FXUS63 KFSD 150834 AFDFSD Area Forecast Discussion National Weather Service Sioux Falls SD 334 AM CDT Wed Apr 15 2026 .KEY MESSAGES... - Patchy and locally dense fog is developing early this morning north of I-90. Visibility may fall below one mile at times. - Scattered showers with isolated thunderstorms continue through this evening, mainly focused across northwestern Iowa and adjacent areas in eastern Nebraska and extreme southeastern South Dakota. - An isolated strong to severe storm is possible this afternoon and evening along/south of a line from Norfolk, Nebraska to Spencer, Iowa. Highest risk is from 3 to 7 PM. If a stronger storm can develop, main threats are hail to ping pong ball size (1.5 inches) and wind gusts to 60 mph. A tornado cannot be ruled out. - Unseasonably warm temperatures, very low humidity, and breezy southwest wind gusts lead to near critical to critical fire danger Thursday. A Fire Weather Watch has been issued along/west of I-29. Additional fire concerns possible Friday but confidence is low. - A pattern shift leads to a brief cool down late this week into the weekend with continued precipitation chances. Uncertainty remains, but an isolated strong to severe storm is possible again Friday. Much colder air could lead to wintry precipitation, although timing and type remain uncertain. && .UPDATE... Issued at 333 AM CDT Wed Apr 15 2026 Calm to light and variable winds are leading to another morning of patchy fog, including locally dense fog, mainly north of I-90 where skies have cleared. Fog should lift through the mid morning hours. Expect any visibility below 1/2 miles to be limited in scope, so not anticipating any headlines. But with guidance handling this a bit poorly, will keep an eye on trends. For later today, SPC Day 1 outlook has shifted both the Marginal and Slight risks (levels 1 and 2 of 5, respectively) back west - with the Marginal into northeastern NE and northeastern IA and the Slight risk southeast of Sloan to Storm Lake line. Some uncertainty in severe risk depending on how far north the lower level front will lift through the day and if there is any morning convection across the area. Regardless, shear values and mid level lapse rates still appear supportive of large hail to ping pong ball size. Damaging wind gusts to 60 mph are also possible with stronger storms. Biggest question will be the instability, with most deterministic guidance limiting MUCAPE to around 1000 J/kg or less, which would temper the severe potential. A tornado cannot be ruled out if the boundary can sneak back into our area with low level shear and increased instability tied to that front. Greatest risk looks to be from 3 to 7 PM. CAMs do overall develop storms across NE and move them northeast into our area during this time. Any storm across the area will be capable of lightning, so keep an eye on the forecast if you have outdoor plans today/tonight. Another change to the forecast in the relatively shorter term was the issuance of a Fire Weather Watch for areas along and west of I- 29 for Thursday afternoon and evening. More details are below in the Fire Weather Section of this discussion, but breezy winds and very low humidity with warmer temperatures combine for near critical to critical fire conditions. Thursday is another day to use extreme caution to prevent fire start. && .DISCUSSION... Issued at 233 PM CDT Tue Apr 14 2026 Radar is picking up on a stripe of showers extending from roughly Marshall, MN to Gregory, SD this afternoon, but most of this will not be reaching the ground due high cloud heights and dry air beneath said clouds. Scattered showers and storms will continue to develop off to our south and west over the next hour or so where the greater surface moisture is. Can't entirely rule out an elevated thunderstorm over northwest Iowa as soundings show a few hundred J/kg of CAPE lifted from around 750 mb this afternoon, but likely not enough for severe weather. However, small hail would be possible with mid level lapse rates around 7-7.5 C/km and 50-60 kts of 0-6 km bulk shear if a thunderstorm can develop. A boundary will be lifting northward across the region late tonight into Wednesday morning. The NAMNest is the fastest with this boundary arrival, bringing in storms to the Highway 20 corridor just before sunrise Wednesday, but this remains an outlier. What's more likely to occur is showers and storms not developing until the afternoon as the boundary continues drifting northward and instability increases due to daytime heating. Isolated strong to severe storms will be possible given mid level lapse rates greater than 8 C/km and bulk shear in the 45-55 kt range. The main threat with any of these afternoon storms would be large hail up to ping pong ball in size followed by damaging wind gusts to 60 mph. If we do get morning showers or storms tomorrow, then that may limit the ability for the atmosphere to recover in the afternoon, thus less afternoon instability. The best chance of an isolated severe storm Wednesday afternoon will be roughly along and east of a Spencer to Sioux City line. Any storms will push east of the area heading into Wednesday evening as the surface low and upper wave move out of the area. We are dry for Thursday, but this may come with the potential for critical fire danger in parts of the area. Southwesterly winds look to return for areas mainly along and west of I-29, which will help drop relative humidity values down to 25% and below Thursday afternoon. With temperatures in the 80s and winds gusting to 25 to 30 mph, a very high fire danger can be expected for most of the area. Uncertainty remains on how strong the winds will get and how far east these stronger winds make it, and if the grasses are starting to green up enough to prevent more widespread fire weather concerns. With that, held off on fire weather headlines for now until certainty grows. The main western US trough that has been helping to send all these impulses across the area over the past couple of days will finally move eastward heading into Friday, pushing a strong cold front into the area. Ahead of the front, warm and moister air will be favorable for thunderstorms, some of which could be strong to severe mainly east of I-29. Timing of the cold front will play a role in how much coverage of storms can be expected, with a faster passage meaning a lower threat and a slower passage leading to a greater threat of stronger storms. One thing is for more certain is the colder air that will follow this system, with lows expected to drop below freezing for most of the area by Saturday morning. This means some rain with this system may at least briefly turn to snow as the precipitation exits the area, but confidence is very low on this potential. Either way, expect much cooler temperatures heading into the Friday night through Sunday morning time frame. After this push of colder air, ridging aloft looks to return and thus a quick warming trend looks possible into early next week. && .AVIATION /06Z TAFS THROUGH 06Z THURSDAY/... Issued at 1228 AM CDT Wed Apr 15 2026 Mainly VFR conditions will persist this TAF period. While mostly clear conditions persist this evening, can't rule out additional showers to start the day on Wednesday especially across the Highway-20 corridor. Otherwise, additional showers and storms will be possible by Wednesday afternoon near KSUX. Added in a PROB30 group for the increased probabilities. Lastly, light and variable winds tonight will become light southerly winds during the day on Wednesday to end the TAF period. && .FIRE WEATHER... Issued at 333 AM CDT Wed Apr 15 2026 Although humidity values today fall to below 25% west of the James River, light southerly winds preclude any widespread concerns. Minimum RH values increase further east with light winds and scattered shower/storm chances, widespread elevated fire danger is not expected today. Attention turns to Thursday with temperatures climbing into the 80s. A dry day is expected, and much drier air moves into the region leading to minimum humidity values as low as 15% and only as high as around 30%. These factors along with strong southwesterly winds gusting to around 30 mph will lead to near critical to critical fire conditions as fuels remain dry. A Fire Weather Watch has been issued along and west of I-29 from noon to 8 PM, where the strongest winds and lowest humidity coincide. Confidence is low in the potential for near critical fire conditions Friday due to a cold front moving through Thursday into Friday. This timing impacts temperatures and there may be some showers with some uncertainty in the precipitation type. Northwesterly winds on Friday will be stronger than Thursday, gusting to around 40 mph. However, RH values are expected to be near or exceed 35%, which with cooler temperatures and precipitation, may temper widespread concerns. Breezy and cooler weather Saturday may lead to elevated concerns, but confidence is low. && .FSD WATCHES/WARNINGS/ADVISORIES... SD...Fire Weather Watch from Thursday afternoon through Thursday evening for SDZ038>040-050-052>071. MN...None. IA...None. NE...Fire Weather Watch from Thursday afternoon through Thursday evening for NEZ013-014. && $$ UPDATE...SG DISCUSSION...Samet AVIATION...05 FIRE WEATHER...SG