641
FXUS63 KFSD 041137
AFDFSD

Area Forecast Discussion
National Weather Service Sioux Falls SD
637 AM CDT Thu Jul 4 2024

.KEY MESSAGES...

- Scattered showers and thunderstorms are expected this
  afternoon and evening. A low end severe weather risk along
  with heavier rainfall potential is possible.

- Chances for rain will continue through the weekend but heavier rainfall
  is not expected.

- Cooler then normal temperatures will continue well into next
  week.

&&

.DISCUSSION...
Issued at 322 AM CDT Thu Jul 4 2024

Light showers with a a few rumbles of thunder begin the day today.
Should see the showers continue to push eastwards while also
diminishing. This will leave a quieter period for most of the
morning hours before an upper level wave passes over the forecast
area and closes off. Abundant cloud cover is expected for most of
the area but locations south of I-90 may see some breaks in the
clouds during the afternoon hours. With the upper low overhead,
better jet energy via a potential vorticity (PV) anomaly and the
lift from the left exit region itself will overspread the area,
allowing for scattered showers and thunderstorms to blossom across
the area this afternoon. A cold front will be passing through the
forecast area today which could serve as a focal point for slightly
stronger storms this afternoon. Instability looks to remain marginal
with only up to around 1,000 J/kg of CAPE expected. Sufficient
vertical shear will be in place thanks to the previously mentioned
jet streak with deep layer shear values up to 40-50 knots, strongest
east of I-29. The cold front will be passing through the area rather
quickly today which makes severe weather chances a bit uncertain. If
the front passes through the area fast enough, then severe weather
chances will be minimal. If the front slows down a bit, then severe
weather will be possible east of I-29. The primary hazards will be
large hail to the size of a quarter (1 inch) and funnels to perhaps
a brief tornado. Only really see the possibility of a tornado IF a
storm is able to develop on the cold front and harness it`s
baroclinically generated vorticity. Funnels are also possible due to
the upper level low over head. The lowest end hazard will be
damaging winds to 60 mph due to 0-3km theta-e difference values
between -10k to -16k despite overall poor lapse rates. To go along
with the severe weather threat, isolated heavier rainfall is
possible. This will not be a widespread heavy rainfall due to the
scattered nature of the showers and storms this afternoon. Rainfall
amounts between 0.25" to 0.75" should be the best range for heavier
rainfall but isolated amounts up to around an inch are possible,
mainly over southwest Minnesota. Shower and storm chances will wane
through the evening hours as the best forcing for ascent pushes east
of the area. Light showers are still possible on the backside of the
system through the night, mainly across southwest Minnesota. Low
temperatures will fall to the upper 50s to low 60s overnight.

Friday will be a calmer day as the previously mentioned upper level
low skirts east of the forecast area, placing cooler northwest flow
across the Northern Plains. High temperatures will be cooler with
highs in the 70s expected. Minor instability is expected which will
lead to another round of afternoon showers. Good news is that
rainfall amounts will be minor between a few hundredths to a tenth
or two. Low temperatures will fall to the upper 50s overnight.

An amplified pattern takes over for the weekend as upper level
ridging builds over the west coast of the US. This will place
predominate troughing over the eastern two thirds of the country and
continue chances for showers and storms. The most likely timeframe
for showers and storms will be Saturday afternoon and evening as a
shortwave trough pushes into the Northern Plains. Some of the storms
could be strong to severe given sufficient instability and shear in
place. Aside from rain chances, highs will be in the 70s to low 80s
for the weekend with lows falling to the upper 50s to low 60s.

The ridge axis pushes a bit further east on Monday. This will rise
heights aloft and also decrease upper level pressure gradients. This
looks to result in drier conditions for the work week along with a
continuation of near to below average temperatures. Ensembles
support a drier pattern as they show only minor probabilities on the
order of 20-30% for exceeding a tenth of an inch of rain. High
temperatures look to remain in the upper 70s and 80s with lows
falling to the upper 50s and 60s overnight.

&&

.AVIATION /12Z TAFS THROUGH 12Z FRIDAY/...
Issued at 636 AM CDT Thu Jul 4 2024

Mid to high level clouds and some showers begin the TAF period early
this morning. Scattered showers are expected to increase in coverage
through the morning and afternoon hours. Lightning may accompany the
showers but due to the scattered nature of the showers, do not have
high enough confidence to include mention of thunder in any TAFs.
Will monitor trends throughout the day. Ceilings look to remain VFR
for today but any shower or thunderstorm could quickly drop ceilings
to MVFR levels. Otherwise, winds will slightly strengthen out of the
northwest today as a cold front passes through the area with gusts
up to 25 knots expected. The strongest gusts will occur across south
central to southeastern South Dakota.

Showers and storms look to wane this evening into the overnight
hours across most of the area. Some light showers may persist
through the night across southwest Minnesota but all terminals
should remain dry to end the TAF period.

&&

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

&&

$$

DISCUSSION...Meyers
AVIATION...Meyers