227
FXUS63 KFSD 191126
AFDFSD

Area Forecast Discussion
National Weather Service Sioux Falls SD
626 AM CDT Fri Jul 19 2024

.KEY MESSAGES...

- Scattered thunderstorms expected to move into the area through
  the day, with initial risks this morning and early afternoon
  and then isolated risks late in the day. Low end risks for
  large hail and some strong wind gusts will focus west of I-29.

- Unsettled weather through the rest of the weekend, with
  scattered showers and thunderstorms again Saturday. Some
  funnel development may be possible Saturday.

- Many outdoor events this weekend will want to make sure to
  have an eye on the radar as activity this weekend will be
  rather variable in location and rapid to develop.

- Cooler temperatures continue into next week, with near daily
  rain chances. Rain however won`t impact all locations, and
  will be very hit-or-miss.

&&

.UPDATE...
Issued at 615 AM CDT Fri Jul 19 2024

Elevated convection lifting off the 800 mb layer continues to
increase in a few areas this morning tied to weak embedded
vorticity maxima in the northwesterly flow. One wave is moving
along the Missouri River approaching Sioux City, a second is
located in north central South Dakota, and a third is crawling
east southeast out of the Badlands.

There seems to be a bit more agreement with the RAP/HRRR updates
that these waves will continue to move southeast through the
morning and early afternoon. The activity from Mobridge to
Miller will likely be the predominate feature riding through an
increasing areas of MUCAPE approaching 1500 J/KG this morning.
Effective shear with this activity is pushing 30-35 kts, so some
elevated hailers may be possible. Following the trends of the
RAP/HRRR, I have pushed PoPs higher throughout the James River
valley through early afternoon along the path of this wave.
This may shift at least at least some severe weather risk into
the morning hours with the wave reaching the MO River/Hwy 20
corridor early afternoon. While the prevailing risk will be from
hail, some signals for 50-60 mph winds could develop if we can
tap into the surface layer.

The passage of this wave could end up stabilizing things for the
rest of the afternoon and evening hours and lead to lower PoPs.
Won`t completely go for that scenario at this time, but those
trends may develop.

&&

.DISCUSSION...
Issued at 243 AM CDT Fri Jul 19 2024

THIS Morning:  Mid-lvl clouds continue to thicken early Friday
morning in response to increasing warm advection.  Through south
central and central South Dakota, some deeper cloud development has
already taken place on the edge of an increasing mid-lvl lapse rate.
 The resultant area of ACCAS has developed a few thunderstorms in
Gregory county.   Short term guidance continues to hint at further
development of elevated clusters of storms through central and
western South Dakota through mid-morning.  Some of this activity may
track down the Missouri River. Additional sprinkles may try to
develop east of I-29.

TODAY:  Elevated convection could linger into the mid morning hours
along and southwest of the James River valley, but eventually this
activity will wane as the LLJ veers.  Southerly return flow will
then develop by mid-day, increasing surface moisture convergence
along a trough extending through central South Dakota, emanating
from a surface low in northern Nebraska. Dew points are already
in the lower 60s this morning, and should rise into the middle
to upper 60s in most locations by early afternoon. If we can
avoid any substancial amount of cloud cover this morning,
temperatures will rise into the 80s by early to mid-afternoon. A
shortwave currently across northern Montana will arrive early
this afternoon to central SD and northern Nebraska, likely
providing a spark to initiate convection along and ahead of the
surface trough/low. Moderate instability upwards of 2000-2500
J/KG will reside west of the James River valley, but overall
effective shear may only climb near 25 to 30 knots. This
combination may be just enough to produce a few semi- organized
clusters of convection that will drop southeast into the late
afternoon hours. A secondary shortwave over southern Alberta
will arrive an hour or two later, assisting in developing
scattered convection over northern and northeastern South
Dakota, which may drift southward into early evening. The
overall severe weather risk remains marginal, but would not be
surprised to see some 1.5" hail reports given shear distribution
and steep mid-lvl lapse rates. DCAPE remains well below
critical thresholds, but a collapsing core could bring 60 mph
winds. Would not rule out the current marginal risk pushing
slightly further east this morning, but feel the greatest
severe weather risk will reside west of I-29 and especially west
of the James River.

TONIGHT: Convection should wane through the evening with the loss of
daytime heating.  However, the synoptic forcing won`t shut-off,
meaning that a few showers and thunderstorms may continue into the
overnight hours.

SATURDAY: An extension of a large Hudson Bay trough will remain
through the Upper Midwest on Saturday, and some models actually show
these aforementioned shortwaves merging and deepening near the Tri-
State area early on Saturday. Should this happen, then a couple more
concentrated areas of rain may form on Saturday near the upper low
core. Where is much more difficult to pinpoint, so a broad PoP will
be maintained. While instability and shear will remain below
severe weather thresholds, the presence of cooling mid-lvl
temperatures and stretching underneath the upper vorticity could
result in afternoon funnels where new updrafts can form. This
diurnally driven rain should diminish in the evening.

SUNDAY:  Temperatures remain in the upper 70s on Sunday, and we`ll
again be having to deal with afternoon and early evening widely
scattered convection.  Pinpointing the exact locations is fruitless
2 days out, so will maintain a broad 30-40 PoP.

MONDAY-THURSDAY:  With much of the region within a large trough
covering the eastern half of the CONUS, it`s time to get used to a
nearly daily afternoon and evening scattered convection risk. Latest
indications point to daily PoPs through Wednesday before the upper
trough shifts east and ridging begins to slide eastward into the
Plains.  Temperatures remain near to slightly below normal through
mid-week, with potential for normal Summer heat to return by the end
of next week.  Typical rainfall amounts in this kind of regime will
vary wildly from location to location.  Some may see just a trace or
a few hundredths while others see a quick inch.

&&

.AVIATION /12Z TAFS THROUGH 12Z SATURDAY/...
Issued at 615 AM CDT Fri Jul 19 2024

Scattered convection will likely track southeast through the
Tri-State area, but especially through the James River valley
this morning and early afternoon. Some hail risk and MVFR
visibility will be possible in passing convection.

Should latest trends continue, this activity would leave the
forecast area and areas south of Sioux City by mid-afternoon
potentially leaving VFR conditions into the overnight hours.
Scattered rain chances may also diminish if the environment
stabilizes enough behind the wave.

Overnight, some potential for fog or low stratus development as
winds turn light and low-lvl flow convergences in the Tri-State
area.


&&

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

&&

$$

UPDATE...Dux
DISCUSSION...Dux
AVIATION...Dux