textproduct: Sioux Falls

KEY MESSAGES

- Decreasing clouds after noon, dry, and cool conditions on today with highs in the low to mid 70s.

- Shower and thunderstorm chances return Friday afternoon and night. Precipitation probabilities of 30 to 60 percent.

- Precipitation chances of 20-30 percent daily this weekend into early next week. Details remain uncertain at this time.

- Temperatures will rise to near or above 90 degrees in many locations by next Tuesday.

DISCUSSION

Issued at 327 AM CDT Thu Jul 17 2025

TODAY: Zonal flow aloft as a surface high pressure builds in from the northwest this morning. This will push the clouds out of the area and by afternoon we should have mostly sunny skies. As the high moves off to the east winds will gradually change from northerly to southerly, remaining light at around 5-10 mph. Weak WAA will warm temperatures slightly higher than yesterday, but still 10 degrees below average for mid July (Average is mid 80s). Highs will be in the 70s with lows in the 50s and 60s.

FRIDAY: Southerly winds increase slightly to around 10-15 mph with gusts up to 20 mph. The highest winds are expected west of the James River Valley. A stronger push of WAA comes with the winds as we begin to warm closer to the average with highs in the upper 70s to 80s. Lows will be in the 60s. In addition, the southerly winds will bring north higher dew points in the upper 60s to mid 70s. Humid conditions can be expected for Friday as a result. At the surface, a weak inverted trough moves in from the west in concert with a subtle short wave trough embedded in the quasi-zonal mid-levels. This with the WAA will support showers and thunderstorms. The GFS indicates showers beginning as early as Friday morning along and north of Highway 14, then expanding in coverage and intensity Friday afternoon and evening. The EC and CAN have more broad showers beginning Friday morning and increasing in intensity for the afternoon and evening. The NAM doesn't have much for showers until Friday afternoon. Due to the inconsistencies, confidence in shower initiation is low.

With the increasing dew points comes increasing instability. CAPE values of 2000-3000 J/kg are possible, with good 0-6km shear of 35- 45 kts, mid-level lapse rates of 7-8 C/km, DCAPE of 800-1500 J/kg and PW values of 1-1.5 inches (90th percentile for climatology). These numbers lend confidence to the storm environment being moderately favorable. However, warming above 850 mb will result in a strong cap on the environment. There is some disagreement on whether or not the cap can be overcome with the generally weak forcing. Considering this I think that the most likely scenario will be elevated showers and thunderstorms. Threats would include heavy rainfall, large hail (1-1.5 inches), and damaging wind gusts (60-70 mph). Timing of strong storms is uncertain due to discrepancies in models, however Friday late afternoon into early Saturday morning looks to be the most active.

SATURDAY-SUNDAY: For Saturday WAA and another week embedded mid- level wave keeps light isolated to scattered showers and thunderstorms going for most of the day. PW water values remain at 1.5-2 inches, and though the storm environment is less favorable for severe, locally heavy downpours remain possible. Highs for Saturday will be warm despite the clouds and rain thanks to the warm southerly winds, in the upper 70s to 80s. Lows will be in the 60s. Sunday will be very similar; isolated to scattered showers and thunderstorms that may include locally heavy rainfall. Highs will be in the upper 70s to 80s with lows in the 60s.

NEXT WEEK: Guidance indicates the active pattern will continue through at least the middle of next week. Nearly daily a weak wave works through the shallow ridge pattern bringing chances for showers and thunderstorms. Highs warm into the 80s and 90s for Monday and Tuesday. Then, a cooling trend for the middle part of the week.

AVIATION /06Z TAFS THROUGH 06Z FRIDAY/

Issued at 1030 PM CDT Wed Jul 16 2025

A mix of VFR and MVFR conditions will likely transition to mostly VFR conditions this TAF period. Taking a look at satellite imagery, areas of stratus continues to move south this evening with KHON return to VFR conditions. Expect the stratus deck to continue pushing southwards overnight potentially leaving the area by daybreak on Thursday. Could see some patchy fog develop across areas east of I-29 and our River Valleys overnight. However, confidence in widespread fog is low. Otherwise, light northerly winds will become more southeasterly by Thursday afternoon to end the TAF period.

FSD WATCHES/WARNINGS/ADVISORIES

SD...None. MN...None. IA...None. NE...None.