458 FXUS63 KFSD 020355 AFDFSD Area Forecast Discussion National Weather Service Sioux Falls SD 1055 PM CDT Tue Aug 1 2017 .SHORT TERM...(This evening through Wednesday) Issued at 318 PM CDT Tue Aug 1 2017 Weak wave pressing across central SD early this afternoon, and have been watching progression of a mini-MCS into areas of west of the James River in advance of this feature. Instability is actually fairly decent with MLCAPE on the order of 2000-2500 J/kg, especially concentrated near the slowly sinking frontal boundary across southwest MN extending through the KFSD area toward south central SD. The problem for existing storm structures is that the overall deep shear is practically non-existent, which means that while initiation to storms gets a strong updraft going, it does not take too long for storms to choke themselves off. However, there is also a healthy amount of DCAPE with around 1000 J/kg, so will have to watch for a damaging wind threat with any briefly organized storms through late afternoon. Should not take long for southward progressing front and the passage of the wave to limit precipitation chances through early evening along the Missouri River, with the remainder of the night likely to feature a light north to northeast wind. At this time, looks like should get enough drying to keep fog from being a widespread threat as winds weaken and start to back toward the east/southeast again late night as stronger complex wave moving into the western Dakotas, with the leading wave moving into western SD and trailing stronger wave into northeast MT. Attention then turns toward these waves moving into the area during the day on Wednesday. Leading wave will approach the western CWA midday, with likely enhancement of clouds, and enough elevated instability to result in at least a scattering of showers/thunderstorms. As one progresses through the day, diurnal heating will become more challenged, and overall instability will not be as strong as today, likely maximizing from 1000-1500 J/kg ahead of the precipitation. Have some concern about clouds/more spotty precipitation with the leading wave perhaps weakening the destabilization potential even more. Deep-layer shear is much greater at 35-45 knots with stronger winds aloft ahead of the frontal boundary, which puts shear/instability in a much more favorable parameter space. Would have to believe that there is at least a lower-end severe weather threat for much of the area, starting early to mid afternoon toward the James River, and continuing into the evening hours as the main convective development pushes eastward. Threat would be primarily wind and some marginal large hail, the latter limited by instability levels. Main increase in div Q forcing comes later in the day along with the approaching jet streak, and should see precipitation become more widespread west of I-29 through the mid to late afternoon. Some areas of heavier rainfall will be possible, but amounts again likely limited by transience of precipitation. .LONG TERM...(Wednesday night through Tuesday) Issued at 318 PM CDT Tue Aug 1 2017 Main concerns in the extended period will be rain and thunderstorms Wednesday night into Thursday morning. Highs on Thursday will also be fairly close to record cold high temperatures. Rain and thunderstorms will move through on Wednesday night and linger into Thursday morning across southwest MN. Shear and instability are nothing to get excited about but an isolated severe thunderstorm will be possible in the evening. Some heavy rainfall will be possible but expecting it to be widespread at this time as the system appears to be fairly progressive and freezing levels are somewhat lower around 11000 feet. By Thursday afternoon the area should be well into the dry slot with pretty chilly air in place. Will be looking at the potential for some record cold high temperatures with highs from the mid 60s to mid 70s. Most record cold highs are in the lower to mid 60s. While Friday will moderate with highs back into the mid and upper 70s another system will pull onto the Plains with an increased threat for rain and thunderstorms Friday night into Saturday. Will maintain the 60 percent to 80 percent chance for rain and thunderstorms. Not planning on a severe threat at this time. After this, from Sunday into Tuesday temperatures should rebound closer to normal with no strong signals for rain and thunderstorms. Highs generally 75 to 85 with lows 55 to 65. && .AVIATION...(For the 06Z TAFS through 06Z Wednesday night) Issued at 1055 PM CDT Tue Aug 1 2017 All 00Z models have slowed the progression of the first wave and thus the onset of precipitation on Wednesday. Expecting VFR conditions at KHON and KFSD through at least 18Z Wednesday. There is the potential for 3-5SM light fog at KSUX around sunrise although expect that any fog will be brief. After 18Z, a wave will move southeast toward central South Dakota. This will likely be accompanied by scattered showers and thunderstorms. The TAFs for all 3 sites will focus on the best chance for thunderstorms. However, persons planning to fly into these locations will want to examine later forecasts as timing will be adjusted. Based upon latest timing of wave expect that the best chance for thunderstorms will not reach KHON until at last 2200 UTC and last through 02Z. For KFSD and KSUX, the best chance for thunderstorms will be after 00Z with the better chance at KFSD than at KSUX. For both locations have included thunderstorms in the TAF between 00Z and 06Z. && .FSD WATCHES/WARNINGS/ADVISORIES... SD...None. MN...None. IA...None. NE...None. && $$ SHORT TERM...Chapman LONG TERM...08 AVIATION...Schumacher