Area Forecast Discussion
Issued by NWS Omaha/Valley, NE

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000 FXUS63 KOAX 152031 AFDOAX Area Forecast Discussion National Weather Service Omaha/Valley NE 231 PM CST Fri Dec 15 2017 .SHORT TERM...(Tonight through Monday) Issued at 230 PM CST Fri Dec 15 2017 The main forecast concerns in this period are the chance for some light precipitation late Saturday night into Sunday morning and temperatures through the period. There were at least three jet streaks noted at 300 mb at 12Z this morning, one over the TN valley area (180 knots) another from southern Manitoba into MN (125 knots) and another punching east from the Pacific NW coast (about 110 knots). Strong height falls at 500 mb (up to 200 meters for the 12 hours ending at 12Z this morning) were moving into western Canada. The height falls were associated with a trough which was flattening the strong ridge which has been in place much of the past few weeks along about 120-130 degrees west longitude. There was a closed low at 500 mb over Mexico, and general model consensus forecasts that feature or the remnants to track northeast. It is expected to become and open wave track toward southeast NE and southwest IA for late Saturday night into Sunday morning. No precipitation is expected from tonight through Saturday evening. We are looking at potential for a light rain and light snow mix (small potential for freezing rain and sleet) moving up into southeast NE late Saturday night. Lift and deeper moisture increase, mostly for the southeast 1/3 of the forecast area. Although the GFS keeps surface temperatures above freezing, some other model guidance does not. Model forecast soundings indicate mixed precipitation types and will stick with that thinking for now. Will need to watch that as we get closer to the event. There are also hints at possible flurries into parts of northeast NE Saturday morning but did not include that in the forecast for now. A weak cold front will push south across portions of the forecast area on Saturday, then stall from parts of KS into southeast NE and southwest IA. The GFS MOS guidance seems to have a decent handle on highs Saturday, while a blend of model output was used for lows tonight and lows Saturday night. As for highs Sunday, we expect generally poor mixing, so kept a blend of GFS and NAM MOS for highs Sunday (upper 30s to around 40 north and in the 40s south). A low pressure system tracking across parts of the northern plains and southern Canada should bring a warmer westerly flow to the local area Monday, with highs mainly in the upper 40s/lower 50s. .LONG TERM...(Monday night through Friday) Issued at 230 PM CST Fri Dec 15 2017 The main concerns in this period are the trend toward colder temperatures and potential for some light snow or a mix of light snow and light rain for the area from Thursday into Thursday night. We will keep the forecast mainly dry from Monday night into Wednesday night. Thursday morning, the 12Z runs of both the GFS and ECMWF show a closed low at 500 mb over UT, but the flow is split, with another branch of the jet stream with a trough from Manitoba into eastern MT. Through Friday, the models dig the closed low southward toward the Gulf of California, while the northern stream trough slides southeast. The result is a highly amplified meridional pattern that is very likely to bring colder air into the region from the north by Friday. We will include POPs in the chance category for now with this potential event. The 12Z GFS did not really generate much QPF, while the ECMWF and Canadian models did generate some light to moderate amounts. The confidence level on amounts at this point is not very high, since there has been quite a bit of model to model and run to run variation. That will likely continue until we get into next week. && .AVIATION...(For the 18Z TAFS through 18Z Saturday afternoon) Issued at 1128 AM CST Fri Dec 15 2017 VFR conditions are expected through the TAF cycle. Mid-level clouds will continue to exit, leaving skies with clear to scattered cirrus (25kft) conditions. Southwest winds around 10-15kt this afternoon will diminish to 5-8kt by sunset, then become light and variable or light and northwesterly by Saturday morning. && .OAX WATCHES/WARNINGS/ADVISORIES... NE...None. IA...None. && $$ SHORT TERM...Miller LONG TERM...Miller AVIATION...Mayes is the U.S. government's official web portal to all federal, state and local government web resources and services.