Area Forecast Discussion
Issued by NWS La Crosse, WI

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418
FXUS63 KARX 230446
AFDARX

Area Forecast Discussion
National Weather Service La Crosse WI
1146 PM CDT Fri Sep 22 2017

.UPDATE...
Issued at 704 PM CDT Fri Sep 22 2017

As of 7 PM, temperatures across the area have fallen below 90
degrees. Temperatures and heat index values will continue to fall
with loss of heating through the evening, allowing the Heat
Advisory to expire.

&&

.SHORT TERM...(Late This Afternoon through Saturday)
Issued at 233 PM CDT Fri Sep 22 2017

Latest upper-air analysis shows our area on the western edge of
strong ridging over the eastern CONUS, while a closed low was
spinning over the Intermountain West. A cluster of strong to severe
thunderstorms attached to a mid-level wave has stayed just off to
our north, moving along a west-east oriented stationary front.
Underneath the ridge, strong southerly flow has brought unseasonably
warm and humid air into the region. Temperatures have already risen
into the 90s, and combined with dewpoints around 70F, heat indices
are approaching 100. A Heat Advisory is in effect until 7 PM this
evening for much of the area.

Not much change in the upper-air pattern heading into Saturday as
the western trough very slowly begins to make its way east. 925 mb
temperatures are progged to be around 1-2C cooler than today, which
will still give us highs in the upper 80s and lower 90s.

.LONG TERM...(Saturday Night through Friday)
Issued at 233 PM CDT Fri Sep 22 2017

The season may officially be autumn now, but the weather won`t
reflect it for a few more days. Stubborn blocked-up flow regime over
much of the CONUS will remain through the weekend, with broad (and
impressive) upper ridging in place across much of the eastern
states, courtesy of tropical cyclones Jose and Maria meandering off
the East Coast. Meanwhile, deeper troughing over the western CONUS
will remain intact, with the "battle ground" centered over the
Plains where a nearly stationary frontal boundary will maintain
periods of precipitation to our west. While today`s highs are likely
to be the warmest, Sunday still looks quite mild with highs pushing
the low 90s once again in spots as 925mb temps hold around 20-25C
during peak heating.

Big changes still on track to arrive into much of next week with
persistent hints the past few days that the western CONUS trough
will finally break through the eastern ridge. During the time of
transition toward the early work week, a slow advancing cold front
should bring at least some risk for rainfall to the area, especially
later Monday into Tuesday per current trends, before things dry out
and cool down significantly into late week as upper troughing and
low level ridging dominate the region. With that said, there is some
small risk that a few showers could be realized during the late week
with any smaller hard-to-time shortwaves dropping through the mean
trough, but by far the bigger impact will be a return to much more
fall-like conditions through the work week.

&&

.AVIATION...(For the 06Z TAFS through 06Z Saturday night)
Issued at 1146 PM CDT Fri Sep 22 2017

Multiple clusters of thunderstorms have developed this evening
across eastern SD into central and northern MN, but all convective
activity will remain north and west of TAF airfields through the
period. For KRST/KLSE, low-level wind shear will be a concern
through 23.09Z to 23.10Z with southwest winds in the 1500 to 2000
ft agl layer between 35 and 40 kts. Thereafter, winds aloft
weaken. Surface winds will remain from the south through the
period, generally under 15 kts, but some gusts to 20 kts are
possible at KRST Saturday afternoon. For the most part, skies will
be mostly clear/sunny, although some scattered cumulus are
possible Saturday afternoon in the 4000 to 5000 ft agl range.

&&

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

$$

UPDATE...Rogers
SHORT TERM...Hollan
LONG TERM...Lawrence
AVIATION...Rogers



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