Area Forecast Discussion
Issued by NWS Jackson, KY

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FXUS63 KJKL 150714

National Weather Service Jackson KY
314 AM EDT Tue Aug 15 2017

Issued at 130 AM EDT TUE AUG 15 2017

Updated the grids mainly to fine tune the PoPs through dawn based
on the latest radar trends and HRRR guidance. Also, tweaked sky
cover and the T/Td grids per the latest obs and trends. These have
been sent to the NDFD and web servers.

UPDATE Issued at 1037 PM EDT MON AUG 14 2017

Have continued to tweak pops throughout the evening based on
latest radar trends and hi-res guidance. Currently scattered to
numerous showers are located over far the far SE portion of the
CWA, with lightning/thunder continuing to wane. Have thunder
diminishing completely over the next few hours. Otherwise, reduced
pops to only scattered for the rest of the night based on latest
hi-res model trends. Also updated the forecast through tomorrow to
change to coverage wording in the weather grids instead of
probabilities. Finally, freshened up the near term grids for
temps, dew points, and winds to make sure they were on track with
current conditions. All changes have been published and sent to
NDFD/web. A new set of zones was also sent out to reflect latest
changes in pops/weather for overnight.

UPDATE Issued at 717 PM EDT MON AUG 14 2017

Made a couple updates, mainly to pops and weather, over the last
few hours. Tried to get pops more on track with current radar
trends. Leaned a bit towards the HRRR for model guidance as it
seemed to be initializing well and has thus far panned out pretty
well. However, some continued adjustments and updates are expected
throughout the rest of the evening as things evolve. Also updated
the near term forecast for temps, dew points, and winds, to make
sure they were on track with current conditions. All updates have
been published and sent to NDFD/web. A new forecast package was
sent out to reflect updated weather earlier in the afternoon. A
new HWO will be sent out later this evening once remaining thunder
has tapered off.


.SHORT TERM...(This evening through Tuesday night)
Issued at 347 PM EDT MON AUG 14 2017

...Locally heavy rains possible this afternoon and overnight...

Scattered thunderstorms with very heavy rains have moved into the
southwest part of the forecast area. These will continue to move
northeast but should decrease in intensity as we move into the
evening. Will mention locally heavy rains in the updated hazardous
weather outlook for the remainder of the afternoon and evening.

As we move into the overnight period another wave of showers
should affect the southern and central part of the forecast area
as a subtle short wave ripples through the mean flow. The GFS and
NAM MOS guidance as well as the blended forecast guidance point
towards likely to high chance rain probabilities for the overnight
period. Will follow that idea for tonight. A concern is locally
heavy rain tonight. The excessive rainfall outlook does not
include SE KY, but with the marginal risk right along the TN and
VA border this will be something to watch especially with precipitable
water right around 2 inches. We also received a spotter report of
1 inch of rain in Floyd County this morning with showers, and
this corresponded well with radar estimates for a small part of
the county. This helped highlight the efficient rain production
of showers in the current warm moist air mass. The NAM continued
its trend of trying to pinpoint an area of heavy rain tonight on
the order of 2-3 inches, and is still trying to point towards the
west central part of the forecast area. Pinpointing the location
of such a local high rain amount cannot be relied upon, and as
noted by the midnight forecast shift the NAM has been rather
inconsistent and an outlier when compared to the other models in
recent runs. This continued with the 12z runs. Despite that, with
the rainfall report this morning of 1 inch, the current radar
trends, the efficient rain production of the shower and storms
we`ve already seen, and the expected efficiency of showers and
storms this evening into the overnight, any showers and storms
will need to be monitored for excessive rain. On Tuesday more
showers and thunderstorms will be possible, but chances will be on
a downward trend through the day.

.LONG TERM...(Wednesday night through Monday)
Issued at 314 AM EDT TUE AUG 15 2017

The extended portion of the forecast begins on Wednesday night with
an active pattern on tap across the CONUS. The period will begin
with a strong trough tracking over the northern Plains and into
the Great Lakes as it drags a cold front over the OH Valley region
during the day on Thursday. Model profiles for Thursday afternoon
show quite a bit of instability and good directional shear. This
will definitely be a set up to monitor as SPC has issued a Day 3
Marginal severe risk. At this point, models so suggest that the
bulk of the dynamics and instability will be north of the Ohio
River where the greater risk will likely be.

Thursday night and into the weekend, the mid level ridge will set
up again over the Southeastern CONUS bringing return flow into the
area. This will be combined with several shortwaves passing
through the OH Valley with the next front passing through late
Saturday. At this time, this feature does not seem to have the
amount of instability and shear as the previous front. With the
return flow continuing into next week, the threat of afternoon
showers and thunderstorms will persist through the end of the
extended forecast period. Overall, a wet extended forecast is
expected through next week.


.AVIATION...(For the 06Z TAFS through 06Z Tuesday night)

Scattered showers and a stray thunderstorm or two continue to
affect eastern Kentucky early this morning. Coverage will be
highest in the south, but even SYM could see a shower, with some
increase in areal extent expected toward dawn in the far SE
portion of the state. Limited instability should keep the thunder
chances low, so just went with VCSH for all TAF sites. For
Tuesday, though, there will be more instability around likely
resulting in additional thunderstorm development in the
afternoon, but given uncertainty whether any particular TAF site
will be impacted, kept with VCTS, at this time. Winds will remain
light and variable throughout the period. Aside from the storm
threats for Tuesday afternoon, the main concern for this TAF is
the potential for low flight categories due to fog and low stratus
clouds through mid morning. With abundant moisture across the
region, we have the potential for LIFR conditions. However, can`t
rule out some brief drops below this category. Conditions should
begin improving shortly after daybreak, but expected no better
than BKN cloud cover in the low end VFR range through the
afternoon with any convection lowering the cigs/vis into the MVFR
or lower range.




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