Area Forecast Discussion
Issued by NWS Jackson, KY

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167 FXUS63 KJKL 061510 AAB AFDJKL AREA FORECAST DISCUSSION...UPDATED National Weather Service Jackson KY 1010 AM EST Tue Dec 6 2016 .UPDATE... Issued at 1010 AM EST TUE DEC 6 2016 The forecast remains on track so far today, with periods of widespread light to moderate rain showers expected across the area. Current temperatures should not change much during the course of the day, due to the ongoing precipitation and widespread cloud cover. Will not be updating the zone forecast text product just yet as the current forecast is good as is. An update will be required around noon today, to remove morning wording from the forecast text product and to make any other changes that may be necessary by then. UPDATE Issued at 728 AM EST TUE DEC 6 2016 Light to moderate rain continues across much of eastern KY, especially the southern half of the CWA. This seems to jive well with the ongoing POP and weather forecast. Still expecting rain to continue across the area throughout the day, so no updates needed to this portion of the forecast at this time. Temperatures will only increase by a few degrees throughout the day given the ongoing cloud cover and rain. Did update the forecasts for the near term temps, dew points, and winds, however, to make sure they were on track with current observations. All changes have been published and sent to NDFD/web. && .SHORT TERM...(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 night through Monday) Issued at 505 AM EST TUE DEC 6 2016 The models are in good agreement concerning the amplified long wave pattern in place across the CONUS during the middle of the week. This regime will transition to more zonal flow through the first part of the weekend, before amplifying once again through early next week. There is more confidence in the smaller scale features through Saturday. Confidence then drops off through the rest of the extended portion of the forecast due to timing and evolution differences. A deep upper level low will shift east from Ontario to Quebec through Thursday, enabling a short wave trough to swing through the Great Lakes and Ohio Valley regions. This will bring the coldest air thus far this season into eastern Kentucky. Winds will shift to the northwest late Wednesday night into Thursday, with some light snow, although impacts looks to be minimal given the shallow depth of the moisture available and most of the better upper level support passing by further north. Highs on Thursday will be in the low to mid 30s at best, with temperatures likely dropping through the afternoon. Despite lingering cloud cover into Thursday night, lows will drop off into the teens for most locations, with highs on Friday only in the 20s. The center of the high pressure looks to pass through the region Friday night into Saturday morning. Clouds should be a bit thinner, as the flow becomes more zonal, allowing at least for some mid teens, if not lower potentially. Highs will recover back to the mid to upper 30s on Saturday. The next system will affect the area from Sunday through Monday, as a trough digs in across the Plains and then moves east, dragging a cold front across the Commonwealth. The GFS is more progressive with this system compared to its mean, with the ECMWF slower still. Have therefore allowed for a slightly slower onset of the precipitation compared to that of the blended guidance. Consequently, this also resulted into hanging onto higher pops deeper into Monday and beyond. Did allow for a small chance of a rain/snow mix for early Sunday; however, given the likely slower trend, any foreseeable impacts look too low confidence to mention at this point. Temperatures will be moderating back closer to normal through early next week, with highs back near the 50 degree mark by Monday. && .AVIATION...(For the 12Z TAFS through 12Z Wednesday morning) ISSUED AT 736 AM EST TUE DEC 6 2016 Rain continues across much of eastern KY, with heaviest coverage currently across KSME and KLOZ. Cigs range across the CWA, anywhere from MVFR to VFR. Tried to trend to most sustained values, though there will continue to be some bouncing around throughout the day. Overall trend should be for deteriorating CIGS throughout the day, reaching IFR conditions by this afternoon, generally between 15 and 18Z. Rain may also cause some VIS restrictions, generally MVFR. The surface low pressure system which is spawning this rain will continue to move across eastern KY through this afternoon before exiting east of the region. Dry air will quickly filter in across eastern KY in the mid and upper levels behind this surface low. This will cut off best rain potential by this evening and into the overnight. However a strong llvl inversion will set up, trapping abundant moisture near the surface. As such, depth of moisture may be enough that drizzle could occur through about 6Z at most TAF sites. After 6Z expect slowly improving conditions for both the VIS and CIGS as rain chances exit the area for good. Winds will generally remain under 10 knots throughout the period, however some of the heaviest rains could mix gusts between 10 and 20 mph to the surface during the day today. 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. && $$ UPDATE...AR SHORT TERM...JMW LONG TERM...GEOGERIAN AVIATION...JMW is the U.S. government's official web portal to all federal, state and local government web resources and services.