Area Forecast Discussion
Issued by NWS Jackson, KY

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217 FXUS63 KJKL 250015 AFDJKL AREA FORECAST DISCUSSION National Weather Service Jackson KY 815 PM EDT Mon Jul 24 2017 .UPDATE...
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Issued at 815 PM EDT MON JUL 24 2017 A broken band of showers and thunderstorms, stretching from Norton, Virginia to Brodhead, continues to make slow progress off to the southeast in advance of a cool front set to cross south of the Ohio River. These will diminish by mid-late this evening as instability further decreases and drier northwest flow gradually oozes in. Still looking at widespread fog development tonight given crossover temperatures generally in the mid 60s or higher. Drier air will likely mix in above the valleys earlier tonight, particularly north of Mountain Parkway and Interstate 64. Valleys here, as well as most locales farther south, will however see lingering low level moisture as subsidence builds into eastern Kentucky. Rather sporadic summertime rainfall the past couple of days, combined with this slow influx of drier air, looks to keep dense fog from becoming widespread at this time.
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&& .SHORT TERM...(This evening through Tuesday night) Issued at 418 PM EDT MON JUL 24 2017 Coverage of showers/t`storms has increased this afternoon and warrants a higher POP than was previously carried. Have used high chance POPs with the broken line dropping south through the forecast area. This line roughly agrees with what the mesoscale models suggested, and have extrapolated the precip southeast across the area and allowed it to dissipate this evening as models depicted. The precip was occurring near a cold front dropping south through the area. It will bring slightly cooler and drier air southward. However, there`s not a strong influx tonight, and it will be difficult to scour out all of our surface air mass, especially in valleys. With drier air arriving aloft, this will set us up for fog. It seems a safe bet in valleys. Just how far it spreads in breadth and depth is the bigger question. Suspect it could get rather dense. Fog and low clouds will dissipate on Tuesday morning. Following this, high pressure passing by to our northeast will provide fair weather through Tuesday night. .LONG TERM...(Wednesday through Monday) Issued at 427 PM EDT MON JUL 24 2017 The continued expansive ridge of high pressure will be in control of Kentucky to start the extended on Wednesday. However, heights will quickly lower into the day Thursday as upper level low moves eastward across Canada, and shortwave develops in the troughing pattern, pushing southward. As this shortwave continues to strengthen throughout the day and into the overnight Thursday, will will result in more NW to SE flow across the state, with the upper level ridge retrograding westward away from the Ohio Valley. Longwave troughing will continue to amplify across the eastern U.S. into the weekend, with heights continuing to fall across the state. Several more shortwaves are expected to follow this SE flow into the Ohio Valley through the weekend. At the surface, high pressure will be in control Wednesday and Thursday. A cold front will push SE into the state starting Thursday night, spawning from a surface low pressure system located over eastern Canada, in coordination with the upper level low. A secondary surface low will also be located along this frontal boundary, passing through the Ohio Valley and just north of the state Thursday. The cold front will push southward through the state Thursday night into Friday, exiting by Friday evening. Surface high pressure and more northerly flow will then take hold for the remainder of the weekend. As for sensible weather, expect dry and continued warm conditions for the day Wednesday with the surface high and upper level ridge in control. Temperatures will reach the upper 80s in the afternoon under mostly clear skies and light winds. Chances for showers and thunderstorms will expand across the CWA Wednesday night into Thursday ahead of the approaching cold front, as winds turn more southerly and a warmer and moister airmass moves into the region. Likely coverage will be possible across the north in the afternoon and across the central and south Thursday night as the front nears closer. Chances will then quickly begin to dissipate from NW to SE Friday into Friday evening as drier and cooler air moves in behind the frontal system. The frontal zone will still likely be in close enough proximity to our SE to spawn isolated to scattered showers and thunderstorms, mainly across the SE portion of the CWA, during the day Saturday. However, temperatures will only be in the low 80s both Friday and Saturday as northerly winds take hold. Surface high pressure will continue to build into the region through the weekend, keeping mostly clear skies in place across much of eastern KY along with cooler temperatures. That being said, upslope flow may lead to some isolated convection in the high terrain in the afternoon. Temperatures will be in the low 80s still with much lower humidity. && .AVIATION...
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(For the 00Z TAFS through 00Z Tuesday evening) ISSUED AT 815 PM EDT MON JUL 24 2017 A broken band of showers and thunderstorms from Norton, Virginia to Brodhead, Kentucky will diminish by mid-late this evening in advance of a cool front near the Ohio River veering winds northerly. Drier air will gradually filter in behind this front tonight, but enough low level moisture will remain to produce widespread fog across eastern Kentucky. This should be more prevalent in sheltered valleys, as well as farther south of Mountain Parkway will drier air will be delayed in mixing in. IFR/MVFR visibilities look very possible for all sites at some point tonight, with periods of sub-IFR conditions certainly possible as well. Conditions will improve to VFR with the onset of daytime mixing by mid Tuesday morning as winds remain light, near 5 knots or less, out of the northeast.
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&& .JKL WATCHES/WARNINGS/ADVISORIES... NONE. && $$ UPDATE...GUSEMAN SHORT TERM...HAL LONG TERM...JMW AVIATION...GUSEMAN is the U.S. government's official web portal to all federal, state and local government web resources and services.