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Area forecast discussion 
National Weather Service La Crosse WI
520 PM CST Monday Mar 2 2015

Short term...(this evening through Tuesday evening)
issued at 321 PM CST Monday Mar 2 2015

At 3 PM...a 1032 mb high was centered over Indiana. The winds have
become southerly across the area...and they will increase into the
10 to 20 miles per hour range tonight as the surface pressure gradient
steadily increases across the region.

Regional radars are already showing radar echoes from Austin
Minnesota northwest to Aberdeen South Dakota. This is associated
with 500 to 600 mb frontogenesis. However the air mass below
650 mb is very precipitation is reaching the
ground at this time. 02.12z models are in general agreement that
this band will move north into central Minnesota and northern
Wisconsin tonight and gradually deepen into the the 800 to 500 mb
range. In addition...southerly winds will gradually moisten. As
this occurs...expect light snow to develop north of Interstate 94
toward midnight and then this band will pivot and become
orientated along the approaching Arctic cold front.

As this occurs a short wave trough ejecting out of the southwest
United States ahead of the main long wave trough over the northern
and Central Plains...will approach the area from southern and
western Iowa. The combination of strong 925 mb and 850 mb moisture
transport and warm air advection and strong 280 k isentropic lift
will result in the rapid development of a snow band across Iowa
between 03.06z and 03.09z. This snow band then will move into
areas along and south of Interstate 90 between 03.08z and 03.10z
and the remainder of the area between 03.10z and 03.13z. Mesoscale
models suggest that this band will move quickly northeast across
the area on Tuesday morning. As a result...the snow may be only
limited to a 6 hour period. Current forecast grids are a bit more
broad brushed than may have to tweak the timing of snow
a bit more. The snow will then quickly end across the area as the
Arctic front moves east across the area during the afternoon. With
950 to 900 mb lapse rates between 8 and 10 c/km...we may see a
brief period of snow showers for an hour or two after the front
passes. Liquid to snow ratios will range from 10-15 to 1. The
highest ratios will be north of Interstate 94. Total snow amounts
of 1 to 2 inches look likely along and south of Interstate
90...and 2 to 4 inches north of this Interstate. The highest
totals look to be north of Interstate 94.

In addition to the snow...the models continue to show that a dry
slot will move into the areas along and south of Interstate 94. If
any precipitation is left during this time frame...there may be a
brief period of freezing drizzle. In addition...the NAM shows that
a 2c warm layer between 800 and 700 mb will nose into Fayette and
Clayton counties in northeast Iowa...and Grant County in southwest
Wisconsin. This may result in a brief period of freezing rain and
sleet ahead of a dry slot.

In the wake of the Arctic cold front...the combination of very
steep 950 to 900 mb lapse rates...strong subsidence...and strong
cold air advection will produce strong wind gusts especially
across northeast Iowa and southeast Minnesota from 03.21z and
04.03z. Both the NAM and GFS suggest that the winds will gust up
to 40 miles per hour. Meanwhile the European model (ecmwf) is producing wind gusts up to 45
miles per hour across northeast Iowa. There is currently one inch of
blowable snow across this area with another 1 to 3 inches of
additional there is a concern that we may have a brief
ground blizzard during this time frame. This is especially the
case...if the European model (ecmwf) wind gusts verify. However with some questions
on whether the heavier snow may limit the existing snow from
blowing and whether a dry slot and mixed precipitation may limit
additional was the consensus to just stay with the
Winter Weather Advisory for now. This would allow US more time to
evaluate the amount of new snow that may fall and whether the wind
gusts will actually be that high.

Long term...(tuesday overnight through monday)
issued at 321 PM CST Monday Mar 2 2015

In the wake of the Arctic cold front...a very cold air mass will
move into the region. 850 mb temperatures range from -22 to -26c.
This will result in high temperatures of 5 to 15f on Wednesday and
Thursday and low temperatures of 5 to -10 on Wednesday morning and
-5 to -15 on Thursday morning. Wind chills on Wednesday morning
will range -15 to -25 north of a Charles City Iowa to Neillsville
Wisconsin line and from -15 to -30 across the entire are on
Thursday morning. Due to these low wind chills...a Wind Chill
Advisory may have to be considered for both of these time periods.


Aviation...(for the 00z tafs through 00z Tuesday evening)
issued at 520 PM CST Monday Mar 2 2015

VFR conditions will erode later tonight as widespread lift occurs
ahead of southwest short wave. Not only will ceilings lower
overnight...but precipitation will break out as warm air advection

Some guidance suggest snow could be a fairly narrow warm frontal
band that advects through early Tuesday morning while others paint a
more broad picture. None the less...expect a period of IFR
conditions during worst snowfall Tuesday morning in 10z to 16z time

Then as snow begins to shift east...northwest winds will be on the
increase behind wave...especially across Minnesota. Some question on
how much snow will blow around but introduced at least idea of
blowing snow at krst with IFR to MVFR conditions. Area wide ceilings
will likely be slow to improve even as snow moves off.


Arx watches/warnings/advisories...
WI...Winter Weather Advisory from 3 am to 9 PM CST Tuesday for wiz017-

Minnesota...Winter Weather Advisory from 3 am to 9 PM CST Tuesday for mnz079-

Iowa...Winter Weather Advisory from 3 am to 9 PM CST Tuesday for



Short term...boyne
long term...boyne

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