Area Forecast Discussion
Issued by NWS Sioux Falls, SD
Issued by NWS Sioux Falls, SD
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110 FXUS63 KFSD 221732 AFDFSD Area Forecast Discussion National Weather Service Sioux Falls SD 1132 AM CST Fri Nov 22 2024 .KEY MESSAGES... - Dry conditions are expected through the weekend, with high temperatures moderating back into the 30s and 40s. - A colder holiday week is expected with high (>80%) probability for sub-freezing highs, especially near/north of I-90 Monday. Tuesday-Wednesday may bring a slight reprieve followed by a stronger push of cold air for Thanksgiving into Friday. - While still non-zero, the chance for light precipitation (snow) for Wednesday-Thursday has trended lower (30-50% probability of measurable precip over the 2 days). This will still be a period to monitor, however, given it is peak holiday travel and higher chances are still in place to our south and northeast. && .DISCUSSION... Issued at 355 AM CST Fri Nov 22 2024 TODAY-TONIGHT: Immediate concern is potential for fog/low stratus development during the late night/morning hours today. Our forecast area remains clear as of 09Z save for some cirrus streaming into south central SD. However, seeing some patches of low stratus (per Watertown observation) or perhaps fog developing near the eastern edge of the snow field north of Highway 14. Have maintained patchy fog mention here as well as in our eastern CWA where Thursday`s stratus was slow to clear and will monitor trends over the coming hours. If fog does develop, some model guidance suggests it could persist well into the morning, which is not unreasonable given the light boundary layer flow within a surface ridge drifting east across the area today. Otherwise today should be a pleasant late autumn day with light winds and seasonable temperatures, topping out in the 30s and 40s. Coldest readings (lower 30s) will be over the lingering snow on the Coteau, while the warmest (mid-upper 40s) will build into south central SD. The ridge axis slides east tonight followed by broad warm advection above the surface. This should lead to areas of mid-level cloud development and steady, if not slightly non-diurnal, temperature trends overnight. Cannot rule out patchy fog development if we see sufficient cooling beneath clear skies, but confidence is not high enough to include in the forecast at this time. SATURDAY-SUNDAY: Broad warm advection continues Saturday into Saturday night as weak mid-upper level ridge builds over the northern Plains. This is followed by a cold front which will push east across the forecast area on Sunday, though exact timing of the front is uncertain due to model differences. Most prevalent solution has the front entering our western CWA late Saturday night, reaching the James River Valley/Highway 81 by daybreak Sunday, then exiting our eastern counties by mid-late afternoon. If the faster solutions are correct, we could end up with some non-diurnal temperatures in this period as well, however this is a low confidence and will be refined in later forecasts. Post-frontal winds will become more gusty as the cold advection pushes east, though not near the levels of this last Wednesday with the 90th percentile of the NBM still holding below advisory levels. HOLIDAY WEEK: Dry weather looks to prevail early in the week, with the post-frontal air mass briefly settling in on Monday and holding high temperatures below freezing in most areas. Temperatures look to rebound slightly for Tuesday-Wednesday in quasi-zonal flow, though seeing increasing spreads between the 10th and 90th percentiles, reflecting diverging model solutions and lower confidence in the temperature forecast for this mid-week period. Still some consensus in a weak upper trough/surface cold front swinging southeast through the northern Plains on Wednesday, followed by a reinforcing shot of even colder air which will bring sub-freezing high temperatures to the region for Thanksgiving and into the weekend. Seeing varying projections on available moisture with these features mid-week, leading to similar low confidence precipitation chances. However, it should be noted that the latest deterministic solutions are largely dry for our forecast area. Those with longer-distance travel plans will want to monitor forecasts, though, as we are still seeing higher precipitation chances to our south on Wednesday, and to our northeast Wednesday into Thursday. These trends are also seen in the broader ensembles, with peak 24-hour probabilities for more than 0.01" liquid equivalent are decreasing (now roughly 30-50%), while higher probabilities remain in place to our south/northeast. && .AVIATION /18Z TAFS THROUGH 18Z SATURDAY/... Issued at 1130 AM CST Fri Nov 22 2024 VFR conditions continue into the early overnight hours. Winds will gradually turn light and variable as a surface ridge moves through. There will be some potential for fog/stratus development across southwest Minnesota to northern Iowa, mostly along higher elevations. Elsewhere, a scattered mid-lvl cloud deck may form in response to increasing southwesterly low-lvl flow. && .FSD WATCHES/WARNINGS/ADVISORIES... SD...None. MN...None. IA...None. NE...None. && $$ DISCUSSION...JH AVIATION...Dux