206 FXUS63 KFSD 092334 AFDFSD Area Forecast Discussion National Weather Service Sioux Falls SD 634 PM CDT Tue Oct 9 2018 .SHORT TERM...(This evening through Wednesday) Issued at 331 PM CDT Tue Oct 9 2018 A strong surface low pressure system currently centered in Kansas will continue to move north-northeastward this afternoon and evening. As the center of this low approaches, the pressure gradient will increase, bringing breezy winds to the area. Given the well- defined parent upper-level trough, and strong synoptic and frontogenetic lift with this system, one can expect rain showers to continue through the evening hours for most locations in the tri- state area. The forecast calls for an additional inch or so of rain with this portion of the system, but slightly higher amounts are possible in areas currently covered by the Flood Watch in northwest Iowa, where a few rounds of thunderstorms could add to totals this evening. Late this evening into the overnight hours, cold air advection in the wake of this system will cool atmospheric profiles west of I-29. Robust mid-level omega will support continued lift and precipitation production in the form of snow. Areas around Gregory, Chamberlain, and Huron in the central part of SD could see 1-3 inches between midnight and noon Wednesday. Those traveling westward will want to take note too, as snow totals increase and chances for slick road conditions increase as one heads toward central Nebraska, Rapid City, Pierre, and Aberdeen. Winter Weather Advisories have been issued to cover this threat. Ground temperatures are still warm, so snow will likely not last long, but the morning commute especially could be winter-like for the aforementioned areas. Snowfall will end during the mid morning over southern parts of SD, as the forcing wanes and lifts into northeastern parts of the state. Areas north of I-90 in both SD and MN could see flurries during the mid to late hours on Wednesday morning, but above-freezing air near the surface will likely mitigate any accumulations. Temperatures top out in the upper 30s to low 40s, and combining this with breezy northwest winds gusting to 30 mph will make it feel winter-like outside during the day Wednesday. .LONG TERM...(Wednesday night through Tuesday) Issued at 331 PM CDT Tue Oct 9 2018 Last remnants of QG forcing in the mid and upper levels departs northeast of our forecast area Wednesday evening. Low pops are warranted in our northern zones for perhaps a bit of remaining areas of light rain or light snow, but honestly do not think anything will measure. The main forecast alteration for the Wednesday night and Thursday periods was to increase the wind speeds. Pressure gradient is tight as surface low pressure strengthens over the northern Great Lakes, and high pressure building over the western plains. So Wednesday night and Thursday will remain quite breezy, if not downright windy, especially east of the James River valley. Because of the winds and anticipated lingering low clouds Wednesday night, lows should not fall off too bad, with readings a couple of degrees either side of 30. Thursday will be very cold for this time of year, with highs a full 20 or more degrees below normal, and an added chill due to wind. But, at least it will be dry. On Thursday night, winds will decrease rapidly. But a big question remains on the degree of cloud cover. In advance of the next upper trough, there could be a decent increase in mid and high level clouds which many models are showing. Right now consensus lows are projected to be in the upper 20s to lower 30s, which also coincides with raw model values. Therefore despite the cloud cover, there could be a decent freeze Thursday night, but again, there is a question of this due to cloud cover. The upper trough moves through on Friday with QG forcing showing most of the forcing moving through our southern zones, with PV at the 1.5 pressure surface quite strong in central NE, reaching down to 530mb on the GFS. The latest 12Z GFS and ECMWF have trended a bit further northward with light precipitation, primarily cold rainfall, all the way up close to I 90. They were showing this several days ago before backing off to a more southerly track more recently, similar to what the NAM has. But with a jet streak orientated north to south over the central Dakotas, our southern zones are placed in a decent left exit region enhancing broad ascent. For now kept pops in our extreme south following the consensus over the past few days. If the models stay with a more northerly trend, we will begin to increase pops further north to I 90. Behind the Friday wave, strong warm air advection occurs Friday night. Blended southerly winds may be a bit light Friday night. At any rate, the warm air advection will keep lows in the 30s. Then another cold front screams through Saturday afternoon and evening. Moisture is limited with this frontal boundary to perhaps northwest IA where a few showers may occur. But the upper flow is split with this frontal passage, with one entering the western Great Lakes, and another digging into southern WY and CO. This front will set us back on temperatures again with only upper 30s and lower 40s for highs on Sunday. Normal highs are in the 60s. Along with the cold, the blend may be woefully underdone on the wind speeds Saturday night and Sunday behind the cold front. Therefore we will have to monitor that and raise wind speeds if this trend continues. If things work out Sunday night with decreasing clouds and winds, we may have our first fairly hard freeze across the entire forecast area. So between Sunday night and this upcoming Thursday night, there may not be much of a growing season left. There is a lot of model discrepancy by Tuesday, but in general much below normal temperatures continue Monday and Tuesday with dry weather. && .AVIATION...(For the 00Z TAFS through 00Z Wednesday evening) Issued at 628 PM CDT Tue Oct 9 2018 Several concerns through the next 24 hours. Rain will continue to stream northward through the region overnight. Colder air arriving late tonight in south central could allow rain to mix or change over to snow late tonight into Wednesday morning. Greatest chances for seeing snow will be west of the James River. Low ceilings and visibility will continue to also impact the region, with MVFR, IFR and brief periods of LIFR ceilings possible. Conditions will gradually improve late in the forecast period as the rain exits the region, allowing visibility and ceilings to improve some, but likely to remain MVFR through 00z Thursday. && .FSD WATCHES/WARNINGS/ADVISORIES... SD...Winter Weather Advisory from 1 AM to 1 PM CDT Wednesday for SDZ050-057. Winter Weather Advisory from 1 AM to 4 PM CDT Wednesday for SDZ038-052. MN...None. IA...Flood Watch until 1 AM CDT Wednesday for IAZ014-021-022-032. NE...None. && $$ SHORT TERM...VandenBoogart LONG TERM...MJ AVIATION...