Area Forecast Discussion
Issued by NWS Omaha/Valley, NE

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000 FXUS63 KOAX 211723 AFDOAX Area Forecast Discussion National Weather Service Omaha/Valley NE 1223 PM CDT Sun May 21 2017 .SHORT TERM...(Today through Tuesday) Issued at 335 AM CDT Sun May 21 2017 Finally a dry day with decreasing clouds today, but thunderstorm chances return for Monday. Upper low that caused our widespread and continued rains the last several days was drifting northeast into Minnesota this morning. Northwest flow at the surface and aloft behind this system will continue to spread low and mid level cloud cover from South Dakota into eastern Nebraska and southwest Iowa early in the day, but a gradual clearing trend from southwest to northeast is expected as low moves farther away. Thus plenty of sunshine is forecast this afternoon, helping to push temperatures back into the 60s most areas. Strong mid level trough rotating south on back side of this system is still slated to arrive over our area Monday afternoon. A weak impulse ahead of that trough is forecast to roll out of the High Plains tonight, and may trigger scattered showers over southeast Nebraska late tonight and Monday morning. Otherwise most of eastern Nebraska and southwest Iowa will wait until Monday afternoon when stronger trough enters the region. Significant cooling aloft will combine with surface temperatures climbing into the 70s to produce moderately steep lapse rates in the afternoon. Moisture will be somewhat limited with surface dew points in the low to mid 50s near and south of I-80 just ahead of expected afternoon cold front position. GFS suggests SBCAPE will top 1000 J/kg with modest bulk shear approaching 40kt. Given cooling aloft, convective temperatures will easily be met, leading to scattered showers and at least isolated thunderstorms all areas in the afternoon. Higher instability and focusing low level boundary in our south may yield more robust storms which could produce hail and gusty winds. We remain in a marginal risk for severe as per SPC`s day 2 outlook. Convection should wane through the evening with loss of daytime heating, but won`t end until after midnight in the southeast when upper trough finally swings southeast. A secondary shortwave trough is forecast to drop into the region again Tuesday afternoon, with associated steepening lapse rates again popping some afternoon showers. Instability and shear forecasts are much lower then, so thunder chance is low. .LONG TERM...(Tuesday night through Saturday) Issued at 335 AM CDT Sun May 21 2017 The longer term will begin relatively benign as upper low from the western Great Lakes sinks southeast into the Ohio Valley region, then swings northeast toward New England by Thursday night. Meanwhile, another upper low progress southeast from the Gulf of Alaska into the Pacific Northwest, then settles into southern Saskatchewan by Thursday. A general rising heights regime in the Plains will lead to warmer temperatures Wednesday through Saturday, with highs back into the 70s or higher. However several mid level impulses rotating around Canadian low are expected to eject through the Rockies and into the Plains beginning Thursday night, leading to several chances for showers and thunderstorms through Saturday. Moisture return appears to be limited ahead of these impulses, so widespread severe seems unlikely at this time. && .AVIATION...
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(For the 18Z TAFS through 18Z Monday afternoon) Issued at 1222 PM CDT Sun May 21 2017 VFR conditions through the period. Northwest winds at 14 knots with gusts up to 22 knots to about 23-24z. Then winds back and southwest through the remainder of the period. There is some mid level moisture approaching the area tonight and Monday. This could trigger spotty showers or sprinkles, but not confident enough to mention at any of the TAF locations.
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&& .OAX WATCHES/WARNINGS/ADVISORIES... NE...None. IA...None. && $$ SHORT TERM...Dergan LONG TERM...Dergan AVIATION...DeWald

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