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Area forecast discussion...updated
National Weather Service Jackson Kentucky
807 PM EDT Thu Jul 20 2017

Update...
issued at 807 PM EDT Thursday Jul 20 2017

Isolated showers have dissipated into the early evening, with
mainly just some thicker cirrus hanging around. This should
gradually dissipate over the next few hours, but did beef up the
cloud cover initially to account for the latest satellite trends.
Forecast lows look on target thus far, and have mainly adjusted
the diurnal drop off over the next few hours to account for the
slightly warmer readings still in place.

&&

Short term...(this evening through Friday night)
issued at 420 PM EDT Thursday Jul 20 2017

As of mid afternoon, a ridge of surface high pressure extended
into east Kentucky from the southern MS valley region. A weak surface
trough is moving southeast across the area and along it some
enhanced cumulus developed along it as well as some showers near
the Daniel Boone Forest/Escarpment. These showers have weakened
over the past half an hour. At mid and upper levels, a ridge
remains in place, centered over the plains to MS valley region.
Meanwhile, south of an upper level low over the Hudson Bay region.
A series of shortwave troughs are moving through the northern
stream, the first is moving into the St Lawrence Valley and
upstate New York at this time and is helping send a cold front south of
the Great Lakes.

The upper level ridge will weaken from tonight through tomorrow
with 594 dm heights or higher decreasing in areal extent though
the center of the ridge should migrate to closer to the confluence
of the Ohio and MS rivers. At the same time, disturbances moving
around the ridge will pass into parts of the Ohio Valley and
appalachian. Weak southerly flow between higher pressure over the
southeast US and the nearly stalled front leading to a slight
increase in surface dewpoints by Friday. Some of the model
guidance brings some convective activity toward northeast Kentucky late
toward dawn including the hrrr. Confidence on convection that far
south is not too high, though given the warm and moist airmass a
couple of stray showers cannot be completely ruled out. Otherwise,
with high pressure dominating and some passing clouds combined
with generally higher dewpoints and crossover temps compared to
yesterday afternoon and night, overnight lows should be a couple
of degrees warmer on average for valley locations. At least patchy
River Valley fog if not greater coverage is also anticipated with
it becoming dense in a few spots overnight.

High pressure will again dominate on Friday though dewpoints
should creep up another degree or two. This combined with similar
Max T to today and yesterday will yield greater coverage of the
area with heat indices peaking at 100 or slightly above. In
general, the current forecast has heat indices in the 88 to 103
range for most locations, but if dewpoints are a degree or two
higher heat advisory criteria will be approached. At this point,
the heat is highlighted in the severe weather potential statement and an Special Weather Statement and later shifts
will evaluate any need that might arise for a headline for a
portion of the area. With higher dewpoints and the ridge
weakening, and the potential for a cluster of convection to move
into the area or send and outflow boundary into the area, the
chances for convection during peak heating should be higher on
Friday as compared to today. The warm and moist airmass lingering
into Friday night with the boundary to the north and weak
disturbances moving around the ridge, the threat for at least
isolated convection will linger into Friday night.

Long term...(saturday through thursday)
issued at 334 PM EDT Thursday Jul 20 2017

A slow moving cold front will push south Saturday into Monday,
providing increasing shower and thunderstorm chances to the area.
Best chances still look to be Sunday and Monday. This of cfront
will wash out as it tries to push south of the area by early next
week and may not do much to diminish moisture over the area. Thus,
an afternoon shower or storm may remain possible into the midweek
period. Heat and humidity will stay around through Sunday, but
will see a slight cool down early next week with the front washing
out just to our south. Thus, we will see a brief break from the
heat.

&&

Aviation...(for the 00z tafs through 00z Friday evening)
issued at 807 PM EDT Thursday Jul 20 2017

A neaby upper level ridge will maintain VFR conditions across the
region throught majority of the period, besides some MVFR or worse
fog to contend with between 06 and 12z. Given the increased low
level moisture, did carry some temporary IFR at sme between 11 and
12z. Building heat and humidity on Friday will allow for a threat
of isolated convection during the afternoon. Winds will remain
light and variable through the overnight, before increasing to
around 5 kts out of the west by Friday afternoon.

&&

Jkl watches/warnings/advisories...
none.
&&

$$

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