Area Forecast Discussion
Issued by NWS Jackson, KY

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000 FXUS63 KJKL 251738 AFDJKL Area Forecast Discussion National Weather Service Jackson KY 138 PM EDT MON JUL 25 2016 .UPDATE... Issued at 1126 AM EDT MON JUL 25 2016 Heat and humidity appears to be peaking today. Moisture pooling near the frontal boundary approaching from the north has sent dewpoints well into the upper 70s over our northern counties, with a few Mesonet stations approaching 80. With temperatures again forecast to reach the low 90s for most locations, this will put afternoon heat indices pretty solidly in the 100 to 105 degree range. I noticed several locations had heat indices briefly peak above 105 late yesterday afternoon. With increased cloud cover and at least scattered showers and thunderstorms expected to develop this afternoon, think most stations will stay below the 105 heat advisory criteria today. Did issue an SPS though since we will be close. Otherwise, forecast database looked good aside from a few upward adjustments to dewpoints per current obs. UPDATE Issued at 752 AM EDT MON JUL 25 2016 Isolated showers beginning to develop near the Bluegrass region back into central Kentucky. Will likely see these continue to develop and strengthen along an outflow boundary stemming from storms overnight across Indiana. && .SHORT TERM...(Today through Tuesday) Issued at 359 AM EDT MON JUL 25 2016 Upper trough swinging through Ontario toward Hudson Bay is currently pushing a frontal boundary through the eastern Great Lakes extending back through the central Plains and Missouri Valley. A broken line of showers and thunderstorms spans much of this region with plenty of moisture and instability to work with downstream. When this arrives locally will be dependent upon how quickly this activity progresses south and east without a significant meridional component to the mean layer flow this far south into eastern Kentucky. Upper ridging across the mid-Atlantic will also delay any of this preexisting convection in making headway through the Commonwealth by way of deep layer subsidence. An outflow boundary across southern Indiana may be the initial instigator of showers and storms later this morning across the Bluegrass region. Regardless if this initial round of storms fires this morning, many more will be in the forecast this afternoon and evening as moisture pooling along and ahead of the approaching boundary increases precipitable water values to near 2 inches. The continued presence of this sultry airmass combined with additional sources of lift will lead to a greater coverage of storms compared to that over the weekend. Storm motions this afternoon of near or below 10 mph combined with abundant moisture will promote the primary threat being heavy rainfall and potential flooding. Additionally, precipitation loading will promote the potential for gusty downburst winds as weak shear leads to quickly collapsing updrafts. Despite slowly lowering heights and lower thicknesses compared to Sunday, temperatures should still climb toward the lower 90s with heat indices once again near the 100F mark by mid afternoon. The potential for storms will continue overnight with eastern Kentucky remaining squarely in the warm/moist sector ahead of the frontal boundary which looks to likely stall in vicinity of the Ohio River. Scattered to perhaps numerous storms will be in the offing Tuesday afternoon as surface ridging across the Ohio Valley attempts to veer winds northwesterly and produce a period of enhanced low level convergence. Another upper wave on the heels of the previous one across Canada will act to keep quasi-zonal/cyclonic flow in place thus promoting passing pieces of energy capable of setting off storms in a warm/moist airmass. Deep layer shear may increase slightly to on the order of 20-25 knots Tuesday afternoon, but continued capping near 600 mb should once again prevent cores from developing substantially before downdrafts become dominant. Given greater cloud cover and more moist conditions along with lower heights aloft, high temperatures should finally top out a little more seasonable in the mid-upper 80s. .LONG TERM...(Tuesday night through Sunday) Issued at 359 AM EDT MON JUL 25 2016 Upper level ridging encompassing much of the southern half of the conus will continue to break down throughout the extended portion of the forecast, with two separated areas of high pressure forming...one over the four corner states, and one just off the southeast Atlantic coast. This will put the weak point across the Ohio River valley, which is where the epicenter for falling heights will be. An upper level low is expected to traverse James Bay in Canada to start the period, which will bring deamplified troughing to points south, including Kentucky. Multiple shortwaves will move through this trough axis, deepening the trough through the week. The first shortwave will be moving through the region as of 0z Tuesday, with multiple smaller waves expected through midweek. Models then show a stronger shortwave taking shape across the upper midwest Wednesday, digging the trough farther and continuing to lower heights across the upper Mississippi River valley and portions of the Ohio River valley. Latest model runs show a weak blocking pattern setting up, with the centers of low pressure centered to the southwest and the southeast of the trough, resulting in amplification but little movement through the first part of the weekend. Eastward progression finally takes control for Sunday, continuing into Monday, though at this point models start to diverge somewhat on their solutions. At the surface, a weak cold front will be moving into the state from the northwest to start the period. With the overall deamplified flow, the front will become elongated from west to east across the state, transitioning into a quasi-stationary boundary. This frontal boundary will then fluctuate slightly northward and southward throughout the rest of the week. As the blocking pattern breaks down late in the period, the frontal zone will finally make a push back southward across the state Monday, before finally exiting to our south by Tuesday. With this frontal zone in place, in addition to continued warm and muggy conditions, expect chances for showers and thunderstorms to occur each day. Peak coverage and intensity will likely be diurnally driven, during the afternoon/early evening. The main concern at this time will be storm motion. Though there will be some improvement going into the weekend, overall mean steering flow will be weak. Meanwhile lift and instability will be enough to spawn some potentially strong storms. In other words, expect pulsy slow moving storms with heavy rain potential, and the possibility of training storms as well...all of which could lead to urban and flash flooding concerns. Will continue to highlight these concerns in the HWO as of now. && .AVIATION...
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(For the 18Z TAFS through 18Z Tuesday afternoon) ISSUED AT 138 PM EDT MON JUL 25 2016 Scattered thunderstorms continue to erupt in a sultry airmass. These will likely remain rather hit and miss and will maintain no more than a VCTS mention in the TAFs for now. Expect these storms to exhibit a diurnal trend and diminish in coverage slowly after sunset, although there will be a small threat for a shower or storm anytime through the night and into tomorrow morning due to a frontal boundary sagging southward toward our area. Fog is another concern but it should remain patchy and is likely to only affect TAF sites that are hit directly by a thunderstorm this afternoon. With that in mind, will go with VFR TAFs for now through 18z Tuesday and let later shifts fine tune.
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&& .JKL Watches/Warnings/Advisories... None. && $$ UPDATE...ABE SHORT TERM...GUSEMAN LONG TERM...JMW AVIATION...ABE

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