Area Forecast Discussion
Issued by NWS Jackson, KY

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840 FXUS63 KJKL 271645 AFDJKL Area Forecast Discussion National Weather Service Jackson KY 1245 PM EDT WED JUL 27 2016 .UPDATE...
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Issued at 1245 PM EDT WED JUL 27 2016 Latest radar trends show showers and thunderstorms popping up in far northeast KY, which seems to be on par with the latest HRRR run. Expect this trend to continue into the afternoon with additional showers likely forming south of the area and moving north (per latest Visible satellite imagery). So updated pops accordingly and refreshed hourly temps. Sent updates to NDFD and web servers. UPDATE Issued at 942 AM EDT WED JUL 27 2016 Early morning showers have lost their gusto and are dissipating as they move east-northeast. The HRRR model reflected this trend well. Also updated hourly grids to reflect recent obs and sent updated to NDFD and web servers. UPDATE Issued at 653 AM EDT WED JUL 27 2016 A cluster of thunderstorms that developed across south central KY and north central TN continues to work its way northeastward during the 6am hour. While they seem to finally be losing steam, they did put down some quick torrential rainfalls along the TN/KY border, with several reports of flash flooding ongoing. The HRRR model is the only model so far that has picked up on this ongoing activity, and shows it expanding but losing strength over the next few hours. Based on radar trends over the last 15 minutes...this seems to be pretty well on track. Trended closer to the HRRR through the next few hours, with isolated to scattered pops expanding northeast through the CWA, before scattered pops take over across all of eastern KY for the afternoon. Also updated the sky cover to accommodate this increase in pops. Finally, loaded in the latest observations for temps, dew points, and winds, to make sure the near term forecast was on track with current conditions. All changes have been published and sent to NDFD/web.
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&& .SHORT TERM...(Today through Thursday) Issued at 405 AM EDT WED JUL 27 2016 Clouds were starting to increase in coverage at 7z, with a few showers starting to pop up across the central TN and moving into south central KY. Kept low end isolated pops in across the southern extent of the CWA to cover these isolated showers through daybreak. Otherwise, today should be much in the same as yesterday, with the stalled frontal boundary still located across the northern half of the state, and a warm, very moist airmass in place. As we head into the daylight hours, expect convection to begin popping here, across our northern CWA, then quickly spreading across the remainder of the CWA throughout the afternoon. Kept with scattered pops across the CWA through the afternoon given the uncertainty of where and when storms will actually form. This may need to be fined tuned a bit as convection starts developing today. PWATs continue to hover around the 2 inch mark today, so any storms that do develop will continue to be heavy rain producers. This, combined with very little directional shear, could lead to some training of storms as well, so will continue to monitor for any localized flooding concerns. Focus then shifts to the overnight hours tonight and heading into the day Thursday. The stationary front across the state will push slightly north of the Ohio River late tonight, and remain just north of the state through the day Thursday. Winds will take on a slightly more SW heading, and increase in intensity, allowing for a deeper pull of moist southerly air. This increase will be due to a deepening shortwave, which is expected to move across the mid Mississippi River Valley tonight, and then across Kentucky Thursday and Thursday night. This wave will interact with the stationary frontal boundary, as well as the phasing of the southern and northern jet streams, to create a large surge of warm deep moisture, and lift for which storms to develop. PWAT values for tonight will be well over 2 inches, and will continue to increase to between 2.25 inches and 2.4 inches in some places during the day Thursday. CAPE values and LIs remain decent from tonight through Thursday, but overall the more long/skinny nature of the CAPE and little wind shear continues to lend itself to heavy rain being the primary concern with any storm. Somewhat unidirectional flow in the mid and upper levels may lend itself to some training of storms, which would be worst case scenario for any peoples under these storm`s path. Flooding will likely be imminent, the question is how isolated will it be, and where will it occur. It may also play directly into which locations receive heavy rainfall today. No flood watch has been posted at this time by our office or any neighboring offices, but will pass along for the day shift for consideration. Temperatures today will continue to be warm and muggy, topping out in the upper 80s to near 90, with heat indices in the mid and upper 90s. With the introduction of thick cloud cover and heavy rains Thursday, temperatures will take a downward turn, with highs only in the low 80s. It will be wet, but a welcome relief from the heat. .LONG TERM...(Thursday night through Tuesday) Issued at 412 AM EDT WED JUL 27 2016 Upper troughing will remain locked in place from the northern Plains and upper Midwest through the Appalachians and mid-Atlantic into early this weekend, in between Great Basin to Four Corners anchored high pressure and the stagnant summertime Bermuda high. Multiple rounds of upper energy look to be in play, with the first and most significant at this point, being the one mentioned in the short term. Still some inconsistency in exactly how quickly and where this lead wave will skirt through eastern Kentucky. GFS/ECMWF solutions phase a southern stream impulse with the shortwave ejecting out of the upper Midwest and lower Great Lakes, thus slowing the coupled system`s eastward progression. The latest NAM is not as robust on the phasing of both systems and subsequently dampens the upper trough as it moves through the Tennessee Valley into Kentucky. There also still remains question as to how deep and therefore exactly where the surface low/wave will track. Nonetheless, a tropical-type airmass characterized by precipitable water values in the 2.25 inch range along with strong omega profiles and ample instability with CAPE in the 1-2 kJ/kg range, suggest a dousing of rain somewhere in vicinity of eastern Kentucky Thursday into Thursday night. Have raised pops to categorical mention Thursday evening to account for the overall consensus and better consistency in a slower dynamic progression. Even without an exact morphing of the southern and northern stream waves, lift will still be plentiful with the combination of energy aloft and in the warm sector of a stationary front near the Ohio River Valley. A flash flood watch seems very likely within the next 12-24 hours for Thursday, but will let a few of these uncertainties with respect to placement and timing refine themselves before pulling the trigger. Additionally, depending on how quickly storms move through Thursday, increasing deep layer shear to near 30-35 knots into the evening could suggest a better threat for organized updrafts and gusty downburst winds. Friday will bring scattered storms to the eastern portion of the Bluegrass ahead of the long-residence frontal boundary, with coverage perhaps somewhat limited by a spout of shortwave ridging following Thursday`s system. Additional waves of some degree look possible both Saturday and Sunday at this time, leading to scattered showers and storms once again, mainly confined to peak heating during the afternoon/evening timeframe. Late weekend into the first week of August looks to see upper ridging expanding east across the Great Plains and into the Midwest. Will keep isolated to scattered storms advertised at this point for early week with uncertainty as to how far east deep layer subsidence will build. Could get into a period of northwest flow and subsequent mesoscale convective system development toward the region. Nonetheless, temperatures will likely see a warming trend from more seasonable readings in the low to mid 80s through this weekend to mid to upper 80s with rising heights next week. Lows should generally reside in the mid-upper 60s before approaching the 70 degree mark next week. && .AVIATION...(For the 12Z TAFS through 12Z Thursday morning) ISSUED AT 700 AM EDT WED JUL 27 2016 A cluster of showers and thunderstorms has developed over south central KY during the last couple of hours, and continues to make its way northeast. While it seems to be losing considerable strength, its coverage is on the increase, so VCTS and light showers may be possible now at KSME...and not to be ruled out at KLOZ within the next 1 to 2 hours. For the remainder of the day, expect additional showers and thunderstorms to develop as a stalled frontal boundary remains placed across the state. Kept VCTS in during this time at all TAF sites, since exact timing and locations of these storms are still unknown. Outside of any storms, conditions should remain VFR. Scattered showers and thunderstorms will continue into the overnight as well. Did add in the mention of some fog development and vis restriction after 3Z tonight, though exact impacts will largely be dependent on the amount of rain each TAF site receives during the day today. Winds will generally be light and variable, though any stronger showers or thunderstorms could produce some briefly gusty conditions. && .JKL Watches/Warnings/Advisories... None. && $$ UPDATE...JVM SHORT TERM...JMW LONG TERM...GUSEMAN AVIATION...JMW is the U.S. government's official web portal to all federal, state and local government web resources and services.