Area Forecast Discussion
Issued by NWS Omaha/Valley, NE

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000 FXUS63 KOAX 231733 AFDOAX Area Forecast Discussion National Weather Service Omaha/Valley NE 1133 AM CST Fri Feb 23 2018 .SHORT TERM...(Today through Sunday) Issued at 345 AM CST Fri Feb 23 2018 Another wintry mix of precipitation on Saturday is the primary forecast concern. Low pressure system that brought our latest wintry mix of snow, freezing drizzle/rain and sleet on Thursday was pushing toward the Great Lakes region this morning. Behind it, cooler high pressure will be settling into the Northern Plains and nosing toward the Mid Missouri River Valley region today before sliding east tonight with approach of next weather system swinging through the Rockies. Thus cold air will not stay around long, with GFS showing 850 0C isotherm remaining in or near southeast Nebraska and southwest Iowa through tonight. As Rockies system rotates into the Plains later tonight and Saturday, low level warm advection will push that above 0C 850 air north toward Interstate 80 by Saturday morning. Forecast soundings show this warmer air riding over colder boundary layer air, with diffluent flow ahead of Rockies wave inducing isentropic upglide resulting in areas of precipitation breaking out in our southern CWA late Friday night and Saturday morning. Forecast soundings suggest mid level dry air over this region, thus no ice introduction into lower moist layer, resulting in freezing drizzle/rain before surface temperatures push above freezing later in the day, and that appears to only affect far southeast Nebraska and southwest Iowa. Farther northwest, modest frontogenetical forcing is shown on cross- sections, and forecast soundings indicate moistening of mid and lower atmposphere will be complete by 12Z Saturday. Thus seeder- feeder processes should produce mainly snow across northeast Nebraska. Models have been lowering storm total QPF the last couple of runs, but specific humidity calculations for a 12-hour event still suggest close to 6 inches of snow is likely in parts of northeast Nebraska. As far as icing potential goes in the area a couple of counties either side of Interstate 80, up to 0.15" is expected during the day Saturday, with a likely mix with snow coming Saturday afternoon totaling an inch or two. Have gone ahead and issued Winter Weather Advisories for much of our CWA where confidence is fairly high on some accumulations of both ice and snow late tonight through most of Saturday. Left a few counties in northeast Nebraska under a Winter Storm Watch where totals could exceed 6 inches. And left out a few counties in our far southeast where warm surface air intrusion early in the day Saturday may limit icing. After precipitation ends Saturday afternoon or evening, clearing skies will allow temperatures to drop into the teens by Sunday morning. However sunshine and westerly low level winds should help temps rebound into the 30s over most of the area Sunday afternoon, with some lower 40s in the south. .LONG TERM...(Sunday night through Thursday) Issued at 345 AM CST Fri Feb 23 2018 Closer-to-normal temperatures are expected much of next week as mid level flow favors a west to southwest direction. Monday could be really mild as southwest low level flow is realized owing to a strong shortwave moving through the Northern Plains. Colder air settles south behind that wave for the rest of the period into Thursday, keeping surface temperatures a bit cooler than mid level flow would suggest. While models begin to diverge at mid week, a blended consensus of model output shows a shortwave ejecting from the southwest into the Plains on Wednesday, bringing another shot of precipitation. GFS would again indicate a mix of precipitation types across our area, while ECMWF is a bit warmer and would suggest mainly a liquid event. && .AVIATION...
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(For the 18Z TAFS through 18Z Saturday afternoon) Issued at 1119 AM CST Fri Feb 23 2018 A deck of MVFR to IFR clouds will continue to spread south across the region through the early afternoon hours. Expect ceilings will rise to VFR levels by this evening, before dropping down once again around 06Z ahead of the next wintry system. Current guidance suggests precip will begin around 10Z-12Z with primarily snow at KOFK and mostly freezing rain/drizzle at KOMA and KLNK, possibly mixing with light snow through the day Saturday.
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&& .OAX WATCHES/WARNINGS/ADVISORIES... NE...Winter Weather Advisory from 3 AM to 6 PM CST Saturday for NEZ015-030>034-042>045-050>053-065>068-078-088>090. Winter Storm Watch from late tonight through Saturday afternoon for NEZ011-012-016>018. IA...Winter Weather Advisory from 3 AM to 6 PM CST Saturday for IAZ043-055-056-069-079. && $$ SHORT TERM...Dergan LONG TERM...Dergan AVIATION...KG

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