Severe Thunderstorm Warning 9, NWS Jackson, KY

AREA FORECAST DISCUSSION
National Weather Service Jackson KY
255 PM EDT Sun May 26 2019

.SHORT TERM...(This evening through Monday night)
Issued at 254 PM EDT SUN MAY 26 2019

The large mid/upper level ridge remains centered over the
southeast U.S. However a couple of mid level short waves will move
through the OH valley on the northern periphery of the ridge this
afternoon and again Monday, bringing chances of showers and
thunderstorms.

The wave today is more pronounced than what is forecast for
Monday. An associated Mesoscale Convective Vortex (MCV) was over
southern IL early this afternoon, and thunderstorms were
increasing in coverage and intensity out ahead of this feature.
MLCAPE in excess of 1000 J/KG was analyzed over central KY
extending into eastern KY and could increase to around 1500 J/KG.
Effective bulk shear ranged from 40 knots over far northeast KY to
30 knots in the far southeast. There is also a surface boundary
across the northern part of the forecast area that appears to be
left from convection that occurred to our north last night and
early this morning. The shear, in combination with some low level
convergence along the remnant boundary, will help support
organized convection over the central and northern part of the
forecast area. This is in line with the current severe
thunderstorm watch. Forecast soundings show a significant mid
level dry layer and DCAPEs around 1000 J/KG. This supports the
idea of damaging wind gusts with storms this afternoon and early
evening. The best chance for severe storms will be from 4 PM this
afternoon to 8 PM this evening.

The other concern this evening will be the heavy rain threat. The
12Z ILN sounding and satellite based data shows precipitable
water (PW) from 1.3 to 1.5 inches, but based on model soundings
this could increase to closer to 2 inches. Current PW is around
the 80th percentile, but could increase to exceed the 95th
percentile. Storms should be progressive this evening, but some
training is possible over the far northern part of the area which
is in the marginal risk area for excessive rainfall per WPC.

With the passage of the short wave and MCV, and loss of daytime
heating, convection will wane this evening, with the severe
threat ending by 9 PM EDT. The short wave that moves through the
OH valley on Monday does not look to be as robust as today's wave,
and the threat for strong to severe storms will be less. However,
it should be noted that the SPC Day 2 outlook does have the
northern part of the forecast area in a marginal risk for severe
storms on Monday.

.LONG TERM...(Tuesday through Sunday)
Issued at 254 PM EDT SUN MAY 26 2019

The extended forecast period begins on Tuesday with an amplified
pattern remaining in place across the CONUS. This pattern features
an active trend with the persistent trough over the west and a stout
Bermuda High over the southeastern CONUS. Return flow remains in
place over eastern Kentucky with the ridge maintaining over the
southeastern CONUS. This will successfully stunt good convection
over eastern Kentucky for Tuesday and Wednesday. With a boundary
draped to the north, there will remain a possibility of a shower or
a storm to creep into the Bluegrass area but this will likely remain
dry. The southerly flow in place will bring continuous warm air into
the region leading to high temperatures into the upper 80s and lower
90s which will be near record temperatures.

A change in the pattern will be likely come Thursday as the mid
level gets pushed eastward with a strong jet stream aloft pushing
the trough eastward into the Midwest. This will drag a cold front
into the region for Thursday and bringing the chance of showers and
thunderstorms. With the boundary pushing eastward against the ridge,
the feature will wash out a bit as it comes into the area. Model
soundings support this with minimal instability and just enough for
general thunderstorms and showers across the area for Thursday
afternoon and as well into Friday. Some remaining subsidence aloft
will still be evident through the day on Thursday and into Friday
and thus will keep the Super Blend recommendation of low chance
pops. Once this front moves through, it gets hung up over the ridge
and remains draped over eastern Kentucky. This feature will become a
firing point for convection for Friday and Saturday. The other
change in the pattern will be the cooler air that moved into the
area which will knock highs into the lower 80s for highs. Thus, the
extended will feature near record warmth to begin the extended but a
cold front will bring a cooldown to more normal high temps for the
rest of the extended. The ridge will lessen its hold for the latter
half of the extended with afternoon showers and thunderstorms each
day from Friday through Saturday.

&&

.AVIATION...(For the 18Z TAFS through 18Z Monday afternoon)
ISSUED AT 147 PM EDT SUN MAY 26 2019

A wave of low pressure moving across the OH Valley will bring
scattered thunderstorms to the northern and central part of the
forecast area late this afternoon and evening. VFR conditions will
prevail outside thunderstorms this afternoon. Will carry VCTS at
SYM, JKL, and SJS, as exact timing at any given TAF site is
uncertain at this time. Will need to update TAFs as convection
moves into the area.

There is some uncertainty in the forecast conditions for tonight.
MVFR ceilings may develop in the wake of today's convection, and
guidance does support this. Fog tonight will depend on where and
how much rain falls this afternoon and evening. Even with the
recent dry weather there were a few hours of MVFR visibility in
fog at LOZ late last night and early this morning. With that in
mind have included some MVFR fog at SME and LOZ around dawn on
Monday.

&&

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

SHORT TERM...SBH
LONG TERM...SHALLENBERGER
AVIATION...SBH

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