Area Forecast Discussion
Issued by NWS La Crosse, WI

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FXUS63 KARX 240403
AFDARX

Area Forecast Discussion
National Weather Service La Crosse WI
1103 PM CDT Fri Sep 23 2016

.SHORT TERM...(Tonight through Monday Night)
Issued at 239 PM CDT Fri Sep 23 2016

Ready for some fall weather? Looks like we`re heading that way into
early next week, though first we need to deal with the potential for
some additional unwanted and unneeded rainfall into the weekend.
Early afternoon analysis places a surface warm front draped just to
our south now into central Iowa, with broad low level ridging
dominating from northern Ontario down through the Upper Miss
Valley/Great Lakes. Classic setup for some low stratus development
with shallow cooler air undercutting moisture aloft (with an
elevated warm front sitting just to our north) and indeed we see
quite a bit of that across the entire region, along with some
earlier drizzle noted in spots. Off to the west, quite the deep
upper trough continues to work toward the Four Corners region, with
that feature expected to work east through the Plains and eventually
Mississippi Valley with time toward Monday, dragging in a
respectable surface cold front. In advance of and along that
feature, do anticipate seeing a round of rainfall later Saturday
into Sunday which is just not good news though there remain some
questions about how much precipitation will occur.

First things first, deepening southerly flow and an uptick in low to
mid level warm advection ascent overnight may prove sufficient to
bring a smattering of mainly light showers just clipping far
northwest and northern areas, mainly north of I-94 through the
evening. Stronger convection should hold west within the best
moisture advection and northward-bowing better instability toward
the Twin Cities. Later this evening and overnight, can envision
another bout of some drizzle as our low level flow shifts more
southeasterly with time, with current late afternoon obs already
showing some visibility values in the 2SM range across Iowa. Should
see another northward expansion of stratus as well, with much of
that stuff probably sticking around for a good chunk of Saturday,
perhaps slowly mixing out from south to north during the afternoon.

Approach of the upper trough and associated cold front/stronger low
level convergence should be more than enough to fire off a band of
showers and storms to our west on Saturday, with that activity
marching eastward into Saturday night and Sunday morning. One good
thing of note is this system does look more progressive than modeled
over the past few days, suggesting overall rainfall amounts may not
get out of control. However, strong dynamics and increasing MUCAPE
values toward 1000+ J/kg definitely argue for convective heavier
rain potential for a time, with a general half to one inch of
additional rainfall possible. Given how incredibly wet we already
are with ongoing flooding in many areas, have to be concerned
about any additional water, with 1 hour flash flood guidance only
around an inch in many areas. Any rain that occurs will simply run
off and may cause additional rises on streams and rivers and also
slow some river crests, especially if some spots happen to pick up
in excess of an inch.

Still looking sharply cooler later Sunday into Monday as upper
troughing works across the region, with some chance for diurnally
enhanced showers into Monday afternoon within broad cyclonic flow
across the region. Still not sure just how amplified the upper
trough will be across our local area, with some discrepancies among
guidance (ECMWF notably less wrapped up than other guidance over the
past 36 hours), though the basic pattern would support at least some
risk for showers during the Sunday night-Monday stretch. Certainly
much cooler with highs Monday potentially stuck only in the 50s for
some areas pending cloud trends.

.LONG TERM...(Tuesday through Friday)
Issued at 239 PM CDT Fri Sep 23 2016

Upper troughing to start the period is progged to be replaced by
building ridging into mid and late week, with a return to some much
needed and well deserved dry weather for much of that period. Recent
runs of the GFS are a little faster to bring a wave through that
ridge toward Friday with maybe a small risk for additional rainfall,
but not ready to bite on that idea just yet given the highly
amplified nature of the upper ridge and likelihood for any
shortwaves to be shunted to the north well west of the area.
Instead, hopefully we will get several days (at least) to dry out
with quite seasonable conditions prevailing for late September.

&&

.AVIATION...(For the 06Z TAFS through 06Z Saturday night)
Issued at 1103 PM CDT Fri Sep 23 2016

The front across Iowa has remained nearly stationary this evening
with the MVFR to VFR ceilings still in place north of the front.
Ceilings have gone down to IFR over portions of southeast
Minnesota into northeast Iowa and expect that this will overspread
KLSE overnight as well. These IFR ceilings should then remain over
both airports into Saturday morning before lifting up to MVFR with
some daytime heating. The 24.00Z NAM forecast soundings suggest
the ceilings will then remain MVFR into Saturday night while some
of the aviation guidance is suggesting these will break up with
VFR ceilings for late afternoon into the evening. For now, will
continue with the pessimistic forecast and keep the MVFR ceilings.
A cold front will begin to approach from the west Saturday evening
with a line of showers and storms along it. The bulk of this
activity should be after 25.06Z but did bring in a VCSH late
Saturday evening for KRST in case the faster solution of the
23.12Z hi-res ARW is correct.

&&

.HYDROLOGY...
Issued at 239 PM CDT Fri Sep 23 2016

River flooding continues across much of northeast Iowa...southwest
Wisconsin and parts of southeast Minnesota. A cold front will spread
another round of showers and thunderstorms across the area Saturday
night into Sunday. Rainfall amounts of a half to one inch will be
possible. This could delay some crests on area rivers.
However...rivers should crest over the next couple of days. For
specific river forecast refer to the latest flood statements.

&&

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

$$

SHORT TERM...Lawrence
LONG TERM...Lawrence
AVIATION...04
HYDROLOGY...DTJ


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