Area Forecast Discussion
Issued by NWS Jackson, KY
Issued by NWS Jackson, KY
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905 FXUS63 KJKL 041719 AFDJKL AREA FORECAST DISCUSSION National Weather Service Jackson KY 119 PM EDT Thu Jul 4 2024 .KEY MESSAGES... - Sultry weather continues through Friday. Afternoon heat indices may reach near 100 in some locations. There is also a persistent threat of thunderstorms through Friday, especially during daytime hours. A few thunderstorms could produce locally heavy rainfall and strong wind gusts. - A cold front finally pushes through as we move into the weekend, with dry and somewhat cooler and less humid weather arriving. - Warmer and more humid conditions will make a noticeable comeback on Monday and continue into the week, along with a potential for more thunderstorms. && .UPDATE... Issued at 119 PM EDT THU JUL 4 2024 ...MESOSCALE UPDATE... A moist air mass over central and eastern Kentucky is beginning to heat up and destabilize in the wake of earlier cloud cover and convection, much of which is exiting into the mid-Ohio Valley. Recent observations at LEX shows a temperature of 90F with a dew point of 75F and Kentucky Mesonet observations indicate dew points in the 72-80F range across across all of central Kentucky. A strong line of thunderstorms has developed along a weak cold front, extending from roughly Madisonville, KY to just west of Louisville, KY. CAMs are struggling to resolve this convection as it presses east and forecaster confidence in their solutions is low. The latest HRRR runs for example, largely show the line of storms dying out as mixing causes dew points to fall back in the 60s -- improbable. The latest mesoanalysis already shows 4,000 J/kg of SBCAPE across central Kentucky (well above that indicated by most of the CAMS) where heating has been most intense. Additionally, increasing flow aloft will lead to increasing effective wind shear reaching 30 to 35 knots roughly near and north of the Mountain Parkway late this afternoon. As long as heating over eastern Kentucky is not substantially hindered by ongoing spotty shower and thunderstorm activity, conditions appear favorable for this upstream line of shower and thunderstorms to intensify as it moves through central Kentucky and then only gradually weaken as it moves through eastern Kentucky late this afternoon and early evening. North of the Mountain Parkway, shear should be sufficient for a few thunderstorm line segments and perhaps embedded supercell structures with primarily a damaging straight-line wind threat. An isolated weak tornado also cannot be ruled with any supercells given moderate low-level bulk shear (up to ~20 knots from sfc-1 km) and modest turning in the low-level hodograph. South of the Parkway, lower shear will tend to favor less organized storm structures, though steep low-level lapse rates, PWATs values of 2.0 to 2.25 inches, and high levels of instability could still favor precipitation-loaded downdrafts collapsing and leading to sporadic downbursts/microbursts. UPDATE Issued at 1205 PM EDT THU JUL 4 2024 Hourly grids were updated to account for observation as well as radar/convective trends. Measurable rain was occurring with showers and some embedded thunderstorms moving across the northern and northeastern portions of the CWA. Much of central KY was devoid of convection at this point, though a warm and moist airmass was leading to increasing instability ahead of convection that is nearing the OH River vicinity at this time. A shortwave trough/instability was also helping to maintain this convection. Convection ongoing over northern and eastern sections of the area should depart over the next couple of hours. Then a round of heating is anticipated over the entire CWA and during the mid to late afternoon, when the activity to the west should approach. By that point, MLCAPE may reach 1500 to 2500 J/kg courtesy of dewpoints in the 70s while shear will be limited. In the south near 20KT effective shear is forecast at 20Z, but 25 to 35KT effective shear is forecast at that point in the north. Some organized convection is possible with these parameters, with locally heavy rain a threat as PW should remain around the 2 to 2.2 inch range along with a threat of locally strong to damaging wind gusts. Some recent HRRR runs track a more robust cell from north central/northern KY with decent 2-5km UH toward the Fleming County vicinity during the late afternoon or roughly into the area when SPC 13Z SWODY1 added in a slight near and north of Interstate 64. Convective trends for mid to late afternoon to early evening will continue to be monitored. After the potential for stronger activity during the late afternoon and evening sliding across at least northern portions of the area, a decrease in coverage of activity should occur toward sunset. UPDATE Issued at 841 AM EDT THU JUL 4 2024 Showers are starting to break out over our western counties. These should continue to expand today. Have updated the POP based on latest model runs, which incorporates a slight shift northward for the likely POP. && .SHORT TERM...(Today through Friday) Issued at 546 AM EDT THU JUL 4 2024 A weakening, stalled frontal boundary is laid out north of the Ohio River early this morning. Its exact position is a bit muddled due to weak surface winds and prior convection. In the upper levels, we reside along the southern edge of the prevailing westerlies, with a weakening high over the Deep South and multiple waves propagating through the westerlies to our our north. Aside from a stronger wave over the northern plains, the features aloft are very weak and difficult for the models to handle. However, our atmosphere is warm/moist and easily destabilized with lifting and/or diurnal heating. That being the case, will look for more convection to develop along and south of the frontal boundary today, but exactly how it plays out is uncertain. Mesoscale features will play a significant role. Using a blended solution from models, will expect convection to pick up as we move into the day, with the greatest coverage over our northern and eastern counties today. The activity should again diminish to some extent as we move into the night. The aforementioned upper level wave over the northern plains will strengthen as it moves east and will lead to a larger scale trough developing over the Midwest by Friday. This will support a strengthening surface low tracking east over the Great Lakes on Friday, which will propel a cold front east southeast into Kentucky. The front will work in combination with the deepening upper level trough and strengthening flow aloft to bring a likelihood of showers and thunderstorms area wide on Friday. Precipitable water should remain near or above two inches through the short term period, which will allow thunderstorms to be efficient rain producers. Should any training of cells occur, there remains a possibility of localized hydro problems. Pockets of higher instability could lead to some strong storms in the afternoon or evening hours. Flow aloft will also be increasing during the short term period, which would be more supportive of some organization and a severe threat. Even so, it does not look overly impressive. .LONG TERM...(Friday night through Wednesday) Issued at 349 AM EDT THU JUL 4 2024 The forecast period begins with the CWA in the midst of FROPA as a cold front is slowly moving through the area. A surface low moving through the Great Lakes will drag the front through the area with showers and thunderstorms occurring at the start of the period. The front will gradually exit the region Saturday afternoon with high pressure building in and remaining overhead for Sunday into Monday. Models continue to hint at the continuation of an active pattern into next week. However, in this evening/overnight model suite, long- term deterministic models begin to diverge on how upper-level forcing will play out for next week. The GFS continues with a dry streak into Tuesday morning before dragging a cold front through the Commonwealth late Tuesday evening. The ECMWF is a little more active with PoP chances building in for Monday night before a surface low moves through the Great Lakes and drags a surface boundary through the area Tuesday afternoon. However, both models keep PoP chances overhead through the remainder of the forecast period. Nonetheless, with the discrepancies between deterministic runs, opted to stick with a weighted NBM solution that keeps periods of showers and storms through the remainder of the forecast period. Overall, the period will highlighted with periods of showers and thunderstorms that`ll bring much needed rain to the area. Also, temperatures will return to more seasonal ranges as daytime highs in the mid-80s to low-90s and overnight lows ranging from the upper-50s to upper-60s. && .AVIATION...(For the 12Z TAFS through 12Z Friday morning) ISSUED AT 841 AM EDT THU JUL 4 2024 Showers/thunderstorms were starting to redevelop between KSME and KIOB at the start of the period. They should continue to expand in coverage as we move into the day, with the greatest coverage likely to be north of the Cumberland Basin. Activity should decline again as we move into the evening. They will not be continuous at any given location, and it would be very difficult to pin down timing. That being the case, VCTS was used in most TAFs. Precipitation will bring sub-VFR conditions to many locations for a time. Outside of precipitation, mainly VFR conditions are expected. Valley fog is a possibility tonight, but the extend will depend on the coverage of rain during the late day and evening and the amount of cloud cover tonight (fewer clouds - more fog). && .JKL WATCHES/WARNINGS/ADVISORIES... NONE. && $$ UPDATE...GEERTSON SHORT TERM...HAL LONG TERM...VORST AVIATION...HAL