Area Forecast Discussion
Issued by NWS Sioux Falls, SD
Issued by NWS Sioux Falls, SD
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813 FXUS63 KFSD 211940 AFDFSD Area Forecast Discussion National Weather Service Sioux Falls SD 240 PM CDT Sat Sep 21 2024 .KEY MESSAGES... - Rainfall amounts remain low for the remainder of the weekend, with low chances (20-30%) for a few hundredths to a tenth of an inch of rain, mainly for southern Woodbury and Ida counties in Iowa. - With the passage of a cold front today, temperatures trend downward to below normal levels tomorrow and Monday. - Temperatures trend back to normal and above normal levels for next week, with limited chances for precipitation through the period. && .DISCUSSION... Issued at 239 PM CDT Sat Sep 21 2024 Surface observations show the cold front moving out of our far eastern counties, with temperature observations showing cold air advection starting to overcome radiational heating out in central South Dakota as temperatures are now beginning to fall. Breezy north- northwest winds continue to gust into the 20s east of I-29 and into the 30s west of I-29. Satellite and radar show an area of scattered showers trying to move into far SE South Dakota and NE Nebraska along some weak frontogenesis in the mid-levels, though dry air in the lower levels have prevented the vast majority from reaching the surface. A secondary band of frontogenesis is lagging behind slightly along a line from Armour to Madison to Marshall, which has been able to develop an isolated thunderstorm sporadically. Instability has waned significantly behind the front, especially for non-surface based thunderstorms, and with the cold front now off to our east and south, not expecting any additional severe thunderstorms in our area today, though a few scattered thunderstorms are possible. For tonight a surface high pressure will begin to slide into the area, continuing to overspread the area with cold air advection resulting in overnight lows in the mid 40s to mid 50, with coldest readings north of I-90. This will keep winds on the semi-breezy side, though much weaker than they have been today already. As a cut- off upper level low begins to interact with the trough axis already sliding across the area, we remain north of the fronts that will be the focus for rainfall. So, outside of our far southern area which may see sporadic light rain overnight into the morning hours on Sunday, most of the area will remain dry with mostly cloudy skies for the start of Sunday. The rest of the day will be largely uneventful weather wise as the surface high pressure remains parked over the area, with daytime highs largely in the mid to upper 60s. Not impossible for some areas to reach 70 degrees, with ensembles keeping the probabilities for 70 or greater temperatures remaining below 10%, largely driven by the warm-biased GFS. Overnight temperatures into Monday dip down into the upper 30s to mid 40s. Southerly return flow sets up again on Monday as the surface high slides off to our east, and a front begins to move towards the area from the west as the parent low pressure slides eastwards in southern Canada. This will begin our upward trend for temperatures, though we`ll only be marginally warmer with highs in the upper 60s to lower/mid 70s. Behind an upper level trough and dry surface front moving through on Tuesday, upper level heights rise into Thursday as a ridge of high pressure aloft builds back into the central/northern plains. Ensemble situational awareness tables show that this ridge will bring temperatures and geopotential heights at or above the 99th percentile of climatology for this time of year for layers above 700mb, while 850mb temperatures don`t quite reach the 90th percentile. So, expect warmer than normal temperatures up into the upper 70s to lower 80s for Wednesday into Friday. Dry conditions are expected, with chances for a tenth of an inch of rain remaining below 10% each day. && .AVIATION /18Z TAFS THROUGH 18Z SUNDAY/... Issued at 1235 PM CDT Sat Sep 21 2024 VFR throughout the period. Strongest north-northwesterly winds have subsided back down into the mid 20s to mid 30s, further weakening/remaining in the lower to mid 20s throughout the rest of the afternoon hours. Can`t rule out an isolated shower/storm along and east/south of a line from Yankton to Sioux Falls to Marshall into the late afternoon hours, but given the isolated nature have left mention out of the FSD & SUX TAF. Winds remain semi-breezy gusting into the 20s for the same aforementioned area overnight, with minimal chances for rain on Sunday. && .FSD WATCHES/WARNINGS/ADVISORIES... SD...None. MN...None. IA...None. NE...None. && $$ DISCUSSION...APT AVIATION...APT