Area Forecast Discussion
Issued by NWS La Crosse, WI

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FXUS63 KARX 120448

Area Forecast Discussion
National Weather Service La Crosse WI
1148 PM CDT Wed Oct 11 2017

.SHORT TERM...(This evening through Thursday)
Issued at 202 PM CDT Wed Oct 11 2017

Afternoon surface/upper air analysis shows a shortwave trough and
surface low along the Indiana/Michigan border, with an upper level
ridge axis centered over the local forecast area. Clouds on the
backside of the low have remained trapped under an inversion, with
light east-southeasterly low-level flow. This has kept temperatures
in the upper 40s to mid 50s.

Surface high pressure to the north will then move east through the
Great Lakes region overnight, leading winds to shift to
southeasterly and bring more moisture into the area. The NAM and
many of the CAMs have consistently suggested the potential for
patchy fog/drizzle through the mid-morning hours on Thursday. With
fog being observed to the south in parts of eastern Iowa on
Wednesday morning, it would make sense, given the wind shift to
southerly, that the same air mass and associated fog would be in
place over the forecast area on Thursday. Not quite as confident in
the occurrence of drizzle, with BUFKIT soundings showing mainly
positive values of omega in the saturated layer. That said, the
saturated layer is just over 1 km deep and guidance does show a bit
of convergence in the low-levels along with some slight isentropic
lift, so cannot completely rule out drizzle and have left patchy
drizzle in the forecast for much of the area through mid-morning.
Otherwise, clouds are expected to remain in place over the area
through Thursday, with high temperatures warming slightly into the
upper 50s to lower 60s with the southerly winds.

.LONG TERM...(Thursday night through Wednesday)
Issued at 202 PM CDT Wed Oct 11 2017

Focus is on what looks to be a rather soggy period for Friday
through Sunday morning. A cold front pushes northwest to southeast
across the area Friday with a wave of low pressure riding
northeast along this baroclinic zone Friday night through Sunday.
The CAPE is virtually nil as the front comes in on Friday due to
cloud cover. As the low moves from northeast IA into southern WI
Saturday afternoon/evening, some smaller-end 0-3km MUCAPE of
200-500J/kg creeps into far southwest WI south of I-90. There is
ample amount of 0-1/0-3km bulk shear available, so will have to
watch how much the warm sector can "clean up" for potentially
higher CAPE, resulting in the potential for some isolated severe
weather. Right now, this potential looks low but bears watching.
Latest models have the bulk of rainfall exiting the area by
Sunday afternoon as the low pulls into the Great Lakes. Otherwise,
appears to be a decent tropical tap with this wave with PW values
across our area ranging from 1 inch across the north to 1.75
across the south by Saturday afternoon. Based on this, there
could be some pockets of heavier rainfall in the Saturday
afternoon/evening time frame.

Drier weather then expected going into next week as heights/ridge
builds across the central CONUS.


.AVIATION...(For the 06Z TAFS through 06Z Thursday night)
Issued at 1148 PM CDT Wed Oct 11 2017

The blanket of clouds remains over the area this evening with
primarily MVFR ceilings. With the low level flow out of the
south/southeast, the majority of the downstream observations
suggest ceilings will remain MVFR, although would not be surprised
to see KRST dip to IFR for a while. Plan to stay with the MVFR
ceilings through Thursday morning before the clouds start to get
pushed to the northeast as the flow strengthens out of the
southwest. This will allow VFR conditions to return late Thursday
afternoon with the clouds expected to scatter out in the evening.
No signs of any fog or drizzle development yet across the area. If
any fog does develop overnight it will likely stay to the south of
both airports where there was more rain Tuesday and will not
include any visibility reductions for either airport. Forecast
soundings from the 12.00Z NAM and 12.03Z RAP continue to show the
lift to be above the moisture layer through Thursday morning so
continue to have doubts about any drizzle developing and have
stayed with a dry forecast.




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