Area Forecast Discussion
Issued by NWS Sioux Falls, SD

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FXUS63 KFSD 131719
AFDFSD

Area Forecast Discussion
National Weather Service Sioux Falls SD
1219 PM CDT Fri Oct 13 2017

.SHORT TERM...(Today and Tonight)
Issued at 336 AM CDT Fri Oct 13 2017

Surface front is about to exit the southeast corner of the CWA as
of 08Z. Band of mid-level frontogenesis remains focused well to
the northwest, from western Nebraska, into south-central and
northeast South Dakota, ahead of weak mid-upper level wave and
130kt upper jet pushing into western South Dakota early this
morning. Seeing fair amount of returns on regional radar near the
mid-level boundary, but deep post-frontal drying beneath this
boundary making it tough for much rain to reach the ground thus
far, with ceilings still largely at or above 9kft.

This frontogenetic band weakens slightly, redeveloping across our
far southeast CWA through the morning as a secondary weak wave
slides northeast out of Colorado into western Iowa. Starting to
see influence of this with increased cloud development just north
of I-80 corridor in central/eastern Nebraska over the past hour,
and this should become the primary focus for today. Greatest
consensus on placement of deeper moisture will hold best chances
for measurable precip south of our forecast area, though should
see spotty light showers or sprinkles as far north as Highway 60
corridor in northwest Iowa by 18Z. Instability lacking north of
the 850mb boundary, which should be near or just north of I-80 by
late morning, so no mention of thunder at this point.

Continued influx of dry air ahead of surface ridge pushing into
the area this afternoon should provide for increasing sunshine,
though cooler air mass will limit highs to mid 50s to around 60.
The ridge and associated dry air will keep precip chances at bay
much of tonight, though approach of a stronger trough into the
western High Plains will allow low-mid level boundaries to begin
lifting northward again later tonight. Prior to 12Z Sunday, deeper
low-level moisture remains generally south of Highway 18. Though
we should see some increase in higher clouds farther north by late
tonight, will keep low precip chances confined to our southern
counties. Lows tonight should range from upper 30s in our north,
to mid 40s far south.

.LONG TERM...(Saturday through Thursday)
Issued at 336 AM CDT Fri Oct 13 2017

Saturday continues to look like the most active period, relatively
speaking, through this forecast, as upper trough and tail end of
associated jet swing across the region. Strong isentropic lift
ahead of the wave should allow for rapid increase in coverage of
showers through Saturday morning, primarily across our eastern and
northern counties, as mid-upper level dry air is already punching
into our southwest by 15Z. Again instability looks pretty limited,
with very modest elevated CAPE values working into far southeast
areas midday-early afternoon ahead of cold front which pushes
through the CWA by mid afternoon.

Despite mid-level drying, plenty of low-level moisture persists
through the afternoon/evening, which along with late day cold
advection will hold temperatures in the 50-60 degree range for
highs on Saturday. Cold advection will also allow some stronger
winds to work to the surface behind the front, with northwest
winds of 20-35mph likely across our western areas by Saturday
afternoon, spreading eastward Saturday night. Sunday will be the
better day of the weekend, with lighter winds and more sunshine
expected. Temperatures will remain on the cool side of normal,
though, with highs still mainly in the 50s.

Upcoming work week will feature a strong warmup as upper ridge
builds into the Plains and upper jet energy largely remains north
of the forecast area. Generally looking at above normal highs in
the 60s-lower 70s and lows in the 40s, with clear to partly cloudy
skies.

Period of greatest uncertainty is Wednesday, with Canadian, and
to a lesser extent the 13/00Z ECMWF, develop a stronger upper
trough over the Canadian Prairies. This drives a cool front deeper
into the Northern Plains/Upper Midwest midweek, with the Canadian
indicating highs about 10-15F cooler than other models Wednesday.
This is an outlier solution at this point, so did not deviate
from the mild model consensus, but will monitor trends on this
feature as we go through the weekend.

&&

.AVIATION...(For the 18Z TAFS through 18Z Saturday afternoon)
Issued at 1217 PM CDT Fri Oct 13 2017

VFR will be found across the area this afternoon and evening.
However after midnight tonight, MVFR ceilings will likely move
back northward impacting the KSUX TAF site. As the southeast winds
continue, lower end MVFR to IFR conditions will proceed northward
impacting the KFSD TAF site by 14Z, and KHON just before the end
of the TAF period.

&&

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

$$

SHORT TERM...JH
LONG TERM...JH
AVIATION...MJ



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