Area Forecast Discussion
Issued by NWS Jackson, KY

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202 FXUS63 KJKL 220003 AFDJKL AREA FORECAST DISCUSSION National Weather Service Jackson KY 703 PM EST Tue Feb 21 2017 .UPDATE...
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Issued at 703 PM EST TUE FEB 21 2017 Showers are starting to expand from central Kentucky up across northern Kentucky, impacting our forecast areas north of I-64 with some light rain. Meanwhile, showers working across the Cumberland Plateau are hitting a wall as they try to push deeper into eastern Kentucky as the low level dry air remains in place, limiting the push of showers into the area. As the night wears on, we should slowly erode some of the dry air from above, but they may be a tough battle as downsloping southeast low level flow also strengthens. Thus, while it looks like we should see rain continuing to expand across the area, most of it will be on the light side, given the low level dry air. Areas that may do best with the rainfall would include our southwestern zones, farther away from the effects of this downsloping and areas north of I-64. It does appear rainfall is still a good bet despite the hostile environment in the low layers. Thus, no changes to the rain chances except to slow them down through the evening hours as it takes awhile to saturate low enough to see more than sprinkles.
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&& .SHORT TERM...(This evening through Wednesday night) Issued at 355 PM EST TUE FEB 21 2017 20z sfc analysis shows a low pressure area moving out of the Southern Plains and into the Deep South. This is attempting to push its pcpn shield into the area from the southwest but so far has been hindered by dry air at the sfc and still high ceiling levels. Sun shine through the earlier high thin clouds allowed temperatures to soar into the lower and middle 70s for much of the area this afternoon setting a record at JKL (75 degrees) and at least matching one at LOZ - 70 degrees. Dewpoints are starting to moisten up from the southwest with values across the CWA ranging from the lower 50s at EKQ in Wayne County to the upper 30s in the far east. Combined with temps in the 70s this is yielding RH values down in the mid to upper 20 percent range in the far east. Winds, meanwhile, are mostly light from the south at 10 mph or less, though a few places with more sunshine did see some gusts as high as 20 mph for a time. The models are in good agreement aloft through the short term portion of the forecast. They all depict a deep closed low breaking out of the pattern and sinking south to the Central Gulf Coast tonight while near zonal flow continues over Kentucky. The southern low then will progress into the eastern Gulf of Mexico on Wednesday while weak packets of energy make their way over Kentucky along with some weak height falls. The flow locally then turns more southwesterly as heights bottom out and start to climb again Wednesday night along with weak energy passing over head. Given the agreement will favor a general model blend for the broad picture and the HRRR/NAM12 for wx details through at least the near term portion of the forecast. Sensible weather will feature showers moving into the area from the southwest as cigs lower in the face of a moistening column. The northern edge of the pcpn shield from the low passing to the south will then slowly cross Kentucky tonight with some places picking up soaking rains on account of enhanced lift from a minor 300 mb jet streak passing to the northeast late tonight into Wednesday morning. Plenty of low level moisture will then be in place over this part of Kentucky into Thursday morning even as the accumulating rains gradually move out of the southeast during the day Wednesday. Showers may redevelop late Wednesday night over the northwest as more energy moves through aloft and a warm front starts to take shape from a developing deep sfc low well to the west. Started with the CONSShort and ShortBlend for the short term grids. Did not make too many adjustments of note to temperatures tonight and Wednesday night owing to the moist environment expected to be in place both nights. As for PoPs, did again adjust them for later tonight into Wednesday morning - translating the highest PoPs across the CWA more cleanly - with a significant nod to the NAM12. .LONG TERM...(Thursday through Tuesday) Issued at 230 PM EST TUE FEB 21 2017 The extended period begins on Thursday with the highlighted feature of the extended bearing down on eastern Kentucky. In the upper levels, a strong closed low ejects from the Front Range into the central Plains and east as it intensifies. Extending east along a stationary boundary, low level flow out of the south increases heading into Thursday afternoon and Thursday night as a warm front develops and lifts north. With the weak wave passing through before the front truly develops, would expect medium to low chance pops for thursday afternoon into Thursday night. Model soundings indicate substantial instability with the southerly flow and increased gradient so will be dealing with some thunder chances during the Thursday and Thursday night period. By Friday, the surface low shifts from the central Plains northeast into the western Great Lakes as it warps up and matures. Convection develops out in the Midwest and in central Kentucky Friday afternoon into Friday evening. Due to timing, the CAPE values of 800 to 1000 J/KG in eastern Kentucky will be on the wane heading into Friday night with the loss of daylight so for now, will keep the severe chances in central Kentucky. Due to the shear with this front a strong storm or two still seems possible. The line of showers and thunderstorms pushes through by midday Saturday. Models have remained consistent on the post frontal trough staying north and the cold air being slower to advect in behind the front for any change over to snow. Will continue to keep snow out of the forecast for this post front CAA. With the current pattern in place, this cold air doesn`t stay entrenched very long as after lows on Sunday morning in the upper 20s, already rebound into the upper 40s to near 50 for highs. With the upper level pattern remaining quite progressive and flattening, a weak wave will track across the north OH Valley by Monday morning into Monday afternoon. Due to the timing of arrival in the morning, temps will be cold enough for the rain to mix with or become all snow, especially in the higher elevations before changing to all rain Monday afternoon. Overall through the extended, temperatures remain abnormally warm and even the cold air push on Saturday and Sunday doesn`t seem to have a good residence time with a rather progressive pattern remaining. && .AVIATION...
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(For the 00Z TAFS through 00Z Wednesday evening) ISSUED AT 703 PM EST TUE FEB 21 2017 Difficult aviation forecast tonight across eastern Kentucky. While most hi-res model output wants to crater ceilings later tonight. The flow will remain out of the southeast and is generally downsloping for eastern Kentucky. This will produce a hostile environment for low level cloud development. Thus, opting to go more optimistic with the TAFS. The flow only strengthens through the night, so at best, perhaps we see some brief periods of MVFR cigs at some of the TAF sites. Best shot at more persistent MVFR conditions would be KSME, farther away from the downsloping winds, but even here will experience some disruptions. Thus, low confidence forecast with very few models picking up on this southeast flow impacting the cloud bases. However, situations like this in the past have resulted in more VFR ceilings across most of the area. Regardless, some very light rain will be seen overnight.
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&& .JKL WATCHES/WARNINGS/ADVISORIES... NONE. && $$ UPDATE...KAS SHORT TERM...GREIF LONG TERM...SHALLENBERGER AVIATION...KAS

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