Area Forecast Discussion
Issued by NWS Omaha/Valley, NE
Issued by NWS Omaha/Valley, NE
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854 FXUS63 KOAX 252027 AFDOAX Area Forecast Discussion National Weather Service Omaha/Valley NE 327 PM CDT Tue Jun 25 2024 .KEY MESSAGES... - Moderate flood stage is ongoing or expected to begin along the Missouri River the next day or two, and lasting through the end of the week. - Heat indices as high as 107 are expected this afternoon across portions of southeast Nebraska and southwest Iowa. - Scattered strong to severe thunderstorms are expected to develop from northeast Nebraska into southwest Iowa. The primary risk will be hail, some of which may be as large as baseballs. Damaging winds and a tornado or two will also be possible. - Another storm system Thursday into Friday will bring several rounds of thunderstorms, some of which may be strong, and heavy rain to the forecast area. && .DISCUSSION... Issued at 213 PM CDT Tue Jun 25 2024 ...This Afternoon and Tonight... This afternoon, high temperatures in the 90s with dew points in the 70s in most locations have resulted in heat indices ranging from 100 to 108. As such, a heat advisory has been issued for portions of southeast Nebraska and southwest Iowa through 7 PM this evening. The primary concern for impactful weather this evening heading into tonight will be the potential for scattered strong to severe thunderstorms to develop from northeast Nebraska into southwest Iowa. At the surface, a frontal zone extends from central Nebraska into southern Iowa. Along and north of this front, moisture pooling at the surface has helped increase dewpoints several degrees, resulting in MLCAPE ranging from 3000 to 4000 J/kg. Aloft, a low-amplitude shortwave is expected to traverse the northern Plains northwest so southeast. As this wave ejects out over the region, bulk shear this evening could be as high as 50 knots in northeast Nebraska, and 30-35 knots as far south as the I-80 corridor. This shear profile in conjunction with extreme destabilization of the boundary layer will result in the potential for scattered strong to severe thunderstorms to develop as early as 5 PM this evening. There is little agreement as to where exactly convection will initiate. General model trends suggest the potential for several areas/rounds of thunderstorms this evening. Wherever storms develop, they are expected to begin supercellular in nature, and grow upscale quickly as they traverse east-southeast along the surface instability axis. Though all modes of severe weather will be possible, large hail appears to be the primary threat, particularly early on during the evening hours. With extreme instability in place, hail up to the size of baseballs will be possible. Storm motions in general parallel the surface boundary/instability axis. As such, fairly quick upscale growth into bowing segments or an MCS is likely, transitioning from a hail threat to more of a damaging wind threat. Convection will last into the overnight hours, with storms exiting the region to the south and east by 2 or 3 AM. With the tendency for thunderstorms to potentially train over the same area, there will also be a risk for flooding. Some locations may see up to an inch of rain, though depending on storm coverage and tracks, could locally be higher. ...Wednesday through Friday... Wednesday is expected to be a pleasant day, with clear skies and afternoon highs in the 80s. Dewpoints in the low to mid 60s will also help keep heat indices much lower than what they have been the last couple of days. By early Thursday morning, troughing is expected over the western CONUS with a low-amplitude short wave ejecting out into the central Plains. This will bring the potential for rain Thursday (30 to 50 percent chance). No severe weather is expected Thursday during the day. Diurnally driven convection over the terrain in the High Plains will initiate another round of storms that will move east across the Plains overnight Thursday night. The timing for these storms would be after midnight, with small hail and gusty winds possible. Scattered showers and thunderstorms may linger through the morning hours on Friday, bringing some uncertainty as to how much destabilization can occur before a cold front sweeps through the region Friday evening. Regardless, strong forcing for ascent as the primary piece of upper level energy moves across the northern Plains and the Midwest and dew points well into the 70s ahead of the surface front will create an environment favorable for strong to potentially severe thunderstorms. Exact timing and hazard details will become more clear as the week progresses. ...Saturday through Monday... Medium range guidance suggests that upper-level pattern heading into this weekend and the beginning of next week will favor additional chances for showers and thunderstorms. Divergence amongst model solutions remains too high to pin down any given day for greatest threat, or if any of these days may see strong to severe thunderstorms. Temperature wise, highs this weekend should be in the 80s, with the region warming back up into the 90s by the end of the forecast period with heat indices across southeast Nebraska and southwest Iowa potentially returning into the 100s. && .AVIATION /18Z TAFS THROUGH 18Z WEDNESDAY/... Issued at 1156 AM CDT Tue Jun 25 2024 A weak surface front is draped across east-central Nebraska into southern Iowa. Areas north of this front (KOFK, KOMA) will see winds prevailing out of the east-southeast. Areas south (KLNK) will see wind prevailing out of the south/southwest. This boundary should remain relatively stationary until thunderstorms develop along it later this evening. After 21Z, scattered strong to severe thunderstorms are expected to develop in northeast Nebraska and move east-southeast across the region. Most likely timing for thunderstorms at KOFK and KOMA have been included in a TEMPO group, with the lower probability but still possible time frame for convection in a -SHRA FM group. There is still substantial uncertainty as to how far south convection will move, so have left precip out of KLNK TAFs for now. Wind gusts up to 60 knots and hail up to the size of baseballs will be possible in the strongest storms (most likely northeast Nebraska into southwest Iowa, KOFK and KOMA). Thunderstorms should move south and east of the forecast area by 06Z. && .OAX WATCHES/WARNINGS/ADVISORIES... NE...Heat Advisory until 7 PM CDT this evening for NEZ045-051>053- 066>068-088>093. IA...Heat Advisory until 7 PM CDT this evening for IAZ055-069-079- 080-090-091. && $$ DISCUSSION...Darrah AVIATION...Darrah