Area Forecast Discussion
Issued by NWS Jackson, KY

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000 FXUS63 KJKL 151125 AFDJKL AREA FORECAST DISCUSSION National Weather Service Jackson KY 625 AM EST Sun Jan 15 2017 .UPDATE...
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Issued at 625 AM EST SUN JAN 15 2017 WSR-88D radar showing the earlier relatively higher returns have waned, but we are still seeing some drizzle is spots. Otherwise biggest issue will be the patchy dense fog in spots this hour. Updated grids to reflect latest obs and trends but otherwise forecast is on track.
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&& .SHORT TERM...(Today through Monday) Issued at 332 AM EST SUN JAN 15 2017 Surface analysis shows area of high pressure centered to the NW this AM across IA/IL region and quasi stationary boundary is now across portions of the TN Valley. Based on the upper level data, would suspect the 925mb boundary still resides across the region and 850mb just to our north. That said, WSR-88D radar does indicate a line of shower/drizzle has developed across the center of the CWA and is near where the SPC mesoanalysis shows weak forcing at the 925mb level as mentioned above. This will progress south through the morning and kept as a drizzle mention given some areas are seeing light drizzle outside this line. Overall the HRRR/CONSSHORT seemed to be handling this idea and therefore nudged my POPs in that direction. Based on the obs this morning would think fog is more of the patchy dense variety and therefore kept that going through early morning before tapering through mid morning. The previously mentioned surface high pressure will progress east today with winds veering around to the NE by this afternoon. The 850mb front will remain north as mentioned before, as a mid level wave/PVA rides along the baroclinic zone. These two forcing mechanisms combined with saturated column will lead to decent chance of rain showers late this afternoon into this evening mainly north of the Mountain Parkway. While this is a decent shot of rain showers, the QPE will remain light with only a couple of hundredths of an inch expected. POPs will wane through the evening from west to east as better forcing pushes east. Given the moisture in place did opt to add patchy fog in for a good portion of the region through Monday morning. For Monday did keep slight POPs in the north and far NE, but this may have to be looked at further. The only fly in the ointment here will be the aforementioned quasi stationary will likely lift back north, and therefore could lead to slight POPs ahead of the eastward progressing cold front. Better POPs for the cold front will take place beyond this forecast period. .LONG TERM...(Monday night through Saturday) Issued at 434 AM EST SUN JAN 15 2017 Models start out in decent agreement, but soon go their separate ways concerning wx systems and precip potential. There is agreement that it will remain mild. It`s a question of how mild. For specifics, a low pressure system will be passing northeast over the middle of the CONUS Monday night. Its cold front will push into KY, with warm air advection ahead of it. This should keep temps nearly steady on Monday night. Showers along the front should be arriving from the northwest on Monday night, and lasting into Tuesday. This is when the first model differences start showing up. The ECMWF is more pronounced and faster with an upper level wave supporting the storm system, which allows the ECMWF to advance the cold front well to our southeast by Wednesday morning. Meanwhile, the GFS is weaker and slower with the upper level system, and still has the front near the KY/VA line early Wednesday. The NAM is in between. The result is a difference in precip/POP for early Wednesday, and a variation in Tuesday night/Wednesday morning low temps. The forecast is a compromise at this point. There is agreement for a period of dry weather from Wednesday afternoon into Thursday, even though upper level pattern differences continue to grow. The upper level differences affect the forecast again beginning late Thursday. The GFS has a shortwave trough dropping southeast out of Canada and phasing with the slower aforementioned upper level wave, morphing into one large trough over the northeast CONUS and Appalachians. This would bring cool temps and stratocu. The ECMWF does not phase the two systems and remains flatter with the flow over the northeast CONUS. Instead, the ECMWF becomes more amplified with a trough/upper low over the middle of the CONUS on Thursday. The resulting system pulls moisture back north, allowing for clouds to increase from top down on Thursday, and an area of showers moving through the JKL forecast area from SW to NE on Thursday night and Friday. The slower and weaker GFS takes this system by mainly to our south late Friday and Friday night. There is a large amount of uncertainty with this system, and have used low chance POPs Thursday night into Friday. Finally, by Saturday there is loose agreement for an upper level ridge to be positioned just to our east, supporting mild and dry conditions. && .AVIATION...(For the 12Z TAFS through 12Z Monday morning) ISSUED AT 620 AM EST SUN JAN 15 2017 Most sites are starting the period flirting or exceeding airport minimums for CIGs, however VIS is varying more across the sites. While no sites are seeing drizzle this hour, some portions of the region are still seeing some drizzle. There will be improvements as we move toward the late morning into the early afternoon where most sites will see low MVFR CIGs. A upper level wave will interact with upper level front to bring rain showers by late this afternoon into this evening. Best chances will reside along and north of the Mountain Parkway. Guidance and models soundings would suggest we lower CIGs once again tonight and would think at least IFR CIGs are possible. Light winds are expected with wind out of the NE through most of the period before becoming more east to round out the period. && .JKL WATCHES/WARNINGS/ADVISORIES... NONE. && $$ UPDATE...DJ SHORT TERM...DJ LONG TERM...HAL AVIATION...DJ

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