Area Forecast Discussion
Issued by NWS Sioux Falls, SD

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FXUS63 KFSD 171736

Area Forecast Discussion
National Weather Service Sioux Falls SD
1236 PM CDT Mon Oct 17 2016

.SHORT TERM...(Today and Tonight)
Issued at 439 AM CDT Mon Oct 17 2016

Another very complex forecast over the next 12 to 24 hours. One
strong wave is leaving northern Minnesota, with strong Pacific jet
punching a path into the central Rockies. Weak boundary has been
settling across the CWA, but is fairly ill-defined sinking
near/south of I-90.  Another area of low pressure was located across
north central Kansas, and was working to develop an inverted trough
toward northeast Nebraska.

Fog for most has been a somewhat erratic and spotty thing overnight,
with visibilities coming up and down. A more persistent area across
northwest Iowa has diminished over the last couple of hours, but
continues along a very narrow corridor from the Pothole highlands
toward a narrow zone along the western side of the Buffalo Ridge.
Considered dropping dense fog advisory for a good portion of the
advisory due to spotty nature of lowest visibilities, but did want
to consider the northward creep to more widespread dense fog ahead
of the surface frontal boundary/inverted trough into the Highway 20
corridor through the early to mid morning hours. May need a
localized extension to advisory through the lower Missouri Valley
as boundary slows and low level flow turns more easterly.

Also have to consider issues with stronger winds and lower RH during
the latter afternoon. Quite a bit of difference in where the
boundary will reside by late day as additional low pressure develops
in the western plains and works eastward along the boundary. By late
afternoon, there appears to be a potential for a small warm sector
to intrude into south central SD with a push of westerly mixing
and sharp drop in RH. For now, it looks to be a late afternoon
timing, too short a duration for any fire weather highlights.

Models are fairly consistent with a signal within the warm advection
zone with northeastward lifting wave coming out of Kansas of
convective potential by early afternoon across parts of northwest
Iowa and southwest MN. Most soundings appear to remain fairly well
capped to upright convection, with exception being the NAM which
deals out its usual greater degree of elevated instability. As
larger scale forcing approaches by mid to late afternoon, would not
be surprised to see isolated to scattered coverage initiate lifting
across northwest Iowa. Shear is fairly strong, perhaps too strong to
maintain any organization for the degree of instability. A few
storms near the eastern border of the CWA around MWM and MJQ could
deserve a bit of special attention before they race northeast of the
CWA.  Otherwise, the strong jet will bring along a good zone of PV
advection across the northern CWA toward late afternoon. While
potential instability is somewhat less in this latter area, have
boosted the chance for showers and isolated thunder across the
northern CWA by very late afternoon and early evening. Rain chances
will start to drop off fairly quickly after 06z with quick exit of

North/south differences in various solutions result in as much as 10
to 15 degrees difference in potential highs today, especially if
considering possibility of some longer duration lower clouds in
vicinity of stalled boundary into parts of southeast SD, northwest
IA and adjacent locations. Have been a bit more pessimistic to temps
near and north of the boundary and favored some cooler raw model
numbers, while increasing the gradient toward the western Missouri
river valley. By tonight, will get a strong push of cold advection
which should drive temps into the mid 40s to near 50.

.LONG TERM...(Tuesday through Sunday)
Issued at 439 AM CDT Mon Oct 17 2016

Tuesday morning will see some residual strong winds with the passing
of the cool front and should remain a little breezy into the
afternoon. Expect abundant sunshine and highs in the 60s.

The chances for light rain on Wednesday not all that impressive and
the trends continue to take the better chances to the south. Still
anticipate some cloud cover south of interstate 90 which will limit
temperatures a bit, but overall with winds kept not too strong and
highs in the upper 50s to mid 60s it will be a pleasant day.

Thursday looking seasonally cool, dry and quiet as a weak wave moves
through with little to no moisture to work with. Morning lows should be in
the 30s with highs from the mid 50s to lower 60s.

Friday through Sunday continues to hint at some warmer air, but with
a fairly strong jet max lurking just north across North Dakota into
southern Canada, cannot get too aggressive with temperatures.
Statistically the ensemble temperatures are also hinting at the
warmer weather with the ensemble mean warmer than the operational
while the operational is at or above climatology. So, next weekend
will be a time to watch when temperatures might need to be raised.


.AVIATION...(For the 18Z TAFS through 18Z Tuesday afternoon)
Issued at 1235 PM CDT Mon Oct 17 2016

Variable sub-VFR ceilings from the lower James River Valley into
northwest Iowa expected to gradually lift/diminish through the
afternoon, though could linger around the Iowa Great Lakes into
this evening. Some models hint that MVFR visibility in BR will
redevelop over northwest Iowa overnight, but low confidence at
this time, so trended toward dominant VFR conditions after 03z.
Potential for isolated thunderstorms near/north of I-90 during the
very late afternoon/evening as well, and with some consistency in
location/timing seen in high-resolution models, have included a
thunder mention for 1-2 hours at KHON/KFSD.




SHORT TERM...Chapman
AVIATION...JH is the U.S. government's official web portal to all federal, state and local government web resources and services.