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Area Forecast Discussion
Issued by NWS Sioux Falls, SD
Issued by NWS Sioux Falls, SD
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978 FXUS63 KFSD 141947 AFDFSD Area Forecast Discussion National Weather Service Sioux Falls SD 247 PM CDT Sun Jul 14 2024 .KEY MESSAGES... - High humidity with temperatures in the 80s and 90s will lead to heat index values of 95 to 105 degrees. Heat Advisory remains in effect for areas along and south of I-90 until 8 PM. - An area of thicker wildfire smoke can be seen on satellite advecting into south central SD. This moves east through the evening along the southern MO River Valley and northwestern IA; however, no surface impacts are currently expected. - Showers and storms are possible tonight through late Monday morning, although confidence is very low in coverage and timing. Strong to severe storms are possible if storms develop, with all hazards possible. - Unsettled pattern continues into mid/late next week with periodic low shower and storm chances. Starting Tuesday, temperatures will be near to below normal for this time of year. && .DISCUSSION... Issued at 236 PM CDT Sun Jul 14 2024 CURRENTS THROUGH MONDAY: Morning cloud cover has diminished/moved east, although diurnal cumulus is developing across the region. Also noting an area of thicker wildfire smoke over south central SD; however, no surface impacts are expected at this time as it moves to the southeast through the evening hours. Temperatures continue to climb into the 80s and lower 90s. Despite being a bit cooler than yesterday, dew points in the mid 60s to mid 70s raise heat indices into the mid 90s to 105 degrees F. Maintained the on-going Heat Advisory for areas along/south of I-90. Now, attention turns to chances for showers and storms overnight through Monday. Models continue to struggle this run in resolving short wave trajectories over the area during this time, including source region (ND v.s. western SD), timing (tonight v.s. mid day Monday), strength, and number of waves. This leads to very low confidence in convective chances through Monday afternoon. In one camp of models, the main short wave ejects out of ND late tonight bringing a complex of storms into portions of southwestern/central MN as it collides with a surface boundary. This scenario is mostly evident in the NAMNest, ARW, and some runs of the HRRR today. The FV3 is in a similar camp, although is much further to the west (bringing the storms to areas west of I-29). Some of the guidance (a couple of HRRR runs and the RAP) either don`t have this feature or shift it much further east in MN. Another short wave is progged to move into the area later Monday morning, and depending on where the boundary ends up after any overnight convection, this may be a catalyst for additional storm development in the late morning tomorrow along/south of I-90. The NAMNest is the most aggressive with this development in northeastern NE, quickly growing upscale along the front into northwestern IA. Given all the uncertainty, generally tried to use an average of the hi-res models and previous forecast for pops. If storms are able to advect into or develop over our area into late Monday morning, they could quickly become strong to severe. MUCAPE is generally 1500 J/kg or higher (at times approaching 3000+ J/kg), bulk shear of 35+ knots, and steep mid level lapse rates of over 8 deg C/km support wind gusts to 70 mph and golf ball sized hail. Based on last night/early this morning`s storms, would not be entirely surprised if a stronger complex of storms produces wind gusts to 80 mph. Can`t rule out a tornado or two with the surface boundary hanging around, low LCLs, and 0-1 bulk shear around 20 knots. Locally heavy rain is possible as PWATs sit between 1.5 and 2 inches. Not anticipating widespread flooding issues as convection is expected to be fairly progressive. Lows tonight in the upper 60s to lower 70s. Highs tomorrow will be highly dependent on morning convection, cloud cover, and how far south the boundary is. Seasonal temps expected with highs in the 80s to lower 90s. High dew points push heat index values into the upper 90s to near 100 in the southern MO River Valley into northwestern IA. MONDAY NIGHT AND TUESDAY: As the boundary moves south Monday night, CAA begins to filter in, bringing cooler temperatures. A couple of weak waves bring some occasional precip chances to the area, but severe weather is not expected. Lows in the upper 50s to mid 60s. Highs Tuesday will be slightly below average thanks to the CAA and cooler surface high pressure moving in. We`ll only warm into the mid/upper 70s to lower 80s. MID WEEK ONWARD: Surface high pressure meanders south around the northern/central Plains mid week, sliding east into the Great Lakes late week. Northwesterly flow regime and CAA to neutral advection keep temperatures cooler than average. Highs in the 70s to mid 80s and lows in the 50s to lower 60s. A few weak waves could bring some shower and storm chances to the region, but probability is low (< 30%). Synoptic pattern becomes more amplified later in the period as troughing digs in over the eastern US and high pressure deepens over the Southwest. && .AVIATION /18Z TAFS THROUGH 18Z MONDAY/... Issued at 1223 PM CDT Sun Jul 14 2024 An area of thicker wildfire smoke is advecting into the area this afternoon; surface impacts are not expected, but expect more SCT to BKN skies. Otherwise, very patchy MVFR stratus in southwestern MN continues to dissipate with scattered diurnal cumulus beginning to form. Showers/storms are possible tonight into Monday morning; however, guidance is struggling to resolve coverage and timing. There may also be multiple rounds of storms during the period. If storms can develop or move into the area, strong to severe storms may occur with all hazards possible. Given low confidence, have included a couple of PROB30 groups at KHON, but omitted from KFSD/KSUX given the uncertainty in the southern extent. Outside of any convection, VFR conditions expected. Winds generally around 5-10 knots through the period with direction varying. && .FSD WATCHES/WARNINGS/ADVISORIES... SD...Heat Advisory until 8 PM CDT this evening for SDZ050-057>071. MN...None. IA...Heat Advisory until 8 PM CDT this evening for IAZ001>003- 012>014-020>022-031-032. NE...Heat Advisory until 8 PM CDT this evening for NEZ013-014. && $$ DISCUSSION...SG AVIATION...SG