Area Forecast Discussion
Issued by NWS Jackson, KY

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000 FXUS63 KJKL 121043 AFDJKL AREA FORECAST DISCUSSION National Weather Service Jackson KY 643 AM EDT Thu Oct 12 2017 .UPDATE... Issued at 638 AM EDT THU OCT 12 2017 A solid area of stratus continues to plague the region this morning, and this is not allowing quite the drop in temperatures that was possible. Therefore needed to freshen the hourly temperatures reflect the trends. Also updated the SKY grids to match the HRRR trends, which have seemed to be the best based on the current observed trends and forecast thinking. Otherwise more minor tweaks were needed to deal with the latest obs and trends. && .SHORT TERM...(Today through Friday) Issued at 343 AM EDT THU OCT 12 2017 The morning surface analysis shows an area of surface high pressure building eastward and centered across eastern MO. This high along with a upper level ridge will build east through the forecast period. The latest GOES-16 Nighttime Microphysics product indicates a vast area of stratus has spilled into eastern KY through the night. This area of stratus is being brought on by a strong inversion at around 900mb level and deep layer of dry air aloft suppressing the low level moisture. There remains some potential for this deck to lower enough to get some patchy fog and therefore did keep this going this morning. The time of year and forecast soundings give way to higher confidence for a mostly cloudy to cloudy skies through the early afternoon at least. The confidence is higher in seeing clearing quicker in the far southeast and higher ridge top locations given the depth of the moist layer. Consequently, the forecast highs for today could suffer from the low stratus and did lean toward a raw model blend that seemed to have a more reasonable handle on this idea. The confidence is lesser on how clouds and/or fog develops tonight. The soundings are not as clear on how much low level moisture will be trapped at the lower levels, and therefore kept the clouds more than the blend but much less than what we saw last night coverage wise. The implications on fog and overnight low temperatures will also suffer from this so did keep closer to previous, but then limited the fog to patchy given the uncertainty. The uncertainty on clouds will likely leak into Friday and for now think we should see more clearing through morning on Friday. Therefore, will lean toward the more optimistic blended guidance for afternoon high temperatures. .LONG TERM...(Friday night through Wednesday) Issued at 330 AM EDT THU OCT 12 2017 Lots of uncertainty continues into Friday night regarding the potential cloud cover. If we can stay clear overnight, then we could see some valley fog develop, but 00z NAM is continuing to support some level of low level cloud cover possibly hanging in through this period. For now, will leave the fog out of the forecast, with models overall doing poorly on this low level cloud cover. Looks like better potential for clearing this weekend and with better confidence on the clear skies, will go with some fog for Saturday night. Sunday into Sunday night, a strong cold front will sweep south across the Commonwealth. This will bring a period of showers to the area from Sunday afternoon through Sunday night. Instability is pretty weak with this system with only a narrow ribbon noted on the NAM. Not sure this will be enough to get thunder as surface instability remains below 100J/kg. However, previous forecast had thunder, so will let it go for now and see if we have better support with the next few model runs. If we can generate some thunder, there is modest shear in place to support a few strong wind gusts Saturday afternoon or evening. However, severe storm threat looks low given the lack of better instability. Rain chances will slowly diminish into early Monday morning, before a massive and very strong ridge builds into the Ohio river valley next week. This coupled with much drier and cooler air filtering in behind the exiting cold front will set the stage for more fall-like weather. Highs will drop back to the 60s for Monday and Tuesday with lows falling well into the 40s. Even some mid to upper 30s will be possible come Tuesday morning. At this point, the combination of rainfall from Sunday/Sunday night, coupled with cross over temperatures from the previous afternoon still in the 40s, would favor more fog formation than frost. However, a few widely isolated instances of frost may be possible Tuesday morning. Better mixing is expected on Tuesday and that should bring those cross over temperatures/dewpoints a bit lower Tuesday afternoon. This would potential support a better frost threat in the sheltered valleys (away from rivers and lakes) Wednesday morning. Fog will still be more likely favored over frost, but there is still that outside chance of some very patchy frost. Ridge will slide east into Wednesday night and Thursday with the boundary layer warming with return flow. This should bring slightly milder temperatures as we head into the mid to late week period. However, at this time, the dry weather should hold through next week. && .AVIATION...
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(For the 12Z TAFS through 12Z Friday morning) ISSUED AT 643 AM EDT THU OCT 12 2017 The morning surface analysis shows an area of surface high pressure continuing to build eastward this morning. The latest satellite data shows a large area of low stratus stretching from the Upper Midwest to the Tennessee Valley regions under this high pressure. This has kept MVFR to IFR CIGs throughout the overnight hours. That said, based on the latest guidance this stratus deck will struggle to lift out until around 18 to 20Z then VFR CIGs make a return. Tonight there remains some uncertainty on if or when the low stratus sets back into the region and for now will lean toward a MVFR CIG/VIS approach. Winds will generally remain light and variable through the TAF period out of the east and north at times.
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&& .JKL WATCHES/WARNINGS/ADVISORIES... NONE. && $$ UPDATE...DJ SHORT TERM...DJ LONG TERM...KAS AVIATION...DJ

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