Area Forecast Discussion
Issued by NWS Omaha/Valley, NE

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000 FXUS63 KOAX 190401 AFDOAX Area Forecast Discussion National Weather Service Omaha/Valley NE 1001 PM CST Sat Feb 18 2017 .UPDATE... Issued at 959 PM CST Sat Feb 18 2017 Temperatures dropped off quickly in northeast Nebraska and western Iowa, thus updated low temperatures for tonight. Low level winds will increase/along with clouds and this should help level temperatures off in parts of eastern Nebraska, however will occur later in Iowa. && .SHORT TERM...(Tonight through Tuesday) Issued at 306 PM CST Sat Feb 18 2017 The primary feature of interest in the short term is a low- latitude trough which is evident in early-afternoon water vapor imagery over Baja. This upper-air system will continue east through the southern Rockies and northwest Mexico tonight into Sunday before phasing with a polar-branch disturbance over the High Plains Sunday night. A full-latitude vorticity ribbon will subsequently translate across the Great Plains on Monday. These upper-air developments will support the deepening of a lee trough over over the High Plains tonight into Sunday, which in turn, will hasten the poleward flux of an increasingly moist boundary layer into the mid MO Valley from the southern Plains. This moisture increase may contribute to areas of fog late tonight into Sunday morning. High clouds will be on the increase Sunday which may temper the degree of diabatic warming with highs commonly in the mid 60s. Sunday night into Monday, latest model guidance remains consistent in suggesting that strengthening large-scale forcing for ascent will coincide with a plume of modestly steep mid-level lapse rates and increasingly low-level moisture to foster a band of showers and a few thunderstorms which will develop northeast across the area. The best chance for measurable precipitation will be late Sunday night through about midday Monday. High temperatures will be dependent on how quickly the precipitation and clouds clear with readings from the mid 60s northwest to lower 70s southeast being included in this forecast. Record highs for Monday, the 20th are Omaha - 67/1930, Lincoln - 71/1991, Norfolk - 66/1930. The record warmest minimum temperature of 37/1996 at Norfolk will also stand a chance of being broken. On Tuesday, quasi-zonal flow aloft will enhance the eastward spread of downslope-induced warming across the central Plains with highs in the to upper 60s to mid 70s. Record highs for Tuesday, the 21th are Omaha - 72/1977, Lincoln - 74/1991, Norfolk - 74/1995. .LONG TERM...(Tuesday night through Saturday) Issued at 306 PM CST Sat Feb 18 2017 On Wednesday, an amplifying polar-branch disturbance over the northern Plains into upper MS Valley will encourage the progression of a cold front into the forecast area with highs ranging from the lower 60s northwest to lower 70s southeast. Thursday and Friday, we continue to focus on the potential impacts of a vigorous storm system which is forecast to track across the central Plains. The 12z run of the deterministic GFS remains an outlier and has been discounted from the forecast process. Instead, we have relied on a blend of the 12z ECMWF, Canadian, and GEFS mean solutions, which depict a slower and more southern track of the synoptic cyclone (than the deterministic GFS). Under this scenario, we expect an increasing chance of rain showers on Thursday, mainly across the northern half of the area within a zone of strengthening warm advection and isentropic upglide. By Thursday night into Friday, intensifying dynamic forcing for ascent will associate with a plume of steep lapse rates to yield an increase in precipitation coverage and intensity with a change over from rain to snow from northwest to southeast across the area. The lower-latitude storm track depicted by the current model runs would suggest a higher probability of accumulating snowfall, especially over northeast NE within the evolving deformation band. A few thunderstorms will also be possible, mainly across southeast NE into southwest IA Thursday evening. Light snow or a mixture of rain and snow may linger into Friday evening over far east NE and southwest IA before ending later Friday night. Temperatures on the backside of the storm system will be notably cooler with highs on Friday and Saturday ranging from the mid 30s north to lower 40s south. && .AVIATION...(For the 00Z TAFS through 00Z Sunday evening) Issued at 515 PM CST Sat Feb 18 2017 Expect mainly VFR conditions through the period, but some MVFR conditions possible Sunday morning. Low level moisture will be increasing tonight but highest potential for low ceilings seems to stay west our south of the three TAF sites. We could see some fog, but for now look for 4 miles or more. That may need to be updated in later TAFs. && .OAX WATCHES/WARNINGS/ADVISORIES... NE...None. IA...None. && $$ UPDATE...Zapotocny SHORT TERM...Mead LONG TERM...Mead AVIATION...Miller

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