070 FXUS63 KFSD 261948 AFDFSD AREA FORECAST DISCUSSION National Weather Service Sioux Falls SD 248 PM CDT Wed Jun 26 2019 .SHORT TERM...(This Evening through Thursday) Issued at 240 PM CDT Wed Jun 26 2019 Quiet weather through the daytime hours today, as lingering MCS across northern Missouri continues to send cirrus across NW Iowa this afternoon. Temperatures have been limited thanks to the light winds and cloud cover. Several areas of concern in the forecast ahead, including severe storm risks later tonight, hot and humid conditions this weekend, and returning thunderstorm chances early next week. Tonight: We'll watch two distinct areas for convective development later today. ACCAS field slowly drifting eastward across central South Dakota this afternoon indicative of initial surge of higher theta-e air aloft and is expected to continue to drift eastward into the evening. This ACCAS will likely begin to intersect with a developing LLJ later this evening, or early in the overnight hours, across SW Minnesota which could spur some development. It will be possible to have an isolated hailer in this development later tonight. However, the main area of concern will be across the western High Plains as an elongated shortwave arrives later this afternoon. Favorable synoptic forcing should force multiple clusters of supercells later this afternoon or early evening as a highly unstable atmosphere has developed. Nearly all model guidance in agreement that cellular merger should take place with cold pool development allowing one or more small scale MCS beginning to move east northeast into the night across the Dakotas and northern Nebraska. The concerning issue for our area is where the primary development takes place. With a surface/850 front remaining somewhat pinned southward this afternoon due to MCS activity, and a stronger EML slightly slower to lift northward, could see convection take a bit more of a southern track than what the 12Z NAM/EC/GEM suggested. High elevated instability approaching 3000 J/KG along with strong synoptic forcing suggest that this activity should be able to sustain some intensity as it crosses the Dakotas. However a bit concerned that the shear/CAPE profiles are too unbalanced to support long duration or widespread severe risks. That said, soundings continue to support a transition from supercellular strong winds/hail/tornado risk towards primarily a damaging wind and heavy rain risk as storms cross the Dakotas. CAMs indicate an increased potential for strong winds at least towards the James River valley. Any organized MCS should slide eastward by daybreak, but the veering LLJ and weaker EML on the eastern half of the CWA (MN/IA) could lead to persistent redevelopment into the ridge through mid- morning Thursday. Some of this activity could also be strong to severe. Thursday: Temperatures will be very dependent on the evolution of the overnight MCS and any lingering stratus/cirrus development. However, temperatures should begin to rise by the afternoon into the 80s, with a distinct increase in dew points. .LONG TERM...(Thursday Night through Wednesday) Issued at 240 PM CDT Wed Jun 26 2019 Friday-Sunday: Mid-level heights really begin to rise as we head into the weekend, allowing hot and humid conditions to enter the region. Some concerns moving through the weekend that high temperatures could be a bit too high, and that boundary layer moisture could limit heating potential. Nevertheless, any offset in heat index values by lowering temperatures would be made up by higher dewpoints. Heat headlines are still anticipated, especially as overnight lows only fall into the lower 70s. The ECMWF has trended towards the GFS for Sunday night through Tuesday, bringing a frontal boundary into the area and increasing the risks for convection to start next week. Shear remains fairly poor given the synoptic setup, but instability would still allow for some severe weather risk late Sunday and again Monday. Tuesday-Wednesday: No real changes made to the extended. A flattening mid-level ridge could leave the area susceptible to daily convection, along with near to slightly above normal highs. && .AVIATION...(For the 18Z TAFS through 18Z Thursday afternoon) Issued at 1205 PM CDT Wed Jun 26 2019 VFR conditions persist into the evening hours. Will be monitoring convection that develops over western South Dakota and the Nebraska panhandle later this evening. Latest convective trends continue to support this convection moving northeast along a stalling boundary. Will increase wording in TAF for increasing confidence in convection. Strong winds will be a risk for all aviation locations. Thunderstorm activity will slide east after daybreak, but could linger along the low level jet axis over SW MN and NW IA into mid-morning. && .FSD WATCHES/WARNINGS/ADVISORIES... SD...NONE. MN...NONE. IA...NONE. NE...NONE. && $$ SHORT TERM...Dux LONG TERM...Dux AVIATION...Dux