Area Forecast Discussion
Issued by NWS Sioux Falls, SD
Issued by NWS Sioux Falls, SD
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430 FXUS63 KFSD 191952 AFDFSD Area Forecast Discussion National Weather Service Sioux Falls SD 252 PM CDT Thu Sep 19 2024 .KEY MESSAGES... - Isolated showers and thunderstorms will be possible through this evening mostly across northwestern IA. - An active pattern aloft will lead to renewed shower and thunderstorm chances (30%-60%) this weekend with the highest chances occurring on Saturday and Saturday. - Confidence continues to increase in a cooler stretch of temperatures starting as early as Sunday. && .DISCUSSION... Issued at 244 PM CDT Thu Sep 19 2024 REST OF THE EVENING/TONIGHT: Another warm and breezy day continues! Taking a look across the area, 18z observations show temperatures in the upper 70s to low 80s area-wide with an abundance of sunshine and mostly clear conditions behind a cold front roughly stretching along a Mountain Lake, MN to Moville, IA line. While there is still some lingering potential for a few isolated showers and thunderstorms to develop ahead of this near-surface feature, any developing activity would have to overcome a weak cap around 700-800 mb which would inhibit its upward growth. With cold front gradually pushing eastwards by the minute, not confident enough in peak heating to eroding the cap in time for any stronger activity to develop. As a result, while the severe weather chances are non-zero; not expecting any significant development in our area from this point onwards. Shifting gears here, expect any lingering cloud cover over areas east of I-29 to gradually clear with the passage of the cold front ushering in cooler and drier air in its wake. From here, expect the mostly clear conditions to translate to the overnight hours as a surface high moves in to replace the departing front. With this in mind, breezy westerly winds should gradually diminish after sunset becoming more light and variable as lows decrease into the low to mid 50s for the night. Lastly, with the surface high overhead and lingering low-level moisture; could see some patchy fog develop mostly along with our River Valleys. THE WEEKEND: Heading into the start of the weekend, warm and mostly dry conditions return by Friday as the mid-level component of the ridging moves overhead. Increasing mid-level warm air advection (WAA) along with southerly surface flow will lead to a slight increase in temperatures for the day as highs peak in the low to mid 80s for the day with the warmest conditions situated along the Missouri River. As the SPG tightens on the backside of this ridge, southerly winds will increase throughout the day especially west of the James River where gust up to 30 mph will be possible. With this in mind and RH values falling below 30 percent, locally elevated fire danger will be possible in our southcentral SD counties especially since the fuel are likely more cured than areas further eastwards. From here, our attention will likely turn northwards as a deepening shortwave trough digs across eastern Montana and central North Dakota with a pretty strong mid-level cold front swinging southeastwards through our area throughout on Saturday. While some isolated precipitation chances will be possible along the front, further analysis of soundings show a pretty significant cap between 700-800 mb likely inhibiting any significant development. This combined with the progressive nature of the cold front will likely keep any potential development to isolated or scattered showers at best mostly across northwestern IA through Saturday night. With that being said, PWATs will likely increase towards the 90th percentile of climatology heading into Saturday night setting the stage for our next precipitation chances. From Saturday night into Sunday, our attention will likely be focused southwestwards as a shortwave and an upper-level low (ULL) lifts into the Mid-Missouri River Valley likely bringing our next rain chances (30%-60%). While overall amounts are still a bit questionable, its worth noting that the NBM has started to trend POPs further southwards with the highest values siting around the Hwy-18 corridor and southwards. This sentiment is echoed in the 19.12z runs of the GFS/Euro which are trending the shortwave and low further southward compared to the NAM which has both features a bit further north. Either way, ensemble guidance is still showing low to medium probabilities (30%-50%) of up to a half inch of QPF with this activity through 00z Monday. This combined with PWATs in the 90th percentile of climatology do give a signal for pockets of heavy rain with any potential development through Sunday. Lastly, with the passage of the previously mentioned cold front and increased precipitation chances through Sunday; expect our temperatures to trend toward more fall-like conditions with daily highs decreasing from the low 70s to low 80s on Saturday to the low to mid 60s by Sunday. NEXT WEEK: Looking into the new week, long-range guidance begins to diverge in terms of solutions as they struggle to handle the passage of the weakening ULL on Monday. The upper-level pattern continues to remain quite active through Wednesday with the passage of a cold front and subsequent shortwave around the region. However, our precipitation chances remain fairly uncertain through this period. An amplified ridge likely moves across the region by the midweek with limited precipitation chances to end the week. Lastly, temperatures will continue to trend near to just below our seasonal normals as daily sit in the upper 60s to mid 70s through Thursday. && .AVIATION /18Z TAFS THROUGH 18Z FRIDAY/... Issued at 1214 PM CDT Thu Sep 19 2024 VFR conditions with occasional MVFR ceilings are expected this TAF period mostly due to lingering low-level stratus. Taking a look at satellite imagery, a cold front continues to gradually push eastwards this afternoon roughly extending along a Windom, MN to Sioux City, IA line with MVFR stratus with a few embedded showers ahead of it and mostly clear conditions behind it. As this surface feature spread eastwards over the next few hours expect mostly clear conditions to continue for the rest of the TAF period. Otherwise, breezy westerly surface winds will continue through sunset before becoming more light and variable overnight to end the TAF period. && .FSD WATCHES/WARNINGS/ADVISORIES... SD...None. MN...None. IA...None. NE...None. && $$ DISCUSSION...Gumbs AVIATION...Gumbs