Area Forecast Discussion
Issued by NWS Jackson, KY

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000 FXUS63 KJKL 230530 AFDJKL AREA FORECAST DISCUSSION National Weather Service Jackson KY 1230 AM EST Thu Feb 23 2017 .UPDATE... Issued at 1025 PM EST WED FEB 22 2017 A few patches of clouds have developed, but still not enough to impact the ongoing fog forecast. Even looks like the trend may be to clear off areas near I-75 and North of I-64 over the next 3 to 4 hours. Models still try to bring cloud cover back into the area towards daybreak and will continue to hold the line on that idea. However, at this point, looks like most of the night will see mostly clear skies. At this point, SPS for fog has the extent of the fog covered well, so no need to make any changes. UPDATE Issued at 839 PM EST WED FEB 22 2017 Skies of continued to clear out with the exception in the far northern portion of our forecast area. With the clearing, valley temperatures continue to fall and are already below cross over temperatures. A fellow coworker noted some fog already forming down in the valley near our office. With these trends, have opted to enhance the fog wording and threats tonight. First off, have including the mention of dense fog in the HWO and also issued an SPS to cover the threat through the night. Also updated the forecast to include the mention of dense fog. As of right now, no plans for an advisory, but will continue to watch trends and see how the next few hours play out and how much the fog expands. So far, no obs sites are reporting fog, but mainly due to the fact, we have very few observing platforms in valley locations. UPDATE Issued at 510 PM EST WED FEB 22 2017 Per satellite trends, mid/upper level clouds starting to exit to the east with low deck of clouds breaking up with southeast flow. This will allow for some partial clearing this evening into the overnight hours. Updated the sky cover to allow for this break up in the sky cover. With less cloud cover, temperatures, particularly in the valleys will likely take a more sizable tumble this evening. Coop guidance suggest mid 40s as the bottom for temperatures tonight and this seems reasonable with dewpoints currently in the mid 50s over much of the region. However, will dip lows into the upper 40s tonight and this should establish some river valley fog. Updated forecast to put this fog mention into the forecast. Finally, clouds look like they may try to redevelop across central Kentucky towards dawn or early Thursday morning and could trigger a few sprinkles. This was in line with the previous forecast, but did slow down the arrival of the sprinkles until closer to dawn in the Bluegrass region. With the increase in sprinkles expected, cloud cover will also move back in, with fog lifting as the clouds arrive in the morning. All updated grids have been saved and sent to NDFD. && .SHORT TERM...
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(This evening through Thursday night) Issued at 400 PM EST WED FEB 22 2017 20z sfc analysis shows East Kentucky between a broad area of low pressure to the northwest and another dropping into the northeast Gulf of Mexico. The showers associated with this southern low have just about dried up over the area with only some lingering sprinkles around along with patches of lower clouds. These clouds are trying to break up over Central Kentucky and in the I-75 corridor. Temperatures are responding to the returning peeks of sunshine in the west with low and mid 60s noted while to the east under the thicker clouds readings are in the mid to upper 50s. Dewpoints, meanwhile, are in the low to mid 50s across the area. Winds are generally from the south to southeast at 5 to 10 mph. The models are in good agreement aloft through the short term portion of the forecast. They all depict the southern low deeply diving west to east through southern Florida while southwest flow will commence over Kentucky for tonight into Thursday. A strengthening band of energy will pass through the Ohio Valley Thursday afternoon as the southwest flow builds in the face of a large trough moving through the northern Rockies and into the High Plains Thursday night. The GFS is a bit faster and further east than the ECMWF with this feature. All in all, though, a general model blend looks reasonable through the short term given the broad model agreement and limited differences seen for eastern Kentucky. Sensible weather will feature a few lingering showers in the far east early this evening before we start to dry out overnight. Have carried a chance of sprinkles an hour or so beyond the measurable PoP before all pcpn comes to an end from northwest to southeast this evening. Do expect the breaks in the clouds to fill back in later tonight which should hamper radiational cooling and fog formation. Have limited the latter to the valleys with a minimal of terrain based differences in temperatures overnight. For Thursday, rather cloudy conditions will continue with moisture left behind and the development of a warm front from a deep low approaching from the west. Ahead of this low, sprinkles will be possible and even a shower or thunderstorm as eastern Kentucky will reside in the warm sector of the larger system. For Thursday night the warm front will lift well north of the area with WAA through the night setting up a good ridge to valley difference in temperatures with very warm readings expected on the hilltops. Will also allow for some patchy valley fog late at night in the valleys. Again started with the CONSShort and ShortBlend for the short term grids. Did not make too many adjustments of note to temperatures tonight owing to the moist environment but did open up a distinct ridge to valley terrain differences in temperatures Thursday night as WAA really kicks in ahead of the next cold front. As for PoPs, did adjust them closer to the previous forecast for Thursday afternoon which also matched up better with the latest NAM12 - maintaining the slight chance values for this time frame. .LONG TERM...(Friday through Wednesday) Issued at 240 PM EST WED FEB 22 2017 The long term portion of the forecast will be active, with several systems affecting the area. Record warm temperatures will be on tap to end the week, with a cool down in store for the weekend. Temperatures will quickly warm again as we move into next week. The first system to affect the area is a dynamic upper low and associated surface low that will move out of the plains Friday and into the Great Lakes region Friday night. The Day 3 Outlook from the Storm Prediction Center indicates a marginal risk for severe storms with this system with the slight and enhanced areas to our west and northwest. Strong southwest flow ahead of the low will help to shatter record highs at Jackson and London on Friday. Currently we are forecasting 77 at Jackson on Friday and 76 at London. The record highs for Friday, February 24 are 71 at Jackson and 70 at London. Model soundings indicate the atmosphere will be capped for much of the day Friday, and it appears there will be little or no shower development in eastern KY on Friday. The most likely scenario for Friday is for thunderstorm development to occur in the late afternoon or early evening in Indiana ahead of an advancing cold front with the storms evolving into a line and developing southwest. There is good model agreement that the line will not move into eastern KY until late Friday night. The best dynamics and instability will exist to our west Friday evening and it is likely the storms will be on a decreasing trend as they move across our area Friday night. However, this will need to be monitored over the next couple of days. The cold front which will be focusing the thunderstorms is forecast to pass to the east of KY by daybreak Saturday, and cooler air will spread into the area for the remainder of the weekend. Temperatures will still be above normal to begin Saturday but then near normal temperatures should prevail for Saturday night into Sunday night. The next system will approach the area from the plains Sunday night, bringing more rain to start the week. However, there is considerable model disagreement with the evolution and track of this system. The GFS is further north and quicker to exit the system to our east, with dry weather returning Tuesday, before the next system moves in on Wednesday. The ECMWF is slower and further south with the early week system, with rain chances lingering through Tuesday. The blended approach used here favors keeping rain chances in the forecast for Sunday night into Wednesday. In either case if precipitation moves into the area quick enough Sunday night, there is a remote possibility a few snow flakes could mix with the rain late Sunday night before quickly transitioning to all rain early Monday morning.
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&& .AVIATION...
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(For the 06Z TAFS through 06Z Thursday night) ISSUED AT 1230 PM EST WED FEB 22 2017 The TAF period will be a complicated one with several dependent variables to deal with. The period is beginning with some lower stratus streaming across the Bluegrass and some high clouds mixed in at times across the remainder of the region. Valley locations that have cleared and decoupled are seeing widespread to areas of dense fog. This will as usual be more dense in areas that saw more rainfall yesterday and/or areas nearer bodies of water. The TAF sites are currently not seeing any issues with most of the ridge sites remaining mixed this hour. The only question at some of the elevated sites will be does any fog actually advect in toward dawn and right now will leave that thought out given low confidence. The next issue will be cloud cover overnight and just how much are we going to see. The guidance is certainly struggling initiation wise including much of the short term guidance, and this is making for a challenging sky cover forecast. Right now sticking close to previous forecast and given the HRRR which is the best guidance right now has clouds developing toward dawn. That said it does look like this will be in the low MVFR range at this point. Winds will remain light through the period.
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&& .JKL WATCHES/WARNINGS/ADVISORIES... NONE. && $$ UPDATE...KAS SHORT TERM...GREIF LONG TERM...SBH AVIATION...DJ

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