Area Forecast Discussion
Issued by NWS Jackson, KY

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000 FXUS63 KJKL 110305 AFDJKL AREA FORECAST DISCUSSION National Weather Service Jackson KY 1005 PM EST Sun Dec 10 2017 .UPDATE...
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Issued at 1005 PM EST SUN DEC 10 2017 The latest obs and satellite trends showing anywhere from mid to high clouds streaming across portions of Kentucky tonight. This continues to be mostly driven by a shortwave riding southeast through the long wave trough across the eastern US. The biggest issue is hourly and minimum temperature forecast and have continued to update the curve with the trends. There has been a stream of lower stratus to our north, and based on the latest trends the lowest clouds will remain north and east of the area. Adjusted grids to latest thinking and updated products to reflect those ideas as well. UPDATE Issued at 640 PM EST SUN DEC 10 2017 The evening surface analysis shows an area of high pressure off to our southwest and a weak surface low to our northwest. We remain more mixed here with winds out of the southwest this evening. The issue tonight will be the valleys decoupling, and for now have continued with the current trends of lower 20s in the deeper valley locations. The next tricky item that will also have a impact on temperatures is a mid to lower deck of clouds skirting the far eastern portions of Kentucky. This will lead to some difficult temperature curves and have adjusted toward the latest obs and trends to account for this.
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&& .SHORT TERM...(This evening through Monday night) Issued at 324 PM EST SUN DEC 10 2017 As of mid afternoon, an upper level trough was in place from eastern Canada south into the Southeastern Conus with ridge in place across the western Conus. Upper level winds across the region were out of the west northwest to northwest with weak shortwaves moving through from time to time. A band of mid level clouds associated with a mid level shortwave is working across northern and far eastern KY while cirrus is also passing through the OH Valley. At the surface, high pressure extends from the Southern Plains across the southeastern Conus with ridging north into the Appalachian region while an area of low pressure is well north of the Great Lakes. Mid level height rises rises are expected on average through early on Monday with the upper level flow becoming more westerly while sfc high pressure is expected to remain in place across the southeastern states. Periodic bands of clouds should moving through the area tonight and models due indicate an increase in lower level moisture, mainly late. This might be sufficient for at least some scattered stratus or stratocu toward dawn. This possibility leads to a low confidence low temperatures forecast, however, due to mostly clear skies or mainly cirrus anticipated during the evening points toward the potential of a quick evening temperature drop in the valleys and at least a small to moderate ridge/valley temperature split. COOP MOS guidance hints at some upper 20s for the normally colder spots, which is possible if skies remain generally free of low and mid level clouds considering current dewpoints. For now opted for some low to mid 20s for the valleys and upper 20s for more open terrain areas and ridgetops. With stronger return flow as the axis of surface high departs further to the south and east and the next clipper system approaches as it drops into the mean eastern Conus/eastern NOAM trough, temperatures will moderate to near normal if not slightly above normal for highs on Monday. Low clouds will be possible early with mid and high clouds expected from time to time in advance of the next clipper. Clouds with the approaching clipper system are not expected to thicken and lower much before late on Monday evening again leading to the possibility for another quick evening drop in temperatures and lows in eastern valleys near midnight possibly in the upper 20s. Temperatures in those locations would rise toward dawn if they make the evening dip as the pressure gradient increase and clouds lower. Moisture increases for late Monday night and may be sufficient for light precipitation prior to dawn. The model guidance hints at some potential for a minimal amount of ice in the clouds for late Monday night or marginal for ice in the clouds though guidance indicates this moisture should begin to deepen before the end of the period. At this point, have isolated to scattered pops for snow showers late in the period. .LONG TERM...(Tuesday through Sunday) Issued at 245 PM EST SUN DEC 10 2017 The models are in generally good agreement with an amplified long wave pattern to remain in place through the end of the work week, before transitioning to more zonal-like flow for next weekend. For the Ohio and Tennessee valleys, this will mean a continuation of well below normal temperatures through Friday, well as a few bouts of light snow/rain at times. Temperatures will then rebound to the 50s for highs by next weekend, with at least a small chance of rain threatening the region. On Tuesday, cold air advection will be ongoing, as an upper level trough is reinforced across the Eastern Conus. Some upslope snow showers will be on tap for eastern Kentucky through the day, and given the available forcing and favorable wind direction, have gone slightly higher than the blended POPs. POPs will taper off into Tuesday evening, with middle teens expected for lows by Wednesday morning. Have favored the valleys west of I-75 for the coldest temperatures, given the thinner clouds. Another front will approach Thursday into Friday, bringing additional small chances of rain/snow, depending on the timing and temperature profile. This system looks weaker, and the ECMWF and GFS differ on the evolution of the small scale features. Temperatures will continue to average below normal through Friday, before a warm up ensues for the weekend, as heights recover across the area. Another front will approach sometime this weekend, but given the model disagreement, have undercut the POPs a bit until the guidance can gel better. && .AVIATION...(For the 00Z TAFS through 00Z Monday evening) ISSUED AT 626 PM EST SUN DEC 10 2017 We see a surface high to our southwest and a weak surface low to our northwest to begin the period. This is keeping us VFR with the mix of mid to high level clouds across eastern Kentucky. Some of the models continue to hint at some low level moisture and potential stratus overnight. The blended guidance and MOS tend to keep this more northeast of the region. This as a weak shortwave moves southeast through the larger upper level trough in the eastern CONUS this evening. Given this did add a lower FEW coverage deck to the more eastern TAF sites of SJS/SYM, but did cap this at 5 kft given the lack of confidence for a lower deck. Winds have decreased this evening, but will remain light out of the south and west. && .JKL WATCHES/WARNINGS/ADVISORIES... NONE. && $$ UPDATE...DJ SHORT TERM...JP LONG TERM...GEOGERIAN AVIATION...DJ is the U.S. government's official web portal to all federal, state and local government web resources and services.