Area Forecast Discussion
Issued by NWS Omaha/Valley, NE

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946 FXUS63 KOAX 152338 AFDOAX Area Forecast Discussion National Weather Service Omaha/Valley NE 638 PM CDT Tue Aug 15 2017 .SHORT TERM...(Tonight through Friday) Issued at 323 PM CDT Tue Aug 15 2017 Showers and storms are affecting northeast NE, while the rest of the area waits its turn. Subjective 12Z upper-air analysis indicates continued rather weak upper-level flow and features, with a ridge axis from IA through MN, upper-level low centered in northern ON, and weaker upper-level low over AB, with trough axis extending through MT/ID/NV/CA. 850mb flow and features also were weak and poorly defined, especially in the central US, but a pool of 12-16C+ dewpoints was in place from NE/southwest IA southward. Surface low at 19Z was centered in eastern CO, with something like a warm front extending from southwest to east central NE/northwest IA, as well as an inverted trough extending through western SD into western ND. Main forecast concerns are convective/rain potential tonight and Wednesday, then after a short respite, active pattern beginning again on Friday. For the rest of today and this evening, the band of thunderstorms across northeast NE will continue to lift northeastward. The band may generate some locally heavy rainfall as it goes across, with some backbuilding into central NE prolonging the event. The area is quite dry and sandy, with full summer vegetation, and should be able to take a lot of rainfall before flooding becomes a widespread or long-lasting concern. That said, some local street flooding (especially in towns) and rises on small streams are possible with this heavy rain, especially during or just after the rain falls. Environment is supportive of at least some hail threat, as well, with a smaller risk of gusty winds. Convection should lift out of the area this evening, with a lull becoming more likely this evening into tonight before showers/storms return. Models have trended much slower with bringing the next round of precipitation into the area, with the eastern CWA possibly not seeing showers/storms until sometime Wednesday afternoon. Northeast NE and southeast NE are the two areas that are more likely to see a return of showers/storms earlier, with the main boundary lingering near southeast NE and a warm sector wing of precipitation more closely tied to the surface low crossing KS. Have toned down POPs this evening and tonight, especially in the east. Potential for rain still exists on Wednesday, though instability and thus strong/severe thunderstorm risk will be lower. Showers/storms could fester for much of the day across the area. That said, without the punch of instability aiding convection, the very heavy rainfall amoutns may be limited, and perhaps the total rainfall will be a gentler 0.5-1" in many locations. Rain finally should exit the area by Thursday afternoon/evening, leaving a break in weather as surface to mid-level high pressure slides across the central US, with moderating temperatures continuing into Friday. Chances of showers/storms will return, though, as a shortwave slides through the upper Midwest and encounters rich moisture in the central Plains. .LONG TERM...(Friday night through Tuesday) Issued at 323 PM CDT Tue Aug 15 2017 Active pattern will continue through the period, as a series of fairly weak and transient upper-level troughs brings the potential for showers/storms on just about every day. Timing and location of any one precipitation event will be challenging, given the low- confidence, fast-moving upper-level pattern, but we can at least say with confidence that the period is unlikely to be dry and sunny across the area. Temperatures should remain a few degrees on either side of normal (which is mid 80s at this time of August), with daily temperatures probably depending pretty strongly on effects of convective cloud debris or lingering showers. ECLIPSE DAY FORECAST (MONDAY)... With a generally active pattern in place, the potential remains for showers/storms to impact the eclipse path. Right now, it still looks like the better chances are for overnight convection to move across eastern Nebraska on Sunday night, heading into Iowa on Monday morning. There is still uncertainty with the timing amd location of that round of convection, of course, as well as with how long clouds would linger in its wake. Have again shaved a couple of degrees off of model guidance and included temperatures dipping downward in the couple of hours on either side of the eclipse peak, consistent with research on the effect of an eclipse. The amount of temperature dip in our forecast remains on the conservative side based on the potential for clouds and general uncertainty of hourly temperatures 6 days from now. If the day is sunny, the amount of dip (and lowering of temperatures away from guidance) would be several degrees more. Also, based on research, have dropped about 2kt from winds near the peak of the eclipse. && .AVIATION...
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(For the 00Z TAFS through 00Z Wednesday evening) Issued at 628 PM CDT Tue Aug 15 2017 Active weather during this TAF cycle with scattered thunderstorms possible across the sites through the period. This will create variable conditions with overall VFR with TEMPO MVFR likely.
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&& .OAX WATCHES/WARNINGS/ADVISORIES... NE...Flash Flood Watch through Wednesday morning for NEZ011-012- 016>018-030>032. IA...None. && $$ SHORT TERM...Mayes LONG TERM...Mayes AVIATION...Kern

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