FXUS63 KFSD 252343
AFDFSD

Area Forecast Discussion
National Weather Service Sioux Falls SD
643 PM CDT Thu Apr 25 2024

.KEY MESSAGES...

- Isolated to scattered showers and storms this afternoon. Additional
  showers and storms move in tonight through Friday. Strong to 
  severe storms are possible tomorrow (greatest risk between 3 
  and 9 PM), along with locally heavy rain. 

- Shower and storm chances taper off Saturday, but increase once
  again on Sunday. Uncertainty remains, but those with outdoor
  plans should keep an eye on the forecast.

- Through Sunday night, widespread beneficial rainfall of an
  inch or more is expected. Some localized areas could see 2 or
  more inches of rain in this period.

&&

.DISCUSSION...
Issued at 354 PM CDT Thu Apr 25 2024

REST OF TODAY AND TONIGHT: Isolated showers and storms continue this 
afternoon and early evening with increasing clouds as the first 
vorticity lobe advects north a wave ejecting out of the Rockies. 
Precip has been struggling a bit with dry air below the cloud bases. 
This low will begin to deepen tonight. Breezy conditions this 
afternoon continue through tonight, with tightening pressure 
gradient and the potential to mix into stronger winds aloft. Expect 
southeasterly winds 20-30 mph, with gusts around 40 mph. Isolated 
gusts as high as 45 mph have been briefly observed (as well as 
sustained winds over 30 mph); however, these have been sporadic and 
isolated enough in nature to preclude any wind headlines. As we lose 
peak mixing later this evening and tonight, should see a slight drop 
in gusts. But, we could see some 40 mph gusts overnight if there is 
any mixing into the strengthening LLJ. Temperatures this afternoon 
range from the upper 50s (cloudy areas along the MO River) to the 
lower 70s (clear skies in SD and MN). Continued southeasterly flow 
helps keep lows in the 40s and lower 50s. 

Once afternoon showers/isolated storms lift north out of the area, 
we'll turn our attention to the development just to our southeast in 
NE through the evening hours. This activity, firing off the nose of 
the LLJ and mid level vorticity lobe coincident with the WAA and 
elevated warm front, will continue to lift north/northeast ahead of 
the deepening low through the overnight hours. Instability is 
elevated, and with values around 700 J/kg, severe weather looks 
unlikely. Mid level lapse rates around 6 deg C/km could produce some 
hail up to nickel sized in a stronger storm, and can't rule out a 
gust or two around 50 mph overnight if showers/storms are able to 
pull down any of the stronger winds. Rain amounts will be quite 
variable due to the convection but areas under stronger and/or 
multiple thunderstorms could see close to an inch, with the highest 
amounts across northwestern IA. 

TOMORROW AND TOMORROW NIGHT: Low pressure continues to deepen as it 
lifts northeast through the day on Friday, lifting into the southern 
MO Valley by the late afternoon/early evening hours - becoming more 
stacked as it treks into our area. Strong to severe storms are 
possible, although there is some uncertainty as we wait and see the 
answers to these three questions: if/how quickly do clouds and 
morning convection clear up during mid day, if/how quickly can the 
atmosphere recover, and where does the surface warm front end up. 
Stratus through the day would help to temper some of the heating and 
conditional instability, and thus limit the threat somewhat (less 
instability to work with). Regardless, Friday is shaping up to be a 
high shear/low CAPE possible severe weather event. MUCAPE varies 
between model runs, but generally is at or below 1200 J/kg. However, 
0-6 bulk shear values of 35+ knots (with some higher res models 
showing 50+ knots) and low level (0-1 km) shear 35-40+ knots is 
enough for supercells (or mini supercells) and a tornado threat. LCL 
heights are hovering around 1500 ft, which is also supportive of a 
tornado threat.  Mid level lapse rates also increase, especially if 
we are south of the warm front and/or clear out, with values around 
6.5-7.5 deg C/km supportive of the threat for large hail of half 
dollar size - which is the main and most likely threat. Shear values 
are more perpendicular to the front than parallel, so anticipate 
that convection will be more discrete than linear. Damaging winds to 
60-65 mph can't be ruled out, although would be a greater threat if 
more of the conditional instability is realized. So, greatest 
concern tomorrow for severe weather falls between 3-9 PM, with the 
risks of large hail, tornadoes, and damaging winds. Rainfall totals 
again could be around an inch or more for some in the convection, 
but most could see a tenth to one half of an inch in this time. 

Otherwise, clouds and breezy conditions prevail with highs in the 
upper 50s to upper 60s (again, depending on how far north the front 
goes and if we can clear out) Low pressure slides into southwestern 
MN by the early overnight, with lingering wrap around showers and 
isolated storms. Lows fall into the upper 40s and 50s.

SATURDAY: Low pressure moves off to the northeast Saturday, but will 
likely see some lingering wrap around precipitation through the day, 
especially early and along the Hwy 14 corridor. Breezy with highs in 
the mid 50s west of the James to the upper 60s southeast of IA/MN 
Hwy 60, where the cold front might not have fully exited until later 
in the day and skies might be more clear due to the position of the 
low. Lows at night fall into 40s to near 50.

SUNDAY: Pattern Sunday is oddly similar to what we're expecting 
Friday and Friday night, with low pressure moving northeast out of 
the Rockies into KS/NE. This low becomes stacked as it moves into 
NE, with attendant warm front lifting north. More questions in the 
track of this system as well as the timing, but could be another 
high shear/low CAPE sort of day. This low is poised to move into the 
MO River Valley a bit more quickly, during the late morning/early 
afternoon Sunday. Similar questions regarding if/when we can clear 
out, which would increase our conditional instability. Those with 
outdoor plans should especially keep an eye on the forecast with the 
chances for showers and storms. Will be keeping an eye on trends 
here, with a potentially shifting severe weather risk.

When all is said and done through the weekend, beneficial rainfall 
of 1-2" is possible to have fallen, as both the ECMWF and GFS 
ensembles showing the entire area with an 80% chance or more of at 
least an inch of rain. Mostly low (~30%) to moderate (40%) chances 
of greater than 2" across the area, although there are higher 
pockets in both the ensembles and the deterministic models. 

EARLY/MID NEXT WEEK: Behind the low Sunday night, mid and upper flow 
becomes more zonal with occasional shortwaves passing through. 
Largely expect near to above normal temperatures with highs in the 
upper 60s and 70s and lows in the 40s. Could see some periodic 
showers or isolated storms with passing waves, but confidence is too 
low to stray from the NBM at this time. Periodically breezy 
conditions expected as well.

&&

.AVIATION /00Z TAFS THROUGH 00Z SATURDAY/...
Issued at 643 PM CDT Thu Apr 25 2024

VFR ceilings will deteriorate over the next few hours as stratus 
clouds move in. A few light showers continue along and north of 
Highway 14. Expect these to continue to move north-northeastward. 

Southeast winds at 15-20 kts sustained with gusts 30-35 kts will 
continue through Friday afternoon. The higher gusts currently over 
central South Dakota will move east along the I-29 corridor, to 
northwestern IA by Friday morning. Gusts gradually decrease Friday 
afternoon to less than 20 kts. There exists some concern for LLWS at 
KSUX near the end of the period. Directional shear may be present 
between 1000 and 2000 feet AGL at 220 degrees and 30 kts. 

Shower and thunderstorm chances increase overnight. Some of these 
storms could be strong to severe with hail up to an inch and 
damaging wind gusts. Several additional waves of showers and 
thunderstorms are expected through Sunday as a low pressure system 
moves through the area. Some of these storms could again be strong 
to severe. 

&&

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

&&

$$

DISCUSSION...SG
AVIATION...AJP