Area Forecast Discussion
Issued by NWS Jackson, KY

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000 FXUS63 KJKL 060939 AFDJKL AREA FORECAST DISCUSSION National Weather Service Jackson KY 439 AM EST Tue Dec 6 2016 .SHORT TERM...
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(Today through Wednesday) Issued at 438 AM EST TUE DEC 6 2016 A strong upper level low was in place across TX as of this past evening, and has quickly transitioned northeast while weakening into an open wave, now located across Mississippi as of 9Z this morning. This will continue to track northeast, moving across TN and eastern KY by this afternoon while dissipating even further, quickly exiting by 0z Wednesday. Meanwhile, the surface low pressure system is outracing the upper level wave, already pushing across TN and heading towards the eastern KY, with an expected direct impact to the CWA between 15 and 18Z today, before quickly shifting northeast out of the state. Fairly good wind sheer is taking place, with light E to SE winds ahead of the surface low, and strong W to SW winds aloft pulling in moisture from the gulf of Mexico ahead of the upper level wave. There was a pretty sharp cutoff, as was forecast, between the high clouds that were across the region, and the time at which these clouds built down and rain began. A sharp llvl inversion is also in place given the wind/temp disparity. As of now, much of the CWA has become saturated, with light to moderate rain reaching the ground. This rain is expected to continue throughout the day as the center of the surface low crosses over the region. As llvl winds begin to shift to a more southerly and then easterly direction on the backside of the surface low, midlevel winds will also become more easterly, generally after 15Z. Once this wind shift takes place, much drier air will be able to filter into the region, with the upper levels drying out by 21Z, and the mid levels following suit by 0Z this evening. This process may be delayed by an hour or two in the far east. The dry air entrainment will essentially cut off best rainmaking processes as well, though will leave a layer of moisture near the surface, stuck below a strong llvl inversion that will setup overnight. This set up looks very similar to that of the last rain system we had, which leans itself to low clouds and drizzle potential through much of the overnight instead of fog. Went ahead and added patchy drizzle into the forecast, generally tapering off from west to east as dry air filters in near the surface throughout the overnight. Temperatures are expected to fall to near freezing in many locations. While this may raise some concerns for freezing drizzle, it appears as most of the drizzle will taper off with the cooler drier winds moving in, before temperatures reach the freezing mark, thereby alleviating concerns. Dry air will continue to infiltrate the region through the day Wednesday as a broad area of surface high pressure sets in. Aloft, strong W to WSW flow will remain in place, also pulling drier air in from the central plains. This will help skies will clear throughout the late morning/early afternoon. Surface winds, while light, will generally be more northerly in direction. This will ultimately result in temperatures just below seasonable normals for afternoon highs on Wednesday, generally in the mid 40s. .LONG TERM...(Wednesday through Monday) Issued at 328 PM EST MON DEC 5 2016 We transition to a much colder weather pattern to end the work week as a deep, but transient, trough digs into the Ohio Valley. Models usher in this colder airmass without much precipitation. However, we come under the influence of the right entrance region of a stout 150kt upper level jet as the cold front works through Thursday morning and models hint that this could force some light snow and/or rain Wednesday night into Thursday morning. Will keep PoPs rather low as moisture is limited. Isolated snow showers and flurries will remain possible Thursday night into Friday with strong cold advection wringing out any lingering moisture. Temperatures will likely not rise out of the 20s on Friday. Cold high pressure settles into the region Friday night and this will likely be our coldest night. However, models show the potential for some high clouds to interfere with our radiational cooling. Nonetheless, temps in the teens are a good bet for just about everyone. Models show a fast transition to southwest flow aloft by Saturday night in advance of a shortwave digging into the northern Plains. This will result in increasing clouds and precipitation chances late in the weekend. Timing remains questionable with this system with large differences in the modeling so stayed close to the blended model guidance. However, 60-70 PoPs on Sunday seemed a bit high with the uncertainty involved, so dropped them down into the chance range. Current forecast timing would introduce the threat for a mix of rain and snow at onset late Saturday night/early Sunday morning, but the bulk of the precipitation Sunday into Monday should be rain.
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&& .AVIATION...(For the 06Z TAFS through 06Z Tuesday night) ISSUED AT 114 AM EST TUE DEC 6 2016 Conditions are beginning to deteriorate at TAF issuance, especially across the southern portion of the state. KSME has now fallen to MVFR, and KLOZ will be soon to follow over the next hour or so. High clouds still persist at the remaining TAF sites, but should begin falling quickly to MVFR generally after 8Z at KJKL and closer to 9Z at KSYM. Rainfall will be on the heals of the CIG drop, expected to start to KSME and KLOZ over the next couple of hours as well. Ceilings will likely lower further to IFR and possibly LIFR by Tuesday morning as rainfall becomes more widespread. Visibilities will also decrease to MVFR and potentially IFR as rain falls. Should see the bulk of the rain taper off by late afternoon, allowing visibilities to increase to VFR criteria. However, IFR ceilings look to be a good bet through the end of the TAF period (6Z). Winds will increase to 5-10 knots through the rest of tonight, while veering southeasterly. Will see these veer further to the west/southwest this afternoon, with speeds increasing to near 10 knots with higher gusts during the latter portion of the afternoon. All this as a cold front gets set to move through the Ohio Valley and Commonwealth. Additionally, southeasterly low level wind shear near 35-40 knots may become an issue tonight across far southeast Kentucky. && .JKL WATCHES/WARNINGS/ADVISORIES... NONE. && $$ SHORT TERM...JMW LONG TERM...ABE AVIATION...JMW

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