000
FXUS63 KFSD 262308
AFDFSD

Area Forecast Discussion
National Weather Service Sioux Falls SD
608 PM CDT Mon Jun 26 2017

.SHORT TERM...(This evening through Tuesday)
Issued at 353 PM CDT Mon Jun 26 2017

Quiet weather conditions will continue to prevail as a surface ridge
moves southeastward into the area. As the ridge axis moves out of
the area, increasing southerly winds will become more dominant after
midnight. With tightening pressure gradient on the backside of
surface high, increasing windy conditions are expected over the area
from west to east. Tonight will be mostly clear and chilly for this
time of year. Lows will range from the upper 40s east of I-29, which
is where the lightest winds will prevail, and in the lower 50s west
where breezy to windy southerly flow are expected.

Increasing southerly surface winds will bring more moisture, and
clouds across the area on Tuesday, but dry conditions will prevail,
at least, through the evening. The main impact on Tuesday will be
strong winds from 20 to 30 mph, gusting to 35-40 mph. The max wind
gusts are expected west of James River. With 850mb temperatures
ranging from 15 to 22 C, a warm day is on tap. Highs will generally
be from the upper 70s near 80, east of I-29, and in the mid to upper
80s west.

.LONG TERM...(Tuesday night through Monday)
Issued at 353 PM CDT Mon Jun 26 2017

Primary focus for this forecast will be on thunderstorms and
associated severe threat moving across the area Tuesday night into
early Wednesday. Axis of instability still works into areas west of
the James River Valley by 00Z, but this area remains moderately
capped with better forcing from mid-level wave/low-level boundary
still west of the Missouri River. GFS/Canadian are a bit faster with
pushing the upper support eastward, so will have to watch this for
possible earlier development, but with the cap in place, later
timing seems more reasonable. These features approach south central
South Dakota through the early-mid evening, so anticipate potential
for storms ramping up west of the James River by 03Z, then tracking
eastward across the forecast area through the overnight hours.

As far as severe potential, greatest threat still looks near/west of
the James prior to 06Z. Will still have a weak cap to overcome, and
as the evening progresses, storms more likely to become elevated in
nature, which will limit effective shear. That said, soundings in
areas of our far west depict steep mid-level lapse rates with modest
effective shear of 30-40kt, which should support potential for large
hail. Lapse rates become less favorable farther to the east thanks
to warming aloft, so threat of large hail should diminish as storms
approach the I-29 corridor late evening/toward 06Z. Dry mid-levels
initially should also support damaging wind threat, but this also
diminishes by late evening as the storms track east. While isolated
severe cannot be ruled out as the MCS tracks into northwest Iowa or
southwest Minnesota later Tuesday night, greater risk for organized
severe remains focused across our western third and will maintain a
mention of severe along and west of the James River Tuesday evening.

As of now, models in pretty good agreement showing the surface
boundary very near or out of our far east by peak heating Wednesday
afternoon, with axis of instability and higher shear southeast of
the forecast area. This should limit the potential for additional
thunderstorm development through the afternoon/evening, though will
hang on to a low chance in our far east during the afternoon for
now, to allow for timing adjustments once evolution of convection
tonight/early Wednesday becomes more clear. Should see a mild start
to the day thanks to lingering moisture/stout southerly flow, but
temperatures will be somewhat slow to recover in the wake of the
morning convection, and highs in the upper 70s-80s look reasonable.

For Thursday/Thursday night, a northern stream trough digs down into
the northern Plains. Our midweek frontal boundary stalls over the
central Plains to mid-Mississippi Valley, so deeper moisture will
remain locked well to our south through Thursday evening, possibly
sneaking back as far north as northwest Iowa later Thursday night.
So while we should see the potential for showers or thunderstorms,
moisture will be limited over much of the area and will keep pops in
the chance range for now.

Precip chances could linger into Friday, depending on how long the
upper trough lingers across the region, but otherwise transitioning
to a little drier pattern with only spotty chances at best as we
head into July on Saturday. Another modest wave slated to track
through the region early next week, though timing is inconsistent
among the models, so periodic low chances Sunday-Monday. As far as
temperatures, daytime readings look to be on the cool side of normal
late this week into early next, but not nearly as cool as we saw
this past weekend.

&&

.AVIATION...(For the 00Z TAFS through 00Z Tuesday evening)
Issued at 606 PM CDT Mon Jun 26 2017

VFR through the period. Patchy fog possible along the MO River
from about Tyndall towards KSUX from about 10z through 13z.
Confidence too low to include in TAF.

&&

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

$$

SHORT TERM...05
LONG TERM...JH
AVIATION...08