Area Forecast Discussion
Issued by NWS Jackson, KY

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000 FXUS63 KJKL 231040 AFDJKL AREA FORECAST DISCUSSION National Weather Service Jackson KY 640 AM EDT Tue May 23 2017 .UPDATE...
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Issued at 640 AM EDT TUE MAY 23 2017 WSR-88D radar continues to indicate some returns across the region and most of this is likely not reaching the ground given the dry air in place. However, a few sprinkles are still possible and we have seen some sprinkles at JKL this morning. Better moisture and convection should remain mostly south of the the region. Other than adding the sprinkles did opt to update with latest obs and trends.
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&& .SHORT TERM...(Today through Wednesday) Issued at 404 AM EDT TUE MAY 23 2017 A low pressure system will continue to take shape as 500mb wave aids in cyclogenesis. This surface low will deepen as it tracks NE into NC through the day. We remain on the fringes of this synoptic scale system and think better convection to the south and track of low pressure could cutoff potential moisture in eastern KY. That said thinking some of the CAMs are a bit overdone with QPF at this time and will limit best POPs in the far SE toward VA. There have been some returns on radar this morning, but this will likely remain elevated as virga given the drier air in the lower levels. While cloud bases are high the skies are mostly cloudy and therefore did bring skies up in general. Overall the CAMs and larger scale synoptic models are showing the region in the middle of two systems by this evening. Therefore, did opt to lower POPs through the evening in most spots, as the forcing for accent slackens. All eyes turn to the deepen upper level system across the Midwest, as it combines divergence aloft and strengthening jet streak to deepen a surface low. Therefore will increase POPs from SW to NE through the overnight into the early morning hours Wednesday. Overall models are in decent agreement with the evolution of this system, but still some differences with regards to the depth of the surface low. Wednesday could not resist bring CAT POPs across the region given the forcing for ascent and the synoptic scale low/front coming across the region. The peak timing will be late morning into the afternoon for best overall POP chances. The thunderstorm chances will be mainly in the afternoon, but morning convection is not out of the question. This leads to complicated afternoon as instability could struggle owing to early local convection/clouds and convection to our SE. This will be the fly in the ointment for any potential for stronger storms as shear environment will be more than ample. Therefore, agree with SPC keeping us in the general for now and see how later forecast data handles this. .LONG TERM...(Wednesday night through Monday) Issued at 404 AM EDT TUE MAY 23 2017 An overall unsettled period looks to be in store from mid this week into next week as quasi-zonal to cyclonic flow remains over eastern Kentucky. The first in a series of upper level lows, referenced in the short term discussion, will move overhead Wednesday night into Thursday. Shower and thunderstorm chances will be greatest across far eastern and southeastern Kentucky Wednesday evening as a cold front moves through. Some semblance of a dry slot will likely materialize into the evening and overnight in wake of the front and underneath the forcing aloft. This will fill back in on Thursday downstream of a secondary surface low/convergence boundary across the Ohio Valley. Forecast soundings show steepening lapse rates Thursday afternoon, perhaps resulting in a few hundred J/kg of CAPE. However, elected to keep thunder out of the forecast given a plethora of low clouds and limited heating in a post frontal airmass characterized by high temperatures likely only warming into the low 60s. Will have to continue monitoring thermodynamic profiles for the possibility of seeing some graupel if saturation can sustain itself aloft with low freezing levels in place. A dry period should develop Friday underneath transient shortwave ridging. Before then, may see at least a minor ridge/valley temperature split Friday morning as the northern edge of surface ridging over Florida noses into the lower Ohio Valley. High temperatures look to rebound into the mid 70s, very close to normal, as partial clearing occurs in conjunction with an influx of warmer air aloft. Shower and thunderstorm chances will return for the weekend as another upper low traverses the Canadian Prairies into south central Canada. Depending on the strength and latitudinal position of this system, may see several shortwave perturbations dive south toward eastern Kentucky, thus keeping a wet Memorial Day weekend in the offing. However, could see a long duration of dry weather if this system and forcing remain north. Temperatures will likely remain near to just above normal south of this low, with a cooldown ensuing at some point into next week if and when frontal passage occurs. && .AVIATION...(For the 06Z TAFS through 06Z Tuesday night) ISSUED AT 121 AM EDT TUE MAY 23 2017 The TAF period will be met with VFR and this is expected to be the prevailing through the period. We are watching an upper level wave to our south that is bringing mostly high clouds into the region this early morning hour. This nearby wave could induce showers and perhaps a few isolated thunderstorms for Tuesday into Tuesday evening. The better forcing should be in the TN Valley and therefore keep best POPs nearer the VA border with a sharp cutoff to the NW. Did add some VCSH and -SHRA to most of the sites given this nearby disturbance, but confidence remains low on how much activity in fact makes it into the region given the low level flow. Winds are expected to remains light through the period. && .JKL WATCHES/WARNINGS/ADVISORIES... NONE. && $$ UPDATE...DJ SHORT TERM...DJ LONG TERM...GUSEMAN AVIATION...DJ

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