Area Forecast Discussion
Issued by NWS Sioux Falls, SD

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FXUS63 KFSD 220340
AFDFSD

Area Forecast Discussion
National Weather Service Sioux Falls SD
1040 PM CDT Sat Oct 21 2017

.SHORT TERM...(This evening through Sunday night)
Issued at 409 PM CDT Sat Oct 21 2017

A couple of lingering showers and thunderstorms very late afternoon,
but progression of trough will end things quickly this evening and
bring clearing into the area. Influx of much drier air and weakening
gradient overnight will allow temps to fall into the 30s overnight,
with a few readings around 40 for the Buffalo Ridge where winds may
stay up a bit better.

A reward for the gloom of today will be Sunday, which promises to
have a great deal of sunshine, and winds veering around to west and
southwest. Another relatively mild day, perhaps closing on 70
degrees once again toward south central SD, but mainly in the 60s.
Sunday night, another strong jet impulse will begin to dig into the
northern plains and drive a cold front across most of the area by
daybreak Monday. Should be a narrow band of cloudiness along the
leading edge of decent PV advection and defined mid-level frontal
boundary, and would not even be shocked to find a few sprinkles the
latter half of the night near/north of I-90.  Northwest winds will
increase behind the boundary to limit temperature fall via mixing,
and also warm enough ahead of boundary to expect mainly 40s for
lows.

.LONG TERM...(Monday through Saturday)
Issued at 409 PM CDT Sat Oct 21 2017

Strong cold advection the story on Monday, especially by the
latter half of the day with cold air lagging behind secondary
trough. Again may find a couple of showers/sprinkles swinging
through southwest MN during the afternoon with main trough
axis/cold core, but won`t amount to much. Temps likely to reach
highs by midday/early afternoon before falling back under more
clouds and cold advection. Strong winds may get close to wind
advisory levels during the afternoon, and the winds will continue
brisk on Monday night into Tuesday, freshened by mixing on Tuesday
especially along/east of I- 29 with 30-40 kt 925 hPa winds.
Coolest day in a while, with highs upper 40s to mid 50s, and ridge
axis Tue night will allow 30s to return to much of the area.

Roller coaster in temps continues Wednesday with see-saw in pressure
pattern as falling pressure to north and west and warm front
spreading eastward through the area. GFS does begin to diverge a bit
with stronger wave reinforcing trough through western Great Lakes
and a bit slower retreat to cooler air. Westerly flow will offset
most of this potential, and see a lot of upper 50s and 60s again on
the warm side of normal for Wednesday.

Big change in the longer range guidance on the 12z runaround was
defection of the ECMWF from the 00z run idea of hanging back a
majority of energy, with at least a 2/3 shift toward the GFS and
ensemble blend of more split and progressive troughing through the
region.  However, GFS ensembles continue to advertise some
significant divergence in solutions late week as they deal with
recurving Typhoon Lan, so while far from cementing the pattern
change toward the end of the week, maybe less uncertain? Seeing 12z
GFS as still likely a bit too northern stream in its solution as is
typical for digging systems. Whatever the result, ensemble guidance
certainly points toward an end result of cooler temps late week and
starting the weekend.  Have increased winds quite a bit over the
blend (which incorporated the out of phase 00z ECMWF solutions) for
Thursday and Friday, and likely not strong enough at this point. As
cold air rushes in Thursday and Friday, there is potentially up to
40 knots available for mixing in southwest quadrant of developing
cyclone over MN/WI. Be ready for big changes by the end of next week.
Precipitation looks to hold back most areas on Thursday, perhaps
dragging across locations north of I-90 Thursday afternoon in the
form of showers only due to warmer near-surface layer. Colder air
will bring snow chances Thursday night into Friday. Of note is some
potential for light accumulating snow, but much could change in
location and exact timing.

&&

.AVIATION...(For the 06Z TAFS through 06Z Sunday night)
Issued at 1040 PM CDT Sat Oct 21 2017

VFR conditions will prevail through the period. Southwest winds
could become briefly gusty Sunday afternoon 18Z-23Z, though gusts
will remain below 25kts. Otherwise expecting winds at or below
10kt.

&&

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

$$

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



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