430
FXUS63 KFSD 191952
AFDFSD

Area Forecast Discussion
National Weather Service Sioux Falls SD
252 PM CDT Thu Sep 19 2024

.KEY MESSAGES...

- Isolated showers and thunderstorms will be possible through
  this evening mostly across northwestern IA.

- An active pattern aloft will lead to renewed shower and
  thunderstorm chances (30%-60%) this weekend with the highest
  chances occurring on Saturday and Saturday.

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

&&

.DISCUSSION...
Issued at 244 PM CDT Thu Sep 19 2024

REST OF THE EVENING/TONIGHT: Another warm and breezy day continues!
Taking a look across the area, 18z observations show temperatures in
the upper 70s to low 80s area-wide with an abundance of sunshine and
mostly clear conditions behind a cold front roughly stretching along
a Mountain Lake, MN to Moville, IA line. While there is still some
lingering potential for a few isolated showers and thunderstorms to
develop ahead of this near-surface feature, any developing activity
would have to overcome a weak cap around 700-800 mb which would
inhibit its upward growth. With cold front gradually pushing
eastwards by the minute, not confident enough in peak heating to
eroding the cap in time for any stronger activity to develop. As a
result, while the severe weather chances are non-zero; not expecting
any significant development in our area from this point onwards.

Shifting gears here, expect any lingering cloud cover over areas
east of I-29 to gradually clear with the passage of the cold front
ushering in cooler and drier air in its wake. From here, expect the
mostly clear conditions to translate to the overnight hours as a
surface high moves in to replace the departing front. With this in
mind, breezy westerly winds should gradually diminish after sunset
becoming more light and variable as lows decrease into the low to
mid 50s for the night. Lastly, with the surface high overhead and
lingering low-level moisture; could see some patchy fog develop
mostly along with our River Valleys.

THE WEEKEND: Heading into the start of the weekend, warm and mostly
dry conditions return by Friday as the mid-level component of
the ridging moves overhead. Increasing mid-level warm air
advection (WAA) along with southerly surface flow will lead to a
slight increase in temperatures for the day as highs peak in
the low to mid 80s for the day with the warmest conditions
situated along the Missouri River. As the SPG tightens on the
backside of this ridge, southerly winds will increase throughout
the day especially west of the James River where gust up to 30
mph will be possible. With this in mind and RH values falling
below 30 percent, locally elevated fire danger will be possible
in our southcentral SD counties especially since the fuel are
likely more cured than areas further eastwards.

From here, our attention will likely turn northwards as a deepening
shortwave trough digs across eastern Montana and central North
Dakota with a pretty strong mid-level cold front swinging
southeastwards through our area throughout on Saturday. While
some isolated precipitation chances will be possible along the
front, further analysis of soundings show a pretty significant
cap between 700-800 mb likely inhibiting any significant
development. This combined with the progressive nature of the
cold front will likely keep any potential development to
isolated or scattered showers at best mostly across northwestern
IA through Saturday night. With that being said, PWATs will
likely increase towards the 90th percentile of climatology
heading into Saturday night setting the stage for our next
precipitation chances.

From Saturday night into Sunday, our attention will likely be
focused southwestwards as a shortwave and an upper-level low (ULL)
lifts into the Mid-Missouri River Valley likely bringing our next
rain chances (30%-60%). While overall amounts are still a bit
questionable, its worth noting that the NBM has started to trend
POPs further southwards with the highest values siting around the
Hwy-18 corridor and southwards. This sentiment is echoed in the
19.12z runs of the GFS/Euro which are trending the shortwave and low
further southward compared to the NAM which has both features a bit
further north. Either way, ensemble guidance is still showing low to
medium probabilities (30%-50%) of up to a half inch of QPF with this
activity through 00z Monday. This combined with PWATs in the 90th
percentile of climatology do give a signal for pockets of heavy rain
with any potential development through Sunday. Lastly, with the
passage of the previously mentioned cold front and increased
precipitation chances through Sunday; expect our temperatures to
trend toward more fall-like conditions with daily highs decreasing
from the low 70s to low 80s on Saturday to the low to mid 60s by
Sunday.

NEXT WEEK: Looking into the new week, long-range guidance begins to
diverge in terms of solutions as they struggle to handle the passage
of the weakening ULL on Monday. The upper-level pattern continues to
remain quite active through Wednesday with the passage of a cold
front and subsequent shortwave around the region. However, our
precipitation chances remain fairly uncertain through this period.
An amplified ridge likely moves across the region by the midweek
with limited precipitation chances to end the week. Lastly,
temperatures will continue to trend near to just below our seasonal
normals as daily sit in the upper 60s to mid 70s through Thursday.

&&

.AVIATION /18Z TAFS THROUGH 18Z FRIDAY/...
Issued at 1214 PM CDT Thu Sep 19 2024

VFR conditions with occasional MVFR ceilings are expected this
TAF period mostly due to lingering low-level stratus. Taking a
look at satellite imagery, a cold front continues to gradually
push eastwards this afternoon roughly extending along a Windom,
MN to Sioux City, IA line with MVFR stratus with a few embedded
showers ahead of it and mostly clear conditions behind it. As
this surface feature spread eastwards over the next few hours
expect mostly clear conditions to continue for the rest of the
TAF period. Otherwise, breezy westerly surface winds will
continue through sunset before becoming more light and variable
overnight to end the TAF period.

&&

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

&&

$$

DISCUSSION...Gumbs
AVIATION...Gumbs