Area Forecast Discussion
Issued by NWS Jackson, KY

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000 FXUS63 KJKL 222340 AFDJKL AREA FORECAST DISCUSSION National Weather Service Jackson KY 740 PM EDT Sat Jul 22 2017 .UPDATE... Issued at 740 PM EDT SAT JUL 22 2017 Issued an update to the forecast to input the latest observations and trend them through the evening hours. Adjusted pops as well through the night to more reflect the progression of upstream convection. It seems that the question of pops through the night will not be whether convection out west develops as it is trending towards further development now but rather how far south it will track. Thus at thus point will keep inherited pops in the forecast through tonight. At the very least, the Bluegrass does seem to be on target for some precip by 03z tonight. && .SHORT TERM...(This evening through Sunday night) Issued at 319 PM EDT SAT JUL 22 2017 Outflow from convection last night has kicked off some convection as it has crossed northern Kentucky this afternoon. A modest shear gradient is over eastern Kentucky with modest unidirectional flow in the north, to much weaker flow to the south. This will keep the stronger storms in the north through this evening with more isolated and weaker activity to the south. All of this should gradually weaken into the evening as the outflow moves on through. Focus will shift back to the north later this evening as a cold front will focus additional convective development back to the north tonight. This activity will likely evolve into an MCS as it outflows to the south. This will carry any shower/storm activity into northern Kentucky once again. Some uncertainty remains in the track of any activity as initiation will play a big part on where a potential MCS tracks. However, most of the CAMS have some activity working into our area overnight into early Sunday morning. With a moist boundary layer remaining, should some gusty winds will remain possible with storms as they track south and east. Tomorrow, the cold front will continue to make slow progress southward across eastern Kentucky and will continue to be the focus for additional shower and storm activity. What happens later in the day may be impacted by how the morning MCS pans out and what boundaries are left behind. However, we will keep the rain chances going through the day and through tomorrow night with better chances gradually shifting south with the front. Modest shear will be place along the cold frontal zone and will aid in the potential for a few severe storms with damaging winds continuing to be the main threat. Overall, looks like a few periods of wet weather will be possible over the next 36 hours. With the increase in clouds and precipitation, temperatures may stay a touch cooler tomorrow, but we may warm up between the morning MCS and afternoon convection, with mid to upper 80s still anticipated. This will keep heat index values in the 90s. .LONG TERM...(Monday through Saturday) Issued at 415 PM EDT SAT JUL 22 2017 A shortwave trough is expected to be moving from the Great Lakes and Ohio Valley into the Northeast and Appalachians with an upper level ridges remaining in place centered east of Bermuda and over the Southern Plains to Four Corners regions. At the surface, a cold front associated with low pressure moving across the Northeast U.S. to start the period is expected to be gradually working south and southeast into and across the area early in the period, while high pressure is expected to be centered over the Upper MS Valley. The shortwave trough is expected to gradually rotate across the northeast and across the Appalachians to the eastern seaboard on Monday. Height rises should ensue from Monday night into midweek as the axis of the ridge works toward and then across the area, although as happened earlier this week, the center of the mid and upper level ridge should remain to the west of the area in the Plains states. Models diverge in the position, areal extent, and magnitude of the ridge during the second half of the week with differences with downstream troughing over eastern Canada to the eastern Conus and shortwave troughs moving around the ridge. The model agreement was better for both the 12Z ECMWF and 12Z compared to 12 hours prior. Downstream of the western Conus ridging, an upper level low and stronger shortwave trough as well as associated sfc low pressure system will move across the Canadian Prairies and across James Bay and into northern Quebec by the end of the period. At the surface, high pressure should build into the area behind the front later Monday into Monday night and usher in a somewhat drier and colder airmass and bring some relief from the recent heat. The boundary should stall south of the area. Behind the front, temperatures will return to near normal with highs holding in the 80s and lows dropping below 70 in all areas. The high, however, should move east of the area by Wed into Wed night, with the boundary lifting north as a warm front at midweek and leading to an increase in humidity from Wednesday into Friday. As has been the case with extended models for the past few days, some uncertainty remains in timing of a cold front that will begin to shear out during the second half of the week associated with the upper low and low pressure system moving across central to eastern Canada. This front should drop south of the Great Lakes and to the OH River and recent trends indicate it moving south across the area around Friday. Isolated to scattered showers and thunderstorms are expected to linger into early in the period, as the front moves through. With the ridge building in or remaining in place across the area, chances for convection should be generally diurnally driven and more or less isolated in nature from Tuesday into Wednesday. Tuesday and Wednesday could be end up dry in most locations, but with the center of the ridge west of the area, the cap could be broken in a few locations each day. More organized convection will be possible during the second half of the week as the upper level flow becomes more northwesterly and a stronger shortwave trough and cold front approaches and moves into and across the Ohio Valley. && .AVIATION...(For the 00Z TAFS through 00Z Sunday evening) ISSUED AT 740 PM EDT SAT JUL 22 2017 Mainly VFR conditions will be seen through much of the period. The question is whether the convection up to the northwest will trend into the area. If this occurs, locations such as SYM, SJS and even JKL may drop to MVFR or IFR. Have input this possibility into the TAFs. SME and LOZ may very well remain VFR through the period if convection does not make it that far south as there is enough wind through the night to stunt fog development. Otherwise, expect some gusty 20 knot winds tomorrow afternoon. && .JKL WATCHES/WARNINGS/ADVISORIES... NONE. && $$ UPDATE...SHALLENBERGER SHORT TERM...KAS LONG TERM...JP AVIATION...SHALLENBERGER

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