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FXUS63 KFSD 260408

AFDFSD



Area Forecast Discussion

National Weather Service Sioux Falls SD

1108 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 /06Z TAFS THROUGH 06Z SATURDAY/...

Issued at 1108 PM CDT Thu Apr 25 2024



VFR ceilings have begun to deteriorate as stratus moves in, and will 

continue to deteriorate to MVFR with scattered IFR for the remainder 

of the period. Scattered showers and thunderstorms have begun across 

the region. This first round is expected to remain sub-severe, 

however dime to nickle size hail and stronger wind gusts up to 50 

mph under thunderstorms are possible. 



Winds are out of the southeast at 15-20 kts sustained with gusts 30-

35 kts. The highest gusts will shift from west to east during the 

overnight period and will be predominate over northwestern Iowa by 

Friday morning. Winds will gradually decrease through the afternoon 

to less than 20 kts. There exists some concern for LLWS at KSUX near 

the end of the period. Directional and speed shear may be present 

between 1500 and 2000 feet AGL at 160 degrees and 45 kts. 



A second, stronger round of showers and thunderstorms will develop 

over northern Nebraska in the next few hours. 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