Area Forecast Discussion
Issued by NWS La Crosse, WI

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FXUS63 KARX 200432
AFDARX

Area Forecast Discussion
National Weather Service La Crosse WI
1132 PM CDT Mon Jun 19 2017

.UPDATE...
Issued at 845 PM CDT Mon Jun 19 2017

The forecast has been updated to increase shower and thunderstorm
chances late tonight into Tuesday morning. Convective allowing
mesoscale models are showing very good agreement in bringing
showers and embedded thunderstorms into the region mainly after 4
am tonight. Looking upstream across northwest Minnesota into
eastern North Dakota, a couple of broken lines of showers/storms
noted. The leading line has been producing wind gusts of 30 to 40
kts and some lightning. This leading line should continue to
dissipate with the loss of daytime heating. So, we will have to
wait for the main shortwave to move into the area to see the
showers and storms really blossom late tonight into Tuesday
morning. Also, the NAM is showing some decent frontogenesis in the
900-600 mb layer associated with the wave. Given the forcing and
good forecast model agreement, decided to increase precipitation
chances into the 70 to 80 percent range across much of southeast
Minnesota into west central and southwest Wisconsin. Have kept
thunderstorm coverage at about 20 percent, but this will likely
have to be increased if trends continue. The main hazards from any
storms will be lightning. Not seeing much CAPE to support hail
growth.

&&

.SHORT TERM...(This evening through Tuesday)
Issued at 312 PM CDT Mon Jun 19 2017

Diurnally driven thunderstorms with some upper level support from
weak short-waves in northwest flow aloft will continue late this
afternoon into the early evening. With upwards of 500 J/kg of
CAPE and cold mid-level temperatures, may see a few storms
produce small hail and gusty winds, especially for areas south of
Interstate 90. Storms should dissipate soon after sunset.

A stronger Canadian short-wave will drop south across the area
tonight into Tuesday morning. This will result in another round
of showers and some isolated thunderstorms from around 09Z tonight
through the noon hour on Tuesday. For this period, increased POPs
into the low-end likely category for areas mainly north of a line
from Dodge Center, MN to Platteville, WI. Some areas could pick up
a quick quarter inch of rain.

Surface high pressure builds across the region Tuesday afternoon
in the wake of the departing wave aloft. This will allow skies to
clear with a return to dry conditions. Temperatures Tuesday will
range from the upper 60s across north central WI to the upper 70s
across portions of northeast IA.

.LONG TERM...(Tuesday night through Monday)
Issued at 312 PM CDT Mon Jun 19 2017

Much of Wednesday now looks dry as an elevated warm layer moves
over the forecast area, providing a thermal capping inversion
between 800 and 700 hPa. At the same time, southerly return flow
across much of the plains will result in an impressive instability
plume across the eastern Dakotas and NE into western MN/IA by
Wednesday afternoon. This plume folds over into a southwest-
northeast orientation Wednesday night into Thursday morning ahead
of an eastward advancing cold front. Amount of available
instability across the forecast area is still somewhat uncertain,
but with 0-3 km shear increasing to between 30 to 40 kts, a few
stronger to severe thunderstorms are possible, especially for
areas west of the MS River. This matches well with the SPC Day 3
convective outlook and bears watching over the next 24 to 48
hours.

12Z model suite then shows the aforementioned cold front stall out
in the vicinity of the IA/IL/WI border region on Thursday.
Placement of front will be critical in areas of greatest
instability and additional thunderstorm chances, but for now, it
looks like there may be additional storms Thursday and Thursday
night mainly south of I-90.

While much of Friday looks dry under the influence of high
pressure, on and off shower chances return for the weekend as a
series of ill-resolved short waves moves across the region. Could
see a few isolated thunderstorms each afternoon, but overall
available instability looks very weak.

Warmest temperatures of the week will be Wednesday/Thursday with
highs in the mid 70s to lower 80s. However, cooler values return
for the weekend with most areas struggling to top the mid 70s.

&&

.AVIATION...(For the 06Z TAFS through 06Z Tuesday night)
Issued at 1131 PM CDT Mon Jun 19 2017

Scattered showers and possibly a thunderstorm or two will move
across the TAF sites after 10Z Tuesday morning. This activity is
high based, with cloud bases only expected to lower to around 6kft
under the rain showers. Brief localized MVFR conditions are
possible if the showers become more widespread. Otherwise, look
for the showers and isolated storms to exit the region by the mid
to late morning hours. Scattered cumulus and maybe an isolated
shower are possible through early afternoon then clouds will
gradually diminish as high pressure builds in.

&&

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

$$

UPDATE...Wetenkamp
SHORT TERM...Rogers
LONG TERM...Rogers
AVIATION...Wetenkamp



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