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Area Forecast Discussion
Issued by NWS Jackson, KY
Issued by NWS Jackson, KY
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342 FXUS63 KJKL 201410 AAA AFDJKL AREA FORECAST DISCUSSION...UPDATED National Weather Service Jackson KY 1010 AM EDT Sat Jul 20 2024 .KEY MESSAGES... - Showers and thunderstorms will impact the region at times over the next week. Probabilities will generally peak each afternoon and evening. - Highs will be near normal to about 5 degrees below normal throughout the period, with humidity running high. && .UPDATE... Issued at 1010 AM EDT SAT JUL 20 2024 13Z sfc analysis shows a nearly stalled frontal boundary slipping north into eastern Kentucky this morning. This is providing a focus for shower development and eventual thunderstorms in accordance with the higher amounts of moisture brought to the region. Currently, temperatures are running in the mid 60s with the rain and up to the mid 70s in the south and western parts of the area where the clouds are less and thinner. Meanwhile, amid light winds, dewpoints have returned to near 70 degrees in the south while lower and middle 60s are found over much of the rest of eastern Kentucky. Any early morning fog has cleared out, as well. Did update the forecast mainly to fine tune the PoPs through the day per the latest radar images and CAM forecasts. Did also add in the current obs and trends for the T/Td/Sky grids. These minor adjustments have been sent to the NDFD and web servers along with a freshening of the zones and SAFs. UPDATE Issued at 758 AM EDT SAT JUL 20 2024 Showers were occurring over portions of east central KY and over the western portions of the CWA with precipitation more of the stratiform nature along the VA border. Short term guidance to a large degree was not handling the showers all that well, and per extrapolations this should continue northeast over the next couple of hours as a shortwave passes. Adjustments were made to pops for the next 3 hours or so as well as thunder probabilities accordingly. && .SHORT TERM...(Today through Sunday) Issued at 455 AM EDT SAT JUL 20 2024 The large scale flow pattern will feature troughiness in place over the southeastern CONUS, with troughs of low pressure also in place over the Pacific Northwest and on down the west coast into the desert southwest. The prominent feature in our part of the country is an extensive frontal boundary that is currently stretching from the southeastern coast, through the Tennessee Valley and southern Mississippi Valley and on into southern Texas. Extensive ridging is in place from New England, through Great Lakes and Ohio Valley regions, and out across the Great Plains. The ridging also extends across and just to the west of the Rocky Mountains. We`re looking a pretty much the same story in the short term as we`ve seen over the past few days. The models are still showing differences in overall timing and coverage of showers and storms across the area this weekend, so there is still some uncertainty with the finer details of the forecast. However, the trend does still seem to be for showers and storms to move in from the south and southwest the next couple of days, as disturbances move from west to east along the front that is still parked just to the south of our area. Shower and storm activity should peak during the afternoon and early evening hours both today and Sunday and when southern stream waves of low pressure move close by, thereby pushing the front north into our area from time to time. We should see activity slack off quickly after sunset tonight, with dry weather expected until very early Sunday morning, when frontal waves begin moving northward toward the area again, bringing showers and storms back in that will peak in coverage Sunday afternoon. We are expecting warm and muggy conditions around the area over the weekend, but with highs only expected to rise into the low to mid 80s for most locations today and Sunday, the heat should be bearable. There are no significant weather concerns to speak of at this time. We will, however, advise everyone to take the necessary precautions if outdoors while a thunderstorm is approaching, as cloud to ground lightning will still pose a hazard that folks need to be aware of today and tomorrow. .LONG TERM...(Sunday night through Friday) Issued at 500 AM EDT SAT JUL 20 2024 The period is expected to begin with an upper level ridge extending from portions of the western Atlantic into the Gulf of Mexico with another ridge centered over the western Conus. In between, an upper level trough is expected to expected to extend from Canada across the Great Lakes region into portions of the Central Conus toward the Arklatex region to southern Plains. Through the middle of next week, upper level ridging is expected to remain in place from the western Atlantic into the Gulf of Mexico. Another upper level ridge will remain centered over the western/southwestern Conus, but this one builds gradually into the Plains. The 500 mb trough axis should continue working further east and southeast across the Great Lakes and into the Northeast to mid Atlantic to the Lower OH Valley. The axis of this trough should near the region toward end the period, though model guidance varies from model to model and run to run with this timing. At the surface, as the trough evolves to the west, a quasi stationary front located east and southeast of the upper trough and more or less the leading edge of deeper moisture across the Southeastern Conus is expected to gradually lift north to near or just north of the OH River as a warm front. This boundary will become diffuse by midweek and serve as a focal point for convection. A separate frontal zone should gradually drop into the Great Lakes in the early part of the long term forecast period, before settling near the OH River to end the period. This will occur in tandem with a shift in the 500 mb trough across the Great Lakes into the Northeast and mid Atlantic states. In the southwest flow ahead of the trough axis, multiple shortwave troughs should impact the region. However, the low predictability of timing of any individual shortwaves into the OH Valley and Appalachians leads to low confidence in details. In general, pops generally had a bit of a diurnal flavor through the period, with the most likely time for the greatest coverage of convection occurring from mid afternoon to early evening each day. Although chances for convection will generally be a bit lower each time, pops of at least isolated to scattered ranges were carried each night. Moisture will increase to begin the period across the region. South to southwest flow between the upper ridging generally extending from near Bermuda to the eastern Gulf of Mexico and upper level troughing extending from eastern Canada into the upper MS Valley/Central Conus to Southern Plains will transport moisture into the Appalachians and OH Valley regions. Per 00Z LREF mean, PW is forecast to initially be in the 1.5 north to 1.6 inch south range Sun evening, before increasing to 1.3 north to 1.5 south around 0Z Monday, the 1.6 to 1.7 inch range on Monday, 1.7 to 1.8 inches Tuesday, and peaks in the 1.7 to 1.9 range at mid week, before decreasing to the 1.5 to 1.7 inch range to end the period. Values in the 1.7 to 1.9 inch range would be close to the 90th percentile for the timeframe for the region. Any repeated rounds of convection or training across over multiple days could eventually lead to hydro concerns. WPC EROs for the Day 3 to Day 5 periods from Monday to Wednesday night include some or all of eastern KY in a marginal risk. Day 4 from Tuesday to Tuesday night appears to be the peak of the threat when all of the the region is in a marginal risk of excessive rainfall. Some concern of possible localized issues could linger beyond that point particularly in the south where moisture is forecast to remain deepest ahead of the approaching trough axis and frontal zone settling into the OH Valley region. With the trough in place, clouds should be quite prevalent throughout the period, especially during each afternoon and evening. This and anticipated convection from time to time will lead to highs near if not as much as 5 degrees below normal for this time of year. Normal highs outside of the highest terrain are generally in the mid 80s. With increasing moisture at the surface and through the column, diurnal ranges will be a bit limited as well with lows anticipated mainly in the mid to upper 60s. && .AVIATION...(For the 12Z TAFS through 12Z Sunday morning) ISSUED AT 805 AM EDT SAT JUL 20 2024 Any lingering valley fog will dissipate by no later than 13Z and the TAF sites are not affected. Showers will affect some locations with generally no reductions below the VFR range this morning, with additional convection anticipated during the afternoon and evening, with coverage peaking between roughly 17 and 23Z. All of the TAF sites could be affected with KSYM having the lowest chances. Low and mid level clouds may scatter out after 0Z and this could give way to some fog formation or low clouds late in the period, especially where heavier rain falls later today. Confidence in timing and what areas may be affected is low. Winds should generally be light and variable through out the period. Any TAF site that experiences a thunderstorm could experience breif periods of MVFR or even IFR conditions and a stronger wind gusts. && .JKL WATCHES/WARNINGS/ADVISORIES... NONE. && $$ UPDATE...GREIF SHORT TERM...AR LONG TERM...JP/Marcus AVIATION...JP