Scientific Forecaster Discussion
fxus63 kmpx 130513
Area forecast discussion
National Weather Service Twin Cities/Chanhassen Minnesota
1113 PM CST Thu Dec 12 2019
issued at 1053 PM CST Thu Dec 12 2019
Updated to include 06z aviation discussion below.
Short term...(this evening through Friday night)
issued at 225 PM CST Thu Dec 12 2019
The storm system that produced locally one to two inches of snow
across central, east central Minnesota, as well as west central
Wisconsin, was rapidly moving east across the Great Lakes. There
was even localized 3 to 5 inch amounts in west central Wisconsin
today as the storm intensified during the morning. Although there
will be some clearing overnight, clouds will once again be on the
increase as the next short wave moves southeast across the
There are a few differences from friday's system, vs today's in
terms of snowfall amounts, timing and more wind.
One of the differences is snowfall amounts will be lighter, and
generally an inch or less. Timing will be more during the
midday/afternoon hours, vs. Morning/early afternoon, and wind
speeds will be slightly stronger following the snowfall.
Tomorrows system was already beginning to move out of the northern
rockies this afternoon. It seems to be more disorganized vs.
Todays system as the main circulation is not quite evident in
water vapor imagery. Light snow was already developing along the
Front Range of The Rockies as the system begins to move out into
There is consistency in the models for the onset of light snow
across far western Minnesota during the pre dawn hours. There is
also a small window where both strong lift associated with this
short wave, and the dendritic growth zone are collocated. The
window is roughly 3-6 hours long, and quickly moves across
Minnesota, and into western Wisconsin by the afternoon. The main
concern is when saturation occurs in the atmospheric column, which
coincides with the dendritic growth zone. There is no doubt that
light snow/flurries will occur for a brief period from west to
east across Minnesota, and into western Wisconsin, the question is
how much snowfall will occur. Quantitative precipitation forecast amounts don't look overly
impressive, especially during the morning. However, by the
afternoon, models start to enhance this stronger dendritic growth
zone feature while the atmospheric column saturates. Therefore,
the best chance of one to locally two inches of snow will occur
along the Minnesota/Wisconsin border, and eastward into parts of
east central Minnesota during the afternoon. Before this
enhancement, a light dusting of snow is more likely over
western/southwestern Minnesota. There is also some evidences that
once we lose the ice seeding clouds, weak lift may cause freezing
drizzle to form, especially in west central Wisconsin where the
best lift remains Friday evening. The best forecast is to add
patchy freezing drizzle, but impacts should be minor.
Long term...(saturday through thursday)
issued at 215 PM CST Thu Dec 12 2019
No significant changes to the long range forecast through next
week. The weather pattern looks dry and cooler than normal. The
coldest air will move in Saturday, with steady or falling
temperatures expected. Wind chill values Saturday night will be 15
to 25 below zero, so getting close to Wind Chill Advisory
criteria across the northwest up near Alexandria Minnesota. Sunday will
remain cold, with afternoon highs remaining in the single digits.
Looking ahead, temperatures will moderate slightly toward the end
of the week, but remain below the seasonal average for mid-
December with highs only in the teens. There is a storm system
that will move across the Ohio River valley, but as of now no
major systems are expected to impact the upper Midwest this coming
Aviation...(for the 06z tafs through 06z Friday night)
issued at 1053 PM CST Thu Dec 12 2019
VFR conditions at initialization for all sites though there are
some isolated pockets of MVFR across central-southern Minnesota and
western WI. Ceilings at all sites will drop to MVFR levels in
advance of the clipper-type system expected to push across the
region Friday and Friday night. As -sn begins, conditions will
likely drop to IFR for a 3-6 hour period depending on the site.
Conditions, mainly ceilings, will likely remain within IFR range
(or very close to it) through Friday evening into early Saturday
morning as the system exits to the Great Lakes.
Kmsp...VFR to start but this is not expected to last more than a
few hours before more sustained MVFR ceilings arrive overnight.
The -sn, likely to start after the Friday morning push, is
expected to be light, with only around an inch accumulation
throughout this event. Not looking for any heavier bursts but some
IFR visibilities cannot be ruled out.
/Outlook for kmsp/
Sat...MVFR/VFR cigs with -sn possible. Wind northwest 10-15 kts.
Sun...VFR. Wind northwest 5 kts.
Mon...VFR. Wind west-northwest 5 kts.