Area Forecast Discussion
Issued by NWS Jackson, KY

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000 FXUS63 KJKL 261147 AFDJKL AREA FORECAST DISCUSSION National Weather Service Jackson KY 747 AM EDT Fri May 26 2017 .UPDATE...
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Issued at 747 AM EDT FRI MAY 26 2017 Low clouds have just about cleared out of eastern Kentucky this morning. Fog has mostly mixed out and dissipated everywhere but down inside deeper valley locations, with this expected to also mix out within the next hour or so given abundant sunshine. Next notable feature of interest will be storms approaching from the northwest later this evening into tonight following a dry and mostly sunny Friday.
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&& .SHORT TERM...(Today through Saturday) Issued at 359 AM EDT FRI MAY 26 2017 Cloud cover continues to push east and dissipate early this morning as a surface ridge axis, extending from Florida to Lake Superior, shifts overhead. This will continue to bring areas of fog to portions of eastern Kentucky through mid morning, including some of this becoming dense in river valleys. Increasing heights aloft downstream of shortwave upper ridging building into the Great Lakes and Ohio Valley will provide for further subsidence, leading to a dry Friday across eastern Kentucky. Stout warm air advection will result in a drastic warmup compared to Thursday, with highs climbing into the upper 70s to right around 80 degrees this afternoon. Shower and thunderstorm chances will increase late this evening and tonight as surface low pressure ejects out of the Missouri Valley into the Ohio Valley, lifting a warm front through Kentucky toward the Ohio River. This along with the first round of shortwave impulses, stemming from an upper low across Manitoba, will serve as focus for convection through tonight. Best chances across eastern Kentucky will thus reside north of the Interstate 64 corridor nearer the greater forcing for ascent. The threat for showers and storms will continue Saturday morning. Elevated bases will begin to become rooted nearer the surface by mid- late morning through the afternoon as diurnal heating allows for steepening low level lapse rates. Not expecting more than scattered shallow-top storms through early afternoon as upper heights will be near-neutral with the core of the upper low still well back to the northwest. Greater heating through the mid-late afternoon combined with arrival of additional shortwave energy and a frontal boundary drawing nearer should support high-end scattered to perhaps numerous coverage. Deep layer shear of 30-40 knots in tandem with surface-based CAPE values approaching 2-3 kJ/kg and dewpoints in the upper 60s should support sustained updrafts, capable of a few robust multicellular storms. Southwest surface winds will provide for weak directional shear and thus a rather low threat for any defined supercells. Hail should be limited given rising freezing levels and greater moistening negating the effect of any wet bulb cooling. Strong to severe winds will certainly be possible underneath collapsing downdrafts, especially by mid-late afternoon. .LONG TERM...(Saturday night through Thursday) Issued at 336 AM EDT FRI MAY 26 2017 The period will start with some weak shortwave ridging over the area Saturday evening. However, convection upstream fueled by a vort max pushing across the area will bring a complex of showers and storms into the Ohio valley region sometime late Saturday night or early Sunday. Timing and areal extent of this activity remain in question. With PW values increasing to just above 1.40 inches, locally heavy rainfall would be a possibility wherever storms do track. Models have all kinds of convective feedback, but the actual vort max aloft should move through early Sunday morning, so that will likely be a period of higher rain chances. While mid level lapse rates are somewhat steep early Sunday, shear is not tremendous, so would not anticipate a big severe weather threat with the early day activity. This all changes as we head through the afternoon and evening hours on Sunday. Models have just above 3000J/KG of SBCAPE developing across the area by mid afternoon on Sunday with LI`s down around -10C. Thus, instability will not be lacking. Shear will also increase, but will be mainly speed shear as very little turning of the winds through the column. There is also quite a bit of dry air in the mid levels which may help to aid in the threat for damaging winds. DCAPE in fact is near 1000J/KG, which is right about what you need for a good damaging wind threat. We also have steep mid level lapse rates supporting a modest hail threat. Now the question is how will convection evolve or materialize? Well, this is not an easy question at this point as early day convection may help to lay out potential boundaries for later convection in the afternoon. The potential for training storms and continued high PW values will lead to a continued threat for flash flooding through at least Sunday evening. Will hold off on any watch right now, but may eventually need to consider one for some of the area. By late in the day, a cold front will bear down on the area and assuming airmass remains untapped, we could see showers and storms develop along this boundary. Either way, it looks like a decent threat of severe weather/flooding at some point on Sunday. Its just a matter of fine tuning the details in the upcoming forecast. For now, given its still 3 days out, highlighting the threat in the HWO and weather stories is the way to go right now. Front sweeps on through by early Monday morning leaving behind a few days of dry weather through Tuesday and perhaps even lasting into Wednesday. Weather may turn more unsettled again by late Wednesday or Thursday of next week. && .AVIATION...
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(For the 12Z TAFS through 12Z Saturday morning) ISSUED AT 747 AM EDT FRI MAY 26 2017 VFR conditions expected to hold strong today and tonight as an approaching ridge of high pressure builds in. May still see some fog inside deeper valleys through mid this morning, but all TAF sites should remain fog free. Southwest winds will increase to 5-10 knots by mid-late morning through this afternoon before diminishing somewhat this evening. Will have to watch a potential round of showers and thunderstorms this evening near the Ohio River, but have kept any SH/TS or CB mention silent for now until trends in this development become better defined. Southwesterly low level wind shear may also warrant watching for this evening, but this currently looks too weak, around 30 knots, to be concerned with at this time.
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&& .JKL WATCHES/WARNINGS/ADVISORIES... NONE. && $$ UPDATE...GUSEMAN SHORT TERM...GUSEMAN LONG TERM...KAS AVIATION...GUSEMAN

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