Area Forecast Discussion
Issued by NWS Omaha/Valley, NE

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000 FXUS63 KOAX 221746 AFDOAX Area Forecast Discussion National Weather Service Omaha/Valley NE 1246 PM CDT Tue May 22 2018 .SHORT TERM...(Today through Thursday) Issued at 315 AM CDT Tue May 22 2018 Forecast concerns over the next few days will be timing of showers and thunderstorms and warmer temperatures. The 00Z OAX sounding had mixed to around 815mb resulting in temperatures warming to the mid and upper 70s with abundant sunshine. The h5 low pressure system was centered over southern California with the h5 low responsible for the weekend damp weather over Minnesota. GOES-16 water vapor satellite imagery highlights these features and the deep convection occurring over New Mexico. An emerging 100kt jet from southern California and increased upper level divergence combined with shortwave trough energy/deep moisture return has a north to south corridor of storms from Mexico northward through New Mexico into southeast Colorado and the Oklahoma Panhandle. H85 dewpoints were around 10deg C at DDC and LBF and 15deg C in West Texas. Latest surface observations and WSR-88D reflectivity show one subtle surface boundary in northeast Nebraska and another in southern Nebraska trailing back toward southwest Nebraska and eastern Colorado closer surface low. The strengthening low level jet to around 40kts has touched off some isolated thunderstorms. Warm air advection continues through the day, the low level jet decreases and the warm front lifts a little farther north. Forecast soundings show a favorable airmass for thunderstorms and during max heating, some could become strong to severe. While the low level jet will be one focus, as it weakens, the focus for storms should be more tied to the warm front. SPC had the risk for severe storms farther north and these could clip parts of northeast Nebraska and west central Iowa where the shear is more supportive of stronger storms. Will include some pops for iso/sct coverage today. The low level jet increases again tonight and noses a bit farther north into SD and northern Iowa and this puts the more favored area for storms northeast of the forecast area, additional storms could develop in northeast Nebraska and west central Iowa tonight within the moist/instability axis and could linger into Wednesday morning. Wednesday, the h5 closed low is over eastern Idaho and western Wyoming with the mid h5 ridge position just east of the Missouri River. Through Thursday, the closed H5 low lifts northeast toward Saskatchewan and Manitoba and extends into western Kansas with a slight eastward progression of the mean ridge to the Mississippi River. Thunderstorms will be ongoing with warm front from South Dakota into western Iowa Wednesday with a weakening trend during the day Wednesday. Wednesday afternoon and Wednesday night...upslope flow combined with the 35-45kt low level jet increasing should resulting in thunderstorms across the western High Plains which gradually migrate eastward overnight and into the forecast area. Due to the weakening forcing, thunderstorm coverage should be isolated in nature. Highs today should be in 85 to 90 each day. .LONG TERM...(Thursday night through Monday) Issued at 315 AM CDT Tue May 22 2018 Thursday night through Friday the 35kt southwest low level jet develops over central Nebraska and the upper trough deepening through the Plains. Steep lapse rates combined with mid-level vorticity advection utilizing 2500-3500 MUCAPE should result in scattered thunderstorms across the forecast area Thursday night although bulk shear vectors (0-3km and 0-6km) tend to be less than 30kts. Friday night through Tuesday, mid level ridging builds into the area. The GFS has more thunderstorm development Friday night and with a shortwave over the Great Lakes trailing into the local area Sunday morning. Left isolated pops in as forecast soundings would support thunderstorms if forcing were sufficient. && .AVIATION...
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(For the 18Z TAFS through 18Z Wednesday afternoon) Issued at 1240 PM CDT Tue May 22 2018 Warm front was located just southwest of KLNK at 18Z with isolated convection to the northeast of the boundary. Expect front to gradually lift north through 00Z with models placing it near the SD border by that time followed by a continued drift to the north into SD and northern IA through 06Z. VFR conditions are expected outside of convection with storm chances diminishing south to north during that time.
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&& .OAX WATCHES/WARNINGS/ADVISORIES... NE...None. IA...None. && $$ SHORT TERM...Zapotocny LONG TERM...Zapotocny AVIATION...Fobert

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