Area Forecast Discussion
Issued by NWS Sioux Falls, SD
Issued by NWS Sioux Falls, SD
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780 FXUS63 KFSD 120344 AFDFSD Area Forecast Discussion National Weather Service Sioux Falls SD 1044 PM CDT Tue Jun 11 2024 .KEY MESSAGES... - Scattered showers and storms expected Wednesday, with the better chances in the afternoon and evening east of I-29. A few storms could be strong to severe. - Near to above normal temperatures continue through early next week, with the warmest day expected Wednesday. - Next more widespread chances for rain anticipated on Saturday, with periodic chances into early next week. && .DISCUSSION... Issued at 250 PM CDT Tue Jun 11 2024 REST OF TODAY/TONIGHT: Near to slightly above average temperatures this afternoon despite northwesterly flow. Temperatures continue to climb into the mid and upper 80s for most of the area. Scattered diurnal cumulus clouds continue to develop, but expect the area to stay dry through this evening. Breezy northwesterly wind gusts to around 30 mph are expected to drop off with the diurnal CU around/just after sunset. Lows tonight remain a touch on the warmer side falling into the 60s. WAA begins to increase through the overnight as the next system approaches as well, with winds beginning to shift to the south and increase toward daybreak. WEDNESDAY/WEDNESDAY NIGHT: Some isolated showers and storms may develop during the morning hours with the WAA and the elevated trough. Elevated instability may climb near/above 1000 J/kg west of the James River before roughly 12.15z (10 AM) ahead of the trough. Can`t entirely rule out a stronger storm during this time if a storm is able to develop given the steep mid level lapse rates above 7 deg C/km. Surface cold front sinks southeastward through the day and into the evening hours. Ahead of it, we`ll continue to see southwesterly flow, allowing temperatures to climb into the 90s. Breezy winds expected between the diurnal mixing and tightening surface pressure gradient. Although winds will be out of the southwest, should see dew points climb into the 60s in the warm sector. These temps and dew points allow our instability to climb into the afternoon and evening hours, with ensemble data showing a > 60% chance of exceeding 2000 J/kg of CAPE. Some deterministic models show 3000+ J/kg possible across our eastern CWA during the afternoon and evening hours. Shear increases as the LLJ strengthens over our eastern forecast area, climbing to around 40-45 kts - with directional shear as well near the surface front. Mid level lapse rates increase as well, around 7.5 deg C/km. All of these parameters indicate the potential for all modes of severe weather (especially during the afternoon and evening hours). Large hail to 2" diameter, damaging wind gusts to 70 mph, and a couple of tornadoes are all possible. Threats may vary with storm mode; more discrete cells may prevail during the morning and into the early part of the afternoon with the WAA/pre-frontal trough and potentially more linear storm mode should things fire near/along the surface cold front later in the afternoon/evening. Widespread heavy rain is not expected, but could see brief heavy rain with thunderstorms. Now, there is some lingering uncertainty in the location and coverage of any potential development. A few questions and issues. First question is what, if any, impact elevated morning convection could have on the early afternoon convection. The other big question is whether or not there is enough forcing ahead of the front to fire any convection and if so, where and what is it. As mentioned in the previous discussion, deterministic guidance continues to vary in where/when/how strong any mid level wave over the area will be. The prefrontal trough timing/strength may also varies between the models. Models also vary in the timing and the surface front, which would impact the location of the surface development. If the front moves fast enough, this convection may develop just east of our CWA. The final uncertainty I`ll mention is whether or not we reach our convective temperatures (yes, even with highs climbing into the 90s) - many of the deterministic guidance keeps convective temps around 33+ deg C (which is the lower to mid 90s). With the cap in place, we`ll need something to break. Main takeaways for tomorrow`s forecast: hot and a bit more humid with showers and storms through the day. Coverage and timing of storms remains in question, although better chances will be later in the day. Storms could quickly become strong to severe with all hazards in play. Stay weather aware and have at least one way to receive warnings should any be issued for your area. Check the forecast for updates, and ensure you have a severe weather plan. THURSDAY ONWARD: With mid/upper jet to the north and a subtle 700mb wave and area of frontogenesis dropping south, may see some isolated showers during the morning hours on Thursday. Confidence is low though, with models struggling with which layer(s) may saturate enough for showers/sprinkles. Any rainfall amounts would be light, likely just a couple of hundredths. Highs near to above normal Thursday. Surface and mid level ridge build in across the Plains late week, with a few waves trekking through the mid level pattern. Near to above normal temperatures remain in place through the weekend (highs in the 80s to lower 90s and lows in the 50s and 60s). Next trough and surface low swing through Saturday which will bring our next and possibly more widespread shower and storm chances. Models struggle to resolve subsequent waves into the latter half of the weekend and the early part of next week - but could see occasional showers and storms into early next week. && .AVIATION /06Z TAFS THROUGH 06Z THURSDAY/... Issued at 1043 PM CDT Tue Jun 11 2024 Expect light and variable winds to gradually turn southeasterly through the overnight period, with gusts between 15 to 25 MPH possible near/after daybreak. As alluded in the previous discussion, will see showers and storms impact the region, with an initial wave likely near daybreak, with perhaps another round of redevelopment possible during the afternoon/evening. A few storms may become strong to severe, resulting in brief periods of MVFR cigs/vsbys. That being said, confidence still remains low concerning the exact location of these storms as model guidance continues to vary - so for now only have vicinity mention. Will continue to monitor trends and adjust as necessary. Otherwise, should see quiet conditions return by the end of the period. && .FSD WATCHES/WARNINGS/ADVISORIES... SD...None. MN...None. IA...None. NE...None. && $$ DISCUSSION...SG AVIATION...SST