Area Forecast Discussion
Issued by NWS Jackson, KY

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000 FXUS63 KJKL 042321 AFDJKL AREA FORECAST DISCUSSION National Weather Service Jackson KY 621 PM EST Sun Dec 4 2016 .SHORT TERM...(This evening through Monday night) Issued at 300 PM EST SUN DEC 4 2016 Active pattern on tap in the short term. The initial weather maker for eastern Kentucky will be an area of low pressure aloft, that is expected to move across the region this afternoon through the overnight period. Scattered to at times numerous light rain showers will move across eastern Kentucky through early this evening. The rain should finally begin to taper off after 4Z tonight, as the upper low moves off to our east. Eastern Kentucky should be precipitation free by around 11Z Monday. Rainfall amounts with this first system should be very light across eastern KY tonight, generally a tenth of an inch or less. After several hours of quiet weather, another area of low pressure is forecast to approach the region from the southwest Monday afternoon and evening. Rain showers associated with this second weather system should have overspread the entire area by around 6Z Tuesday. This second weather system will provide a more robust shot of rain. We could see rainfall amounts Monday night into early Tuesday morning rain from around 0.4 inches in our far north, to between 0.5 and 0.8 inches in our far south. Temperatures should be running at or slightly below normal during the day on Monday, with highs ranging from the mid 40s in our northern areas to around 50 in our southern areas. Tonights lows should bottom out with above normal values in the mid to upper 30s, due to the influence of cloud cover and precipitation. Tomorrow nights lows look to be even warmer, as winds shift from the east to south and increase in strength and cloud cover and precipitation also increase in coverage. Monday nights lows are expected to fall into the low to mid 40s, with a non diurnal hourly temperature pattern also expected due to cloud cover and wind influences. .LONG TERM...(Tuesday through Sunday) Issued at 434 PM EST SUN DEC 4 2016 There are three potential systems to deal with, and the unusual situation where the greatest uncertainty is in the middle of the forecast period. System number one will be here as the period begins. Surface low pressure is expected to be over middle TN at 12z Tuesday, with an affiliated shortwave aloft just a bit further to the southwest. The low should be tracking northeast along the western edge of the Appalachians during the day while coastal development occurs over the Carolinas. Rain is expected, mainly Tuesday morning. It looks as if cold air advection will bring a nondiurnal temperature, with temperatures starting to drop off Tuesday afternoon. The coastal low will take over as the main low while the system is pulling out Tuesday night, and surface ridging will build in just to our north and bring quiet weather lasting into Wednesday. The effects of the model controversy come Wednesday night into Thursday for our area. It involves a shortwave moving east from the central Rockies Tuesday night into Wednesday, and its interaction with an upper low over southern Canada. The ECMWF holds a substantial portion of this upper low over southwest Ontario Wednesday, while the GFS allows it to take off to the east and leaves a weaker portion behind. The aforementioned shortwave phases with whatever of the upper low is left behind. This results in the ECMWF having a stronger system than the GFS. The ECMWF has weakened with its related surface system and is slightly more progressive with it when compared to earlier runs, which is a trend toward the GFS. The stronger and slower system of the ECMWF would briefly pull in milder air and result in rain. the GFS would have much less precip, but would allow for snow or a mix. At this point, have continued to use a blend. The resulting forecast has high chance pops Wednesday night into Thursday, mainly in the form of rain, but does mention snow. Better agreement comes to finish the period. Cold air advection and northwest flow brings scattered snow showers Thursday night, followed by the coldest air of the season so far as strong high pressure drops into the central CONUS from Canada and then heads east. Both the GFS and ECMWF show warm air advection and isentropic lift bringing a potential for precip on Sunday, with borderline temperatures allowing for rain or snow. && .AVIATION...(For the 00Z TAFS through 00Z Monday evening) ISSUED AT 621 PM EST SUN DEC 4 2016 Tricky TAFs for the period as we see southern stream system exits east this hour and northern stream system approaching from the west. Overall we will see TAF sites drop through the night with rain and drizzle aiding in restricting VIS. Many sites will approach if not exceed airport mins overnight into early Monday. We will see improvements as the rain exits by Monday, and possibly VFR by the afternoon before another system approaches. Winds will be light and not a concern through the TAF period. && .JKL WATCHES/WARNINGS/ADVISORIES... NONE. && $$ SHORT TERM...AR LONG TERM...HAL AVIATION...DJ

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