Area Forecast Discussion
Issued by NWS La Crosse, WI

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FXUS63 KARX 162028

Area Forecast Discussion
National Weather Service La Crosse WI
228 PM CST Mon Jan 16 2017

.SHORT TERM...(This evening through Thursday)
Issued at 228 PM CST Mon Jan 16 2017

Early this afternoon, water vapor satellite showed the closed
upper level low along the Kansas/Nebraska line with the surface
low over northeast Kansas. Local and regional radars showed the
main band of precipitation was ahead of the system from eastern
Nebraska across northern and eastern Iowa into southern Wisconsin
and Illinois. The predominant precipitation type has been freezing
rain or freezing drizzle. However, how long this is able to
continue, especially across the south is in question. Surface
temperatures have risen to freezing or just above across all of
northeast Iowa into southwest Wisconsin and parts of central
Wisconsin. In addition, dew points have also come up and are the
same or within a degree of the air temperatures which will keep
the surface wet bulb temps at or above freezing as well. Road
temperatures have also been creeping up with most, if not all, of
these now above freezing. Even with the approach of night,
temperatures may not have the opportunity to drop much as the
surface low approaches and this should limit the amount of icing
that will occur. Overall, these are mainly fine tuning adjustments
to the general forecast with the big picture not changing a whole

As the whole system comes northeast tonight there is still
expected to be a loss of ice aloft from south to north for all but
the far northwest and north sections of the forecast area. The
warm air aloft will continue to be warm enough for melting except
in the areas that keep the ice aloft. This will keep the primary
precipitation types as freezing rain/drizzle except where there is
the combination of air and surface temperatures above freezing.
The most likely locations for mainly non-freezing liquid
precipitation appears to be across our far southern three
counties, but still concerned there could be some localized areas
of additional icing. However, if the roads temperatures start fall
with the loss of daytime heating, the icing problems could come
back. Confidence is not high enough yet to start dropping counties
out of the winter weather advisory.

To the north where is looks like snow may end up the dominant
precipitation type there are some concerns about the snow ratios
and how much accumulation there will be. Snow ratios have been
raised closer to a 6/7 to 1 which gives accumulations of 1 to 2
inches. Concerned that the ratios may still be too low and amounts
could end be a little higher with some 3 inch amounts possible.

The main period of precipitation is still expected to be late this
afternoon into this evening when the forcing is maximized. As the
upper level system approaches, the main short wave trough will
produce a period of moderate pv advection in the 500-300 mb layer
and moderate qg convergence in the 1000-300 mb layer. This forcing
will be aided by some jet dynamics with the divergence aloft
maximized from a coupled jet structure over the region. The warm
air advection ahead of the system will continue to provide 2 to 3
ubar/s of up glide on the 290K surface with the moisture transport
aimed right into the area. All this forcing should then diminish
through the overnight into Tuesday morning with the precipitation
expected to quickly shift east Tuesday morning.

.LONG TERM...(Thursday night through Monday)
Issued at 228 PM CST Mon Jan 16 2017

Southwest flow aloft will remain in place for much of the period.
This will allow the next system coming up out of northwest Mexico
to approach the area but then weaken by the end of the week as
another system crossing the southern Rockies becomes the dominant
system. This system is then expected to also weaken early over the
weekend as yet another one crossing the southern Rockies again
takes over and then tracks across the mid Mississippi River Valley
into the Appalachians. With all these systems coming close to the
region, there will be an extended chance for some precipitation
from Thursday night right into next Monday. It continues to look
warm through this period as well, with highs in the 40s and
overnight lows in the mid to upper 30s. This should allow most of
this precipitation to fall as rain.


.AVIATION...(For the 18Z TAFS through 18Z Tuesday noon)
Issued at 1140 AM CST Mon Jan 16 2017

MVFR/IFR conditions in low clouds/BR/-RA/FZRA to continue spreading
across the area this afternoon and evening. Temps to continue slowly
warming to near above 32F, especially at valley sites like KLSE.
This will help limit the icing, which is looking to be more common
at higher elevations and ridge tops were temps may end up more in
the 30-32F range thru the evening. Precip to gradually diminish/
move out after midnight and thru Tue morning, but a broad low
IFR/MVFR stratus deck and some BR is looking to remain over the area
thru the morning. Some improvement Tue afternoon as the main sfc-mid
level circulation pulls away and drier sfc-850mb air spreads in from
the NW as ridging starts to build into the area.


WI...Winter Weather Advisory until noon CST Tuesday for WIZ029-

MN...Winter Weather Advisory until noon CST Tuesday for MNZ079-

IA...Winter Weather Advisory until noon CST Tuesday for IAZ008>011-



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