Area Forecast Discussion
Issued by NWS Jackson, KY

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000 FXUS63 KJKL 261143 AAA AFDJKL AREA FORECAST DISCUSSION...UPDATED National Weather Service Jackson KY 643 AM EST Sun Feb 26 2017 .UPDATE...
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Issued at 635 AM EST SUN FEB 26 2017 Hourly grids have been freshened up based on recent observations mainly for temperature and dewpoint trends. Areas in the Big Sandy region that experienced persistent stratocu have finally cleared out over the past couple of hours and temperatures there have fallen into the middle 20s in valleys. Temperatures will moderate today back toward normal levels as warm air advection commences though dewpoints will remain on the low side and low min rh is anticipated this afternoon.
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&& .SHORT TERM...(Today through Monday) Issued at 410 AM EST SUN FEB 26 2017 As of early this morning, the region was under westerly flow aloft within a broad trough extended from the Rockies east into the eastern Conus. 500 mid level heights are not all that high, but surface high pressure has built into the Lower OH and TN Valley region south into the southeastern Conus. A mid and upper level low was centered in the vicinity of the Hudson Bay Region with a shortwave trough rotating around it that is currently approaching the upper MS Valley and western Great Lakes regions. Another shortwave is moving across the Central Plains while a series of shortwaves are moving across the southern and central Rockies with the main mid and upper level shortwave trough nearing the southwestern Conus. The airmass in place across the region is dry with dewpoints on the ridges generally in the teens though some decoupled valleys have dewpoints in the 20s. The surface high will begin to depart to the east today before settling off the Mid Atlantic coast late tonight. Mid level heights are also expected to increase today across the southeastern Conus as ridging builds across the Caribbean. The northernmost shortwave will rotate through the Great Lakes today and then into Ontario and Quebec and St Lawrence Valley while the one now over the Central Plains region merges with it. These should bring an increase in cirrus to the area late today. Warm advection will begin today and high temperatures should fall only a couple of degrees below normals for late February. Tonight, a couple of lead shortwaves eject toward the Oh Valley while the main mid and upper level trough moves into the southern Plains. Another shortwave trough will move across the Plains and approach from the west. An area of low pressure should develop over the Plains while return flow and isentropic lift should bring increasing initially mainly mid and high level moisture to the region tonight and into the day on Monday with the atmosphere moistening up from the top down as a lingering result from the ridging that will be departing. Valley locations should decouple Winchell and with the dry air in place some locations in the far east may fall to near 30 degrees before mid level clouds increase and temperatures warm by the overnight hours. In addition, there will be downslope flow in the southeast. At this time, it appears the best chance precipitation late tonight and early on Monday will be across the western and northern fringes of the area as a shortwave moves passes through the OH Valley. After this shortwave passes there may be a relative lull in the precipitation chances with warm air advection and isentropic precipitation beginning to increase mainly south of the area late on Monday as warm front starts to lift toward the area. Higher chances for more substantial precipitation will come during the long term period. .LONG TERM...(Monday night through Saturday) Issued at 330 AM EST SUN FEB 26 2017 The period will be met with broad southwesterly flow with surface high pressure parked off to the east. Meanwhile quasi-zonal flow aloft with perturbations riding through the flow will keep the period active Monday night into Tuesday night. There is some instability Tuesday into Tuesday night that will lead to slight chances of thunder. That said there will be a period of transition Tuesday night that will lead to little to no POPs particularly in the southeast. This period of transition will occur, as an upper level wave moves into the central plains and low pressure deepens across the Great Lakes. A trailing cold front and height falls, as upper wave progresses east will lead to best chances of POPs late Tuesday into Wednesday. There are some timing differences, with GFS being the faster solution and digs the trough a bit more than other solutions. The ensemble mean seems to better align with slower solutions seen in the long term guidance, and therefore think the overall model blend POPs look good at this point. Given the reasonable consistency did go ahead and keep the model blends CAT POPs. We stand to get a good soaking rain, but still a bit uncertain on exact axis of heavier precipitation. Right now total amounts of 1 to 1.5 inches would be quite possible throughout the region Tuesday night into Wednesday evening. The severe chances look relatively low with SPC MARS and CIPS analog keeping better chances to the west and southwest. This lines up better with the SPC climatology as well. However given deep layer shear and at least some meager instability some of these storms could be strong. Cold air mass will arrive Wednesday night into Thursday, but this will primarily bring us back closer to normal values for this time of year. These near to a little below normal temperatures will remain through Friday. A clipper does drop into the Ohio Valley Thursday night into Friday and perhaps a few sprinkles/flurries or rain/snow showers pass across NE portions of the CWA. Right now feel the better forcing will reside NE of the CWA and therefore low confidence on any measurable precip in KY. Canadian high pressure quickly pushes southeast late Friday into Friday night leading to a decent night for ridge/valley splits. Right now with some uncertainty will go 5 degrees, but the COOP MOSGUIDE suggests possibility of a larger split. Temperatures are set to warm some as high shifts east Saturday, but air mass will still keep low to mid 50s in place. Given upper level ridging we should also remain dry to round out the long term period. && .AVIATION...
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(For the 12Z TAFS through 12Z Monday morning) ISSUED AT 642 AM EST SUN FEB 26 2017 The center of sfc high pressure is nearing the region. All the stratocu has cleared and light winds are occurring. Just some high clouds are expected to pass by from time to time today increasing during the 20Z to 0Z period as an upper level disturbance passes. Overall, VFR is expected through the period, though mid level clouds are expected to arrive and spread south and east between 0Z and 6Z should move into the area by the end of the period with moistening from the top down ahead of another disturbance leading to a few low clouds and possibly a few stray showers across the far west and northwest late. Winds will remain light through the period.
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&& .JKL WATCHES/WARNINGS/ADVISORIES... NONE. && $$ UPDATE...JP SHORT TERM...JP LONG TERM...DJ AVIATION...JP

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