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Area forecast discussion
National Weather Service Jackson Kentucky
1049 am EDT Fri Jul 28 2017

Update...
issued at 1049 am EDT Friday Jul 28 2017

Main issue continue to be the concern for heavy rain and flash
flooding. Most of the synoptic set-up is favorable for locally
very heavy rainfall. Precipitable water is high (~2"), steering
winds and storm motion will be slow (~15 kts or less), upper
level diffluence will be increasing today due to a shortwave
trough rotating through a northeast Continental U.S. Trough, and cape
profiles are tall and thin. Much of the area was primed with rain
in the last 24 hours. However, we are still socked in under
clouds, and significant destabilization is lacking so far today.
If we can muster enough instability and start seeing more
significant convection, our Flash Flood Watch may need expansion.
At the present it already encompasses the locations which saw the
heaviest rain in the last 24 hours, and will let it ride.



Update issued at 819 am EDT Friday Jul 28 2017

Convection filled in during the overnight hours, with some
training taking place across far eastern Kentucky. The last few
runs of the hrrr have been playing up convection across the east
through the day, and given the recent priming, have hoisted a
Flash Flood Watch until 8 PM this evening. Also freshened up the
hourly temperatures and dew points based on the latest trends in
observations. Updates have been sent.

&&

Short term...(today through saturday)
issued at 359 am EDT Friday Jul 28 2017

The latest surface map features a cold front draped east to west
near the Ohio River. Pwats are currently running around 2 inches
across eastern Kentucky, with some shower and thunderstorm
activity ongoing across portions of the area. Aloft, a short wave
trough was rotating south out of the western Great Lakes region.

The models are in good agreement with this short wave trough
turning more southeastward as it encounters flow around an upper
level ridge axis centered near the Southern Plains. This will
allow the cold front to pass south across our area through the
day and into this evening. Expect another day of unsettled
weather, with locally heavy rainfall and isolated flash flooding
the main concern. Confidence in where the axis of heaviest
rainfall will set up remains on the lower side. So, will only
highlight the threat in the severe weather potential statement. Another more limiting factor
today will be instability, given the amount of cloud cover in
place. Highs will be around 80.

Pops will diminish from northwest to southeast this evening and
into Saturday, as the trough axis and deeper moisture exit to our
east. Lows tonight will range from the lower 60s north of I-64, to
the mid 60s near the Tennessee/Kentucky border. Some showers will
continue to threaten far southeastern Kentucky through the
morning hours, before high pressure builds in across the area.
Highs on Saturday will be mainly in the upper 70s, with dew points
down into the lower 60s.

Long term...(saturday night through thursday)
issued at 333 am EDT Friday Jul 28 2017

The period begins with an upper level trough continuing to dig southeast
across the East Coast through a good portion of the week. This
will combine with a surface high that crests to the northwest across the
upper Mississippi River valley to lead to a extended period of
below to near normal temperatures for this time of year. The best
reflection of below normal heights for this time of year reside in
the 700 to 850 mb levels at 3 plus Standard deviations below
normal giving way to the aforementioned cooler temperatures, and
lesser but still noticeable at the 500 mb level at around 2
Standard deviations below normal. Also given the clockwise flow
(north to northeast winds) around the surface high the region will
experience a welcome decrease in moisture and therefore a break in
the sticky airmass normally seen this time of year. This will all
combine to lead to a 4 to 5 day period of dry weather.

The pattern will begin to swing back toward Summer to round out
the period. This as the previously mentioned surface high
progresses southeast and becomes less defined. Also a upper level
trough will sink southeast toward the Ohio Valley leading to better
chances of pops. Thinking the slight chance of thunderstorms
picked up by the blended guidance is sufficient at this point.
High temperatures to round out the period will be near normal for
this time of year, but the moisture/muggy conditions will creep
back into the region hints with pwats climbing back above 1 inch
by Thursday.

&&

Aviation...(for the 12z tafs through 12z Saturday morning)
issued at 819 am EDT Friday Jul 28 2017

An approaching cold front will bring mainly MVFR ceilings as well
as numerous showers and scattered thunderstorms through early this
evening. Convection will diminish from north to south this
evening, with any partial clearing leading to some lower IFR
stratus towards dawn. West southwest winds at 5 to 10 kts, will
veer to the north northwest at around 5 kts behind the frontal
passage.

&&

Jkl watches/warnings/advisories...
Flash Flood Watch until 8 PM EDT this evening for kyz086>088-104-
106>120.

&&

$$

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