Area Forecast Discussion
Issued by NWS Omaha/Valley, NE
Issued by NWS Omaha/Valley, NE
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462 FXUS63 KOAX 162338 AFDOAX Area Forecast Discussion National Weather Service Omaha/Valley NE 638 PM CDT Mon Sep 16 2024 .KEY MESSAGES... - Periodic shower and storm chances through the weekend, typically peaking at night. Highest chances are currently Tuesday night into Wednesday and Friday night into Saturday night (peak probabilities of 40-70%). - Temperatures are expected to remain above-normal through the work week with highs in the 80s. - Cooler weather favored this weekend into next week with highs in the 70s. && .DISCUSSION... Issued at 322 PM CDT Mon Sep 16 2024 Tonight and Tuesday: Early afternoon water vapor imagery shows a prominent mid/upper-level low centered over CA/NV with a minor short-wave trough situated over CO. The CO disturbance will track northeast into SD and NE tonight, while a nocturnal low-level jet (LLJ) develops from western KS into northeast NE, eastern SD, and western MN. Similar to last night, those two features will contribute to the development of widely scattered showers and thunderstorms across portions of eastern NE, perhaps into western IA late tonight through much of Tuesday morning. The models differ on the timing and specific location of the showers and storms, so the maximum PoP values will be limited to 30-40%. The strongest storms will be capable of brief periods of heavy rain with localized amounts of 0.25-0.5" possible. Considerable morning cloudiness will diminish by afternoon with highs in the mid to upper 80s. Readings may end up cooler in areas where precipitation and/or clouds linger a bit longer. We`ll see stronger south winds tomorrow with sustained speeds of 15 to 25 mph with gusts up to 30 to 35 mph, especially in northeast NE. Tuesday night into Wednesday night: The above-mentioned CA/NV low is forecast to progress northeast, deepening over the northern Rockies into northern High Plains. Meanwhile, an associated short-wave trough is expected to pivot through the eastern semi-circle of the parent low with height falls/forcing for ascent overspreading the northern and central Plains into upper MS Valley. That forcing for ascent will combine with a zone of enhanced moisture transport along a 40-50 kt LLJ to foster a complex of showers and thunderstorms which will move into eastern NE late Tuesday night into Wednesday morning (30-60% PoPs). It still looks like the showers and thunderstorms will diminish/dissipate prior to reaching western IA Wednesday afternoon. Similar to previous days, morning convective cloud debris will diminish by afternoon with highs in the mid to upper 80s. Another round of showers and thunderstorms are possible (20-50% PoPs) across much of the area Wednesday night into Thursday morning, again aided by the LLJ. Thursday: The northern High Plains upper low will continue northeast into south-central Canada with an embedded vorticity maximum moving through the base of that system across the northern Plains and upper MS Valley. At the surface, a weak front attending the mid- level system will advance southeast into the area during the afternoon and evening. The potential for early-day showers and storms (see previous section) leads to some uncertainty on how unstable the air mass will become ahead of the front by afternoon. However, some of the models suggest the development of moderate amounts of instability and vertical shear during the afternoon/early evening. Should that scenario unfold, some severe-weather threat would exist if storms are able to redevelop along the front at that time. The forecast will call for hot temperatures ahead of the front with highs in the low 90s. Friday through the weekend: Another mid-level trough/low will slowly track from the Desert Southwest into the central and southern Rockies by Saturday, and eventually into the Great Plains Sunday. In the low levels, a surface front initially stalled to the south of the area Friday morning is projected to lift north into the mid MO Valley before eventually moving back south as a cold front. The overall synoptic setup will be supportive of a potentially more widespread, heavier rainfall event, especially from Friday night into Saturday night. Any severe-weather threat will largely be dictated by the location of the primary synoptic boundary; along and south of which the most unstable air will reside. The forecast will indicate highs in the 80s to low 90s on Friday with 70s on Saturday and Sunday. Similar to the severe-weather potential, those numbers will ultimately be dependent on the surface front location. && .AVIATION /00Z TAFS THROUGH 00Z WEDNESDAY/... Issued at 638 PM CDT Mon Sep 16 2024 Mid-level clouds linger early this evening, remnants of convection earlier in the day. Radar network is detecting isolated showers, but none are impacting TAF sites. An upper level disturbance moving into the plains from the southern Rockies will combine with a LLJ 35-40kts to produce overnight scattered thunderstorms across central NE and southern SD. Current CAM indicate storms will move into the forecast area around midnight and progress slowly eastward. Coverage of storms is in question, as CAM output indicate a spread of solutions on exactly where storms will be. Nonetheless, current indications are for 25-40% coverage. Introduced Prob30 group into all three TAF between 17/11-17/14z, then a prevailing group of P6SM -SHRA. Left ceilings in VFR category per both NBM and HREF, with ceilings dropping into the FL050-080 range when showers are more persistent. Band/area of showers will move east of the TAF sites between 17/17-17/19z. && .OAX WATCHES/WARNINGS/ADVISORIES... NE...None. IA...None. && $$ DISCUSSION...Mead AVIATION...Fortin