Area Forecast Discussion
Issued by NWS La Crosse, WI

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FXUS63 KARX 181933
AFDARX

Area Forecast Discussion
National Weather Service La Crosse WI
230 PM CDT Mon Jun 18 2018

.SHORT TERM...(Tonight through Tuesday night)
Issued at 230 PM CDT Mon Jun 18 2018

Sfc cold front has slid south of I-90 early this afternoon and is
progged to continue its gradually decent southwards - roughly from
central IA into northern Il this evening. Upper level shortwave
lifting northeast out of the southern/central Plains will track
across the boundary tonight, providing another focusing mechanism
for showers/storm development. Not a ton of push for the shortwave,
and will likely continue to help with pcpn chances across the south
into Tue. Moisture transport/LLJ initially into and across the
front this evening, but quickly becomes more parallel - and not as
convergent. All said, plenty of lift for available saturation for
more showers/storms from late this afternoon into Tue. Setup,
positioning of the various features continues to favor chances
mostly south of I-90.

As for the strong/severe question - latest satellite has kept much
of the local area under bkn clouds from the morning into early
afternoon. Hot, humid air mass remains in place south of the front.
Instability is building with MUCAPEs of +2K J/kg possible across
parts of NE IA/SW WI by 00z this evening. Deep shear remains
confined to the cool sector well north of the front, but 0-3km shear
suggested around 20-30 kts. That will provide some aid for storm
development. See a strong/severe threat ala yesterday, but much
depends on where the front/clearing line is at mid/late afternoon.
Better chances just to the south, and southwest where the shortwave
will have more of an influence this evening. Heavy rain (flooding?)
threat remains - and more details below in the HYDROLOGY section.

On the plus side, the passage of the cold front will usher in a
cooler, less humid airmass. Temps looking to be at or below the
seasonable normals into the weekend.

.LONG TERM...(Tuesday night through Monday)
Issued at 255 PM CDT Mon Jun 18 2018

For Tuesday night thru Thursday night: Main fcst concerns this
period are SHRA/TSRA chances mainly Tue night.

Model runs of 18.12z offering a tightening consensus for the mid
level low over the northern Rockies today to hold together (vs.
opening up) and move SE from WY/MT into the mid MS valley thru this
period. Fcst confidence for Tue night thru Thu night is average to
good this cycle.

Tightening consensus track of the mid level low now keeps it and
much of the assocaited forcing/lift south/west of the fcst area this
period. Some lower level thermo-dynamic forcing, aided by a lead
shortwave, still impinges on the SW side of the fcst area Tue night.
Some 20-40% SHRA/TSRA chances mainly across the S end of the fcst
area Tue night, followed by SHRA/TSRA chances limited to the SW end
of the fcst area Wed thru Thu night, are reasonable. An easterly sfc-
850mb flow out of high pressure over the great lakes is looking to
keep highs Wed/Thu close to the mid June normals.

For Friday through Monday (days 4 to 7): main fcst concerns this
period are SHRA/TSRA chances Fri/Fri night and continued unsettled
pattern Sat thru Mon.

Medium range model runs of 18.12z continue with the tightening
consensus on the evolution of the mid level low Fri/Sat, lifting it
NE and opening it up Fri thru Sat. Plenty of between model and run-
to-run differences by later Sat thru Mon, as an active looking flow
pattern remains over the northern CONUS. Fcst confidence for Fri-Mon
is average for a day 4-7 period.

Mid level low opening up and lifting NE Fri into Sat would spread
increasing moisture transport and some lift northward into the fcst
area. SHRA/TSRA chances across much of the fcst area Fri afternoon/
evening reasonable at this point. Unsettled look of the flow pattern
and model detail differences, cannot argue against the small
consensus SHRA/TSRA chances much of the Sat-Mon period. Not all of
the Sat-Mon periods will end up with some rain chances, but little
confidence in picking out the dry ones at this time. Even with
variability for precip chances Fri-Mon, consensus is for high
pressure to hold over the great lakes, with persistent E to NE low
level flow across the Upper Midwest. Blend of day 4-7 guidance highs
a few degrees either side of normal looks good at this time.


&&

.AVIATION...(For the 18Z TAFS through 18Z Tuesday afternoon)
Issued at 1155 AM CDT Mon Jun 18 2018

Cigs: generally mostly mvfr (ifr?) for the TAF period, with bufkit
soundings suggesting a bump into VFR for a period later this
afternoon. Some agreement with sfc obs/satellite trends. Should drop
back into mvfr later tonight as shortwave approaches from the west,
and probably holds there for the better part of Tue.

WX/vsby: sct shra/ts around frontal boundary could impact KLSE for a
few hours this afternoon, then expect a break as storm focus shifts
farther to the south for later this afternoon/tonight. Several meso
models suggest some shra/ts potential north of southward moving cold
front, but not a lot of consistency. Will trend dry for now, update
as needed. Looking like a better shot for showers by Tue morning as
a shortwave trough spins eastward into the area. There could be some
periodic mvfr restrictions in heavier showers.

Winds: cold front is sliding south of the TAF sites and expect
northerly winds to become more easterly overnight.

&&

.HYDROLOGY...
Issued at 230 PM CDT Mon Jun 18 2018

Heavy rainfall (2-4") has resulted in flooding (generally localized)
across portions of western/north-central Wisconsin. Conditions have
improved through the morning-early afternoon hours, and the areal
flood warnings that were in effect were allowed to expire.

The setup for heavy rain shifts south of Interstate 90 for this
afternoon/night. Warm cloud depths close to 4.5K km and PWs in
excess of +2 inches prime the pump for efficient heavy rain
producers.

Models point to cold front laying up west-east from central IA into
northern IL this evening. Low level moisture transport/jet runs into
the boundary, but generally more parallel to the boundary - not as
favorable of an orientation. Still, with convection expected along
and north of the boundary tonight, and west-east running storms for
training, localized flooding could become a concern. Northeast IA
and southwest WI hasn`t seen much rain of late and a widespread
flash flood threat doesn`t look likely at this time - so don`t
anticipate the need for a watch.

Rainfall across the region will contribute to rises on area rivers
and streams, including along the Mississippi. Some river flooding
could/will result over the next few days, dependent on where the
heaviest rainfall occurs.

&&

.ARX WATCHES/WARNINGS/ADVISORIES...
WI...None.
MN...None.
IA...None.

&&

$$

SHORT TERM...Rieck
LONG TERM....RRS
AVIATION.....Rieck
HYDROLOGY....Rieck



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