Area Forecast Discussion
Issued by NWS Sioux Falls, SD
Issued by NWS Sioux Falls, SD
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867 FXUS63 KFSD 190745 AFDFSD Area Forecast Discussion National Weather Service Sioux Falls SD 245 AM CDT Fri Jul 19 2024 .KEY MESSAGES... - Scattered thunderstorms expected to move into the area through the day, but especially Friday afternoon and evening. Low end risks for large hail and some strong wind gusts will focus west of I-29. - Unsettled weather through the rest of the weekend, with scattered showers and thunderstorms again Saturday. Some funnel development may be possible Saturday. - Many outdoor events this weekend will want to make sure to have an eye on the radar as activity this weekend will be rather variable in location and rapid to develop. - Cooler temperatures continue into next week, with near daily rain chances. Rain however won`t impact all locations, and will be very hit-or-miss. && .DISCUSSION... Issued at 243 AM CDT Fri Jul 19 2024 THIS Morning: Mid-lvl clouds continue to thicken early Friday morning in response to increasing warm advection. Through south central and central South Dakota, some deeper cloud development has already taken place on the edge of an increasing mid-lvl lapse rate. The resultant area of ACCAS has developed a few thunderstorms in Gregory county. Short term guidance continues to hint at further development of elevated clusters of storms through central and western South Dakota through mid-morning. Some of this activity may track down the Missouri River. Additional sprinkles may try to develop east of I-29. TODAY: Elevated convection could linger into the mid morning hours along and southwest of the James River valley, but eventually this activity will wane as the LLJ veers. Southerly return flow will then develop by mid-day, increasing surface moisture convergence along a trough extending through central South Dakota, emanating from a surface low in northern Nebraska. Dew points are already in the lower 60s this morning, and should rise into the middle to upper 60s in most locations by early afternoon. If we can avoid any substancial amount of cloud cover this morning, temperatures will rise into the 80s by early to mid-afternoon. A shortwave currently across northern Montana will arrive early this afternoon to central SD and northern Nebraska, likely providing a spark to initiate convection along and ahead of the surface trough/low. Moderate instability upwards of 2000-2500 J/KG will reside west of the James River valley, but overall effective shear may only climb near 25 to 30 knots. This combination may be just enough to produce a few semi- organized clusters of convection that will drop southeast into the late afternoon hours. A secondary shortwave over southern Alberta will arrive an hour or two later, assisting in developing scattered convection over northern and northeastern South Dakota, which may drift southward into early evening. The overall severe weather risk remains marginal, but would not be surprised to see some 1.5" hail reports given shear distribution and steep mid-lvl lapse rates. DCAPE remains well below critical thresholds, but a collapsing core could bring 60 mph winds. Would not rule out the current marginal risk pushing slightly further east this morning, but feel the greatest severe weather risk will reside west of I-29 and especially west of the James River. TONIGHT: Convection should wane through the evening with the loss of daytime heating. However, the synoptic forcing won`t shut-off, meaning that a few showers and thunderstorms may continue into the overnight hours. SATURDAY: An extension of a large Hudson Bay trough will remain through the Upper Midwest on Saturday, and some models actually show these aforementioned shortwaves merging and deepening near the Tri- State area early on Saturday. Should this happen, then a couple more concentrated areas of rain may form on Saturday near the upper low core. Where is much more difficult to pinpoint, so a broad PoP will be maintained. While instability and shear will remain below severe weather thresholds, the presence of cooling mid-lvl temperatures and stretching underneath the upper vorticity could result in afternoon funnels where new updrafts can form. This diurnally driven rain should diminish in the evening. SUNDAY: Temperatures remain in the upper 70s on Sunday, and we`ll again be having to deal with afternoon and early evening widely scattered convection. Pinpointing the exact locations is fruitless 2 days out, so will maintain a broad 30-40 PoP. MONDAY-THURSDAY: With much of the region within a large trough covering the eastern half of the CONUS, it`s time to get used to a nearly daily afternoon and evening scattered convection risk. Latest indications point to daily PoPs through Wednesday before the upper trough shifts east and ridging begins to slide eastward into the Plains. Temperatures remain near to slightly below normal through mid-week, with potential for normal Summer heat to return by the end of next week. Typical rainfall amounts in this kind of regime will vary wildly from location to location. Some may see just a trace or a few hundredths while others see a quick inch. && .AVIATION /06Z TAFS THROUGH 06Z SATURDAY/... Issued at 1045 PM CDT Thu Jul 18 2024 VFR conditions expected for the duration of this period. Winds will be southeasterly 3-8 kts becoming southerly 5-10 kts with gusts 14- 18kts by sunrise and continuing through sunset. Clouds increase through the day as well as the chances for showers and thunderstorms. Ceilings will gradually decrease as the clouds thicken, settling around 4000-7000 ft AGL. Showers and thunderstorms will come in two waves. The morning wave should remain isolated to scattered and weak. In the afternoon, coverage increases and some storms could become strong to severe. Reduced ceilings to 2000 ft AGL under thunderstorms. && .FSD WATCHES/WARNINGS/ADVISORIES... SD...None. MN...None. IA...None. NE...None. && $$ DISCUSSION...Dux AVIATION...AJP