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Area Forecast Discussion
Issued by NWS Jackson, KY
Issued by NWS Jackson, KY
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982 FXUS63 KJKL 171204 AAA AFDJKL AREA FORECAST DISCUSSION...UPDATED National Weather Service Jackson KY 804 AM EDT Sat Aug 17 2024 .KEY MESSAGES... - Strong to severe storms are expected to impact the area today. Damaging wind gusts appears to be the greatest hazardous weather threat and would most likely be associated with more organized storms...i.e. line segments and storm clusters. - Below normal temperatures are expected Sunday through Wednesday behind a cold front passage late Saturday night. - Showers and thunderstorms will remain possible Sunday and Monday, especially in the afternoon and early evening, with a drying trend for Tuesday into Wednesday. && .UPDATE... Issued at 659 AM EDT SAT AUG 17 2024 Area webcams and a couple incoming COOP reports indicate that visibilities are improving at the surface, and much of the fog appears to be lifting across the area. Consequently allowed the special weather statement to expire and this early morning update is mainly to bring forecast products in agreement with current trends. Otherwise, grids were in good shape. No other changes to the forecast package at this time. && .SHORT TERM...(Today through Sunday) Issued at 448 AM EDT SAT AUG 17 2024 Aloft, low over the Great Lakes Region will spin its way from Lake Superior to Lake Erie/Ontario during the short term. Two short wave disturbances will be rotating around the southern periphery of the trough early in the period as the low slides southeastward. The first is expected to pass through the Commonwealth very early in the period, while the second of the two short waves drops southeast into the Ohio Valley later this evening. Recent model guidance has been somewhat inconsistent with the evolution of sensible weather, putting into question the exact amount and timing of convection each wave will generate across the area. Overall, the bulk of guidance suggests at least two general rounds of precipitation today. Earlier solutions had convection firing across eastern Kentucky during the morning, but trends delay the start of convection until mid-day or just after. The second round has been more consistent and transits our forecast area this evening. Thinking is today`s rainfall may be broken up in several rounds, similar to Friday, where segments of organized convection transit different portions of the area at various times through the afternoon and evening. Based on some of the latest CAM solutions, the best bulk shear is found across our southern zones Saturday, but is marginal at 30-35 kts. Better environmental shear (35-45 kts) develops by late afternoon into this evening. The best instability is realized during the daylight hours with heating, with MLCAPE climbing to 1500-2500 J/kg...with greater CAPE centered more across our southwestern zones. Wind fields aloft could be more favorable with H500 and H850 winds averaging less than 35 kts over eastern Kentucky. In addition, the best diffluent flow aloft is earlier in the day. Low level lapse rates appear strong (7-8C/km+), but mid level lapse rates are relatively weak (~ 5C/kg). Overall have definitely seen more impressive storm environments. But SPC does have the area within a marginal to slight risk today. Consequently, strong storms could be possible, and a few storms producing severe weather can not be ruled out. If analysis of the storm environment is accurate, damaging wind gusts would be the greatest hazardous weather threat and would most likely be associated with more organized storms...i.e. line segments and storm clusters. Without steeper lapse rates aloft and other more favorable storm environmental parameters, feel the hail threat will be minimal. A third short wave rounds the bottom of the trough by Sunday. Forecast soundings show ample instability across the area with MLCAPES climbing to between 1000-1500 J/kg during peak heating of the afternoon. However, bulk shear is around 15 kts or less, which is not favorable for organized convection. Interestingly, the NBM blend continues to advertise a consistently high 80-90% PoP for Sunday; quite high considering the nature of convection will be strongly driven by diurnal heating...instability showers and thunderstorms. Thus while activity will be scattered, effectively there is high probability most of the forecast area will measure. .LONG TERM...(Sunday night through Friday) Issued at 448 AM EDT SAT AUG 17 2024 After one last day of active weather on Monday, the upper level low responsible for this weekend`s convection will open up into broader troughing and eject up into New England next week. In its wake, forecast guidance places Eastern Kentucky in a regime of generally weak meridional flow aloft. At the surface, the model suite collectively suggests that a high pressure will push into the Great Lakes region. Together, these features reinforce the idea that next week`s weather will be both cooler and drier than what we have witnessed here as of late. As hinted at above, rain chances remain in the forecast for Monday, albeit at slightly lower values than the previous days. With the passage of Sunday`s frontal boundary, the best surface- level support for organized convection will be removed far from the forecast area. Thermodynamic support will also be fairly meager, with afternoon highs only in the mid to upper 70s. However, favorable PVA on the backside of the troughing aloft will support scattered shower activity into the afternoon hours. The greatest PoPs will be in our eastern tier counties, where northwesterly flow throughout the column may locally enhance chances on the windward side of higher terrain via orographic lifting processes. Rain chances dwindle down during the evening and overnight hours on Monday as dry air advection begins to dominate and skies correspondingly clear. Overnight lows on Monday will be in the low to mid 50s, and these cooler temperatures foreshadow the fall-like conditions in the forecast for the much of the work week. Under mostly clear skies and a modified continental polar airmass, temperatures will be below average values on Tuesday and Wednesday. Afternoon highs will be in the mid to upper 70s, with efficient diurnal mixing processes reducing the dewpoint and thus the relative humidity. Overnight, expect pretty potent ridge/valley thermal splits, with some of the deepest valleys potentially dropping into the upper 40s on Tuesday and Wednesday nights. Elsewhere, expect MinTs in the 50-55 range. While it will feel great outside for much of next week, this little taste of fall will not last forever. The surface high responsible for this will shift east on Thursday, bringing about a shift to southerly winds by Friday. Temperatures respond by increasing a little each day, and highs will return to near climatological norms (mid to upper 80s) on Friday. As the high shifts east, ridge/valley splits will be favored in the more eastern locations for Thursday night and perhaps additional nights. PoPs will remain below 10 percent through the rest of the period though. Thus, with the exception of Monday, the weather in this particular long term forecast package will be pleasant. && .AVIATION...(For the 12Z TAFS through 12Z Sunday morning) ISSUED AT 803 AM EDT SAT AUG 17 2024 At issuance time, conditions ranged from LIFR to VFR as fog and low stratus are gradually lifting and in the process of mixing out. In addition to any low clouds or fog, some high clouds were passing by from time to time as well. The fog and stratus should continue to lift and dissipate through 13Z or no later than 14Z and give way to VFR areawide. KSME and KSJS are not affected by reductions initially, however, KJKL, KLOZ, and KSYM are. Rounds of convection are expected to affect the area at times after 15Z as a series of disturbances cross the area and interact with daytime heating. Disturbances continuing to cross the area will lead to lingering chances for convection even after 00Z. Reductions to MVFR and IFR will be possible briefly as these pass a location. Winds initially light and variable, will average from the southwest at around 10KT or less during the 14Z to 00Z timeframe. Light and variable winds are expected thereafter. Stronger gusts are anticipated in thunderstorms, especially during the afternoon and evening. Late in the period, guidance suggests some reductions down into the MVFR range or lower are possible && .JKL WATCHES/WARNINGS/ADVISORIES... NONE. && $$ UPDATE...RAY SHORT TERM...RAY LONG TERM...MARCUS AVIATION...JP