Area Forecast Discussion
Issued by NWS Jackson, KY

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495 FXUS63 KJKL 042136 CCA AFDJKL AREA FORECAST DISCUSSION...CORRECTED National Weather Service Jackson KY 436 PM EST Sun Dec 4 2016 .SHORT TERM...
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(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.
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&& .AVIATION...(For the 18Z TAFS through 18Z Monday afternoon) ISSUED AT 1227 PM EST SUN DEC 4 2016 Look for VFR conditions through around 21Z today as we see a lull from the rain for a few hours. Conditions are expected to deteriorate to MVFR as low clouds and rain showers move back into the area from the west between 22 and 23Z today. CIGS should fluctuate between 2.5 and 3K. Conditions will worsen slightly between 0 and 1Z, as an approaching cold front brings more widespread showers and lower level cloud cover to eastern Kentucky. That MVFR conditions should persist between 0 and 3Z this evening. After that, we can expected a period of IFR CIGS as rain showers and even lower level cloud cover invade the area. These conditions should last until roughly 12Z tomorrow, before things gradually improve through out the morning. MVFR conditions should once again be in place as the rain departs and cloud levels rise a bit from 12Z onward. && .JKL WATCHES/WARNINGS/ADVISORIES... NONE. && $$ SHORT TERM...AR LONG TERM...HAL AVIATION...AR

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