Area Forecast Discussion
Issued by NWS Sioux Falls, SD

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000
FXUS63 KFSD 112335
AFDFSD

Area Forecast Discussion
National Weather Service Sioux Falls SD
635 PM CDT Wed Oct 11 2017

.SHORT TERM...(This evening through Thursday)
Issued at 359 PM CDT Wed Oct 11 2017

On the large scale, the area will reside in the short term between a
deep trough across the Pacific northwest and ridge axis building
into the Great behind exiting wave, putting area into a
strengthening southwest flow aloft.  As surface ridge axis across
eastern Minnesota and Iowa pulls away, surface gradient will
continue to increase tonight, and winds settling toward 8 to 15 mph,
perhaps stronger and a bit gusty at times at elevation, will keep
temperatures much milder than the last couple of nights, residing
mainly in the 40s.  Watching potential for some sneaky stratus to
brush through parts of NW IA and SW MN late night into early morning
hours as near surface flow turns more south-southeast and
potentially advects bordering locations of stratus field today. High
res models and especially NAM showing a great potential back toward
I-29 corridor, but unimpressed with handling of some lower cloud
potential and inversion/near surface moisture fields for current
day, so likely will keep a bit more wishy-washy view on potential
for the time being.

As long as the lower clouds fail to substantially materialize,
Thursday, other than the gustier southerly winds, shaping up to be a
decent Autumn day. Should see some wind gusts 20-30 mph into at
least the early afternoon, especially across southwest MN. Plenty of
upper 60s to lower 70s to share, warmest near the James and Missouri
River valley locations. As a wave pushes through the western trough
and lifts north of ND late day, a cold front will push into areas
near/west of the James late afternoon, but not with enough to keep
from warming nicely with the little mixing boost. The front will
continue to slide through the area on Thursday night, with
reinforcement of drier air mass from the north as surface ridge
becomes centered in ND and northern SD by daybreak.

.LONG TERM...(Thursday night through Wednesday)
Issued at 359 PM CDT Wed Oct 11 2017

Right entrance of jet will drag through the area on Friday, but
while there will be some mid-level baroclinicity and moisture to
work with, it will be largely battling the drier air intrusion
below from the north. At most, the period of stronger
frontogenetic forcing (in absence of instability aloft) will
probably top out at a few sprinkles. Closer to stalling surface
boundary and in presence of a little better moisture toward the
southern areas across northeast NE and northwest IA, could see a
little very light measurable rainfall later morning through the
afternoon.

Between systems on Friday night should again return to quiet, with
any clearing being masked again later night by increase in clouds
late as main upper trough energy moves into the central Rockies. The
main precipitation event in the intermediate term will evolve on
Saturday into Saturday evening as the positively tilted trough moves
eastward across the region.  The main lower-level baroclinicity
remains tied up during the period south of the area, while mid- and
upper-level forcing moves across the area.  Low pressure will
develop along this boundary and remain south/east into Saturday
night with the main focus of heavier precip threat. To the north,
precipitation will be much lighter, but still fairly widespread with
the strength of frontogenetic forcing. Just a touch of elevated
instability could combine with strongest forcing Sat aftn to get an
isolated rumble to around the Ida Grove and Storm Lake areas.
Clouds and precipitation will keep readings among the coolest for
the period, mainly mid to upper 50s.

Progression of the trough and orientation suggests a fairly
definitive ending to the precipitation chances on Saturday night.
On the fringes of possibility, if system was to wrap up or come out
with less positive tilt, there would be an outside chance for precip
to linger long enough to perhaps mix with a little snow around
KBKX/KMML before ending, but again anything looks to be quite light
that lingers into Saturday night.

Brisk northwest winds will mix across the area on Saturday night and
continue through at least early Sunday, as low pressure deepens to
the east and stronger cold advection steepens the low-level thermal
profile.  Winds will drop off heading through Sunday as conditions
change to warm advection behind ridge axis, which is expected toward
the SD/MN border by 18z, and through the area by 00z.  Again
somewhat cool for the date, with highs in the 50s.

The first half of the following week will take a turn toward warmer,
dry and downright pleasant as flat ridging takes over on the large
scale with periodic waves focused along the International Border.
Diurnal ranges could be extended a bit with the drier and
periodically downslope component to flow. Highs in the 60s, with
perhaps a few lower 70s will prevail early week, with lows in the
mid 30s to mid 40s.

&&

.AVIATION...(For the 00Z TAFS through 00Z Thursday evening)
Issued at 629 PM CDT Wed Oct 11 2017

VFR conditions will predominate during the TAF period. Only
concerns are potential fog and stratus east of Interstate 29 early
Thursday morning. Winds overnight will be in the range of 5 to 10
knots, so current thinking is that models are overdoing the fog
potential. Will leave only a mention of a small visibility
reduction in the SUX TAF. Additionally, with modeled low level
moisture being higher than reality this afternoon and modeled
stratus trending away from FSD and SUX, have kept the stratus out
of those terminals.

&&

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

$$

SHORT TERM...Chapman
LONG TERM...Chapman
AVIATION...Ferguson



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