Area Forecast Discussion
Issued by NWS La Crosse, WI

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FXUS63 KARX 200735
AFDARX

Area Forecast Discussion
National Weather Service La Crosse WI
230 AM CDT Sun May 20 2018

.SHORT TERM...(Today through Tuesday)
Issued at 230 AM CDT Sun May 20 2018

Latest watervapor satellite imagery highlighting an upper level
shortwave across the central plains-ia, with various curls in the
flow spinning across southern parts of the region. The upper level
forcing was having a healthy hand in the ongoing convection that
stretched from ia into southern wi.

Meso models gradually weaken/diminish the area of showers as the
morning wears on and as the the upper level energy shears out.
Mostly the pcpn holds south of I-90 as strong drying persists in the
north (900-800  mb td depressions near 20 C later this afternoon).
Parent shortwave trough eventually gets a nudge east later
tonight/Mon which should result in a smattering of more light
showers. Weakly forced, no instability to speak of, and likely minor
qpf.

Temperatures are going to take a tumble for the next couple days,
thanks in part to widespread clouds and the scattered showers.
Warmest areas today will be north of I-94 where sunshine is more
likely.

.LONG TERM...(Wednesday through Saturday)
Issued at 230 AM CDT Sun May 20 2018

The suite of models continue to trend toward inching an upper level
shortwave trough (maybe more of an mcv) eastward from the plains tue
night, sliding it across what`s likely a west-east sfc boundary
hanging out somewhere near the ia/mn border. Should be an area of
showers/storms with the forcing, but as it moves east, it moves away
from the main branch of low level moisture transport and the better
CAPE pool. Plus, it will have to contend with a drier atmosphere in
residence across WI and a rather weak, ridging flow a loft. How much
the expected convection will hold together as it advances east might
be the biggest question. Feel there should be a good shot for
showers and a few storms west of the Mississippi River, and likely
diminishing in coverage as they move east. Will sketch out the pcpn
chances to reflect that.

The ridge will gradually edge to the east toward the end of the work
week as a shortwave trough in the northern branch of the upper level
flow drops southeast from Canada. The EC and GFS spin this across
the Upper Mississippi River Valley Friday night, driving it into the
eastern great lakes later on Sat. Some low level moisture transport
to help fuel showers/storms. SBCAPEs overdone in the GFS due to an
overly rambunctious sfc dew point, but should be at least
weak/marginal instability to help aid convection. Shear still looks
weak.

As for temperatures, look for a rebound as the weak ridging a loft
and return to a southerly flow pulls milder air back into the
region. Highs expected to be 5 to 10 degrees above the late May
normals.

&&

.AVIATION...(For the 06Z TAFS through 06Z Sunday night)
Issued at 1028 PM CDT Sat May 19 2018

Weak upper level low pressure just to our south will slowly spin
northeast and weaken through the coming day, maintaining widespread
cloud cover mainly in VFR range but with some potential for MVFR
ceilings at times to work in from the east overnight. Ahead of that
feature, some showers are very much possible at LSE and RST
overnight and into Sunday morning, though confidence in how
widespread they will be remains low. Will maintain a "vicinity"
wording for now but will have to watch trends as some briefly
heavier showers can`t be ruled out. Will also have to watch the
northern extent of cloud cover by later tomorrow as drier air erodes
the northern edge of the cloud deck, with the potential for LSE to
scatter out while RST likely sits just on the edge, though still
with mainly just VFR ceilings. Winds will be from the east to
northeast, generally 10-15 knots but occasionally higher at RST.

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

$$

SHORT TERM...Rieck
LONG TERM....Rieck
AVIATION...Lawrence


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