Area Forecast Discussion
Issued by NWS Omaha/Valley, NE

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000 FXUS63 KOAX 191713 AFDOAX Area Forecast Discussion National Weather Service Omaha/Valley NE 1213 PM CDT MON SEP 19 2016 .UPDATE... Issued at 1023 AM CDT MON SEP 19 2016 A very narrow band of MVFR clouds has developed immediately behind the front, stretching from Columbus to just north of Denison, IA at 1445z, and moving south. Have updated the Sky grids to reflect this. And while this band does show up on KOAX 88D radar as a fine line, the latest HRRR model runs suggest that this band should not generate any precipitation. && .SHORT TERM...(today through Wednesday) Issued at 317 AM CDT MON SEP 19 2016 A continuation of warm temperatures through mid week is one highlight of the forecast. The main concern however is when to reintroduce thunderstorm chances. Main upper flow pattern was characterized by strong westerlies extending from off the Pacific Northwest coast across the Northern Plains this morning. 130kt 300mb jet was noted punching into North Dakota just past midnight. Surface cold front tied to upper low spinning into northern Manitoba was arcing south and southwest through Minnesota and into western Nebraska early this morning. That front will progress east and southeast through eastern Nebraska and southwest Iowa through the day, and settle along the Kansas border into southeast Iowa by this evening. While there will be decent low level moisture return ahead of the front as mid 60s dew points surge into southeast Nebraska and southwest Iowa, layer moisture is paltry. Models are in agreement that best combination of moisture and forcing will lie well east of our area today, so will maintain dry forecast. Wind will turn northerly behind the front today, so we may shave a few degrees off recent highs in our north, but still plenty of sunshine should push highs well into the 80s for most areas. Cold front is forecast to lift back north as a warm front Tuesday as westerlies begin to buckle in the west as trough settles into the Pacific Northwest. Downstream ridging will begin here, sufficiently capping potential convection in eastern Nebraska and southwest Iowa despite Mixed Layer CAPE topping 2000 j/kg in the afternoon. However convection is expected to fire not too far north of our area Tuesday evening/night north of retreating warm front where increasing low level jet enhances forcing in northern Iowa. Given warming mid level temperatures, south winds and plenty of sunshine, expect highs to surge well into the 80s, and likely hitting the lower 90s in the southern half of eastern Nebraska. Southwest mid level flow overspreads the Plains on Wednesday as western trough settles farther south along the coast. Both GFS and ECWMF indicate a significant perturbation in that flow will be entering eastern Nebraska Wednesday afternoon, while NAM portrays this wave farther north. Expect surface frontal boundary to have slipped a little south into eastern Nebraska as southwest upper flow settles south, providing a focus for convection on which to fire as instability increases during afternoon heating under cooling temperatures aloft. Moisture return will not be robust as easterly flow is maintained along the Gulf Coast much of the week. However Pacific moisture plume is advertised at mid and upper levels, and surface dew points in the mid 60s should remain in place. Thus will maintain our current forecast of thunderstorms firing Wednesday afternoon, especially in our north where frontal boundary should lie. Highs again in the 80s are expected. .LONG TERM...(Wednesday night through Sunday) Issued at 317 AM CDT MON SEP 19 2016 A continued unsettled weather pattern will take us right through the weekend as upper low/trough moves through the Rockies and into the Northern Plains by Sunday. Rising heights ahead of system will lift cold front north of our area on Friday, perhaps bringing a break to convective activity for a time before trailing frontal system surges into eastern Nebraska on Saturday. Convection should expand along cold front Wednesday night with upper impulse riding overhead. Convection will likely enhance baroclinicity along front for Thursday and Thursday night, providing focus for storms under increasingly diffluent flow aloft. With rising heights Friday, front should lift into South Dakota leaving our area under sufficient inhibition to limit storm potential much of the afternoon and evening before cold front approaches from the west on Saturday. Timing of all these features will likely change with successive model runs, and finer details outlining severe and heavy rain potential will be dealt with in time. Nonetheless there will be several opportunities for stronger storms and pockets of heavy rain during the longer term period. && .AVIATION...
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(18Z TAFS for KOFK...KLNK and KOMA.) Issued at 1212 PM CDT MON SEP 19 2016 A band of MVFR clouds could affect KOMA/KLNK through about 20-21z. Otherwise, VFR conditions through the period. North to northeasterly winds this afternoon, with a few gusts to 18-22 knots, then light after that, but increasing again by 20/15z.
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&& .OAX Watches/Warnings/Advisories... NE...None. IA...None. && $$ UPDATE...DeWald SHORT TERM...Dergan LONG TERM...Dergan AVIATION...DeWald

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