Area Forecast Discussion
Issued by NWS La Crosse, WI

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FXUS63 KARX 261742
AFDARX

Area Forecast Discussion
National Weather Service La Crosse WI
1142 AM CST Sun Feb 26 2017

.SHORT TERM...(Today through Tuesday)
Issued at 231 AM CST Sun Feb 26 2017

Water vapor satellite early this morning shows a positive tilt
long wave trough extending from an upper level low near Hudsons
Bay into the Central Plains. A couple of short wave troughs were
embedded in this long wave trough with one over southwest Ontario
and the other over southern Saskatchewan. A weak area of low
pressure was associated with the lead short wave trough with a
cold front extending west back across northern Minnesota into
North Dakota. Surface observations and regional radars indicate
some light snow was falling with this system from northwest
Wisconsin back into North Dakota. Neither of the short wave
troughs is expected to get any farther south than the
International border so there will not be a strong push for the
surface low or cold front to go very far south either. The short
wave troughs should only produce some weak pv advection in the
500-300 mb layer across the northern portions of Minnesota and
Wisconsin which is about as far south as the weak frontogenesis
gets in the 1000-700 mb layer as well. This could be enough to
produce a little bit of light snow over the northern sections of
the forecast area and will continue with a small snow chance for
much of the day across Clark and Taylor Counties.

As the long wave trough currently off the West Coast moves inland,
it is expected to weaken with several pieces of energy coming out
of it. The first of these looks to arrive Monday night and move
across the area Tuesday. This wave looks to be able to produce a
band of weak to at times moderate pv advection in the 500-300 mb
layer that comes across late Monday night into Tuesday morning. A
weak surface low is expected to develop over Nebraska and then
track northeast into southern Wisconsin by the end of Tuesday. The
left over baroclinic zone from the cold front the moves in today
will still be stuck over northern Wisconsin into South Dakota as
well. It looks like the low level frontogenesis will be focused
ahead of the surface low with a weak to moderate band in the
1000-500 mb layer moving across the southern sections of the
forecast area. The isentropic upglide with this system looks to be
on the order of 2 to 4 ubar/s on the 285K surface. This system
also brings a precipitation type challenge with it. As it comes
in, there does not look to be a lot of ice clouds with it, which
sets up the potential for rain or freezing rain based on surface
temperatures and dew points. With an increase in cloud cover and a
south flow through the Monday night, temperatures and dew points
may not have the opportunity to drop much and bumped these up a
little bit which should keep most of the precipitation as rain
with a little bit of freezing rain possible across the far
northern sections. If this warming does not occur at the surface,
then there will be a possibility of more ice accumulations about
as far south as Interstate 90 along with the possible need for an
advisory.

.LONG TERM...(Tuesday night through Saturday)
Issued at 231 AM CST Sun Feb 26 2017

The fun with precipitation types will continue right into Tuesday
night and Wednesday. More pieces of energy from the West Coast
trough will be moving across the region. The surface low over
Wisconsin will move off into lower Michigan as another forms over
Oklahoma and tracks northeast toward the Ohio River Valley. With
the loss of ice clouds Monday night and Tuesday, the forcing from
this next system does not look to be strong enough to allow for
the ice clouds to redevelop setting up the potential for some
additional icing. Fortunately, the qpf amounts look to be rather
low, which will keep the icing amounts low as well, but again, a
system that will have to be monitored closely.

Once this system moves past the area, no big systems appear to be
on the horizon. A weak system could drop in from the northwest for
some light precipitation chances Wednesday night into Thursday.
The GFS suggests another system could also drop in from the
northwest for Friday and Friday night.

&&

.AVIATION...(For the 18Z TAFS through 18Z Monday afternoon)
Issued at 1142 AM CST Sun Feb 26 2017

VFR conditions continue the next 24 hours, with some brief passing
mid level clouds possible at RST/LSE through 19Z then mainly clear
conditions prevailing, save for a bit of cirrus arriving later
overnight. There is a very small risk for some fog development
at RST overnight as high pressure/light winds arrive, though the
chance appears quite low at this time over the existing snow pack
given stronger southerly flow returning later tonight.

&&

.HYDROLOGY...
Issued at 231 AM CST Sun Feb 26 2017

The Black River at Galesville has dropped below flood stage and
that warning was canceled earlier this morning. Elevated water
levels/flows will continue along the Yellow and Wisconsin Rivers
at Necedah and Castle Rock Dam. For specific information on these
sites, see the latest flood statements.

&&

.ARX WATCHES/WARNINGS/ADVISORIES...
WI...None.
MN...None.
IA...None.
&&

$$

SHORT TERM...04
LONG TERM...04
AVIATION...Lawrence
HYDROLOGY...04



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