375 FXUS63 KFSD 110858 AFDFSD Area Forecast Discussion National Weather Service Sioux Falls SD 358 AM CDT Thu Oct 11 2018 .SHORT TERM...(Today and Tonight) Issued at 358 AM CDT Thu Oct 11 2018 Main concern the next 24 hours is how fast the stratus erodes and then concerns about below freezing temperatures overnight. Current satellite picture shows stratus east and north of the Missouri River. So, except for a portion of Gregory County in SD, the entire region is overcast. 925 mb winds are running nearly parallel to the back edge of the stratus at this time so the clouds will only very slowly advect eastward until the ridge axis moves farther east into the Dakotas and force the wind to switch to west aloft. Probably the more significant way clouds will erode will be a combination of subsidence aloft and heating of the surface producing dry adiabatic lapse rates and enhancing mixing. So really not expecting significant eastward movement of the back edge much of this morning - perhaps just crossing the Missouri River. However by 18Z, lapse rates should become dry adiabatic which will then erode some of the clouds and allow some sunshine - beginning first near the Missouri River and rapidly spreading northeast. Even with some sun later this afternoon, highs will be cool in the upper 30s to mid 40s. Overnight an upper level wave will move eastward. The wave will bring clouds into the Missouri Valley this evening and across the entire area after midnight. The best dynamics with this wave will move from southwestern South Dakota into Nebraska. However, enough warm advection will set up that weak ascent could develop int south central South Dakota late tonight. Surface temperatures will be at or just above freezing so precipitation will either be snow or a mix of rain and snow. With little moisture, snowfall will generally be less than a half inch. This wave will also force the surface ridge into Minnesota and Iowa meaning winds will rapidly drop off in this area. This is expected to allow temperatures to quickly drop this evening to freezing or below. Therefore have issued a freeze warning for all of southwestern Minnesota, most of northwestern Iowa except Woodbury County, which will stay at or above freezing, and most of southeastern South Dakota except for the Missouri Valley Counties which will be above freezing. Also did not issue along Highway 14 in South Dakota as they are expected to fall below freezing this morning. .LONG TERM...(Friday through Wednesday) Issued at 358 AM CDT Thu Oct 11 2018 The upper wave will continue to move southeast on Friday morning. Large scale ascent will be limited to the Missouri Valley and adjacent areas of northwestern Iowa. Any snow or rain/snow mix will quickly change to all rain as temperatures rise toward 40 degrees. Again, any precipitation will be light with less than 0.10 inch of rain expected. Any precipitation should quickly end during the afternoon as the wave moves into Missouri. With weak southerly flow and skies clearing by afternoon in all but the Sioux City area, highs will warm into the mid to upper 40s with the warmest readings in the James River Valley and east of the Buffalo Ridge around Marshall. After Friday, generally dry conditions are expected. Friday night will see lows near seasonal normals in the mid 30s due to southwest winds ahead of cold front bringing mild air into the area. This front will move through the area on Saturday. With a deep northwesterly flow and cold advection behind the front, the air mass should become fully mixed near and behind the front. For this reason have raised highs into the mid 50s east of the James River. However, if temperatures aloft are as warm as shown in the GFS, highs could be another 3 to 5 degrees warmer in northwestern Iowa with the potential for 60 degrees in some places. Behind the front, it will get windy with sustained winds of at least 20 to 30 mph and gusts approaching 40 mph. While winds will abate some Saturday night they are expected to remain at 10 to 20 mph. Even with windy conditions, the cold air moving south will result in lows in the 20s to around 30 degrees. Sunday will be breezy and cold with highs again in the 30s across the area. After Sunday there is a gradual warming trend expected as a broad upper ridge begins to build over the Rockies. After a very cold Sunday night with lows in the lower to mid 20s, winds will turn to west or southwest and bring warmer air into the region. Highs will begin the week in the 40s but by Wednesday 50s and possibly even 60s can be expected. In fact the GFS and ECMWF are hinting that some places could hit 70 degrees. However, this is the first day models have hinted at this type of warmth so will not raise highs to those temperatures yet. It will be dry except for a small chance of rain Tuesday morning in southwestern Minnesota associated with a weak move moving from Canada into the Great Lakes. && .AVIATION...(For the 06Z TAFS through 06Z Thursday night) Issued at 1048 PM CDT Wed Oct 10 2018 A few flurries will linger for a few hours tonight, mainly across the central portion of the forecast area near I-29. Activity will be light enough that visibility reductions are not expected. Otherwise, MVFR ceilings will continue through much of the overnight hours, however some gradual improvement is expected to arrive late tonight into Thursday morning. Most locations should be VFR by 18z, but lower ceilings may linger longer across portions of southwest Minnesota. Mid and high clouds will be on the increase Thursday evening with the approach of the next system from the west, late in the TAF period. Right now low ceilings and any precipitation will hold off for TAF locations. && .FSD WATCHES/WARNINGS/ADVISORIES... SD...Freeze Warning until 9 AM CDT this morning for SDZ038>040-050- 052>071. Freeze Warning from 1 AM to 9 AM CDT Friday for SDZ052>062- 064>067. MN...Freeze Warning from 1 AM to 9 AM CDT Friday for MNZ071-072-080- 081-089-090-097-098. IA...Freeze Warning from 1 AM to 9 AM CDT Friday for IAZ001>003- 012>014-020>022-032. NE...Freeze Warning until 9 AM CDT this morning for NEZ013-014. && $$ SHORT TERM...Schumacher LONG TERM...Schumacher AVIATION...