Area Forecast Discussion
Issued by NWS Omaha/Valley, NE
Issued by NWS Omaha/Valley, NE
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384 FXUS63 KOAX 250241 AFDOAX Area Forecast Discussion National Weather Service Omaha/Valley NE 941 PM CDT Mon Jun 24 2024 .KEY MESSAGES... - Flooding is expected to continue along the Missouri River this week. See the Hydrology section for more details. - Hot temperatures are expected to continue tomorrow, with a heat advisory in effect for heat indices as high as 105 degrees. - A stray thunderstorm or two will be possible (~20 percent chance) later this evening. Scattered strong to severe thunderstorms will be possible (40-60 percent chance) tomorrow afternoon and tomorrow night. - Scattered thunderstorms will return to the region Thursday night into Friday. Some locations may see up to an inch of additional rain heading into next weekend. A few storms may be strong to severe. && .UPDATE... Issued at 940 PM CDT Mon Jun 24 2024 Made some adjustments to the Pops overnight. We have failed to see any development along the stalled frontal bounary in northeast NE through the eveing. And CAMs now suggest that even the activity in northeast NE and south central NE will probably fizzle before it gets here. Bottom line, I still kept a 20% chance of a thundershower north of I80, but that`s also an 80% chance that something doesn`t happen. Hydro Concerns We did extend the flood warning in Butler county through Tuesday morning as Clear Creek remains elevated. On the Missouri River, we are likely seeing the crest at Sioux City now, and the flood wave will continue to work downstream over the next several days. Of note, there is an ongoing national hydrologic data outage on our NWPS website that technicians continue to troubleshoot. Observed stage data may be old, but the forecast is current and just updated within the last hour. Any USGS gauge is still posting data on their waterdata.usgs.gov website. && .DISCUSSION... Issued at 233 PM CDT Mon Jun 24 2024 This Afternoon and Tonight... Temperatures in the mid to upper 90s are widespread across eastern Nebraska and southwestern Iowa. Some locations along the I-80 corridor have hit 100 degrees today, or will do so the next couple of hours. With dew points well into the 70s, heat indices have been on the order of 105 to 115 degrees. Further to the northwest, a weak cold front will slowly push its way south and east across our area into the overnight hours. Isolated showers are expected to develop along this front, particularly near and north of US Highway 20. Due to very warm temperatures aloft, the chances of thunderstorm development along this front are much lower, on the order of 15 to 20 percent. Nonetheless, surface temperatures are expected to be within a few degrees of the convective temperature, keeping a couple thunderstorms later this evening, likely after 5PM, within the realm of possibility. If thunderstorms are able to develop, they will pose a risk for strong gusty winds and small hail. The greatest chance for a thunderstorm or two will be north of US Highway 30, but can`t be rules out as far south as the I-80 corridor. Tomorrow and Wednesday... To our northwest, a weakening surface low pressure will slowly move southeast into the central Plains, likely tracking through western and southern Nebraska tomorrow afternoon. East of this surface low, a quasi-stationary surface boundary is expected to drape across east-central Nebraska into western Iowa. Surface moisture is expected to pool along this boundary, resulting in an instability axis paralleling the front. Surface dewpoints as high as the mid 70s will yield MLCAPE potentially exceeding 4000 J/kg. Aloft, a subtle shortwave is expected to eject out into the central/northern High Plains by midday. As such, thunderstorm development is expected near and northeast of the intersection of the surface front and the low-pressure center. Thunderstorms that are able to develop should quickly strengthen as they ride the instability axis to the east-southeast through eastern Nebraska and into western Iowa. Bulk shear potentially in excess of 40 knots and storm motions paralleling the boundary will favor bowing segments capable of damaging straight line winds, large hail, and a brief spin up tornado. CAMs show an erosion of the capping inversion sometime between 5 and 7 PM, however warm temperatures in the mid-levels still yield some uncertainty as to whether updrafts will be able to persist and strengthen through the evening hours. There is also some uncertainty with regards to how far north this surface boundary will set up. Nonetheless, even if early storm development is sparse in nature, upscale growth and increased coverage of convection is expected heading into tomorrow night, with storms likely moving east and south of the region by 1 AM. Hot and humid conditions south of the surface front will bring heat indices of 100 to 105 in the afternoon. As such, a heat advisory has been issued, primarily for locations south of I-80. Warm and mild weather returns to the region on Wednesday, with afternoon highs in the upper 80s, approaching 90 across the region and clear skies. Wednesday night, there will be the potential (30 to 40 percent chance) for decaying storms out west to make it into portions of eastern Nebraska. The greatest chances for rain will be north of US Highway 30 and west of Us Highway 77. The timing for these storms would be after midnight. Thursday Through Sunday... By Thursday, the next upper-level disturbance is expected to approach our region from the west. A trough over the northern Rockies on Thursday should eject out into the northern Plains by Friday. Height falls overspreading the Great Plains in advance of this disturbance will provide enough lift for widely scattered showers and thunderstorms (30 to 50 percent chance of rain) to develop across the region. Moisture return from the south will allow PWATs to potential reach 2 inches. This in conjunction with tall and skinny instability profiles will allow any convection that can develop across our area Thursday afternoon into Thursday night to be efficient rain producers. Some locations Thursday may see over half an inch of rain. Some thunderstorms may be on the stronger side, however with the strongest forcing for ascent lagging further west and the surface cold front still in the northern Plains, severe potential appears low at this time. On Friday, the main piece of upper-level energy will approach and move over our area. At the surface, a cold front will push south and east across the region during the afternoon hours. Ahead of this front, moderate stabilization of the airmass is expected, with SBCAPE on the order of 2000 to 3000 J/kg. Bulk shear is also expected to increase throughout the day on Friday, with shear magnitudes as great as 50 knots possible. Scattered thunderstorms are expected to develop along this boundary and persist into the overnight hours. Uncertainties in the exact timing of the upper-level disturbance, timing of the surface front, storm motions, the strength of the capping inversion, etc. preclude any further or more detailed discussion on exact timing and threats associated with these storms. However stronger storms appear possible, with a severe thunderstorm or two not out of the question. After Friday, and through the rest of the forecast period, ridging is expected over the central CONUS, bringing several days of dry weather across our region. Afternoon highs next weekend will likely range from the mid 70s to the low 80s before we begin to warm back into the upper 80s/lower 90s by next week. && .AVIATION /00Z TAFS THROUGH 00Z TUESDAY/... Issued at 606 PM CDT Mon Jun 24 2024 VFR conditions through the period. Winds at TAF issuance at KOMA/KLNK will be from the south southwest at 14-16 knots with gusts up to 22 to 24 knots. We lose the gusts by 01z, wind surface wind speeds around 12 knots. There does appear to be some LLWS at KOMA 04-10z with winds at 1500` from around 210 degrees at 40 knots. There is a 20-30% chance of thunderstorms through the night at various times, but confidence is too low to mention in the forecast at this time, and will update the TAFs if convection will impact the TAF locations. && .OAX WATCHES/WARNINGS/ADVISORIES... NE...Heat Advisory from 1 PM to 7 PM CDT Tuesday for NEZ051>053- 066>068-088>093. IA...Heat Advisory from 1 PM to 7 PM CDT Tuesday for IAZ069-079-080- 090-091. && $$ UPDATE...DeWald DISCUSSION...Darrah AVIATION...DeWald