Area Forecast Discussion
Issued by NWS La Crosse, WI

Home | Current Version | Previous Version | Graphics & Text | Print | Product List | Glossary Off
Versions: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41

000
FXUS63 KARX 221711
AFDARX

Area Forecast Discussion
National Weather Service La Crosse WI
1211 PM CDT FRI JUL 22 2016

.SHORT TERM...(Today and tonight)
Issued at 230 AM CDT Fri Jul 22 2016

Heat remains the primary focus for one more day across the area.
Large convective complex that dropped south across WI last evening
and then propagated southwest into parts of IA has left a sizable
cold pool over the area...with lower temps and dewpoints. But
looking at the model thermal profiles, we still have plenty of warm
air in the lower atmosphere. This should be enough to reach highs in
the upper 80s to lower 90s. Dewpoints look to be much lower over
northern WI, with values down into the mid 60s. Models continue to
hold with dewpoints in that range into the afternoon, but that
doesn`t seem likely given the transpiration of plants and presence
of lower 70s over nearby eastern MN. Granted, this area is on the
northern side of the front now, but do anticipate some upward
recovery. Meanwhile, where it has yet to rain over our western
forecast area, dewpoints remain in the mid 70s and are likely to
push 80 again today. This is all important because of the Heat
Headlines we have in place. The Heat Index that results from all of
this still ends up getting into at 95-110 range across the forecast
area, with the higher end values from Austin and Charles City, over
toward Dubuque. These values are borderline for true Excessive Heat
Warning criteria, but given that this is the 3rd hot day in a row,
the duration of the heat leads me to keep the Warning where it is
until expiration this evening. Will also leave the Heat Advisory in
place where it is for the same reason, despite not quite reaching
criteria today. It really is just a matter of semantics and a few
nearly indistinguishable ticks on the thermometer.

The other concern is a continued small chance for convection.
Predicting the timing and location of rainfall the past few days has
been very challenging, and today is not much different. Most signals
suggest that there will not be enough of a short wave trough or
other such disturbance to help drive development in the presence of
the warm cap still in place over much of the area. Still, despite
this, once again this morning satellite imagery and observations
show a developing field of ACCAS across MN, and a few of these are
creating showers from the Twin Cities down toward Winona. Today we
feel that only light showers or sprinkles will result, without a
major upscale to full-fledged convection like the past 2 days. But
the presence of the boundary just to the south, along with good
moisture pooling, might be enough to break the cap across IA. So
have maintained a low chance over the south later today just in
case. The next short wave disturbance currently crashing the West
Coast will be moving east toward the region for the weekend. This
will bring an increasing threat of rain starting late tonight over
the west, and spreading east through the local area during the day
Saturday and Saturday Night.

.LONG TERM...(Saturday through Thursday)
Issued at 230 AM CDT Fri Jul 22 2016

There will be two main shots of convective potential Saturday and
Saturday night as the short wave trough tracks from WA/ID today,
into southern MB by Sunday morning. The front that is currently
south of us will lift back north as a warm front tonight. As the
moisture transport and LLJ impinge upon it, expect to see some
convection fire. Will still be warm and sticky south of the front so
anything that fires could produce heavy rainfall. As the wave moves
closer late Saturday, it will drive a cold front into the area
overnight. Additional convection will be possible. Instability and
shear will be sufficient for some severe storms, so this will have
to be monitored. Any lingering activity will shift east of the area
Sunday as high pressure builds in behind the departing system. The
next waves in the flow will bring rain chances for late Tuesday
into Wednesday, and again later Wednesday into Thursday.
Temperatures will be more normal for mid-summer.

&&

.AVIATION...(For the 18Z TAFS through 18Z Saturday afternoon)
Issued at 1211 PM CDT Fri Jul 22 2016

The MVFR clouds have persisted through the morning at KRST with
the 22.12Z NAM indicating this band of moisture is trapped
underneath the inversion. The concern through the afternoon is
whether there will be enough mixing to break the low level
inversion and allow the clouds to scatter out. The NAM holds onto
the inversion and clouds while the 22.15Z RAP continues to suggest
the clouds will break up. Will go with the more pessimistic
solutions and keep the clouds through the afternoon. The
possibility of fog exists again for the overnight hours with all
the low level moisture in place. The NAM forecast soundings show
saturation occurring at KRST with light winds so will include some
MVFR reductions to the visibility. At KLSE, saturation could also
occur at the surface, but the winds just above the surface could
be increasing late tonight and could prevent the fog from forming.
For now, will not include any fog at KLSE. Any showers and storms
from the system coming in Saturday looks to be in the afternoon
and evening.

&&

.ARX Watches/Warnings/Advisories...
WI...Excessive Heat Warning until 7 PM CDT this evening for WIZ032-
     033-041-053>055-061.

     Heat Advisory until 7 PM CDT this evening for WIZ034-042>044.

MN...Excessive Heat Warning until 7 PM CDT this evening for MNZ079-
     086>088-094>096.

IA...Excessive Heat Warning until 7 PM CDT this evening for
     IAZ008>011-018-019-029-030.

&&

$$

SHORT TERM...MW
LONG TERM...MW
AVIATION...04



USA.gov is the U.S. government's official web portal to all federal, state and local government web resources and services.