Area Forecast Discussion
Issued by NWS Omaha/Valley, NE

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000 FXUS63 KOAX 261728 AFDOAX Area Forecast Discussion National Weather Service Omaha/Valley NE 1228 PM CDT Mon Jun 26 2017 .SHORT TERM...(Today through Wednesday) Issued at 321 AM CDT Mon Jun 26 2017 A more active weather pattern is developing over the next couple of days as thunderstorm chances increase markedly Tuesday night and Wednesday. However precipitation chances will not be confined to those periods as we already have showers and isolated thunderstorms on radar this morning. Shortwave traveling southeast from the Dakotas into eastern Nebraska and western Iowa was sparking those showers, which will track across parts of eastern Nebraska and western Iowa through the morning. Trailing surface front is forecast to settle into central sections of eastern Nebraska and western Iowa this afternoon as another shortwave and upper level jet streak dives into the region. A good majority of synoptic- and meso-scale model output suggests additional development near and south of this front will occur this afternoon. Instability progs are relatively tame, so severe is not a real concern, but isolated thunderstorms are certainly possible. Expect activity to affect the southern halves of eastern Nebraska and western Iowa early in the afternoon, then shift south of the state borders early this evening. Upper flow will begin to shift from northwest orientation in the Plains to shortwave ridging on Tuesday as deep trough over the Great Lakes into the Southeast U.S. finally begins to shift east. Meanwhile a potent shortwave crossing the Rockies should be approaching the High Plains Tuesday afternoon, and tracking across our area Tuesday night, leaving mainly zonal flow in the Plains for Wednesday. Increasing mid level flow will induce lowering pressures in the High Plains on Tuesday, promoting stronger southerly low level winds and rapid transport of moisture north. Associated instability increases with strong daytime heating Tuesday will feed thunderstorms in the High Plains during the afternoon, with that activity spreading east into eastern Nebraska and southwest Iowa overnight as theta-e advection continues on 50kt low level jet. While instability will decrease overnight, 1000-1500 J/kg of MLCAPE is advertised by ECMWF/GFS across northeast Nebraska where bulk shear near 40kt is forecast. Thus some strong to potentially severe storms are possible there through midnight or so. Convection will likely linger through the morning on Wednesday as shortwave slowly works to the east. Southwest low level jet near 40kt is forecast into the afternoon as well, suggesting continued development on backside of system will maintain convection for much of the day. By late in the day, focus for convection should favor southeast Nebraska and southwest Iowa where surface front will likely reside as storm outflows meet synoptically-driven southerly flow. Where storms do maintain/fire Wednesday afternoon, even the more conservative ECMWF says over 2500 J/kg MLCAPE will be available to fuel potentially severe storms with large hail and damaging winds. .LONG TERM...(Wednesday night through Sunday) Issued at 321 AM CDT Mon Jun 26 2017 Convection from Wednesday afternoon activity will linger into Wednesday night, most likely affecting southeast Nebraska and southwest Iowa. Forcing should be dwindling as shortwave tracks well to the east and 850 flow decreases as it turns more westerly after midnight. However another round of potentially severe weather is expected Thursday. Strong shortwave ejecting from upper low centered over southern Saskatchewan is forecast to dive into the High Plains of western Nebraska Thursday afternoon then rotate east through our area overnight. Broad northward transport of higher theta-e air in response to lowering pressures with approach of shortwave is expected to drive Wednesday frontal boundary back north into Nebraska and Iowa, offering focus for convective development. Upper 60s to near 70F dew points are suggested by ECMWF/GFS, yielding 3000 J/kg or more of MLCAPE. Increasing mid level flow will also contribute to an increase in bulk shear to 40-50kt range. Certainly will see a wind and hail threat if this pans out. We should see a dry period Friday into Saturday behind this exiting system. However Saskatchewan low/trough is forecast to settle into the Northern Plains this weekend, maintaining cyclonic flow regime over Mid America. Impulses rotating through this flow could spark showers and thunderstorms beginning Saturday afternoon, with somewhat better chances on Sunday. && .AVIATION...(For the 18Z TAFS through 18Z Tuesday afternoon) Issued at 1227 PM CDT Mon Jun 26 2017 Showers and possibly a thunderstorm will affect the KLNK TAF through about 19z. Otherwise, VFR conditions at all TAF sites. && .OAX WATCHES/WARNINGS/ADVISORIES... NE...None. IA...None. && $$ SHORT TERM...Dergan LONG TERM...Dergan AVIATION...DeWald is the U.S. government's official web portal to all federal, state and local government web resources and services.