Area Forecast Discussion
Issued by NWS Sioux Falls, SD

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FXUS63 KFSD 221730
AFDFSD

Area Forecast Discussion
National Weather Service Sioux Falls SD
1230 PM CDT Sat Jul 22 2017

.SHORT TERM...(Today and Tonight)
Issued at 440 AM CDT Sat Jul 22 2017

Convection very much on the downtrend with stronger cells now
limited to the lower Missouri River valley. Larger scale forcing
will continue to weaken and shift southeast with subtle mid-level
wave, allowing storms to end by shortly after daybreak. With
convective threat ended, the next question to answer is - when will
the heat and humidity break?

Moisture at least partially recycled with the convection overnight,
and flow aloft has brought some degree of drying into the central
portions of SD overnight. However, will still have a slightly
chaotic surface pattern this morning with various convective
residual influences, and moisture will again being to pool
especially east of the James River through the morning hours.
However, mixing should allow a more northwest component to establish
this afternoon, and push a more notable drying into southeast SD as
dewpoint readings mix into the 50s west of the James. Drying will be
slower to occur further eastward, but even will see a gradual drying
kick in during the afternoon.  Afternoon RH will drop to 25 percent
or less west of the James River, but looks like winds will remain
modest enough to limit fire danger to the high category in parts of
the James River valley.  Temperatures will be quite warm, again
above normal from the upper 80s in southwest MN, to the mid 90s in
lower Brule locations.  A few areas of overlapping warmer temps and
higher moisture will mean some heat index values in the mid 90s for
northwest Iowa, still somewhat uncomfortable.  While keeping less
than mentionable, the threat for a rogue storm this afternoon from
the Missouri River valley into areas of northwest Iowa and southwest
Minnesota is non-zero with lingering moisture resulting in some
modest instability, and residual weak boundaries in place. A little
stronger upper support exists toward the lower Missouri River valley
in right entrance of jet streak, but quite a layer of dry air
between near surface and mid to upper levels suggests a challenge
to break any capping.

As stronger wave digs into the northern Great Lakes tonight, will
see the real synoptic push of cooler and drier air fall across the
area with secondary frontal boundary settling into areas south of I-
90 during the evening, and a more invigorated push of cooling for
the night. A few temperatures should dip into the 50s along the
highway 14 corridor, with mainly lower 60s elsewhere.

.LONG TERM...(Sunday through Friday)
Issued at 440 AM CDT Sat Jul 22 2017

Sunday into Monday the upper level jet will dip south across
Minnesota and allow the cooler air to settle south. Weak ridging
will build later Monday allowing warmer temperatures to build back
into central SD. Will continue highs Sunday and Monday of about 80
to 90 with the less humid conditions. Lows will also be more
pleasant from about 55 to 65. Highs closer to 95 will be likely west
of the James on Monday.

As the upper level jet begins to work onto the Plains Monday night
warm air advection in the low to mid levels will bring a small
chance for showers and thunderstorms from central into northeast SD.

Tuesday into Wednesday a marginally agreed upon upper level jet max
will move along the Canadian border into North Dakota with upper
level ridging building behind. This should bring seasonally warm
temperatures to the area and decent chances for showers and
thunderstorms. The better chances should be Tuesday night into
Thursday.

&&

.AVIATION...(For the 18Z TAFS through 18Z Sunday afternoon)
Issued at 1227 PM CDT Sat Jul 22 2017

VFR will be the primary category through the TAF period. It is
very likely that upper end MVFR ceilings will move southward into
southwest MN Sunday morning. However the latest indications are
that these clouds will remain east of KHON and KFSD.

&&

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

$$

SHORT TERM...Chapman
LONG TERM...08
AVIATION...MJ



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