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Area forecast discussion 
National Weather Service Nashville Tennessee
1136 PM CDT Friday Apr 17 2015

Update...for aviation.

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Aviation...bna/ckv/csv...the main concern and challenge for
overnight into Saturday morning will be the formation of fog and
stratus. Conditions are expected to drop to mainly MVFR
overnight...with tempo IFR or perhaps LIFR around daybreak.
Specific ceilings/visibilities will vary considerably...so expect several
amendments. On Saturday...conditions will improve to VFR by 16z.
Around the end of the taf period (19/06z) a low pressure and warm
front will bring widespread showers and some thunderstorms across
the area.

13

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Previous discussion... /issued 928 PM CDT Friday Apr 17 2015/

Update...
updated to remove mention of light evening showers for tonight from
the suite of forecast products. Remainder of forecast remains on
track.

Previous discussion.../issued 631 PM CDT Friday Apr 17 2015/

Have updated the suite of forecast products based on current surface
observation...satellite...and regional radar trends...along with consensus
of short range models...in showing some lingering showers through the middle
evening hours across locations approaching the Tennessee/Alabama border and the
southern half of the Cumberland Plateau region. Believe the middle state
will remain dry reminder of tonight. Will extend areas fog through middle
morning hours.

31

Previous discussion.../issued 318 PM CDT Friday Apr 17 2015/

Short term...it was mostly cloudy and seasonably mild across the
middle state this afternoon, with 2 PM temperatures mainly in the
upper 60s to around 70. An upper level disturbance, scooting to
our south, across Mississippi and Alabama, was producing some
isolated showers extreme southern parts of the middle-state and
those could linger into the evening hours as well. In fact,
wouldn't be surprised to see a shower or thunderstorm pop up as
far north as csv this evening.

Once the shortwave moves east of our area late this evening, believe
at least partial clearing will ensue over most of our forecast
area and allow for the development of areas of fog. Any fog that
forms will have a tendency to lift and form a low overcast ceiling.
However, it's possible that some of the fog could become locally
dense, especially over about the western two-thirds of middle
Tennessee.

Models continue to slow down the return moisture on Saturday, and
it looks like the best chance for afternoon showers and
thunderstorms will be confined to our southwestern counties. That
means, much of the middle-state could Eek out another mostly dry day.

Still looks like showers and thunderstorms will overspread the
region Saturday night, as a surface low moves northward across
western Tennessee into western Kentucky. One of the main concerns with these
showers and storms will be locally heavy downpours, with precipitable waters
forecast to be around 1.5" the rains we had earlier this week
have saturated the ground pretty well. So, any heavy downpours
that occur Saturday night and Sunday morning will likely produce
ponding of water in low lying areas and could lead to isolated
flash flooding.

We will have a Low Cape/high helicity environment during the
Sat/sun event, and with the surface low tracking just to our west,
we'll have to keep an eye out to see if any of the convection is
able to tap that minimal cape and produce any strong-to-severe
thunderstorms. Swath of low level helicities around 300 m2/s2
spreads across the area between 09z and 13z early Sunday morning, but
as of now, Storm Prediction Center has the middle-state only in a general thunderstorm area
through 12z sun. Most recent model runs suggest the best chance
for isolated strong-to-severe storms would probably be over our
eastern counties during a relatively brief window between 11z and
15z, when the Rising Sun should be able to kick up the convective available potential energy just
a bit. If helicities reach forecast values, it wouldn't be out of
the question to see a few brief tornadoes try to spin up. However,
on the other hand, with skies expected to remain mostly cloudy,
surface-based convective available potential energy may be difficult to generate and tap.

A cold front pushes across the area Sunday night, and will likely
be attended by a squall line and the potential for isolated
strong-to-severe thunderstorms. Storm Prediction Center has US in a slight risk for
severe storms between 12z/19 and 12z/20 and right now it looks like
the main concern with those storms will be heavy downpours, gusty
straight line winds, and hail.

We finally get to see at least a brief stretch of dry weather next
Tuesday and Wednesday, as high pressure builds in over the area
and gives US a few chilly mornings, with lows in the 40s.
Meanwhile, daytime highs will be seasonably mild, and average between
65 and 70 degrees each day.

Long term...we may see a warm front lift across our area as early
as Wednesday night, bringing another chance for showers and
thunderstorms, and there will be at least a small chance for
showers in the forecast into Friday as well.

19

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Ohx watches/warnings/advisories...none.

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