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Area Forecast Discussion
Issued by NWS Jackson, KY
Issued by NWS Jackson, KY
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365 FXUS63 KJKL 040749 AFDJKL AREA FORECAST DISCUSSION National Weather Service Jackson KY 349 AM EDT Thu Jul 4 2024 .KEY MESSAGES... - Sultry weather continues through Friday. Afternoon heat indices may reach near 100 in some locations. - A potential for rain arrives tonight and lasts at least into Friday night. A few thunderstorms on Thursday and Friday 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. && .UPDATE... Issued at 1042 PM EDT WED JUL 3 2024 The NBM seems to continue to have a good handle on PoPs, so blended in the latest NBM PoPs with inherited PoPs from the afternoon forecast package through early afternoon Thursday. Changes otherwise were minimal, mainly to blend the forecast with the latest hourly temperature and humidity observations. UPDATE Issued at 711 PM EDT WED JUL 3 2024 The early evening update raises PoPs along Interstate 64 and points north in accordance with more CAMS indicating convection impacting this area this evening into the overnight. Most of these CAMS indicate that the current activity will move into northern parts of the forecast area later this evening, generally weakening as they do so especially daytime heating diminishes. Other changes were minimal and were to blend in latest observed temperatures with the forecast for the next several hours. && .SHORT TERM...(This evening through Thursday night) Issued at 430 PM EDT WED JUL 3 2024 Late this afternoon, an upper level ridge of high pressure was centered across the southeastern Conus and extended into the Northeast Conus and west to TX. Meanwhile an upper level low was centered over northern Canada with a broad trough to the south and southwest into the Upper MS Valley to Four Corners vicinity and another upper level ridge was in place over the eastern Pacific. At the surface, a frontal zone extended from Quebec to the eastern Great Lakes to mid MS Valleys to the southern Plains with a ridge of sfc high pressure extending from the Southeast Conus to off the eastern seaboard. Southerly flow continues to advect a warm and moist airmass into the region with dewpoints in the mid 60s in the higher terrain along the VA border and then upper 60s to low 70s elsewhere. Meanwhile, PW continues to increase with about 1.5 inches in Pike County to near or in excess of 1.8 inches in the west. Ahead of the boundary, convection has developed from OH southwest into portions of IN and western KY. An isolated shower has recently developed to the west of the Lake Cumberland area. Thus far, cirrus has been thick enough for temperatures in the central and southern portions of the area from reaching 90 or higher for the most part. This evening and tonight, the axis of upper level ridging is expected to shift east and south with the ridge weakening a bit. At the same time, a gradual trend of height falls is expected over the Lower OH Valley region and the Commonwealth as the rather broad area of upper level trough begins to expand east into the Great Lakes and MS Valley. One or more weak shortwaves or impulses may track into or near the OH Valley late tonight. PW should increase tonight, especially across the northern two thirds of the region nearer to the sfc cold front as the boundary sags toward the OH River. PW may remain near 1.7 to 1.8 in the southeast, but climb to 2 to 2.25 inches further north and west. This would bring PW values well above the 90th percentile and as high as the 95th to 99th percentile. Convection ahead of the boundary may spread southeast and into the area during the evening or possibly an outflow from that activity may arrive as well. This and the subtle height falls could lead to isolated to scattered activity mainly in the evening and then later at night. The highest probability for any storms is north of the Mountain Parkway. With the boundary becoming nearly parallel to the upper flow and the high PW values, some spotty very heavy downpours may occur. Thursday, the boundary should remain nearly stationary near the OH River before gradually becoming a bit diffuse while a shortwave trough/impulse moves across the OH Valley region on Thursday. On Thursday night, another stronger shortwave to the south of an upper low moving from the Plains and upper midwest to near the western Great Lakes approaches the OH Valley preceded by a cold front. PW during this time should climb to around or in excess of 2 inches areawide or well above the 90the percentile. With the boundary to the north and generally parallel to the upper flow, the threat of some training cannot be ruled out. Although mid level level lapse rates will be meager, steep low level lapse rates on the order of at least 7 to 8C/km may develop and MLCAPE may reach at least 1000 to 2000 J/kg in the afternoon to early evening if not a bit higher near 2500 J/kg in the southwest where less heating may contribute to temps near 90 with mid 70s dewpoints expected. Bulk shear will be a bit limited though possibly peaking near 20KT in the south and approach 30KT in the north. This might allow for some multicells or line segments to form if cold pools were able to amalgamate and given the high moisture content in the column a microburst or two cannot be ruled out. Some strong to locally damaging wind gusts will be a threat with convection for the Independence Day holiday along with torrential downpours. Coverage of convection may peak during the afternoon to early evening per recent CAMS and then decrease in coverage as the impulse departs during the evening, though confidence in this timing and coverage scenario is not high. In between shortwaves a lull in coverage in the late evening into the overnight may occur with a possible uptick in coverage again toward dawn on Friday ahead of the cold front and next shortwave. Current dewpoints and guidance suggest most locations will not fall below 69 or 70 tonight with coalfield ridgetops and more open terrain areas likely not falling below the mid 70s unless wetbulbing form convection occurs there. Otherwise, more in the way of cloud cover is expected in the north on Thursday nearer to the boundary with mid 80s north and upper 80s to low 90s south for highs. Dewpoints should be well into the 70s with heat indices peaking in the low 90s north and mid 90s to around 100 south. .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 06Z TAFS through 06Z Thursday night) ISSUED AT 229 AM EDT THU JUL 4 2024 A few showers/thunderstorms were affecting the far northern portion of the forecast area around KSYM at the start of the period, while others in central KY were heading eastward. Although new cells occasionally pop up, the activity continues on an overall decline and is unlikely to affect TAF sites. Outside of the precip or some spotty valley fog in far southeast KY, VFR conditions are expected into the day. Showers/thunderstorms are forecast to develop during the late morning and last through the afternoon. 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 TAFs with the realization that it is likely that at some point in time there will be precipitation with sub-VFR conditions. Precipitation is expected to diminish late in the day into the evening, leaving mainly VFR conditions. && .JKL WATCHES/WARNINGS/ADVISORIES... NONE. && $$ UPDATE...CMC SHORT TERM...JP LONG TERM...VORST AVIATION...HAL