Area Forecast Discussion
Issued by NWS Sioux Falls, SD

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FXUS63 KFSD 180353

Area Forecast Discussion
National Weather Service Sioux Falls SD
1053 PM CDT Thu May 17 2018

.SHORT TERM...(This evening through Friday)
Issued at 309 PM CDT Thu May 17 2018

Isolated showers and thunderstorms continued into the early
afternoon west of the James River. This appeared to be consistent
with the eastern edge of the EML and some very weak
forcing/instability based around 7-8kft. This bit of mid level
moisture and instability look to continue through late afternoon
before drying out. Some hint that the the low and mid level winds
will back late this afternoon and evening as a mid and upper level
wave lifts northeast into western ND. This will likely keep the
brunt of new development tonight to the west of the Missouri River.
After about 6z some of the showers and thunderstorms may propagate
into central SD and get close to Interstate 29 as the low and mid
level winds turn a bit more south to southwest. With stronger winds
and more cloud cover lows will be mild in the upper 50s to lower

There may be a bit of a lull late morning into early afternoon
before the chances for showers and thunderstorms increase again late
Friday afternoon into Friday evening. Will keep the chance for rain
and thunderstorms generally west of Interstate 29. The chance for
any severe weather continues to be low as the mid and upper level
lapse rates are not nearly as steep as today. But with weak winds
slow storm motion will be possible with localized heavy rainfall
possible. Highs will still be warm, but not quite as warm as the
past couple of days.

.LONG TERM...(Friday night through Thursday)
Issued at 309 PM CDT Thu May 17 2018

The axis of moisture and instability shifts east and all but parts
of northwest IA should see a decent chance for rainfall and a few
thunderstorms Friday night. The main threat from these thunderstorms
should be lightning and heavier rainfall but at this time not
anticipating any widespread heavy rain concerns. Plus the better
chance for heavier rainfall will likely come west of the James River
where there is a little less impact from heavy rainfall. Closer to
Interstate 29 the chances will start to drop off but do expect at
least some scattered activity by afternoon as the low level
thermal/moisture ridge moves over Interstate 29. With the increase
in clouds and a cool front coming in from the north temperatures
will be cooler. Highs in the 70s in northwest IA and 55 to
65 elsewhere.

Saturday night into Sunday will include some higher chances for rain
and thunderstorms but again the chance for severe is pretty low.
There is also some room for error with a wobbling upper level low to
the south expected to lift north. If this low does not wobble north
the chances will decrease a bit. Right now banking on some rainfall
and a lot of clouds so highs in the 60s for everyone. If a little
more cool air and rain than expected there is a decent chance for
highs in the 50s.

Monday through Thursday will see temperatures more in line with the
seasonal normal, back into the 70s. While early week will see some
ridging aloft bringing an increased chance for dry conditions, the
models are hinting at some troughing mid week and will need to have
a chance for showers and thunderstorms in the forecast.


.AVIATION...(For the 06Z TAFS through 06Z Friday night)
Issued at 1050 PM CDT Thu May 17 2018

A line of thunderstorms with strong winds will move through KHON
during the early morning hours on Friday. Sites in south central
South Dakota will see periods of moderate to heavy rain as this
line moves through. As these storms approach the I-29 corridor
Friday morning, they will continue to weaken, but numerous rain
showers with a few embedded thunderstorms will still be a threat
west of KFSD. South winds persist for most of the region, becoming
gusty a couple hours after sunrise. Another round of
thunderstorms is likely to develop Friday evening across the




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