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fxus63 kmpx 090550 

Area forecast discussion
National Weather Service Twin Cities/Chanhassen Minnesota
1150 PM CST sun Dec 8 2019

Updated for 06z aviation discussion...
issued at 1142 PM CST sun Dec 8 2019


Short term...(this evening through Monday night)
issued at 231 PM CST sun Dec 8 2019

Surface analysis this afternoon shows a draped cold front from the
Great Lakes through the northern plains to a conglomerate low
pressure area over southern Montana. Arctic high pressure sits
over southern Canada.

A primary center of low pressure will develop along the front over
eastern Wyoming/western Nebraska this evening then gradually
traverse through Nebraska and Iowa tonight and into southern
Wisconsin and Michigan during the day tomorrow. This low will be
aided by a potent longwave trough axis emanating from a deep 500 mb
low over Hudson Bay. This system will already have a fair amount
of Pacific moisture with it but will also pick up some Gulf of
Mexico moisture as it crosses Iowa into Wisconsin. This additional
moisture plus a more southerly track, allowing more cold air into
the system, will allow it to produce a bit more snow than previous
forecasts. Collaborative forecasts plus model forecasts indicate a
swath of 6-8" of snow in central Minnesota with a wider and further south
swath of 3-6" of snow into southern Minnesota and western WI. While the
timing hasn't changed much it's the amount that has so have opted
to raise a Winter Storm Warning for Douglas thru Kanabec counties
and pushed the Winter Weather Advisory south to a Montevideo-Twin
Cities-Eau Claire line. South of the advisory, snow amounts will
be less than 3" and likely 1" or less from Mankato and points
south. The main question still is how quickly the atmosphere
saturates, translating to how much freezing drizzle will be
realized before the snow begins. There is still some potential for
a slight duration of freezing drizzle at the onset of
precipitation but this shouldn't last much at all, potentially an
hour or Two Tops before mixing and changing to all snow begins.
Unfortunately, greatest intensity of snowfall looks to occur
straight through the Monday morning rush hour so precautions
should be taken by motorists during what may be a hazardous
commute Monday morning. The snow will diminish Monday morning over
western Minnesota, Monday afternoon in eastern Minnesota and western WI. No
additional snowfall is expected from Monday evening Onward.

There is still the strong likelihood of strong winds during the
daytime hours on Monday, northwest 15-25mph with gusts to 40mph,
potentially creating blowing/drifting snow issues over much of the
weather forecast office mpx coverage area. With this snowfall expected to be a more
dry/powdery type of snow, reduced visibility and slippery roads
will be viable concerns.

Temperatures will likely fall during the early morning hours
through Monday and Monday evening, making temperatures at midnight
tonight the expected high temperatures for Monday. Temperatures
will run from the single digits in western Minnesota to the 20s near the
Mississippi River to near 30 in interior WI. By early Tuesday
morning, temperatures will run in the single digits above and
below zero. Wind chill values will run in the negative single
digits to around -20 deg f from late tonight through early Tuesday

Long term...(tuesday through sunday)
issued at 231 PM CST sun Dec 8 2019

At the start of the extended period, a very amplified pattern with
a upper ridge centered over the Canadian rockies, southward over
the western tier of the nation, will break down and become
progressive/zonal by the end of the week. Thus, a cold period will
become modified quickly to more seasonable temperatures. However,
at the same time as the flow becomes more progressive and zonal,
several weak short waves will move across the northern tier of the
nation. Usually, the onset of the more milder air mass returning
to the region, light precipitation can't be ruled out. However,
the location and strength of these short waves will be dependent
on the mean upper level flow and energy associated with it. The
GFS/ec are not in phase as the change over occurs by midweek, so
the placement of the qpf, surface features are different.
Currently, a blended approach of the models have 20-30% chances of
light precipitation starting Thursday, and continuing through the
extended period. But, based on the differences in the models,
there doesn't seem to be any impactful events from Tuesday
evening, through next Sunday. There is also no indications of
another Arctic outbreak based on the progressive/zonal type of
flow developing after monday's system.


Aviation...(for the 06z tafs through 06z Monday night)
issued at 1142 PM CST sun Dec 8 2019

Confidence increasing in a band of snow moving through the region
tonight and this morning. Visibilities are around 1/2 mile under
this band, so have added a tempo of LIFR conditions. Look for
northerly wind to increase as well overnight and into Monday
morning. Eventually wind gusts will decrease and clouds will
scatter out Monday night.


We could see some IFR snow showers around 11z, but it appears that
the main band of heavy snow will move through between 12 and 15z
this morning. Hires models are showing hourly snowfall rates of
1-2 inches per hour within this band, so may need an aww if sites
out west are confirming this guidance. The heaviest snow will end
by mid morning, and should have VFR conditions settle in late this
evening or early Tuesday night.

/Outlook for kmsp/
Tue...VFR and cold. Wind northwest 10 kts.
Wed...VFR and cold. Wind northwest 5-10 kts.
Thu...VFR. Wind south-southeast 5 kts.


Mpx watches/warnings/advisories...
WI...Winter Weather Advisory from 3 am to noon CST Monday for wiz014-

Winter Weather Advisory from 3 am to 3 PM CST Monday for wiz015-

Minnesota...Winter Storm Warning until noon CST Monday for mnz041>045.

Winter Weather Advisory until noon CST Monday for mnz049>051-058-

Winter Weather Advisory until 9 am CST Monday for mnz047-048-

Winter Weather Advisory from 3 am to noon CST Monday for mnz052-

Dense fog advisory until 3 am CST Monday for mnz082-091-092.



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