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Area Forecast Discussion
Issued by NWS Jackson, KY
Issued by NWS Jackson, KY
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832 FXUS63 KJKL 042149 AFDJKL AREA FORECAST DISCUSSION National Weather Service Jackson KY 549 PM EDT Thu Jul 4 2024 .KEY MESSAGES... - After a threat of stronger diminishes early this evening, chances for thunderstorms will linger through Friday, mainly during daylight hours. - A few thunderstorms mainly on Friday afternoon to early evening could produce locally heavy rainfall and strong to damaging wind gusts. - Dry and somewhat cooler and less humid weather arrives behind a cold front over the weekend. - Warmer and more humid conditions will make a noticeable comeback on Monday and continue into next week, along with a potential for more thunderstorms. && .SHORT TERM...(This evening through Friday night) Issued at 549 PM EDT THU JUL 4 2024 Convection that had worked across northern sections of the area, has weakened after producing some locally heavy rain and a couple instances of wind damage as well. Current trends suggest convection in the north and southeast should work east toward VA and WV and diminish over the next couple of hours while convection in south central KY works toward the Lake Cumberland area. With a warm and moist airmass in place, an isolated shower or storm could develop outside of these areas, but with meager mid level lapse rates and weak shortwave to shift east over the next couple of hours coverage of all convection should generally wane toward sunset. With convection in the severe thunderstorm watch having dwindled some cancellations will be upcoming. An upstream cold front will approach the lower OH Valley tonight and work across the OH Valley region including the Commonwealth on from Friday into Friday night ahead of a more robust shortwave trough. Some showers or storms will remain possible in the warm sector tonight, though coverage should peak again on Friday afternoon to early evening ahead of the cold front and associated mid level wave. Pre convective MLCAPE may be as high as 2000 to 2500 J/kg with bulk shear during the afternoon on the order of 25 to 35KT. Mid level lapse rates should be 6C/km or less, but low level lapse rates could be in the 7C to 8C/km range given sufficient heating into the 80s to perhaps near 90. Some CAMS such as the 18Z HRRR suggest the potential for some potentially robust activity from midday into the afternoon or a bit later than earlier runs and wind gusts should be the primary threat and locally heavy rain also possible with PW in the 2 to 2.25 inch range. SPC has a marginal risk for severe thunderstorms on Friday and this will continue to be highlighted in the HWO. As the front shifts east on Friday night along with the associated shortwave trough, chances for convection will diminish from west to east as the night progresses. .LONG TERM...(Saturday through Thursday) Issued at 530 PM EDT THU JUL 4 2024 The period is expected to begin with broad upper level troughing from Canada south into the Central Conus/MS Valley with a narrow axis of ridging from the Gulf of Mexico to just east of the eastern seaboard while another stronger ridge is expected to be anchored along the west Coast of the Conus. At the surface, behind a cold front that will have shifted to the southeast, a ridge of high pressure extending across portions of the Central Conus is expected to be nosing into the OH Valley region and ushering in a somewhat cooler and drier airmass. Saturday through Sunday night, an upper level low and associated shortwave trough should lift east/shear on out to the east and northeast on Saturday. A gradual trend of height rises into the OH Valley, Appalachians, and OH Valley by Saturday night and Sunday is forecast with the trough over the Central Conus sharpening up a bit in between ridging centered over the eastern Gulf of Mexico into the southwest and ridging over the western Conus. At the same time, Beryl should be working across portions of the Bay of Campeche into the Gulf of Mexico. Sfc high pressure ridging sliding across the OH valley and then toward the eastern seaboard combined with a general trend toward 500 mb height rises and a drier airmass will lead to a period of drier weather and also somewhat cooler and less humid conditions for eastern KY. From Monday to midweek, however, return flow of more warm and humid air should return between high pressure near the eastern seaboard and the next cold front and mid level trough and preceding shortwaves that generally pass to the north and northeast. A trough at 500 mb will linger to the southwest into the Southern Plains area. Convection may occur as early as Monday afternoon, especially in the more southern locations, but a peak is anticipated on Tuesday to Tuesday night ahead of the next shortwave that moves east of the MS River and across the Great Lakes, parts of the OH Valley, the Northeast, and mid Atlantic. How much moisture from the remnants of Beryl is drawn northeast from the Southern Plains is uncertain, but regardless, sufficient return moisture should reach eastern KY for possible multiple rounds of convection from Monday evening into Wednesday and the cold front itself may tend to become more diffuse as it reaches eastern KY on Wednesday. Guidance suggests Monday will the warmest of the Monday to Wednesday timeframe with highs near the 90 degree mark for many areas, before convection and clouds should keep highs in the 80s on Tuesday and Wednesday. Wednesday night to Thursday, the axis of troughing at 500 mb may remain west of the OH Valley as the cold front becomes diffuse by this timeframe. Another cold front could approach the OH Valley at that point and some disturbances may cross the area as well. Chances for any convection should peak on Thursday afternoon, although some ECMWF guidance for instance suggests it could be dry on that day. && .AVIATION...(For the 18Z TAFS through 18Z Friday afternoon) ISSUED AT 210 PM EDT THU JUL 4 2024 Some convective activity lingering near KSYM is expected to depart to the east northeast to begin the period. Otherwise, convection near to just east of the OH River ahead of an upper disturbance is expected to move east and approach eastern KY toward 20Z. Although some guidance weakens it, a warm, moist, and rather unstable airmass is in place to its east and strong to perhaps severe storms could affect KSYM as well as KJKL and perhaps KSJS as well after that time. Confidence in strength of storms on their arrival is not high, but brief wind gusts of 30KT or greater as storms pass is a possibility. Within any stronger showers and thunderstorms reductions down to MVFR and IFR if not briefly near airport mins in the strongest storms can be expected as they pass. As sunset approaches and the upper disturbance passes coverage of convection may decrease for much of the overnight, before a potential increase ahead of a cold front and a stronger shortwave trough later in the period. Valley fog is a possibility tonight as well following rain that has fallen so far today and anticipated rain during the afternoon and evening. The extent of cloud cover overnight could be a limiting factor, but reductions to MVFR or IFR are possible and if clouds are few LIFR or below airport mins cannot be ruled out. At this point this should have little affect on the TAF sites. Winds will average 10KT or lest outside of convection, from southwest to west to begin the period, before trending to southwest to south around or after 00Z. && .JKL WATCHES/WARNINGS/ADVISORIES... NONE. && $$ SHORT TERM...JP LONG TERM...JP AVIATION...JP