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 44 45

FXUS63 KARX 290757

Area Forecast Discussion
National Weather Service La Crosse WI
255 AM CDT MON AUG 29 2016

.SHORT TERM...(Today through Tuesday night)
Issued at 255 AM CDT Mon Aug 29 2016

Strong/severe cluster of thunderstorms over northern MN being fed by
the low level jet and axis of instability, and associated with
sfc/low level frontogenetic forcing + warm air advection. The
anticipation is for the bulk of these showers/storms to weaken and
hold across northern mn/northern wi today as the low level
jet/moisture transport focuses into the UP of Mich and the low level
warming/weak frontogenetic lift also hangs in the north. Perhaps
some small chances north of hwy 29 in northcentral WI.

Farther south, a few showers/storms continue to fire along mostly
outflow boundaries, in an unstable and weakly sheared environment.
This activity will likely continue today, with the outflows
providing some focus, but with additional help from a weak/narrow
ribbon of upper level vorticity that the models have been adamant on.
Some of this activity could drift north across portions of northeast
IA/southwest WI.

Cold front hanging out over the northern plains will finally get a
push into and through the region on Tue as its parent upper level
trough tracks eastward across Canada. Only meager frontogenetic
forcing with this boundary in such a baggy/weak flow. Still, SBCAPES
upward 2k J/KG. No wind shear to speak of, and no aid from the low
level jet/moisture transport either. This keeps confidence low in
widespread activity along the front - seeing isolated/scattered
chances more probable. Any left over outflow boundaries from
convection to the north or south certainly could play a roll too,
obviously more of a very near term question. Will continue small
chances tonight/Tue.

Without much shear, see the severe risk as minimal for now - but not
completely eliminated. Enough instability that hail could develop in
a more pulse like environment. Whether it could make severe limits
is hampered by the poor wind environment. As for heavy rain, the
deeper warm cloud depths/pws still expected to hang to the south.
Heavy downpours could accompany any stronger storms, but its not an
ideal setup for widespread heavy rain production. That said, with
the steering flow rather light, if heavy rain would develop, it
could sit over any one location for a bit. Something to watch.

.LONG TERM...(Wednesday through Sunday)
Issued at 255 AM CDT Mon Aug 29 2016

The GFS and ECMWF in lockstep now with amplifying an upper level
ridge over the plains Wed, transiting east to across the eastern
Great Lakes by 12z Sat. An associated sfc high makes its way across
the region during this time, with a cool and much drier airmass also
dropping back in for the later 1/2 of the work week. The main
forecast challenge here is coming up with different ways to say
"nice". Highs Wed-Fri will hover in the 70s, with lows mostly in the
50s. Thu/Fri mornings looking like decent shots for valley fog.

Decent agreement between the GFS and EC with moving an upper level
trough west-east across southern Canada for the weekend. The bulk of
the upper level energy would hold well north, but its associated sfc
front would slip through the upper Mississippi River valley. With a
ribbon of higher moisture/warmer air to play with, shower and storm
chances result.


.AVIATION...(For the 06Z TAFS through 06Z Monday night)
Issued at 1033 PM CDT Sun Aug 28 2016

VFR conditions continue at the moment but with light winds and a
moist airmass in place, still believe fog development is in order.
Based on ambient conditions at 0330Z with low temp/dew point spreads
at LSE and a quite light wind layer aloft up through 500mb/15kft,
don`t see why that site won`t see at least a period of dense fog
centered on sunrise. RST on the other hand may keep enough of a
gradient wind on the back side of the departing low level ridge axis
to preclude any widespread dense fog, but still can foresee a period
of brief IFR visibility in some fog before sunrise. Outside of that,
still looking for a quick return to VFR conditions by 14Z with some
diurnal cumulus and cirrus aloft through the afternoon on Monday.


.ARX Watches/Warnings/Advisories...


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