


Area Forecast Discussion
Issued by NWS Sioux Falls, SD
Issued by NWS Sioux Falls, SD
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637 FXUS63 KFSD 261802 AFDFSD Area Forecast Discussion National Weather Service Sioux Falls SD 102 PM CDT Thu Jun 26 2025 .KEY MESSAGES... - Scattered showers/isolated storms will continue to diminish in coverage through this afternoon. Still a low risk for an isolated strong/severe storm in our far southeast counties this afternoon, but greater threat will be east of Highway 71 corridor. - Periodic thunderstorm chances continue Friday evening through the weekend. Some indication that storms could become strong to severe at times. Begin monitoring this time period if you have outdoor plans. - Warming temperatures and increasing humidity this weekend will bring a risk of heat indices above 100F in some areas Saturday afternoon. Otherwise seasonably warm temperatures will prevail much of next week. && .UPDATE... Issued at 1255 PM CDT Thu Jun 26 2025 A slow-moving wave has been maintaining an area of showers across the Highway 14 corridor while coverage farther south continues to slowly decrease. Subtle boundaries may become a focus for weak funnels this afternoon, but need at least some partial clearing to boost instability a bit more. Will also be monitoring our far southeast counties for an isolated strong-severe storm over the next 2-3 hours, but that threat should shift east of Highway 71 fairly quickly. && .DISCUSSION... Issued at 351 AM CDT Thu Jun 26 2025 TODAY: Elevated showers and weak thunderstorms continue this morning, triggering along an area of convergence supported by the nose of the LLJ and a mid to upper level shortwave. These are expected to remain sub-severe due to low instability (only a couple hundred J/kg CAPE) and shallow upper lapse rates (< 6 Deg C). As the surface front makes its final push through northwestern Iowa late this morning into the early afternoon there is a chance of renewed convection. CAMS show a line of stronger thunderstorms forming along this boundary as it moves off, but there is disagreement in the location of initiation. Some have storms initiating as far west as a rough line from Sioux City to Spencer. Others don`t have the stronger convection initializing until it`s east of our area. Looking at the dynamics, 0-6 bulk shear of 30-40 kts could support a few isolated stronger cells. However, the instability is looking less favorable, only a few hundred J/kg, with the better thermal profile just east of our area. In either case, PWAT values are at or near the maximum for climatology. Considering this, the deep, warm cloud layer of 12,000+ feet, and long skinny sounding profiles, these will likely still be efficient rain producers. An additional quarter to an 1.5 inches of rain is possible by the time rain ends this afternoon. Higher pockets are possible for areas in northwestern Iowa. As such, will leave the Flood Watch that is already in place. In addition, as the low passes over the region, an area of enhanced stretching potential and vorticity advection sets up over northwestern Iowa and southwestern Minnesota. Here a few brief funnels are possible this afternoon through this evening. Threat of funnels should wane as the sun sets and afternoon heating dissipates. Storms will gradually cease by late this afternoon. Clouds will gradually decrease from west to east this afternoon. As the sun comes out we can expect temperatures to begin to rise into the upper 70s to 80s for areas along and west of the James River. Slightly cooler east of there where clouds last longer, in the 70s. Overnight lows will be in the upper 50s to low 60s. FRIDAY-SATURDAY: Surface high pressure moves in for Friday, keeping us dry. Through the day, winds will turn to the south-southeast. Areas to the west of James River will see winds increase in response to a tightening SPG as a shortwave approaches from western South Dakota. Gusts in the afternoon will be 15-25 mph in this area, less than 10 mph to the east. As the wave continues to progress east, a warm front will push into the region from the west. This will help our highs for Friday warm into the 80s to low 90s over central South Dakota. As the wave continues its progress, a quick shot of rain is possible early Saturday morning. The best shear remains north of the area, but instability and steep mid-level lapse rates could support a storm or two becoming stronger. The threat is short lived as the wave clears the area quickly. Location of activity is uncertain, as there is low consensus in the model guidance. The rest of the afternoon a very strong push of WAA on southwesterly winds will help our highs for Saturday reach into the 90s. Dew points will be in the upper 60s to mid 70s. These combine to create heat index values in the upper 90s to low 100s. We will need to continue to monitor this trend as it may become necessary to issue a heat headline in the future. SUNDAY-NEXT WEEK: The hot weather will be short lived this time as another short wave and cold front move through the region. Highs will be in the mid 80s to low 90s, with the warmest temperatures along and south of the HWY 20 corridor. Showers and thunderstorms are expected to trigger off this system late Saturday night into Sunday. Guidance is in low agreement on track of this system. The GFS keeps the track to the north, just clipping out Minnesota counties. The EC, CAN, and NAM vary on coverage, but all have the system traversing from northwest to southeast through the day Sunday. The best shear will lag behind the best instability. Soundings are well capped, but do indicate some elevated storms are possible. Plentiful instability will be present with steep lapse rates, however shear will be marginal. It is possible a few isolated to scattered severe thunderstorms may develop. If they do, the primary threats will be large hail and damaging wind gusts. Next week the active pattern aloft looks to continue. Periodic rain chances will be in the forecast through the end of the week. That includes the 4th of July. If you have outdoor plans for that day, keep an eye on the forecast, you may need to make adjustments. && .AVIATION /18Z TAFS THROUGH 18Z FRIDAY/... Issued at 1255 PM CDT Thu Jun 26 2025 Low MVFR-IFR stratus is still rather prevalent across the forecast area to start this TAF period, though expect this to slowly lift through the afternoon. Limited mixing will leave behind plenty of boundary layer moisture, though, and with light winds expected overnight, should see areas of fog develop later tonight into early Friday morning. MVFR-IFR visibility seems most likely, but cannot rule out sub-1SM LIFR visibility in some areas. Fog should diminish pretty quickly after sunrise. && .FSD WATCHES/WARNINGS/ADVISORIES... SD...None. MN...None. IA...None. NE...None. && $$ UPDATE...JH DISCUSSION...AJP AVIATION...JH