Area Forecast Discussion
Issued by NWS Omaha/Valley, NE

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412 FXUS63 KOAX 250436 AFDOAX Area Forecast Discussion National Weather Service Omaha/Valley NE 1136 PM CDT Thu May 24 2018 .SHORT TERM...(Tonight through Sunday) Issued at 340 PM CDT Thu May 24 2018 Thunderstorm chances tonight into Friday, then heat through the weekend, are the primary forecast concerns. A couple of areas of convection were popping up this afternoon and will likely affect our area during the evening. One was in northeast Nebraska where 2000-2500 J/kg of MUCAPE as focused under weak upper level diffluence. Mid level theta-e was maximized here as well, and persistent afternoon heating will likely translate to continued development of storms along weak surface convergent zone. Shear profiles are weak, thus organized storms are not expected, but a few could pulse up rather quickly and produce some hail and gusty winds. Another area of convection was noted in eastern Kansas and northwest Missouri. These were bubbling up in another instability axis characterized by MLCAPE approaching 2500 J/kg and little CINH where dew points were in the upper 60s. Convection was aided by diffluent mid level flow ahead of well-defined MCV in central Kansas seen on visible satellite imagery. Cumulus cloud field was becoming more robust-looking in southeast Nebraska and southwest Iowa adjacent to current convection, so expect some development in those areas late today. Much of this activity will likely die with diminishing afternoon heating, however will maintain chances later into the evening in far southeast Nebraska where influence of MCV may be felt for a longer period of time. For the overnight period, things are still a little iffy in regards to thunderstorm coverage as short-range hi-res model output is fairly bearish on widespread development. However there is some overlap in solutions between hi-res and synoptic-scale models in showing development associated with mid level shortwave and ahead of weak surface front tracking into our area overnight. The most likely scenario will be for storms to develop later in the evening or after midnight in plume of highest low and mid level theta-e advection carried along by strengthening low level jet from eastern Kansas into northwest Iowa. Some strong storms are certainly possible during this time as elevated MUCAPE shown on forecast soundings reaches 2000 J/kg with little CINH. Much of the convection will push east of the Missouri River by mid Friday morning, and out of southwest Iowa shortly after. Light southwest low level flow will follow, but weak surface front will settle south into eastern Nebraska and west central Iowa during the afternoon and evening. An isolated afternoon storm could pop along this boundary, but better chances will focus along moisture plume from eastern Kansas into southern Iowa. Beyond Friday, mid level ridging is expected to build into the region through Sunday, with temperatures on the upswing with it. Highs in the 90s are likely both days. Dew points should only be in the 50s to around 60 on Saturday, but increase back into the 60s by Sunday making that day feel more humid. Still, heat indices won`t be much higher than actual air temperatures each day. .LONG TERM...(Sunday night through Thursday) Issued at 340 PM CDT Thu May 24 2018 We are still looking at a more active weather pattern returning for much of next week as upper ridge slides east with approach of upper low from the west. That low should open up by Tuesday, keeping our area under southwest flow aloft, and several impulses riding through that flow could trigger convection from time to time. And again today, there are run-to-run and model-to-model discrepancies in timing and strength with these systems, so trying to nail down exact timing right now is futile. Suffice it to say periodic thunderstorm chances will rule the forecast at least Tuesday through Thursday. Otherwise temperatures generally in the 85 to 90 degree range are expected for afternoon highs. && .AVIATION...(For the 06Z TAFS through 06Z Friday night) Issued at 1135 PM CDT Thu May 24 2018 Unstable conditions will continue across the area through the forecast period. This will provide the potential for an isolated thunderstorm to pop up just about anywhere with limited focus in place and better forcing north and south of the area. VFR conditions will prevail at all three sites during the period. && .OAX WATCHES/WARNINGS/ADVISORIES... NE...None. IA...None. && $$ SHORT TERM...Dergan LONG TERM...Dergan AVIATION...Fobert

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