Area Forecast Discussion
Issued by NWS Sioux Falls, SD

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FXUS63 KFSD 172026

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

.SHORT TERM...(This evening through Tuesday)
Issued at 325 PM CDT Mon Oct 17 2016

A lingering band of light fog/stratus across far southeast South
Dakota/northwest Iowa/southwest Minnesota has created quite the
temperature variance across the forecast area this afternoon, with
temperatures beneath the stratus holding in the mid 60s, which
readings on either side have climbed into the lower-mid 70s. This
really only an impact to our near-term temperature trends though,
with primary concerns overnight shifting to a potential for isolated
thunderstorms and/or gusty winds moving through the forecast area

Surface low currently located in southwest South Dakota, with a
surface boundary extending east through extreme northern Nebraska
into west/northwest Iowa. Lowest stratus located just north of this
boundary and has obviously stabilized the atmosphere to potential
for surface-based storms. Question becomes how much convective
activity will be generated on the elevated boundary, which appears
to be located closer to I-90, as the upper wave currently spinning
through eastern Wyoming tracks east along the elevated boundary.
High-res models have been fairly consistent in showing some isolated
to scattered convection develop in central South Dakota toward 23Z,
though progressive runs have trended farther to the south with the
activity as the stratus has limited anticipated northward push to
the surface boundary this afternoon. Timing remains consistent,
though, with storms then tracking east through the I-29 corridor in
the 02Z-04Z window, weakening as it continues to move east through
northwest Iowa/southwest Minnesota overnight.

Strong winds aloft just above a weak surface based inversion could
mix down as the surface wave and associated storms initially move
through our South Dakota counties, but think the threat of stronger
winds will diminish as they move toward the existing stratus area
where inversion is stronger/deeper.

Much calmer day expected on Tuesday, though could again start the
day with some light fog across northwest Iowa where moisture will be
slowest to scour out overnight. Should be a cooler day with highs in
the lower to mid 60s, more sunshine and modest westerly flow.

.LONG TERM...(Tuesday night through Monday)
Issued at 325 PM CDT Mon Oct 17 2016

A rather quiet medium and extended range forecast is ahead, with the
primary concerns for weather focused on Wednesday and Wednesday

Model guidance is in good agreement bringing a progressive upper
wave through the Central Rockies and into the Midwest by Wednesday.
Isentropic lift on the 300-305K surfaces increases sharply by
daybreak, however soundings continue to show a rather dry sub-cloud
layer remaining in place. NAM/ECMWF are stronger solutions as
compared to the GFS, suggesting precipitation may drift even further
north than the current forecast indicates.  Have boosted PoPs a bit
today, but wouldn`t be surprised if these aren`t increased further.

Mid-level heights are expected to build for the end of the week with
mid-level ridging centered over the Central CONUS by Sunday. Within
this flow transition, it`s possible a weak wave could impact the
area on Friday (especially Minnesota counties), bringing increased
cloud cover and a low end risk of light rain.

The broad forecast consensus however is that the forecast will favor
dry, and above normal temperatures. The biggest issues moving
forwards will again be potential for stratus/fog impacting


.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.




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