Area Forecast Discussion
Issued by NWS Omaha/Valley, NE

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000 FXUS63 KOAX 201658 AFDOAX Area Forecast Discussion National Weather Service Omaha/Valley NE 1158 AM CDT TUE SEP 20 2016 .SHORT TERM...(today through Thursday) Issued at 317 AM CDT TUE SEP 20 2016 Warm temperatures the next couple of days with a return to thunderstorm chances Wednesday afternoon into Thursday are the primary concerns of this forecast. Surface high pressure was settling into eastern Nebraska and western Iowa this morning, behind cold front that had slipped south into northern Kansas and northern Missouri. Strong westerlies aloft across the northern tier of states was inducing lowering pressures in the Northern High Plains, promoting southerly return flow across the Plains this morning. As such, cold front is forecast to surge/bridge north of our CWA early in the day with gusty south winds and rapid increase in low level moisture in its wake. Lower 70s dew points noted in eastern Kansas and western Missouri are scheduled to spread across most of our area this afternoon, contributing to surface-based CAPE values over 2500 j/kg along the Missouri River and east. However building heights leading to pronounced inhibition and lack of mid level forcing suggests no convection expected here. High temperatures between 85 and 90 should be common this afternoon, with heat indices in the middle 90s in many areas. Southerly flow and dew points remaining in the mid to upper 60s tonight will keep lows from falling very far into the 60s, and will likely hold in the lower 70s over the southern half of the CWA. Things become a little more interesting later Wednesday afternoon and night as shallow mid level ridging breaks down somewhat with approach of shortwave from the southwest. GFS and ECMWF have been consistent in showing this feature while NAM maintains a Wednesday night arrival. Our forecast is and has been more in-line with GFS solution over the last several days, and run-to-run consistency of that model inspires maintaining the status quo. Thus, expect a gradual weakening of inhibition through the day as mid level temperatures cool with approach of shortwave. Lowering heights should also promote a gentle southward drift of surface front into northeast Nebraska by the afternoon. Mid to upper 60s dew points will remain available to contribute to over 2000 j/kg of SBCAPE near and south of the front with bulk shear increasing to near 30kt. So expect scattered convection to become more likely as we head toward late afternoon, allowing time for cap to erode. There is some severe potential given instability, but only modest shear suggests maintaining threat will be difficult. Uptick in shear with increasing low level jet during the evening will be offset by loss of heating/instability, but certainly will see continued storm development overnight before shortwave exits our area Thursday morning. Overnight and morning convection will play havoc with surface boundaries, but best bet is cold front will begin lifting back north again Thursday afternoon as heights rise in wake of shortwave and ahead of larger upper trough drifting into the Rockies. Could see some redevelopment Thursday afternoon, but chances are much more conditional. .LONG TERM...(Thursday night through Monday) Issued at 317 AM CDT TUE SEP 20 2016 Evolution of western low/trough into the weekend and the affects on our weather remains the primary longer term forecast highlight. GFS and ECMWF again have been fairly consistent in regards to sensible weather for our part of the world this weekend, while progression of at least part of western trough/low has shown some inconsistency. This morning, there is some consensus that a significant chunk of mid level energy will be ejected into the Northern Plains on Sunday, with our area on the back side of system by Sunday evening into Monday. Ahead of the trough, lingering convection Thursday night will likely be shut off by mid level warming under rising heights in sharpening ridge axis on Friday. Moisture plume and instability axis will gradually push east as wave lifts into the Northern Plains, and is currently scheduled to arrive in eastern Nebraska and western Iowa on Saturday before shifting east by Sunday night. We will see continued chances for showers and thunderstorms under this plume, but severe risk should be low given saturated atmosphere and lack of significant instability. However heavy rain is possible given slow eastward progression of moisture, potential training of storms, and precipitable water values rising into the 175-200 percent of normal range. && .AVIATION...
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(18Z TAFS for KOFK...KLNK and KOMA.) Issued at 1156 AM CDT TUE SEP 20 2016 Winds will again be the primary issue at all TAF sites. South southeasterly winds at 12-20 knots initially, with gusts diminishing by 23-00z. Non convective LLWS develops by 21/04-06z with winds around 2000 from 35 to 45 knots, which ends by 21/15-16z.
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&& .OAX Watches/Warnings/Advisories... NE...None. IA...None. && $$ SHORT TERM...Dergan LONG TERM...Dergan AVIATION...DeWald

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