783
FXUS63 KFSD 182336
AFDFSD

Area Forecast Discussion
National Weather Service Sioux Falls SD
636 PM CDT Wed Sep 18 2024

.KEY MESSAGES...

- Isolated shower and thunderstorm chances (20%-30%) will be
  possible this afternoon and evening. While a stronger storm or
  two isn`t completely out of the question, confidence is low
  in any widespread development.

- An active pattern aloft will lead to renewed shower and
  thunderstorm chances (40%-60%) this weekend with the highest
  chances occurring on Saturday and Saturday.

- Confidence continues to increase in cooler stretch of
  temperatures starting as early as Sunday.

&&

.DISCUSSION...
Issued at 211 PM CDT Wed Sep 18 2024

REST OF THE EVENING/TONIGHT: Taking a look at satellite imagery,
areas of lingering stratus continue to lift northeastwards across
our eastern-most column of counties with a few pockets of light
showers. Expect this lingering activity to continue to progress
northeastwards before exiting our area around 18z. Looking
aloft, a vertically stacked ULL situated over Eastern Montana
and the far western Dakotas continues to rotate northeastwards
keeping our overall flow locked into a northeasterly regime
through tonight. Shifting gears to our precipitation chances,
isolated shower and thunderstorm could develop by as early as
21z as a subtle shortwave rotates around the ULL.

However, with rather weak forcing and a modestly stable airmass in
play due to this morning`s rain/lingering cloud cover; not too
confident in our overall severe weather chances this afternoon
and evening. Nonetheless, with up to 1500 J/kg of instability,
30-35 kts of speed shear, and a dry sub-cloud layer; can`t
completely rule out a stronger storm or two mostly between the
James River Valley and I-29 corridors with the main threats
being damaging winds up to 60 mph and quarter sized hail.
Otherwise, expect mostly quiet conditions to return overnight as
breezy southerly winds gradually decrease with the approaching
surface high. Lastly, lingering cloud cover and southerly
surface winds will keep temperatures elevated overnight as lows
gradually decrease into the low to upper 60s for the night.

THURSDAY: By Thursday morning, could potentially see a few isolated
pockets of light to moderate showers develop east of I-29 as the LLJ
strengthens ahead of the cold front. Expect this area of activity to
gradually scoot eastwards through parts of the morning with most of
the activity exiting our area by about 15z. From here, cloud cover
should begin to clear out from west to east with an abundance of
sunshine returning for the rest of the day. With this in mind,
expect our overall temperatures to stay above normal with highs
topping out in the upper 70s to upper 80s with the warmest
conditions expected across portions of the Missouri River Valley and
northwestern IA.

THE WEEKEND ONWARDS: Heading into the weekend, mostly quiet and
breezy conditions will continue as a surface high moves across the
region by Friday. A tightening SPG will lead to periodic breeziness
over the weekend with wind gusts up to 25 mph possible each
afternoon. From here, an active pattern returns aloft with a
northern stream trough progressing eastwards across Montana and an
ULL ejecting out of the four-corners region. Both these features
will likely influence the precipitation chances across our area from
Saturday through Sunday. However, to what degree is still in
question. Most long-range guidance continues to vary on the
strength of both systems which has result in some uncertainty.
Nonetheless, most ensemble guidance continues to show low to
medium confidence (30%-50%) chances of up to half an inch of QPF
with the focus being areas south of I-90 which could mean some
beneficial rain is on the way for parts of our area. Either way,
we`ll have to monitor these systems as they approach. Lastly,
the increasing precipitation chances will lead to temperatures
trending downwards heading into the new week with daily dropping
from the low to mid 80s on Friday to the low to upper 60s by
Monday.

&&

.AVIATION /00Z TAFS THROUGH 00Z FRIDAY/...
Issued at 636 PM CDT Wed Sep 18 2024

While there is still a 20-30 percent chance for showers and
thunderstorms this evening at KFSD/KSUX, recent observational
trends suggest a drier evening overall, so have removed all
shower/thunder mention from the 19.00Z TAFs. Will continue to
monitor observations for possible updates.

One caveat with precipitation is that multiple runs of the HRRR
this afternoon have tried to develop a cluster of showers and
storms across southeast SD late tonight into Thursday morning.
This is currently an outlier compared to other high resolution
guidance, but something to watch.

For the rest of the evening, expect some scattered VFR ceilings
to give way to cirrus and/or clear skies overnight. VFR
conditions are then expected to continue through the rest of
Thursday with mostly sunny skies.

Southerly breezes with some gusts up to 20 kts are likely to
continue into the overnight at KHON/KFSD, whereas winds will be
lighter and from the southeast at KSUX. Do expect some low-level
wind shear at KSUX overnight, with winds at 2000 ft agl to
increase to near 40 kts from the southwest. Surface winds to
veer to the southwest and eventually the west Thursday morning,
gusting at times between 20 and 25 kts by the afternoon.

&&

.FSD WATCHES/WARNINGS/ADVISORIES...
SD...None.
MN...None.
IA...None.
NE...None.

&&

$$

DISCUSSION...Gumbs
AVIATION...Rogers