Area Forecast Discussion
Issued by NWS Omaha/Valley, NE

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952 FXUS63 KOAX 152312 AFDOAX Area Forecast Discussion National Weather Service Omaha/Valley NE 612 PM CDT Fri Sep 15 2017 .SHORT TERM...(Tonight through Monday) Issued at 317 PM CDT Fri Sep 15 2017 A prominent vorticity maximum over the northern High Plains this afternoon will weaken as it translates northeast across the western Dakotas tonight. The trailing influence of this disturbance is presently tracking through central into eastern NE, and is responsible for weak elevated convection ongoing across the area. Meanwhile, a related surface low over southeast SD as of 20z will continue northeast into MN tonight while an associated cold front edges southeast into the forecast area. Strong boundary-layer heating ahead of the cold front is contributing to deepening cumulus development from north-central into western NE. Current SPC mesoanalysis data indicate that the cap is weakening along the boundary with warm-sector mlCAPE vales of 1000-1500 J/kg. Latest convection-allowing model guidance is suggestive that widely scattered storms will eventually develop late this afternoon into evening with this activity potentially affecting portions of northeast NE. Given the presence of steep low to mid-level lapse rates and modest vertical shear, the potential will exist for a strong storm or two capable of gusty winds and perhaps some hail. Persistent warm advection and isentropic upglide along a nocturnal LLJ will support a continued chance of thunderstorms overnight; especially over the northern half of the forecast area. On Saturday and Saturday night, another strong shortwave trough will eject from the northern Rockies into the northern Plains, depressing the mid-level height field over the mid-MO Valley. This will encourage the southward advance of the surface cold front through the area with afternoon temperatures ranging from the upper 80s over southeast NE to mid 60s north of the boundary across northeast NE. The warm and humid conditions ahead of the front will fuel thunderstorm development by mid to late afternoon from portions of western IA into southeast NE. A few of these storms could be severe and capable of large hail and damaging winds. The showers and storms should taper off from north to south on Saturday night as the front shifts south of the area. Sunday and Sunday night, surface high pressure will quickly build through the area ahead of a deepening lee trough over the High Plains. Strengthening low-level warm advection on the backside of the high will support increasing clouds through the day with highs ranging from upper 70s south to around 70 north. Shower and thunderstorm chances will increase Sunday night as the warm advection is augmented by the approach of a low-amplitude shortwave trough from the High Plains. It appears that showers and thunderstorms will continue across parts of the area through at least the first part of Monday with the arrival of the aforementioned shortwave trough. High temperatures will be affected by how quickly the clouds and precipitation clear with readings in the mid 70s to lower 80s currently forecast. .LONG TERM...(Monday night through Friday) Issued at 317 PM CDT Fri Sep 15 2017 An active weather pattern will persist through the long-term period with a strong shortwave trough moving through the northern and central Plains Tuesday night into Wednesday, and potentially another system affecting the region by the end of the work week. A surface front will oscillate back and forth across the area, supporting a chance of showers and thunderstorms, especially from Wednesday night into Friday. && .AVIATION...(For the 00Z TAFS through 00Z Saturday evening) Issued at 612 PM CDT Fri Sep 15 2017 The aviation weather will be more active than it has been recently. Low clouds are likely to fill in behind a cold front that will be pushing through eastern Nebraska through Saturday. TSRA possible this evening, mainly at KOFK but we could see isolated activity at all three TAF sites later tonight. Did mention some LLWS just at KLNK and KOMA for now, where low level jet may be the strongest. Winds will shift to north or northwest with the frontal passage. && .OAX WATCHES/WARNINGS/ADVISORIES... NE...None. IA...None. && $$ SHORT TERM...Mead LONG TERM...Mead AVIATION...Miller

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