Area Forecast Discussion
Issued by NWS Omaha/Valley, NE

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000 FXUS63 KOAX 220533 AFDOAX Area Forecast Discussion National Weather Service Omaha/Valley NE 1133 PM CST Wed Feb 21 2018 .UPDATE... Issued at 902 PM CST Wed Feb 21 2018 A short-wave trough presently over the southern Plains is promoting a strengthening downstream belt of warm advection across the central Plains into mid-MO Valley which is being manifest as increasing echoes in mosaic radar data. 00z OAX/TOP soundings revealed a considerable amount of dry air in the low levels which will have to be overcome before precipitation begins to reach the ground. Latest convection-allowing model guidance and 00z NAM data indicate light snow developing within the next 2-3 hours mainly south of I-80 and gradually spreading northeast through daybreak Thursday. Snow accumulations with this initial wave of precipitation (though about 8 AM Thu) will range from less than half an inch generally north of I-80 to around 2" over southeast NE. The initial warm-advection-related precipitation should largely shift to the east of the area by mid morning Thu with forecast soundings indicating a developing warm nose aloft and loss of ice in the dendritic-growth zone. The net result is a transition of any light, lingering precipitation to freezing drizzle or light freezing rain. The exception is over northeast NE where predominant precipitation type may remain snow. By late tomorrow afternoon into evening, large-scale forcing for ascent re-intensifies in response to the approach of the next disturbance aloft. At that time, we would expect to see an increase in precipitation rates with predominantly freezing rain along and south of I-80 with a transition to sleet and then snow northward into northeast NE and west-central IA. The current forecast appears in reasonably good shape and we have made only minor adjustments. && .SHORT TERM...(Tonight through Saturday) Issued at 447 PM CST Wed Feb 21 2018 Timing precip and location of dominate type late tonight through Thursday evening is initial concern followed by Snow event on Saturday. Regional mosaic already showing batch of precip beginning to lift northward into eastern KS. HRRR/RAP13 indicate activity should reach the southern CWA shortly before midnight. Per RAP13 MaxT aloft prog...there will definitely be a fine line separating freezing/frozen precip. As of now, appears likely snow will be the predominate type between midnight tonight and early Thursday morning as it advances northward through the CWA. However, as layer MaxT go above freezing from south to north, and feeder- seeder process begins to weaken, expect snow to give way to light freezing drizzle from south to north, expanding across the rest of the CWA the remainder of the day into the evening hours. Snow accumulations should be relatively even over the CWA ranging from about 1 to 2 inches. Brunt of ice accumulations will be found over southwest IA south of I-80 with anywhere from one to two tenths possible. Over the rest of the CWA, five hundredths to a tenth looks possible. Given this, will post a Winter Weather Advisory to be in effect from late tonight through Thursday evening. Turning to Saturday, a potent system lifting into the central Plains will be the focus for the next snow accumulation event over the region. Synoptic scale forcing will increase substantially as 500mb hgt falls of 15dam precedes a quite potent vort max as it pushes across NE/KS. Associated precip activity will develop within the warm sector of the surface reflection which is progged to be in western KS 12z Saturday. The GFS and CMC are in rather good agreement depicting the axis of heaviest lining up from southwest NE to southeast SD, just to the left of the 500mb HFC track. And as of now, there appears to be a distinct possibility for significant snow accumulations over the northern CWA where dendritic omega will be maximized...per the GFS...advertising over 40 microbars of lift. .LONG TERM...(Saturday night through Wednesday) Issued at 447 PM CST Wed Feb 21 2018 GFS/CMC in agreement extended periods will be dry from Sunday through at least Tuesday before the next chance for precip. Tuesday night and Wednesday, model show a cold front dropping into the central Plains with the possibility a snow/rain mix event. && .AVIATION...
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(For the 06Z TAFS through 06Z Thursday night) Issued at 1132 PM CST Wed Feb 21 2018 Radar data and surface observations indicate light snow beginning to fall across portions of south-central and southeast NE with the snow expected to overspread much of eastern NE and southwest IA through daybreak on Thursday. Periods of moderate snow are possible, especially at KOMA and KLNK where visibilities may fall to a mile or so. Ceilings should also continue to lower with prevailing MVFR conditions developing after 12z Thursday. Snowfall should taper off by mid morning on Thursday with a phase change to freezing drizzle possible at KOMA and KLNK through much of the day. Precipitation rates are expected to increase again by late afternoon into evening with snow expected to be the predominant weather at KOFK. At KOMA and KLNK, a mixture of freezing rain and snow is possible. Precipitation should end by mid to late evening with a continuation of MVFR ceilings.
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&& .OAX WATCHES/WARNINGS/ADVISORIES... NE...Winter Weather Advisory from 3 AM Thursday to midnight CST Thursday night for NEZ034-044-045-050>053-065>068-090>093. Winter Weather Advisory from 3 AM to 6 PM CST Thursday for NEZ078-088-089. Winter Weather Advisory from 6 AM Thursday to midnight CST Thursday night for NEZ012-015-017-018-031>033-042-043. Winter Weather Advisory from 6 AM to 6 PM CST Thursday for NEZ011-016-030. IA...Winter Weather Advisory from 3 AM Thursday to midnight CST Thursday night for IAZ043-055-056-069-079-080-090-091. && $$ UPDATE...Mead SHORT TERM...DEE LONG TERM...DEE AVIATION...Mead

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