Area Forecast Discussion
Issued by NWS Omaha/Valley, NE

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000 FXUS63 KOAX 210528 AFDOAX Area Forecast Discussion National Weather Service Omaha/Valley NE 1128 PM CST Mon Feb 20 2017 .SHORT TERM...(tonight through Thursday) Issued at 307 PM CST Mon Feb 20 2017 One would expect it to struggle to warm up on a cloudy February day, but temperatures are in the 50s to 60s across the area, with a few lingering showers. Granted, we had a warm start in the 50s in the first place. Subjective 12Z upper-air analysis indicates an upper- level trough from the MT/ND border through eastern CO/eastern NM/western TX, with downstream ridge from the Great Lakes through the Southeast. Modest 500mb height falls of up to 60m were noted in the central US ahead of the trough. Upper-level jet of 130kt was coming ashore in northern CA, with ejecting jet segment up to 125kt ahead of the trough and nearly south to north. Unusually warm 850mb temperatures in the teens extended as far north as the US-Canada border in the western Great Lakes and as far west as the High Plains, with a pool of 8C+ dewpoints from eastern NE into IA/MO ahead of the 850mb trough. Surface low at 19Z was centered near the ON/SK border, with surface cold front extending through western MN and northwest IA toward eastern NE to north central KS. Temperatures were maybe 10 degrees lower on the cool side of the boundary, with gusty winds just behind it and significantly lower dewpoints. Main forecast concerns are near-record temperatures through Wednesday, then the storm system on Thursday-Friday. After something of a lull in temperatures today, both Tuesday and Wednesday easily should reach the upper 60s to mid-70s, with favorable westerly low- to mid-level winds. A weak front may reach northeast NE/northwest IA on Wednesday and hold back temperatures just a touch in those areas. Airmass will be on the dry side, making fire weather a hazard on both days. Will continue the fire weather watch for parts of eastern NE, and likely will need one on Wednesday, as well. Cooler air will continue to descend into the area on Thursday behind the Wednesday cold front, holding temperatures in the 40s in northeast NE to around 60 in southeast NE. Most solutions begin to bring rain into northeast NE by Thursday afternoon, and despite sub-0C 850mb temperatures, precipitation type should remain rain through the daytime with near- surface temperatures holding warmer. .LONG TERM...(Thursday night through Monday) Issued at 307 PM CST Mon Feb 20 2017 Precipitation will continue to spread into eastern NE/western IA and expand in coverage on Thursday night and Friday as an upper-level trough closes into a low and ejects across the central US, with the deepening surface low sliding across the central Plains. Track differences remain, with ECMWF currently faster and slightly weaker and further southeast than GFS (which is a bit of a shift from earlier runs, where the GFS was the faster/weaker model) and GEM the slowest and farthest northwest of all. Still going with a consensus/blended solution for now, which would change precipitation from rain to snow from roughly I-80 northward through Thursday night. There is enough weak instability that thunder also is possible in the warm sector, mainly in southeast NE to southwest IA, and have included an isolated thunder mention. Moisture availability will not be an issue, nor will forcing for ascent/vertical motion. One of the main challenges to the snowfall forecast will be the track of the surface low and where the heaviest band lies; relatedly, another issue is the rain-snow changeover line that will limit accumulations on the warm side of the gradient. It is possible that somewhere in NE to IA, there will be a band of 6+-inch snowfall amounts. Right now, that risk looks highest along and north of I-80. The deepening surface low and tight pressure gradient behind it will help induce gusty northeast to northwest winds, which in turn could lower visibilities and create some blowing and drifting snow concerns. The snow might be of a fairly wet character (low snow-to- liquid ratio), which would dampen some of the blowing snow potential. Behind the system, temperatures will remain near to slightly below normal, with highs in the upper 30s to lower 40s and lows in the 20s. In all likelihood, areas with deeper snow cover will err on the cold side of that range, while areas that miss the snow may err warmer, especially in bare ground. The respite may be brief, with models hinting at least at the potential for another fast-moving shortwave/clipper with possibly light snow on Saturday night into Sunday. && .AVIATION...
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(For the 06Z TAFS through 06Z Tuesday night) Issued at 1127 PM CST Mon Feb 20 2017 VFR conditions will prevail through the TAF cycle with southwest surface winds.
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&& .OAX WATCHES/WARNINGS/ADVISORIES... NE...Fire Weather Watch Tuesday afternoon for NEZ016-030>032-042>044- 050>053-065>068-078-088>090. IA...None. && $$ SHORT TERM...Mayes LONG TERM...Mayes AVIATION...Kern

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