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Area forecast discussion 
National Weather Service La Crosse WI
528 PM CST Tuesday Nov 25 2014

Short term...(this evening through wednesday)
issued at 353 PM CST Tuesday Nov 25 2014

At 3 PM...a surface low was located over western North Dakota.
This system was producing moderate to heavy snow with
visibilities as low as a half mile at Harvey Municipal Airport in
central North Dakota. As this low moves southeast into eastern
South Dakota...moderate to strong warm air advection and weak to
moderate 275 to 285k isentropic lift will develop across southeast
Minnesota and northeast Iowa. This will result in a rapid
saturation of the soundings between 26.06z and 26.09z. This will
result in the development of snow. With soundings showing up to
75 mb in the dendritic growth zone...went with a 13-15 to 1 snow
to liquid ratios. As far as quantitative precipitation forecast trended the forecast more toward
the European model (ecmwf). Believe that both the GFS and Gem have too much
phasing taking place between the short wave passing to our
southwest and south and the approaching Arctic cold
front...therefore...higher quantitative precipitation forecast. Like previous runs of the 25.15z
Storm Prediction Center srefs for Charles City Iowa and Albert Lea Minnesota continue
to show 3 distinct solutions. The first group brings the snow into
the area between 06z and 12z...and then continue to snow through
Wednesday. This set of 7 models produce anywhere from 1.5 to 4
inches of snow for Charles City and 2 to 5 inches for Albert Lea.
The second group develops snow between 12z and 18z Wednesday with
much higher rates and also ends around 00z Thursday. Snow totals
are very similar to the first family. The remaining 5 models have
very little snow with the short wave passing to our southwest and
then brings up to an inch with the Arctic cold front. Trended the
forecast toward the first set of models. At this time...it looks
like 2 to 4 inches of snow will fall across Mower in southeast
Minnesota... and Mitchell...Floyd...and Chickasaw counties in
northeast Iowa from 3 am through 6 PM Wednesday. Elsewhere across
southeast Minnesota and northeast Iowa expect 1 to 2 inches of
snow. Finally in western Wisconsin snow totals will be less than
an inch.

Long term...(wednesday night through tuesday)
issued at 353 PM CST Tuesday Nov 25 2014

On Wednesday night...an Arctic cold front will move quickly
southeast through the forecast area. The best synoptic lift
associated with front will closer to the short wave trough moving
across northeast Minnesota and northern Wisconsin. Soundings north
of Interstate 90 show up to 100 mb of Omega located in the
dendritic growth zone mainly during the evening. As a result went
with snow to liquid ratios closer to a 15 to 1 ratio. This results
in snow totals up to a half inch north of Interstate 90.

On Thanksgiving...expect dry conditions as the Arctic high builds
east across the area. High temperatures will likely occur close
to midnight...and then temperatures will slowly throughout much of
the morning. Temperatures will then rise back into the 10 to 20
degree range for the afternoon. The current forecast high
temperature for La Crosse is 16 degrees. The last time that we had
a Thanksgiving with a high in the teens was 1958 when the high
temperature was 19 degrees. There have only been 11 thanksgivings
since 1872 that have had high temperatures in the teens or colder.
The coldest high temperature for Thanksgiving is 3 in 1872.

On Thursday night and Friday...moderate to strong warm air
advection develops across the area as a short trough moves across
northern Minnesota. Soundings suggests that there will be 200 to
300 mb of Omega located in the dendritic growth zone. This will
increase snow to liquid ratios into the 20-25 to 1. This has the
potential of producing snow totals into the 2 to 4 inch range
across Taylor and Clark counties. Soundings also show some dry air
moving into areas between Interstate 94 and 90. This may result
in some freezing drizzle if the lift has not left the area.

On Saturday afternoon and night...another Arctic cold front will
push south through the area. This will result in high temperatures
of 15 to 30 on Sunday.

&&

Aviation...(for the 00z tafs through 00z Wednesday evening)
issued at 528 PM CST Tuesday Nov 25 2014

The main concern during this period is whether the main snow band
will move over the taf sites or remain off to the west. The short
wave trough over the western Dakotas is expected to continue
moving southeast toward northern Missouri through Wednesday. The
25.18z NAM suggests this will only produce some weak pv advection
in the 500-300 mb layer as it GOES by but should be able to
generate moderate to strong qg convergence in the 1000-500 mb
layer. The 25.18z GFS is very similar with this pattern but where
the models differ is with the amount of frontogenesis on the back
side of the weak surface low and with the isentropic up Glide that
occur. The GFS is stronger with both of these compared to the NAM
and thus generates more snow with the 25.12z European model (ecmwf) looking very
similar to the NAM as does the 25.15z sref. So for now...have
trended toward the weaker solutions which also maintains
continuity with the previous forecasts. Will continue to show
flurries coming into krst around 12z with a MVFR ceiling with more
persistent snow developing in the middle of the morning with the
visibility also going down to MVFR. The best chance for IFR
conditions should come in the afternoon as a secondary short wave
trough moves across adding some additional forcing. The best
forcing from the lead short wave trough may not reach east into
Wisconsin so have continued to show just flurries developing in
the morning at klse before the additional forcing arrives in the
afternoon for a period of MVFR conditions.

&&

Arx watches/warnings/advisories...
WI...none.
Minnesota...Winter Weather Advisory from 3 am to 6 PM CST Wednesday for
mnz094.

Iowa...Winter Weather Advisory from 3 am to 6 PM CST Wednesday for
iaz008-018-019.

&&

$$

Short term...boyne
long term...boyne
aviation...04

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