Scientific Forecaster Discussion
fxus63 kdlh 091747
Area forecast discussion
National Weather Service Duluth Minnesota
1147 am CST Mon Dec 9 2019
Short term...(today through tuesday)
issued at 318 am CST Mon Dec 9 2019
Winter storm continues across the Northland this morning. Snow
will end from west to east today and this evening. Bitterly cold
air arrives tonight and wind chill headlines will likely be
A low pressure system centered over southwest Iowa this morning
will move toward the east-northeast today to northern Upper
Michigan tonight. The system will strengthen through today as the
associated upper-level trough becomes neutrally and eventually
negatively tilted. Early this morning areas of freezing drizzle
were found over portions of Ashland, Iron, Sawyer, and price
counties with snow farther west. Snowfall rates of around an inch
per hour were reported near Brainerd within the last hour. Snow
Crystal habits at National Weather Service Duluth were mainly Needles and shattered
dendrites with a few whole dendrites observed. Rap soundings at
dlh suggest the dendritic growth zone (dgz) is located between 10
and 14 kft above ground level with a large area which favors needle and plate
habits below. Diabatic cooling will deepen the dgz during the next
several hours, which will increase snow ratios and run up the
score on snow totals. Look for a similar progression elsewhere
across the Northland this morning into the afternoon. The forecast
remains on track and I did not make substantive changes at this
time. Winter storm warnings and advisories are still in good
Attention then shifts to tonight and Tuesday. Strong cold air
advection at the surface and aloft should keep the boundary layer
mixed tonight, with elevated wind speeds expected. The combination
of winds 5 to 15 mph and temperatures dipping to 5 to 15 below
zero will produce wind chill values of 15 to 30 below zero. Wind
chill headlines will likely be needed for portions of our
Minnesota zones overnight and into Tuesday morning. Highs on
Tuesday will climb to the low single digits either side of zero,
with the warmer temps over northwest Wisconsin.
Long term...(tuesday night through sunday)
issued at 318 am CST Mon Dec 9 2019
A sharp upper level short wave trof digs across the area Tuesday
night. This is the leading edge of the Arctic air which will
envelope the region. A potent vorticity maxima at the base of the
trof will not have much moisture to work with, as it is primarily
around 5k feet. High pressure will build over the forecast area as
well. The result should be scattered clouds, but lake effect snow
showers along the higher terrain of the South Shore of Lake
Superior. The wind direction is not favorable for accumulations
until late and will have chance pops as a result. The Arctic air
will result in minimum temps below zero. Surface winds will be
relatively light with low wind chill values.
The short wave departs on Wednesday and the high settles over the
region. Warm air advection gets underway and will end the lake
effect by afternoon. Will have some low pops in the morning while
the wind direction still supports the mention.
Model differences Wednesday night with the handling of a short
wave trof. The NAM/GFS are similar with the location in the
eastern Dakotas, and the strength of the trof. The Gem/European model (ecmwf) are
much further south with the trof location, but also how it affects
the region. Blended the models and have small chance pops over
the southern half of the area. The short wave departs quickly on
Thursday and maintain the blend as model differences persist.
The unsettled pattern for Thursday night through Saturday
continues to be featured by the models. All offer different
solutions at the surface with respect to a surface low location,
timing, and quantitative precipitation forecast. Maintained the blend for this period which
equates to chance pops. The surface low slowly departs Saturday
night with ridging building into the area through Sunday.
Aviation...(for the 18z tafs through 18z Tuesday afternoon)
issued at 1147 am CST Mon Dec 9 2019
IFR to MVFR conditions this afternoon should improve to VFR at all
sites for a period of time this evening as skies clear out, then a
return of MVFR to perhaps IFR ceilings as a secondary cold front
moves through late tonight into early Tuesday morning. Moderate to
heavy snowfall will end early this afternoon from west to east,
but winds gusting to 20-25 knots today may cause some blowing snow
to continue to reduce visibility. Weaker northwest winds tonight
as skies partially clear out, around 5 mph. Then late tonight into
Tuesday morning a weak front may bring MVFR to IFR ceilings for a
few hours before skies clear out again. Confidence in how low
ceilings could fall is low, so for this forecast issuance just
stuck to a period of MVFR ceilings at most sites. There may also
be lake effect from Inland Lakes and/or other sources, which given
the predicted wind direction could cause snowfall and visibility
reductions at hib.
issued at 950 am CST Mon Dec 9 2019
Northeast wind 15 to 25 knots this morning quickly turn
northwesterly this afternoon as a cold front moves across Western
Lake Superior. While higher waves will linger along the South
Shore today, eventually winds and waves diminish late tonight.
Northwest to west winds of 10 to 15 knots will linger through
mid-week until an area of high pressure builds in Wednesday
night. Temperatures will fall to near zero by mid-week, but winds
and waves should be low enough that the risk for heavy freezing
spray is low.
Preliminary point temps/pops...
dlh 15 -8 1 -15 / 100 20 0 0
inl 7 -9 -1 -15 / 40 10 0 0
brd 12 -13 0 -16 / 90 0 0 0
hyr 24 -8 4 -15 / 100 20 0 0
asx 24 0 6 -8 / 100 60 10 10
WI...Winter Storm Warning until 5 PM CST this afternoon for
Winter Weather Advisory until 6 PM CST this evening for wiz009.
Winter Storm Warning until 9 PM CST this evening for wiz002>004.
Winter Storm Warning until 6 PM CST this evening for wiz001.
Minnesota...Winter Storm Warning until noon CST today for mnz019-020-026-
Winter Weather Advisory until noon CST today for mnz011-012-021.
Ls...Small Craft Advisory until 4 PM CST this afternoon for lsz121-
Small Craft Advisory until 3 PM CST this afternoon for lsz144-
Small Craft Advisory until 1 PM CST this afternoon for lsz142-
Small Craft Advisory until 10 PM CST this evening for lsz148.