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Area Forecast Discussion
Issued by NWS Sioux Falls, SD
Issued by NWS Sioux Falls, SD
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368 FXUS63 KFSD 021732 AFDFSD Area Forecast Discussion National Weather Service Sioux Falls SD 1232 PM CDT Tue Jul 2 2024 .KEY MESSAGES... - Below normal temperatures continue today and through most of the week with high temperatures on the order of near seasonable to 5 to 10 degrees below average. - A cold front passing through the area today could provide another round of strong to severe storms and heavy rain along and southeast of a Spencer, IA to Sioux City, IA line. However, confidence is low (<=30%) in this happening. - An active pattern aloft will continue periodic rain chances for the rest of the week and weekend. && .DISCUSSION... Issued at 342 AM CDT Tue Jul 2 2024 The previous light rain showers have pushed off to the east early this morning leaving low level stratus in its wake. Given light winds across the forecast area, some very patchy fog has developed in a few locations. Should see continued patchy fog persist through the rest of the overnight and early morning hours. A cold front is beginning to push into the forecast area early this morning. The front will move through the area rather quickly, pushing all the way through most of northwest Iowa come the afternoon hours. Some low level stratus looks to hang around the area through the early afternoon hours which may put a hamper on high temperatures. Due to this possibility, have tempered high temperatures a bit, with highs now expected to warm to the upper 70s to low 80s rather then purely into the 80s. Dew points will be lowering in the wake of the passing cold front but moisture looks to pool along and just ahead of the front. This will push dew points into the low 70s which will make for another round of showers and thunderstorms. Convection looks to fire along the front as the base of an upper level trough encroaches on the front. This will place the right entrance region of the upper level jet right over the front which will provide adequate instability and shear for potential strong to severe storms. Some questions remain regarding severe weather potential though as the front will most likely be out of the forecast area by the mid afternoon hours, thus keeping any severe weather chances at bay. There remains a small chance (<=30%) chance that convection could fire along the front as it is just about the exit the forecast area. Should this scenario come to fruition, locations along and southeast of a Spencer, Iowa to Sioux City Iowa could see strong to severe storms for a few hours before the storms push east of the area. This area could also see a quick inch of rain as well from the storms. Non-severe storms and showers are expected develop along the 850-700 mb front late this morning into the afternoon hours as the vort max with the wave catches up to the elevated boundary. Only light rain is expected with these showers with amounts from a few hundredths to a tenth or two expected. Any chance for rain will come to an end this evening leaving dry conditions for the overnight hours. Low temperatures will fall to the upper 50s to low 60s overnight. Wednesday will begin on the dry side as a surface ridging quickly slides through the area. However, southwesterly return flow on the backside of the ridge will set up through the afternoon hours. High temperatures will warm back to seasonable with highs in the 80s expected. The return flow will not advect in high moisture air though as the higher theta-a air will reside on the front edge of the previously mentioned surface ridge. However, dew points look to moisten up to about 60 degrees F across portions of north central Nebraska and south central South Dakota. With an upper level jet remaining parked over the Northern Plains and an approaching mid level wave from the west, showers and thunderstorms are again expected. Convection looks to develop along the warm front along the Nebraska/South Dakota border during the afternoon hours but questions remain how far east can the storms progress. Deep layer shear is sufficient at around 40 knots but instability will be on the low side, only around 700-1,000 J/kg of CAPE keeping severe potential questionable. As of now, think storms may be on a downward trend as they approach the Missouri River valley during the evening hours. Medium range guidance has come into better agreement in a closed low passing through the Northern Plains on Thursday/Independence Day. This will keep high temperatures on the cool side with highs in the 70s expected. Thermal profiles will be on the order of moist neutral and with enough saturation to support scattered showers across the area. Thunderstorms are also possible as the cooling from the low will steepen mid level lapse rates enough to generate some instability. However, with the upper low overhead, cold air funnels may be possible. The showers and storms look to persist into the overnight hours but on a downward trend as the upper low pivots off to the east. Low temperatures will fall to the upper 50s and 60s overnight. The upper level low continues to push off to the east of Friday, leaving cool northwest flow in its wake. The cooler airmass in place will continue below average high temperatures with highs in the 70s expected. Some light precipitation is possible throughout the day given wrap around moisture from the exiting low. Ensembles support this as they show a 50-80% chance for exceeding a tenth of an inch of rain throughout the day. Upper level ridging builds across the western CONUS during the weekend, placing northwest flow aloft across the Northern Plains. Typically, upper level subsidence lies downstream of a ridge, resulting in dry conditions. However, ridge riding shortwaves could result in additional shower and storm chances through the weekend and into next week. Tough to say when and where just yet so will continue to keep an eye on trends. Have left model blended PoPs through this period as well to account for the uncertainty. High temperatures will remain near to below seasonal in the 70s and 80s. && .AVIATION /18Z TAFS THROUGH 18Z WEDNESDAY/... Issued at 1224 PM CDT Tue Jul 2 2024 VFR conditions with occasional MVFR and lower are expected this TAF period mostly due to developing showers and thunderstorms along with low hanging stratus. Taking a look satellite imagery, areas of developing showers and thunderstorms continue to lift into our area this morning especially across portions of northwestern Iowa. While most of the areas should begin to clear this afternoon with the passage of a cold front, expect developing showers and thunderstorms to continue across portions of northwestern IA into the evening hours leading to MVFR and lower ceilings as more stratus moves overhead. Otherwise, expect conditions to completely clear overnight as lighter winds set in with the arrival of a surface high to our southwest. && .FSD WATCHES/WARNINGS/ADVISORIES... SD...None. MN...None. IA...None. NE...None. && $$ DISCUSSION...Meyers AVIATION...Gumbs