Area Forecast Discussion
Issued by NWS Sioux Falls, SD
Issued by NWS Sioux Falls, SD
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363 FXUS63 KFSD 121732 AFDFSD Area Forecast Discussion National Weather Service Sioux Falls SD 1232 PM CDT Sun May 12 2024 .KEY MESSAGES... - Another day with temperatures 10+ degrees above normal on Sunday. - Scattered thunderstorms will be possible by mid-late afternoon ahead of a cold front. Severe weather risks remain very low, but some stronger wind gusts are possible. Those with outdoor plans should stay weather aware. - Potential for wildfire smoke to move southward into the area Sunday evening into Monday. Some minor visibility reductions may be possible. - Temperatures cool slightly, but remain above normal for much of the upcoming week. - Scattered thunderstorm risks increase by late Tuesday through Wednesday. Outside of a small window Tuesday evening, most of the thunderstorms will stay well below severe limits. && .UPDATE... Issued at 402 AM CDT Sun May 12 2024 One quick addition to the forecast not previously mentioned in earlier discussion. Northerly winds behind the late afternoon frontal passage are likely to transport smoke from wildfires across southern Canada into the Tri-State area. Good agreement from RAP/HRRR smoke guidance in the potential for some sky obstructions later this evening and into Monday. However, good signals for subsidence pushing smoke down to the surface after dark and into at least early Monday afternoon. This could produce some marginal visibility reductions (AOA 5SM at times) and reductions in air quality. Have added smoke to the grids and increased sky cover to 30% into Monday. && .DISCUSSION... Issued at 259 AM CDT Sun May 12 2024 THIS MORNING: Light southerly winds continue to keep morning temperatures in the 50s in most locations. Scattered mid to high level clouds have develop in response we weak warm advection moving through the region. TODAY: Another very warm day is expected on Sunday, with temperatures rising a couple degrees warmer than on Saturday. The warmup is expected ahead of a slowly advancing cold front that will be entering the far northwestern portions of the CWA by mid-morning and then bisect the CWA from southwest to northeast by 21Z. Weak surface convergence along this boundary is expected to lead to a narrow band of scattered thunderstorms that will slowly drift southeast into the evening. Instability along and ahead of the front will be highly dependent on the quality of surface moisture that moves into the area from the southwest. Some models such as the RAP are pushing dew points into the upper 50s and lower 60s by late this afternoon (resulting in nearly 1500 J/KG MLCAPE). Most other models are much more pessimistic with surface dewpoints only in the lower 50s resulting in only 500 to 1000 J/KG MLCAPE. This seems more realistic given the deep mixing up to nearly 8000 ft AGL, and the fact that dew points in southern Nebraska and northern Kansas are only in the lower 50s this morning. The general severe weather threat remains low, given effective shear only around 10 to 15 knots, and a more thin CAPE profile. However the high-base activity does present some risk for localized weak downbursts as DCAPE values are pushing 1500 J/KG. Some high resolution CAMs are suggesting this potential with simulated pockets of 40 to 45 knot gusts associated with weakening convection. QPF should remain light in most areas, but did blend in some PMM numbers from the HREF which would suggest some potential for very localized 0.50-0.75" totals. TONIGHT: While the majority of convection will weaken as sunset arrives, a portion of the convection may continue into the early overnight hours as weak dPVA moves in from the northwest and secondary band from the southwest. This area would mainly be in eastern Nebraska and northwestern Iowa. Elsewhere, temperatures will fall and dew points should drop quickly overnight, leading to a cooler start to Monday morning. MONDAY: Mid-lvl shortwave ridging moves in for Monday, and temperatures will again rise a few degrees above normal. Winds should stay rather light under a passing surface ridge of high pressure. TUESDAY: A shortwave crosses the Northern Rockies into the Dakotas early Tuesday. There seems to be some agreement in surface low development over southwestern South Dakota which then moves towards central South Dakota by the evening. While most of the convection may remain across the far western and northwestern portions of the state in the evening, there are hints that depending on surface heating and boundary layer moisture quality, we could see a risk of convection into south central South Dakota in the evening. The NAM seems to be the most aggressive with convection, with other models showing a stubborn EML that would hold any convection from developing. Have nudged temperatures up slightly given less signal for cloud cover and deeper mixing. WEDNESDAY: Any overnight convection will push cloud cover, along with a weak surface boundary, eastward for Wednesday. This should lead to slightly cooler temperatures and a few lingering showers. A secondary wave approaches in the middle of the day, likely leading to renewed scattered showers though the signal for widespread activity continues to trend lower. The lack of instability will preclude any severe weather risk. THURSDAY-SATURDAY: The sharpening upper trough slides through the region on Thursday, and could produce some widely scattered afternoon sprinkles or showers. However temperatures will remain near seasonal normals. We`re stuck in an active northern stream flow through the upcoming weekend with one trough passing through the Dakotas Friday and a second arriving towards the end of the weekend. At this point, with the lack of moisture advecting back northward, the severe weather risk should remain very low. && .AVIATION /18Z TAFS THROUGH 18Z MONDAY/... Issued at 1232 PM CDT Sun May 12 2024 VFR conditions begin the TAF period. A weak boundary is pushing into the area this afternoon which will set the stage for scattered showers and thunderstorms. A second area of rain is between I-80 and highway-20. No lightning is expected with these showers so have only included VCSH in KSUX`s TAF. The storms though are most likely to affect locations around and south of I-90. As such, have included VCTS in both KFSD and KSUX`s TAFs. Winds behind the front will turn northerly but remain on the lighter side with speeds between 5-10 knots. The other aspect to the front coming through is smoke. Smoke will push into the majority of the area this evening and night. Some uncertainty remains regarding how far south the smoke may push along with visibilities in the smoke due to the showers and storms. For now, have included smoke in both KHON and KFSD with VFR visibilities but visibilities could fall to MVFR levels. Trends will be monitored. Winds will turn northeasterly along with the smoke to finish out the TAF period. && .FSD WATCHES/WARNINGS/ADVISORIES... SD...None. MN...None. IA...None. NE...None. && $$ UPDATE...Dux DISCUSSION...Dux AVIATION...Meyers