Area Forecast Discussion
Issued by NWS Sioux Falls, SD

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FXUS63 KFSD 240925

Area Forecast Discussion
National Weather Service Sioux Falls SD
425 AM CDT Sun Sep 24 2017

.SHORT TERM...(Today and Tonight)
Issued at 424 AM CDT Sun Sep 24 2017

Short term remains the primary focus through the forecast, with a
few items of note over the next 24 hours. As anticipated at this
time yesterday, precipitation has again backed to the far western
edge of the CWA, west of a diffuse surface boundary now located
between the James Valley and I-29. Lightning activity within the
rain has been very sparse over the past few hours, and instability
over our far west remains minimal to non-existent throughout the
morning, so will carry little if any thunder mention through 15Z.

Mid-level wave lifts northward along the boundary late morning
through the afternoon, which should aid in pushing the front east
toward the I-29 corridor through the day. Temperatures will still
feature a fairly sharp gradient across the boundary by midday,
with western areas locked in the 50s-lower 60s, while eastern
areas climb into the 70s-lower 80s. Similar to the past couple of
days, expect to see some isolated to scattered storms develop
closer to the surface boundary as the wave lifts north. CAMs
develop isolated intense updrafts in storms along the surface
boundary this afternoon, but mid-level lapse rates near moist
adiabatic indicate we would likely looking at more intense rain
rates than any risk of hail. Temperatures should drop off behind
the front rather quickly as it moves east, and while hourly grids
do show a downward trend in afternoon temperatures through the
central portion of the CWA, likely do not capture the full extent
of how quickly readings could fall.

For tonight, the surface boundary continues a slow eastward trek,
with rain and embedded storms expected to persist, and possibly
even expand in coverage as low level jet continues to feed
moisture into the elevated boundary across northwest Iowa and
southwest Minnesota. Unlike in our far western CWA tonight, this
area does maintain weak instability this coming night, so could
continue to see periods of heavier rain overnight, mainly along
and east of a KYKN-KBKX line. While this area has seen little of
the rain the past couple of days, the intense rates could still
produce ponding water and possibly some urban flooding, and will
continue to highlight this in the HWO.

In addition to the rain, also monitoring and area of fog which has
developed in the higher terrain across southwest Minnesota early
this morning. A few locations have reported occasional visibility
down to a quarter mile, but with current small coverage area, will
forgo advisory for now and highlight in SPS/social media.

.LONG TERM...(Monday through Saturday)
Issued at 424 AM CDT Sun Sep 24 2017

Monday should begin with the surface boundary just southeast of
the forecast area, with numerous showers/isolated thunderstorms
persisting across the southeast half of the CWA. Still a potential
for isolated heavier rain, mainly east of Highway 60 corridor.
Temperatures will be quite cool beneath widespread cloud cover,
with highs only in the 50s west/north and 60s southeast.

The upper trough does begin to lift more northeast Monday night,
allowing drier mid level air to push across the forecast area on
Tuesday. Could still see some lingering showers in our east in the
morning, before the dry air shunts the precip east of the area.
Drying in lower levels builds in through the afternoon, which
should provide a fair amount of sunshine by late in the day.
Overall air mass remains chilly, though, so still looking for
highs only in the upper 50s-mid 60s.

The remainder of the week continues to look dry, with daytime
temperatures moderating closer to late September normals.


.AVIATION...(For the 06Z TAFS through 06Z Sunday night)
Issued at 1044 PM CDT Sat Sep 23 2017

The showers and isolated thunderstorms have retreated west and
should stay in central SD through the night into Sunday morning.
The surface cool front has shifted into southwest MN which will
bring a better chance for stratus farther east. Guidance showing a
lot of low visibilities under the stratus but not going to buy
into that just yet, although it really does not matter with the
IFR ceilings the main concern. By tomorrow afternoon into the
evening showers and thunderstorms will work from west to east with
new stronger development possible over northwest IA.




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