Area Forecast Discussion
Issued by NWS Sioux Falls, SD

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FXUS63 KFSD 282320

Area Forecast Discussion
National Weather Service Sioux Falls SD
620 PM CDT Wed Sep 28 2016

.SHORT TERM...(This evening through Thursday)
Issued at 300 PM CDT Wed Sep 28 2016

Large upper-level low pressure continues to spin south of the Great
Lakes, wrapping bands of lower clouds westward.  For the most part,
the South Dakota border has been limiting boundary of clouds during
the midday and afternoon hours, with mixing eroding successive
advancements.  With larger scale ridge axis surface and aloft, the
challenge in the short term is primarily with trends in clouds as
easterly component to low-level flow continues to pull moisture
westward toward the area.

Clouds will be somewhat more perishable through the close of the
afternoon and early evening, but renewed development/push to lower
clouds likely to start up again during the later evening and
overnight. A majority of higher resolution solutions which have
handled clouds decently today indicate stratus coverage will be most
focused in southwest MN and NW IA, and likely to impact temperatures
with lows not as cool as those to the west near the ridge axis.
In proximity to ridge axis, could see a little patchy fog develop
late tonight or very early tomorrow morning, with greatest chance in
the James Valley and northern I-29 corridor, where should see a few
temps dip to the mid to upper 30s overnight.  Would not be shocked
for a couple spots of isolated frost as well.

Ridge will remain nosed in across the area on Thursday. Will again
have to work on eroding/mixing out lower clouds across the eastern
CWA.  Should have mainly sunny to partly cloudy skies by afternoon,
allowing temps to reach mid 60s in parts of southwest Minnesota and
northwest Iowa, to near 70 in south central South Dakota. Overall,
should see less wind, outside where some slightly stronger southeast
return flow initiates in south central SD.

.LONG TERM...(Thursday night through Wednesday)
Issued at 300 PM CDT Wed Sep 28 2016

Not a whole lot going on Friday and Saturday with pleasant weather,
mostly clear to partly cloudy conditions and south to southeast
winds generally around 15 mph or less. Lows will be in the 40s with
highs in the 70s. The only small concern will be a chance for some
patchy fog each morning with the surface ridge axis in place.

In the outer periods (Sunday through Wednesday), Sunday and Monday
will see a strong southerly flow and mild temperatures as low
pressure deepens across the Rockies. This will bring above normal
temperatures, especially overnight lows. Highs will be in the 70s
with lows from the mid 50s to lower 60s. Tuesday into Wednesday
model agreement is marginal. While the models all are hinting at a
deepening trough over the rockies Monday into Tuesday, they diverge
quite a bit on how to eject this energy onto the Plains. Therefore
will continue with chances for showers and thunderstorms Monday into
Wednesday and a gradual cooling without much change to guidance


.AVIATION...(For the 00Z TAFS through 00Z Thursday evening)
Issued at 615 PM CDT Wed Sep 28 2016

A couple of concerns that need to be detailed regarding the 00Z
TAF set. First, there is still a possibility of some patchy fog
developing just before sunrise in the James River valley which
could impact the KHON TAF. Went with a tempo MVFR group to alert
the users of this possibility. Further east just east of
Interstate 29, organized cumulus behind low pressure just inside
the VFR category will likely exist through the night and into
Thursday morning. The question is, will this higher based stratus
begin to back into the KFSD and KSUX TAF sites as winds off the
surface become more easterly overnight. This is a possibility, but
the stratus development at KFSD and KSUX could also be hindered by
an overall dry air mass above the surface. It is difficult to
ascertain which way this will play out, with many of the models
suggesting that KFSD and KSUX will only become scattered with a
higher end MVFR deck. For now, hedged this way and will closely
monitor for any changes.




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