Area Forecast Discussion
Issued by NWS Sioux Falls, SD
Issued by NWS Sioux Falls, SD
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778 FXUS63 KFSD 050343 AFDFSD Area Forecast Discussion National Weather Service Sioux Falls SD 1043 PM CDT Thu Jul 4 2024 .KEY MESSAGES... - Intermittent periods of scattered showers with an occasional rumble of thunder will continue into the overnight hours with additional accumulations of up to a tenth or two possible. - Multiple rain chances will continue through the weekend before mostly dry conditions return to start the new week. - Slightly cooler temperatures will continue into the new week with highs expected to be between 5-10 degrees below normal. && .DISCUSSION... Issued at 354 PM CDT Thu Jul 4 2024 The Short Term (Rest of the Afternoon/Tonight): A cool and wet day continues! Taking a look aloft, an upper level low (ULL) continues to rotate across areas north of I-90 bringing completely clear conditions to one part of our area and scattered showers and thunderstorms to the other parts of our area. As of 19z, the focus continues to be east of Hwy-59 as scattered showers and thunderstorms continue to push eastwards ahead of slow moving cold front. Looking at the environment, long-skinny CAPE values between 500-1500 J/kg and 35-45 kts of deep layer shear should be sufficient enough to continue the isolated severe weather threat through 21z with the primary threat being large hail up to quarter size. While widespread heavy rainfall isn`t expected with this activity, PWATs closer to 1.50 inches along with the back building nature of developing cells could lead to quick accumulations of up to a quarter inch with heavier cells. From here, the focus will turn to the backside of the low as increased isentropic lift and a strengthening LLJ help develop additional showers and thunderstorms across the northern and northwestern portion of South Dakota. Expect this developing activity to rotate into our area this evening and overnight as the mid-level low slowly drifts to our southeast. While the severe weather risk will be low for this time period, lingering instability overnight could lead to a few rumbles of thunder with developing cells. Lastly, an increasing warm sector on the backside of the mid-level low could lead to mostly cloudy conditions to start the day on Friday. The Long Term (Friday-Wednesday): Heading into the start of the weekend, an active pattern continues aloft as the base of the mid-level low pushes eastwards into southeastern Minnesota and western Wisconsin. With our area now on the backside of this system, could see some scattered showers with an occasional rumble of thunder redevelop on Friday mostly due to a combination of lingering isentropic lift and wrap around moisture. While most of this activity should be focused in areas east of I-29, accumulations are expected to be fairly limited with accumulations up to a tenth of two possible especially underneath heavier cells. Otherwise. lingering cloud cover and northwesterly surface winds will keep temperatures below our seasonal normals with highs only expected to peak in the low to upper 70s for the day. By Friday night, a quick mid-level ridge will slide southeastwards bringing increasing mid-level WAA to the area setting the stage for our next precipitation chances. By Saturday and Sunday, an amplified pattern will continue aloft as an upper-level ridge builds over the western coastline. Continued westerly to northwesterly mid-level flow will lead to a particularly wet pattern through Sunday as multiple shortwaves rotate through our area bringing intermittent periods of scattered showers with isolated thunderstorms. A few developing thunderstorms could become severe by Saturday afternoon as a cold front sides through the area. While the exact timing and location of our severe risk chances is still uncertain, long-skinny CAPE values between 1000-1500 J/kg along with 30-40 kts of deep layer shear could make for a decent environment for large hail and damaging winds to develop with any isolated activity. With this risk in mind, SPC has issued a Day 3 marginal risk (Level 1 of 5) for most of southeastern SD and portion of northwestern IA/southwestern MN. Looking aloft, the base of the main upper-level wave begins to drift southeastwards with its associated cold front during the day on Sunday. Increasing isentropic lift along with upper-level support from the left exit region of a jet could lead to the development of scattered showers with isolated thunderstorms during the day. Otherwise, expect the cooler conditions to continue into Monday as highs peak in mid to upper 70s and low 80s. Looking into the new week, mostly quieter conditions should return by Monday as the building upper-level ridge over the western CONUS pushes eastwards. While a brief period of showers will be possibly by Monday afternoon, most ensemble guidance shows only shows low to medium confidence in up to a tenth of an inch of QPF. Otherwise, mostly quiet conditions will continue into the midweek. Lastly, the cooler conditions will continue through Monday with slight warmer conditions building from Tuesday onwards as highs climb towards the upper 70s to mid 80s. && .AVIATION /06Z TAFS THROUGH 06Z SATURDAY/... Issued at 1043 PM CDT Thu Jul 4 2024 An area of stratiform rain has developed and is slowly moving south down the I-29 corridor, but is expected to shift eastwards before reaching the I-90 corridor as it dissipates during the overnight hours. Observations show very light accumulations on the orders of a trace to a few hundredths, with some very isolated MVFR/IFR cigs/visbys occuring across SW MN. Formerly breezy northwest winds will remain light tonight, becoming gusty again tomorrow morning with gusts into the teens and 20s. Our next round of scattered showers and thunderstorms is likely tomorrow afternoon for areas generally east of the James River Valley, with no severe weather expected. && .FSD WATCHES/WARNINGS/ADVISORIES... SD...None. MN...None. IA...None. NE...None. && $$ DISCUSSION...Gumbs AVIATION...APT