Area Forecast Discussion
Issued by NWS Jackson, KY

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758 FXUS63 KJKL 190918 AFDJKL AREA FORECAST DISCUSSION National Weather Service Jackson KY 418 AM EST Fri Jan 19 2018 .SHORT TERM...
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(Today through Saturday) Issued at 359 AM EST FRI JAN 19 2018 Early this morning, a trough extended from the Canadian Maritimes into the Mid Atlantic States. A shortwave ridge was off the mid Atlantic states while a shortwave trough with little moisture extended from the OH Valley to TX. At the surface, high pressure was centered over the Gulf Coast States with ridging north into the Appalachian region. A considerable ridge to valley temperature split was in place this morning, with some of the normally colder valley locations in East KY around 10 above at this time and ridges and more open terrain areas in the low to mid 20s. 850 mb temperatures have warmed considerably over the past 24 hours and were around 1C at this time. Snow cover remains in many locations with about 2 inches at JKL with 2-4 inches likely in many locations, with lesser amounts on south and west slopes and in some deeper valleys. The snow cover and cold valley start should again limit how far temperatures can climb today despite continued warm advection as the center of the surface high moves to the south and east with return flow between this high and lower pressure over the High Plains continues. 850 mb temperatures should moderate to around 4C by this evening and or roughly 3 or 4C higher than Thursday evening. This and less of a snow pack and mostly sunny skies with just some high clouds should yield high temperatures around 10F higher than Thursday. The MET MOS seems to again be a high outlier with the MAV MOS and Superblend in the low to mid 40s or very close to normal for this time in January. Did not stray far from the Superblend guidance though with the snow cover opted to undercut it by about a degree or two. High pressure will remain across the Southeast Conus tonight and into the day on Saturday. However, models have a west to west southwest low level jet developing tonight and into Saturday which combined with an upper low moving into the Southeast bring increasing low level and moisture and clouds late tonight and into the day on Saturday. After another night with rather steep nocturnal inversion and ridge/valley temperature split and normally colder eastern and southeastern valleys in the upper teens to around 20 and ridges in the upper 20s to around 30, the increasing low clouds should suppress highs on Saturday below previously forecast values in the mid 50s to closer to Superblend numbers nearer to the 50 degree mark. The low level moisture will increase in depth on Saturday and some sprinkles or light drizzle cannot be ruled out completely late on Saturday or Saturday evening. Confidence in timing of the moisture increase and depth was not high enough just yet to introduce any sprinkles or slight pops late in the period. At this time any measurable precipitation should hold off until the start of the long term period when low level moisture will deepen further. .LONG TERM...(Saturday night through Thursday) Issued at 350 AM EST FRI JAN 19 2018 The models are in reasonable agreement with the long wave pattern for most of the extended period. The period will begin with the closed near the Gulf Coast region and pseudo zonal pattern across the Ohio Valley. The system of interest for the period will be centered near the four corners region. This upper level closed low will eject into the Central Plains by Sunday and eventually move into the Upper Midwest by the Monday. This upper low will track across the Great Lakes Monday night into Tuesday and then the pattern flattens again in wake of the upper level trough. The period will begin will solid return flow in place across the Ohio and Tennessee Valleys. The issue for Saturday night into Sunday will be the isentropic lift ahead of the approaching cold front. We will see enough low level moisture in place to produce some light rain and maybe even drizzle at times Saturday night into Sunday. This shallow moisture will begin to lift by late Sunday afternoon into Sunday and provide a brief period of dry weather. As the closed low ejects into the Central Plains it will bring a PV anomaly east and lead to deepening of a surface low as it moves northeast into the Upper Plains. This previously mentioned system will eventually send a cold front across the Ohio and Tennessee Valleys and lead to widespread rain showers across the region Monday into Monday evening. The timing on the front has been a bit slower in the ECMWF compared to the GFS, but given the front and low level jet felt the categorical POPs were warranted. In the wake of the front the models disagree on the amount of left over moisture Monday night into Tuesday. Given this will stick with the lower blended guidance for now. The soundings do suggest you get into the ice eventually so at least some spots could see a mix of rain and snow before the better moisture exits. It should be mentioned, ahead and on the backside of this system will be the potential for gusty winds given the tightening pressure gradient and strengthening low level jet. We will be cooler and drier in the wake of the cold front Tuesday into Wednesday night, but these numbers will be close to normal values for this time of year, with highs in the low to mid 40s and lows in the upper 20s.
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&& .AVIATION...(For the 06Z TAFS through 06Z Friday night) ISSUED AT 135 AM EST FRI JAN 19 2018 High pressure across the southeast Conus will lead to mostly clear skies and VFR conditions with winds of 10KT or less through the TAF period. && .JKL WATCHES/WARNINGS/ADVISORIES... NONE. && $$ SHORT TERM...JP LONG TERM...DJ AVIATION...JP

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