Area Forecast Discussion
Issued by NWS Sioux Falls, SD
Issued by NWS Sioux Falls, SD
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871 FXUS63 KFSD 231729 AFDFSD Area Forecast Discussion National Weather Service Sioux Falls SD 1229 PM CDT Mon Sep 23 2024 .KEY MESSAGES... - Temperatures remain near to slightly above normal today with highs in the low 70s to up to about 80 degrees across parts of central South Dakota. - Chances (20-25%) for scattered light showers return this evening and night as a cold front moves through. Rainfall amounts at or below a tenth of an inch is expected. - Temperatures trend back to normal to above normal levels for the middle of the week. Chances for precipitation remain low. && .DISCUSSION... Issued at 201 AM CDT Mon Sep 23 2024 Calm to nearly calm conditions continue through the overnight hours as a surface ridge continues to slide through the region. With light to calm winds in place beneath mainly clear skies, shallow patchy fog is possible. This will most likely take place in and around river valleys. Any minor patchy fog that does develop will quickly burn off through the morning hours, resulting in a pleasant rest of the day! Temperatures will warm to the 70s this afternoon with a few locations across central South Dakota having the potential to see highs barely creep into the low 80s ahead of an incoming cold front. Southerly winds will also be a bit stronger just ahead of the front with gusts up to 20-25 mph expected. The cold front is tied to a strong upper level wave which will bring chances for light rain to the forecast area tonight. This wave is moisture starved though but the large scale ascent ahead of the wave as well as the cooling from the base of the wave itself will cool upper an mid level thermal profiles to saturation. The question will be if the low levels can saturated via top down saturation. As of now, soundings suggest that there could be some saturation. At the same time, the same soundings show a hint of CAPE up to 100 J/kg or less which could be just enough to develop very weak convection and allow rain to reach the surface. Rainfall amounts are expected to be light with amounts of a few hundredths to up to a tenth of an inch expected. Have nudged up overnight low temperatures in response to the cloud cover associated with the wave and now have lows bottoming out in the upper 40s to low 50s. Isolated light showers could persist into Tuesday morning but as a whole, Tuesday will be another nice day as high temperatures remain in the 70s with lows falling to the upper 40s overnight. The previously mentioned upper level wave will set the stage for the upper level pattern for the rest of the week as it breaks off from the strong northern jet stream across Canada as it becomes vertically stacked over parts of the Midwest. The vertically stacked low will allow for a narrow area of upper level ridging to get squeezed over the area. This upper level ridging will allow for a return of near to above average temperatures in the 70s to even low 80s for Wednesday, Thursday, and Friday. Beginning on Friday, rain chances have the potential to return to the area but this chance is uncertain due to how the vertically stacked upper level low travels. Medium range guidance depicts different evolutions of this low which, contributing to this uncertainty. Ensembles also show differing probabilities for a hundredth of an inch of rain as the GFS and Euro ensembles show a near zero probability for the end of the week and weekend. The Canadian ensemble is the main outlier as it`s probabilities are up to about a 50% chance for exceeding a hundredth of an inch of rain. Despite these differences, the upper low will remain southeast of the forecast area which will keep any rainfall amounts to a minimum. Another chance for rain is possible early next week as medium range guidance shows the potential for a shortwave trough to pass through the Northern Plains. There is quite a bit of variance regarding this waves evolution so have stuck with model blended PoPs for now. Temperatures look to cool to near seasonable as the wave comes && .AVIATION /18Z TAFS THROUGH 18Z TUESDAY/... Issued at 1229 PM CDT Mon Sep 23 2024 VFR conditions are expected to prevail this TAF cycle. Should see southerly winds continue through the afternoon, as cloud cover increases ahead of an advancing cold front. Overall moisture is rather meager, suggesting that coverage should remain isolated in nature. Have opted to forgo mention at any TAF site as confidence in exact location remains low at this time. Otherwise, look for light and variable winds overnight to turn northwesterly in the wake of FROPA. && .FSD WATCHES/WARNINGS/ADVISORIES... SD...None. MN...None. IA...None. NE...None. && $$ DISCUSSION...Meyers AVIATION...SST