Area Forecast Discussion
Issued by NWS Jackson, KY

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134 FXUS63 KJKL 161448 AFDJKL AREA FORECAST DISCUSSION National Weather Service Jackson KY 948 AM EST Thu Nov 16 2017 .UPDATE... Issued at 948 AM EST THU NOV 16 2017 Latest satellite imagery and short range guidance indicates clouds will be more extensive today than previous forecast, especially across the northern and central parts of the area. However even the short range guidance does not seem to have a very good handle on this, but is trending in the right direction. Have updated NDFD and associated products to account for more cloud cover today. UPDATE Issued at 635 AM EST THU NOV 16 2017 The challenge this morning has been the isolated spots of lower stratus and/or fog that has set up on the back side of a weaker boundary from last night. Overall was more liberal with the patchy fog given this and keep some reasonable amount of clouds going as well. The other issue has been to advancement of an area of low stratus to our northwest this morning. The model guidance has struggled to hone in on this, but the HRRR has been the most consistent in regards to this area of stratus. Therefore leaned that direction for now and this will bring the better coverage of clouds into the Bluegrass through the morning. This will likely have to be updated as a better handle can be had in subsequent updates. Also updated temperatures given some of the eastern valley sites have seen decoupling early this morning under clearing skies. These thoughts and ideas have been added to the grids and also updated with the latest obs and trends. && .SHORT TERM...(Today through Friday) Issued at 331 AM EST THU NOV 16 2017 This morning the surface analysis shows a weak and more diffuse cold front has generally moved east of eastern Kentucky. The model theta-e gradient magnitude would suggest another front is west and this is also seen on the surface analysis charts this morning. This is a little stronger and will introduce more changes in wind and possibly some temperature differences. The challenge that has been presented this morning is in relation to the lower stratus. Behind the first front, we have seen some clearing but there has been some left over stratus/fog at times. This maybe tough to clear out until second front moves across the region and therefore did keep some clouds going and patchy fog through the morning. The second front has a area of stratus slowly progressing southward toward at least the BLuegrass portions of eastern Kentucky. The models have been having a tough time handling this and leaned toward a combo of NAMnest and HRRR with adjustments. Later today, the lower stratus will slowly scatter out in the north as we move toward the afternoon. This will lead to more sun by the afternoon, but highs will remain in the upper 40s to lower 50s under cold air advection pattern. Tonight, an area of high pressure will crest across the Ohio Valley as upper level ridge builds eastward. Given the potential for mostly clear skies this will lead to a decent shot of ridge/valley temperature splits. The question will be how much fog do we see in the valleys to mitigate lower temperatures. Right now will lean toward previous forecast of upper 20s in the deeper valleys and lower 30s elsewhere. There could be some freezing fog similar to yesterday morning, but think similarly this will be more of the heavy frost scenario. By Friday, a warm air advection pattern will take hold as surface high pressure moves east out the region. However, winds will be more in the way of southeasterly and this will probably lead to downsloping. Consequently, this will likely lead to lower afternoon RH values in the mid 20s to lower 30s, but winds will remain light. The superblend was overdone on the dewpoints and trended these closer to the adjusted MAV and MET. This will continue to be highlighted in the FWF. Otherwise, we are looking at a nice day with some increasing high clouds in the afternoon. Temperatures are in expected to top out in the mid 50s to lower 60s. .LONG TERM...(Friday night through Wednesday) Issued at 445 AM EST THU NOV 16 2017 The models are in only fair agreement aloft through the entirety of the long term portion of the forecast. They all start off well with an amplifying trough sweeping across the Plains and into the Upper Midwest/Mid Mississippi Valley by midday Saturday. This amplified, but progressive, system will then punch its way into and through the Ohio/Tennessee Valleys by early Sunday morning with the core of the energy running east along the Ohio River. The GFS is slightly faster and stronger than the ECMWF with this wave, but they are much closer than they were 24 hours ago. This has raised confidence in the blended solution for this time frame. Confidence lowers in its wake, though, as heights will slowly rebound over Kentucky even as more energy pours into and through the Great Lakes/eastern Ohio Valley on Sunday. A muddled picture emerges by mid week in the long wave pattern as energy and strong waves move into the Northern or Southern Plains depending on the model. As such, the evolution is still quite up in the air for this time step and through the rest of the extended, though the latest ECMWF is in between the faster GFS and slower/southern Canadian model. Going with the ECMWF idea does bring a closed low through the northern Great Lakes by Tuesday night with some limited height falls possible for Kentucky. The Canadian model, though, tries to develop a closed low over the Tennessee Valley Wednesday - now completely out of step with the other models. Accordingly, have discounted this solution and dampened its influence on the blends in GFE. With that being the case, am looking at slightly northwest flow for the area from mid week on but not much in the way of mid level energy affecting Kentucky - though that is subject to change due to low confidence. Sensible weather will feature breezy conditions building Friday night through Saturday considering the approach of the cold front and its strong parent low nearby. BUFKIT momentum transfer indicates that winds to 40 mph at the sfc will be possible ahead of and just behind the boundary as it passes eastern Kentucky on Saturday afternoon/evening. Have highlighted this potential in the HWO and will monitor it for potential wind headlines as we get closer. The front should go through with good soaking rains along with convective showers and perhaps a thunderstorm. Have not introduced that threat to the forecast, yet, but the possibility will need to be monitored with time. Colder air will follow in the front`s wake for Saturday night and Sunday. Lingering moisture and upslope flow may bring some mixed pcpn (rain and snow) to the ridges for a time early Sunday and this will also have to be watched in future forecasts. Chilly high pressure stars as the weather maker to start the new work week. This high will start to move off to the east Monday night and moderate, while also allowing a return flow of moisture north into the area from the Gulf. Meanwhile, another sfc low will be moving into the northern Great Lakes with a weak front stretched down to the Southern Plains. At this point, it seems that this will not be able to activate much of the return flow moisture keeping conditions mainly dry through Wednesday across the area before another cool high pressure bubble slides into the region from the northwest. Again, confidence in the latter half of the forecast is rather low due to model discrepancies at the sfc and aloft after Monday. Did make some fine tune adjustments to low temperatures each night depending on the flow regimen and potential for inversions/mostly clear conditions. As for PoPs, kept them high through fropa Saturday evening before taking them down by Sunday afternoon and through the rest of the forecast - primarily to remove the Candian`s input late. && .AVIATION...(For the 12Z TAFS through 12Z Friday morning) ISSUED AT 626 AM EST THU NOV 16 2017 It is quite the mix of conditions across eastern Kentucky this morning. We have seen isolated pockets of low stratus/fog in the wake of a weak frontal boundary that went through last night. This will lift and dissipate through the late morning. The other issue is a slightly stronger boundary will move through this morning and upstream we have been tracking an area of MVFR clouds moving southeast behind the front. The guidance has had a difficult time handling this, but the most reliable model so far has been the HRRR. That said, did lean my sky grids in that direction and given it has the best handle it does dissipate this as it moves the deck of clouds into eastern Kentucky. Therefore leaned toward MVFR deck at SYM/SJS/JKL only at this time. This lower stratus deck will diminish by around 17 to 18Z at the latest. Then we will be left with VFR conditions through the remainder of the period. Winds will remain generally light at most sites out of the southwest and west before veering around to the northwest later today. && .JKL WATCHES/WARNINGS/ADVISORIES... NONE. && $$ UPDATE...SBH SHORT TERM...DJ LONG TERM...GREIF AVIATION...DJ

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