Area Forecast Discussion
Issued by NWS Omaha/Valley, NE

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007 FXUS63 KOAX 241800 AFDOAX Area Forecast Discussion National Weather Service Omaha/Valley NE 1200 PM CST Tue Jan 24 2017 .SHORT TERM...(today through Thursday) Issued at 301 AM CST Tue Jan 24 2017 ...A significant winter storm will impact the area today into Wednesday... Manual 00z upper-air analysis and early-morning water vapor imagery indicate a substantial mid-level trough stretching from the far eastern Pacific to spine of the Rocky Mountains. Pronounced mid and upper-level wind maxima observed within the basal portion of the trough over the lower CO Valley will eject northeast into the central and southern Plains, driving the deepening of an associated mid-level trough and related surface cyclone over the central Plains today. At the same time, a plume of steep mid-level lapse rates --best observed by the 00z soundings at Denver, CO and North Platte, NE-- will advect east/northeast in the mid MO Valley, conditioning the environment for robust vertical motion within a frontogenetically forced precipitation band evolving to the north of the surface cyclone. Latest short-term model guidance indicates that strengthening lower to mid-tropospheric warm advection and isentropic upglide will foster a broadening band of light snow (perhaps mixed with sleet) this morning from the vicinity of the western KS surface low northeast into east NE and perhaps west IA. This band will pivot north into northeast NE and west-central IA by afternoon and strengthen with time as the steepening mid-level lapse rates couple with intensifying frontogentical forcing. Embedded upright convection is not out of the question with periods of moderate to heavy snow occurring through the afternoon. Farther south across east-central NE, slightly warmer boundary-layer temperature profiles will yield a rain-snow mix. Some sleet or graupel is possible, as is a rumble of thunder. By tonight, precipitation will change over to all snow from northwest-to-southeast across the area as cold air deepens on the backside of the surface cyclone passing to the east. Strengthening gradient flow in the low levels will promote strong northwest winds, creating areas of blowing and drifting snow, especially across northeast NE and west-central IA. The 00z models continue to converge on a more southern track to the surface low along with higher QPF within the deformation axis. As a result, it is reasonable to expect storm-total snowfall accumulations in excess of a foot along the NE-SD border with as much as six to eight inches possible along a line from Albion, NE to Onawa, IA. We, therefore, have included Boone, Madison, Stanton, Cuming and Burt counties in NE and Monona county in Iowa to the Winter Storm Warning, and added Saunders and Washington counties in NE and Harrison and Shelby counties in IA to the Winter Weather Advisory. Light snow along with gusty northwest winds will continue Wednesday before tapering off Wednesday night. .LONG TERM...(Thursday night through Monday) Issued at 301 AM CST Tue Jan 24 2017 We will remain in a high-amplitude mid-level pattern through next weekend, featuring a western U.S. ridge with a downstream trough over eastern North America. A number of disturbances will translate from central Canada into the central U.S. during that time frame. One such impulse is forecast to move into the mid MO Valley Saturday into Saturday night when a chance for flurries or light snow will exist. Thereafter, medium-range guidance suggests that a significant short-wave trough will temporarily dampen the western U.S. ridge prior to moving through the northern Plains into upper Great Lakes next Monday/Monday night. These data indicate that the strongest forcing for ascent and associated precipitation potential would remain to the north of our area. The above-mentioned large-scale pattern will favor below normal temperatures into next weekend. This will especially be the case in areas that receive more significant snowfall over the next 24-36 hours. && .AVIATION...(For the 18Z TAFS through 18Z Wednesday afternoon) Issued at 1200 PM CST Tue Jan 24 2017 Snow band associated with H7 frontogenetical forcing lifting north across northern portions of the CWA, taking with it heavier IFR/MVFR snow and visibilities. Expect a pause in persistent, widespread precipitation in the short term, as dry slot associated with upper/low level system moves across the area. Area sounding are showing decent mid-level instability, and as large scale forcing increases with approach of upper level system, may see increase in convective precipitation, thus introduced a period of sleet in KOMA TAF, and may do the same for KLNK during the afternoon hours. Another round of persistent, widespread snow is expected this evening and overnight. Maintained previous forecast of IFR/MVFR visibilities due to SN BR/FG and IFR cigs through 12 utc. && .OAX WATCHES/WARNINGS/ADVISORIES... NE...Winter Weather Advisory until 9 AM CST Wednesday for NEZ042>045- 050-051. Winter Storm Warning until 9 AM CST Wednesday for NEZ011-012- 015>018-030>034. IA...Winter Weather Advisory until 9 AM CST Wednesday for IAZ055-056. Winter Storm Warning until 9 AM CST Wednesday for IAZ043. && $$ SHORT TERM...Mead LONG TERM...Mead AVIATION...Fortin

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