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Area forecast discussion 
National Weather Service La Crosse WI
604 PM CST Wednesday Nov 26 2014

issued at 604 PM CST Wednesday Nov 26 2014

Still have some light snow and flurries falling across the area
early this evening...but most of the accumulating snow has already
moved out of the advisory area. Have thus allowed the advisory to
expire as scheduled. For the rest of the area...some spots across
western and central Wisconsin into northeast Iowa could still
receive another half inch or so of accumulations this evening
until the snow band moves out of the area. This looks to be driven
by some weak forcing ahead of a short wave trough moving across
Minnesota along with some weak frontogenesis in the 1000-500 mb
layer. Both of these forcing signals move past the area as the
wave moves east this evening with the 26.18z NAM suggesting the
frontogenesis weakens in addition to moving out.


Short term...(this evening through thursday)
issued at 351 PM CST Wednesday Nov 26 2014

At 3 PM...a surface low was located over northeast Missouri.
An inverted trough extends north northwest of this low through
central Iowa into south central Minnesota. Further northwest an
Arctic cold front extended from the western tip of Lake Superior
southeast to Sioux Falls South Dakota. Temperatures ahead of this
cold front were in the middle and upper 20s. Meanwhile in the wake of
this front...temperatures ranged from 0 to the lower 20s. The
combination of lift associated with the trough and the cold front
produced snow across much of south central and southeast Minnesota
and eastern Iowa. The highest snow total /mainly due to the axis
pivoting across this area for a long duration/ was 11 inches
8 miles west of Faribault. Our highest total is 3.8 inches in
Mantorville Minnesota /Dodge County/.

For tonight...the 26.12z models are in good agreement that the
trough will continue to pull south away from the area and take
with it the inverted trough with it. They also show that the
Arctic cold front will move southeast through the area. This front
will likely extend from Wisconsin Rapids to Oelwein Iowa around
midnight and will be south of the forecast area by 3 am. The
models show that that the 900 to 700 frontogenesis will quickly
weaken across the area this evening. As a result...went with a
rapidly diminishing trend in the snow. Additional totals will be
up to an inch in northeast Iowa and southeast Minnesota...and from
a trace to a half inch in western Wisconsin. With it still
snowing...will just let the Winter Weather Advisory continue
through 6 PM.

With strong cold air advection in the wake of this front...expect
high temperatures for Thanksgiving to occur between midnight and
3 am tonight. Naefs Standard 850 mb temperature anomalies are
running around 2 Standard deviations below normal. As a
result...expect high temperatures to range from near 10 to 25.
This will be the coldest Thanksgiving in southeast Minnesota and
northeast Iowa since 1985...and the coldest in western Wisconsin
since 1958. More on this can be found in the climate section of
this product.

Long term...(thursday night through wednesday)
issued at 351 PM CST Wednesday Nov 26 2014

On Thursday night and Friday...moderate to strong 925 to 700 mb
warm air advection will develop across the area as a short wave
trough moves east across northern Minnesota. It continues to look
like this system will produce between 1.5 and 3 inches along and
north of Interstate 94...and from a trace to 1.5 inches south of
this Interstate. Soundings continue to show that dry air above
850 mb will move northeast into the area from the Central Plains
on Friday. This dry air will shutoff ice Crystal seeding from
aloft. However there appears to be a deep enough cold layer near
the surface that some snow could still develop initially...and
then as this layer warms up this precipitation could potentially
shift over to some light freezing drizzle...but a bit concerned
that by this time there may be enough dry in the low levels to
preclude this from happening.

On Friday night...the NAM develops freezing rain near the
Interstate 90 corridor. Meanwhile the other deterministic models
have the area trended the forecast toward them. Another
issue on Friday night is that the low temperatures look too cold
considering southwest wind of 10 to 15 miles per hour and the models looking
like they have too much snow initialized in them. The NAM in
particular is about 2 to 3 inches too high with its snow depth
already. Due to this...raised them a few degrees and also raised
Saturday maximum temperatures too.


Aviation...(for the 00z tafs through 00z Thursday evening)
issued at 522 PM CST Wednesday Nov 26 2014

The last remaining band of light snow associated with the
secondary short wave trough and weak frontogenesis band in the
1000-500 mb layer will continue to move east and weaken this
evening. Until it is past the area though...expect the IFR
conditions to continue at klse until about 01z or so and then a
couple hour period of MVFR conditions until the snow ends
completely by the middle of the evening. Should still be an hour
or so of MVFR visibilities at krst as well. Not expecting much
change in the ceilings to occur through the overnight hours with
MVFR predominating. Satellite does show a clearing trend moving
into northwest Minnesota as an area of high pressure drops south
out of Canada. The 26.21z rap indicates this clearing moves into
both taf sites by 12z while the 26.18z NAM holds onto the moisture
underneath the inversion and keeps the clouds in place into the
morning at krst and afternoon at klse. For now...have stayed with
the timing of the previous forecast which essentially split the
difference between these two models.


issued at 351 PM CST Wednesday Nov 26 2014

With a high temperature near 10 degrees...Rochester Minnesota will
be within the top 5 for their coldest Thanksgiving high
temperature. They are...

1/ 7f 1930
2/ 12f 1985
3/ 14f 1952
4/ 14f 1886
5/ 17f 1956
17f 1919

It will be only the 10th time that Rochester has been 19 degrees
or colder on Thanksgiving. The last time it occurred was 1985.

In La Crosse Wisconsin...there is still some question on whether
the high for the day will be in the teens or not. At midnight...the
hrrr...NAM...sref...and rap have the high temperature between 20
and 22f. Meanwhile both the GFS and European model (ecmwf)...has a midnight high
of 18f. This would place this Thanksgiving in the 9 to 15 rank.
They are...

7/ 17f 1919
17f 1952
9/ 19f 1958
19f 1956
19f 1952
12/ 20f 1938
20f 1905
20f 1881
15/ 21f 1903
16/ 23f 1877

The coldest is 4 degrees in 1872. Our temperature records for
La Crosse started just over a month before this record was set on
October 15 1872. If we are in the teens for a high temperature it
will only be the 11th time that this has occurred. It will
definitely be the coldest Thanksgiving as far as high temperature
since 1958 /19f/.

Also this could potentially be the 21st consecutive Thanksgiving
without measurable precipitation in La Crosse. This stretch is the
longest. Prior to this stretch...the record was 6 years /1900-1905
1909-14 and 1986-91/.


Arx watches/warnings/advisories...


short term...boyne
long term...boyne

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