Area Forecast Discussion
Issued by NWS Sioux Falls, SD

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FXUS63 KFSD 182319

Area Forecast Discussion
National Weather Service Sioux Falls SD
619 PM CDT Sun Jun 18 2017

.SHORT TERM...(This evening through Monday)
Issued at 319 PM CDT Sun Jun 18 2017

Afternoon showers/isolated thunderstorms across our northeast should
wane pretty quickly with loss of heating this evening, as will the
gusty northwest winds. Another subtle wave sliding across the region
in northwest flow will keep skies partly cloudy, with some models
hinting at some light precip accompanying the mid-level clouds.
Confidence in this precipitation chance is rather low given a deep
sub-cloud dry layer and minimal instability, so other than some very
low pops in our far southwest this evening, opted for non-measurable
pops throughout the night. Will hang on to a slight chance in our
far east through the late morning/early afternoon Monday, as daytime
heating brings a modest increase in instability by 15Z. However, the
moisture becomes increasingly shallow through the afternoon, and as
a result, expect a decrease in clouds and any spotty showers/storms
in our area by 21Z.

Weak surface ridging will provide light winds after sunset tonight,
but mixing will bring an increase from the west-northwest again by
late morning. The light winds/dry air mass will allow for another
seasonably cool night with lows in the lower-mid 50s. Low level
temperatures Monday similar to just a shade warmer than today, but
should be able to mix slightly higher with the drier air, allowing
for high temperatures 3-5 degrees warmer than today.

.LONG TERM...(Monday night through Sunday)
Issued at 319 PM CDT Sun Jun 18 2017

Monday night and Tuesday: Northwesterly surface flow will keep
seasonably mild temperatures with lows in the mid 50s. A few
passing light showers are possible in the nighttime over the extreme
northeast of the FA, as a weak shortwave moves eastward across central
Minnesota. Surface high pressure builds in on Tuesday, keeping the
area mostly dry with near-normal temperatures from the upper 70s to
mid 80s.

Tuesday night into Wednesday night: Unsettled weather returns
late Tuesday night as a warm front moves northward into the
area. Southerly surface winds will advect warmer and more humid
air across the High Plains as depicted in the 850-700 mb Theta-E
models. Increasing instability, and strong LLJ across central
South Dakota will enhance the chance for thunderstorms across
across the area. At upper levels, models prog the jet max north of
CWA, increasing the forcing and destabilization of the
atmosphere. Depending on timing of the surface boundary, this
event could produce strong/severe storms; but confidence is not
quite high yet. GFS shows the low near the CWA by 12Z Wednesday,
while the Canadian and ECMWF prog the arrival of the low later in
the afternoon. At this point, better chances look to be during the
evening hours. It is early to determine risks/severity of storms,
but it is a period that we should keep an eye on.

Rest of the week: Zonal flow aloft will become more dominant for the
remainder of the extended. This result in different impulses of
energy/shortwaves developing across the Central Plains. Periods of
scattered showers are possible into the weekend. Models differ on the
evolution, and timing of these systems; but as for now, looks like the
instability will be weak for this time period. Therefore left mainly
a chance for showers on Friday through the weekend.


.AVIATION...(For the 00Z TAFS through 00Z Monday evening)
Issued at 618 PM CDT Sun Jun 18 2017

VFR is expected through the TAF period.




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