Area Forecast Discussion
Issued by NWS Omaha/Valley, NE

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000 FXUS63 KOAX 192035 AFDOAX Area Forecast Discussion National Weather Service Omaha/Valley NE 335 PM CDT Sat Aug 19 2017 .SHORT TERM...(Tonight through Tuesday) Issued at 335 PM CDT Sat Aug 19 2017 The main forecast concerns are thunderstorm chances from tonight into Tuesday, and sky cover for Monday. Upper air charts from 12Z had the following main features of interest. 300 mb winds were strongest around the mid/upper level trough over the Great Lakes and Ohio Valley. At 500 mb, 12 hour height falls of 30-50 meters extended from southwest Canada down to northern California. Thermal ridge at 700 mb was over the Rockies with the +10 C isotherm extending from southwest South Dakota into central Kansas. Water vapor imagery early this afternoon showed a weak shortwave trough moving through the central Plains with stronger pieces of energy from Montana back into the Pacific Northwest. Some monsoonal moisture was in a couple of bands over the southwest United States, with one band of interest curving from the Gulf of California toward southern Colorado. Altocumulus type clouds were moving east into parts of eastern Nebraska as of mid afternoon, but no precipitation was occurring. Convection allowing models (CAMs) suggest that storm chances will increase this evening from west to east. Main area of focus for severe potential will be mostly to our west but may spread into parts of eastern (mainly southeast) Nebraska by midnight. The low level instability axis will be to our west into early evening, but may increase to over 2000 J/kg in parts of southeast Nebraska 06Z-12Z. Main hazards through sunrise Sunday would be hail and gusty winds. Some storms may linger into Sunday morning, with at least small chances into the afternoon. Better focus may be along and north of a northward lifting warm front, Sunday evening into Sunday night. Model guidances varies with respect to where best chances will be but proximity of front and low level jet suggest the southwest half of Iowa. --Eclipse Outlook-- Monday, well things are not going to be clear but probably won`t be completely cloudy either (although the cloud trends are looking a bit higher than the past few days). We will also have a small chance of thunderstorms (mainly north of a line from Albion to Red Oak) for the eclipse window (about 1130 am to 230 pm). A warm front should stretch from west to east through the area. Generally you would expect a trend of clearer conditions south of the front, but no so in this case. The low clouds (if there are any) may clear, but models continue to show mid and high level moisture, at least immediately to the south at 18Z. For now, will hold sky cover percentages for eclipse time mainly from 45 to 65 percent. Models suggest that surface low pressure may track/develop quickly into central Iowa by mid evening Monday, allowing a front to push south toward Interstate 80. There should be heavy rain potential for the area, especially along and north of that boundary, which will be sinking south into Missouri and Kansas by Tuesday morning. Some showers could linger into Tuesday morning but overall trend should be for decreasing precipitation chances as a ridge of high pressure at the surface build over the area Tuesday. .LONG TERM...(Tuesday night through Saturday) Issued at 335 PM CDT Sat Aug 19 2017 Most of this period looks drier, and have POPs 14 or less from Tuesday night into Friday. Thunderstorm chances return by Friday night and continue Saturday. Lows in the 50s Tuesday night should slowly moderate to lower 60s by Friday night. Highs are expected to be mainly upper 70s and lower 80s. && .AVIATION...(For the 18Z TAFS through 18Z Sunday afternoon) Issued at 117 PM CDT Sat Aug 19 2017 VFR conditions are forecast at KOFK, KOMA, and KLNK during the forecast period. Convection chances will increase after 00Z tonight over eastern Nebraska as low level jet increases over the area.. VCTS has been added to KOFK after 03Z, KLNK after 05Z and KOMA aft 06Z. && .OAX WATCHES/WARNINGS/ADVISORIES... NE...None. IA...None. && $$ SHORT TERM...Miller LONG TERM...Miller AVIATION...Smith

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