Area Forecast Discussion
Issued by NWS La Crosse, WI

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867
FXUS63 KARX 240859
AFDARX

Area Forecast Discussion
National Weather Service La Crosse WI
259 AM CST Fri Feb 24 2017

.SHORT TERM...(Today through Saturday)
Issued at 259 AM CST Fri Feb 24 2017

Early this morning, water vapor satellite showed the upper level
low was over central Nebraska. The surface low was displaced from
the upper level system and was over northern Missouri.
Precipitation was falling across much of the area from this system
with snow along and north of Interstate 90 and rain/drizzle or a
mix to the south.

The upper level low still has a positive tilt to it, but the
24.00Z models along with the 24.06Z RAP all continue to show this
taking on more a neutral tilt as it works east today into this
evening. This will cause the pv advection in the 500-300 mb layer
to increase but the models all take the stronger advection south
of the forecast area. Some jet dynamics will help to increase the
forcing on the poleward side of the upper level low as the
divergence aloft should be amplified by coupled jet structure.
Good low level thermodynamics will produce 5 to 10 ubar/s of up
glide on the 290K isentropic surface this morning and then 3 to 6
ubar/s from late this afternoon through much of the afternoon.
This will be come lighter, but continue well into this evening
with a weak trowal that is expected to form on the back side of
the surface low.

With plenty of forcing, no doubt the precipitation will continue,
but the concern going forward is how much additional
precipitation, what type will it be and will blizzard conditions
be reached. A bit of a lull in the precipitation at this time, but
all the meso scale models suggest the deformation zone should
spread back across most of the area by the start of the morning
commute. The heaviest precipitation should then be this morning
before diminishing some but continuing through the day with the
forcing from the trowal. With the decrease in intensity for this
afternoon and evening, the qpf amounts from the latest guidance
look to be not quite as high as before which will then cut into
the overall snow accumulations. Thinking another 4 to 8 inches
today in the warning areas and with what has already fallen, some
locations still likely to get a foot or more, but not sure about
the 16 inch totals we were forecasting on the high end.

As for the precipitation types, the dry slot on the east side of
the upper level low was working north across southern Iowa. As
this spreads into the area, especially the southeast sections, it
will take the ice out of the clouds and set up the potential for
more rain or freezing rain depending on air and road temperatures.
The dry slot looks to remain into the afternoon before moving east
and allowing ice clouds to spread back over the area. However,
this could result in some ice accumulations of a 1 to maybe 2
tenths of an inch across northeast Iowa into southwest and central
Wisconsin.

Observations across southeast Minnesota indicate that blizzard
conditions have yet to be reached with the visibility only briefly
dropping below a mile for short periods of time. The strongest
winds will be through this morning before these start to diminish
as the surface low moves from northern Illinois into lower
Michigan. The wet, heavy nature of the snow will also have some
impact on just how much it can be picked up and moved around.
Concerned that there may not be prolonged periods of whiteouts and
that the blizzard warning may have to be downgraded. Do not plan
to make any changes to this headline this morning but the dayshift
may have to do so once the winds start to diminish.

So for now, no significant changes to the forecast. All headlines
will continue as is, but maybe a bit less snow than earlier
expected. Storm total amounts of 6 to 14 inches in the warnings
with up to a tenth of an inch of ice accumulations possible south
of a Austin to Black River Falls line. In the advisory area, snow
totals of 2 to 5 inches with 1 to 2 tenths of an inch of ice
accumulation.

.LONG TERM...(Saturday night through Thursday)
Issued at 259 AM CST Fri Feb 24 2017

A weak system will zip across the Upper Midwest Saturday night and
Sunday morning and could drop a little bit of light snow across
portions of central and northern Wisconsin. The next chance for
some precipitation will come Monday night and Tuesday as a system
comes out of the central Rockies and lifts northeast toward the
Great Lakes. With highs Tuesday expected to be in the 40s, the
precipitation should start out as light snow and then go over to
rain. Another chance for mainly light snow will come Wednesday
night into Thursday as a system dives southeast out of Canada.

&&

.AVIATION...(For the 06Z TAFS through 06Z Friday night)
Issued at 1123 PM CST Thu Feb 23 2017

IFR/LIFR conditions will be the general rule for the foreseeable
future at both KRST/KLSE as a winter storm moves across the
region. KLSE could see a rain/snow mix for a portion of the night
before changing to all snow, but KRST will see periods of
moderate to heavy snow through the night and into Friday. When
combined with northeast wind gusts up to 30 kts, visibility likely
to drop to 1/2SM or less for the majority of the period in
blowing/drifting snow. Visibility not expected to be as impacted
at KLSE until later Friday as a heavier snow band moves across the
MS River Valley. On top of all this, some thunder snow is possible
in the early overnight hours at both TAF sites. Conditions may
slowly improve at KRST late in the period as snow pushes east and
winds begin to diminish, but snow should continue at KLSE through
the period. Overall, very poor conditions for aviation operations
through the period.


&&

.HYDROLOGY...
Issued at 259 AM CST Fri Feb 24 2017

A few forecast points remain above flood stage or are forecast to
reach flood stage in the near future as a result of the recent
warm conditions and precipitation. For information on specific
forecast points see the latest river flood statements.

&&

.ARX WATCHES/WARNINGS/ADVISORIES...
WI...Winter Weather Advisory until 6 AM CST Saturday for WIZ043-044-
     053>055-061.

     Winter Storm Warning until 6 AM CST Saturday for WIZ017-029-
     032>034-041-042.

MN...Blizzard Warning until 6 AM CST Saturday for MNZ079-086>088-
     094>096.

IA...Blizzard Warning until 6 AM CST Saturday for IAZ008>010-018-019.

     Winter Weather Advisory until 6 AM CST Saturday for IAZ011-029-
     030.

&&

$$

SHORT TERM...04
LONG TERM...04
AVIATION...Rogers
HYDROLOGY...04



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