Area Forecast Discussion
Issued by NWS Sioux Falls, SD

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000 FXUS63 KFSD 211809 AFDFSD Area Forecast Discussion National Weather Service Sioux Falls SD 1209 PM CST Mon Jan 21 2019 .SHORT TERM...(Today Through Tuesday) Issued at 308 AM CST Mon Jan 21 2019 Early this morning, we`re continuing to watch a narrow burst of warm advection snows move northeast across the CWA. Periods of 1-3 mile snows have been reported with this band, and it will likely bring anywhere from a dusting to 1.5" of snow to portions of the CWA. Highest snow totals may be found along the Highway 14 corridor. Otherwise, biggest concern in the short term portions of the forecast focuses on precipitation chances later today through Tuesday. Model guidance still not in great agreement with the passage of a shortwave trough through the Plains tonight and Tuesday. GFS/EC/CMC all much stronger with the mid-level wave moving across Nebraska and into Iowa Tuesday morning. NAM is a bit of an outlier with this upcoming system, but does suggest a few areas worth monitoring. As weak low level warm advection spreads northward later this afternoon and evening, we`ll begin to see the development of very light snow or freezing drizzle ahead of an inverted trough stretching northward across central Nebraska and east central South Dakota. Soundings suggest the greatest risk for impactful freezing drizzle may form along the Missouri River, with probabilities trending lower towards I-90 and then Highway 14. To the West, a mid-level band of frontogenesis will aid in developing a linear band of snow across northwest and central South Dakota after midnight. This band of snow will slowly creep eastward, arriving in our western zones by daybreak. Where uncertainty builds in the forecast is with the progression of potential intensification of a mid-level vorticity maximum ejecting out of eastern Colorado prior to daybreak Tuesday. EC/GFS/CMC all indicating this wave deepens sufficiently to enhance lift and produce a new area of frontal banding in areas from Yankton to Sioux City and Spencer Tuesday morning, with the western band quickly decaying after daybreak. This area of snow would then traverse across the southeastern third of the CWA through the afternoon hours. Accumulation Potential: While there may be a broad area of light snow across the entire region (Dusting - 2"), feel there could be two distinct areas of slightly more enhanced snowfalls. First area associated with initial banding through central SD and into the western third of the CWA, and a second enhanced area associated with the secondary frontogenesis across NW Iowa and NE Nebraska. Snow amounts in these enhanced areas could approach 2-5". As far as icing is concerned, most areas should remain with a glaze. An area to watch would be from Sioux City to Storm Lake and Spencer where there could be some potential of a change from freezing drizzle to convective freezing rain. Hazards: A difficult approach to headlines, given most areas will see light snows, but remaining under advisory criteria. At this point, feel most confident issuing an advisory based on the combination of freezing drizzle and light snow potential, segmenting areas of NW Iowa where totals could be slightly higher if enhanced banding takes place Tuesday. That said, travel even outside any advisory may be impacted for an extended period given the prolonged nature of the light snow. .LONG TERM...(Tuesday Night through Sunday) Issued at 308 AM CST Mon Jan 21 2019 Tuesday night: Temperatures should fall quickly Tuesday night, as light winds and surface ridging move through. Wednesday: Warm advection and a west to southwest surface wind will allow temperatures to warm into the 20s again on Wednesday. We should see an increase in cloud cover as well. Wednesday Night and Thursday: A period of concern for the middle of the week, as models are all indicating an arctic front will blast through the region by daybreak Thursday. A burst of light to moderate snow will accompany this front, and could produce a quick 1- 2" of snow. The biggest concern though will be with winds. Behind the arctic front, soundings indicate nearly 40 knots of flow at the top of the mixed layer Thursday morning. Given the very fluffy snow over much of the area, significant blowing and drifting of the snow could take place through day. In open areas, visibility could be significantly impaired. Friday-Sunday: As a large upper trough becomes established over the eastern half of the CONUS, the CWA will be stuck in the more active sector of the trough, dealing with systems moving through the northwest flow nearly every other day. These system will also bring a parade of cold fronts across the region through next weekend. && .AVIATION...(For the 18Z TAFS through 18Z Tuesday afternoon) Issued at 1150 AM CST Mon Jan 21 2019 Gusty winds from 25 to 35 mph will continue to impact the region through late this afternoon. This will lead to patchy blowing snow and MVFR/IFR visibility conditions at times, mainly at KHON and KFSD. KSUX: The main concern is -FZDZ this evening into the overnight hours. Precipitation is expected to change all to snow by early Tuesday morning. KHON and KFSD: MVFR to IFR conditions are likely as light snow moves over the area. Patchy freezing drizzle cannot be ruled out at KFSD during the evening hours. && .FSD WATCHES/WARNINGS/ADVISORIES... SD...Winter Weather Advisory from 6 PM this evening to 6 PM CST Tuesday for SDZ050-063>071. MN...Winter Weather Advisory from 6 PM this evening to 6 PM CST Tuesday for MNZ081-089-090. IA...Winter Weather Advisory from 6 PM this evening to 6 PM CST Tuesday for IAZ001-002-012. Winter Weather Advisory from 6 PM this evening to midnight CST Tuesday night for IAZ003-013-014-020>022-031-032. NE...Winter Weather Advisory from 6 PM this evening to 6 PM CST Tuesday for NEZ013. Winter Weather Advisory from 6 PM this evening to midnight CST Tuesday night for NEZ014. && $$ SHORT TERM...Dux LONG TERM...Dux AVIATION...05

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