239 FXUS63 KFSD 020348 AFDFSD Area Forecast Discussion National Weather Service Sioux Falls SD 1048 PM CDT Sun Jun 1 2025 .KEY MESSAGES... - High level Canadian wildfire smoke continues through tonight. Ground level smoke/haze is producing widespread reduced air quality with conditions slowly improving this evening and tonight from west to east. All those sensitive to air quality should use caution. - Thunderstorm risks return late Monday afternoon into Monday night. A narrow corridor of severe weather risk is expected to develop over eastern South Dakota and adjacent areas of Minnesota, Iowa, and Nebraska after 4pm Monday. Severe risk diminishes toward midnight. - Severe weather risks include hail up to ping pong ball size and brief downburst winds of 65 mph. Locally heavy rainfall is possible, but any flooding risk should be contained to urban areas. - Temperatures return to seasonal normals for the remainder of the week, with some potential for widely scattered diurnal showers/thunderstorms each day. && .DISCUSSION... Issued at 245 PM CDT Sun Jun 1 2025 CURRENTS THROUGH TONIGHT: Wildfire smoke aloft and at the surface continues to stream over the area, with visibility at or below 5 miles for much of the area through early this afternoon. Air quality has been in the moderate category or worse throughout the day; those who are sensitive to poor air quality should continue to take precautions. Winds have generally remained light to almost calm as we have struggled to mix. Expect mixing to commence later this afternoon with southwesterly winds. Temperatures have been a bit slower to rise due to the smoke and the lack of mixing, and lowered highs by a degree or two. Still expect to warm into the mid and upper 80s. Mid level ridge slides east tonight, shifting winds aloft to more southerly. This slowly clears smoke from west to east overnight. We`ll remain a bit breezy overnight with a tightening surface pressure gradient and a bit of mixing overnight. Temperatures will remain on the warmer side because of this, with lows in the lower to mid 60s. MONDAY-MONDAY NIGHT: Ridge axis moves east into IA Monday with split flow - mid/upper level northern jet trough axis moves west out of the Rockies and southern jet low pressure treks into the southern Plains. 01.12z guidance came in with a bit stronger of a leading mid level wave. This should bring an increase in mid level cloud cover, and may provide a catalyst for development with WAA, especially with 01.12z guidance (namely the GFS and NAM) have come in a touch slower with the surface cold front than previous and other models. Expect instability to increase during the afternoon as dew points climb into the 50s and lower to even mid 60s just ahead of the front and temperatures across the area warm into the 80s and lower 90s. Storms may begin to fire as early as 2-3 pm, and quickly become severe in the narrow corridor of MUCAPE over 2000 J/kg. Most CAMs are later in the development, with storms firing around 4-5 pm between the I-29 corridor and James River Valley. Storms should move east with the front and the instability, with CAPE quickly dropping off through the late evening hours. Shear values in our area around 25 knots or less, with mid level lapse rates around 7 deg C/km. Expect the severe threat to wane by midnight, especially given the strongest shear values (0-6 km shear 40+ knots) are well offset to the west of the instability. Greatest risk of severe storms is along and northwest of a Tracy to Sioux Center to Sioux City line after 4 pm with storms weakening east of MN/IA State Hwy 60. Storm mode will generally be multi-cell clusters given the shear vectors and values. Hazards: Hail to the size of ping pong balls (1.5") is possible, especially with more discrete cells in initial development with the aforementioned instability. 0-6 km bulk shear being around 25 knots may limit this potential somewhat, but discrete storms may be able to overcome lack of shear. Strong wind gusts to 65 mph are possible with DCAPE values around 1000 J/kg and high PWAT values in addition to the more linear mode expected. Tornadoes are not expected due to the lack of shear and LCL heights over 4kft. Rainfall: PWAT values are in the top 2.5% of values compared to climatology. PWATs of 1.5-2", deep warm cloud layer (near or exceeding 10kft), and efficient moisture transfer should lead to efficient rainfall rates - with moderate (40-60%) chances of exceeding 0.5" per hour and low (less than 20%) chances of 1"+ per hour. 1 hour FFG ranges from 1.75" in northwestern IA to 2.5" in south central SD. Widespread flash flooding is not expected; however, heavier rainfall rates could lead to localized flash flooding in urban areas as well as localized ponding on roadways and other poor drainage areas. May also see some issues if locations see multiple rounds of training storms. Rainfall totals for much of the area half an inch to 1.5 inches, with lower amounts along a line from Chamberlain to Huron and higher amounts south of I-90 into northern NE. TUESDAY: Upper level trough continues to move through during the day on Tuesday, with surface high pressure sliding into western SD during the day. Expect cooler than average temperatures with highs in the 60s to lower 70s. Rain and clouds diminish from west to east through the day and evening hours with the mid/upper level wave. WEDNESDAY ONWARD: Numerous mid and upper level waves track through broad upper trough stretching from the Hudson Bay to the southwestern US. This leads to periodic and diurnally driven shower and thunderstorm chances. Severe weather risk looks low at this time. Temperatures return to near average for the first week of meteorological summer - highs in the mid/upper 70s and lows in the mid 50s. && .AVIATION /06Z TAFS THROUGH 06Z TUESDAY/... Issued at 1048 PM CDT Sun Jun 1 2025 Southerly winds will increase after day break to sustained 18-22 kts with gusts of 26-30 kts. Strongest gusts are expected between the James River Valley and I-29 corridor. Winds will decrease slightly after sunset, but continue to gust 20-25 kts through the end of the period. A brief window of LLWS is possible at KHON as winds begin to respond to the approach of a strong cold front. There is a chance KFSD may experience sporadic LLWS between 02.11Z and 02.14Z, but confidence was too low to include it in the TAF. As the cold front progresses southeastward, showers and thunderstorms are expected to develop along the front. Initially these storms may become strong to severe, producing hail to the size of ping pong balls, and wind gusts to 56 kts. Timing of the greatest severe threat is between 4 pm and 9 pm. Showers will then decrease in severity but continue into the overnight period. && .FSD WATCHES/WARNINGS/ADVISORIES... SD...None. MN...None. IA...None. NE...None. && $$ DISCUSSION...SG AVIATION...AJP