Flash Flooding and Debris Flows in Kentucky, June 9 to 11, 2021

AREA FORECAST DISCUSSION
National Weather Service Jackson KY
609 AM EDT Wed Jun 9 2021

.SHORT TERM...(This afternoon through Thursday evening)
Issued at 609 AM EDT WED JUN 9 2021

A cluster of showers and a couple of embedded thunderstorms is
working across central KY/Bluegrass Region into the northwest
portions of the CWA near and north of I 64. This activity should
continue to lift north/northeast toward the OH River and diminish/
decrease over the next couple hours as the sun comes up, similarly
to activity early yesterday morning. Otherwise, at the
upper levels, a slow moving low will progress eastward from the MS
Valley into the Ohio Valley. This low should move only slowly
through Thursday.

As the upper low moves into the Lower OH Valley, it will lead
to an increase in cumulus and scattered to numerous coverage of
convection by midday to the early afternoon for most of the CWA
as convective temperatures are reached, due to the moist airmass
across the OH Valley. The greatest chances lie across the western
half of the CWA where instability is best here with MUCAPE in the
1000-1500 J/kg range. Cloud cover will be quite prolific which could
hamper coverage of afternoon convection convection to an extent.
With that said, PW values are 2 standard deviations above the norm,
around the 90th percentile climatologically. Heavy rainfall could be
possible at times as storm motions will be on the slow side, leading
to localized flooding and high water levels. Some of the CAM members
suggest the potential for training storms, which would also aid in
the flooding potential if it were to materialize.

Thursday will feature similar conditions with PW values near if not
above 2 inches across the CWA during the afternoon and evening
hours. With the center of the upper low nearer to the area,
steering flow may be a bit weaker compare to today. CAMs also
suggest slightly better instability during peak heating of the day,
which could again lead to localized flooding and high water
levels. Convection both today and Thursday should wane with the
onset of nightfall, due to the nocturnal cooling and associated
increasing stability of the BL. The heavy rain and flood threat for
today has been highlighted in the HWO along with the potential for
gusty winds from any stronger highly water loaded convection.

Falling heights and additional cloud cover will lead to cooler
afternoon highs today compared to Tuesday. Have lowered temperatures
a couple of degrees from the blended guidance, given the agreement
among operational guidance and extent of cloud cover expected
through the day. Nonetheless, highs will top out in the upper 70s to
low 80s both days, which is average for this time of the year. Lows
into Thursday morning will range from the mid to upper 60s with some
river valley locations picking up patchy fog prior to dawn.

.LONG TERM...(After midnight Thursday night through Tuesday)
Issued at 602 AM EDT WED JUN 9 2021

A strong upper level low will be in place across the Ohio Valley
through the day Friday, slowly shifting eastward and becoming an
open wave during this time. This wave will straddle the Central
Appalachians and Mid-Atlantic States (continuing to impact eastern
KY) through much of the weekend, as it deepens and stretches down
along the coast. Meanwhile, a strong upper level low will drop
southward into the SE Canada by Monday afternoon, with heights
quickly lowering across much of the eastern Conus. Unlike yesterday,
the ECMWF and GFS are now in great agreement about this deepening
upper level low pressure system and digging trough now, as it
continues to impact the region through the rest of the forecast
period, which brings much more confidence to the forecast.

At the surface, a low will also be in place across the Ohio Valley,
with a frontal system draped across the Great Lakes Region to our
north. This will put KY in the warm sector, advecting vast amounts
of moist warm air from the Gulf of Mexico, with the area of low
pressure providing ample lift. Widespread rainfall is expected
Thursday evening, dropping off somewhat during the overnight with
the loss of diurnal heating/instability. It should quickly ramp back
up Friday, with storms remaining low centroid and showing high
PWATs, likely resulting in some continued instances of heavy
rainfall. The only saving grace is that the surface low will begin
to pull SE of the state during the day, which could help to pull the
best QPF away from the CWA. WPC downgrades eastern KY this day as a
result, but is still keeping the entire CWA in a marginal risk for
excessive rainfall.

A brief area of high pressure will then take hold for Saturday and
the first part of Sunday. However, with lingering moisture in the
area, and upslope flow, isolated to scattered convection can't be
ruled out, mainly in the far SE portion of the state. These
showers/thunderstorms will dissipate heading into the overnight
again with the loss of daytime heat and lift. For Sunday afternoon,
a low passing to our north will allow a cold front to quickly drop
southeastward and into the Commonwealth. While this should be weak,
it could result in another round of scattered showers and
thunderstorms through Sunday evening. The GFS has a secondary front
moving through Monday afternoon and night, with another round of
showers and thunderstorms. However, the ECMWF is not on board with
this solution, and therefore the NBM averaged the majority of these
pops out, leaving only slight to low end chance pops in the far
eastern portion of the state. Given uncertainty, did not deviate
from the NBM at this time. Strong high pressure then takes hold from
the NW by Tuesday, finishing out the forecast period.

As for temperatures, Friday will be mild, given the ongoing clouds
and precipitation. Highs will range from the upper 70s to the low
80s. Temperatures then warm back into the mid and upper 80s for
Saturday through Monday. If this strong upper level trough holds
true, Canadian air will likely begin filtering into the CWA for
Tuesday and Wednesday. Highs will be in the upper 70s and low 80s.
Lows will generally be in the mid and upper 60s, lowering to the
upper 50s by Tuesday night with the cooler air advecting in.

&&

.AVIATION...(For the 06Z TAFS through 06Z Wednesday night)
ISSUED AT 222 AM EDT WED JUN 9 2021

VFR conditions will start the period off before valley fog
develops in more of the eastern TAF sites near 07z. This could
lower visibility at SJS and SYM, and to a degree LOZ and JKL, to
MVFR conditions prior to dawn. During the day on Wednesday,
convection will initiate across most areas, bringing MVFR or lower
conditions at times. Winds will average around 5 kts or less
generally out of the south and southwest through Wednesday
morning, before peaking in the 5 to 8 kt range during the
afternoon. Higher gusts will be possible in thunderstorms.

&&

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

SHORT TERM...BB/JP
LONG TERM...JMW
AVIATION...BB/JP

Hazardous Weather Outlook
National Weather Service Jackson KY
527 AM EDT Wed Jun 9 2021

KYZ044-050>052-058>060-068-069-079-080-083>088-104-106>120-101230-
Fleming-Montgomery-Bath-Rowan-Estill-Powell-Menifee-Rockcastle-
Jackson-Pulaski-Laurel-Wayne-McCreary-Whitley-Knox-Bell-Harlan-
Elliott-Morgan-Johnson-Wolfe-Magoffin-Floyd-Lee-Breathitt-Knott-
Owsley-Perry-Clay-Leslie-Letcher-Martin-Pike-
Including the cities of Flemingsburg, Camargo, Jeffersonville,
Mount Sterling, Owingsville, Morehead, Irvine, Ravenna,
Clay City, Stanton, Frenchburg, Brodhead, Mount Vernon, McKee,
Annville, Burnside, Somerset, London, Monticello, Stearns,
Whitley City, Corbin, Williamsburg, Barbourville, Middlesboro,
Pineville, Cumberland, Harlan, Sandy Hook, West Liberty,
Paintsville, Campton, Salyersville, Prestonsburg, Wheelwright,
Beattyville, Jackson, Hindman, Pippa Passes, Booneville, Hazard,
Manchester, Hyden, Jenkins, Whitesburg, Inez, Coal Run,
Elkhorn City, Pikeville, and South Williamson
527 AM EDT Wed Jun 9 2021

This hazardous weather outlook is for portions of eastern Kentucky.

.DAY ONE...Today and Tonight.

Scattered to numerous thunderstorms are anticipated, especially
during the afternoon and evening. Any storms are capable of
producing strong wind gusts as well as torrential downpours,
which may result instances of high water and/or flooding.

.DAYS TWO THROUGH SEVEN...Thursday through Tuesday.

Thunderstorms with torrential downpours and gusty winds are
possible from Thursday through Friday evening as well. If heavy
rain materializes, high water and/or flooding could result.

Thunderstorms are also possible from Saturday through Monday,
mainly during the afternoon and evening.

.SPOTTER INFORMATION STATEMENT...

Spotters are encouraged to report any instances of high water,
flooding, or wind damage.

JP/JMW