668
FXUS63 KFSD 141703
AFDFSD

Area Forecast Discussion
National Weather Service Sioux Falls SD
1203 PM CDT Fri Jun 14 2024

.KEY MESSAGES...

- After mostly quiet conditions through the morning, a few
  scattered showers and isolated thunderstorms will develop west
  of I-29 and spread eastward by the late evening. Accumulations
  are expected to be light.

- More widespread shower and thunderstorm chances (60%-90%) will
  develop to start the day on Saturday. Additional isolated
  shower and storm development will be possible by Saturday
  afternoon with a few storms potentially becoming severe.
  Accumulations of up to half an inch are expected.

- An active pattern aloft will continue into next week with the
  potential for severe weather although details remain
  uncertain.

&&

.DISCUSSION...
Issued at 402 AM CDT Fri Jun 14 2024

The Short Term (Today/Tonight & Saturday):

Another warm and mostly quiet day is ahead. Taking a look across the
area, the clear conditions are set to continue as the surface high
continues to drift southeastwards. Similar to yesterday, some patchy
fog development will be possible mostly along our river valleys by
daybreak as light and variable winds and lingering cold air
advection (CAA) help our temperatures decrease towards our dew
points (upper 40s to low 50s). However, as mixing restarts after
daybreak and southeasterly winds increase expect any developing fog
to quickly dissipate. From there, quieter conditions temporarily
return for the rest of the morning as southeasterly flow helps pull
in more warm and moist air to our area. With this in mind, expect
similar conditions to yesterday as highs approach the low to mid 80s
for the day.

Shifting gears to our precipitation chances, little bits of
isentropic lift ahead of a subtle shortwave will likely trigger a
few scattered showers with isolated thunderstorms west of the James
River and along the Missouri River Valley by the early afternoon.
Expect this developing activity to gradually spread eastwards as the
previously mentioned wave moves in to replace the departing surface
high. As mentioned in the previous discussion, an occasionally
strong wind gust wouldn`t be completely out of the question with
developing cells around south-central South Dakota along the leading
edge of the warm front/instability gradient. However, with the
location of the warm front still in question; confidence still
remains low in any severe weather chances. By tonight, the LLJ will
strengthen as the main wave ejects out the Colorado Rockies leading
to widespread shower and thunderstorms developing across South
Dakota and Nebraska into Saturday morning. More specifically, most
high resolution guidance continue to show high confidence in an
Mesoscale Convective System (MCS) developing across western Nebraska
and spreading eastwards overnight. However, as the developing
convection outruns/eats up the better instability expect gradually
weakening to occur as it heads towards the Nebraska/Iowa border.

From here, most of the developing shower activity should exit our
area by early parts of Saturday afternoon. Continuous southeasterly
surface flow and effective mixing will allow for the atmosphere to
slightly recover heading into the evening hours as highs vary
between the mid 70s to mid 80s with the warmest conditions situated
along the Missouri River Valley with the warm front. Looking at
soundings across the area, while the set up will be conducive
for scattered shower development, its going to be a bit more
difficult to get much true convection during the time period
mostly due to borderline convective temperatures and a strong
cap in certain areas. However, there is a chance that once the
cap begins to weaken near sunset that a few isolated strong
storms could get going along the warm front/sector near the
Missouri River and portions of northwestern IA. If this does
occur, developing parcels would have between 1500-2000 J/kg of
MLCAPE and 20-30 kts of shear to work with. With mid-level
lapse rates expected to reach between 6.5-7 degrees C/km at this
time, could see some large hail develop with stronger cells up
to quarter size. With all this in mind, SPC has outlined portion
of far southeastern SD and northwestern IA in a Day 2 Slight
Risk (Level 2 out of 5) with the primary focus being areas south
of Hwy-18 corridor. Lastly, Expect most of this developing
activity to exit our region by Saturday night as quieter
conditions temporarily return to the area into Sunday.

The Long Term (Sunday-Thursday):

Heading into Sunday, mostly quiet conditions temporarily return to
our area as a mostly dry cold front slides through the region
throughout the day. Increased southerly surface winds will become
more northerly with the passing of the near-surface boundary with
gusts between 20-30 mph possible especially east of I-29. While some
weak cold air advection (CAA) likely moves in aloft, +20 to +25 850
mb temps along with efficient mixing will likely help our daily high
warm into mid to upper 80s and low 90s with the warmest conditions
expected along in northwestern IA. From there, our attention will
likely pivot to the Colorado Rockies by Sunday night as a closed low
ejects into the northern plains likely bringing our next
precipitation chances (40%-70%). While exact rainfall amounts remain
uncertain, PWATs up to 1.50" and an lingering stationary boundary
ahead of inverted trough gives some decent signals for some heavy
precipitation heading into Monday morning. The one remaining
question is where the stationary boundary and subtle shortwaves
tracks and thats still a bit too early to tell. Looking at ensemble
guidance though, there`s continues to be low to medium confidence
(20%-40%) in up to an inch of QPF across the area which is always
beneficial. Nonetheless, we`ll have to continue to monitor the
trends to get a better idea of how this will pan out.

Looking into the new week, an active pattern continues aloft as an
Upper-level ridging strengthens over the eastern CONUS shifting our
area to southwesterly flow aloft. Some deterministic guidance does
show some decent potential for periodic rain chances on Wednesday
and Thursday. However, with long-range deterministic guidance
starting to diverge with the placement of features its too early to
tell how things will pan out. As a result, left the default NBM in
for the extended. Lastly, temperatures will trend downwards towards
our seasonal normal through Thursday with highs expected to be
largely in 70s to 80s with a few low 90s possible across
northwestern IA on Tuesday.

&&

.AVIATION /18Z TAFS THROUGH 18Z SATURDAY/...
Issued at 1200 PM CDT Fri Jun 14 2024

Showers and isolated thunderstorms will move into central SD
early this afternoon, but struggle to progress east as dry air
below about 12 kft does not support much in the way of showery
activity. Later tonight, after about 3-6z, moisture in the mid
levels as well as a little bit of instability should support the
expansion of showers and thunderstorms which will gradually
shift into southwest MN and northwest IA on Saturday morning.
LIngering showery activity will remain possible in eastern SD
and northeast NE through Saturday morning. Some MVFR ceilings
will be possible late tonight into Saturday morning.

&&

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

&&

$$

DISCUSSION...Gumbs
AVIATION...08