195
FXUS63 KFSD 040819
AFDFSD

Area Forecast Discussion
National Weather Service Sioux Falls SD
319 AM CDT Tue Jun 4 2024

.KEY MESSAGES...

- Scattered showers & a few thunderstorms move across southeast
  SD this morning, with coverage of showers/storms increasing
  near and east of I-29 this afternoon. A few strong to severe
  storms are possible in northwest Iowa/southwest Minnesota.

- Windy midweek, especially Wednesday as northwest winds may be
  briefly enhanced by scattered sprinkles. Lighter winds are
  expected Friday into the weekend, though afternoons may still
  be on the breezy side.

- Precipitation chances Friday into early next week are low (at
  or below 30%). Neither severe weather nor heavy rain are
  expected.

&&

.DISCUSSION...
Issued at 317 AM CDT Tue Jun 4 2024

TODAY: Elongated area of showers and a few embedded thunderstorms
pushing across our western counties early this morning, aided by low
level jet/warm advection ahead of an approaching mid-upper level
trough. Coverage of this activity may briefly wane near to shortly
after daybreak as these features weaken, but anticipate increasing
coverage again by mid-late morning as lead wave rotating through the
base of the trough slides across the area. Limited instability prior
to 18Z so would expect mainly an increase in showers with embedded
non-severe thunderstorms.

As the associated cold front approaches the I-29 corridor around
18Z, it will encounter an increasingly unstable air mass. Aided by
moderate heating into the mid-upper 70s and dew points climbing into
the mid to perhaps upper 60s, should see MLCAPE values up to 1500-
2000J/kg with an eroding cap allowing for rapid storm development.
As we often see with cold frontal passages, instability is maximized
ahead of the front, while favorable deep layer shear is displaced
near/behind the boundary. The weak shear (generally <30kt) in place
where instability is greater will likely lead to pulsy multicell
activity capable of isolated quarter to half dollar size hail from
the stronger cores. May also see isolated 50-60 mph wind gusts with
collapsing cores as a secondary threat. While rainfall rates may be
briefly heavy within a narrow corridor of precipitable water values
near or above 1.5 inches, progressive storm movement should limit
total rainfall amounts. However, still have to monitor for ponding
water and additional rises on area rivers/streams, some of which are
still holding near to above flood stage.

TUESDAY NIGHT-WEDNESDAY: Upper trough and associated cold front push
east of the forecast area by 05/00Z or shortly thereafter, leading
to a comfortable night with light winds, clearing skies, and cooler
temps as strong drying behind the cold front drops dew points into
the 40s. Wednesday will see a trailing wave slide southeast through
the region, along with a secondary cold front in the late morning
and afternoon. Limited moisture should preclude measurable rain
chances, but cannot rule out a few sprinkles. Main impact will be
the potential for mixing stronger wind to the surface. In general,
the cold advection will support gusts approaching advisory levels,
mainly near/north of I-90. However, deeper post-frontal mixing may
tap into 40-45+kt atop the mixed layer per forecast soundings, which
could lead to isolated 50+ mph gusts, especially if sprinkles do
materialize. Mixing of the westerly flow ahead of the boundary will
allow for temperatures warming into mid 70s to lower 80s, though
highs may be reached earlier than the typical diurnal timing with
readings leveling off or falling back a bit during the mid-late
afternoon.

THURSDAY-MONDAY: Upper low digs into the Great Lakes through the
latter part of this week while a modest ridge builds across the
Rockies. This will maintain primarily dry northwest flow across our
forecast area. Could see a few showers or storms with a subtle wave
late Friday-Friday night, though moisture is sparse, so any rainfall
would be light. Models diverge on the evolution of the upper low
from Sunday onward, so confidence in temperatures and rain chances
early next week is on the lower side. Could see scattered showers or
storms by Monday if the upper low lags back across the western Great
Lakes, but these chances would be lower if the upper low weakens and
slides off to the east more quickly. Temperatures through Saturday
should be close to seasonal normals. More uncertainty by early next
week, again dependent on whether the upper low lingers in the west
(cooler air for the northern Plains) or slides off to the east
(seasonable temperatures are more favored).

&&

.AVIATION /06Z TAFS THROUGH 06Z WEDNESDAY/...
Issued at 1039 PM CDT Mon Jun 3 2024

Convection as of 330z in south central SD has been pulsy over
the last 30 minutes or so. If it is able to hold together, could
impact 9V9 and surrounding areas by 5z.

Otherwise, largely VFR conditions expected, with lower
ceilings/visibility possible with periodic convection chances.
Would expect most of the MVFR/IFR conditions Tuesday afternoon
east of I-29 where -TSRA coverage is expected to be greatest.
Isolated to scattered showers and storms are possible through
mid morning, with increasing coverage late morning near I-29.
Better chances will be early to mid afternoon east of I-29 as a
cold front goes through. Rain/storms end during the evening.

Winds increase overnight into the early morning hours Tuesday.
Direction overnight will be largely southerly until daybreak,
when a cold front begins to move through and shift winds to the
northwest. Winds shift through the period and could gust around
25 knots near the front. Lighter and variable winds expected
toward the end of the period.

&&

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

&&

$$

DISCUSSION...JH
AVIATION...SG