Area Forecast Discussion
Issued by NWS Jackson, KY

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000 FXUS63 KJKL 211455 AAA AFDJKL AREA FORECAST DISCUSSION...UPDATED National Weather Service Jackson KY 1055 AM EDT Sun May 21 2017 .UPDATE...
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Issued at 1055 AM EDT SUN MAY 21 2017 14z sfc analysis shows a warm front just east of Kentucky with a cold front approaching from the west. In between these boundaries the warm sector is maintaining scattered to numerous showers through the eastern portion of the area under overcast skies and with light winds. Temperatures through the CWA are running in the mid to upper 60s as the thick clouds and showers hold them back with dewpoints not far below the air temperature. This environment contains fairly high PW air in place making excessive rainfall a concern for any showers and storms that redevelop later this afternoon - particularly for places that saw heavy rains over the past two days. The latest HRRR and NAM12 indicate that the showers and a few storms will remain a threat over the far eastern parts of the CWA into the afternoon. They also suggest that more convection will bubble up during the afternoon through the rest of the area with the approaching cold front representing a back edge as it moves into eastern Kentucky this evening. Have adjusted the PoPs and storm chances through the next 12 to 18 hours for these thoughts. In the near term, tweaked the T and Td grids per the latest obs and trends. The updated forecast grids have been sent to the NDFD and web servers. UPDATE Issued at 753 AM EDT SUN MAY 21 2017 Showers have become more numerous across the area in the past hour. The short term models continue to struggle with initialization, although the latest HRRR has come in a bit more reasonable than previous runs. The 06z NAM was still overplayed on the precipitation rates. Will stick with the current forecast, having a steady increase in coverage through the rest of the morning out ahead of the approaching cold front. Temperatures will be slow to rise through this morning, before warming up this afternoon, with perhaps some breaks in the action. Updates have been sent.
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&& .SHORT TERM...(Today through Monday) Issued at 400 AM EDT SUN MAY 21 2017 The latest surface map features low pressure centered across southern Minnesota, with a cold front aligned south, nearly along the Mississippi River. Aloft, an upper level low is displaced just slightly west of the surface low, with a stout short wave trough lifting northeast into western Illinois. An upper level ridge is retreating towards the Eastern Seaboard. So far, the mesoscale has been the main convective driver across eastern Kentucky, as yet another round of scattered to numerous showers and thunderstorms affected portions of the area earlier, mainly driven by outflow boundary interaction. Currently, some scattered to numerous showers, with an isolated rumble of thunder, is moving in from the Tennessee Valley. This uptick in activity is mainly in response to a low level jet building in from the southwest, but so far, the convection has been light. Most of the model guidance suggests more intense convection to build in before dawn; however, am a little skeptical based on the latest radar and satellite trends. The cold front will gradually push east today, with plenty of moisture advecting northward out ahead it. This should lead to numerous to widespread showers, with some thunderstorms, although cloud cover will limit instability, as highs will be in the mid to upper 70s. High PWATs for this time of year will continue to bring an isolated flash flood threat; however, given the isolated nature of the heavy rainfall coverage over the past few days, will forego a watch at this time. The front will shift to the east late tonight, with showers and a few storms diminishing from west to east. Cooler air will move in behind the front, with lows in the mid to upper 50s. A few showers may linger in the far east into Monday morning, before drying up by the afternoon. Highs will be in low to mid 70s. .LONG TERM...(Monday night through Saturday) Issued at 408 AM EDT SUN MAY 21 2017 An area of high pressure will be moving across the Ohio Valley and exiting east to begin the period Monday night. Given the lower confidence of cloud cover will lean away from the ridge/valley splits. Then all eyes turn to a deepening upper level system across the Northern Midwest. Models continue to struggle with the overall evolution, but jet dynamics do develop a surface low to our south on Tuesday. That said, leaned toward a compromise of the wet NAM and dry GFS which was the ECMWF for Tuesday. After this really leaned toward the blended POPs, as the guidance remains out of sync with respect to the overall synoptic pattern. The GFS and ECMWF respective 00Z solutions did make some progress toward agreement with the overall depth of the 500mb heights. The wettest periods right now will be Tuesday night into Thursday. Subsequently given the amplitude of this upper level system being fairly anomalous, the temperatures will drop to below normal values for this time of year Wednesday and Thursday as column temperatures lower. This high amplitude trough is set to exit to the east by Thursday night and guidance is in decent agreement on a flattening ridge building east. This will bring higher heights and send temperatures back closer normal values to round out the week. This will also lead to the dry day by Friday. However, this ridge becomes dirty quickly and almost more in the way of zonal. There could be some weak waves move along the flow, but we remain fairly displaced from most of these waves. Keep some slight POPs in the western portions of the CWA on Friday night into early Saturday, but thinking some height rises could bring a lull by Saturday afternoon. && .AVIATION...(For the 12Z TAFS through 12Z Monday morning) ISSUED AT 753 AM EDT SUN MAY 21 2017 An approaching cold front will bring periods of showers, and perhaps a few thunderstorms to the area through the day. Expect a gradual lowering in the ceilings and visibilities, with most locations eventually seeing MVFR conditions. Showers will gradually diminish from west to east tonight, as the cold front passes through the area, with MVFR ceilings scattering out from west to east through the end of the period. South to southwest winds at 5 to 10 kts will eventually shift to west northwest after the frontal passage. && .JKL WATCHES/WARNINGS/ADVISORIES... NONE. && $$ UPDATE...GREIF SHORT TERM...GEOGERIAN LONG TERM...DJ AVIATION...GEOGERIAN

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