Area Forecast Discussion
Issued by NWS Sioux Falls, SD
Issued by NWS Sioux Falls, SD
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919 FXUS63 KFSD 170820 AFDFSD Area Forecast Discussion National Weather Service Sioux Falls SD 320 AM CDT Wed Jul 17 2024 .KEY MESSAGES... - A few sprinkles to isolated showers will be possible this afternoon with only light accumulations expected. - Near to below normal temperatures will continue through the weekend as cooler air funnels into the region. - More rain chances (30%-70%) will likely return over the weekend with the better chances expected Friday night into Saturday. While some details remain uncertain, an isolated severe risk and pockets of heavy rain remain possible with developing showers and storms. && .DISCUSSION... Issued at 316 AM CDT Wed Jul 17 2024 The Short Term (Today & Tonight): A cooler day will be on tap for today! Taking a look across the area, the combination of a surface inversion and lingering low-level saturation in response to a descending surface high have led to a few areas of patchy fog developing mostly along our River Valleys and areas east of I-29. While rapid changes in visibility will be possible heading into these areas this morning, expect any lingering fog to dissipate by mid-morning as mixing restarts. As for the rest of the day, mostly quiet conditions will persist with light northerly to northeasterly surface winds. Surface temperatures will likely cool a touch from the previous days as lingering cold air advection (CAA) continues to sit over the area aloft. With this in mind, expect highs to vary between the low to upper 70s and low 80s. Looking aloft, a deepening upper-level trough will continue to dig into the northern plains and Great Lakes regions with the base of the trough sitting somewhere across central and southern MN by this afternoon. As bits of isentropic lift rotate around the trough, its wouldn`t be impossible for a few isolated showers to develop with the elevated instability above the boundary layer. While the confidence is low (<20%), decided to mix in a few sprinkles roughly along a Huron-Mitchell-Sioux City, IA line through this evening to capture the potential. Lastly, as winds become more light and variable overnight with the surface high overhead; we`ll have to watch for more areas of patchy fog to develop east of I-29 as temperatures gradually decrease into the low to upper 50s for the night. The Long Term (Thursday-Tuesday): Heading into the latter parts of the week, much quieter conditions will continue through Thursday as the mid-level ridge moves overhead. As warm air advection (WAA) strengthens on the backside of the previously mentioned ridge, surface temperatures will slightly increase for parts of the area with highs expected to reach the mid to upper 70s and low 80s. By Friday, another surge of mid-level WAA along with southerly to southeasterly surface winds will lead to another warm day as highs reach the upper 70s to low 80s. Our attention will then turn towards eastern Wyoming as a clipper wave dives southeastwards into our area bringing our next precipitation chances (30%-70%) through Saturday. While details remain far from certain, it`s worth noting that the open wave has slightly shifted a bit further westwards from yesterday`s guidance. With this in mind, the better shower and thunderstorm chances have shifted further southwards towards areas south of I-90 and along the Missouri River Valley. While the timing for the better coverage continues to look like Friday night into Saturday, intermittent periods of scattered showers and thunderstorms remain possible through Saturday. Looking at the environment, long-skinny CAPE profiles along with 30-35 kts of deep layer could support a limit severe risk by Friday afternoon but there is still some uncertainty there. With PWATs up to 1.75 inches and warm cloud depths of up to 11kft, the most likely hazard would be pockets of heavy rainfall. However, the overall amounts remain questionable with ensemble guidance only showing low to medium confidence (20%-40%) in up to half an inch of QPF through Sunday. With all this in mind, a wet and dreary weekend is ahead to say the least. As the closed low begins to drift southwards by Sunday, our rain chances should begin to thin heading into the new week. Looking into the early parts of next week, an active pattern continues aloft as upper-level ridging continues to build across the western CONUS. While a few smaller rain chances will be possible on both Monday and Tuesday, difference between long-range guidance have lead to low confidence in occurrence. Nonetheless, left the default NBM POPs in for this period. Lastly, below normal temperatures will continue through Tuesday as high approach the upper 70s to low 80s. && .AVIATION /06Z TAFS THROUGH 06Z THURSDAY/... Issued at 1036 PM CDT Tue Jul 16 2024 With the latest round of showers exiting off to our east, the recent moisture with a strengthening surface inversion introduces chances for patchy fog across the region. Latest HREF data suggests the best chances (scattered 30-40%) for visibilities below a mile are expected for areas west of I-29, with probabilities along and east of I-29 lagging behind some of the latest models which show patchy visibilities of 3-5 miles. Winds will remain light and variable into the morning hours, becoming north-northeasterly throughout the day on Wednesday. Mostly dry conditions expected, though an isolated sprinkle can`t be ruled out. && .FSD WATCHES/WARNINGS/ADVISORIES... SD...None. MN...None. IA...None. NE...None. && $$ DISCUSSION...Gumbs AVIATION...APT