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Area forecast discussion
National Weather Service La Crosse WI
529 am CST Wed Nov 13 2019

Short term...(today and tonight)
issued at 222 am CST Wed Nov 13 2019

Water vapor satellite shows two short wave troughs approaching the
upper Midwest. The first was over the western Dakotas with the
second over southern Montana/western Wyoming. The first wave will
move directly over the area this afternoon into the evening while
the second wave looks to continue on a more southern track going
across Kansas, Missouri and Illinois overnight. The first wave
already has a positive tilt to it and maintains this orientation,
thus limiting the forcing with only weak pv advection expected in
the 500-300 mb layer. The second wave also looks to take on a
positive tilt and again should only be able to produce some weak pv
advection. Two bands of mid-level frontogenesis are expected to
develop in response to these short wave troughs. The first and
weaker of the two bands, looks to set up from eastern/central
Minnesota into eastern Wisconsin this morning and gradually pivot to
the southeast through the day and weaken as the second band forms
over southern Iowa into Missouri. The northern band will also get
some additional lift from 1 to 2 ubar/S of up Glide on the 280k
isentropic surface. This forcing should focus the light snow today
into this evening into one band generally along and north of
Interstate 94 with the second band over northeast Iowa/southwest
Wisconsin and points south during the afternoon and evening. In
between, there may not be much more than some flurries or occasional
very light snow. Accumulations in the two bands are expected to
generally be in the 1 to 2 inch range with at most a half inch
expected in between the bands.

Long term...(thursday through tuesday)
issued at 222 am CST Wed Nov 13 2019

Behind the departing system, zonal flow aloft and surface high
pressure will build in on Thursday and lead to a few days of dry
weather. In addition, high temperatures will gradually increase
into early next week, with widespread highs in the 30s Friday
through Sunday, and many spots getting to the lower 40s by Monday.

The first precipitation chances in the long term period will be
Saturday evening into Sunday. Guidance remains in good agreement
of a trough amplifying over the central Continental U.S. With some weak
shortwave energy moving through the forecast area along with a
weak surface front. Overall forcing looks rather weak, with not
much of a frontogenesis signal and the surface front washing out a
bit as it advances eastward. In addition, model soundings from
the last several runs of the GFS show the column dancing in and
out of saturation, which is reflected in the spotty quantitative precipitation forecast fields.
Something of note is that the 12.18z and 13.00z runs of the GFS
have trended toward a drizzle signal in the soundings lasting into
the evening hours with loss of in-cloud ice, saturation up to 750
mb or so and decent lift through the layer. At this point, it
looks like surface temperatures should be above freezing, but it's
close enough that it bears watching as we get closer to Sunday.
Overall, looking like a light precip event, with a rain/snow mix
and possibly a transition to drizzle as it comes to an end.

Troughing will remain in place over the forecast area into
Tuesday, with another bit of shortwave energy sliding through and
a surface low in Canada dragging another weak cold front through
the area Monday night into Tuesday. Once again, the combination
looks to be just enough to get some spotty precip.

&&

Aviation...(for the 12z tafs through 12z Thursday morning)
issued at 529 am CST Wed Nov 13 2019

VFR conditions this morning at both airports is expected to go
down to MVFR during the afternoon with a little bit of light snow
as well. A band of snow will develop this morning to the north of
both airports. This band will begin to rotate to the
east/southeast through the afternoon with the tail end expected to
come across both airports. This is expected to bring in the MVFR
ceilings along with some light snow/flurries. For now, will not
include any visibility reductions, but these could during the late
afternoon depending on the strength of the snow band. The
snow/flurries will end early in the evening but look for the MVFR
ceilings to remain for most of the night.

&&

Arx watches/warnings/advisories...
WI...none.
Minnesota...none.
Iowa...none.
&&

$$

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