Area Forecast Discussion
Issued by NWS Omaha/Valley, NE

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000 FXUS63 KOAX 182327 AFDOAX Area Forecast Discussion National Weather Service Omaha/Valley NE 627 PM CDT Mon Sep 18 2017 .SHORT TERM...(Tonight through Thursday) Issued at 304 PM CDT Mon Sep 18 2017 Showers are exiting the area this afternoon. Subjective 12Z upper- air analysis indicates west-northwesterly upper-level flow across the central US, with a few weak ripples through the flow and with ridging in the eastern US. Mid-level warm and moist air advection had brought dewpoints of 12C+ into eastern NE/southwest IA, with southwesterly winds and continuing warm air advection. Surface high at 19Z was centered in southern MO, with a surface low in central MT and a relatively weak pressure gradient between the two. Main forecast concerns through Thursday include a chance of storms on Tuesday evening/night. Showers and clouds will continue to exit the area this evening and tonight. Given recent rain and relatively rich low-level moisture, along with decreasing winds and clearing skies, would not be surprised by at least patchy fog anywhere in the area, with dense fog not out of the question. For now, have included patchy fog mention in the few hours on either side of daybreak. Temperatures will warm up in earnest tomorrow under good mixing conditions. As a shortwave trough slides across the Dakotas on Tuesday afternoon/evening, bringing a cold front with it, showers/storms are likely to develop in SD in the afternoon/evening. Wind shear is quite strong, given backed low-level winds and very looping low-level hodographs, along with abundant shear at 0-3km and effective bulk layers. However, capping inversion will limit southward extent of convective development, with most likely southward extent just reaching northeast NE into northwest IA. Should storms reach into the area, they will carry the risk of severe weather, including gusty winds, hail, and perhaps even a tornado. Front will progress through the area on Tuesday night, bringing cooler temperatures on Wednesday, as well as the risk of showers/storms redeveloping on the front on Wednesday afternoon and evening, mainly in southwest Iowa. Quick temperature recovery to readings well above normal is expected on Thursday as return flow again brings much warmer mid-level temperatures, with southerly winds providing good mixing. .LONG TERM...(Thursday night through Monday) Issued at 304 PM CDT Mon Sep 18 2017 As an upper-level low digs into the western US - there to stay for the rest of the forecast period - prolonged moderate to heavy rainfall is possible this weekend. Warm air advection and good pre- frontal mixing will continue on Friday, and the area should remain ahead of the surface trough and associated precipitation at least through Friday night. Do have some POPs in northeast NE beginning on Friday afternoon, but honestly think chances really will hold off until Saturday in northeast NE and possibly Saturday night/Sunday in the rest of the forecast area, as models are trending toward the slower ECMWF solution in this stagnant pattern. Once precipitation does arrive, it is not likely to progress out until at least Monday and potentially beyond. Strong frontogenetical forcing and unstable (convectively and conditionally) airmass should foster efficient rainfall production. Combined with slow progression of heavier rain areas, the potential for heavy rainfall and perhaps some areas of flooding is possible if the scenario does materialize. && .AVIATION...(For the 00Z TAFS through 00Z Tuesday evening) Issued at 626 PM CDT Mon Sep 18 2017 Variable conditions expected overnight as areas of fog likely develop and bring potential LIFR conditions into the TAFs. Otherwise, mostly VFR conditions are expected with increasing and gusty southerly surface winds Tuesday afternoon. && .OAX WATCHES/WARNINGS/ADVISORIES... NE...None. IA...None. && $$ SHORT TERM...Mayes LONG TERM...Mayes AVIATION...Kern

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