Area Forecast Discussion
Issued by NWS Jackson, KY

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888 FXUS63 KJKL 190605 AAA AFDJKL AREA FORECAST DISCUSSION...UPDATED National Weather Service Jackson KY 105 AM EST Thu Jan 19 2017 .UPDATE...
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Issued at 1250 AM EST THU JAN 19 2017 Touched up the public grids with respect to current conditions and trends specifically with sky cover as high clouds move in and T/Td for the latest obs. These have been sent to the NDFD and web servers. UPDATE Issued at 930 PM EST WED JAN 18 2017 Clouds remain a challenge this evening in more ways than one. The first will be the slow moving stratus deck that is still plaguing the far east and northeast. Based on the trends and guidance that will move NE through the late evening hours. Surface analysis shows high pressure cresting just to our west, but near and along the surface high we are seeing surface divergence. This has lead to lower tripe of temperatures generally south of the Mountain Parkway and generally north of the Hal Rogers Parkway. The second has been the higher clouds aiding in the stripe like fashion of the temperature split mentioned above. This will make for difficult hourly temperature forecast grids, and therefore will load closer to obs and trends as possible with some of the short term guidance lending additional aid. Otherwise only minor updates to other elements were made for this update. UPDATE Issued at 640 PM EST WED JAN 18 2017 Surface analysis shows high pressure is cresting across central KY and will continue to move east. The challenge tonight will be with far eastern stratus deck and the implications of this temperatures/fog production. That said the stratus deck has hit the breaks and updated sky grids to better deal with this. Right now only high clouds are moving into areas south of the stratus and would suspect these areas to drop off temperature wise quicker than the far eastern typically colder valley sites. Therefore will have to keep an eye on this and update as needed to deal with latest obs and trends.
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&& .SHORT TERM...(This evening through Thursday night) Issued at 415 PM EST WED JAN 18 2017 As of mid afternoon, an upper level ridge extended from the Caribbean northwest into the Lower OH Valley and Mid Ms Valley region. Meanwhile a broad upper level low extended from the Central Plains to the Southern Rockies. Meanwhile, surface high pressure was centered over the Lower OH Valley while low pressure was starting to organize over the East TX/Arklatex region. A stationary front extended northeast and then east from this developing system across the Southeastern States. Tonight, the axis of the upper ridge should gradually move east and be over the region by dawn on Thursday. Meanwhile, the upper level low will meander across the Central and Southern Plains Region. Surface low pressure should continue to organize and reach southern AR late with the boundary to the east lifting north as a warm front and into southern TN. The upper level low should meander toward slowly east and northeast toward the MS Valley on Thursday into Thursday night and gradually weaken. The surface low should track northeast during that time as well and reach IL by the end of the period. During the same time, the warm front should begin to lift into the area. Clouds should continue to erode to the north and east through the evening as mid level heights rise. This clearing or partial clearing and the surface high building into the area should lead to valleys decoupling and some valley fog is anticipated to develop due to the lingering low level moisture. Mid and high clouds will also begin to thicken and lower late tonight and into the day on Thursday. However, these will reach the northern and eastern locations last so those valleys should be the coldest and have not that far to fall from current readings to approach the freezing mark. The warm front and upper level system will begin to approach the area on Thursday as the upper level ridge axis moves east. Moisture will increase from the top down through the day and thickening and lowering clouds are expected from southwest to northeast and rain showers should move in from the TN Valley and encroach on the Lake Cumberland Region by early to mid afternoon. The precipitation should gradually spread north and east through late afternoon, but the low level flow will have a downslope component and this should slow down the progression into the southeastern counties and lead to lower initial QPF there as well. Temperatures should moderate again to the 15 to 20 degree above normal range for this time of year. As the warm front and shortwave trough approaches the area on Thursday evening and Thursday night and even takes on a bit of a negative tilt, an area of showers should move across the area on Thursday night and appears to peak between about midnight and 4 AM on Thursday when best combination of lift and moisture should be over the region. Some limited elevated instability is also expected to be present at that point so isolated thunder will also be a possibility during that time. Categorical pops look to be in order given the projected moisture and lift and statistical MOS guidance also in the categorical range. Rainfall from this system should generally be moderate, though some heavier amounts will be possible across the southwest where 12 to 18 hour amounts could near an inch. .LONG TERM...(Friday through Wednesday) Issued at 337 PM EST WED JAN 18 2017 The extended forecast period begins on Friday with an active and progressive pattern in place. A short wave will track northeast through the Midwest and Middle Atlantic states on Friday. The general progression of this feature seems to push through rather quickly and the Euro and GFS agree on this. Precip will be brief as it will exit the area by Friday night. In this active pattern and on the heels of Fridays system another wave develops in the lower MS River Valley and tracks northeast into the central Appalachians by Saturday afternoon bringing another shot of rainfall to the area. Isentropic ascent with this next feature will pose the possibility for thunder but being well capped at onset will hinder this possibility so will leave out of the forecast for now. The active pattern continues into the beginning of next week as a secondary upper low dives into the lower MS Valley and lifts northeast again through the area late Sunday and into Monday. This shot of rainfall will appear to be the most out of the series as the GFS and Euro agree with up to an additional 3 quarters of an inch QPF expected in far eastern Kentucky by Tuesday. Most of this rainfall appears to fall in the headwaters of Eastern Kentucky. Total rainfall for this period looks to be up to 2 inches over a 48 hour period. At this time, its nothing to be too concerned about with rainfall but will put a mention in the HWO. Through the extended forecast, the warm trend continues with temperatures in some days nearly 20 degrees above normal. So, will not expect any frozen precip through the extended. && .AVIATION...
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(For the 06Z TAFS through 06Z Thursday night) ISSUED AT 105 AM EST THU JAN 19 2017 The earlier MVFR deck has dissipated as high clouds moved into the area over the past several hours and these clouds should limit the develop of fog through the rest of the night. Accordingly, have left the sites VFR through the bulk of the period, though cannot rule out a brief rebuild of stratus in the east and some MVFR BR in the western sites but will leave that out of the actual TAFs, for now. A warm front is still on track to move north and its precip will creep back into the region for the latter half of the TAF period. Have brought the best chance of showers to LOZ/SME by late Thursday afternoon. Winds will remain light through the period - becoming more southeasterly on Thursday.
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&& .JKL WATCHES/WARNINGS/ADVISORIES... NONE. && $$ UPDATE...GREIF SHORT TERM...JP LONG TERM...SHALLENBERGER AVIATION...GREIF

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