Area Forecast Discussion
Issued by NWS Jackson, KY

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000 FXUS63 KJKL 031003 AFDJKL AREA FORECAST DISCUSSION National Weather Service Jackson KY 503 AM EST Sat Dec 3 2016 .SHORT TERM...
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(Today through Sunday) Issued at 356 AM EST SAT DEC 3 2016 Surface high pressure will continue to overspread the state throughout the day today, passing just to our east by 6Z tonight. Overall this will result in light winds at the surface with llvl stratus clouds continuing to pull into the region from the NE through at least mid day in many locations. Llvl winds will begin to lighten and become more variable as the center of the high passes to our north and then heads east, allowing the llvl clouds to begin breaking up throughout the afternoon. Meanwhile, aloft, a shortwave will begin digging across the northern plains throughout the day, shifting eastward. This shortwave is expected to reach the Mississippi River Valley by Sunday, then move across the Ohio River Valley and points to the north by 0Z Monday. The upper level wind pattern will feature a jet streak across the Ohio River Valley ahead of the shortwave, increasing in strength as the shortwave nears. Mid/upper level winds will be westerly across KY and then SW just to our east. This will effectively pull moisture from the Gulf of Mexico northward and then eastward into the state. As such, this will result in high clouds expected to push northward into the CWA by later this afternoon. Moisture and clouds will continue to build this evening with the nearing mid/upper level wave, however it will have a hard time overcoming the bubble of dry air at the surface with the surface high pressure center still in place just to our east. Latest forecast soundings show moisture finally overcoming the drier air between 6 and 9Z at KSME and KLOZ in our southern CWA, between 6 and 12Z in the mid sections, and a few hours later in the northern CWA. Despite W to SW flow aloft, temperatures in the mid and upper levels will still be on the cooler side as precip moves into the region overnight Saturday, below freezing through much of the column. As such, even as temperatures at the surface may be at or above freezing at precip onset, rain may still mix with snow for the first couple of hours. However, temperatures will quickly warm as we head into the daytime hours, with the surface high continuing eastward and allowing warmer return flow at the surface. All precip will change over to rain during this time, with generally no snow accumulation or impacts expected. Rain is expected to continue through the day Sunday as the mid/upper level shortwave closes in on the region. This will produce generally between 0.10 and 0.20 inches or rain across the CWA, an overall light system but much needed none the less. .LONG TERM...(Sunday night through Friday) Issued at 503 AM EST SAT DEC 3 2016 Challenging extended package this morning. Models are in good agreement for DYS 3-4 but diverge significantly beyond that both with the details of the mid/upper level pattern as well as with sensible weather. Mid/Upper level cut off low moving out of Texas Monday opens up into a wave by Tuesday as it transits the MS/TN/OH valleys. This feature will provide another soaking rain to the area with models spitting out around an inch of rainfall on average, mainly from Monday night through Tuesday. Forecast gets complicated thereafter as a series of disturbances rotate around a low pressure system residing along the Northern Tier and southern Canada. Models appear to have difficulty with the strength and timing of several lobes of energy rounding this parent low. The GFS presents a quicker solution with weaker disturbances. The ECMWF advertises stronger disturbances which dig a bit further south resulting in an overall slower solution and correspondingly stronger surface features. The Canadian generally provides partial support for both solutions. For sensible weather we can expect a seasonably warm start to the extended but cool significantly through the period after Tuesday. Rain will be tapering off Sunday night before redeveloping across the region Monday night into Tuesday. There is very low confidence with respect to precipitation types and amounts beyond that. Depending on your model of choice we could see anything from rain to snow from Wednesday night through Friday. At this time felt the best approach was to stay close to the blend of model solutions and guidance which suggest that a wintry mix of precipitation will be possible through that time frame depending on the time of day/night.
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&& .AVIATION...(For the 06Z TAFS through 06Z Saturday night) ISSUED AT 107 AM EST SAT DEC 3 2016 Models continue to struggle with the llvl stratocu deck moving across the region, bordering the line between MVFR/VFR, as high clouds also override across our SW, including KSME and KLOZ. Latest trends will support these generally MVFR llvl clouds continuing to take over all TAF sites through the overnight. A BKN (or at times SCT) MVFR deck will likely persist through much of the day tomorrow as well. A mid/upper level disturbance will begin to approach the region tomorrow afternoon/evening, starting in the south. Meanwhile high pressure will be in control at the surface. So as llvl clouds begin to clear out (as early as 16Z for KSME and KLOZ), high clouds will begin thickening to OVC. This occurrence will happen a little later, closer to 22Z at KSYM. Expect high clouds to continue to build down throughout the remainder of the night, but should stay within the high cloud vicinity through the TAF period. Overall winds will remain generally light and variable near the surface through the period, with stronger WNW to W flow aloft. However, the directional change and increase in flow will be gradual enough to not cause any wind shear problems throughout the period. && .JKL WATCHES/WARNINGS/ADVISORIES...NONE. && $$ SHORT TERM...JMW LONG TERM...RAY AVIATION...JMW

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