Area Forecast Discussion
Issued by NWS Jackson, KY

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000 FXUS63 KJKL 230558 AFDJKL AREA FORECAST DISCUSSION National Weather Service Jackson KY 158 AM EDT Tue May 23 2017 .UPDATE... Issued at 158 AM EDT TUE MAY 23 2017 IR SAT continues to show high clouds streaming into the region as an upper level wave moves NE across the TN Valley. Given the drier air in the lower levels anything on radar is likely virga at best at this point. However, does look like much the initial precip will be high based, with KCHA reporting -RA with 9 KFT cloud bases. Right now will leave POPs as is and evaluate more for the upcoming forecast package. Otherwise updated grids with latest obs and trends. UPDATE Issued at 1110 PM EDT MON MAY 22 2017 Hourly grids were freshened up based on recent observations, which led to no substantial changes at this time. UPDATE Issued at 835 PM EDT MON MAY 22 2017 The region remains under the influence of a broad trough that encompasses much of the Conus east of the Rockies. Within this trough, a shortwave was moving from the Lower MS Valley and into the Southeastern Conus. This shortwave is expected to track into the Southern Appalachians tonight and then northeast of the area during the day on Tuesday. This system is still expected to bring a threat of isolated to scattered rain showers late tonight and on Tuesday mainly across the southeast parts of the area. A thunderstorm cannot be ruled out on Tuesday as well. As for tonight and tomorrow, the inherited forecast looks on track with only slight adjustments to hourly temperatures and dewpoints. && .SHORT TERM...(This evening through Tuesday night) Issued at 430 PM EDT MON MAY 22 2017 19z sfc analysis shows high pressure in place over Kentucky, though it was not effective enough to keep the high clouds at bay. These, along with light north winds, have helped to keep temperatures contained in the 60s through the afternoon for most places. Readings did hit the low 70s in the far south but only mid to upper 60s, so far, elsewhere. Meanwhile dewpoints are running in the mid 40s to lower 50s. The models are in good agreement aloft through the short term portion of the forecast. They all depict a deep and broad trough over the mid section of the nation amplifying and dipping southeast into the mid Mississippi Valley during the next 36 to 48 hours. This will place eastern Kentucky in broad southwest flow with plenty of energy breaking free to ride over the JKL CWA from Tuesday afternoon into Wednesday. Toward the end of the period the GFS solution starts to separate from the ECMWF with the core of its trough digging a bit closer to Kentucky. Will favor a general blend through the period with a lean toward the higher resolution HRRR and NAM12 models through the first part. Sensible weather will feature a quiet night with some ridge to valley distinctions opening up after sunset but mitigating late in the night due to increasing clouds from the south. These clouds will be the vanguard of a sfc low moving into the southern Appalachians tomorrow with a few showers possibly sneaking past the border and into our CWA by dawn. The shower chances will continue in the far east Tuesday with a few thunderstorms possible by mid afternoon in these areas. A better chance of showers and storms then develops to our southwest - pushing in later Tuesday night - likely washing over the bulk of the CWA by sun-up Wednesday. Again used the CONSShort and ShortBlend as the grids` starting point with some adjustments to lows tonight owing to a ridge to valley split developing early but mixing out in the east late. As for PoPs, did tighten them up along our southern and eastern border late tonight into Tuesday. .LONG TERM...(Wednesday through Monday) Issued at 347 PM EDT MON MAY 22 2017 Models are in good agreement with mid and upper level features through DY5 Friday, then increasingly diverge in solutions from there. Amplified and somewhat progressive flow will dominate the pattern through the extended. Upper level low and associated deep long wave trough will track slowly across the eastern half of the CONUS through week`s end. Short wave ridging will then transit the region before a second upper level low or trough drops out of Canada and into the Midwest and/or Great Lakes region. Most of the differences showing up after DY5 center around the evolution and timing of the second main storm system. The 0Z ECMWF is fastest with this system and the 6Z GFS the slowest. The 0Z Canadian appears to split the difference. The 12Z Canadian is showing better run to run continuity than the 12Z GFS and even trends closer to the ECMWF. The GFS suggests some phasing of the Canadian low with energy moving out of the Pacific, causing a futher deepening and digging of the system across the plains and into the Great Lake, a much slower and stronger solution overall. As a result confidence is quite low for the last 48 hours of the period. With respect to sensible weather, unsettled weather with periods of showers and thunderstorms will tend to keep daily highs near to or below normal levels for this time of the year and overnight lows above normal. Good forcing coupled with some instability will probably bring the threat of some thunder to the area on Wednesday. In addition, lowering freezing levels may allow for some of the showers/storms to contain small hail/graupel at times. A short lived window of dry weather can be expected across eastern Kentucky Friday, as the aforementioned transient short wave ridge moves across the Ohio and Tennessee Valleys. The threat of rain returns to the area Friday night and lingers through the weekend. && .AVIATION...(For the 06Z TAFS through 06Z Tuesday night) ISSUED AT 121 AM EDT TUE MAY 23 2017 The TAF period will be met with VFR and this is expected to be the prevailing through the period. We are watching an upper level wave to our south that is bringing mostly high clouds into the region this early morning hour. This nearby wave could induce showers and perhaps a few isolated thunderstorms for Tuesday into Tuesday evening. The better forcing should be in the TN Valley and therefore keep best POPs nearer the VA border with a sharp cutoff to the NW. Did add some VCSH and -SHRA to most of the sites given this nearby disturbance, but confidence remains low on how much activity in fact makes it into the region given the low level flow. Winds are expected to remains light through the period. && .JKL WATCHES/WARNINGS/ADVISORIES... NONE. && $$ UPDATE...DJ SHORT TERM...GREIF LONG TERM...RAY AVIATION...DJ

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