834
FXUS63 KFSD 061100
AFDFSD

Area Forecast Discussion
National Weather Service Sioux Falls SD
600 AM CDT Sat Jul 6 2024

.KEY MESSAGES...

- Patchy fog this morning and again tonight-early Sunday.
  Widespread dense fog is not expected, but isolated visibility
  below a mile is possible.

- Increasing coverage of showers and thunderstorms through this
  afternoon to early evening, diminishing again by midnight
  tonight. A few strong to severe storms are possible with large
  hail and damaging winds the primary threats.

- Unsettled weather continues early next week with spotty
  afternoon to early evening showers/storms Sunday-Tuesday.
  Severe weather is not expected.

- Cooler than normal temperatures for early July through the
  early part of next week, but trending closer to normal by the
  end of the week.

&&

.DISCUSSION...
Issued at 359 AM CDT Sat Jul 6 2024

TODAY-TONIGHT: Light winds, mostly clear nighttime skies and plenty
of surface moisture from recent rains will favor at least patchy fog
development this morning and again tonight into early Sunday. Seeing
some of this already on satellite and in some surface obs as of 08Z
so have expanded mention to most areas near/east of the James River
Valley through 7-8am this morning.

As the fog is burning off shortly after sunrise, attention will turn
to a well-defined shortwave currently spinning east-southeast out of
far eastern Montana. This wave will slide east toward the eastern
Dakotas by this afternoon, providing some upper level support during
our diurnal peak of instability. Models continue to show broad area
of MUCAPE 1500-2000 J/kg ahead of the wave, though model consensus
indicates 700-500mb lapse rates remain on the weak side (mainly 6-7
C/km, perhaps as high as 7.5 near the Missouri River and slightly
steeper in a more shallow layer). At the same time, modest deep
layer shear of 30-40kt builds into southern parts of our forecast
area as the wave slides through. While stronger shear and steeper
lapse rates are focused south of our forecast area in Nebraska, this
combination could support a few organized storms capable of large
hail up to half dollar size (1.25 inches) and damaging wind gusts
to 60 mph. Tornadoes appear unlikely given high LCLs seen in the
soundings.

Stronger storms could also produce locally heavy rain, but given
progressive storm movement and PWAT (precipitable water) values near
to slightly above average for this time of year, widespread heavy
rainfall is not expected. Although CAMs do not show great agreement
on timing/location details, there is modest consensus that greater
storm coverage/persistence will be focused from east central SD into
southwest MN, which can also be seen in moderate (40-60%) HREF
probabilities of rainfall exceeding 0.50" and low (10-30%) probs of
exceeding 1 inch.

Timing of stronger storms should be focused from mid afternoon
through shortly after sunset, with the wave sliding east and
instability quickly waning thereafter.

A weak surface pressure gradient and decoupling after sunset will
allow for light winds again tonight, which could again lead to
patchy fog after midnight into early Sunday.

SUNDAY-TUESDAY: The broad mid-upper level trough remains in place
across the northern Plains/Upper Midwest early next week, slowly
drifting east by later Tuesday. Modest afternoon instability along
with optimally timed shortwaves sliding through the base of the
trough could support scattered showers/storms, mainly during the
afternoon to early evening aided by the diurnal heating. However,
weak mid-level flow leads to minimal shear across our area, so do
not expect severe storms during this period.

WEDNESDAY-FRIDAY: The early week trough tries to slide east by
midweek, but appears a little slower than seen in previous runs.
This could allow for another day of spotty afternoon showers on
Wednesday, though confidence is too low to include at this time. As
we progress through the latter part of next week, the upper ridge
makes a stronger push eastward by the end of the work week. This
should allow for dry conditions and gradually warming temperatures
for the end of this forecast period.

&&

.AVIATION /12Z TAFS THROUGH 12Z SUNDAY/...
Issued at 600 AM CDT Sat Jul 6 2024

Areas of reduced visibility in fog as we start this TAF period,
but expect this to burn off rather quickly by 13-14Z.

Main concern through this evening will be increasing potential
for scattered thunderstorms, especially as we progress through
the afternoon and evening. Timing consensus among various high-
resolution models is poor, so will try to target a relatively
narrow 2-4 hour window when TS is more favored at TAF sites.

Convective threat begins to wane after 07/03Z-05Z, with patchy
fog once again possible by late in the period. Confidence is on
the lower side regarding extent, though, so will not include in
TAFs at this time.

&&

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

&&

$$

DISCUSSION...JH
AVIATION...JH