Scientific Forecaster Discussion
fxus63 kmpx 091147
Area forecast discussion
National Weather Service Twin Cities/Chanhassen Minnesota
547 am CST Mon Dec 9 2019
Update...for 12z aviation discussion below
Short term...(today through tuesday)
issued at 350 am CST Mon Dec 9 2019
The two main changes to the short term portion of the forecast
were to extend the Winter Weather Advisory south to the Iowa
border, and to include colder wind chill values for tonight into
Moderate to heavy snow will continue shifting eastward across the
forecast area this morning. We did see some freezing fog/precip
develop ahead of the main band of snow overnight, particularly
over south central Minnesota. Additionally, the corridor of progged
-15 to -20 (ubar/s) Omega looks to extend into Iowa this morning,
so snow amounts could push 2 inches all the way into our southern
forecast area. With the anticipation of a quick 1-2 inches
combined with the freezing fog/drizzle experienced overnight,
thought the advisory expansion was warranted. Elsewhere, forecast
snowfall amounts look to be in good shape, so only tweaks were
By the afternoon, snow should come to an end west of the i35
corridor, but linger to the east near Ladysmith/Eau Claire through
late afternoon. Did therefore extend the advisory end time until
5 PM for that portion of west central WI.
We look to see a period of clearing this evening as Arctic air
blasts into the region, and given the fresh snowpack, sub-zero
lows look to be imminent across the area. Could see locations near
15 below in central Minnesota, and given winds will not have receded much
below 10 mph, wind chills could dip in the -25f to -30f range.
Will need to keep an eye on temp/cloud/wind trends to assess
whether a Wind Chill Advisory will be needed for tonight,
particularly over west central Minnesota.
Can't rule out a few flurries on Tuesday in the cold air advection
regime, but an overall dry day is expected with highs from -5f to
+5f still looking reasonable.
Long term...(tuesday night through sunday)
issued at 350 am CST Mon Dec 9 2019
The latter portion of the forecast continues to look fairly quiet.
The large scale pattern will de-amplify by midweek as the eastern
upper trough lifts out. Zonal flow across the northern Continental U.S. Will
prevail through the end of the week, with some troughing
redeveloping over the central part of the continent by the end of
next weekend (although there is significant disagreement in the
guidance in terms of the position and amplitude of that upper
trough). Arctic high pressure will bring dry weather and cold
temperatures Tuesday night through Wednesday night. Went slightly
cooler than consensus guidance on temperatures during that period
given the fresh snowfall that should be in place. Return flow will
develop by late Wednesday night, and the forecast will unfortunately
need low chance pops for much of the period from Thursday into the
weekend as we see a series of weak shortwave troughs move through
the region. As we get closer in time and guidance comes into better
agreement we'll likely see pops increased some of more restricted
time frames, but for now can't see much reason to stray from the nbm
given the uncertainty. Regardless, nothing points toward any
significant system in the region through the forecast period, so
precipitation amounts would be light with near normal
Aviation...(for the 12z tafs through 12z Tuesday morning)
issued at 548 am CST Mon Dec 9 2019
Snow with IFR conditions and occasional reductions to LIFR will
prevail through this morning at Minnesota sites, spreading east across
west central WI sites through this afternoon. Clouds clear out
for a period this evening, but stratus clouds look to build back
in to the west overnight. Northwest winds generally 15g25kt
decrease below 10 knots this evening.
Kmsp...snowfall rates of 3/4-1.5 inches per hour expected between
13z and 16z, with light snow lingering into mid afternoon. Total
amounts around 3-4 inches. Some minor blowing possible with wind
gusts to 25 knots. Temperatures drop below zero around midnight
tonight, with wind chills dipping to around -20f overnight.
/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.
WI...Winter Weather Advisory until noon CST today for wiz014-023-024-
Winter Weather Advisory until 5 PM CST this afternoon for wiz015-
Minnesota...Winter Weather Advisory until noon CST today for mnz049>053-
Winter Storm Warning until noon CST today for mnz041>045.
Winter Weather Advisory until 9 am CST this morning for mnz047-