Area Forecast Discussion
Issued by NWS Jackson, KY
Issued by NWS Jackson, KY
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149 FXUS63 KJKL 251958 AFDJKL AREA FORECAST DISCUSSION National Weather Service Jackson KY 358 PM EDT Tue Jun 25 2024 .KEY MESSAGES... - Heat and humidity returns for today and Wednesday. - Next best chance of rain will be Wednesday into Wednesday evening. - Hotter weather is expected to make a comeback by Friday and especially Saturday, with afternoon highs in the low to mid 90s and heat index values peaking around or in excess of 100 degrees. && .SHORT TERM...(This evening through Wednesday night) Issued at 358 PM EDT TUE JUN 25 2024 Current surface analysis is rather active but synoptically surface high pressure is situated over the region. Mesoscale wise, an MCS, from last night`s activity in the Upper Great Lakes, is continuing to dive south-southeast toward the CWA. Dry air over the region is causing the MCS to weaken as it approaches the CWA but a shower or two my clip areas along and north of I-64. Those showers and storms will linger over the next couple of hours before a brief lull in activity is expected for a few hours this evening. Then CAMs try to bring another round of showers and storms to the area as the western half of the current MCS tries to dive southeast into the region after 03Z and lingering through the early morning hours of Wednesday. Wednesday brings about another round of showers and storms. A couple small shortwave perturbations are revolving around a parent trough that will bring a surface low across southern Canada and a cold front through the CWA during the day Wednesday. The SPC has placed areas along and north of the Mountain Parkway in a Slight Risk of severe weather. The rest of the area is under a Marginal Risk of severe weather for cold frontal passage Wednesday afternoon. The timing of the boundary will allow for the best instability building. This is shown in forecast soundings as there`s decent forecast severe weather indices in place across the area. Steep low and mid level lapse rates are in place, instability ranging from 2,000 to 2,500 J/kg of CAPE in the afternoon is favorable, PW`s around 1.80" (which if materialized could bring some heavy rainfall) even from yesterday`s soundings, effective bulk shear has increased slightly across the region which could help promote some longer-lived stronger storms Wednesday afternoon. The biggest threat of the day appears to be damaging wind, but large hail and possibly an isolated tornado cannot be ruled out. However, the potential for increased cloud cover Wednesday morning could limit the ability to build in the best instability which alone could limit the coverage of the thunderstorms. Thunderstorms will taper off from northwest to southeast through the overnight Wednesday but an H850 shortwave is forecast to develop with a surface feature riding along the departing cold front. This secondary surface feature will keep lingering shower and thunderstorm chances across the far eastern third of the CWA through the end of the period. Overall, the entire period will be highlighted by multiple rounds of showers and thunderstorms with high temperatures remaining in the mid-80s to low-90s and overnight lows in the upper-60s to mid-70s. .LONG TERM...(Wednesday night through Monday) Issued at 500 PM EDT TUE JUN 25 2024 The 25/00z model suite 500H analysis beginning Wednesday evening shows troughing over eastern North America associated with a parent ~534 dam low spinning over southern Baffin Island. At the surface, a cold front extends from a low over the Labrador Sea southward to along the New England Coast and then southwestward across the Appalachians to near the mid and lower main stem Ohio River. To the west, an ~595 dam high is found over the New Mexico/Mexico border and an associated ridge axis extends northward along the eastern slopes of the Rockies to an ~571 dam high over the upper Yukon River basin. Surface high pressure is centered over the Upper Midwest but extends from the Central Plains all the way into the Mackenzie River basin of Northern Canada. Another ~560 dam low is coming ashore the Pacific Northwest. The axis of the upper level trough will pass through eastern Kentucky on Wednesday evening, nudging the cold front through before it hangs up just off to our south and east on Thursday. PoPs wane from northwest to southeast behind the front as drier and somewhat cooler air arrives on northerly winds. By Thursday, the ridging aloft moves in from the west while subsiding ahead of the Pacific Northwest low/trough. At the surface, high pressure passes through the Great Lakes on Thursday and Thursday night. As that high departs through the Northeast on Friday, mild and moist southerly flow redevelops over the Ohio Valley. There is a small chance for deep convection on both Thursday and Friday, primarily over and near the high terrain adjacent to Virginia border. PWATs continue rising heading into Saturday and Saturday night, potentially peaking around 2.0 inches (near climatological maximums for this time of year). With 850 mb temperatures climbing to between 20-22C on Saturday and those anomalously high PWATs, expect dew points to rise in the 70s coincident with air temperatures well into the 90s. This will set the stage for heat indices approaching 105F -- advisory criteria -- at some locations. There is a better chance (30-40%) for deep convection on Saturday, particularly over the southeastern high terrain, though neutral to weak height rises should temper overall storm coverage and updraft intensity. In the meantime, a low pressure system develops over eastern Wyoming/Montana (ahead of the Pacific upper low) before trekking across the Upper Great Lakes on Friday night and over eastern Canada this weekend. This low will drag another cool front through eastern Kentucky on Sunday and Sunday night. This will bring more widespread rain chances for the second half of the weekend. Another high pressure builds across the Great Lakes on Monday behind the cool front, bringing a briefly cooler and drier air mass before the heat returns again as Independence Day approaches. This weather pattern may bring on deja vu for some as multiple weak cool fronts will bring the opportunity for some rainfall, followed by a day a cooler and drier weather before heat and humidity quickly return on subsequent days and persist until the next weak cool front arrives. While there is at least a slight chance of rain on every day, at least over the higher terrain of southeast Kentucky, the best rain chances will come ahead of and along the frontal boundaries. In sensible terms, look for showers and thunderstorms to diminish from northwest to southeast Wednesday evening and night such that only a stray shower or storm is possible by Thursday. Similar to earlier in the week, temperatures will cool off to the mid 80s for highs on Thursday and will likely be followed by a sharper ridge-valley split on Thursday night as high pressure returns with clear skies and light winds. Look for lows in the upper 50s in northern sheltered valleys to the upper 60s on thermal belt ridges/slopes. Daily high temperatures rebound to the lower 90s on Friday and lower to middle 90s on Saturday. A stray shower or storm (10-20% chance) cannot be ruled again on Friday afternoon and evening, mainly in those counties adjacent to the Virginia border. Unlike the recent heat that was accompanied by moderate humidity levels, dew points by Saturday are forecast to rise into the 70s, which will support oppressive heat indices in the 100 to 105 range for most lower elevation locations. Better rain chances (30-40%) are also forecast for Saturday afternoon, though again the higher elevations closer to the Virginia border will be most favored. The next cold front will brings the best rain chances (50-70%) of the period on Sunday. Any leftover rain chances become confined to southeast Kentucky on Monday as cooler and drier air filters back across eastern Kentucky, holding highs in the mid 80s for most. Nighttime lows, which rise in the upper 60s to mid 70s over the weekend, retreat to the upper 50s to mid 60s early next week behind that front. && .AVIATION...(For the 18Z TAFS through 18Z Wednesday afternoon) ISSUED AT 125 PM EDT TUE JUN 25 2024 VFR conditions are prevailing across the area and will persist through much of the TAF period. Increasing and lowering CIGS are expected over the next few hours as an MCS approaches the area. However, the MCS is expected to continue to weaken as it approaches the area with minimal chances for showers and storms. Lingering cloud cover and the approach of a cold front will lower CIGS even more across the area but remaining VFR. Opted to add VCTS to all TAF sites after 12Z/Wednesday with VCTS being possible at KSYM after 08Z and persisting through the period as the cold front moves through the region. Lastly, south to southwesterly winds at less than 10 knots are expected. && .JKL WATCHES/WARNINGS/ADVISORIES... NONE. && $$ SHORT TERM...VORST LONG TERM...GEERTSON AVIATION...VORST