Area Forecast Discussion
Issued by NWS Jackson, KY

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FXUS63 KJKL 270559 AAA
AFDJKL

AREA FORECAST DISCUSSION...UPDATED
National Weather Service Jackson KY
159 AM EDT Sun May 27 2018

.UPDATE...
Issued at 159 AM EDT SUN MAY 27 2018

There are two features of interest to affect the rest of the
overnight period. Outflow is moving in across northern Kentucky,
with a broken line of storms forming along this boundary. The
latest IR Satellite reveals the better storms consolidating on the
western flank of the boundary, towards the better instability.
This will likely continue to be the case through the overnight;
however, can not rule out a few showers or stray storm as the
outflow approaches the Bluegrass closer to the 4-5 am time frame.

An approaching mid-level wave and 850 mb convergence is also noted
across Tennessee, with a cluster of showers and storms moving
north. The HRRR has been overplaying the initial activity;
however, it seems reasonable that portions of southeastern
Kentucky will be affected by this convection at some point
through dawn. As such, increased POPs generally south of the Hal
Rogers Parkway and Highway 80 corridors. Updates have been sent.

UPDATE Issued at 1156 PM EDT SAT MAY 26 2018

Hourly grids were updated based on recent observation and
satellite trends. Thunder chances were decreased overnight. The
amount of fog overnight is uncertain due to lingering cloud cover
so held onto patchy fog at this time.

UPDATE Issued at 855 PM EDT SAT MAY 26 2018

Showers and thunderstorm activity has been waning over the past
hour overall and continue to wane. Most of the available
instability has been consumed and with sunset having passed, a
continued downward trend is anticipated. Pops have generally been
adjusted down over the next couple of hours based on satellite and
radar trends, though have opted to maintain slight chances of
showers overnight as the weakening mid and upper level trough
continues to work across the OH Valley region. Otherwise,
remaining hourly grids such as temperatures, dewpoints, and winds
were updated based on recent observations and trends. If current
trends of little if any thunder continue, an update to remove
thunder for the rest of the overnight will be considered over the
next hour or so. Some valley fog should develop toward 6z as
climo favors. Some localized dense fog is possible, especially
near where heavier rain fell today. However, debris clouds remain
and with the upper trough in place more clouds should persist
tonight so in general fog should be no worse than last night for
the bulk of the area.

&&

.SHORT TERM...(This evening through Sunday night)
Issued at 353 PM EDT SAT MAY 26 2018

The afternoon surface analysis shows the high pressure is still
off the Atlantic coast and no influence by any synoptic
boundaries. However, we are seeing influence from the mid and
upper levels as a weak trough progresses east. This combined with
unstable environment and ample moisture has lead to the
development of showers and thunderstorms across the region. The
main threat will be for heavy rainfall, with some locations seeing
an inch or more per hour rates at times and some storms are back
building as well. The good news is we have seen signs of better
steering flow to the east and this should help mitigate the
flooding risk to a extent. The overall coverage this afternoon and
evening will be dependent on mesoscale boundaries and this will
be somewhat tough to nail down. Right now, the coverage is
expected to decrease through the evening and overnight given the
loss of diurnal heating helping fuel these thunderstorms, but some
of the short term guidance has shown indications of outflows
developing new convection tonight. Given the lack of confidence
will lean toward slight POPs tonight. Also, will lean toward only
river valley fog, but this could be more widespread depending on
how precipitation evolved this afternoon.

For Sunday, the upper level help will wane and this will lead to
better convective coverage along the higher terrain near the
Virginia border once again. This is also where the better axis of
PWATs will reside and we could see some localized heavy rain
issues if the storms move across the same areas. Then sunday night
we will see some showers continue into the night, but the overall
coverage should remain limited. The fog will once again become a
issue given the moisture from the rainfall.

.LONG TERM...(Monday through Saturday)
Issued at 507 PM EDT SAT MAY 26 2018

Models have come into better agreement on the handling of Tropical
system Alberto during the period. They bring it onshore over the
western portion of the Florida panhandle on Monday, then track the
weakening system north to the lower Ohio valley by Wednesday, with
the remains picked up by the westerlies and moving northeast over
the Great Lakes late in the week. Although there is still
potential for forecast change at this time range, the model
agreement is at least supporting more confidence. This path would
take the heaviest precip with the core to our west. However the
general pattern will still favor convective precip in a deep
moisture environment over our area through much of the period,
especially during afternoon and evening hours during peak
instability. An exception is over the northern portion of the
area on Monday into Tuesday, where some drier mid/upper level air
initial over that area may limit the precip. The best shot at
precip with Alberto passing by should be on Wednesday. It may also
be close enough and deep enough yet for winds to kick up a bit as
well, but nothing of too much concern at this point.

Models show Alberto`s mid/upper level remains merging with a
shortwave trough over southeast Canada and then dropping back
south toward the Mid Atlantic states for Saturday. Timing of
system is critical for this to happen, and there is not a lot of
confidence in the exact outcome. If it were to happen, this would
potentially allow for a slightly drier air mass to make its way
south, and a lower POP has been used for Saturday.

&&

.AVIATION...(For the 06Z TAFS through 06Z Sunday night)
ISSUED AT 159 AM EDT SUN MAY 27 2018

Clouds will remain prevalent overnight, as a disturbance tracks in
from the Tennessee valley. Scattered showers and a few
thunderstorms will affect areas mainly south of a line form KSJS
to KLOZ. Meanwhile, an outflow boundary will approach the
Bluegrass from the north. This may spread at least a few showers
nearing KSYM by around 09z. Expect a gradual weakening trend to
this activity, so will maintain VFR, as clouds should keep the fog
confined to the deeper river valleys, as well as locations that
saw more significant rainfall on Saturday. Once this early morning
activity subsides, expect another round of scattered convection
which will peak in the afternoon. For now, will continue to
generalize at the TAF sites, keeping the mention of VCTS. Storms
will generally dissipate by around dusk. Winds will remain light
and variable through the period.

&&

.JKL WATCHES/WARNINGS/ADVISORIES...
NONE.
&&

$$

UPDATE...GEOGERIAN
SHORT TERM...DJ
LONG TERM...HAL
AVIATION...GEOGERIAN



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