Area Forecast Discussion
Issued by NWS Sioux Falls, SD
Issued by NWS Sioux Falls, SD
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123 FXUS63 KFSD 151732 AFDFSD Area Forecast Discussion National Weather Service Sioux Falls SD 1232 PM CDT Sun Sep 15 2024 .KEY MESSAGES... - Temperatures remain above normal through at least the middle of this week. Nighttime lows show greater departures above normal (10-15F) than daytime highs (5-10F) due to anomalously high low level moisture/dew points. - Greater chance for rain (40-70+%) returns mid-week, mainly focused near and west of I-29 Tuesday night to early Wednesday. Moderate (40- 50%) probability of rainfall exceeding 0.25", but low (10-30%) probability of exceeding 0.50". - Moderate chances (40-60%) for showers/storms late week, currently focused Thursday night-Saturday night, though exact timing and location details are still uncertain. && .UPDATE... Issued at 1125 AM CDT Sun Sep 15 2024 Scattered showers and thunderstorms have developed around Yankton and are drifting northeast. These appear to be tied to a weak mid level wave and some weaker elevated instability, CAPE values around 500 J/kg. Not expecting any severe storms, but brief heavy downpours and lightning will be possible. Will have to keep an eye on these if they can persist for 2-4 hours as they would approach the Sioux Falls area around mid afternoon. At this time none of the models are indicating any of this activity. && .DISCUSSION... Issued at 355 AM CDT Sun Sep 15 2024 TODAY-TUESDAY: A large blocking high from the Great Lakes into New England will persist early this week while a mid-upper level trough deepens over the Intermountain West. This pattern is not conducive to significant rains for us. However, subtle waves and nighttime low level jet interaction may trigger isolated activity west of I-29, mainly nocturnal with low (20-30%) chances late tonight-early Monday and again Monday night. Any rainfall would be light & severe storms are not expected. Daytime hours will feature gusty southerly winds, generally 15-25 mph today, increasing to 20-35 mph on Monday and slightly higher on Tuesday. Temperatures will remain above normal for mid-September with highs in the 80s and lows in the 60s. Could still see periods of wildfire smoke aloft, but expect improving conditions as southwest flow aloft becomes more established. TUESDAY NIGHT-WEDNESDAY: Models have been trending slower/farther west with the energy lifting out of the southwest CONUS trough during this time. Still seeing a low level jet of 40-50kt across the eastern Dakotas Tuesday night which along with the tail end of the wave moving through Montana should bring increasing rain chances to areas west of I-29 Tuesday night. Still see moderate-high (60-80%) probabilities for measurable rain west of I-29 through 12Z Tuesday, with chances decreasing as any showers slide east Wednesday morning. While exact rainfall amounts are uncertain, the broad ensemble probabilities indicate a moderate (40-50%) chance of exceeding 0.25" Tuesday night and Wednesday, but generally low (10-30%) chances of exceeding 0.50". Severe weather risk during this time appears low given weak deep layer shear <20kt and mid-level lapse rates near to below 7C/km. THURSDAY-SUNDAY: The latter part of the week is still looking more active than the relative dry pattern we`ve seen in recent weeks. However, model consistency is lacking, so confidence in the day to day details of timing/location of favored rain chances is on the low side. Above normal temperatures are still favored at least through Friday, but trends are currently pointing to a least a brief cool down for next weekend. && .AVIATION /18Z TAFS THROUGH 18Z MONDAY/... Issued at 1230 PM CDT Sun Sep 15 2024 Mainly VFR conditions through the TAF period. The challenge will be some spotty shower and thunderstorm potential, both difficult to time and place. Otherwise strong southerly flow will develop with gusts around 20 knots through tonight, then gusts around 30 to 35 knots near and west of the James River late tomorrow morning into Monday afternoon. && .FSD WATCHES/WARNINGS/ADVISORIES... SD...None. MN...None. IA...None. NE...None. && $$ UPDATE...08 DISCUSSION...JH AVIATION...08