Area Forecast Discussion
Issued by NWS Sioux Falls, SD
Issued by NWS Sioux Falls, SD
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769 FXUS63 KFSD 161116 AFDFSD Area Forecast Discussion National Weather Service Sioux Falls SD 616 AM CDT Mon Sep 16 2024 .KEY MESSAGES... - Temperatures remain above normal through mid to late week. Nighttime lows show greater departures above normal (10-15F) than daytime highs (5-10F) due to anomalously high low level moisture/dew points. - Low (generally < 20%) rain chances today through Tuesday afternoon. Confidence in timing and placement is low, but expect amounts to remain light, with less than a quarter inch through this period at any location. - Greater chance for rain (40-70+%) Tuesday night through Wednesday, mainly focused Tuesday night west of I-29. Moderate (~ 40%) probability of rainfall exceeding 0.25", but low (< 25%) probability of exceeding 0.50". - Moderate chances (40-60%) for showers/storms late week into the weekend, with highest chances currently focused Thursday night and Friday night through early Sunday. Exact timing and location remain uncertain. && .UPDATE... Issued at 604 AM CDT Mon Sep 16 2024 Storms this morning have been more robust in development than was previously expected west of I-29, likely aided by the combination of the LLJ and a very subtle vorticity lobe moving northeast out of NE. Although severe weather is not expected, some storms may produce wind gusts to 50 mph and dime size hail in addition to frequent lightning and locally heavy rain. Hi-res guidance continues to handle this activity poorly, but based on how these LLJ enhanced events typically trend, expect storms to taper off late this morning. && .DISCUSSION... Issued at 348 AM CDT Mon Sep 16 2024 TODAY AND TONIGHT: Early this morning, watching a wave track through the western and central portions of the Dakotas, and the main upper low across central CA. This leading wave continues to lift off to the north-northeast through the morning and early afternoon, which may bring some isolated showers and storms to areas west of the James River this morning, and toward the southern MO River Valley into the afternoon. Models show some of the forcing splitting off of the wave, and hence the lower end pops through the afternoon into the southern MO River Valley. Given how the hi-res guidance has been handling convection the last few days, did not focus on any one model, but did try to incorporate some of the broad trends for timing and location. Next wave ejects out through the overnight hours, leading to some additional low (20%) pops west of I-29 tonight. Precipitation may struggle at times to reach the surface with dry air below the cloud layer. Severe weather is not expected, but some stronger gusts are possible. Storms may be elevated, so can`t entirely rule out some small hail. Breezy southeast winds are expected today and tonight - especially west of I-29. Surface pressure gradient (SPG) is compressed, and we may mix down some gusts to 35 mph west of the James River. Should stay below Wind Advisory criteria though. Warmer than average temperatures remain in place, with highs in the mid and upper 80s. Lows in the mid and upper 60s with southeast flow aiding in the mild overnights. TUESDAY AND TUESDAY NIGHT: Any isolated to scattered showers and storms on-going Tuesday morning continue through the afternoon as the strongest wave and WAA lift through the area. Not expecting any severe weather, but again, a stronger storm could produce some gustier winds and small hail. Today through Tuesday afternoon, light rainfall is expected with totals less than a quarter of an inch. More widespread breezy conditions expected Tuesday and into Tuesday night as the SPG tightens in response to developing low pressure on the lee side of the Rockies. As of now, low probability (less than 20%) of sustained or gusts reaching Wind Advisory criteria, but will keep an eye on potential if mixing is more robust than expected. Highs on Tuesday again in the mid to upper 80s, with lower 90s west of the MO River. Lows in the 60s. WEDNESDAY THROUGH MONDAY: Continued chances for rain mid week through the first half of the weekend thanks to the unsettled pattern. Mid week, low pressure swings northeast out of the Rockies. Although the center of the low is progged to move into ND, we`ll see a plethora of shortwaves track across the area into the end of the week. As this low lifts north, the next one is already deepening over the southwestern US. This second wave and upper jet support move east through the first part of the weekend and into the central Plains Sunday. There is more agreement in the 16.00z runs than the 15.12z runs in the track of the second low, but timing remains uncertain. Currently, best chances for rain and isolated storms are expected Thursday night and again Friday night through Saturday night. However, expect further refinements as agreement in the details increases. Above average temperatures continue into at least Friday. Near to possibly below normal temperatures for the weekend, depending on the timing and exact track of the second low pressure system. Given uncertainty, rainfall amounts are uncertain through this period. && .AVIATION /12Z TAFS THROUGH 12Z TUESDAY/... Issued at 604 AM CDT Mon Sep 16 2024 Outside of convection, expect VFR conditions to prevail. As mentioned in the Update section of this discussion, activity has been more robust than previously expected west of I-29. Included a VCTS mention at KHON, but will watch trends in case storms hold together and move into the airspace. Additional showers and storms are possible this afternoon in the southern MO Valley, and along/west of I-29 tonight; however, given low confidence in coverage and occurrence, have omitted from KFSD and KSUX with this forecast. Southeasterly winds increase today, with gusts around 25 to 30 knots west of I-29. Gusts around 20 to 25 knots expected elsewhere. Gusts are expected to continue tonight, and thus have not included any mention of LLWS. If gusts drop off overnight, LLWS is possible across the area, with the greatest threat west of I-29. && .FSD WATCHES/WARNINGS/ADVISORIES... SD...None. MN...None. IA...None. NE...None. && $$ UPDATE...SG DISCUSSION...SG AVIATION...SG