947 
FXUS63 KFSD 031136
AFDFSD

Area Forecast Discussion
National Weather Service Sioux Falls SD
636 AM CDT Mon Jul 3 2017

.SHORT TERM...(Today and Tonight)
Issued at 358 AM CDT Mon Jul 3 2017

A few areas of concern regarding the forecast for today and tonight. 
We have a broad area of isentropic lift nosing across the Missouri 
Valley this morning. Light east to southeast low level flow today 
will tap into increased moisture through the day, with dewpoints 
expected to rise to 60 to 70 degrees by afternoon for much of the 
forecast area. Meanwhile, a weak shortwave is crossing the Wyoming 
border into western SD early this morning, and is expected to follow 
a slightly more northerly track than previous model runs suggested. 

Ongoing Scattered showers and thunderstorms will continue to track 
east, but so far this morning, activity has been struggling to move 
into south central SD. Models generally fizzle out this activity 
this morning as it moves eastward, however cannot rule out some weak 
isolated showers or thunderstorms to survive into our western 
border. Meanwhile some very isolated shower or thunderstorm activity 
to pop up near the isentropic lift along our southern border later 
this morning into the afternoon near the Missouri Valley into the 
highway 20 corridor. With the leading shortwave tracking into south 
central SD this afternoon, and aided by the heat of the day, 
activity may reinvigorate enough across southeast SD and the highway 
20 corridor for scattered thunderstorm mention. CAPE profiles remain 
quite skinny, while shear is once again fairly weak, especially in 
the mid levels. Severe weather is unlikely, but a few stronger 
storms may have small hail, heavy downpours, and gusty winds. 

Additional activity is expected to develop late evening into the 
overnight hours as the main shortwave finally digs across southeast 
SD and the low level jet cranks up along the I-29 corridor by 
midnight. Showers and thunderstorms will spread eastward across the 
forecast through the overnight hours. Precipitable water values are 
pretty high at around 1.75, so could see some heavy rainfall with 
this activity.

.LONG TERM...(Tuesday through Sunday)
Issued at 358 AM CDT Mon Jul 3 2017

The upper level trough/shortwave continues to slide across the 
Northern Plains on Tuesday, keeping thunderstorm chances going 
into the evening. Not expecting it to rain through the entire day,
as there will probably be a lull in the activity by mid morning, 
before heating and increasing instability results in redevelopment
in the afternoon. The better chances for this still appears to be
from the I-29 corridor and eastward. There will be plenty of 
instability around by Tuesday afternoon with ML CAPE values 
running 1500-2000 J/KG, but shear is on the weaker side, though 
cannot completely rule out an isolated severe storm with large 
hail/damaging winds in the afternoon and early evening. Highs on 
Tuesday will be mainly 80s, though touching on 90 over south 
central SD.

By Wednesday the upper level trough pulls off into the Mississippi 
Valley with decreasing thunderstorm chances across our area. In 
conjunction with that, an upper level ridge over the western CONUS 
begins to nudge eastward. This will be reflected in temperatures as 
highs climb into the mid 90s over portions of the James River 
Valley/south central SD.

On Thursday upper level heights continue to rise with the thermal 
ridge sliding across the region and 850 mb temps in the range of 25 
to 30C. With that, stayed on the high side of guidance which will 
bring highs into the 90s over most of our area, closing in on 100 
over south central SD.

For the end of the week, upper level energy drops out of Canada into 
the western Great Lakes/Mississippi Valley region, dampening the 
ridge over our area and bringing temperatures back into the 80s for 
Friday and Saturday. It looks to remain dry both days. May begin to 
see more warming by next Sunday as the ridge begins to build back 
into the region.

&&

.AVIATION...(For the 12Z TAFS through 12Z Tuesday morning)
Issued at 630 AM CDT Mon Jul 3 2017

Main concern will the potential for isolated to scattered
thunderstorms developing this afternoon along the Missouri Valley
and into south central SD. Right now it looks like this activity
is too spotty for mention in the HON or SUX TAF. Later this
evening and tonight, additional storms are expected to develop in
south central SD and spread east through the overnight hours. Have
added VCTS and VCSH mention to the TAFs for this evening and
tonight. Models suggest that with this activity late tonight,
MVFR ceilings will become prevalent at times. Expect the 
potential for reduced visibility and ceilings in thunderstorms as 
well.

&&

.FSD WATCHES/WARNINGS/ADVISORIES...
SD...None.
MN...None.
IA...None.
NE...None.
&&

$$

SHORT TERM...
LONG TERM...JM
AVIATION...