Area Forecast Discussion
Issued by NWS Jackson, KY

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000
FXUS63 KJKL 270851
AFDJKL

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE JACKSON KY
451 AM EDT SUN JUL 27 2014

.SHORT TERM...(TODAY THROUGH SUNDAY NIGHT)
ISSUED AT 337 AM EDT SUN JUL 27 2014

A DEEP UPPER LEVEL TROUGH WILL CONTINUE TO DIVE INTO THE OHIO RIVER
VALLEY TODAY...WITH A SHORTWAVE RIDING ALONG THE TROUGH AND CREATING
A DYNAMIC WEATHER SITUATION ACROSS EASTERN KY. MODELS HAVE BEEN IN
GOOD AGREEMENT FOR A COUPLE OF DAYS NOW...BUT THE MESOSCALE
PARAMETERS CONTINUE TO EVOLVE AS WE HEAD INTO TODAY. OVERALL...A
WARM FRONT WHICH PASSED THROUGH THE AREA AND IS NOW LOCATED TO OUR
NORTH EARLY THIS MORNING...HAS ALLOWED FOR A STRONG SURGE OF WARM
UNSTABLE SOUTHERLY AIR INTO THE REGION. THIS...COUPLED WITH A LARGE
MCS THAT PASSED THROUGH EASTERN KY OVERNIGHT...HAS CREATED AN
ABUNDANT AMOUNT OF MOISTURE...ESPECIALLY IN THE LOWER LEVELS. AS A
COLD FRONT APPROACHES FROM OUR NW TODAY...EXPECT THESE FACTORS TO
INTERACT WITH THE FRONTAL BOUNDARY TO CREATE UNSTABLE CONDITIONS AND
AN ENHANCED SEVERE WEATHER THREAT.

DIVING FURTHER INTO THE LATEST MODEL GUIDANCE...
WHILE THERE ARE MANY PARAMETERS AT PLAY HERE...MODEL SOUNDINGS ARE
STILL SOME OF THE MOST TELL-ALL INFORMATION WE HAVE AT THIS POINT.
AS HAS BEEN NOTED IN PREVIOUS FORECASTS...LATEST NAM12 AND GFS40
SOUNDINGS ARE STILL SHOWING THE LOSS OF A LOW LEVEL DIURNAL CAPPING
INVERSION BY 15Z THIS MORNING...WITH DRY AIR FILTERING INTO THE MID
AND UPPER LEVELS BY 18Z. WITH STEEP LAPSE RATES STILL AROUND THE 6
TO 6.5 C/KM RANGE...AND SEASONABLY STRONG MID LEVEL WINDS...ALL
THINGS SEEM TO LINE UP FOR THE POTENTIAL FOR DAMAGING WINDS AND LARGE
HAIL. HIGH 6 HOUR PWAT VALUES ARE ALSO STILL INSINUATING THAT ANY
STORM THAT DEVELOPS COULD PRODUCE LOCALIZED HEAVY RAINFALL AS WELL.
WHAT IS STILL RAISING SOME UNCERTAINTY...HOWEVER...IS THE FACT THAT
THERE IS DECENT LOW LEVEL DIRECTIONAL SHEAR IN THE LOWEST 2KM AROUND
12Z...BUT IT WEAKENS LOOKING AT THE 15Z AND LATER SOUNDINGS. THIS
WILL CUT DOWN ON THE BEST HELICITY AND HODOGRAPH SIGNATURES...BUT IT
DOES NOT COMPLETELY RULE OUT THE THREAT OF SOME ISOLATED TORNADOES.
AND GIVEN THE OTHER FAVORABLE PARAMETERS...IF A TORNADO DOES
DEVELOP...IT COULD BE STRONG.

NOW LOOKING AT SOME OTHER PARAMETERS OF CONCERN. THE UPPER LEVEL
SHORTWAVE...AND THE SURFACE LOW...WILL REMAIN MUCH FARTHER TO OUR
NORTH...PUSHING EASTWARD ALONG THE UPPER GREAT LAKES REGION. THIS
PUTS THE BEST FORCING AND CONVERGENCE NORTH OF EASTERN KY...WITH A
STRONG QVECTOR CONVERGENCE MAXIMUM MOVING ACROSS MICHIGAN...NORTHERN
OHIO...AND INTO NEW ENGLAND BY SUNDAY AFTERNOON. THE 300MB JET WILL
SET UP ALONG WITH THE LONGWAVE TROUGH ORIENTATION...ALSO WEST TO
EAST...YIELDING THE HIGHEST WINDS MAINLY NORTH OF THE OHIO RIVER.
EXPECT THE SURFACE BOUNDARY TO SET UP ALONG THE SAME PATH. BUT THE
JET IS NOT SHOWING A DEFINITIVE STREAK...IT IS QUITE BROAD. SO THERE
IS THE POTENTIAL THAT THE BOUNDARY COULD ESTABLISH ITSELF JUST
SLIGHTLY NORTH OR SOUTH OF WHAT IS FORECASTED. WITH THIS IN
MIND...IT ALMOST SEEMS THAT THE BEST POTENTIAL FOR THE COLLOCATION
OF FORCING AND LIFT WOULD BE CLOSER TO THE SURFACE LOW...AND
THEREFORE NORTH OF KY.

PUTTING ALL OF THIS TOGETHER...IT COULD BE THAT CELLS BEGIN
DEVELOPING NORTH OF OUR REGION IF THE BOUNDARY ORIENTS ITSELF
FURTHER NORTHWARD. IF THE BOUNDARY PUSHES SLIGHTLY SOUTHWARD...CELLS
WILL START DEVELOPING ACROSS THE NORTHERN CWA. REGARDLESS...IT WILL
LIKELY BE THE OUTFLOWS OF THESE STORMS THAT DETERMINES HOW THE
REMAINDER OF THE DAY WILL PLAY OUT. AS OUTFLOWS PUSH AWAY FROM THE
STORMS...AND SOUTHWARD INTO THE MORE UNSTABLE AIR...THIS WILL CREATE
ENOUGH LIFT TO INITIATE NEW CELL DEVELOPMENT. GIVEN THE FORECAST
SOUNDING CHARACTERISTICS MENTIONED ABOVE...ALL STORM MODES ARE
POSSIBLE...FROM SQUALL LINES...QLCS/S...MCS/S...AND INDIVIDUAL
SUPERCELLS. AND THOUGH THE TORNADO THREAT IS NOT WELL DEFINED...DO
WANT TO MAKE SPECIFIC MENTION THAT OUTFLOW BOUNDARIES COULD PRODUCE
THE NEEDED LOW LEVEL WIND SHEAR TO INITIATE A SUPERCELL CAPABLE OF
PRODUCING A STRONG TORNADO.

AS WE HEAD INTO SUNDAY EVENING...THE SHORTWAVE AND FORCING WILL
CONTINUE TO PUSH EASTWARD...PULLING THE BEST INSTABILITY AWAY FROM
EASTERN KY. EXPECT ONGOING SHOWERS AND THUNDERSTORMS TO
CONTINUE...BUT DRY AIR WILL FILTER INTO THE LOW LEVELS FROM WEST TO
EAST...CUTTING OFF THE BEST CONVECTIVE AND PRECIP POTENTIAL BY 12Z.

.LONG TERM...(MONDAY THROUGH SATURDAY)
ISSUED AT 451 AM EDT SUN JUL 27 2014

AN AMPLIFIED LONG WAVE PATTERN WILL DOMINATE ACROSS THE CONUS
THROUGH THE PERIOD...WITH RIDGING IN THE WEST AND TROUGHING IN THE
EAST.

MONDAY WILL BEGIN WITH CYCLONIC FLOW ENTRENCHED ACROSS THE OHIO
AND TENNESSEE VALLEYS...WITH AFTERNOON HEATING KICKING OFF SOME
ISOLATED TO SCATTERED CONVECTION ACROSS EASTERN KENTUCKY. THE AIR
WILL CONTINUE TO DRY OUT IN THE LOW LEVELS...LEAVING ONLY THE THREAT
OF SOME SPRINKLES FOR TUESDAY. HIGHS WILL AVERAGE IN THE LOW TO MID
70S FOR MOST LOCATIONS. DRIER WEATHER CAN BE EXPECTED ACROSS THE AREA
FOR THE MIDDLE OF THE WEEK...AS THE TROUGH TEMPORARILY DAMPENS. HIGHS
WILL MODIFY A BIT...REACHING THE LOW 80S BY THURSDAY. BY FRIDAY AND
SATURDAY...THE TROUGH WILL REASSERT ITSELF...WITH THE THREAT OF
DIURNALLY INFLUENCED CONVECTION RETURNING ACROSS THE AREA...WITH
HIGHS STILL AVERAGING A BIT BELOW NORMAL FOR THIS TIME OF YEAR.

&&

.AVIATION...(FOR THE 06Z TAFS THROUGH 06Z SUNDAY NIGHT)
ISSUED AT 140 AM EDT SUN JUL 27 2014

A LARGE BUT WEAKENING MCS IS MOVING ACROSS EASTERN KY...BRINGING
LIGHT RAIN AND SOME RUMBLES OF THUNDER TO THE TAF SITES OVER THE NEXT
FEW HOURS. STORMS HAVE LOST CONSIDERABLE STRENGTH...AND CIGS SEEM TO
BE MAINTAINING VFR STATUS...THOUGH SOME HEAVIER RAIN SHOWERS COULD
TEMPORARILY DROP VSBYS DOWN TO MVFR. MAIN FOCUS NOW SHIFTS TO TOMORROW.
ONGOING FORECAST SEEMED TO HIGHLIGHT THE POTENTIAL THREATS VERY
WELL...SO MADE LITTLE CHANGES AFTER 15Z ON THIS ISSUANCE. THE LATEST
MODEL DATA IS STILL POINTING AT AN EVENT THAT IS RARELY SEEN IN
EASTERN KENTUCKY IN JULY. EXPECTING MOSTLY MVFR CIGS AND VSBY FOR THE
AREA...HOWEVER SOME OF STRONGER STORMS COULD BE CAPABLE OF DROPPING
THE VSBY TO AROUND A MILE AND PRODUCE WIND GUSTS OF 40 TO 50 KTS.
THERE IS ALSO THE THREAT OF SOME LARGE DAMAGING HAIL WITH ANY
THUNDERSTORM THAT DEVELOPS...WHICH WAS INCLUDED IN THE TAFS AS WELL.
KEPT THE TEMPO GROUP IN THE TAFS TO REFLECT THE MOST LIKELY TIMES
THAT THE STORMS WILL BE IN THE AREA...HOWEVER THUNDERSTORMS ARE
POSSIBLE ANYTIME AFTER DAWN THIS MORNING. WE WILL CONTINUE TO MONITOR
THE DEVELOPING SITUATION AND MAKE UPDATES FOR THE TAF SITES AS NEEDED
ONCE STORMS BEGIN INITIATING TOMORROW.


&&

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

$$

SHORT TERM...JMW
LONG TERM...GEOGERIAN
AVIATION...JMW







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