Area Forecast Discussion
Issued by NWS Sioux Falls, SD
Issued by NWS Sioux Falls, SD
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499 FXUS63 KFSD 301740 AFDFSD Area Forecast Discussion National Weather Service Sioux Falls SD 1240 PM CDT Sun Jun 30 2024 .KEY MESSAGES... - Rivers across the area have crested, with a slow downward trend in river levels this weekend as dry conditions are expected to prevail. - Well below normal temperatures (~10 deg F) continue through Monday, and remain a touch below normal (0-5 deg C) Tuesday through Saturday as well. - Monday and especially Monday night will be the next better chance for severe weather and heavy rain. Higher confidence in showers and storms (70-90%) with decent chances for more than an inch of rain in northwest IA and southwest MN (30-50%). Certainly a time frame to keep an eye on. - Stronger westerly flow aloft continues through the end of the week, resulting in a busy pattern. && .DISCUSSION... Issued at 312 AM CDT Sun Jun 30 2024 High pressure at the surface will slide eastward today allowing a southerly flow to develop, with gusts around 25 mph west of I-29 this afternoon. While today should be mostly quiet, some elevated instability within roughly the 700-500 mb layer along with some moisture increase from 800-700 mb may allow some isolated shower and thunderstorm development. The more aggressive Nam is indicating about 300 J/kg of available energy while the GFS is even lower. With a weak mid level wave moving into the area some weak forcing will also aid potential development. Right now the moisture in the mid levels is a bit skiddish and not very well agreed upon so will keep chances from about 10-20 percent. The chances for showers and storms continues tonight as upper level troughing spreads across the area and increases low to mid level flow, thus bringing an increase in moisture and instability aloft. Model soundings suggest that late tonight enough moisture will advect northward to break the weak mid level cap and allow showers and storms to develop. Currently not enough instability to support any severe storms. Through the day Monday, showers and thunderstorms will gradually lift northeast as deeper instability, especially that about 900 mb or lower, builds to the south of the area. The main focus for our area will be the mid level wave moving through from late morning into the afternoon and then waiting to see the response from the low level jet Monday evening into the overnight. Not surprisingly the Nam indicates way more elevated instability than the GFS, roughly 3500 J/kg vs 1000 J/kg lifting from about 800 mb. Overall right now this is not a big concern as we will need to get through the day on Monday to figure out how much the morning and daytime showers and thunderstorms play a role in the low to mid level flow and instability in the evening and overnight hours into Tuesday morning. Right now this activity does not appear to be too widespread to suppress at least some aggressive elevated activity, likely in the form of hail to golf ball and wind gusts to 60 mph. The other concern, and likely more important, is the threat for heavy rainfall. Plenty of moisture in the environment as well as very strong forcing with the developing low level jet to support some higher rainfall rates. While upper level flow is not perfectly parallel to the low to mid level boundary with new updrafts likely to develop on the southwest flank there could be some short term training that would support some locally heavy rainfall amounts. Really tough to determine at this time, but a few locations could reach 3-4" on MOnday night, and unfortunately that focus could be across far southeast SD and northwest IA. Continued weak warm advection and a weak mid level wave will keep the chances for showers and thunderstorms in the area, but instability will likely be diminished as the earlier activity pushes east. By late in the day most of the activity should be out of the area. If this activity does diminish quickly enough Tuesday should be a nice day with highs in the 70s and northerly winds about 10 to 15 mph. This drier more stable air should bring quieter conditions Tuesday night into Wednesday with lows in the 60s and highs in the upper 70s to mid 80s. The next system of interest will be Wednesday night into Thursday as upper level low pressure deepens to the north and swings through some mid level warm advection then a front at the surface. Right now it looks like the better chances for showers and storms will be Wednesday night into Thursday morning, as the cold front will likely be east of the area by late afternoon. Some spotty chances remain for Friday then another possible wave will move into the area Saturday. Temperatures remain below normal. && .AVIATION /18Z TAFS THROUGH 18Z MONDAY/... Issued at 1240 PM CDT Sun Jun 30 2024 Southeasterly winds will become somewhat breezy west of I-29 this afternoon, sustained in the teens with gusts into the upper 20s and lower 30s, while areas along and east of I-29 will see the light winds continuing. Overnight, winds will be increasing aloft and changing direction, resulting in a couple hours of LLWS across central South Dakota affecting the KHON terminal. Monday will feature breezy south-southeasterly winds gusting into the upper 20s and mid 30s, with a couple chances for scattered showers and thunderstorms throughout the day, bringing MVFR/IFR conditions along with them. && .FSD WATCHES/WARNINGS/ADVISORIES... SD...None. MN...None. IA...None. NE...None. && $$ DISCUSSION...08 AVIATION...APT