Area Forecast Discussion
Issued by NWS Sioux Falls, SD
Issued by NWS Sioux Falls, SD
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047 FXUS63 KFSD 280415 AFDFSD Area Forecast Discussion National Weather Service Sioux Falls SD 1115 PM CDT Thu Jun 27 2024 .KEY MESSAGES... - Rivers across the area have crested or are presently at crest. Expect rivers to slowly trend downward. - Shower and storm chances remain in the forecast through Friday night. Strong to severe storms are possible overnight tonight and again Friday afternoon. More uncertainty exists with Friday`s threat. - Although widespread heavy rainfall is not expected, isolated pockets of an inch or more are possible with thunderstorms tonight - with a worst case scenario of up to a localized 2". Otherwise, generally expect new rainfall amounts of 0.25" to 0.50" through Friday night. - Active pattern brings rain chances back to the region early next week. Locally heavy rainfall could be a threat, although confidence is low due to location/timing issues. && .DISCUSSION... Issued at 305 PM CDT Thu Jun 27 2024 A broad area of scattered showers continues across much of the CWA this afternoon - this in association with midlevel warm air advection in conjunction with a shortwave tracking over the region. Rainfall amounts have generally been on the lighter side through the day, though heavier showers over the northern James River Valley have produced nearly an inch of rain at Huron. Latest CAMS have this precipitation dwindling from west to east through the remainder of the day as the upper level forcing drifts eastward. Attention then turns to the potential for a few stronger to severe storms for tonight. A surface low presently over eastern MT/WY will slide into western SD by this evening, then into central SD during the overnight hours. In the presence of MUCAPE around 2000 J/KG, bulk shear of 40 to 50 kts, and midlevel lapse rates of 7 to 8 C/KM over that area, strong to severe storms are expected to develop through western/central SD by early this evening. These storms will then push to the east through the early night time hours. As these storms move into our area, they will become increasingly elevated with soundings suggesting a deep cap in place over our area. This would suggest that storms will weaken as they continue to move east - eventually moving into a much more stable atmosphere east of the James River. Even so, cannot completely rule out isolated severe storms over south central SD and the James River Valley, generally prior to midnight. With model PWATs running between 1.5" to 2", there will be the potential for heavy rain with any stronger or more persistent storms. A couple models - most notably the HRRR and NAM12 suggest a potential for 1 to 2 inches of rainfall from 00Z to 12Z on Friday - although these models are not in agreement with the placement of heaviest rainfall. In addition, other hi-res models do not indicate this much rain overnight, and the 12Z HREF would suggest only a 30-40% probability of receiving 1.5 inches of rainfall overnight - focused over the northern James River Valley. That being said, it will bear watching overnight. Southerly winds will remain fairly breezy overnight with the approach of the aforementioned frontal trough. Lows will be in the mid to upper 60s. The surface low/frontal boundary pushes across the CWA on Friday, exiting the area by late afternoon/early evening. Latest CAMs suggest there could be shower and thunderstorm - generally east of Interstate 29 in the mid to late afternoon. There will be another potential for strong to severe storms over that area in the afternoon with progged MUCAPE around 2000 J/KG - though midlevel lapse rates will remain in the 6 to 7 C/KM range, and bulk shear will only be moderate -running around 35 kts. In addition, uncertainty remains how any earlier showers will impact the potential for afternoon convection. The potential for heavy rain looks to be lower on Friday, though higher amounts would of course be possible in a heavier storm. It will be a warm day with highs in the upper 70s to lower 80s. A few light showers may linger even into Friday night, though rainfall amounts would be very light. With the passage of this system, a nice weekend is in store as a surface ridge builds into the region through the period. With that will come below normal temperatures with highs only in the 70s and lows in the 50s. Rainfall chances return to the area by the beginning of next week as an upper level trough swings through the Northern Plains and moisture returns on a southerly low level flow for Monday into Tuesday. Cannot rule out the potential for heavy rain for portions of the area by Monday with model PWAT values of 1.5" to 2"+. With that could also come the potential for severe weather as outlined by SPC Day 5 convective outlook. There looks to be a warming trend through the middle of the week. && .AVIATION /06Z TAFS THROUGH 06Z SATURDAY/... Issued at 1115 PM CDT Thu Jun 27 2024 Area of showers with isolated thunder over northwest Iowa at the start of the period will slowly shift east through daybreak. Main focus will be on line of strong to severe storms in central SD which will push east through areas near/north of I-90 through the overnight into Friday morning. Expect this line to gradually weaken as it progresses farther east, but may still be producing 40+kt gusts as it approaches the James River/KHON. Will carry a few hours of thunder at KHON and KFSD as this line moves through prior to 12Z Friday. Additional storms may develop ahead of a cold front across northwest Iowa Friday late morning/afternoon with a low (30%) probability for KSUX. Stout southerly low level jet will produce areas of low level wind shear through daybreak, though still seeing occasional surface gusts to around 25kt as well. Cold front will bring a wind shift to west and northwest winds as it progresses east across the area on Friday. && .FSD WATCHES/WARNINGS/ADVISORIES... SD...None. MN...None. IA...None. NE...None. && $$ DISCUSSION...JM AVIATION...JH