Area Forecast Discussion
Issued by NWS Sioux Falls, SD

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856
FXUS63 KFSD 242320
AFDFSD

Area Forecast Discussion
National Weather Service Sioux Falls SD
620 PM CDT Fri Mar 24 2017

.SHORT TERM...(This evening through Saturday)
Issued at 400 PM CDT Fri Mar 24 2017

Surface warm frontal boundary has set up well south of the region in
southeast Nebraska and southern Iowa this afternoon, while a well
defined upper low spins over the Texas Panhandle. With the upper low
expected to very slowly wobble to the east through Saturday, the
shower focus has likewise shifted primarily south of the area. Some
spotty showers have popped up across northeast Nebraska and east
central Iowa, just south of the forecast area, with additional storms
expected to develop near the aforementioned quasi-stationary warm
front later this afternoon and evening. Scattered rain showers will
remain possible across far southeast SD into northwest Iowa, mainly
focused near the highway 20 corridor. With the system slowly
shifting eastward, expect the rain showers to gradually taper off
through Saturday afternoon. Most areas will be dry throughout
Saturday, but chances linger into the afternoon into the Storm
Lake/Cherokee area.

Temperatures will remain mild enough for entirely rainfall. Lows
will be in the 30s, but the areas below freezing temperatures in
south central SD will remain dry overnight. Low clouds stick around
into Saturday, gradually diminishing in south central through east
central SD with the tail end of the surface high working subsidence
into the area. Northeast winds will feature tonight and Saturday,
and will remain rather breezy east of I-29 where the pressure
gradient remains tightest.

.LONG TERM...(Saturday night through Friday)
Issued at 400 PM CDT Fri Mar 24 2017

By Saturday night, upper low to the southeast will make its closest
pass, but distant enough that direct impacts will be minimal and
perhaps limited to scattered light precipitation wrapping back
toward areas east of I-29 as the night progresses. Chance remains
fairly low however with large scale flow weak within deformation
between northern stream and closed wave. Gradually, models agree
that easterly component will begin to siphon off a more moist
trajectory at lowest levels ahead of ridge axis. Mainly more shallow
moisture profile brings a concern for fog development as the night
progresses. At this time, any more significant fog coverage would be
anticipated to tie toward the western edge of the westward spreading
stratus field, and also where stratus could be low enough and be
favored to northeasterly upslope to directly impact the higher
terrain in southwest MN. Any fog which develops would likely persist
well into the morning, as inversion and overall east to
northeast flow will be slow to provide improvement.

Kicker wave moving into the Northern Plains on Sunday. Actually do
get a bit of better lift forcing which may help to erode cloudiness
a touch toward the ridge axis across central to southeast SD through
the day. Some spotty light rainfall or even drizzle potentially for
areas mainly near/east of I-29, where as a result some locations
likely to keep temps restrained in the upper 40s, with lower to mid
50s progressively toward south central SD.

Monday into at least early Tuesday would appear to be a more solid
bet for a period of lesser precipitation threat as flow aloft takes
on a more westerly tilt along with weak ridging set to rebuild ahead
of reloading western U.S. trough.  One change will be prospect for
more sunshine and improved low-level mixing from weak cold
advection, which should help temps moderate from 5 to 10 degrees
from a more cloudy Sunday.

Confidence remains lower, but perhaps a bit more encouraging for
later in the week. Differences continue in longer range solutions
dealing with the continuous wave train of southern branch closed
systems along with impact from the northern stream. Most noteworthy
is that 12Z operational ECMWF has side-stepped somewhat toward the
more consensus of GFS/GEFS which suggest that there will be more
northern stream component to any troughing working into the plains
states mid- to late-week.  The latter solutions keep more flow
separation, and less impact from the closed wave passing well to the
south, rather than allowing wave to drift on a more northerly track.
Wednesday would look to be a period for slightly better precip
chance in the more northern stream dominant pattern with pulse of PV
advection, even with some moisture limitation in the lower levels.
Any precipitation chance mentioned by Thursday night and Friday is
of very low confidence.  Walked back some of the more excessive
blend PoPs scattered across the area from Thursday into Friday, a
trend toward but not fully encompassing a more GFS solution. Could
easily see fully removing these chances with later forecasts.
Daytime temps looks to be more into a 50s to lower 60s regime, with
lows mainly 30s, but would have to watch for some upper 20s around
midweek if less clouds become apparent when ridge in proximity.

&&

.AVIATION...(For the 00Z TAFS through 00Z Saturday evening)
Issued at 620 PM CDT Fri Mar 24 2017

MVFR-IFR conditions, largely due to widespread low stratus, will
persist near and east of Highway 81 through much of the forecast
period. Stratus may break up enough into portions of the I-29
corridor near and north of KFSD by Saturday afternoon, but stratus
and/or fog likely to redevelop and bring a return to MVFR-IFR
conditions as far west as the James River Valley after the end of
this TAF period Saturday evening.

Areas of light rain could also reduce visibility at times in far
southern portions of the forecast area, primarily from KSUX-KSLB,
into early Saturday.

&&

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

$$

SHORT TERM...
LONG TERM...Chapman
AVIATION...JH



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