Area Forecast Discussion
Issued by NWS La Crosse, WI

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FXUS63 KARX 210812

Area Forecast Discussion
National Weather Service La Crosse WI
212 AM CST Sat Jan 21 2017

.SHORT TERM...(Today through Monday)
Issued at 212 AM CST Sat Jan 21 2017

Observations this morning continue to show dense fog covering most
of southeast Minnesota, northeast Iowa and southwest into central
Wisconsin. The dense fog has recently shown some expansion into
parts of north central Wisconsin while the higher terrain of the
remainer of western Wisconsin was also likely experiencing dense
fog. Will expand the dense fog advisory to cover the remainder of
the forecast area. The 20.21Z SREF probabilities look to have the
best handle on this fog once again this morning and suggest there
should start to be a general increase in the visibility as the
rain works across the area, starting between 12Z and 15Z with what
looks to be a pretty rapid improvement after that.

Water vapor satellite early this morning shows the remains of the
upper level low that impacted the region Friday was over North
Dakota. The next short wave trough was lifting north across
southwest Iowa. This wave will continue to lift north through the
day and is expected to reach the northern Great Lakes tonight. As
it moves across the region, it is expected to produce some
moderate pv advection in the 500-300 mb layer through the morning
hours along with some weak qg convergence in the 1000-500 mb
layer. The warm air advection ahead of the wave will produce a
broad area of 2 to 4 ubar/s of up glide on the 290K isentropic
surface that will also work across the area this morning. This
forcing is already producing an area of rain across western Iowa
that is expected to lift north/northeast with the wave and across
the area. The best chances for rain should be across the western
sections of the area where the forcing will be the strongest, but
the entire area will have a chance of seeing some rain with this
system. While the best chance for rain will be this morning, there
will be some lingering chances through the night across the north
until the upper level trough axis moves past the area.

.LONG TERM...(Monday night through Friday)
Issued at 212 AM CST Sat Jan 21 2017

Both the 21.00Z ECMWF and GFS continue to show a short wave trough
coming across the central Rockies early next week. A closed upper
level low should quickly form with this wave over the Missouri
River Valley Tuesday but then just about as quickly start to
become an open wave as it begins to merge with the strong system
that is working its way up the the East Coast. The surface low
track looks to have shifted just a bit to the south with the
latest runs now taking it from Kansas across southern Iowa into
northern Illinois. Looking at the GFS forecast soundings, the bulk
of the precipitation from this system should fall as snow, except
on the leading edge when low level temperatures may be warm enough
for a change over to rain or a mix of rain and snow. With the
current timing, some of the precipitation could start to move in
Tuesday afternoon with the majority of the precipitation then
falling Tuesday night into Wednesday morning. With the current
track, accumulations will occur that would likely be in the
advisory range. Behind this system, it looks like temperatures
will return to more seasonable values with some on and off light
snow chances as the upper level flow pattern remains cyclonic with
some weak short wave troughs moving across the region.


.AVIATION...(For the 06Z TAFS through 06Z Saturday night)
Issued at 1138 PM CST Fri Jan 20 2017

LIFR/IFR ceilings will persist at KRST/KLSE through the period as
low stratus continues to hang tough across the region. Dense fog
with 1/4SM visibility at KRST may improve slightly overnight as an
area of light rain lifts northward. However, conditions should
tank back to 1/4SM once the rain moves north of the TAF airfield.
Visibility at KLSE has been slow to fall this evening, but should
eventually drop at least into the MVFR range overnight and
possibly IFR by daybreak Saturday morning. Some light rain is also
expected at KLSE overnight. Only slight improvements in visibility
are expected the latter half of the period. Light south-southeast
wind will be the rule, turning to the southwest at KRST late in
the period.


WI...Dense Fog Advisory until noon CST today for WIZ017-029-032>034-

MN...Dense Fog Advisory until noon CST today for MNZ079-086>088-

IA...Dense Fog Advisory until noon CST today for IAZ008>011-018-019-



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