Area Forecast Discussion
Issued by NWS Jackson, KY

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000
FXUS63 KJKL 010915
AFDJKL

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE JACKSON KY
515 AM EDT WED JUL 1 2015

.SHORT TERM...(TODAY THROUGH THURSDAY)
ISSUED AT 417 AM EDT WED JUL 1 2015

A WET PERIOD WILL BE IN STORE. WE WILL START OFF THIS MORNING
WITH A LARGE LONGWAVE TROUGH CONTINUING ACROSS THE REGION. THE
SHORTWAVE WHICH SPARKED RAIN AND STORMS YESTERDAY WILL BEGIN
SHIFTING NORTHEAST AND OUT OF THE REGION WHILE ANOTHER SMALLER
SHORTWAVE BEGINS TO TAKE FORM UPSTREAM OF EASTERN KY. THE
GFS...NAM...AND ECMWF ARE ALL IN GOOD AGREEMENT THAT AN MCS WILL
FROM AS A RESULT OF THIS SHORTWAVE...SETTLING ACROSS MISSOURI BY
12Z THIS MORNING. WITH NW FLOW STILL IN PLACE...EXPECT SOME OF THE
MOISTURE FROM THIS SYSTEM TO ADVECT INTO KY...IN CONJUNCTION WITH
ANY LEFT OVER MOISTURE FROM YESTERDAY/S SYSTEM. AS WE BEGIN
HEATING THROUGH THE DAY...THIS MOISTURE WILL BEGIN RISING AND SCT
SHOWERS AND THUNDERSTORMS TO START DEVELOPING ACROSS THE REGION.
WHILE A WEAK FRONTAL BOUNDARY WILL BE POSITIONED ALONG THE OHIO
RIVER VALLEY...IT SEEMS AS THOUGH THE WARMEST AND MOST UNSTABLE
AIR WILL PROVOKE THE BEST STORM POTENTIAL ACROSS THE SOUTHERN
CWA...CLOSER TO THE TN BORDER. ACCORDING TO SOUNDINGS IN THIS
AREA...THE LAST TWO RUNS OF THE NAM12 MODEL HAVE BEEN IN GOOD
AGREEMENT WITH SHOWING CAPE VALUES TOPPING OUT NEAR 4000 J/KG
BETWEEN 18 AND 21Z...A STRONG FAT CAPE...AND DRYING ALOFT WHICH
MAY PROMOTE SOME DECENT HAIL POTENTIAL. LI/S WILL EVEN BE TOPPING
OUT AROUND -9 AT KSME AND KLOZ...SUPPORTING THE IDEA FOR UNSTABLE
CONDITIONS CONDUCIVE TO STRONG THUNDERSTORM DEVELOPMENT. THAT
BEING SAID...AS YOU HEAD FARTHER NORTH...INSTABILITY AND WIND
SHEAR DROPS SIGNIFICANTLY AS YOU LOSE INFLUENCE FROM THE UPSTREAM
MCS. THIS CORRELATES WELL TO THE MRG AND SLIGHT RISK AREAS OF THE
SPC DAY 1 CONVECTIVE OUTLOOK.

BY THIS EVENING...IT ALMOST APPEARS AS THOUGH THE MODELS ARE TRYING
TO PULL SOME OF THE OUTFLOW MOISTURE FROM THE DIMINISHING MCS
EASTWARD ACROSS CENTRAL AND EASTERN KY...SPAWNING ADDITIONAL SHOWERS
AND THUNDERSTORMS ACROSS THE REGION AS IT MOVES EASTWARD.
HOWEVER...THIS IS ALSO WHERE WE START TO GET INTO SOME DIFFERENCES
BETWEEN THE MODELS AS WELL. THE ECMWF SOLUTION IS ALMOST CREATING
TWO MCS/S. THE FIRST OF WHICH WAS MENTIONED ABOVE...QUICKLY WASHING
OUT AS IT SHIFTS EASTWARD ACROSS KY...THEN A SECONDARY MCS
DEVELOPING IN IT/S PLACE LATE TONIGHT. THIS SOLUTION SEEMS
UNLIKELY...AS THE EXITING SHORTWAVE SEEMS TO TAKE AN UNREALISTIC
STRAIGHT EASTERLY PATH...AND THE NEW MCS REDEVELOPS TOO FAST. WOULD
LEAN MORE TOWARDS THE GFS AND NAM FOR THE OVERNIGHT PERIOD...WHICH
SHOW A GRADUAL INTENSIFICATION OF THE MCS OVER MISSOURI...AND ALSO
PEG SLIGHTLY LOWER QPF COMPARED TO THAT OF THE ECMWF ACROSS THE JKL
CWA.

BY THURSDAY...THE MCS WILL FOLLOW THE SHORTWAVE AND ROUND THE
LONGWAVE TROUGH AXIS. IN THIS SCENARIO...WOULD TEND THE LEAN TOWARDS
THE ECMWF AND THE NAM 12...SINCE THE GFS SEEMS TO BE PULLING THE
TROUGH AXIS MUCH FURTHER SOUTHWARD...AND THEREBY PRODUCING A
STRONGER SYSTEM...COMPLETE WITH A DEVELOPING SURFACE LOW TRACKING UP
THE OHIO RIVER. THIS PEGS THE HIGHEST QPF ACROSS THE NORTHERN CWA
AND ALONG AND NORTH OF THE OHIO RIVER VALLEY...WHICH IS OUT OF
AGREEMENT WITH EVERY OTHER MODEL...AND WAS HIGHLIGHTED BY THE WPC
MODEL DIAGNOSTIC DISCUSSION AS BEING UNREALISTIC. INSTEAD...EXPECT
THE BEST MOISTURE TO RIDE ALONG THE TROUGH AXIS WITH BEST
INSTABILITY AND QPF THEREFORE LOCATED ACROSS OUR SOUTHERN CWA AND
IN THE TN VALLEY.

CONCERNING THE AMOUNT OF MOISTURE...PWATS IN THE 1.75 TO 2.00 INCH
RANGE ARE POSSIBLE THROUGH THE DAY THURSDAY...WITH WPC PEGGING
AROUND AN INCH OF PRECIP OVER A 6 HOUR PERIOD DURING THE DAY NEAR
THE TN BORDER. SOME OF THE HEAVIER STORMS/SHOWERS MAY PRODUCE
LOCALLY HIGHER AMOUNTS AS WELL. THIS MAY CREATE SOME PROBLEMS AS WE
HEAD INTO THURSDAY NIGHT AND THE HEART OF THE MCS TRAVELS ACROSS
EASTERN KY AND BRINGS WIDESPREAD HEAVY RAINFALL. EXPECT FLASH
FLOODING TO BE A CONCERN...ESPECIALLY HEADING INTO THE BEGINNING OF
THE EXTENDED PERIOD WHEN PWATS ARE EXPECTED TO TOP OUT BETWEEN 2.1
AND 2.25 INCHES ACROSS THE SOUTHERN CWA. AFTER SOME DISCUSSION WITH
MRX ABOUT WHETHER OR NOT TO GO AHEAD AND ISSUE A FLASH FLOOD
WATCH...ULTIMATELY DECIDED TO HOLD OFF UNTIL DURING THE DAY
TOMORROW. THE PRIMARY REASON BEING THAT THE MODELS ARE STILL SHOWING
SOME DISAGREEMENT AND EACH ONE HAS SOME UNREALISTIC SCENARIOS...NOT
TO MENTION THIS LATEST RUNS OF THE ECMWF SHOWED SOME INCONSISTENCIES
COMPARED TO THE PREVIOUS RUN. WOULD HOPE THAT IN THE NEXT ONE TO TWO
RUNS...AS THE MCS GETS GOING TODAY...THE MODELS WILL START TO GET A
BETTER HANDLE ON THE UPCOMING SITUATION...AS WELL AS HOW FAR NORTH
INTO OUR CWA FLASH FLOODING MIGHT BE OF CONCERN.

.LONG TERM...(THURSDAY NIGHT THROUGH TUESDAY)
ISSUED AT 515 AM EDT WED JUL 1 2015

SEEING MORE SIGNIFICANT DIFFERENCES IN THE DETERMINISTIC ECMWF
AND GFS THROUGH THE EXTENDED. OVERALL UPPER LEVEL PATTERN BECOMES
LESS AMPLIFIED THROUGH THE PERIOD. GFS IS MORE AMPLIFIED...
STRONGER WITH SHORT WAVE ENERGY DROPPING INTO THE MID-MISSISSIPPI
AND OHIO VALLEY AT THE START OF THE EXTENDED...FRI INTO SAT.
NATIONAL GUIDANCE SUGGEST THE OPERATIONAL GFS IS TOO STRONG WITH
THIS SYSTEM CONSIDERING UPSTREAM ENERGY AND ITS INFLUENCE ON
EVOLUTION OF THE WAVE THROUGH THE OHIO VALLEY. A BLEND OF
SOLUTIONS/GUIDANCE APPEARS TO BE THE BEST APPROACH FOR THE
EXTENDED PORTION OF THE FORECAST...PERHAPS WITH A NUDGE TOWARDS
THE DETERMINISTIC ECMWF.

SENSIBLE WEATHER STILL LOOKS UNSETTLED WITH AT LEAST A CHANCE OF
RAIN EACH DAY. BAROCLINC...OR FRONTAL ZONE APPEARS TO STALL OUT
ACROSS THE REGION. MODELS ARE SHOWING SUBTLE DIFFERENCES IN THE
EXACT LOCATION OF THIS ZONE OF UNSETTLED WEATHER. MOST LIKELY
LOCATION APPEARS TO BE SOUTH OF THE OHIO RIVER BUT NORTH OF THE TENN
VALLEY. THE WEATHER WILL BE QUITE ACTIVE WITHIN THIS SECTOR WHICH
INCLUDES THE COMMONWEALTH. CONSIDERING THE RECENT RAINFALL WE HAVE
EXPERIENCED OVER THE LAST FEW DAYS...HYDRO ISSUES COULD BECOME A
CONCERN AS MULTIPLE DISTURBANCES TRACK THROUGH THE AREA.
TEMPERATURES WILL PROBABLY TREND A BIT CLOSER TO NORMAL THROUGH THE
PERIOD...ESPECIALLY TOWARDS THE END OF THE FORECAST WINDOW.

&&

.AVIATION...(FOR THE 06Z TAFS THROUGH 06Z WEDNESDAY NIGHT)
ISSUED AT 200 AM EDT WED JUL 1 2015

SHOWERS CONTINUE TO DIMINISH ACROSS THE REGION OVERNIGHT WITH LOSS
OF HEAT INDUCED INSTABILITY. HOWEVER...A LARGE AMOUNT OF MOISTURE
HAS BEEN LEFT OVER ACROSS MUCH OF EASTERN KY...ESPECIALLY IN AREAS
THAT RECEIVED RAINFALL THIS EVENING. AS TEMPERATURES CONTINUE TO
COOL OVERNIGHT...FOG WILL CONTINUE TO FORM AND THICKEN. SEVERAL
TAF SITES ARE ALREADY REPORTING FOG...AND IF THEY CONTINUE TO DROP
IN VISIBILITY SOME MAY ACTUALLY GO BELOW AIRPORT MINS FOR A PERIOD BY
LATE TONIGHT/EARLY MORNING. THAT BEING SAID...SOME TAF SITES MAY
CONTINUE TO FLUCTUATE BETWEEN CATEGORIES DEPENDING ON THE VARYING
DEGREE OF THE FOG OVERNIGHT. AS THE FOG BURNS OFF IN THE
MORNING...IT WILL BE REPLACED BY A RENEWED CHANCE OF SHOWERS AND
THUNDERSTORMS...ESPECIALLY IN THE AFTERNOON AND EVENING. TRIED TO
GEAR TAFS TOWARD THIS IDEA...BUT ACTUAL VIS AND CIGS WILL VARY
THROUGHOUT THE DAY AS STORMS DEVELOP AND PASS NEARBY...OR EVEN
OVER THE TAF SITE. A HEAVIER AREA OF RAIN WILL MOVE IN LATE IN THE
EVENING...WITH ALL TAF SITES EXPECTED TO BE AFFECTED. THE EXACT
IMPACTS ARE STILL UNCERTAIN...BUT TRENDED TOWARDS MVFR CIGS AND
MVFR/HIGH END IFR VIS AT THIS TIME.

&&

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

&&

$$

SHORT TERM...JMW
LONG TERM...RAY
AVIATION...JMW



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