Area Forecast Discussion
Issued by NWS Sioux Falls, SD

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FXUS63 KFSD 240916
AFDFSD

Area Forecast Discussion
National Weather Service Sioux Falls SD
416 AM CDT Sat Jun 24 2017

.SHORT TERM...(Today and Tonight)
Issued at 415 AM CDT Sat Jun 24 2017

The primary concern is chances for thunderstorms this afternoon in
southwestern Minnesota.

Current mid-level and upper level water vapor imagery from GOES-16
shows very strong wave centered near Minot, ND at 07Z.  This wave is
expected to move southeast through day bringing a core of
unseasonably cold air aloft over much of Minnesota. Per WRF-NMM
and NAM soundings, this will result in modest CAPE of 200-300 J/kg
along and east of the Buffalo ridge by early afternoon. With strong
lift combined with this low level instability, expect scattered
thunderstorms to develop during the afternoon east of a line from
Ivanhoe MN to Spirit Lake Iowa. While severe weather is not
expected, there could be a funnel cloud with a couple of these
storms in the updraft phase due to the high low level lapse rates
and a surface vorticity maximum across southern Minnesota this
afternoon. For now will not put into HWO but day shift will want to
examine evolution of low level lapse rates and surface vorticity for
potential of funnel clouds. Otherwise, showers and storms should
move east of the area by 00Z.  Farther to the west skies will be
partly to mostly sunny. It will also be another breezy day with
sustained winds of 15 to 25 mph and gusts approaching 40 mph in the
James Valley. Highs today will be mid 60s to mid 70s. Overnight
skies will rapidly clear and winds will go light. Lows will be in
the 40s...with a few location such as Huron and Sioux City expected
to be within 3 degrees of record lows.

.LONG TERM...(Sunday through Friday)
Issued at 415 AM CDT Sat Jun 24 2017

Sunday not a great deviation from Saturday, other than lacking any
chance for showers.  It will again become breezy to windy, but
primarily for areas near/east of I-29. Diurnal cloud development
should be less - and less developed. Temps unseasonably cool with
highs mainly upper 60s to lower 70s. The chill will return on
Sunday night as surface ridge lingers. While clearing will be
present earlier in the night, will see another jet increase slide
southeast with induced mid-level warm advection starting after
06z. Lapse rates are fairly meager in the mid-levels, and mid-
level moisture depth is only marginal for precipitation, so have
maintained a late night and early morning threat for light showers
mainly through the lower Missouri River valley. Behind wave, high
pressure will again strengthen across the heart of the area for
lighter winds, and a slight moderation in temperatures. With
lingering ridge axis and associated dry air mainly over northwest
Iowa, have tapered back lows Monday night into the mid to upper
40s where it will take much of the night to begin to develop a
southerly component. Further west, winds will become more steady
southeast and resulting in lower to mid 50s for lows.

For the most part, Tuesday appears to be a dry and warmer day as
upper ridge shifts temporarily across the area, but eastward advance
of steeper mid-level lapse rate gradient/moisture and weak wave
moving over ridge suggests perhaps an accas field developing across
southeast SD by later morning and spreading east through the
afternoon where around 8 C/km or more becomes present. GFS too
aggressive in return of near-surface moisture, but consensus in
models that low-level jet will crank up to 45 to 55 knots by evening
which will provide enough moisture increase to potentially generate
a couple thousand MLCAPE and some decent low-level weighted deep-
layer shear. Will have a decent capping inversion, but potential to
weaken by ACCAS induced cooling and eventually breaking down with
cooling aloft due to approach of upper wave on Tuesday night. There
should be enough ingredients for strong to severe storms in the area
on Tuesday night, perhaps lingering into Wednesday morning as low
level jet veers toward Minnesota. Cold front will follow on
Wednesday, but uncertain on recovery behind overnight convection and
lack of stronger upper support will mean lower PoPs at best for the
moment focusing more so on northwest Iowa by late day. Potential for
some readings around 90 degrees in wake of convection through the
lower James and western Missouri River corridor.

Weak wave will push across the northern plains on Thursday. With
expectations that main frontal band will be shoved well south of the
area by Thursday, as well as the bulk of instability and deeper
moisture, would expect dynamics associated with upper jet entrance
draped across South Dakota to be associated with mainly mid-based
showers and thunderstorms with lesser overall coverage. Another weak
wave around Friday, but again with larger instability potential tied
up well south, would only be a chance of showers/isolated
thunderstorms with little severe threat at this point as temps
settle back to a bit below normal.

&&

.AVIATION...(For the 06Z TAFS through 06Z Saturday night)
Issued at 1047 PM CDT Fri Jun 23 2017

VFR conditions are expected through the TAF period. Breezy
northwest winds with gusts to 25 kt return Saturday mid morning
through early evening.

&&

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

$$

SHORT TERM...Schumacher
LONG TERM...Chapman
AVIATION...



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