Area Forecast Discussion
Issued by NWS La Crosse, WI

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FXUS63 KARX 212318

Area Forecast Discussion
National Weather Service La Crosse WI
618 PM CDT SUN AUG 21 2016

.SHORT TERM...(Tonight through Tuesday)
Issued at 240 PM CDT Sun Aug 21 2016

Temperatures on the upswing for the early part of the new work week
as high pressure moves east and southerly flow returns. Highs should
bump back into the 80s for most locations, with Tue looking like the
warmest days of the week.

Still some see threat for showers/storms across the far northern
Monday night, although those chances may be shifting north and out
of the local area. Both the GFS and NAM surge 850:700 mb warm air
advection northward across MN and into northern WI Mon night, with
some push of the low level jet/850mb moisture transport into this
thermodynamic forcing. Setup looks reasonable for at least some
scattered shower/possible storm development. However, saturation may
be lacking. North-south running x-sections via the GFS/NAM show very
little RH, with plan view projections keeping any deeper moisture
over northern MN-lake superior. Think its still worth small rain
chances over the far north Monday night for now.

.LONG TERM...(Tuesday night through Sunday)
Issued at 240 PM CDT Sun Aug 21 2016

Models have been in pretty good agreement with developing
showers/storms over the southern plains Tue evening, taking this
shortwave/mcv fueled cluster northeast and across the area on Wed
morning. Meanwhile, the mean upper level trough will be moving west-
east across southern Canada/northern plains, with its accompanying
sfc cold front running ahead of it. The front looks to reach the
Mississippi River by 18z or so Wed, and will interact with the
shortwave/mcv from the southwest. The GFS builds some CAPE along and
ahead of the sfc...but the deep shear is relatively weak...mostly
confined to the 0-3 km layer (about 25 kts). Given the dynamics and
instability, some stronger storm threat. Timing though limits the
potential instability and severe threat. If the system moves in
earlier Tue, or later Wed, the severe threat would increase. That
said, it looks like a heavy rain threat will accompany the likely
storms. Warm cloud depths are climbing to near 4 km while pws near 2
inches. Add in the nose of the low level jet/850 moisture transport,
and the setup, and 1 to 2 inch per hour rainfall rates look

High pressure looks to build in for the later half of the work week,
with a shower/storm threat returning for the weekend as the GFS/EC
suggest a few shortwaves could spin across the region.

For temperatures, with the passage of the front Wed, look for a
drop back to cooler than normal for late August. Expect highs
mostly in the 70s with lows in the 50s.


.AVIATION...(For the 00Z TAFS through 00Z Monday evening)
Issued at 618 PM CDT Sun Aug 21 2016

High pressure at the surface, currently centered over Missouri,
will move east into the Ohio River Valley through Monday. Some
concern for fog overnight with light south winds expected on the
back side of the surface ridge axis and with clear skies. However,
the 21.18Z NAM forecast soundings show the winds just above the
surface will increase rapidly and should become too strong to
allow the fog to form and there is not a deep enough layer of
moisture to allow a low stratus deck to form. The gradient will
become tight enough Monday afternoon for the south winds to gust
into the 20 to 25 knot range.


.ARX Watches/Warnings/Advisories...


LONG TERM....Rieck
AVIATION...04 is the U.S. government's official web portal to all federal, state and local government web resources and services.