685
FXUS63 KFSD 171108
AFDFSD

Area Forecast Discussion
National Weather Service Sioux Falls SD
608 AM CDT Wed Jul 17 2024

.KEY MESSAGES...

- A few sprinkles to isolated showers will be possible this
  afternoon with only light accumulations expected.

- Near to below normal temperatures will continue through the
  weekend as cooler air funnels into the region.

- More rain chances (30%-70%) will likely return over the
  weekend with the better chances expected Friday night into
  Saturday. While some details remain uncertain, an isolated
  severe risk and pockets of heavy rain remain possible with
  developing showers and storms.

&&

.DISCUSSION...
Issued at 316 AM CDT Wed Jul 17 2024

The Short Term (Today & Tonight):

A cooler day will be on tap for today! Taking a look across the
area, the combination of a surface inversion and lingering low-level
saturation in response to a descending surface high have led to a few
areas of patchy fog developing mostly along our River Valleys and
areas east of I-29. While rapid changes in visibility will be
possible heading into these areas this morning, expect any lingering
fog to dissipate by mid-morning as mixing restarts. As for the rest
of the day, mostly quiet conditions will persist with light
northerly to northeasterly surface winds. Surface temperatures will
likely cool a touch from the previous days as lingering cold air
advection (CAA) continues to sit over the area aloft. With this in
mind, expect highs to vary between the low to upper 70s and low 80s.

Looking aloft, a deepening upper-level trough will continue to dig
into the northern plains and Great Lakes regions with the base of
the trough sitting somewhere across central and southern MN by this
afternoon. As bits of isentropic lift rotate around the trough, its
wouldn`t be impossible for a few isolated showers to develop with
the elevated instability above the boundary layer. While the
confidence is low (<20%), decided to mix in a few sprinkles
roughly along a Huron-Mitchell-Sioux City, IA line through this
evening to capture the potential. Lastly, as winds become more
light and variable overnight with the surface high overhead;
we`ll have to watch for more areas of patchy fog to develop east
of I-29 as temperatures gradually decrease into the low to
upper 50s for the night.

The Long Term (Thursday-Tuesday):

Heading into the latter parts of the week, much quieter conditions
will continue through Thursday as the mid-level ridge moves
overhead. As warm air advection (WAA) strengthens on the backside of
the previously mentioned ridge, surface temperatures will slightly
increase for parts of the area with highs expected to reach the mid
to upper 70s and low 80s. By Friday, another surge of mid-level WAA
along with southerly to southeasterly surface winds will lead to
another warm day as highs reach the upper 70s to low 80s. Our
attention will then turn towards eastern Wyoming as a clipper wave
dives southeastwards into our area bringing our next precipitation
chances (30%-70%) through Saturday.

While details remain far from certain, it`s worth noting that the
open wave has slightly shifted a bit further westwards from
yesterday`s guidance. With this in mind, the better shower and
thunderstorm chances have shifted further southwards towards areas
south of I-90 and along the Missouri River Valley. While the timing
for the better coverage continues to look like Friday night into
Saturday, intermittent periods of scattered showers and
thunderstorms remain possible through Saturday. Looking at the
environment, long-skinny CAPE profiles along with 30-35 kts of deep
layer could support a limit severe risk by Friday afternoon but
there is still some uncertainty there. With PWATs up to 1.75 inches
and warm cloud depths of up to 11kft, the most likely hazard would
be pockets of heavy rainfall. However, the overall amounts remain
questionable with ensemble guidance only showing low to medium
confidence (20%-40%) in up to half an inch of QPF through Sunday.
With all this in mind, a wet and dreary weekend is ahead to say the
least. As the closed low begins to drift southwards by Sunday, our
rain chances should begin to thin heading into the new week.

Looking into the early parts of next week, an active pattern
continues aloft as upper-level ridging continues to build across the
western CONUS. While a few smaller rain chances will be possible on
both Monday and Tuesday, difference between long-range guidance have
lead to low confidence in occurrence. Nonetheless, left the default
NBM POPs in for this period. Lastly, below normal temperatures will
continue through Tuesday as high approach the upper 70s to low 80s.

&&

.AVIATION /12Z TAFS THROUGH 12Z THURSDAY/...
Issued at 605 AM CDT Wed Jul 17 2024

VFR conditions with occasional MVFR/IFR conditions are expected
across the area mostly due to patchy areas of developing fog.
Taking a look at satellite imagery, mostly clear conditions
continue with a few patchy areas of fog developing in our River
Valleys this morning. While the fog shouldn`t stick around past
15z, temporary MVFR to IFR (and lower) visibility reductions
will be possible. Otherwise, a stray sprinkle to light shower
will be possible this afternoon as cumulus field develops.
Lastly, light and variable winds this morning will transition to
light northerly to northeasterly winds by this afternoon.

&&

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

&&

$$

DISCUSSION...Gumbs
AVIATION...Gumbs