Area Forecast Discussion
Issued by NWS Sioux Falls, SD
Issued by NWS Sioux Falls, SD
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705 FXUS63 KFSD 022330 AFDFSD Area Forecast Discussion National Weather Service Sioux Falls SD 630 PM CDT Tue Jul 2 2024 .KEY MESSAGES... - Any lingering shower activity will continue to clear by this evening. - Another round of scattered showers with isolated thunderstorms will be possible Wednesday afternoon for areas west of I-29. Strongest thunderstorms may be capable of quarter-sized hail and gusts to 60 mph. - An active pattern aloft will lead to multiple rain chances throughout the week with more widespread chances (60%-90%) occurring on Thursday. - Slightly cooler temperatures will continue for most of the week with highs expected to be between 5-10 degrees below normal mostly due to the multiple precipitation chances. && .DISCUSSION... Issued at 403 PM CDT Tue Jul 2 2024 REST OF THE AFTERNOON/TONIGHT: A wet and dreary day continues! Taking a look at radar, our main focus continues to be in northwestern IA along the cold front as areas of light to moderate showers and isolated thunderstorms continue to push northeastwards with the isentropic lift associated with a nearby shortwave. As the base of the main wave swings through our area this evening, could see some additional light showers develop along and west of I-29. However, expect the majority of this activity to slowly exit our area by sunset tonight. Accumulations will likely vary between 0.25"- 0.75" of an inch with isolated pockets of 1.00"+ possible underneath heavier cells. From here, expect the cloud cover to slowly diminish from west to east overnight as a weak surface low slides to our southwest. Otherwise, lingering cold air advection (CAA) and light surface winds will lead below normal temperatures overnight as lows fall into the upper 50s to low 60s. WEDNESDAY: Heading into the extended period, an active pattern continues aloft as quasi-zonal flow returns. By Wednesday, a much warmer day will be on tap as weak warm front slides along the SD/NE boarder. This combined with southerly to southwesterly surface winds and efficient mixing will allow our highs to make a temporary return to the low to mid 80s for the day. By Wednesday night, our attention will then shift to the Rockies as the influx of warm and moist air coupled with the arrival of a quick shortwave triggers the development of some scattered showers and thunderstorms over portions of southcentral and southeastern SD. While the severe risk associated with this developing activity is still a bit questionable, the environment ahead of the activity could be favorable for damaging winds with inverted V soundings and 30-40kts of speed shear present. However, with limited instability (500-1500 J/kg); the question becomes how far east does the severe threat extend before diminishing which is uncertain at this time. With this in mind, the general expectation is for any developing activity to gradually weaken as it approaches the James River Valley. THURSDAY/FRIDAY: By the end of the week, our attention will again pivot to the Rockies by Thursday morning as an open mid- level wave begins to occlude over our area leading to more widespread showers and thunderstorm chances (60%-90%) through Friday. While the exact timing and potential amounts are still a bit uncertain at this time, medium-range ensemble guidance continues to show low to medium confidence (20%-50%) in up to an inch of QPF through Friday with the highest probabilities occurring over southwestern MN. Looking into the environment for this time period, long-skinny CAPE profiles with between 500-1000 J/kg of instability along with 40-50 kts of shear ahead of the closed low could result in an isolated severe weather risk by Thursday afternoon east of I-29. However, the severe weather risk will be conditionally dependent on 1. how quick the atmosphere can recover from the morning activity and 2. if things can clear out enough for true convection to develop. Either way, the environment combined with low LCLs will likely promote some potential for cold air funnels. Lastly, while the bulk of the precipitation is expected to fall from Thursday night into Friday morning, could see additional precipitation chances develop on the back side of the ULL through late Friday afternoon. Shifting gears to temperatures, the increased precipitation chances will likely lead to below normal temperatures to start the weekend with highs varying between the upper 60s to upper 70s on both Thursday and Friday. REST OF THE WEEKEND/MONDAY: Looking into the rest of the weekend, quieter conditions will temporarily return by Saturday as a quick mid-level ridge slides through the region. Unfortunately, the quieter conditions will be short-lived as more precipitation chances potentially return from Sunday night into Monday as a deepening long wave trough swings through the region. However, with timing and progression difference among long-range guidance its too uncertain to make out the finer details at this time. Lastly, near to just below normal temperatures will continue through Monday as highs peak in the upper 70s to low 80s. && .AVIATION /00Z TAFS THROUGH 00Z THURSDAY/... Issued at 625 PM CDT Tue Jul 2 2024 Vast majority of previous showers/storms have dissipated, though there are some scattered thunderstorms heading towards the KHON terminal from central South Dakota. Those will be short-lived as they enter more stable air, with the patchy fog being the main concern for the overnight period. At the moment models keep fog confined to the southern Big Sioux, but would not be surprised to see that expand. Dry conditions continue into the morning hours, before chances for scattered showers and thunderstorms return throughout the afternoon hours well west of I-29. && .FSD WATCHES/WARNINGS/ADVISORIES... SD...None. MN...None. IA...None. NE...None. && $$ DISCUSSION...Gumbs AVIATION...APT