Area Forecast Discussion
Issued by NWS La Crosse, WI

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499
FXUS63 KARX 231133
AFDARX

Area Forecast Discussion
National Weather Service La Crosse WI
630 AM CDT MON MAY 23 2016

.SHORT TERM...(Today and tonight)
Issued at 319 AM CDT Mon May 23 2016

Latest water vapor satellite imagery shows upper level trough over
the southern Canadian Rockies and the northern United States Rockies
and upper level ridge over the Upper Great Lakes Region. Several
shortwave troughs wrapping around the upper level trough are
producing showers and thunderstorms from the Northern Plains to the
High Plains.

Main forecast concerns are precipitation chances today into tonight.
The 23.00z GFS/NAM are in good agreement in breaking down upper
level ridge over the Great Lakes Region and developing southwesterly
flow aloft over the central United States. The 23.00z GFS/NAM are in
good agreement in weakening ongoing convection in association with
first impulse over the Northern Plains...as instability weakens out
of ahead of the convection. Second piece of energy embedded in
southwesterly flow aloft pushes into the Upper Great Lakes region
late this afternoon and tonight. The 23.00z GFS/NAM/ECMWF indicate
moisture transport/convection and lift in association with this
piece of energy. However...the models show some weakening of the
moisture transport/convergence and focus this across the far
northern and southern sections of the forecast area. This is
evident...as the hi-resolution/CAMS models indicate redevelopment
convection to form across the far northern/southern sections of
the forecast area late this afternoon. Continued trend of higher
chances of showers and thunderstorms over these areas.

Confidence in severe potential remains very low...as the 23.00z
GFS/NAM continue indicate 20-25 knots of 0-3 km shear and up to
1000 J/kg of CAPE. Not anticipating any severe weather with the
thunderstorms.

.LONG TERM...(Tuesday through Sunday)
Issued at 319 AM CDT Mon May 23 2016

Unsettled weather pattern continues Tuesday into Wednesday
night...as the 23.00z GFS/NAM/ECMWF eject a couple of shortwave
troughs out of the upper level trough over the western United States
into the Upper Great Lakes Region. Differences occur between the
models on timing/placement of the shortwave troughs. The 23.00z
GFS/NAM/ECMWF hint at focusing the stronger moisture
transport/convergence and placement of surface front south of the
forecast area Tuesday night into Wednesday. This would result in
developing stronger convection south of the forecast area.
However...if the forecast area builds enough instability and given
the wind shear at 0-3km of 20 to 30 knots...some of the
thunderstorms could be strong with gusty winds and hail.

Main forecast concerns Thursday into Sunday continue to be
precipitation chances across the forecast area...as the 23.00z
GFS/ECMWF/GEM show southwesterly flow aloft and embedded
shortwave troughs tracking into the Upper Great Lakes Region.
Timing and placement of individual shortwave troughs continue to
be the main issues between the long range models. Will continue
with trend of shower and thunderstorm chances across the forecast
area through the period.

&&

.AVIATION...(For the 12Z TAFS through 12Z Tuesday morning)
Issued at 630 AM CDT Mon May 23 2016

Decaying convection to the west has led to more cloud cover this
morning but still looking at VFR conditions area-wide. Some of the
outflow may trigger mid level sprinkles or showers for a few hours
this morning but guidance suggests this should weaken with bulk of
day dry.

As airmass to the west continues to saturate in southwest flow,
expect lowering ceilings tonight, which could become at least MVFR.
Besides that, a lot will depend on if and where convection forms
with lots of uncertainty. Forcing is not strong and instability will
be limited so will keep idea of scattered showers and isolated
thunder risk in with idea that more details can be added in short
term.

&&

.ARX Watches/Warnings/Advisories...
WI...None.
MN...None.
IA...None.
&&

$$

SHORT TERM...DTJ
LONG TERM...DTJ
AVIATION...SHEA



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