326 FXUS63 KFSD 170846 AFDFSD Area Forecast Discussion National Weather Service Sioux Falls SD 346 AM CDT Thu Apr 17 2025 .KEY MESSAGES... - Isolated showers and thunderstorms through late this morning; strong to severe storms unlikely. - Greatest storm chances this afternoon and evening along and southeast of a Vermillion to Slayton line. Strong to severe storms are possible, mainly between 4 PM and 10 PM. Large hail to the size of ping-pong ball sized (isolated larger) is the main threat, with damaging wind gusts to 60 mph a secondary hazard. - Showers continue tonight through Friday afternoon with cooler and breezy conditions. - Periodic low rain chances and near normal temperatures return for the weekend through mid next week. Confidence in precipitation chances and timing is low (less than 30%). && .DISCUSSION... Issued at 345 AM CDT Thu Apr 17 2025 NOW-TONIGHT: A few returns on radar this morning across southwestern MN and northern IA with the first weak short wave, but have not seen any precipitation reach the ground through 3 AM CDT/08z. It`s a mild but breezy start to the day, with current temps in the 50s. Looking back to the west, increased cirrus exists over northern NE with the next wave, which we`ll be watching as it moves northeast through daybreak for potential shower/storm development. Although this area is coincident with WAA, nose of the upper jet, and the developing surface low pressure, any shower/storm development looks to be highly isolated. Strong cap remains in place, so we`d either need to break the cap or have storms develop off of roughly 700 mb. The issue is that despite elevated instability at this level, we`re lacking moisture through and below this level. Therefore, limited mention to sprinkles and pops to less than 15% through late morning. Concern shifts to the afternoon and evening hours as surface low pressure, attendant fronts, and elevated cold front move east through the forecast area. Guidance this morning is beginning to mix more efficiently along and southeast of a Vermillion to Slayton line, eroding the cap more quickly (as early as 2-3 PM CDT/19-20z) near and just ahead of the cold front. This area is at the greatest risk of strong to severe storms through the afternoon and evening, though there remains some question in moisture return in the lower mid levels - especially given the convection on-going at the time of this discussion across KS and western MO. Timing could be as early as 2 PM for a rogue storm but think the greatest risk is 4 PM CDT/21z continuing through 10 PM CDT/18.03z. MUCAPE 1200-1500+ J/kg along with steep mid level lapse rates over 7.5 deg C/km and 0-6 bulk shear values increasing to over 40 knots support a large hail threat of ping-pong ball size (1.5") hail. Can`t entirely rule out larger hail for more isolated, supercellular storms ahead of any linear (tied to the front) storms. Wind gusts to 60 mph are possible with DCAPE values progged over 800 J/kg over northwestern IA. Could see locally heavier rainfall rates with PWAT values 1-1.5"; however, convection should be progressive enough to limit concerns to localized ponding of water this afternoon through tonight. Rainfall amounts largely less than half an inch, with the highest chances (40-50%) for more than half an inch of rain across southwestern MN. For temperatures, this will be timing dependent. Expect areas west of Wagner to De Smet to warm into the 60s, with 70s to near 80 further east where we`ll remain in the warm sector the longest. If moisture return is efficient, we could see dew points today in the east in the 50s. Lows tonight fall into the mid 30s (west) to mid 40s (east) behind the cold front. Breezy conditions prevail today and tonight, especially behind the fropa. FRIDAY: Elongated mid and upper level trough continues to slide to the east Friday. Southwesterly flow aloft and a few mid level short waves will allow for light precipitation to continue through at least the first half of the day Friday. Cooler and breezy conditions prevail with lower level northerly flow. Highs in the upper 40s to lower 50s with wind gusts to 30 mph. Chillier conditions Friday night with lows falling into the upper 20s to lower 30s. SATURDAY-MONDAY: Closed mid/upper low develops in the Four Corners region out of the aforementioned trough. This feature moves to the northeast through the weekend; however, guidance has been continually trending further to the south with the track of this low and the attendant surface low. Will maintain the NBM pops, with moderate chances (40-55%) of measurable (0.01" or more) rainfall along/east of I-29 Sunday into Monday. Deterministic guidance is quite varied on the track of the surface low. At 21.06z, the GFS has the center of the low in western IL, the ECMWF is in central IA, and the Canadian is still centered in far northwestern MO. So low confidence in precip chances. Temperatures start off the weekend cooler than average with highs in the 50s Saturday, warming to the 60s and 70s Monday. Lows in the lower to mid 30s. TUESDAY-THURSDAY: Quasi-zonal to zonal flow regime sets up for mid next week. Near to above average temperatures expected. A few short waves could bring periodic precipitation chances so will maintain the low (~30% or less) chances populated from the NBM. && .AVIATION /06Z TAFS THROUGH 06Z FRIDAY/... Issued at 1018 PM CDT Wed Apr 16 2025 Scattered mid-lvl and upper clouds continue to move northeast late this evening. Eventually a few showers or even a thunderstorm may develop in SW Minnesota with this activity. An additional surge of mid-lvl clouds arrives around daybreak, bringing a risk for sprinkles elsewhere through mid-morning. Gusts ahead of a surface front moving into southeastern South Dakota may approach the 30 mph mark into early afternoon. Eventually this front will reach Sioux Falls around 19-20Z turning winds west of the front to the west and then sharply northwest. East of the boundary, scattered strong thunderstorms may develop over SW Minnesota and NW Iowa into early evening. Greatest potential from Sioux City to Windom. MVFR stratus may begin to move southeast into the Tri-State area in the evening, as gusty northerly winds continue. && .FSD WATCHES/WARNINGS/ADVISORIES... SD...None. MN...None. IA...None. NE...None. && $$ DISCUSSION...SG AVIATION...Dux