Area Forecast Discussion
Issued by NWS Omaha/Valley, NE

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000 FXUS63 KOAX 092319 AFDOAX Area Forecast Discussion National Weather Service Omaha/Valley NE 519 PM CST Sat Dec 9 2017 .SHORT TERM...(Tonight through Tuesday) Issued at 306 PM CST Sat Dec 9 2017 Our dry forecast continues the next several days with a warm end to the weekend followed by cooling trend through Tuesday. Mostly sunny skies were noted across eastern Nebraska and southwest Iowa this afternoon. Temperatures had rebounded into the 40s in our west, but struggled to reach the lower and middle 30s in southwest Iowa. Brisk north winds gusting over 20 mph kept wind chills in the 20s in many spots. Mid level flow pattern featured a deep mean trough to our east, extending from Hudson Bay into the Deep South, and a ridge to the west, extending from the Baja through western Canada. This leaves our part of the country under north to northwest flow aloft, which is forecast to remain wholly unchanged much of the coming week. Perturbations dropping through that flow will help reinforce our cooler temperature regime, with only modest warming ahead of each shortwave. The first shortwave of consequence was noted topping ridge in northern British Columbia this afternoon, and is forecast to drop southeast toward the western Great Lakes on Sunday. Main sensible weather affect in our area will be modest warm advection regime induced in the Plains to the west of the track, characterized by 850 temps warming some 10C from this afternoon into Sunday. We`ll still see some weak cool advection Sunday afternoon and an increase in mid and high level cloud cover, but temperatures should top 50 in much of our CWA. A second and more potent shortwave was currently tracking northeast through the Gulf of Alaska, and is expected to top ridge and race south into the Plains on Monday. Strong warm advection ahead of this wave will come mainly during the overnight period Sunday night with strong cold advection commencing Monday morning and continuing into Monday night. Thus it is quite likely a non-diurnal temperature trace will result with rising temperatures after midnight Sunday night, then falling afternoon temps on Monday. Strong winds approaching advisory levels are likely on Monday as well. Unidirectional flow increasing with height and steep low level lapse rates behind cold front suggest efficient momentum transfer of 40 mph average boundary layer winds to the surface. A few sprinkles or flurries are possible as well given steep lapse rates, but nothing of any consequence. Cooler temperatures will follow for Tuesday, but still rebounding toward normal for this time in December. .LONG TERM...(Tuesday night through Saturday) Issued at 306 PM CST Sat Dec 9 2017 Western ridge/eastern trough upper air pattern will remain in place until late week before a pattern shift is advertised by all major long-range guidance. Another strong shortwave diving into the Plains Wednesday will again push temperatures upward Tuesday night before strong cold advection ensues during the day Wednesday. GFS is fastest with this wave while Canadian and ECMWF delay arrival a bit, allowing some rebound in temperatures on Wednesday before cooling takes hold. A weak secondary shortwave follows closely behind for Wednesday night and Thursday, but behind these waves, mid level flow begins to shift for the weekend. Eastern upper trough flattens over the eastern half of the CONUS Friday into Saturday as last of shortwaves rotates off the East Coast. Meanwhile, western ridge is flattened by a series of shortwaves suppressing heights. One of those waves will be entering the Rockies on Friday and moving into our part of the world on Saturday. With overall height rises, expect warming potential to increase accordingly. However increased mid and upper level clouds in mid level warm advection regime will likely hinder maximum warming on Saturday. There is at least a small chance light precipitation may be squeezed out of this system, but most model output is pretty bearish on this. Thus will maintain a dry forecast for now. && .AVIATION...(For the 00Z TAFS through 00Z Sunday evening) Issued at 515 PM CST Sat Dec 9 2017 Expect VFR conditions through the period, with mainly just high level clouds expected. Some MVFR ceilings appear possible at KOMA on Sunday, but chances not high enough to mention in TAF at this time. && .OAX WATCHES/WARNINGS/ADVISORIES... NE...None. IA...None. && $$ SHORT TERM...Dergan LONG TERM...Dergan AVIATION...Miller

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