Area Forecast Discussion
Issued by NWS Jackson, KY

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000 FXUS63 KJKL 230600 AAA AFDJKL AREA FORECAST DISCUSSION...UPDATED National Weather Service Jackson KY 200 AM EDT Sun Apr 23 2017 .UPDATE... Issued at 140 AM EDT SUN APR 23 2017 Did a quick update to the grids to fine tune the next surge of pcpn north into the area. Also, added some drizzle around through the rest of the night along with matching up the latest obs and trends for the T/Td grids. These have been sent to the NDFD and web servers. UPDATE Issued at 1040 PM EDT SAT APR 22 2017 Currently across eastern Kentucky, much of the heavier shower activity has pushed off to the east. A few pockets of light showers or drizzle remain over the southeast. Have pushed the bulk of the pops off to the southeast leaving some slight chances in the far southeast and eastern counties. With the next moisture surge from the south developing, the low lift north into Kentucky by tomorrow pushing showers back into eastern Kentucky by dawn. So will reintroduce moderate to heavy showers and increased pops just after dawn. In the north, possibly a few breaks in the cloud cover and moist conditions in place will lead to a few pockets of fog development through early tonight and have put this in the forecast as well. Models still show decent qpf with the moisture surge tomorrow so will keep the Flood Watch going. Issued a new zfp with this update. UPDATE Issued at 750 PM EDT SAT APR 22 2017 Updated the forecast to lessen pops through the evening hours and through early tonight in the north. Also, lessening instability will make thunder unlikely through much of tonight so removed thunder for this evening. After inputing the latest observations a new forecast was sent out. && .SHORT TERM...(This evening through Sunday night) Issued at 425 PM EDT SAT APR 22 2017 As of mid afternoon, an upper level trough extended from Quebec south and then southwest into the OH Valley and Mid MS Valley region. At the surface, an area of low pressure was over the Atlantic with a cold front to its south and southwest that becomes wavy or nearly stationary from near the VA Tidewater region west and then southwest into southern middle TN where a stronger wave of low pressure was located. Rounds of showers and thunderstorms continue to move east near the boundary one of which is moving across the southern part of the CWA in advance of the upper trough. A steadier rain or drizzle was falling across the more northern locations. The heaviest rain today has fallen near the TN and VA borders with the heaviest rain from Bell to Letcher Counties. The southwest part of the upper level trough should close off as it is left behind as the northern portion of the trough departs to the northeast. The upper level low will meander to southern middle TN and the northern Gulf Coast states through Sunday evening. The upper level low should meander further southeast into southern GA by the end of the period. Meanwhile the surface low is expected to move across the northern Gulf Coast states through Sunday afternoon with an inverted trough developing to its north working east across the Commonwealth tonight through Sunday evening. The surface low should also move southeast on Sunday night further away from East KY. Some right entrance region jet dynamics appears to be aiding the current round of convection along with some isentropic lift over the boundary to our south. Near term convective allowing models appear generally in line with radar trends as convection should affect mainly the southern part of the area through around sunset. A relative lull then may ensure for much of the night until the center of the upper level low closes off and gets nearer to the region. This and the inverted trough may help focus another round of steadier rain or moderate showers mainly from the TN border northeast along the VA border late tonight and into Sunday. The 12Z GFS has higher qpf with this while the 12Z NAM and 12Z ECMWF have lesser amounts. For qpf stayed closed to the model blend guidance that was a compromise of the higher and lower values. If multiple thunderstorms affect the south or the showers become more intense across the south than the threat for flash flooding would increase. The counties that have been wettest over the past 24 to 48 hours are Bell, Harlan, and Letcher along with parts of Whitley and McCreary. Uncertainty also remains and if the 12Z GFS heavier qpf were to verify the threat for high water and flash flooding or river flooding would increase. The current forecast qpf would generally confine the flash flood threat from Bell to Letcher and perhaps Pike County. Multiple rounds of rain will contribute to high water and perhaps a downstream point or two along the Cumberland or Kentucky such as Williamsburg or Ravenna reaching minor flood stage by the end of the weekend. Uncertainty does remain. The qpf from this afternoon through Sunday night is minimal a quarter inch or less in the north where only lighter showers or drizzle are expected this evening and on Sunday. More numerous to widespread rounds of showers will occur to the south especially nearer to the VA and TN borders. Expected rainfall increases to about a half of an inch to three quarters of an inch nearer to the Mtn Parkway and an inch or more along or south of Hazard to or more south of a Monticello to London to Pikeville line. Amounts near 2 inches are expected from near Middlesboro along the VA border to near Jenkins. Locally higher amounts are possible and the rainfall amounts and flood threat will be determined by the evolution of convection and rainfall rates. At this time, the current areal extent and valid time of the Flash Flood Watch appear to be in good shape. The shower threat will diminish from late Sunday afternoon to Sunday night even in the far southeast as the upper system and surface low depart. The nocturnal range form tonight into Sunday night will be very limited by cloud cover with Sunday highs near 10 degrees below normal. .LONG TERM...(Monday through Saturday) Issued at 335 PM EDT SAT APR 22 2017 Models are in decent agreement through the extended with mid/upper level flow. In general, the southern Appalachian region will fall under the influence of mean southwesterly flow aloft. That would indicate warmer weather than not, and an occasional shot at showers and thunderstorms should any disturbances in the mean flow get close enough to affect our area. One such disturbance does appear to skirt just close enough to provide a chance of showers Wednesday night into Thursday. Forecast soundings suggest instability is lacking but considering the time of year, will maintain inherited Isold thunder for this time frame. When compared to the ECMWF and Canadian, the GFS is somewhat of an outlier towards the end of the extended window with the potential of a second disturbance. The ECMWF and Canadian swing this second disturbance through the area by late Friday into Saturday, though the ECMWF is much more subtle with this feature. Once again forecast soundings indicate instability is lacking, but considering the synoptic pattern feel it would be prudent to maintain at least a slight chance of thunder. Sensible weather will seem closer to a summer like pattern than spring with temperatures averaging some 5 to 10 degrees above normal. Temperatures warm nicely through the week, with highs climbing into the lower to mid 80s for much of the week. Lows fall generally in the upper 50s to lower 60s each night. Outside of the two disturbances mentioned earlier, any chance for rainfall would be quite low based on soundings as a substantial cap appears to be in place for most of the period. && .AVIATION...(For the 06Z TAFS through 06Z Sunday night) ISSUED AT 200 AM EDT SUN APR 23 2017 Main concern for aviation through the rest of the night will be low cigs in the LIFR or IFR range but with the showers in a lull through dawn, some cigs may briefly bounce up to MVFR. The next surge of showers will push in from south to north during the day Sunday with cigs bouncing between low MVRF and IFR and times of visibility down to MVFR. SYM will have the best shot at remaining VFR through Sunday night as the main influence of the weather system passing by to the south wanes for locations north of a JKL to SJS line. Winds will remain north to northeast through Sunday night with speeds averaging around 5 kts but up to 10 kts at times. && .JKL WATCHES/WARNINGS/ADVISORIES... Flash Flood Watch through this afternoon for KYZ079-080-083>088- 110-113-115>118-120. && $$ UPDATE...GREIF SHORT TERM...JP LONG TERM...RAY AVIATION...GREIF

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