Area Forecast Discussion
Issued by NWS Jackson, KY

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000 FXUS63 KJKL 102024 AFDJKL AREA FORECAST DISCUSSION National Weather Service Jackson KY 324 PM EST Sun Dec 10 2017 .SHORT TERM...
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(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.
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&& .AVIATION...(For the 18Z TAFS through 18Z Monday afternoon) ISSUED AT 135 PM EST SUN DEC 10 2017 A surface high centered to the south and southeast of the area and mid level height rises through about the first 18 hours of the period should lead to vfr through the period. Models do have an increase in low level moisture between 850 mb late tonight so some low stratus or stratocu cannot be completely ruled by the 6Z to 9Z or after, but confidence in this was too low to include at this time due to lack of model blended guidance and mos guidance support. Winds should average out of the southwest nearing 10KT through around 23Z especially on ridges and in more open terrain locations, with locations outside of valleys generally in the 5 to 10KT range also from the southwest through the end of the period. && .JKL WATCHES/WARNINGS/ADVISORIES... NONE. && $$ SHORT TERM...JP LONG TERM...GEOGERIAN AVIATION...JP

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