Area Forecast Discussion
Issued by NWS Omaha/Valley, NE

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000 FXUS63 KOAX 232050 AFDOAX Area Forecast Discussion National Weather Service Omaha/Valley NE 350 PM CDT SAT JUL 23 2016 .SHORT TERM...
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(tonight through Tuesday) Issued at 350 PM CDT Sat Jul 23 2016 12z Upper-air analysis and early afternoon water vapor imagery revealed a polar-branch short-wave trough from Saskatchewan into the northern High Plains with downstream ridging present from Manitoba into Ontario. Meanwhile, a lower-latitude perturbation, embedded within a sub-tropical moisture plume was progressing from the mid Missouri Valley into upper Midwest. Expect the former impulse to track across the Canadian Prairie Provinces late today and tonight, effectively flattening the antecedent mid-level ridge over the north-central states. Meanwhile, an associated cold front stretching from the central Dakotas through north-central into southwest Nebraska as of 20z will advance southeast through much of the mid Missouri Valley tonight, with this feature eventually clearing our southeast Nebraska and southwest Iowa counties Sunday morning. Persistent mid and high-level cloudiness has stunted daytime heating, especially across our southern CWA today with 20z temperatures commonly in the upper 80s to lower 90s. However, given heat indicescurrently hovering around advisory criteria at many locations, we will maintain the going excessive heat warning until 7 PM. Otherwise, consensus of latest model guidance is suggestive that the strongest large-scale forcing for ascent and associated pre- frontal thunderstorm development will remain to our northeast tonight. However, recent visible satellite imagery shows a growing ACCAS field ahead of the front from north of YKN to near ONL to BBW. As such, we will maintain slight chance POPs along the front tonight. Mid and high-level clouds will increase across the area Sunday in advance of a short-wave trough amplifying from the upper Mississippi Valley into central South Dakota. Weak vorticity advection and some frontogenetical forcing may be sufficient to promote a few mid-level showers and storms across our far northern counties Sunday afternoon. Meanwhile, in the south, weak warm advection atop a shallow frontal surface will maintain a chance for isolated showers and thunderstorms there as well. The increased clouds and slightly cooler, post-frontal air mass should yield highs largely in the mid 80s. A surface high will develop southeast through the mid Missouri Valley Sunday night with the subsequent deepening of a lee trough over the northern High Plains on Monday. Aloft, mid-level heights will build over the northern Plains during that time frame, ahead of low-amplitude disturbance which will emerge into the northern High Plains Monday afternoon. Warm advection will strengthen over southeast Nebraska Sunday night in conjunction with the nocturnal LLJ, where we have maintained the going slight chance to chance POPs. Conditions will generally be dry Monday with highs in the mid to upper 80s. The aforementioned short-wave trough moving into the northern High Plains Monday afternoon will be the first in a series of disturbances tracking east-southeast through the Dakotas and mid Missouri Valley Monday night through the middle part of this upcoming week. This pattern will favor multiple rounds thunderstorms over the region with a risk for flooding rains and possible severe weather, namely in the Tuesday night to Wednesday night time frame. .LONG TERM...(Tuesday night through Saturday) Issued at 350 PM CDT Sat Jul 23 2016 As mentioned above, the polar-branch of westerlies will become increasingly active around midweek as the prevailing flow transitions to northwest over the north-central CONUS. By the end of next week into early next weekend, the 12z deterministic runs of the ECMWF and GFS indicate pronounced ridging over western North America with a broad downstream trough near or east of the Mississippi Valley. This large-scale pattern configuration will continue to support a chance of thunderstorms with temperatures near or slightly below seasonal normals.
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&& .AVIATION...(For the 18Z TAFS through 18Z Sunday afternoon) Issued at 1218 PM CDT Sat Jul 23 2016 VFR conditions are expected through the TAF cycle, with scattered to broken ceilings largely at or above 15kft. Winds will change from south to southwest today to northwest tonight and Sunday, with speeds remaining below 10kt. Isolated showers and even more isolated thunderstorms are moving away and should stay out of the TAF sites this afternoon, with potential too low yet to mention tonight. && .OAX Watches/Warnings/Advisories...
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NE...Excessive Heat Warning until 7 PM CDT this evening for NEZ012- 015-018-033-034-044-045-052-053-067-068-091-093. IA...Excessive Heat Warning until 7 PM CDT this evening for IAZ043- 055-056-069-079-080-090-091.
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&& $$ SHORT TERM...Mead LONG TERM...Mead AVIATION...Mayes is the U.S. government's official web portal to all federal, state and local government web resources and services.