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Area Forecast Discussion
Issued by NWS Sioux Falls, SD
Issued by NWS Sioux Falls, SD
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256 FXUS63 KFSD 151720 AFDFSD Area Forecast Discussion National Weather Service Sioux Falls SD 1220 PM CDT Mon Jul 15 2024 .KEY MESSAGES... - Scattered showers and thunderstorms will continue mainly across southwestern MN through the mid-morning with a few stronger storms possible. Additional scattered showers will be possible with a secondary wave through the evening hours. - As area of thicker wildfire smoke pushes eastwards across our area today, skies may become a bit milky through this evening. However, no surface impacts are expected at this time. - An active weather pattern will continues into the middle/latter parts of the week with periodic low shower and storm chances. Starting Tuesday, temperatures will begin a cooling trend with highs dropping below our seasonal normals. && .DISCUSSION... Issued at 414 AM CDT Mon Jul 15 2024 The Short Term (Today & Tonight): Taking a look across the area, another warm and muggy night continues as temperatures sit in the upper 60s to low 70s across the area with dew points in the 60s and low 70s. Similar to the previous days, more wildfire smoke is expected to push through the area this morning. While surface impacts will likely be kept to a minimum, skies may become a bit milky towards the midday as a thicker plume of smoke pushes across the I-29 corridor through the early afternoon. Looking northwards, our main focus continues to be on the developing Mesoscale Convective System (MCS) currently situated over eastern North Dakota and portions of northeastern South Dakota. Looking at the environment up there, the MCS is currently working with about 1500-2000 J/kg of MUCAPE and 50-60 kts of deep layer shear as it continues its gradual develop. With pattern recognition signaling that the MCS will likely take its environment with it, expect this developing line of showers and thunderstorms to follow the 850-350 mb mean winds which has due easterly flow through the ND/MN border then east-southeasterly flow across central and southern MN. With this in mind, expect this activity to arrive in our area between 09z-10z this morning with the greatest area of concern being across southwestern MN. Similar to yesterday, the line of storms will likely be strong to severe with the primary hazards being large hail up to hen egg size (2 inches) and damaging winds up to 70 mph. With this line expected to quickly progress through our area, expect most of the severe threat to be out of our area by 14- 15z. Unfortunately, our rain chances won`t likely stop there as a secondary shortwave interacts with a weak 850 LLJ as early as 14z leading to renewed shower and thunderstorm chances (20%-30%) throughout the day. However, there likely will be a low-end severe weather risk associated with this developing activity by the afternoon hours. Taking a look at the environment, we`ll have plenty of instability and shear with 1000-2000 J/k of MLCAPE and 30-40 kts of deep layer shear respectfully. Nonetheless, as we continue to warm throughout the day the question becomes if any of the developing parcels can overcome the cap between 700-800 mb. If so, storms will quickly become severe with golf ball sized hail and damaging winds up to 65 mph being the primary threats. If not, expect most of the developing activity to stay sub-severe with pockets of heavy rain and frequent lightning being the primary threats. Shifting gear here, with high expected to peak in the mid to upper 80s and low 90s for the day; elevated dew points in the upper 60s to low 70s will lead more muggy conditions with heat index values up to 100 degrees possible through this evening. With this in mind, make sure to stay hydrated and to avoid prolonged outdoor activities if possible. Lastly, as cold air advection (CAA) begins to funnel into the area behind today`s series of waves; expect our overall temperatures to gradually cool with overnight lows expected to decrease into the upper 50s to mid 60s. The Long Term (Tuesday-Sunday): Heading into the extended period, an active pattern continues aloft as the Hudson Bay trough drifts southeastwards into the Northern Plains and Great Lakes regions on Tuesday. Scattered showers with a few rumbles of thunder will develop by mid-morning as bits of isentropic lift interact with the left exit region of weak upper- level jet ahead of a weak shortwave across northeastern SD. Expect this developing activity to quickly migrate to southeastwards into our area throughout the afternoon before exiting to our south by the evening hours. While confidence is low, an isolated strong storm or two isn`t completely out of the question as developing showers approach the Missouri River Valley. Looking at the environment, instability will be limited except along a narrow corridor extending from Gregory to Yankton which is where 500-1000 J/kg of MLCAPE resides. Combine this with the 30-40 kts of unidirectional shear already available and there is a small chances for large hail up to the size of quarters. However, everything would have to play out just right for this to occur. With this risk in mind, SPC has outlined the Missouri River Valley in a marginal risk (Level 1 of 5) for severe weather. From here, cold air advection (CAA) will continue to funnel into our area through Wednesday helping our temperatures gradually decrease below our seasonal normals. With this in mind, highs will decrease into the 70s and low 80s through Wednesday with overnight lows in the 50s to low 60s. Looking into the latter parts of the week, much quieter conditions will continue through Thursday as the upper-level ridging situated over the western CONUS builds. By Friday, more shower and thunderstorm chances (20%-30%) will return as a strengthening upper- level low (ULL) intersects with increasing warm air advection over our area. While some details remain uncertain due to intensity and location differences among medium-range guidance, ensemble guidance shows low to medium confidence (20%-40%) in up to 0.50" an inch of QPF through Saturday with the highest probabilities situated along the Missouri River Valley. Otherwise, expect any developing activity to exit the region by Sunday morning as the ULL gradually sinks southwards. Lastly, expect temperatures to stay near to below normal through Sunday as highs top out in the 70s to low 80s. && .AVIATION /18Z TAFS THROUGH 18Z TUESDAY/... Issued at 1218 PM CDT Mon Jul 15 2024 Isolated very light showers will spread from west to east through the afternoon. An isolated stronger thunderstorm will be possible in parts of northeast NE and northwest IA from about 22z through 0z, but confidence is low. Scattered showers and isolated thunderstorms will be possible mainly west of I-29 from about 12z-18z Tuesday. Away from any showers or thunderstorms VFR conditions are expected. && .FSD WATCHES/WARNINGS/ADVISORIES... SD...None. MN...None. IA...None. NE...None. && $$ DISCUSSION...Gumbs AVIATION...08