Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Twin Cities/Chanhassen Minnesota
1134 PM CST sun Nov 29 2015
Short term...(this evening through Tuesday night)
issued at 320 PM CST sun Nov 29 2015
The overall thinking in the first couple days of this forecast has
not changed - a significant snow storm will impact S-central Minnesota
into west-central WI mainly early Monday morning through Tuesday night with mainly
heavy wet snow.
Aside from the 12z GFS which takes a much farther western storm
track...a conglomeration of the remaining operational models bring
the low pressure center from central New Mexico northeastward to nearly atop
Kansas City to southeastern Minnesota into northwestern WI tonight through Tuesday evening. In
conjunction with this surface low...a large 500 mb low aloft...taking up
much of the western Continental U.S....will shift into the Central Plains by Tuesday
morning...then move into the southern Great Lakes by midday Wednesday. This low will
aid in the development of the surface low and also help drag
unseasonably high amounts of Gomex moisture well north into the upper
miss River Valley region in advance of this system. Precipitable waters will
approach 1 inch for this event...and this will translate nicely to
liquid quantitative precipitation forecast amounts of one half to one inch for this snow event.
There will be a small period of blyr saturation needed at the
immediate onset of precipitation...which would spell a p-type of
freezing drizzle and sleet for a brief period before the snow
begins. Because of the impressive amount of Omega lift with this
system...combined with cooler temperatures aloft being brought down with
accelerated precipitation rates...colder is expected to be brought down
with the falling precipitation which will aid in changing over the p-type
to snow shortly after precipitation commences. Precipitation will then remain as
wet heavy snow throughout the event...which will be prolonged due
to the slow movement of the overall system. Snow will likely
overspread the entire weather forecast office mpx County warning forecast area by late Monday afternoon...with snow
continuing Monday night and much of Tuesday.
A small amount of warming was brought in by the model consensus...
which did ever-so-slightly bring down snow ratios to around the
10 to 1 ratio for Monday night...then ratios grow to around 12 to 1
Tuesday and Tuesday night. However...the cooling of the dendritic growth
zone along with surface temperatures dropping below freezing by late day and
the increase in quantitative precipitation forecast will translate to significant snow amounts
for mainly western through southern Minnesota. Snowfall accums in those
areas do look to hit the 7-10 inch range...with some model output
as high as 12-15 inches south of the Minnesota river in southwestern Minnesota.
This does line up with wpc thinking in their snowfall products.
However...the timing is still a bit in question because of the
multiple pieces coming together to form this event. Hence... only
western and southern portions of Minnesota have been upgraded to a warning while
central and eastern portions of Minnesota /including the tc metropolitan/ remain in
a watch. The thinking there is because of the slower onset of
precipitation and that the counties in watch are on the 6 inch
cusp between warning and advisory thresholds...leading to some
uncertainty which will likely be resolved with another model run
tonight. For west-central WI...confidence is high enough that
snowfall amounts look to remain less than 6 inches...plus have
some freezing rain/ice pellets mixed in...such that an advisory can be issued now.
Have also tried to time the band of heaviest precipitation to move
northeastward across the area Monday afternoon through Monday evening...with lesser intensities
starting early Tuesday morning with lingering light snow through much of
Tuesday...with precipitation tapering off Tuesday night. However...the point
needs to be driven home that this snow will be a wet heavy snow
and that travel will be heavily impacted...particularly the Monday
evening and Tuesday morning commutes.
Long term...(wednesday through sunday)
issued at 320 PM CST sun Nov 29 2015
As the storm system departs by middle week...an upper ridge will begin
to build across the upper Midwest...allowing for milder temperatures for
the bulk of the extended period...at least through Saturday. Due to the
fact that the potential of significant snow will fall across most of
mpx County Warning Area...even with mild flow from the SW/west by the latter part
of the week...the anticipated snow cover/depth will keep temperatures
from rising significantly. 30s look good for the reminder of the
period on highs...with lows generally in the 20s...to around 30.
Also...depending upon the amount of melting...there could be more
cloud cover then expected...along with fog.
A split flow regime is also evident on both the GFS/ec next weekend
which means that a developing cutoff low /which is similar to
Monday/Tuesday system/ may begin to impact the upper Midwest the week of
December 7th. Otherwise...dry weather is expected.
Aviation...(for the 06z tafs through 06z Monday night)
issued at 1134 PM CST sun Nov 29 2015
One corridor of precipitation moving north-northeast out of central Iowa will affect
eastern metropolitan and into Wisconsin next 6-8 hours. Might be a bit of
freezing rain or sleet but upper air profiles suggest mostly snow.
Could be some IFR visibilities in this area for a couple hours
with a quick inch or two of snow.
Otherwise...best forcing for storm system is holding off a
little...and looks like krwf will not be affected by LIFR snow
until midday. That will spread north and northeast. Probably will
not reach east central Minnesota until late Monday afternoon. Rain/snow
line still looks to be just east of the Twin Cities metropolitan...and so
wisc will be most prone to mixed precipitation.
Kmsp...looks like rain/snow line will set up just east of kmsp.
Corridor of showery precipitation from Iowa will graze kmsp this morning and
there could be a bit of sleet...but should mostly be snow. After
that... should be persistent light snow through early afternoon...
then the heavier snow will develop late afternoon and persist well
into the evening. Confidence about average.
/Outlook for kmsp/
Tuesday...MVFR/IFR in -sn. Poss VFR late. Winds NE becoming northwest 5-10 kts.
Wednesday...VFR. Winds northwest around 10 kts.
Thursday...VFR. Winds SW 5-10 kts.
WI...Winter Weather Advisory from 6 am Monday to midnight CST Tuesday
night for wiz014>016-023>028.
Minnesota...Winter Storm Warning from 6 am Monday to midnight CST Tuesday
night for mnz047-048-054>058-064>067-073>077-082>085-
Winter Storm Watch from 6 am CST Monday through Tuesday evening
Winter Weather Advisory from 6 am Monday to midnight CST Tuesday
night for mnz078.