Area Forecast Discussion
Issued by NWS La Crosse, WI

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FXUS63 KARX 221810

Area Forecast Discussion
National Weather Service La Crosse WI
1210 PM CST Sun Jan 22 2017

Issued at 1210 PM CST Sun Jan 22 2017

Visibilities have been improving over the course of the morning so
have allowed the Dense Fog Advisory to expire as scheduled at 18Z.
Patches of locally dense fog will persist into the afternoon,
mainly along ridge tops, and will issue an SPS to account for
this, given the patchy nature of the remaining fog.


.SHORT TERM...(Today through Monday night)
Issued at 237 AM CST Sun Jan 22 2017

Another morning, more fog. The visibility was being reduced the
most for locations east of the Mississippi River and then back
into east central Minnesota. Similar to the previous two mornings,
the 21.21Z SREF is doing the best at depicting where the dense fog
was located. For the rest of this morning, the SREF would suggest
no significant changes in the areal coverage of the dense fog
other than some that was located over east central Minnesota could
get advected south into southeast Minnesota. Will most likely not
make any changes to the dense fog advisory until later this
morning to see what happens after sunrise when a dip in the
visibility normally occurs.

Fog is not expected to be as big of a problem for tonight. High
pressure will start to build into the Plains States. This will set
up a more low level northwest flow which is expected to advect in
some slightly drier air. So, while some fog will likely be around
again tonight, at this time it is not expected to be dense. The
area of high pressure will then move across the region for Monday
and Monday night for a couple of periods with quiet weather.

.LONG TERM...(Tuesday through Saturday)
Issued at 237 AM CST Sun Jan 22 2017

Water vapor satellite this morning is showing the next system was
currently off the northern California and Oregon coasts over the
Pacific. The 22.00Z models all showing differences on how this
system is handled once it comes inland and moves across the
Rockies. The NAM solutions definitely looks to be out of line
compared to the other models as it looks to be too flat with the
short wave trough and never develops a closed upper level low. The
ECMWF and GFS are much more similar with the system, although the
GFS continues to be faster with it. As the main short wave trough
crosses the Rockies Tuesday, a closed upper level low is expected
to form over Nebraska. These two features will then move
east/northeast across the Midwest Tuesday night and Wednesday. A
round of weak to moderate pv advection in the 500-300 mb layer
should move across the southern half of the area Tuesday afternoon
and evening. The surface low is still expected to come out of
Kansas and move across southern Iowa and into norhtern Illinois or
southeast Wisconsin from Tuesday through Wednesday morning. This
should place the best low level warm air advection and isentropic
up glide across the southern sections of the forecast area. Would
expect a band of mid level frontogenesis to develop north of the
surface low which is where the best qpf and snowfall should occur.
The ECMWF has shown the most continuity with this system and
continues to show this band of higher QPF and snowfall occurring
from about Interstate 90 and south for Tuesday afternoon and night
before the whole system moves past the area with just lingering
light precipitation into Wednesday. Currently expecting a band of
2 to 4 inches of snow across the area with the highest totals
along and south of Interstate 90.


.AVIATION...(For the 18Z TAFS through 18Z Monday afternoon)
Issued at 1210 PM CST Sun Jan 22 2017

Low clouds/fog will continue to be the main aviation impact for this
TAF cycle. Have begun to see some improvement in visibility late
this morning and this trend should continue into the afternoon,
with additional fog development possible overnight tonight.
Confidence is low regarding visibilities overall. However, expect
ceilings to remain generally IFR/LIFR into tonight.




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