Area Forecast Discussion
Issued by NWS Omaha/Valley, NE
Issued by NWS Omaha/Valley, NE
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587 FXUS63 KOAX 200441 AFDOAX Area Forecast Discussion National Weather Service Omaha/Valley NE 1141 PM CDT Sun May 19 2024 .KEY MESSAGES... - A line of severe thunderstorms may impact portions of southeast Nebraska this evening or early tonight. Straight line winds appear to be the greatest risk at this time. - Several additional rounds of strong to severe thunderstorms will be possible Monday evening into Tuesday afternoon. All modes of severe weather will be possible including flash flooding. - Additional rounds of thunderstorms will be possible beginning Thursday night. Timing and potential for severe weather is unclear at this time. && .DISCUSSION... Issued at 1258 PM CDT Sun May 19 2024 Today and Tonight... Widespread cloud cover and light rain will continue to shrink and move east through the rest of the afternoon. There is already clearing for much of the area west of US-77. To the south in Kansas, less cloud cover has helped to destabilize the atmosphere, yielding MLCAPE up to 3000 J/kg across portions of southwest Kansas. Between our area and the more unstable airmass to the south, a residual outflow boundary extends across north- central Kansas before turning north into western Nebraska. The general consensus amongst short term guidance is to lift this boundary north into southern Nebraska by 5 PM this evening, and to continue lifting it north through the early overnight hours. The severe risk today will almost exclusively be south of this boundary. An area of thunderstorms that has persisted in south- central Nebraska is expected to track through east-central Nebraska this evening. These storms will pose a low end wind and hail threat. Being north of the aforementioned boundary, the tornado threat with these storms will be near zero. There is potential for the main complex of storms in Kansas to build north into southeast Nebraska later this evening. The threat in this area is more uncertain, as CAMs are still in disagreement with how to develop these storms as they move east. Nonetheless, if the north side of this complex can build north into southeast Nebraska, it will pose a risk for all modes of severe weather. The highest threat should these storms build north would likely remain south of Highway 2, though stronger storms will be possible as far north as I-80. All storms should dissipate and/or move east of the region by midnight. Tomorrow through Tuesday Night... With the approach of the primary upper-level disturbance from out west, surface cyclogenesis is expected in northwest Oklahoma/southwest Kansas tomorrow afternoon. Arcing northeast out of the developing surface low will be a warm front. This should extend somewhere across eastern Nebraska and western Iowa by tomorrow afternoon. Moisture return at the surface is more confident for tomorrow afternoon across eastern Nebraska and southwest Iowa, with dewpoints well into the 60s. A capping inversion is expected to be in place across the warm sector, though SREF and GFS signal the cap might weaken substantially by 7 PM tomorrow evening. General consensus amongst short term guidance is to develop a few isolated strong to severe thunderstorms by the early overnight hours tomorrow night, with coverage and intensity increasing as the main upper-level disturbance ejects out into the central Plains. With the development of a low-level jet expected, bulk shear increasing to somewhere between 40 and 50 knots, and CAPE ranging from 1500 to 2500 J/kg, all modes of severe weather will be possible. Though it is unclear whether the severe potential lasts through the entire night tomorrow night, showers and thunderstorms are expected to be ongoing into Tuesday morning. By Tuesday morning, the surface low is expected to be somewhere in the vicinity of south-central Nebraska, tracking quickly to the northeast over the course of the day. A cold front will extend to the southwest from the low-pressure. The airmass ahead of this front is expected to destabilize quickly, with surface based CAPE likely exceeding 2000 J/kg by noon. HREF suggests the 0-1km SRH will range somewhere between 100 and 200 m2/s2 Tuesday morning. With a jet streak rotating up the downwind side of the trough, bulk shear values will be on the order of 50 to 60+ knots. This setup favors early convection to develop along the cold front by late morning, with strengthening into the afternoon hours. Once storms become severe, all modes of severe weather will be possible. This front should be fairly progressive, with most model solutions having the front east of our area into central Iowa and Missouri by 5 PM. Wednesday through Saturday Night... A high pressure system is expected to build into the central Plains on Wednesday, bringing a beautiful day across the region with highs in the low 70s, dewpoints in the 40s and mostly clear skies. Beginning Thursday night, a series of shortwaves coinciding with moisture return from the south will bring several chances for showers and thunderstorms. Timing and strength of these disturbances and the amount of moisture return at the surface is too uncertain at this time to discuss exact timing and potential for any stronger convection. && .AVIATION /06Z TAFS THROUGH 06Z TUESDAY/... Issued at 1141 PM CDT Sun May 19 2024 Considerable uncertainty exists this forecast period, specifically in regard to the timing of shower and thunderstorm development at the terminal locations. Several runs of the HRRR have indicated the development of showers and thunderstorms in the vicinity of KLNK and KOMA in the 14-17z timeframe. However, other model solutions do not indicate that scenario. As such, no precipitation be included in the forecast at that time. About that same time, there is some model signal for periods of MVFR ceilings at the terminal locations. While VFR conditions will be maintained, observational trends will have to be monitored. Finally, it does appear that thunderstorms will become increasingly likely after 20/00z, and subsequent forecasts will likely include that potential once details become more clear. && .OAX WATCHES/WARNINGS/ADVISORIES... NE...None. IA...None. && $$ DISCUSSION...Darrah AVIATION...Mead