Area Forecast Discussion
Issued by NWS Jackson, KY
Issued by NWS Jackson, KY
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701 FXUS63 KJKL 050350 AAA AFDJKL AREA FORECAST DISCUSSION...UPDATED National Weather Service Jackson KY 1150 PM EDT Tue Jun 4 2024 .KEY MESSAGES... - The threat of showers and thunderstorms will increase through mid-week. - Relatively cooler and drier weather arrives behind a cold front which will pass through eastern Kentucky on Thursday. && .UPDATE... Issued at 1150 PM EDT TUE JUN 4 2024 The next in line upper wave is bringing a renewed threat of showers and possible thunderstorms to the area late this evening. Have updated the forecast mainly to add in the current radar and CAMs` trends for the PoPs and thunder chances. Did also include the current obs and tendencies for the T/Td/Sky grids with this update. These minor adjustments have been sent to the NDFD and web servers along with a freshening of the zones, SAFs, and HWO. UPDATE Issued at 745 PM EDT TUE JUN 4 2024 23Z sfc analysis shows a very weak area of high pressure over the central Appalachians while low pressure is noted to the west. This high has been ineffectual at keeping the convection out of the this part of the state this afternoon and evening. Plenty of instability, but little shear resulted in mainly pulse storms, though a few clusters were able to push several stout and photogenic gust fronts and shelf clouds through the area. In addition, moderately high PWS led to an incident of localized high water from training storm cells. The worst of these are now exiting stage right and using up the remaining instability for the JKL CWA, though a few weaker storms will remain possible through the night. Currently, temperatures vary from the mid and upper 60s in the rain cooled areas to the upper 70s just ahead of some storms in the far northeast. Meanwhile, dewpoints remain elevated in the upper 60s to lower 70s most places - but mid 60s in the rain. Did update the PoPs and thunder forecast through the night per near term radar trends and the latest CAMs` guidance. Did also include the latest obs and tendencies in the T/Td/Sky grids with this update. These adjustments have been sent to the NDFD and web servers along with a freshening of the zones and SAFs. && .SHORT TERM...(This evening through Wednesday night) Issued at 407 PM EDT TUE JUN 4 2024 As of mid afternoon, the axis of a mid and upper level ridge extended from off the southeast U.S. coast north through the Carolinas and VA toward the eastern Great Lakes while an upper level low was centered over Saskatchewan and an associated upper level trough south through portions of the Plains. Upper ridging extended into portions of the southwestern Conus while multiple shortwaves were moving around it toward western Canada and the northwest Conus. A couple of shortwaves/disturbances moving through the flow ahead of the 500 mb through axis were nearing the region at this point with the first moving across the western KY to TN Valley area while another shortwave was nearing the mid MS Valley. At the surface, a ridge of high pressure extended from the southeast Conus into portions of the Atlantic with a frontal zone extending from the Atlantic to VA/Mid Atlantic vicinity and then west and northwest across the Central Appalachians to the Great Lakes to the triple point of a sfc low in Alberta. A cold front extended south from that system into the Northern to portions of the Central Plains and then into the western Conus. Moisture has been increasing across the region today, with PW analyzed in the 1.3 range east to nearly 1.75 inches near Lake Cumberland region. Daytime heating of this airmass with temperatures rising into the 80s and dewpoints in the 60s to near 70 was yielding an analyzed MLCAPE generally in the 500 to 1200 J/kg range with SBCAPE a bit higher in the 1500 to 2500 J/kg range. Low level lapse rates are generally 7C/km if not 8C/km,but mid level lapse rates are quite meager about 5.5C/km at best. Winds aloft are weak and shear is rather minimal at this time. Earlier activity was generally pulse type with a bit greater coverage and longevity of the activity nearer to the shortwave that is mainly just producing brief downpours. The initial shortwave trough nearing the area should continue east and northeast across the region through the evening, while the second shortwave upstream generally passes northeast. These shift east overnight generally and this combined with the loss of daytime heating should result in a lull in activity from the late in the evening into the overnight. However, the 500 mb trough axis will approach late tonight and on Wednesday downstream of the upper low meandering into Manitoba. In addition, during this time, sfc low pressure will track into northern Ontario with the trailing cold front working across the western and into the Central Great Lakes to mid MS and near the OH Valley before becoming stationary in the Southern Plains. This trough is expected to work across eastern KY late Wednesday and Wednesday night with the weakening cold front also moving into eastern KY, but likely not completely clearing the region before dawn on Thursday. The moist airmass will remain across the region through the near term period, with PW rising to generally 1.6 or higher this evening and then climbing to the 1.7 to 1.9 inch range on Wednesday. There should be a breif drop off in between shortwaves late this evening in PW back toward 1.5 inches briefly. PW will remain generally 1.8 to 1.9 inches into Wednesday evening, before decreasing as the next shortwave and cold front enter and move into the region on Wednesday night at which point values drop toward 0.8 northwest to about 1.5 inches late tonight along the VA border. Another uptick in coverage of convection should occur by the diurnal cycle on Wednesday in advance of the next shortwave or front and as the PW increase again after the overnight lull some activity may develop in the moisture/PW gradient toward dawn or shortly thereafter. The rather high PW values combined with 6 hour HREF max QPF of about 2 to 2.5 inch range in the region on Wednesday lead to some concern with torrential downpours and if a location receives torrential downpours the threat of high water. Storm motions should be a bit swifter on Wednesday with 0-6km mean winds rising toward 20 to 25KT and at that point effective shear should be near 20KT. During peak heating on Wednesday, MLCAPE is forecast in the 850 to 1300 J/kg range and with this in mind activity on Wednesday should be a bit more organized with a strong storm or two with gusty winds a possibility with low level lapse rates about 7C/km or higher. Temperatures will remain mild through the near term ahead of the front with highs on Wednesday averaging a couple of degrees above normal while low will about 5 to 7 above normal for early June. .LONG TERM...(Thursday through Tuesday) Issued at 248 PM EDT TUE JUN 4 2024 General agreement continues with respect to the mid/upper level patterns aloft. An elongated low and associated trough will have spun its way into the Great Lakes region at the start of the extended. The low...or mean low sets up residence over the Great Lakes for the remainder of the period, sending additional short wave impulses around the southern periphery of the mean low, into the Ohio Valley. At the surface, a relatively strong surface cold front will move through eastern Kentucky late Thursday or Thursday night. A stacked low over the Great Lakes, will keep our area under the influence of northwest flow. Subtle short wave disturbances passing across the region combined with wrap around moisture and diurnal heating will keep a general 20-30 PoP going through the period, with a noticeable diurnal flavor to activity. Sensible weather features generally dry weather for many, though isolated to widely scattered showers, commonly referred to as hit or miss showers and thunderstorms could impact anyone on any given day and at any given time. However, the most likely window of time for rain would be in the afternoon and early evening time frames. Other than Thursday morning at the start of the period, Saturday afternoon/evening and again Sunday afternoon are the next most likely day of more widespread rain as PoPs increasing to around 30- 35% as another cold frontal system approaches and passes through the Ohio Valley. After Thursday`s low to mid 80s for max temps, daily highs will average around 5 degrees below normal, or mid 70s through the period. Our coolest day through the extended will be Friday, with Saturday being slightly warmer by a degree or two. With lower surface dew points in the low 50s and a gradient wind around 10 mph, Friday will feel the coolest. Overnight lows will run in the 50s, though we may be flirting with upper 40s in some of our coolest valley locations by Saturday morning. Not seeing any solid signals with respect to hazards through the period. Instability will be relatively low, with MLCAPES only climbing to between 750 and 1250 J/kg Thursday afternoon. Instability looks even weaker for Sunday. At this time effective shear is not even reaching marginal levels. Thus any organized convection will likely be limited to features such as frontal boundaries. && .AVIATION...(For the 00Z TAFS through 00Z Wednesday evening) ISSUED AT 825 PM EDT TUE JUN 4 2024 Scattered shower and thunderstorm activity will linger through the evening, but with a general decrease in coverage through 04Z. Some periods of MVFR or lower vis and or ceilings are anticipated where the stronger showers and storms pass along with a brief gust into the 20 to 30 kt range. Fog could also be a concern tonight where the rain occurred, if clearing becomes substantial enough. Have included a tempo at many terminals for some late night restrictions due to fog. After an anticipated lull in activity between about 06Z and 12Z, shower and storm coverage will probably increase through Wednesday afternoon. Outside of any storms, winds will be mainly from the south to southwest at less than 10 kts through the aviation forecast period. && .JKL WATCHES/WARNINGS/ADVISORIES... NONE. && $$ UPDATE...GREIF SHORT TERM...JP LONG TERM...RAY/CMC AVIATION...JP/GREIF