Area Forecast Discussion
Issued by NWS Jackson, KY

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444 FXUS63 KJKL 232100 AFDJKL AREA FORECAST DISCUSSION National Weather Service Jackson KY 400 PM EST Thu Feb 23 2017 .SHORT TERM...
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(This evening through Friday night) Issued at 400 PM EST THU FEB 23 2017 South-southwest flow aloft will keep our weather warm through the short term. Potent trough/low will plow into Great Lakes Region swinging a trough through the Commonwealth by late in the period. At the surface, high pressure is anchored over the Appalachians with a nearly stationary frontal boundary draped from roughly DTW southwest to STL. Low pressure currently taking shape over the central plains will march east-northeast along the boundary and into the Great Lakes by late Friday night. This feature will also pull a cold front eastward through the region, and into eastern Kentucky Friday night. This dynamic storm system could bring a round of severe weather to our forecast area Friday night. Main threat at this time appears to be winds, with hail being a secondary threat. Shear is quite strong with this system as well. Consequently could not rule out an isolated tornado. Gradient winds will increase across the area Friday ahead of the system, and from all appearances will become gusty. Main limiting factor to severe weather will be moisture as dew points struggle to climb to near 60 Friday into Friday night. Timing of the cold front is also not favorable for severe weather as it will not enter into our area until sometime just after midnight. Consequently any nocturnal inversion that develops will have to be scoured out, though surface gradient winds appear to be able to do just that, but generally only as the frontal boundary is approaching. Bulk shear is quite strong with this system as well, 40-60 kts, with the majority of the shear realized in the lowest 3 km. Thus the potential for bowing cells and line segments will be favored. Surface based instability to support this storm mode is not ideal but does appear to be sufficient, again mainly just ahead and with the frontal boundary itself. This has a distinctive QLCS flavor to it and considering the environment as a whole feel an isolated tornado can not be ruled out, though features of this type tend to be weaker than most and short lived. Strong gradient winds mixing down may have the potential for more damage should they occur. Low wet bulb temperatures and freezing levels mean hail is a possibility as well. .LONG TERM...(Saturday through Thursday) Issued at 400 PM EST THU FEB 23 2017 The long term portion of the forecast will be active, with several systems affecting the area. However there remains considerable uncertainty on the timing, track and strength of a series of short waves and associated surface lows and fronts that will affect the area next week. By 12Z Saturday the cold front which brings our severe weather threat Friday night will be east of the area, but some showers will linger across the area mainly during the morning. Gusty west winds will usher in cooler air on Saturday, with lows by Sunday morning expected to dip down into the mid to upper 20s. Surface high pressure will be over the area Sunday morning, but will shift to the east during the day. This result in dry weather Sunday with near normal afternoon temperatures in the upper 40s to lower 50s. The mean flow for the first half of next week will be southwesterly with a mean long wave trough axis centered over the western part of the country. This will result in warming temperatures with highs back in the 60s for Tuesday and Wednesday. The first in a series of short waves looks to affect the area from Sunday night into Monday, with rain shower chances increasing from Sunday night into Monday. If precipitation moves in quick enough Sunday night a few flakes of snow could mix with the rain before changing to all rain quickly by Monday morning. Tuesday still remains one of the least certain days of the forecast, with the GFS quickly moving out Monday`s system, while the ECMWF points to lingering rain chances for Tuesday. We will continue to follow the blended forecast for Tuesday which maintains rain chances but with probabilities generally lower than on Monday. There is better agreement that a stronger short wave, surface low and associated cold front will bring a better chance of showers and thunderstorms on Wednesday. In fact we will be be going with likely rain probabilities Wednesday. After the cold front passage cooler air will spread into the area Wednesday night and Thursday.
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&& .AVIATION...(For the 18Z TAFS through 18Z Friday afternoon) ISSUED AT 131 PM EST THU FEB 23 2017 Seeing isolated reports of marginal MVFR CIGS. Exception being SYM which is under a band of considerably thicker cloud cover. This band is pushing northward and should be north of SYM by around 19Z. Elsewhere CIGS should lift a bit more with afternoon heating. Seeing some decent CU developing across our southwest but not seeing anything on radar yet. Forecast soundings suggests a cap may be building across the area that would otherwise help retard development. However, could not rule out a renegade shower. Looking at VFR conditions for the remainder of the forecast period. Winds will be the main challenge as gradient winds increase ahead of an approaching cold front. Maintained some non- convective LLWS for our valley sites through the predawn hours as a southerly jet begins to increase across the area just above the boundary layer. Winds will continue to increase through the day Friday as the nocturnal inversion mixes out. In addition, winds will become gusty through the afternoon. May have underplayed gusts just a bit for late in the period but forecast soundings suggest the greater threat for highest gusts was beyond the TAF forecast period, or after 18Z. && .JKL WATCHES/WARNINGS/ADVISORIES...NONE. && $$ SHORT TERM...RAY LONG TERM...SBH AVIATION...RAY

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