Area Forecast Discussion
Issued by NWS Jackson, KY

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000 FXUS63 KJKL 150714 AFDJKL AREA FORECAST DISCUSSION National Weather Service Jackson KY 314 AM EDT Tue Aug 15 2017 .UPDATE... Issued at 130 AM EDT TUE AUG 15 2017 Updated the grids mainly to fine tune the PoPs through dawn based on the latest radar trends and HRRR guidance. Also, tweaked sky cover and the T/Td grids per the latest obs and trends. These have been sent to the NDFD and web servers. UPDATE Issued at 1037 PM EDT MON AUG 14 2017 Have continued to tweak pops throughout the evening based on latest radar trends and hi-res guidance. Currently scattered to numerous showers are located over far the far SE portion of the CWA, with lightning/thunder continuing to wane. Have thunder diminishing completely over the next few hours. Otherwise, reduced pops to only scattered for the rest of the night based on latest hi-res model trends. Also updated the forecast through tomorrow to change to coverage wording in the weather grids instead of probabilities. Finally, freshened up the near term grids for temps, dew points, and winds to make sure they were on track with current conditions. All changes have been published and sent to NDFD/web. A new set of zones was also sent out to reflect latest changes in pops/weather for overnight. UPDATE Issued at 717 PM EDT MON AUG 14 2017 Made a couple updates, mainly to pops and weather, over the last few hours. Tried to get pops more on track with current radar trends. Leaned a bit towards the HRRR for model guidance as it seemed to be initializing well and has thus far panned out pretty well. However, some continued adjustments and updates are expected throughout the rest of the evening as things evolve. Also updated the near term forecast for temps, dew points, and winds, to make sure they were on track with current conditions. All updates have been published and sent to NDFD/web. A new forecast package was sent out to reflect updated weather earlier in the afternoon. A new HWO will be sent out later this evening once remaining thunder has tapered off. && .SHORT TERM...
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(This evening through Tuesday night) Issued at 347 PM EDT MON AUG 14 2017 ...Locally heavy rains possible this afternoon and overnight... Scattered thunderstorms with very heavy rains have moved into the southwest part of the forecast area. These will continue to move northeast but should decrease in intensity as we move into the evening. Will mention locally heavy rains in the updated hazardous weather outlook for the remainder of the afternoon and evening. As we move into the overnight period another wave of showers should affect the southern and central part of the forecast area as a subtle short wave ripples through the mean flow. The GFS and NAM MOS guidance as well as the blended forecast guidance point towards likely to high chance rain probabilities for the overnight period. Will follow that idea for tonight. A concern is locally heavy rain tonight. The excessive rainfall outlook does not include SE KY, but with the marginal risk right along the TN and VA border this will be something to watch especially with precipitable water right around 2 inches. We also received a spotter report of 1 inch of rain in Floyd County this morning with showers, and this corresponded well with radar estimates for a small part of the county. This helped highlight the efficient rain production of showers in the current warm moist air mass. The NAM continued its trend of trying to pinpoint an area of heavy rain tonight on the order of 2-3 inches, and is still trying to point towards the west central part of the forecast area. Pinpointing the location of such a local high rain amount cannot be relied upon, and as noted by the midnight forecast shift the NAM has been rather inconsistent and an outlier when compared to the other models in recent runs. This continued with the 12z runs. Despite that, with the rainfall report this morning of 1 inch, the current radar trends, the efficient rain production of the shower and storms we`ve already seen, and the expected efficiency of showers and storms this evening into the overnight, any showers and storms will need to be monitored for excessive rain. On Tuesday more showers and thunderstorms will be possible, but chances will be on a downward trend through the day. .LONG TERM...(Wednesday night through Monday) Issued at 314 AM EDT TUE AUG 15 2017 The extended portion of the forecast begins on Wednesday night with an active pattern on tap across the CONUS. The period will begin with a strong trough tracking over the northern Plains and into the Great Lakes as it drags a cold front over the OH Valley region during the day on Thursday. Model profiles for Thursday afternoon show quite a bit of instability and good directional shear. This will definitely be a set up to monitor as SPC has issued a Day 3 Marginal severe risk. At this point, models so suggest that the bulk of the dynamics and instability will be north of the Ohio River where the greater risk will likely be. Thursday night and into the weekend, the mid level ridge will set up again over the Southeastern CONUS bringing return flow into the area. This will be combined with several shortwaves passing through the OH Valley with the next front passing through late Saturday. At this time, this feature does not seem to have the amount of instability and shear as the previous front. With the return flow continuing into next week, the threat of afternoon showers and thunderstorms will persist through the end of the extended forecast period. Overall, a wet extended forecast is expected through next week.
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&& .AVIATION...(For the 06Z TAFS through 06Z Tuesday night) ISSUED AT 200 AM EDT TUE AUG 15 2017 Scattered showers and a stray thunderstorm or two continue to affect eastern Kentucky early this morning. Coverage will be highest in the south, but even SYM could see a shower, with some increase in areal extent expected toward dawn in the far SE portion of the state. Limited instability should keep the thunder chances low, so just went with VCSH for all TAF sites. For Tuesday, though, there will be more instability around likely resulting in additional thunderstorm development in the afternoon, but given uncertainty whether any particular TAF site will be impacted, kept with VCTS, at this time. Winds will remain light and variable throughout the period. Aside from the storm threats for Tuesday afternoon, the main concern for this TAF is the potential for low flight categories due to fog and low stratus clouds through mid morning. With abundant moisture across the region, we have the potential for LIFR conditions. However, can`t rule out some brief drops below this category. Conditions should begin improving shortly after daybreak, but expected no better than BKN cloud cover in the low end VFR range through the afternoon with any convection lowering the cigs/vis into the MVFR or lower range. && .JKL WATCHES/WARNINGS/ADVISORIES... NONE. && $$ UPDATE...GREIF SHORT TERM...SBH LONG TERM...SHALLENBERGER AVIATION...JMW/GREIF

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