Area Forecast Discussion
Issued by NWS Omaha/Valley, NE

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000 FXUS63 KOAX 232117 AFDOAX Area Forecast Discussion National Weather Service Omaha/Valley NE 317 PM CST Thu Nov 23 2017 .SHORT TERM...
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(Tonight through Sunday) Issued at 312 PM CST Thu Nov 23 2017 Temperatures well above normal are forecast through the weekend, with a cold front bringing breezy conditions Friday afternoon and a bit of a cooldown on Saturday the caveats for the short term period. Weak mid level ridging was over the Plains today, stretching from the Baja into Nebraska. Main feature of note was a shortwave trough moving onto the southwestern Canadian coastal region, which is forecast to swing across the northern Plains on Friday, pushing attendant cold front through eastern Nebraska and southwest Iowa Friday afternoon. Ahead of the front, warm temperatures will continue as downsloping southwest low level flow helps warm surface temperatures under an already unseasonably warm airmass characterized by 16C 850 temperatures Friday morning. Given airmass and some compressional warming component ahead of cold front, expect temperatures to reach the 60s for highs all of our CWA, with some 70s likely in southeast Nebraska. Cold front is slated to be along I-80 around 18Z Friday, with cooling effects felt in northeast Nebraska by then, but later in the afternoon southeast of the Interstate. Also, strong northwest winds approaching advisory levels will follow front Friday afternoon. Straight model output may be a bit low given increasing speeds with height and a modestly conducive momentum transfer regime under cold advection and mostly unidirectional flow. Gradient and mixing will decrease markedly Friday evening as high pressure begins to build into the region. Clearing skies and light winds should allow lows to settle back into the 30s with only light winds continuing on Saturday keeping mixing at a minimum. Neutral temperature advection is expected Saturday as well, thus our main warming influence will be lots of sunshine. Highs should still be above normal in the 50s. Warmer airmass begins building into the region again on Sunday when 850 temps gain a few degrees over Saturday. However still relatively light winds through the afternoon, so mixing will be limited despite favorable southwest direction. Still lots of sun, though, so we`ll keep highs at or above 60 as per going forecast. .LONG TERM...(Sunday night through Thursday) Issued at 312 PM CST Thu Nov 23 2017 We are still looking at a warm start to the work week before a colder airmass settles into the region for Tuesday through Thursday. Precipitation chances will remain low through the period as well. Mid level ridging will expand across the Plains Sunday night before flow becomes southwesterly with approach of strong trough swinging into the Rockies. Models are coming in better agreement with timing of the trough and its associated cold front. GFS is still faster, bringing front into northeast Nebraska late Monday afternoon, with ECMWF showing a later evening arrival. However both suggest our area will remain in warm sector through heating of the day Monday, and both indicate 850 temps approaching 20C ahead of front. This is a warmer airmass than is expected Friday, so temps could potentially top 70 in much of our area. However there remains concern with thickening mid and high cloud cover dampening max warmup a bit. Thus will maintain highs well into the 60s for now. Cold front should clear our area Monday night with much colder airmass to follow for Tuesday when we lose about 15C or more at 850. A short-lived warming trend is likely Wednesday as mid level shortwave ridging overspreads the area ahead of secondary trough reinforcing colder airmass for Thursday. With limited moisture with each of these systems, precipitation chances are low through Thursday. However we are still watching the Wednesday timeframe when ECMWF has been flip-flopping in showing a significant surface low wrapping up in the Plains and spreading a swath rain or snow in its northwest quadrant. 12Z runs from Wednesday and this morning indicate parts of eastern Nebraska and western Iowa would be affected by this, but the 00Z run last evening suggested a track much farther south. GFS shows no support for either solution, and this morning`s Canadian supports a farther south track. Again, something to watch, but for now will follow consistency between our going forecast and GFS/Canadian blend.
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&& .AVIATION...(For the 18Z TAFS through 18Z Friday afternoon) Issued at 1109 AM CST Thu Nov 23 2017 VFR conditions will prevail thru the fcst pd. && .OAX WATCHES/WARNINGS/ADVISORIES... NE...None. IA...None. && $$ SHORT TERM...Dergan LONG TERM...Dergan AVIATION...DEE

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