Area Forecast Discussion
Issued by NWS Omaha/Valley, NE

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086 FXUS63 KOAX 172300 AFDOAX Area Forecast Discussion National Weather Service Omaha/Valley NE 500 PM CST Fri Feb 17 2017 .SHORT TERM...(Tonight through Monday) Issued at 305 PM CST Fri Feb 17 2017 Early-afternoon water vapor imagery depicted a polar-branch short-wave trough over the Dakotas with a sub-tropical-branch mid to upper-level low over the southern Plains. The former disturbance will continue northeast into the upper MS Valley tonight, supporting the equatorward advance of a surface cold front through the mid MO Valley. This boundary will dissipate on Saturday to our south as a weak surface high moves through the area. Slightly cooler low-level thermodynamic profiles and shallower boundary-layer mixing will result in highs generally in the lower to mid 60s. Saturday night into Sunday, a sub-tropical-branch short-wave trough will track from the lower CO Valley and northern Baja into the central and southern Rockies, inducing the deepening of a lee trough over the High Plains. A resultant strengthening of southerly low-level winds and the concurrent poleward flux of an increasingly moist boundary-layer will commence with patchy fog possible late Sunday night into Saturday morning. It still appears that this low-latitude trough will tap into a plume of mid to high-level moisture originating over the sub-tropical Pacific, yielding mostly cloudy skies on Sunday with highs in the lower to mid 60s. Sunday night into Monday, aforementioned short-wave trough will continue northeast into the central Plains, gradually phasing with a polar-branch disturbance moving into the Dakotas. Strengthening forcing for ascent coupled with the continued low-level moistening/destabilization occurring ahead of the system cold front will result in increased chances of showers and a few thunderstorms, mainly late Sunday night through midday Monday. Relatively poor mid-level lapse rates will limit the degree of destabilization and no severe weather is currently anticipated. .LONG TERM...(Monday night through Friday) Issued at 305 PM CST Fri Feb 17 2017 The mid-level flow pattern will transition to quasi-zonal in the Tuesday-Wednesday time frame, in the wake of the trough moving through the MS Valley, and ahead of the next trough evolving over the Interior West. Southwest to west, downslope winds will enhance warming potential on Tuesday with temperatures rising into the mid 60s to lower 70s. Readings may be a bit cooler on Wednesday --especially over our northern counties-- as a weak cold front settles south into the area. Thursday into Friday, attention then turns to a potent mid-level trough emerging into the Great Plains from the Rockies. Differences exist amongst 12z model guidance with respect to the amplitude and track of this system. The deterministic GFS is most progressive with this synoptic system, indicating the associated surface low over eastern NE by midday Thursday, prior to pushing the trailing cold front through the entire forecast area by Thursday evening. The ECMWF and Canadian deterministic models as well as the GEFS mean suggest a slower progression of the synoptic wave; which is the direction we are inclined to lean with the forecast at this point. Under the slower scenario, we would see increasing chances of showers and thunderstorms on Thursday afternoon and continuing into Thursday evening. Thursday night into early Friday, a change over from rain to snow is possible. && .AVIATION...(For the 00Z TAFS through 00Z Saturday evening) Issued at 500 PM CST Fri Feb 17 2017 Expect VFR conditions through the period. Some small potential for a little fog toward sunrise, but a little better chance of low clouds or fog late Saturday night. && .OAX WATCHES/WARNINGS/ADVISORIES... NE...None. IA...None. && $$ SHORT TERM...Mead LONG TERM...Mead AVIATION...Miller

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