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 46 47 48 49 50

FXUS63 KARX 291745

Area Forecast Discussion
National Weather Service La Crosse WI
1245 PM CDT FRI JUL 29 2016

Issued at 1245 PM CDT Fri Jul 29 2016

Another day of pesky lower clouds and some showers/few storms,
especially southern half of the area. The culprit remains slow
moving/nearly cutoff low pressure meandering eastward toward
northern IL at this hour. Weakish warm advection ascent and
moisture band wrapping north of the circulation center remains
just enough to release some very skinny instability (elevated CAPE
only around 300 J/kg). Similar to yesterday, storm motion remains
only around 5-10 knots, with higher PWAT values and deep warm
cloud depths supporting some localized heavy rains in spots. Don`t
see that setup changing much through late afternoon, with the main
rain band into northeast IA and toward Crawford/Richland Counties
in WI nearly stationary or slowly pivoting southward. North of
there, lower stratus is filling in westward toward the Mississippi
River but with some sunshine far northern spots likely to fill in
with some diurnal cumulus for a time.


.SHORT TERM...(Today through Sunday)
Issued at 231 AM CDT Fri Jul 29 2016

Water vapor satellite early this morning showed a short wave
trough over the Nebraska/Iowa border, another over central South
Dakota with a third over Montana. All these waves are expected to
move rather slowly to the southeast today taking a track across
Iowa into Illinois. While these waves will not produce much
forcing for the local area as they move by to the south, they will
help to hold a surface trough essentially stationary across the
southern sections of the forecast area. Weak moisture convergence
in the low levels will be focused on this surface trough and with
some vertical motion along the trough from the passing waves, this
should be enough to generate some scattered showers and possibly a
rumble or two of thunder during the afternoon across the southeast
sections of the forecast area. These showers should taper off this
evening with a dry overnight expected as the short wave troughs
move east of the region. However, by Saturday, another short wave
trough will be moving in from the northwest that could generate
some more showers as the surface trough will still be in the area.
Once the Saturday short wave trough moves by the area, upper level
heights will start to build which should lead to a dry Sunday.

.LONG TERM...(Sunday night through Thursday)
Issued at 231 AM CDT Fri Jul 29 2016

The weak upper level ridging that builds in over the area Sunday
will quickly get flattened starting Sunday night. An upper level
low should be in place over central Manitoba by this time with a
short wave trough coming through the flow underneath the low which
will flatten the ridge. This will lead to a chance for some
showers and storms from late Sunday nigh into Monday night. The
upper level ridge tries to rebuild over the area starting Tuesday
but does so just enough that additional short wave troughs topping
the ridge will be pretty close to the area. This will keep the
chance of showers and storms in the forecast for most of next week
with some higher chances Wednesday night into Thursday as a cold
front moves into the area.


.AVIATION...(For the 18Z TAFS through 18Z Saturday afternoon)
Issued at 1245 PM CDT Fri Jul 29 2016

Lower level MVFR clouds continue to build back westward toward LSE
and will likely remain through much of the afternoon with ceilings
flirting with the 2500-3500 foot range while RST stays VFR with
some higher based cumulus development. Cloud cover into tonight
remains a tough call as the low level flow turns more easterly.
Given how much cloud cover is upstream of us at the moment,
suspect there will be some thicker clouds drifting through the
region overnight, but mainly of the VFR variety. However, cloud
cover will highly dictate the potential for some fog overnight.
For the moment, with our expectation of more cloud cover, the fog
threat looks much lower but if skies do clear, then a period of
IFR or lower conditions is very much possible at LSE with moist
conditions and light winds.


.ARX Watches/Warnings/Advisories...


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