Area Forecast Discussion
Issued by NWS Jackson, KY

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430 FXUS63 KJKL 050903 AFDJKL AREA FORECAST DISCUSSION National Weather Service Jackson KY 403 AM EST Mon Dec 5 2016 .SHORT TERM...(Today through Tuesday) Issued at 403 AM EST MON DEC 5 2016 As the mid/upper level wave that impacted the area yesterday continues to shift northeast of the region, more zonal flow is taking hold with surface high pressure moving eastward across the state. That being said, MVFR clouds continue to plague much of the region under a pretty steep inversion that has set up. Dry air will continue to filter in aloft and in the mid levels throughout the day, eventually working its way down to the surface and allowing the low cloud deck to mix out, generally after 15 to 18Z. Attention then turns to a strong upper level low positioned over southern TX this afternoon. At the surface, the center of low pressure will be located just off the TX/Louisiana coast, but will continue to push northeastward throughout the day following the upper level low, quickly reaching Mississippi by this evening, and TN late tonight, before traversing eastern KY and eastern TN during the day tomorrow. This will push the center of high pressure currently across the state to our northeast, and allow deeper moisture to quickly begin filling into the state from the south, reaching our southern CWA between 21Z and 0Z this afternoon/evening. That being said, upper level winds will continue to pull moisture into the region well ahead of this system, so even as the low clouds begin to mix out today, high clouds will already begin building in ahead of this system. Overall, it is not likely that we will see much of a break in the clouds throughout the day as a result. According to the latest forecast soundings from the NAM12, the transition from high clouds to moisture build down and precip will be very quick. Only slight chance pops are in the forecast along the TN border before 0Z, but widespread rain is expected to encompass the entire southern half of the CWA by 6Z, and and the entire eastern portion of the state by 12Z. A steady rain is expected to continue throughout the day Tuesday. Still not seeing enough support for instability, even aloft, to include thunder at this time. The upper level low is expected to decrease in strength, becoming an open wave by the time it moves over eastern KY. As the surface low pressure center moves across the CWA in the afternoon, drier air will be quick to filter in behind, weakening the surface low and cutting off best rain potential. As such, rain is likely to end just as quickly as it started, with only low end chances expected across far eastern KY by 0Z Tuesday. While temperatures today will be near seasonable normals despite cloud cover, the surge of warmer moist air into the region will actually boost temps well into the 50s for the day tomorrow. .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 06Z TAFS through 06Z Monday night) ISSUED AT 127 AM EST MON DEC 5 2016 Tricky TAFs for the period once again. Upper level wave is continuing to exit northeast of the region, with surface high pressure moving in across the state. In most situations the lingering moisture and high pressure center would suggest fog, however in this situation, we are still seeing thick llvl clouds across much of the region, including well upstream of the TAF sites. As such, redid TAFs to remove mention of fog, as this will likely be a low stratus event, with generally MVFR CIGS expected. Can`t rule out some IFR at times however, though it seems like the majority of the obs upstream are within the MVFR range. Tomorrow, low clouds will likely persist into the afternoon, before finally starting to scour out. About this time, another system will begin approaching from the southwest. This will allow for high clouds to enter back into the region, and quickly build down after 0Z, with rain chances soon to follow. Went ahead and included VCSH at most TAF sites between 3 and 4Z, except for the far northern KSYM, where chances will likely occur closer to the end of the forecast period. Overall winds should remain light and variable, though more gusty conditions may continue at KSYM through the next several hours before finally dissipating. && .JKL WATCHES/WARNINGS/ADVISORIES... NONE. && $$ SHORT TERM...JMW LONG TERM...HAL AVIATION...JMW

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