Area Forecast Discussion
Issued by NWS Jackson, KY

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000 FXUS63 KJKL 121855 AFDJKL AREA FORECAST DISCUSSION National Weather Service Jackson KY 255 PM EDT Thu Oct 12 2017 .UPDATE... Issued at 1043 AM EDT THU OCT 12 2017 Updated earlier this morning to include the mention of patchy light drizzle throughout the morning, based on current conditions and the fact that llvl clouds were not anticipated to lift and break apart until this afternoon (if at all). Also made several updates to make sure the near term temps, dew points, and winds were on track with the current observations. All updates have been published and sent to NDFD/web. A new forecast package was sent out earlier to include drizzle wording through the morning. Will resend another update once drizzle is out of forecast. UPDATE Issued at 638 AM EDT THU OCT 12 2017 A solid area of stratus continues to plague the region this morning, and this is not allowing quite the drop in temperatures that was possible. Therefore needed to freshen the hourly temperatures reflect the trends. Also updated the SKY grids to match the HRRR trends, which have seemed to be the best based on the current observed trends and forecast thinking. Otherwise more minor tweaks were needed to deal with the latest obs and trends. && .SHORT TERM...
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(Today through Friday) Issued at 343 AM EDT THU OCT 12 2017 The morning surface analysis shows an area of surface high pressure building eastward and centered across eastern MO. This high along with a upper level ridge will build east through the forecast period. The latest GOES-16 Nighttime Microphysics product indicates a vast area of stratus has spilled into eastern KY through the night. This area of stratus is being brought on by a strong inversion at around 900mb level and deep layer of dry air aloft suppressing the low level moisture. There remains some potential for this deck to lower enough to get some patchy fog and therefore did keep this going this morning. The time of year and forecast soundings give way to higher confidence for a mostly cloudy to cloudy skies through the early afternoon at least. The confidence is higher in seeing clearing quicker in the far southeast and higher ridge top locations given the depth of the moist layer. Consequently, the forecast highs for today could suffer from the low stratus and did lean toward a raw model blend that seemed to have a more reasonable handle on this idea. The confidence is lesser on how clouds and/or fog develops tonight. The soundings are not as clear on how much low level moisture will be trapped at the lower levels, and therefore kept the clouds more than the blend but much less than what we saw last night coverage wise. The implications on fog and overnight low temperatures will also suffer from this so did keep closer to previous, but then limited the fog to patchy given the uncertainty. The uncertainty on clouds will likely leak into Friday and for now think we should see more clearing through morning on Friday. Therefore, will lean toward the more optimistic blended guidance for afternoon high temperatures. .LONG TERM...(Saturday through Thursday) Issued at 255 PM EDT THU OCT 12 2017 The focus of the Saturday through Thursday period will be the passage of a cold front on Sunday and a period of more autumn like weather early next week. The 12Z models have trended faster with the short wave trough pushing east from the plains late in the weekend, and as a consequence an earlier passage of the surface cold front in our area Sunday afternoon and evening. Based on most guidance, instability in advance of the front still looks to be very limited on Sunday. However the NAM is an exception, bringing a brief period Sunday afternoon with CAPE values above 1300 over parts of the area. Some moderate shear still appears possible as well. Considering everything we will continue to carry a slight chance of thunder for Sunday afternoon and evening. Model guidance, including MOS, has also trended colder with early morning lows on Tuesday and Wednesday and this is reflected in the standard blended temperature loads for these periods. Some upper 30 or possibly even a few mid 30 readings will be possible, especially Tuesday morning. Use of the forecast builder frost tool resulted in some patchy frost in a few spots Tuesday morning, and a spot or two on Wednesday morning. As is often the case this time of year there may also be fog in river valleys on these mornings which would limit frost formation. We will be adding the mention of patchy frost in the HWO for Tuesday and Wednesday morning to at least highlight the threat.
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&& .AVIATION...(For the 18Z TAFS through 18Z Friday afternoon) ISSUED AT 220 PM EDT THU OCT 12 2017 Cooler flow into the region has kept a llvl inversion in place, trapping low clouds across eastern KY through the morning and into the early afternoon. Better mixing to our SE has allowed for some clearing of skies to occur, and is now eroding away at clouds from SE to NW across our CWA, with KLOZ, KJKL, and KSJS expected to scatter out over the next hour. Scattering may continue into the other TAF sites as well throughout the afternoon. However, as we head into the overnight, the inversion will steepen once again and re-trap moisture. As was the case last night, this may be more of a low stratus event and less of a fog set up. Trended towards MVFR CIGs during the overnight, though there is still a bit of uncertainty, so conditions could fall below this at times. Clouds will slowly scatter out during the afternoon tomorrow, but exact timing of this is also somewhat uncertain. Winds will remain light and variable through the period, with general from from the SW to W aloft. && .JKL WATCHES/WARNINGS/ADVISORIES... NONE. && $$ UPDATE...JMW SHORT TERM...DJ LONG TERM...SBH AVIATION...JMW

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