← Previous June 17, 2024 10:56 PM

FXUS63 KFSD 180356

Area Forecast Discussion
National Weather Service Sioux Falls SD
1056 PM CDT Mon Jun 17 2024


- Continued uncertainty for severe weather risks through
  tonight, given cloud cover, lingering showers/storms, and the
  surface warm front displaced from guidance projections. May
  see renewed potential for elevated storms, mainly north of
  I-90. Overall severe threat is low.

- A progressive front moves through on Tuesday, bringing yet
  another risk for strong storms and locally heavy rainfall.
  Brief bursts of 60 mph winds and marginally severe hail

- An unsettled week is ahead, with numerous thunderstorm risks 
  into next weekend. The risk for locally heavy rainfall will be
  possible each day, with slightly more muted severe weather 
  risks with lower shear.


Issued at 303 PM CDT Mon Jun 17 2024

Surface effective warm front was pushed well south of earlier
projections by our morning convection, and has returned to near
a Norfolk NE-Storm Lake IA line as of 1930Z. Additional storms
have developed along/north of the suspected 850mb warm front,
now near and north of US Highway 18 in northwest Iowa with the
storms extending north into southwest Minnesota. This activity
continues to progress to the northeast ahead of a triggering
mid-level wave. Southeast portions of the CWA have seen the
greatest clearing this early afternoon. We are also seeing a 
decrease in coverage of the lower stratus across southeast SD
per satellite and surface obs, though still plenty of mid-level
cloud cover around to reinforce the cooler air currently north
of the warm front.

TONIGHT: Confidence in high-res models is on the low side given
poor handling of ongoing convective line now in IA/MN. However,
they seem to show fair agreement in developing scattered to
numerous showers/storms ahead of the elevated warm front as it 
lifts north of I-90 during the later afternoon and evening. 
Forecast soundings toward the Highway 14 corridor show steep 
mid-level lapse rates that could support isolated larger hail,
but effective shear for the elevated parcels is much lower (near
30kt) than the full 0-6km bulk shear of over 40-45kt, and thus
an unsure whether elevated storms will become organized enough
for more than a pulsy hail threat through this evening. By
~04Z, the elevated warm front is focused well north of our 
forecast area, and should take much of this convective threat
north along with it. 

Will have to watch for potential afternoon development to our 
southwest in western Nebraska, as some CAMs indicate these 
storms evolving into a linear cluster lifting northeast across 
Nebraska through the evening. This activity would be closer to 
the surface warm front, which could present a slightly greater 
threat of damaging wind gusts. However lack of agreement in this
scenario among the models (some have a notable lack of activity
in this area) leads to lower confidence in seeing additional 
rain moving into the Missouri River Valley overnight.

TUESDAY-TUESDAY NIGHT: After an expected quiet late night into 
Tuesday morning, will see a renewed threat of strong to severe 
storms near and more likely east of I-29 as a cold front and 
associated upper trough slide east across the region. Strong 
influx of low level moisture ahead of the front will lead to 
MUCAPE values 1500-2000 J/kg, though soundings remain strongly 
capped to surface-based convection until the front arrives, so 
may again be looking at potential for elevated storms for which 
shear is on the weaker side. Similar to tonight, expect large 
hail and pockets of heavy rain to be the greatest threats.

The cold front is expected to exit our eastern counties by mid
Tuesday evening, but the southern end of the front may hang up
to the southwest, keeping a lingering chance for additional
showers/storms across at least the southeast half of the area
into later Tuesday night.

WEDNESDAY-SATURDAY: Unsettled pattern continues through much of the 
extended forecast as blocking high pressure remains stagnate across 
the eastern US - keeping us in a southwesterly flow regime. Outside 
of a cooler day on Wednesday, temperatures largely near normal (+/- 
5 degrees or so). Periodic breezy conditions prevail.

Showers and storms continue Wednesday, mainly focused during the day 
across our southeastern counties with the focus of a weak mid level 
wave, lower level WAA, an elevated boundary, and the right entrance 
region of the upper jet all line up. Showers and storms continue 
into Wednesday night, likely becoming more widespread as the next 
weak mid level short wave tracks out of western NE. This wave 
continues to move northeast through Thursday, keeping more 
widespread storm chances in place. Severe weather looks unlikely 
from Wednesday into at least the first half of Thursday as 
instability is lacking. PWATs during the day on Wednesday look to be 
around 1.0-1.5", highest across northwestern IA. Higher values (up 
to 2") lift northward into the day Thursday as moisture advection 
increases and lifts north.

Next slightly stronger wave moves through during the latter half of 
the day Thursday into Thursday night, with instability increasing to 
around 1500 J/kg. However, best bulk shear is offset from the 
instability to the north and west, so severe threat appears low at 
this time. Again, heavy rainfall remains a concern with PWATs still 
around 1.5-2" and becoming more widespread over the area.

Mid level waves train overhead in quick succession Friday into 
Saturday, with a shift to more westerly flow into the weekend thanks 
to a more defined mid/upper trough diving southeast from southern 
AB/SK and northern MT. Rain and storm chances continue, although 
timing and location are a bit more uncertain due to timing issues 
with the short waves during this period. Surface low in tandem with 
the more defined trough will lift off to the northeast through the 
latter half of the weekend. 

SUNDAY-MONDAY: May see a reprieve from rain Sunday into Monday as 
some ridging begins to develop in the western portions of the 
northern/central Plains; however, confidence is low given variance 
in model data. Additionally, nearly all deterministic guidance 
brings another short wave in on the heels of this ridge, so not sure 
how long of a break from the unsettled pattern we might have. 
Continued near normal (+/- 5 to 10 degrees from average) 


Issued at 1039 PM CDT Mon Jun 17 2024

Continued development of isolated showers/storms possible
through the overnight hours between I-90 and Hwy 14. Watching
development at the time of this discussion across western SD and
NE as this may slowly propagate eastward overnight as well.
Confidence is low if convection will reach areas near the James
Valley, so have left KHON dry for now. Additional showers and
storms are expected through the day tomorrow, with the best
chances in the afternoon along/east of I-29 as storms develop
near the cold front. Storms may linger east of I-29 into late
evening. Severe risk looks low tonight, but strong to severe
storms are possible Tuesday. Locally heavy rainfall is possible.

Stratus and lower visibilities with storms are expected, with
lower end VFR to patchy IFR stratus around already tonight.
Expect conditions to deteriorate as convection expands.
Improvement in conditions anticipated behind the cold front
later in the period. 

Finally, LLWS prevails across the entire area overnight as the
LLJ strengthens to 45+ knots. There is both a directional and
speed component to this. Wind gusts 20-35 knots through the
Tuesday afternoon/evening. Direction will shift to more
northwesterly by the end of the period behind the cold front.