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 42 43

FXUS63 KARX 180738

Area Forecast Discussion
National Weather Service La Crosse WI
235 AM CDT Fri May 18 2018

.SHORT TERM...(Today through Saturday)
Issued at 235 AM CDT Fri May 18 2018

Overall weather layout favors dry conditions into Sat for the local
area, but a couple features of note to keep an eye on.

First is the frontal boundary/upper level trough combo currently
over the northern plains - with ongoing convection in response to
this forcing. Models press the front into central MN late this
afternoon/evening, with parent shortwave lifting northeast into
southern Canada. The boundary will also vacate the favorable low
level jet/moisture transport that is currently feeding it. Some
instability builds over MN later today - skinny/long CAPE per bufkit
soundings with generally weak shear. Might be enough to trigger
isold/sct showers/storms late afternoon/night. Pretty dry as you
near the Mississippi River eastward though, evidenced in RH fields
and bufkit soundings. With this in mind, will keep any pcpn threat
off to the west/northwest of the local area.

The other feature of note is a shortwave lifting northeast from the
mid mississippi river valley. While most models take this feature
across the Oh river valley, some spin enough energy northward for
small rain chances across parts of southern WI later tonight. Dry
air in place will hamper the threat somewhat, and trends again favor
chances east of the local area.

All in all, dry forecast still looks good into Sat - with a couple
feature to monitor.

.LONG TERM...(Sunday through Thursday)
Issued at 235 AM CDT Fri May 18 2018

What originally looked like a solid bet for widespread rains Fri
night/Sat continues to get pushed back a day or two...and at least
in one model (the GFS), any wide spread threat could hold off until
Mon night/Tue.

Overall, the models favoring a weak upper level trough over the
rockies/desert southwest with a meandering, cutoff low gradually
lifting toward the region Sat night/Sun. Sfc front likely hanging
around west-east across mid mississippi valley for the upper level
forcing to work on. Not much moisture transport to speak of, with
the nocturnal low level jet favored to point into northern MO/central
IL Sat/Sun nights. The GFS and NAM`s CAPE pool also well south with
best deeper shear also south. Still some thunder threat, but any
stronger/severe threat should hold south.

Flow relatively weak, so trying to pinpoint timing on any of the
various shortwaves can be problematic. Going to hold with the
consensus solution for pcpn chances for now. With that in mind,
generally higher shower/storm chances south of I-90 with proximity
of sfc boundary and ripple coming out of the southwest.

High pressure starts to build in for Tue, with the GFS holding onto
its influence for the local area through Friday. The EC is not as
bullish, pealing off a bit of upper level energy out of a weak
Rockies trough Fri - resulting in some pcpn chances for the Upper
Mississippi River Valley. Relatively weak flow persists in the EC, so
confidence low in this outcome.

Both models do favor a shot for pcpn on Sat with the GFS adding in
some influence of a northern stream 500mb shortwave. The EC does not
have this feature, and thusly not as robust of a system, nor with as
much cooler air. Differences keeps confidence low in the details,
although expectation is still for a decent shower threat Sat.
Depending on timing, instability meager, and very little/if any
shear. Should have some thunder threat, but potential for strong
looks low for the moment.


.AVIATION...(For the 06Z TAFS through 06Z Friday night)
Issued at 1149 PM CDT Thu May 17 2018

Scattered high clouds will be seen across the area through Friday
evening. With diurnal heating, the east southeast winds will gust up
to 20 knots at KRST on Friday afternoon.




LONG TERM....Rieck
AVIATION...Boyne is the U.S. government's official web portal to all federal, state and local government web resources and services.