Area Forecast Discussion
Issued by NWS La Crosse, WI

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FXUS63 KARX 191751
AFDARX

Area Forecast Discussion
National Weather Service La Crosse WI
1251 PM CDT Sat May 19 2018

.SHORT TERM...(Today through Tuesday)
Issued at 130 AM CDT Sat May 19 2018

Fine line of showers/storms currently sparking along a sfc front
across northeast MN/northwest WI, with some aid from low level
moisture transport. Expectation is for the bkn line to continue to
lift northeast, diminishing as it does.

The front will slowly sag south/southeast during the day, roughly
extending from northeast WI into southern IA later this afternoon.
Models pool some instability around the front - with the NAM a bit
more rambunctious with upwards of 1500 J/kg of SBCAPE - due to its
overly moist sfc dewpoints (progged mid 60s while mid/upper 50s more
reasonable). That said, bufkit soundings still suggesting some long,
skinny CAPE would be available for the frontal boundary to work on.
Wind shear is weak. All said, wouldn`t surprise to see another fine
line of sct/bkn showers/storms develop late afternoon around this
boundary. Will continue small pcpn chances for this period -
although a bit broader then would like based on uncertainty of
placement of front later this afternoon.

Both the GFS and the NAM continue to sink the front south tonight as
its parent shortwave slides east across southeast Canada. Another
piece of upper level energy is slated to lift northeast out of the
southern plains, working along and north of the boundary tonight
into Sunday. The 850 mb jet and moisture transport are focused well
south (northern MO), as is the instability. Still, soundings and x-
sections point to enough saturation for the forcing to work on, and
areas of showers and a few showers should result. How far north has
been the question - and continues to be. A lot of dry air in the
north. 900-800 mb dew point depressions north of I-90 for Sun
upwards of 30 C in both the GFS and NAM - significant barrier to
overcome. Will continue shower/isold storm threat across the south
for tonight/Sun.

.LONG TERM...(Wednesday through Friday)
Issued at 130 AM CDT Sat May 19 2018

Nebulous, very weak flow a loft continues into next weekend.
Generally a broad trough over the west coast could/will/maybe spit a
few shortwaves northeast - but where these go, how fast they move is
difficult to pin down. Confidence low in any pcpn chances through
much of the work week.

Models a bit more in step for next weekend with a shortwave trough
in the northern branch of the 500 mb low taking aim on the Upper
Mississippi River Valley. This would provide a good shot for
showers/storms in the Fri/Sat period. No shear to speak of, and no
tap to gulf moisture. However, GFS suggests SBCAPES in excess of
1000 J/kg. Ample to support storm development. Any severe risk still
looks low at this time given the lack of any shear.

Overall, will continue to let the consensus drive the pcpn chances.

For temps, the trends for above normal looks to continue for Tue
through the weekend.

&&

.AVIATION...(For the 18Z TAFS through 18Z Sunday afternoon)
Issued at 1251 PM CDT Sat May 19 2018

Challenging cloud/ceiling forecast over the next 24 hours. A
nearly stalled frontal boundary extends from near KMDZ to KPRO.
Behind this front is an extensive MVFR cloud deck across east-
central MN into northern WI, although there are large breaks
farther south across north-central IA. General idea is for these
clouds to slowly move south and east, keeping KRST in MVFR
conditions for most of the afternoon/early evening. Cloud bases
are a bit higher at KLSE and should remain above 3000 ft agl.
RST may break back into VFR ceilings later this evening before
forecast guidance hints at clouds lowering again overnight. Less
certain at KLSE, but VFR conditions should be the rule.

Some showers and thunderstorms are possible later this evening
and overnight, but should remain mainly south of TAF airfields, so
will maintain a dry forecast. Light northwest winds into this
early evening will gradually turn to the north-northeast overnight
into Sunday.

&&

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

$$

SHORT TERM...Rieck
LONG TERM....Rieck
AVIATION...Rogers


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