FXUS63 KFSD 171137

Area Forecast Discussion
National Weather Service Sioux Falls SD
637 AM CDT Tue Jul 17 2018

.SHORT TERM...(Today and Tonight)
Issued at 341 AM CDT Tue Jul 17 2018

Subtle shortwave swinging across southern SD tonight has led to an
area of persistent slow moving thunderstorms in Gregory County this
morning. Expect these to diminish shortly as available instability
in the area is used up, but not before some locally heavy rainfall
amounts accumulate across Gregory County.

A tad warmer and more humid today across the CWA. Light
southeasterly winds will get going this morning and continue through
the day as the well advertised wave begins to eject off the northern
Rockies. Warm air aloft should keep a lid on any showers or storms
save for our far southwestern zones.

Tonight, with a light breeze and increasing sky cover as the wave
approaches, have held lows slightly above consensus. PoPs will trend
upward as the night goes on.

.LONG TERM...(Wednesday through Monday)
Issued at 341 AM CDT Tue Jul 17 2018

Main period of focus in the entire forecast package arrives
Wednesday through Thursday morning. Guidance agrees on a classic
synoptic evolution with ridge firmly in place over the
southwestern CONUS and a deepening closed low off the coast of BC
driving a zonal jet streak aloft over OR/ID/MT/WY/SD. The exit
region of this jet will serve to deepen the lead wave, forcing
ascent across the upper Midwest. The slow motion of this lead wave
could lead to heavy rainfall as forcing for ascent is present
across the CWA for an extended period of time. Have bumped up QPF
slightly using a mix of Superblend and WPC values with a
widespread 1 to 2 inches of rain expected and some locally heavier
amounts possible as well.

Highest chance for severe weather during the active Wednesday-
Thursday period will be early Wednesday afternoon before the
atmosphere becomes too worked over as the rain continues. Difficult
to truly assess parameters given the amount of convective
contamination seen in progged soundings, but marginal shear and
instability look to be present in our southwestern zones, so will
have to keep an eye on things for now.

Friday night into Sunday morning look to be pretty nice as ridging
builds in aloft, allowing for minimal chances of precipitation. The
remainder of the extended forecast features near normal temperatures
and spotty chances for precipitation.


.AVIATION...(For the 12Z TAFS through 12Z Wednesday morning)
Issued at 634 AM CDT Tue Jul 17 2018

Quiet weather is expected over the next 24 hours with light
afternoon winds. High level clouds over the region this morning
will quickly dissipate as storms south of KSUX continue to weaken.




SHORT TERM...Ferguson
LONG TERM...Ferguson
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