Area Forecast Discussion
Issued by NWS Jackson, KY

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000 FXUS63 KJKL 270922 AFDJKL AREA FORECAST DISCUSSION National Weather Service Jackson KY 422 AM EST Mon Feb 27 2017 .SHORT TERM...
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(Today through Tuesday) Issued at 415 AM EST MON FEB 27 2017 Isentropic lift in advance of a shortwave trough moving into the OH Valley region has combined with return flow of moisture to the north to bring thickening and lowering clouds and mainly virga so far to east KY due to dry low levels. However, rain has been reported to have reached the ground recently at KSYM near Morehead and there have been upstream observations of rain reaching the ground over parts of western KY and western TN. This shortwave trough will move through the OH Valley today and the best chance for showers and or sprinkles will be in the morning to around midday when moisture is expected to be the deepest. Once this shortwave passes a lull in precipitation chances is anticipated although mid level clouds should linger for a few hours into the afternoon. Continued warm air advection with a low level downslope component to the flow will lead to a return to above normal temperatures. Locations across the south and east should reach near the 60 degree mark today with some locally higher high temperatures possible in valleys downwind of the high terrain near the VA border. Meanwhile, a series of more significant shortwave troughs are currently working across the western Conus. The first of these should move across the Rockies later today and tonight and reach the Great Lakes by the end of the period. Corresponding surface low pressure should begin to develop over the lee of the Rockies later today and then track into the Central Plains tonight and then into the Great Lakes by the end of the period reach eastern NB/western IA area late tonight and then near the Great Lakes late in the period. As this system deepens, the pressure gradient between this system and high pressure over the Atlantic will continue to transport moisture into the region on southwest flow and isentropic lift in advance of the warm front should bring an increase in showers late tonight and into the day on Tuesday as the warm front lifts across the area. The initial dry low level air and downslope component to the flow should limit the eastward extent of showers late tonight and early on Tuesday when combined with the best combination of lift and moisture will be across the western CWA and points west. The main trough axis is expected to enter the Plains late in the period. Southwest flow aloft should prevail through the near term period resulting in unsettled weather. With the increasing gradient later tonight and particularly on Tuesday winds aloft will increase and so will shear. Instability will also increase through the day so chances for thunder have been mentioned by late Tuesday morning through early evening. A stronger storm or two cannot be ruled out in the afternoon with gusty winds and possibly small hail being the main threats given projected drying between 700 mb and 500 mb along with stronger winds aloft. The northwest part of the area will be most favored for this. Outside of any thunderstorms, 925 to 850 mb winds should average 30kt or more on Tuesday. Mixing of this momentum down in and outside of showers and mixing should lead to gusty winds at times on Tuesday with gusts of 20 to 30kt possible. Locally stronger winds and gusts are also expected in the highest terrain near the VA border later tonight and on Tuesday with gusts over 30 mph possible on exposed ridges. There will be a downslope component to the flow across the southeast again on Tuesday. Depending on the degree of cloud cover LOZ and JKL could reach the 70 degree mark for one final time during this warm February, but upper 60s should at least be reached. .LONG TERM...(Tuesday night through Sunday) Issued at 340 AM EST MON FEB 27 2017 The period will start off unsettled with a shortwave trough pushing east across the Ohio river valley through Wednesday. A surface low is expected to track across the southern great lakes with a trailing cold front pushing east across our region. While models are in generally good agreement on the mid/upper level features, there is still some details that remain uncertain in the lower levels. Particularly, how unstable we can get either Tuesday night through early Wednesday afternoon. 00Z NAM continues to be an outlier showing the slowest frontal progression and most instability (just over 1000J/kg of SBCAPE). The 00z GFS was much weaker with the instability (almost none), but showed better potential for heavier rainfall. 00z ECMWF remained in the middle of those two solutions, but fell closer to the GFS. Given low confidence on NAM solutions beyond 60 hours, opting to keep thunder chances below 50 percent. If instability can materialize, the available shear would lead to a good risk for severe thunderstorms with strong 60-80 knot unidirectional flow in the mid levels. This corresponds to the severe storm prediction center issuing an enhanced risk of severe storms for Wednesday. The highest threat would be damaging winds risk for much of the area. A QLCS tornado could not be ruled out given the likely 0-3km shear being sufficient. Hopefully models can come together in the next 12 to 24 hours and provide a little more confidence on this emerging threat for Wednesday. Precipitable water values may climb to just a hair over 1.20 inches which is fairly high for late February. Based on climo, this would be near the 99th percentile for this time of year and also is over 3 standard deviations above normal for this time of year. For this reason, will include the mention of heavy rain in the HWO to go along with the severe threat. As the cold front exits to the south Wednesday evening, much colder air will filter into the region for the latter half of the week. A clipper system will work across the northern Ohio river valley late Thursday night into Friday and could spread some light snows across the region. As of right now, most of the area will be too far south to cash in on any of this light snow, but a light dusting may be possible north of I-64 around daybreak Friday. Certainly nothing that will be all that impactful right now. This system will help to provide another reinforcing shot of colder air for the end of the week. More zonal flow will take hold for the weekend, with a warming trend anticipated again. We could see highs back into the 60s by Sunday. Isentropic ascent develops by Sunday night into Monday bringing rain chances back into the picture again. At this point, pretty decent model agreement between the GFS and ECMWF to support rain chances on Monday, so will go with likely rain chances right now.
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&& .AVIATION...(For the 06Z TAFS through 06Z Monday night) ISSUED AT 137 AM EST MON FEB 27 2017 Surface high pressure continues to depart to the east while return flow and the approach of a shortwave trough from the Plains into the MS Valley and lower OH Valley is leading to increasing moisture from the top down. Mid level clouds will continue to increase with cloud bases lowering toward 6Kft or perhaps lower during the first 6 to 9 hours of the period or near 12Z or so as the wave passes by. VFR is expected to continue although there will be some sprinkles or perhaps light rain showers or patchy light rain falling from these, especially across the west and northwest starting during the first 3 to 4 hours of the period as low level moisture increases. Once the wave passes by, cloud bases will likely return toward 10kft or higher by the 16Z to 19Z window with a lull in the precipitation chances. Winds will average out of the southeast to southeast at 10KT or less. && .JKL WATCHES/WARNINGS/ADVISORIES... NONE. && $$ SHORT TERM...JP LONG TERM...KAS AVIATION...JP is the U.S. government's official web portal to all federal, state and local government web resources and services.