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Area forecast discussion 
National Weather Service La Crosse WI
538 PM CST Sat Jan 24 2015

Update...
issued at 538 PM CST Sat Jan 24 2015

Made two adjustments to the forecast for tonight and Sunday.

The first is related to a south/southwestward trend in pop/quantitative precipitation forecast
from 24.15z sref...24.18z NAM and latest rap/hrrr runs. This seems
reasonable as the shortwave trough responsible for the
precipitation over the next 18 hours continues to dig more to the
south on the latest water vapor loop...versus southeast. Have
shifted the probability of precipitation slightly southwestward...especially for 06-18z
Sunday where the northern part of the frontogenetic circulation
helps to drag drier air into the forecast area.

The second adjustment is related to precipitation type.
Temperatures warmed up much more than expected today...and with
warmer air over Nebraska and Iowa being pulled northeastward
tonight into northeast Iowa/far southwest WI...those locations
could see more rain than snow for much of tonight. Mississippi
River valley locations would also be included for a little more
rain. This is depicted nicely in latest rap/hrrr data. Thus...some
of the snowfall amounts have been reduced slightly.

&&

Short term...(this evening through sunday)
issued at 256 PM CST Sat Jan 24 2015

Main forecast focus is on light snow tonight into Sunday morning.

A light rain/snow mix is occurring across portions of central
North Dakota through eastern South Dakota...tracking southeast.
This activity is associated with a shortwave pushing across
these areas which is expected to track southeast into portions of
the upper Mississippi River valley late this evening into the
overnight hours. Forecast models have latched onto a more
southwest solution compared to previous runs taking the bulk of
the accumulating snow across portions of southeast
Minnesota...northeast Iowa and far southwest Wisconsin. The wave
deepens as it moves into Iowa this evening placing an enhanced
band of snow along the northern edge of the deepening surface low.
18z guidance is trickling in and is suggesting a shift even
further to the southwest...with the main accumulating snow
occurring south and west of the Highway 52 corridor across
southeast Minnesota/northeast Iowa. Another feature to keep an eye
on this evening is a weak shortwave/cold front dropping southwest
out of northern Wisconsin. We could see some light snow out of
this feature as it moves in this evening. Given the southward
shift and snow accumulations mainly in the 1 to 3 inch
range...will not be issuing a Winter Weather Advisory at this
time. West central into central Wisconsin should only see light
accumulations...mainly in the trace to 1 inch range.
Also...temperatures are pretty warm late this afternoon so we
could see a period of light rain before the precipitation switches
over to snow. The low exits the region on Sunday with snow ending.
Additional accumulations of 1/2 inch to around 1 inch are possible
south of Interstate 90. Plan on slippery travel at times late
tonight into Sunday morning.

Long term...(sunday night through saturday)
issued at 256 PM CST Sat Jan 24 2015

A weak front moves across the region Sunday night though Monday an
may generate some light snow with a switch over to freezing drizzle
Monday afternoon into Monday evening as ice is lost aloft. A light
glaze of ice is possible if the freezing drizzle develops. Ridging
slides across the area Wednesday leading to a rather pleasant day
for late January...with highs climbing well into the 30s and
possibly even the lower 40s along and west of the Mississippi River.
A trough then sweeps through Wednesday night into Thursday bringing
a chance of snow to the region. Temperatures look to cool slightly
for the end of the week with highs slipping into the lower to upper
20s. Another system looks to move through Friday night into Saturday
brining snow chances back into the area. Temperatures look to cool a
little more behind this system with highs falling into the lower
teens to lower 20s.

&&

Aviation...(for the 00z tafs through 00z Sunday evening)
issued at 538 PM CST Sat Jan 24 2015

Conditions look to stay VFR for much of the evening with just a
broken-overcast deck of altostratus in place. However...as we approach
05-07z...a surface low marching across Iowa will help turn winds
to the northeast...dragging an MVFR stratus deck over northern WI
into the taf sites. Additionally...light precipitation mostly in
the form of snow...though could begin as rain initially at
lse...looks to cross the taf sites shortly thereafter. Once the
precipitation switches over to snow...around 08z...visibilities
should fall to IFR. Plan on the snow to last through about middle
morning at which time it should shift to the south of the taf
sites with the storm system exiting. Looking at around 1 inch of
snow at both sites. The northeast winds are likely to pick up
late tonight too as the pressure gradient increases...with gusts
up to 25 knots possible at rst. Expect these winds to diminish
throughout the day Sunday as high pressure begins to build in.
This incoming high will help to bring much drier air into the taf
sites from Ontario...scattering out the low clouds between 18-19z.

&&

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

$$

Update...aj
short term...wetenkamp
long term...wetenkamp
aviation...aj

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