Area Forecast Discussion
Issued by NWS Jackson, KY

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000 FXUS63 KJKL 200558 AFDJKL AREA FORECAST DISCUSSION National Weather Service Jackson KY 1258 AM EST Mon Feb 20 2017 .UPDATE... Issued at 1151 PM EST SUN FEB 19 2017 As mentioned earlier main concern overnight was the fog formation. Areas in the north did finally clear out as expected and with the low temperature/dewpoint depressions left behind, dense fog has already begin to develop across much of northern and central Kentucky. The areas impacted are generally north of the differential temperature boundary we saw earlier tonight. We may see the dense fog develop to the south with time, so will need to monitor the trends overnight for any possible extension to the south. Updated to include more widespread fog in the forecast and to issue the advisory. UPDATE Issued at 653 PM EST SUN FEB 19 2017 Narrow band of clouds continue to hold on just north of the I-64 corridor. While the erosion of the clouds has slowed some with sunset, the subsidence building into the region should help to gradually erode the remainder of the clouds as the night goes on. Something to note is that we have a nice boundary showing up on JKL radar this evening associated with the differential temperature boundary from the cooler/cloudy areas in the north today to the areas that cleared out to the south. This boundary appears to be sagging southward towards our office. Behind the boundary, valley locations have already reached the upper 40s. We should see a sharp fall continue with temperatures in the valleys this evening. MOS guidance is supporting some mid 30s and based on current conditions, this doesn`t seem that unrealistic. Thus, will drop the valley locations a bit colder tonight. Regardless, temperatures will fall well under cross over temperatures, setting up a good night of radiational fog. Current forecast has this covered well. Also tweaked sky cover down overnight. Outside of the clouds in the north early on, probably only dealing with some high clouds moving in late tonight. && .SHORT TERM...(This evening through Monday night) Issued at 335 PM EST SUN FEB 19 2017 19z sfc analysis shows high pressure moving over Kentucky. While rather weak it has mustered enough strength to start the clearing process through the southern two thirds of the CWA. With the returning sunshine temperatures have rebounded into the lower 60s in the south but still are in the low 50s under the clouds for locations north of Interstate 64. Dewpoints, meanwhile, have held rather steady in the mid and upper 40s along with light and variable winds. Look for the ceilings continue to erode into the early evening with most places seeing clear skies through sunset. The models are in good agreement aloft through the short term portion of the forecast. They all depict a strong ridge passing over Kentucky and the Deep South tonight through Monday in advance of a full latitude trough crossing thr Rockies. This trough starts to split apart later Monday night with the southern portion closing off as it exits into the western Gulf. Meanwhile, the northern portion pushes quickly into the Great Lakes stretching the energy with this trough. Some of that energy will look to ride over eastern Kentucky early Tuesday ahead of the main trough axis. Given the decent agreement among the models have favored a general blend with a significant lean toward the higher resolution HRRR and NAM12 in the near term. Sensible weather will feature mostly clear skies to start the night leading to good radiational cooling. With the fairly high low level moisture in place we will likely see fog develop rather early in the night in the valleys and spread through much of the CWA - becoming dense late - particularly in the valleys. Have hit this in the grids (and TAFs) and will highlight it in the forthcoming HWO. Later shifts will need to monitor cloud cover and vsby changes tonight for a possible SPS or Dense Fog NPW. The fog will burn off quickly Monday morning with a very warm day on tap ahead of the slowly approaching cold front. For Monday night, the front starts to move into the state, but likely remain too far west through dawn for any significant rain chances. Will also apply some patchy fog to the valleys early Tuesday under increasing and thickening high clouds. Used the CONSShort and ShortBlend as the starting point for the grids through the short term portion of the forecast. Did make some adjustments to temperatures each night to account for a small ridge to valley difference tonight and a bit larger one tomorrow night. As for PoPs, kept them as initialized with no impact expected before 12z Tuesday. .LONG TERM...(Tuesday through Sunday) Issued at 330 PM EST SUN FEB 19 2017 The extended portion of the forecast will begin on Tuesday with an active and progressive pattern setting up. At this time, the main features of concern will be a wave tracking across the northern CONUS as well as another low tracking over the lower MS Valley undercutting the upper level ridge along the Front Range. During this time, eastern Kentucky falls in between the bulk of the forcing of these two features leading to a bit less QPF over the area, especially as it seems this boundary passing through the area begins to shear out by Wednesday morning. The super blend seems to hint at some lingering moisture behind this feature but with the new 12z Euro showing no indication, will leave pops out on Wednesday. By Thursday, a vigorous low ejects from the Front Range and into the central Plains as strong southerly flow develops just east of the MS River. Model profile indicate some good instability developing with the formation of the warm front on Thursday and into Thursday night. Therefore have introduced some thunder into the forecast during this period. By Friday morning, the warm front has lifted north of the area putting eastern Kentucky firmly in the warm sector. In fact, expect highs to reach into the lower 70s across the area. For this period, some of the best baroclinicity develops that has not been seen for a few weeks. Model profiles indicate a renewal of some good instability with the developed cold front. Have indicated some thunder for late Friday and into Friday night as well. While severe convection is still a low chance for eastern Kentucky, it is worth noting that SPC has highlighted a slight severe chance in central Kentucky for the Friday period. After passage of the most significant cold front not seen in a few weeks, temps on Saturday morning and into the day on Saturday will either be slowly rising or steady through the day. At this point, the bulk of the CAA is slow to enter the area with much of the moisture exited by the time the colder air filters into the area. While now apparent at this time, a post front would chance this chance but it seems the profile dries and clears out after passage, which also means for some of the coldest low temps of the extended. && .AVIATION...
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(For the 06Z TAFS through 06Z Monday night) ISSUED AT 1258 AM EST MON FEB 20 2017 Fog and subsequent visibility restrictions continue to be the primary concern of note tonight and early Monday morning. SYM is already seeing LIFR/IFR visibilities with VLIFR possible later tonight through the morning commute, especially near Mountain Parkway to the Interstate 64 corridor and points north. This will mix out by mid morning as heating ensues and VFR conditions return with nothing more than some high clouds streaming in. Easterly winds will remain light near or below 5 mph through the day.
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Dense Fog Advisory until 10 AM EST this morning for KYZ044- 050>052-058>060-104-106.
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&& $$ UPDATE...KAS SHORT TERM...GREIF LONG TERM...SHALLENBERGER AVIATION...GUSEMAN is the U.S. government's official web portal to all federal, state and local government web resources and services.