggest drier
air advection aloft will erode the cloud tops, resulting in warmer
cloud top temperatures. These warmer temperatures will limit ice
nuclei activation and change precip type to a snow/freezing
drizzle mix or to freezing drizzle. The areas which will see the
greatest potential for ice accumulation are generally along and
north of the Iron Range east into The Arrowhead. We have issued a
Winter Weather Advisory from 10 PM tonight until 10 am Sunday
morning for the northern 2/3 of St. Louis County and all of lake
and Cook counties, where the ice accumulation is expected to be
greatest. This advisory may need to be expanded into portions of
northwest Wisconsin and possibly into north-central Minnesota
should precipitation change over to a mix or to all freezing
drizzle earlier than currently forecast. A glaze of ice is
possible along with snow accumulation from a dusting up to 2
inches. The highest snow totals will be found in The Arrowhead and
portions of northwest Wisconsin east of a line from Ashland to
Hayward to Spooner.

Temperatures trend cooler for Sunday in the wake of the cold
Front. Lake effect snow showers are possible in the snowbelt areas
of northwest Wisconsin and scattered snow showers are also not
out of the question over the remainder of the Northland in
response to cold air advection aloft. Look for highs to reach the
low 30s over much of our Minnesota zones to the middle 30s in
northwest Wisconsin.

Long term...(sunday night through saturday)
issued at 400 PM CST Sat Nov 16 2019

Sunday evening the snow and/or freezing drizzle will be moving
out of the area at the tail end of the strong low pressure system
that moves through the area late tonight and Sunday. Soundings
during the evening hours show that we lose enough moisture aloft
yet still have enough in the lower layers to leave US with a
lingering layer of stratus and freezing drizzle/flurries for a few
more hours over parts of northwest Wisconsin, but the remainder
of the area should dry out enough to cut off the precipitation.
The lingering clouds should keep temperatures from dropping off
too far under the ridge axis as it moves into the area toward
Monday morning, but we are still looking at some lower 20s
overnight. The next shortwave is due to move into the area Monday
afternoon and night, before moving out Tuesday afternoon. This is
a relatively weak shortwave with not very much precipitation
associated with it, and I only expect a dusting to maybe a half
inch out of it at this point.

We have been watching a potential storm system for Wednesday and
Thursday, which still has a lot of model uncertainty associated
with it. This storm has the potential to have some significant
impacts on somewhere in Minnesota and/or Wisconsin in the
Wednesday night/Thursday time frame, but the model agreement at
this time is too poor to determine timing, amounts or even
specifics of location. The Canadian and previous model runs hit
Wednesday harder and kept the Thursday portion of this storm too
far southeast of the area to affect US. However, some of the later
runs are pulling the system farther northwest, which has a
greater impact on our area in the Wednesday night/Thursday time
frame. They also bring a period of mixed precipitation into the
area which complicates things still farther. For now will only be
mentioning this system briefly in the severe weather potential statement.

&&

Aviation...(for the 00z tafs through 00z Sunday evening)
issued at 607 PM CST Sat Nov 16 2019

VFR conditions will quickly deteriorate to IFR conditions late
tonight into Sunday morning. A round of a wintry mix changing to
snow will move across most sites causing some reductions in
visibility, then snow ends in northeast Minnesota by 12z, ending
in northwest Wisconsin late Sunday morning. As snow ends, ceilings
should improve to MVFR, with these low clouds persisting through
much of Sunday. Gusty south winds will switch to the west as the
cold front responsible for the wintry precipitation moves from
west to east across the region, with west-northwest winds around
10 knots expected through the day Sunday in the wake of the front.



&&

Marine...
issued at 400 PM CST Sat Nov 16 2019

Southerly winds of 10 to 20 knots with gusts to 20 to 25 knots is
causing building waves over Western Lake Superior today. The
highest waves remain along the North Shore from Taconite Harbor
northward, where waves of 5 to 8 feet will be possible. Small
craft advisories have been issued from Taconite Harbor to Grand
Portage and from Chequamegon Bay to Saxon Harbor today for the
strong south winds. Waves will not be as high elsewhere in Western
Lake Superior, but winds will still be strong into tomorrow
morning. A cold front will move across Western Lake Superior
Sunday morning and shift winds to the northwest at 5 to 10 knots
with gusts to 15 knots. Winds and waves should diminish Sunday
afternoon and night as high pressure builds from the west.

Winds on Western Lake Superior appear relatively quiet for at
least the first half of the work week. There is a storm system
that may impact the area in the Wednesday-Thursday time range,
which may produce a period of strong northwest winds. This may
lead to a period of dangerous conditions for small craft.

&&

Preliminary point temps/pops...
dlh 33 34 22 33 / 80 30 0 20
inl 29 30 21 33 / 40 20 0 30
brd 32 33 23 36 / 70 10 0 20
hyr 33 35 23 35 / 100 70 0 10
asx 33 36 26 36 / 90 60 10 10

&&

Dlh watches/warnings/advisories...
WI...none.
Minnesota...Winter Weather Advisory until 10 am CST Sunday for mnz011-012-
019>021.

Ls...Small Craft Advisory until 10 am CST Sunday for lsz140-141.

Small Craft Advisory until 2 am CST Sunday for lsz148.

&&

$$

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