Area Forecast Discussion
Issued by NWS Omaha/Valley, NE

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000 FXUS63 KOAX 180535 AFDOAX Area Forecast Discussion National Weather Service Omaha/Valley NE 1135 PM CST Sun Dec 17 2017 .UPDATE... Issued at 1124 PM CST Sun Dec 17 2017 Added some areas of fog/patchy fog to parts of the forecast area and adjusted temperatures due to the clearing skies and rapidly falling temps. CONSSHORT seemed to have the best handle on the fog. Issued an SPS for parts of southeast Nebraska and southwest Iowa to account for patchy dense fog due to wet ground/calm winds and temperatures below freezing. Winds aloft should pick up in the western part of the forecast area and spread east. && .SHORT TERM...(Tonight through Wednesday) Issued at 347 PM CST Sun Dec 17 2017 Fast moving disturbance interacting with western warm conveyor belt gave eastern portions of forecast area a period of wintry precipitation this morning; however, that system has moved rapidly northeast leaving only mid-high level clouds across the region. How quickly these clouds clear will have role in low temperatures tonight, as expect minimums will occur earlier during the 03-09z timeframe before surface winds shift to a west- southwest direction. Decided to nudge going forecast minimums up just a little based on this scenario. On Monday, expect at 10 to 15 degree bounce in temperatures upward as compared to today, due to combination of downslope and warm advection. Dry low levels may allow temperatures to trend slightly warmer than guidance. A cyclone moving across the middle Canadian provinces sends another surge of cooler air into the forecast area for Tuesday. Even with the cooler surge of air, as has been the case most of this fall, temperatures through the short term will be 10 to 15 degrees above normal. Temperatures will rebound Wednesday as H8 temperatures as warm as 10C advect into the region ahead of large scale trough developing across western U.S., as such should realize surface temperatures in the lower to middle 50s for highs. Precipitation chances will be near zero through Tuesday night. There is some hint of that a shortwave moving across the southern plains could generate a few showers across southeast Nebraska and southwest Iowa on Wednesday depending if it tracks slightly north; however, will leave things dry for now. .LONG TERM...(Wednesday night through Sunday) Issued at 347 PM CST Sun Dec 17 2017 Big changes to sensible weather coming to the area beginning Thursday with large scale pattern change. Thursday will be a transition day, as front moves through the area. How quickly it moves through will be dependent on the syncing of large scale trough moving out of the southwest U.S. and Canadian cyclone. At this time, best chance of accumulating snows appears to be across extreme northeast Nebraska and northwest Iowa where thermal profiles support all snow from Thursday into Thursday night. The rest of eastern Nebraska and southwest Iowa likely will experience a mixture of precipitation as the colder air settles south, giving these areas a transition of rain to a mix to snow through the afternoon and evening. Much colder air will settle into the region Friday through Sunday. Long range forecast models are showing some discrepancy as to the orientation of the large scale pattern, which will have an impact on surface temperature and precipitation chances. GEFS members are weighted more toward EC/CMC operational solutions. As such decided to lower temperatures for Saturday and Sunday. Timing of precipitation a little tricky, as flow becomes somewhat channeled with main upper system shearing and ejecting energy in discretely. As such kept precipitation changes in the slight to low chance side through next weekend. && .AVIATION...(For the 06Z TAFS through 06Z Monday night) Issued at 1124 PM CST Sun Dec 17 2017 Some MVFR visibilities possible with the patchy fog at KOMA and KLNK. Winds aloft should increase later tonight enough to limit the fog. Nearly calm winds will become southwest and increase to 10 to 15kts by noon Monday. && .OAX WATCHES/WARNINGS/ADVISORIES... NE...None. IA...None. && $$ UPDATE...Zapotocny SHORT TERM...Fortin LONG TERM...Fortin AVIATION...Zapotocny

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