Area Forecast Discussion
Issued by NWS Omaha/Valley, NE

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050 FXUS63 KOAX 090906 AFDOAX Area Forecast Discussion National Weather Service Omaha/Valley NE 306 AM CST Fri Dec 9 2016 .SHORT TERM...
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(today through Sunday) Issued at 306 AM CST Fri Dec 9 2016 The main forecast concerns center around several small chances for light snow through the short term. The 00Z upper air analysis indicated relatively low-amplitude flow over the CONUS with a broad trough over the eastern third of the country, and west to northwest flow over the western two-thirds. A 115 kt H25 jet was noted over the Pacific Northwest associated with some 30-50 m H5 height falls. Downstream over the Plains a strong thermal gradient existed, mainly over the southern Plains that was evident at H7. This thermal gradient will be the source of a couple of chances of light snow as jet segments and associated generally weak shortwave troughs translate along this high contrast ribbon. Models are in general agreement today that as the upstream 115 kt H25 moves into then northern Plains the ageostrophic response will be low to mid level WAA over northern Neb into SD. This will lead to increasing clouds over most of the CWA today, and lift may prove sufficient for some flurries or a brief period of -sn over the far northwest CWA later this morning and into the early afternoon. Accumulations are not expected. The tonight period should be dry over the CWA, but with clouds and southeast winds we have increased lows most areas to tighten up the diurnal range. As the current Pacific Northwest height falls move into the northern Rockies Saturday the central and northern Plains become located in the right rear entrance of the upper level jet, and although the static stability on cross sections appears high per EPV >.1, a frontal circulation is expected to develop given the isentropic ascent and jet placement. The placement on this band differs in the models though with the GFS farthest south and the NAM farther north. At this time given the cross sections where the better saturation, thermal profile, and lift are juxtaposed appear to be north and east of our FA. We feel that an initial band of -sn will likely develop in our northern CWA Saturday morning, but quickly lift north into MN/SD. We will continue with high pops during this period with up to around an inch of snow possible in Cedar/Knox Counties and less south. This initial band of -sn will lift out of the area and the rest of Saturday and Saturday night will be dry. Relatively mild temperatures are expected during this time with the continued southerly flow and clouds in the area. The previously mentioned height falls and associated QG forcing will then move through the CWA on Sunday with an associated cold frontal passage by afternoon. Again it appears that most if not all of the snow associated with the shortwave-trough will fall to our north, but will maintain some chance pops over the northern/eastern CWA closest to the important mid-level thermal gradient. .LONG TERM...(Sunday night through Thursday) Issued at 306 AM CST Fri Dec 9 2016 A continued unsettled pattern is expected through the extended as a seasonably fast jet continues to extend across the CONUS and a strong thermal gradient remains in play. Any shortwave trough riding along this gradient can lead to a period of isentropic ascent and a period of -sn, and confidence in timing these waves and associated precipitation is very low currently. The global models do tend to agree in another strong arctic surge from Tuesday night into Wednesday /the GFS is certainly stronger with this than the EC/ and we will include some chance of light snow with this front. If the GFS were to prove closer to reality than our forecast temperatures are to warm for Wednesday through Thursday, but little change to this period was done due to the uncertainty. The GFS and EC then to some degree want to buckle the flow toward the end of next week that may lead to some chance of precipitation, but again uncertainty in precipitation is very low with confidence in continued cold weather very high.
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&& .AVIATION...(For the 06Z TAFS through 06Z Friday night) Issued at 1124 PM CST Thu Dec 8 2016 VFR conditions through the period. Clouds will thicken through the day Friday, and could see scattered flurries near KOFK 20-24z. && .OAX WATCHES/WARNINGS/ADVISORIES... NE...None. IA...None. && $$ SHORT TERM...Boustead LONG TERM...Boustead AVIATION...DeWald

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