Area Forecast Discussion
Issued by NWS Omaha/Valley, NE

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890 FXUS63 KOAX 210811 AFDOAX Area Forecast Discussion National Weather Service Omaha/Valley NE 311 AM CDT Wed Jun 21 2017 .SHORT TERM...
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(Today through Friday) Issued at 345 AM CDT Wed Jun 21 2017 Forecast concerns in the short term will be thunderstorm potential/evolution through Thursday night and severe weather potential. The h5 pattern during the period has a large high pressure system over the desert southwest U.S. that extends toward Alberta and Saskatchewan. Hot temperatures...127 degrees at Death Valley, CA...and numerous excessive heat warnings and advisories were over the southwest U.S. Meanwhile Tropical Storm Cindy was in the Gulf. Through Thursday night...a broad tough will flatten the ridge with fast flow across the Northern Plains and a couple and closed low pressure over Ontario. This morning, the front will lift north as a warm front and southwest extent of elevated thunderstorms is still questionable. It is common for storms to develop as the low level jet increase and the warm nose returns to the region. Pooled h7/H85 moisture was noted over parts of the Plain and a few storms developed near the KS/Nebraska border near the surface cold front. Warmer h7 air will spread into the forecast area and the h85 low level jet increases to 40 to 50kts. Moisture transport vectors increase overnight and are oriented southwest to northeast across the forecast area, however Corfidi vectors show that elevated storms that form will travel from northwest to southeast. There are accas/mid clouds, therefore will have to monitor...a stronger WAA signal is farther north over the Northern Plains into Iowa. Thunderstorms can develop southwest into the low level jet, especially if the cap is weaker in that region and moisture is adequate. Will maintain pops for these features The cold front will push into central Nebraska by 21Z. 14 to 15 deg C H7 temperatures are in place. Very steep lapse rates over the western High Plains will stretch from southwest Minnesota into eastern South Dakota into southwest Nebraska and western Kansas back toward New Mexico by 18z...shifting into western Iowa by 00Z. Instability increases to 2000 to 4000 J/kg near the front. The forecast soundings maintain a cap...however near the front...isolated strong to severe thunderstorms could develop. SPC has the area outlooked in a slight risk with all modes of severe weather possible including isolated tornadoes and locally heavy rain. Trimmed pop area and focused in northeast Nebraska...although something isolated may try to get going elsewhere. There is some pooling of moisture in southeast Nebraska and southwest Iowa and the cap may be weaker here. The storm coverage with the cap appears limited on the NAM12/EC/GFS...however with the forcing from the shortwave and convergence with the front in the 00-06Z timeframe thought it prudent to include scattered thunderstorms during the evening. The wave pushes east and the surface front tries to lift back north with another round of showers and thunderstorms for thursday afternoon and thursday night and the stronger shortwave pushes the front south. Again we are in the slight risk as temperatures heat up into the 80s and 90s with the area on the southern edge of a belt of stronger winds aloft. There may be some lingering showers Friday, however this would be behind the front. Highs today should top out well into the 90s and more humid with stronger south winds. Highs Thursday will again depend on the frontal position, but have highs in the 80s north and 90s south. Cooler for Friday with highs in the 70s .LONG TERM...(Friday night through Tuesday) Issued at 345 AM CDT Wed Jun 21 2017 Cooler for the extended with highs in the 70s then a return to the 80s Monday and Tuesday. We remain in a general northwest flow aloft pattern. There may be some showers Saturday, however the medium range models have backed off on the coverage; although the EC still has better coverage. Dry weather is forecast for Sunday and Monday with some small rain chances Tuesday.
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&& .AVIATION...(For the 06Z TAFS through 06Z Wednesday night) Issued at 1130 PM CDT Tue Jun 20 2017 VFR conditions are likely through the TAF cycle, with clear to scattered cirrus skies and unrestricted visibility. Isolated to scattered showers and thunderstorms are possible in the late afternoon to early evening, especially affecting KOFK. Have included a VCSH mention for now to hint at potential. Should a shower/storm happen to pass directly over the site, it could temporarily restrict visibility or lower ceilings. Guidance has become inconsistent and sporadic regarding low-level wind shear potential both tonight and Wednesday evening, so for now, have left out mention. Light winds overnight will increase to around 10-15kt out of the south at all sites by late morning to midday. && .OAX WATCHES/WARNINGS/ADVISORIES... NE...None. IA...None. && $$ SHORT TERM...Zapotocny LONG TERM...Zapotocny AVIATION...Mayes

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