Area Forecast Discussion
Issued by NWS Sioux Falls, SD
Issued by NWS Sioux Falls, SD
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831 FXUS63 KFSD 310328 AFDFSD Area Forecast Discussion National Weather Service Sioux Falls SD 1028 PM CDT Thu May 30 2024 .KEY MESSAGES... - Multiple chances for showers and thunderstorms through the weekend. Locally heavy rainfall may result in isolated flooding concerns and small river rises if training occurs. - A Marginal Risk (Level 1 of 5) for severe storms remains in place for much this afternoon, with damaging winds to 60 MPH and quarter size hail being the primary hazards. Additional strong to severe storms may occur over the weekend, especially Sunday afternoon and evening. - Near normal temperatures and periodic breezy conditions continue through the weekend, with above normal temperatures forecast to prevail heading into the new week. && .DISCUSSION... Issued at 311 PM CDT Thu May 30 2024 CURRENT THROUGH FRIDAY NIGHT: Latest radar imagery shows a line of showers and storms developing ahead of an advancing cold front just west of the James River. Will see this line push eastward through the afternoon and evening before it stalls out near/east of I-29. Though cloud cover has plagued much of our area this morning, have seen a bit of clearing ahead of the front, which may provide enough destabilization to see a few strong to severe storms. In regard to dynamics, do have CAPE values ranging between 500 to 1500 J/kg, depending on which model you look at. Dewpoints have also risen a bit in the last few hours, with most locations in the upper 50s to lower 60s. While there is a decent amount of moisture to work with, effective shear remains rather lacking, and mid-level lapse rates still hover in the 6-6.5 degC/km range. That being said, there is a decent amount of sfc vorticity along the aforementioned front, which could support the development of perhaps a few funnel clouds or landspouts. SPC`s latest Day 1 Outlook has maintained a Marginal (Level 1 of 5) risk for severe weather - so don`t want to entirely rule things out, especially if we can destabilize enough. As such, think the primary hazards with any storm that does become severe will be damaging gusts up to 60 MPH and quarter size hail. In regard to timing, believe the best window for seeing severe weather will be between 3 to 9 PM. Instability quickly diminishes as we approach midnight, which should limit the overall severe threat. Given that the front is expected to stall/slowly meander eastward, have scattered showers and storms lingering for the remainder of the overnight period. Similar to the last forecast package, PWATs still look to approach 1.5 inches, suggesting that locally heavy rainfall will be possible. While widespread flooding is not expected at this time, any heavy rain that occurs over urban or already saturated areas may result in ponding of water and perhaps isolated flash flooding. In an effort to mitigate impacts around your home, ensure that your sump pump is turned on and that your downspouts are attached. And remember, Turn Around, Don`t Drown, if you encounter a flooded roadway. Trough axis swings north of the area on Friday, with another weak short wave ahead of it. This keeps at least scattered activity around through the end of the week, especially along and east of I- 29. In regard to rainfall totals, currently have amounts through Friday evening ranging between a tenth of an inch to near/just above half an inch along and west of I-29. Areas east could see upwards of half an inch to 2 inches, with the highest totals likely across SW Minnesota. SATURDAY: Should see a brief reprieve from showers and storms throughout much of Saturday morning and afternoon as sfc high pressure slides overhead. Winds look to be light and variable with afternoon highs in the mid to upper 70s under partly cloudy skies. SATURDAY NIGHT THROUGH TUESDAY: Upper level wave near the Rockies ejects northeastward toward the region Saturday evening, causing precipitation chances to return to forecast. Could see showers and storms develop as early as sunset with the initial surge of WAA, though the better chances look to occur Sunday afternoon and evening. As noted in days past, CIPS analogs continue to show a 15% chance for severe weather, with CSU Machine Learning probabilities now ranging between 15-30%. SPC`s latest Day 4 Outlook has also highlighted a 15% chances of seeing severe weather for much of our area. In regard to dynamics, still seeing a decent amount of support from both deterministic and ensemble guidance that CAPE values will near/exceed 1500 J/kg. Shear and low level moisture will also be on the rise ahead of an advancing cold front, with a few models forecasting dewpoints to rise into the 60s to lower 70s. Certainly something to keep an eye on in the coming days. In addition to this, will need to monitor today`s and Friday`s rainfall amounts, as periods of heavy rain will also be possible with this system. Certainly more moisture in the soils of late, which may result in localized flooding and river rises - especially if training storms were to develop. Nonetheless, there are still a bit of moving parts in place to put too much confidence behind any one solution just yet, as timing, amounts, and hazards will largely depend on how sfc and upper level boundaries evolve. For now, encourage folks with outdoor plans to keep an eye on the forecast and have a way to receive warnings. Outside of a few lingering showers on the far eastern fringes of our CWA Monday morning, should see largely dry conditions prevail across the region. Models vary in timing and strength of the next wave/trough Tuesday, but expect more shower and storm chances. Depending on the track and evolution of this system, additional strong to severe storms may be possible, but very low confidence at this time. Otherwise, look for afternoon highs to rise into the upper 70s to lower 80s. Overnight lows will also remain quite mild, as temperatures only fall into the 50s to lower 60s. WEDNESDAY AND BEYOND: Upper level ridging builds across the western CONUS mid-week, keeping us in NW flow aloft. As a result, should see dry conditions prevail for the remainder of the extended period. Winds will be fairly breezy, with gusts between 20 to 30 MPH possible during the afternoons. && .AVIATION /06Z TAFS THROUGH 06Z SATURDAY/... Issued at 1027 PM CDT Thu May 30 2024 Scattered showers and thunderstorms are ongoing across the region this this evening and are expected to continue through the overnight. A few storms may become strong to severe with the greatest threats being wind gusts of 60 mph and hail up to the size of quarters. Ceilings are currently VFR, but expect these to bounce around a bit between VFR and MVFR, especially under any stronger storms that develop. Visibility may also be reduced under stronger storms. Winds have decreased to mostly light and variable. By daybreak they will become east-northeasterly at 5-10 kts. Daybreak sees another round of showers over central South Dakota and move east-northeast across the region through Friday afternoon. Severe weather is not expected with Friday`s showers. && .FSD WATCHES/WARNINGS/ADVISORIES... SD...None. MN...None. IA...None. NE...None. && $$ DISCUSSION...SST AVIATION...AJP