Scientific Forecaster Discussion
fxus63 karx 120542
Area forecast discussion
National Weather Service La Crosse WI
1142 PM CST Mon Dec 11 2017
Short term...(this evening through tuesday)
issued at 245 PM CST Mon Dec 11 2017
11.20z analysis shows the strong short-wave responsible for
today's wintry mix spinning across the MO/IA/IL border region.
Deformation precipitation continues across portions of northeast
Iowa and southern WI, but is expected to move out of the forecast
area by 4-5 PM. For the most part, it has changed over to snow,
but could still see a mix of sleet at times with additional
accumulation generally a half inch or less. Slick roads will
continue to be a concern until plowed/treated.
Winds have shifted to the northwest and will increase into the
evening. With roughly 30 to 40 kts in the mixed boundary layer,
expect frequent gusts between 25 and 40 mph before diminishing
late tonight into Tuesday.
A secondary weaker short-wave currently across the northern shores
of Lake Superior will drop south across central WI this evening
and overnight. The majority of snow is expected to fall across
northern WI into the up of mi, but the wave will drag a cold
front across the forecast area, ushering in much colder air.
Temperatures tonight will fall into the single digits to mid-teens
above zero, and with the stronger winds, wind chills for the
Tuesday morning commute will be in the single digits below zero.
Tuesday will see more sunshine and gradually diminishing wind as
high pressure builds across the region. That said, it will be cold
with highs only in the mid teens to mid 20s above zero.
Long term...(tuesday night through monday)
issued at 245 PM CST Mon Dec 11 2017
Two short-waves move through the upper Midwest on Wednesday. The
first drops south along the MO River Valley with little overall
local impact. The second, however, moves across central/northern
WI later in the day, bringing a chance for snow mainly along and
north of I-94. As with recent clipper systems, a quick 1-2 inches
is possible for these areas. Significant drying on the western
edge of this precipitation could result in a loss of ice and some
light freezing rain/drizzle...something that will need to watched.
On and off light snow chances are possible to end the week, but
poor model agreement on timing, placement, and strength of short-
waves aloft, makes it difficult to favor one time period over
another. Temperatures the latter half of the week will be near or
slightly below seasonal normals with highs in the 20s to low 30s
and lows in the teens to low 20s.
Still on track for a bit of a pattern change Saturday into next
week as the large-scale trough that has plagued the eastern Continental U.S.
The past week or more will finally move into the western
Atlantic, allowing for a more zonal flow across the upper Midwest.
An eastern Pacific wave races through this flow on Saturday,
winding up a surface low somewhere across the central Continental U.S..
problem is the 12z GFS low track is along the I-94 corridor,
whereas the 12z European model (ecmwf) track is much farther south along the I-70
corridor. This results in a warmer/drier GFS solution, but a
colder/snowier European model (ecmwf) solution. Given vastly different model
output, forecast details are lacking, but something to watch
through the week.
Aviation...(for the 06z tafs through 06z Tuesday night)
issued at 1142 PM CST Mon Dec 11 2017
Northwest winds will gradually subside overnight with VFR
conditions expected. Clouds increase by Tuesday afternoon with
conditions lowering to MVFR in stratus Tuesday evening. Plan on
ceilings lowering into the 2000 to 2500 ft range after 00z.