Area Forecast Discussion
Issued by NWS La Crosse, WI

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FXUS63 KARX 241203

Area Forecast Discussion
National Weather Service La Crosse WI
703 AM CDT Sat Mar 24 2018

.SHORT TERM...(This afternoon through Sunday)
Issued at 346 AM CDT Sat Mar 24 2018

Challenging Spring system moving through this morning. Have had
recent reports of 3-5 inches across northeast Iowa, south of a
KCCY-KOLZ line. Snow is struggling to the northeast in dry air
battle with Austin at 2.5mi vsby thus far and only 0.5". GOES-E
water vapor very impressive with shortwave trough west of Omaha
still many hours away.

Concerns now are how much along the southern forecast area. With
track of trough and per model deformation and
E-W band should set up very close to Hwy 20/18 areas in northeast
IA and 14" is not out of the question depending on the placement.
This band will provide many more hours of snow into the late

Have decided to trim the northeasternmost area snow totals and
downgrade to, or cancel, advisories. Just cannot get enough
accumulation in easterly flow on far northeast edge of
precipitation band.

Will also extend the warnings/advisories to 4 pm in an effort to
allow some clean up and because it will snow into the late
morning. Right now, the 7am-1pm snow accumulation forecast is 5-7"
across southern Floyd-Fayette counties.

.LONG TERM...(Sunday through Friday)
Issued at 346 AM CDT Sat Mar 24 2018

Hudson Bay high pressure dominates the weather for Sunday and
Sunday night with dry easterly flow and anomalously dry easterly
in the low-levels. NAEFS data from 23.12Z suggests 850mb specific
humidity in the 5 percentile range over WI. With some easterly
pressure gradient and mostly sunny skies expected, mixing will
promote a dewpoint drop Sunday below model guidance. 24.00Z NAM
and GFS both suggest dewpoint depressions of 30 to 40C. This
should support single digit dewpoints and RH values less than 20%.
In combination with winds of 15-20 mph, an elevated fire danger
will be present.

Southwest flow aloft brings shortwave trough energy and a nice
surge of moisture and warm advection to the area Monday afternoon
and evening. This is well agreed upon in the models with a
moderate 850 mb moisture transport convergence signal moving
through while isentropically lifting. Dewpoints in the 850-700mb
layer jump about 30C with this air mass change promoting higher
rain chances and possibly some thunder with CAPE in the low
hundreds. While some wintry mix would be supported Monday
morning, but by the time the forcing arrives later in the day the
air mass in place should have freezing levels around 6-8kft. The
24.00Z NAM is fairly aggressive with a 2.5km deep surface-based
supercooled liquid layer Monday morning under very weak forcing -
so it just may be clouds. For now, have left a chance of a wintry
mix in the forecast Monday morning in sern MN and nern IA.

Tuesday through Friday...Some model spread presents itself on
Tuesday if the light rain or drizzle will continue or push east as
a cold front moves through. Otherwise, it appears a longwave
trough will be building over the CONUS as the period progresses
with what looks like a cool down late week with possibly highs in
the upper 20s Saturday. This is remarkably consistent in the
medium range guidance. Its a long way away and for now just stuck
with the model consensus blend after Tuesday.


.AVIATION...(For the 12Z TAFS through 12Z Sunday morning)
Issued at 700 AM CDT Sat Mar 24 2018

A dry easterly flow will continue to provide VFR ceilings and
visibilities at the TAF sites. The winds will remain rather gusty
today with wind gusts of 15 to 30 knots.


MN...Winter Weather Advisory until 4 PM CDT this afternoon for MNZ094.

IA...Winter Storm Warning until 4 PM CDT this afternoon for IAZ008-

     Winter Weather Advisory until 4 PM CDT this afternoon for IAZ010.



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