Area Forecast Discussion
Issued by NWS Sioux Falls, SD
Issued by NWS Sioux Falls, SD
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209 FXUS63 KFSD 300849 AFDFSD Area Forecast Discussion National Weather Service Sioux Falls SD 349 AM CDT Thu May 30 2024 .KEY MESSAGES... - Multiple chances for showers and thunderstorms continue into next week. Locally heavy rainfall is possible today through the weekend. - A Marginal Risk (Level 1 of 5) for severe storms is in place for much of our area today. Damaging wind gusts to 60 mph and quarter sized hail are the main threats, with timing between 3 and 9 PM. Additional strong to severe storms may occur over the weekend, especially Sunday afternoon through Sunday night. - Near normal temperatures and periodic breezy conditions expected through the weekend, with above normal temperatures forecast to prevail heading into next week. && .DISCUSSION... Issued at 346 AM CDT Thu May 30 2024 TODAY THROUGH FRIDAY NIGHT: Convection is on-going this morning across western SD into central NE as the first short waves tracks to the east. Cloud cover is keeping temperatures above average, with most in the mid 50s to lower 50s. Already seeing wind gusts this morning around 20-35 mph from the southeast as the surface pressure gradient tightens and we mix into the stronger LLJ. Biggest challenge with this portion of the forecast is how precipitation will evolve. Main issue lies in which model scenario will play out. One solution brings a slower fropa, but earlier initiation of the WAA wing of precipitation. The second solution speeds up the cold front, and keeps most of the precipitation development near/just ahead of the front. Have generally narrowed the highest pops from the previous forecast a bit, trying to split the difference between the two main scenarios. Storms should begin to develop into a more defined line just after daybreak close to the MO River valley (further west if tied more to the WAA), tracking east with the WAA and front. Severe weather is not expected this morning with instability lacking, although storms could produce some brief heavy rainfall. The next area of precipitation begins to develop once again near/west of the MO River during the early to mid afternoon hours, with CAMs keeping this activity tied closer to the surface cold front with a secondary 700mb wave and WAA. These showers and storms move east through the evening hours, at least until the front stalls/washes out. Could see a couple of isolated strong to severe storms with this round of storms. With southeasterly flow ahead of the cold front, moisture return and warming could be enough (despite AM showers/storms) to bring in near/over 1000 J/kg of CAPE, with the NAM/RAP/Canadian solutions showing more. Although 0-6 km bulk shear is lacking during the early part of the day, this is expected to increase to near or above 30 kts through the evening as the surface front and next mid level wave approach. Mid level lapse rates around 6-6.5 deg C/km could support some hail to quarter size, but hail threat may be tempered slightly by freezing levels around 12kft. However, with DCAPE values over 500 J/kg, think that wind gusts to 60 mph would be the main threat. Timing for severe weather would likely be between 3 and 9 PM. Today`s mid level wave splits tonight into Friday morning, stagnating over IA. This along with the washed out surface front keeps isolated to scattered showers and storms in place Friday into Friday night until another approaching wave can push things along. Most of the activity should remain close to the relatively better forcing aloft in northwestern IA and southwestern MN. However, with the next short wave edging in from the west, can`t rule out some isolated activity west of the MO River in the afternoon hours. Locally heavy rainfall is possible through tomorrow night as PWAT values climb near to above 1.5". Could see localized ponding and some rises on smaller tributaries. Flash flooding risk looks low at this time with guidance across the area above 1.5" per hour, and very low and isolated probability (< 20%) of hourly rainfall rates above 0.5" and 1.0 inches. The caveat to this threat would be if multiple storms train over the same area, especially east of I-29 where most of the 6 hourly FFG is closer to 2.25" than 3"+. Through Friday night, probability of areas east of I-29 receiving more than 1" of rain is around 40%. Most of the area has moderate to high (> 40%) chances of seeing more than 0.5" in this time, with the lowest chances in south central SD. Outside of precip chances, expect highs in the 70s with lows in the 50s to near 60 - with cloud cover keeping things a bit more mild and limiting the diurnal range somewhat. Winds will be breezy from the south to southeast through this evening. As the front moves through and washes out, lighter and somewhat variable winds are expected into Friday night. SATURDAY THROUGH MID NEXT WEEK: Those with weekend plans (including travel) will want to keep an eye on the forecast, with unsettled pattern leading to continued shower/storm chances. A few storms could be strong to severe and produce locally heavy rain. Friday night`s wave/trough axis in western SD will lift to the north into the day on Saturday with another wave across KS/MO. This split should provide a break in widespread precip chances through at least the first half of the day. Next short wave ejects out of the Rockies and moves into the forecast area by Saturday evening in the quasi zonal flow. Expect showers and storms to develop ahead of the wave with the initial push of WAA. More widespread chances with a couple rounds of showers/storms on Sunday into Sunday night as the more defined trough axis and surface low move into our area. Strong to severe storms are possible, with the better chances Sunday afternoon through Sunday night. Ensemble data continues to show moderate to high probability (50%+) of CAPE above 1500 J/kg. Highest probabilities are from the GFS and Canadian ensembles; however, the ECMWF ensemble still shows a moderate to high (near 40% to 80%) chance of this value being exceeded. Shear also looks to be on the increase as well, which could also support severe weather. Again, there are some issues with timing and location of any development, so keep an eye on the forecast if you have outdoor or travel plans this weekend. Continued chances for locally heavy rainfall, although impacts will be dependent on what happens today through Friday night. Ensembles show a moderate (40-60%) chance of more than 0.5" of rain in 24 hours Sunday into Monday for areas east of the James River (greatest chances in southwestern MN). High (> 85%) chances for PWAT values to exceed 1". 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. Although details vary on strength and timing, guidance indicates ridging and surface high pressure mid week could provide at least a brief reprieve from showers and storms. Temperatures remain near to above normal, with a couple of days in the 80s possible early next week with a short lived ridge. Lows in the 50s and lower 60s. Periodic breezy conditions prevail. && .AVIATION /06Z TAFS THROUGH 06Z FRIDAY/... Issued at 1113 PM CDT Wed May 29 2024 VFR conditions are expected through at least 09-10z, lingering longer the further east you go. Southeast winds increase overnight with low level wind shear 35 to 45 kts from a developing low level jet. Winds turn more southerly during the day. Cirrus already are spreading in from showers and thunderstorms upstream in central SD/NE. Isolated showers and thunderstorms may spread in from central SD before 12z west of I-29, becoming more numerous during daylight hours. IFR to MVFR ceilings will spread east through the morning. Isolated strong to severe storms are possible Thursday late afternoon through evening with large hail and strong, gusty erratic winds as the main threats near storms. && .FSD WATCHES/WARNINGS/ADVISORIES... SD...None. MN...None. IA...None. NE...None. && $$ DISCUSSION...SG AVIATION...BP