Area Forecast Discussion
Issued by NWS Sioux Falls, SD
Issued by NWS Sioux Falls, SD
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407 FXUS63 KFSD 160851 AFDFSD Area Forecast Discussion National Weather Service Sioux Falls SD 351 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. && .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 /06Z TAFS THROUGH 06Z TUESDAY/... Issued at 1043 PM CDT Sun Sep 15 2024 VFR conditions are expected to begin the TAF period. Showers and thunderstorms that developed across the front range of the Rocky Mountains persist late this evening. Confidence has started to increase in the potential for showers and storms to push into the area early tomorrow morning. Any chance for rain looks to remain along and west of the James River. As such, have included VCSH in KHON`s TAF for part of the morning hours tomorrow. Chances for showers and storms could persist through the rest of the morning and afternoon hours tomorrow but confidence is far too low to include in a TAF at this time. Trends will be monitored. Otherwise, southerly winds will pick up during the morning hours tomorrow with gusts up to 20-30 knots expected. The breezy southerly winds will finish out the TAF period. && .FSD WATCHES/WARNINGS/ADVISORIES... SD...None. MN...None. IA...None. NE...None. && $$ DISCUSSION...SG AVIATION...Meyers