Area Forecast Discussion
Issued by NWS Sioux Falls, SD
Issued by NWS Sioux Falls, SD
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164 FXUS63 KFSD 192305 AFDFSD Area Forecast Discussion National Weather Service Sioux Falls SD 605 PM CDT Wed Jun 19 2024 .KEY MESSAGES... - The main concern through Saturday morning will be heavy rain with periods of showers and thunderstorms each day. - Showers and isolated thunderstorms will build into the area late tonight through Thursday. Severe weather threat is very low, but have high confidence in widespread rain. Better chances for a half an inch or more of rainfall tonight into Thursday morning will be west of I-29. - Moisture deepens and instability increase late Thursday afternoon into Thursday night which will being a higher risk of heavy rain and isolated severe storms. Looking like a 50-70% chance for an inch or more of rainfall in southeast SD and southwest MN. - Risks for thunderstorms continue into Friday, with potential for strong to severe storms Friday afternoon and night and periodic chances for heavy rainfall. All modes of severe weather will be possible but with all of the expected Activity tonight through Friday morning confidence is low on this occurring.. - Cooler temperatures and likely dry conditions Saturday night into early next week, though rain chances return Monday night through Wednesday.&& .DISCUSSION... Issued at 237 PM CDT Wed Jun 19 2024 Moisture has been pushed south of the area and will take a bit of time to return. The right entrance of the upper level jet and attendant mid level wave will move onto the Western High Plains tonight into Thursday morning. This will help moisture to return but initially tonight this moisture will mainly be in the mid levels. Because of this instability will be limited with CAPE values generally less than 500 J/kg. So overnight the main threats should be lightning and locally heavy rainfall. Any higher amounts should be limited to areas mainly west of I-29. The GEFS is more limited in producing a half an inch more more of rainfall during this time while the EC ensemble is suggesting a very good (roughly 60%) chance for a half an inch or more. With the limited elevated moisture and weak instability think that any higher amounts of rainfall before 12z Thursday morning will limited in area. As this wave slowly drifts northeast through the morning on Thursday another wave will move onto the Western High Plains which will continue to the mid level warm advection. This should bring an increase in low and mid level moisture into Thursday night, but the latest model soundings still suggest marginal instability with CAPE values around 1000 J/kg. Deep layer shear values are not too bad and given some decent instability could see some isolated severe storms and once again the threat for heavy rain given the freezing level around 13 kft and upper level winds close to normal of the low level front. Currently the better chance will be central SD into areas north of I-90. Overall the threat for heavy much higher on Thursday night into Friday morning with a much stronger LLJ, a bit more instability, continued deep warm layer and a slightly stronger wave. Latest HREF showing a fairly widespread 2-4" of rain near and north of I-90 into central SD Thursday night into Friday morning with the axis of higher chances for 2+" of rain on the GEFS along the same corridor as well as the EC Ensemble which is showing a 40-50% chance for 2+". Friday night into Saturday poses the next better severe weather threat with a surface warm front expected to be in place near and north of I-90. With all of the potential activity between now and then confidence is pretty low on coverage and severity, but with moderate instability and shear and the surface front nearby, all modes of severe weather will be possible. Latest ensemble projections place this front near highway 14 late Friday afternoon into the evening. An of course if the majority of the activity develops near and north of I-90 and the potential for heavy rain Thursday night into Friday happens we may see some flooding concerns. Once this system passes Saturday night into Monday looks mainly dry as upper level ridging builds in. The should allow for seasonally warm temperatures with lows in the 60s and highs in the 80s. Scattered showers and thunderstorms will become possible again Tuesday into Wednesday next week as westerly flow increase and swings through a few weak waves. This should increase low and mid level southerly flow and help return moisture and instability to the area. && .AVIATION /00Z TAFS THROUGH 00Z FRIDAY/... Issued at 600 PM CDT Wed Jun 19 2024 Scattered showers are expected to develop later tonight. Periodic showers and thunderstorms, with occasional MVFR visibility in heavier rain, will then be possible through the remainder of the TAF period. Ceilings will lower into the MVFR/IFR range by early Thursday morning. && .FSD WATCHES/WARNINGS/ADVISORIES... SD...None. MN...None. IA...None. NE...None. && $$ DISCUSSION...08 AVIATION...JM