Area Forecast Discussion
Issued by NWS Jackson, KY

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FXUS63 KJKL 050339 AAB
AFDJKL

AREA FORECAST DISCUSSION...UPDATED
NATIONAL WEATHER SERVICE JACKSON KY
1139 PM EDT TUE AUG 4 2015

.UPDATE...
ISSUED AT 1115 PM EDT TUE AUG 4 2015

THE CONVECTION ACROSS THE NORTH HAS BEEN WEAKENING OVER THE PAST
HOUR WHILE THE SOUTHERN CONVECTION HAS NOT STRENGTHENED. WITH THE
LOSS OF DAYTIME HEATING AND THE PASSING OF A DISTURBANCE TO THE
EAST...CONVECTION SHOULD WANE OR AT LEAST DECREASE IN COVERAGE
OVERNIGHT. A RESURGENCE OF CONVECTION MAY OCCUR NEAR OR AFTER DAWN
AS THE NEXT WAVE MOVES IN. HOURLY GRIDS HAVE BEEN UPDATED BASED ON
THESE CONVECTIVE TRENDS AND OBSERVATIONS.

UPDATE ISSUED AT 845 PM EDT TUE AUG 4 2015

CONVECTIVE ACTIVITY CONTINUES ACROSS PARTS OF THE REGION WITH A
COLD FRONT NEARLY STALLED OUT ACROSS THE AREA. THE STRENGTH OF
THIS OVERALL HAS DECLINED ACROSS EASTERN KY AS EARLIER CONVECTION
HAS HELPED TO STABILIZE THE ATMOSPHERE IN SEVERAL LOCATIONS.
HOWEVER...A DISTURBANCE MOVING THROUGH THE FLOW IS BRINGING
ANOTHER ROUND OF CONVECTION TO CENTRAL KY. THIS CONVECTION SHOULD
MOVE INTO EASTERN KY AFTER DARK. WITH LOSS OF DAYTIME
HEATING...THE THREAT FOR ANY SEVERE STORMS HAS DIMINISHED ALTHOUGH
THE THREAT FOR LOCALLY HEAVY RAIN AND POSSIBLE ISOLATED FLOODING
WILL REMAIN.

A BREAK IN THE CONVECTION SHOULD OCCUR FOR A TIME DURING THE
OVERNIGHT HOURS...ONCE THIS DISTURBANCE PASSES...ALTHOUGH MORE
CONVECTION WILL BE POSSIBLE LATE AS THE NEXT WAVE APPROACHES.

HOURLY GRIDS HAVE BEEN ADJUSTED BASED ON RECENT OBSERVATIONS AND
TRENDS. THIS LED TO HIGHER POPS ACROSS THE AREA UNTIL AFTER
MIDNIGHT AND COOLER TEMPERATURES DURING THE EVENING. DUE TO THE
RECENT RAINFALL...FOG SHOULD ALSO FORM OVERNIGHT...AND MAY AFFECT
MANY AREAS AND NOT JUST THE VALLEYS.

&&

.SHORT TERM...(THIS EVENING THROUGH WEDNESDAY NIGHT)
ISSUED AT 352 PM EDT TUE AUG 4 2015

A NEARLY STATIONARY BOUNDARY REMAINS DRAPED FROM WEST TO EAST
ACROSS THE CENTRAL PART OF THE FORECAST AREA. THIS HAS SERVED AS A
FOCUS FOR CONVECTION THIS AFTERNOON...AND ONCE AGAIN WE ARE DEALING
WITH SOME HEAVY RAINERS. WE DO EXPECT THIS ACTIVITY TO DISSIPATE
THIS EVENING...AND WILL DECREASE RAIN CHANCES AS THE EVENING
PROGRESSES.

THE SURFACE BOUNDARY WILL REMAIN ACROSS THE AREA FOR THE NEXT
COUPLE OF DAYS...WHILE A COUPLE OF MID/UPPER LEVEL SHORT WAVE
TROUGHS MOVE EAST FROM THE PLAINS INTO THE OH VALLEY. A RATHER
NEBULOUS WAVE WILL AFFECT THE REGION LATER TONIGHT...AND HAVE
INCREASED RAIN CHANCES AGAIN LATE TONIGHT FOR THE WESTERN PART OF
THE AREA.

A SECOND AND MUCH STRONGER WAVE WILL BEGIN TO AFFECT THE AREA
WEDNESDAY NIGHT. WHILE THERE IS GOOD MODEL AGREEMENT ON A STRONG
WAVE MOVING INTO THE OH VALLEY...EXACTLY WHERE THE HEAVIEST RAIN
AXIS WILL SET UP IS IN QUESTION. HOWEVER WITH PRECIPITABLE WATER
INCREASING...THE POSSIBILITY FOR TRAINING...AND THE THREAT FOR
MORE WIDESPREAD THUNDERSTORMS WITH HEAVY RAIN HAVE DECIDED TO GO
WITH A FLASH FLOOD WATCH BEGINNING 11 PM WEDNESDAY AND RUNNING TO
7 AM FRIDAY. THIS IS FOR ALL BUT THE MOST SOUTHERN TIER OF
COUNTIES.

.LONG TERM...(THURSDAY THROUGH TUESDAY)
ISSUED AT 352 PM EDT TUE AUG 4 2015

MODELS CONTINUE TO COME INTO BETTER AGREEMENT WITH A MODESTLY
AMPLIFIED MID/UPPER LEVEL LONG WAVE PATTERN TO START OUT THE
EXTENDED. WE FIND OUR AREA UNDER THE INFLUENCES OF NORTHWEST FLOW
ALOFT WITH WEAK EMBEDDED IMPULSES THROUGH THE MID TERM. THEN WE
FINISH UP THE EXTENDED WITH ANOTHER RESPECTABLE SHORTWAVE THAT MOVES
OUT OF THE UPPER MIDWEST AND THAT REINFORCES AN EASTERN CONUS MEAN
TROUGH.

FIRST TROUGH IS EXPECTED TO MOVE ACROSS THE OH/TN VALLEY REGIONS
WEDNESDAY NIGHT THROUGH THURSDAY. HOWEVER...THERE CONTINUE TO BE
SOME SIGNIFICANT DIFFERENCES AT THE SFC. ATTM AMPLE MOISTURE...A
RELATIVELY SLOW MOVING SFC SYSTEM...THE POTENTIAL FOR TRAINING AND
OTHER FAVORABLE HYDRO PARAMETERS SUGGEST THAT LOCALLY HEAVY RAINFALL
MAY BECOME A CONCERN FROM WEDNESDAY NIGHT THROUGH LATE THURSDAY
EVENING. HOWEVER...MUCH WILL DEPEND ON THE EXACT TRACK OF THE SFC
WAVE WHICH THE 12Z GFS TAKES FURTHER TO OUR SOUTH. WITH THE MORE
SOUTHERLY PATH OF THE GFS ITS AXIS OF HEAVIEST RAINFALL IS...AS
WOULD BE EXPECTED ACROSS THE HEART OF THE COMMONWEALTH. THE 0Z ECMWF
AND 12Z NAM KEEP THE STORM TRACK FURTHER NORTH AND CONSEQUENTLY
HEAVIEST AXIS OF RAIN ALONG AND EITHER SIDE OF THE OHIO RIVER.
THOUGHTS ARE TO ISSUE A FLASH FLOOD WATCH FOR THE WINDOW OF
CONCERN...WHICH WILL STRADDLE THE SHORT AND LONG TERM FORECAST
PERIODS.

THEREAFTER DETAILS ASSOCIATED WITH THE EVOLUTION OF THE PATTERN
REMAIN LOWER CONFIDENCE. AS SUCH...STAYED PRETTY CLOSE TO THE
OFFERED BLENDED GUIDANCE. WILL BE INCREASING POPS INTO CATEGORICAL
TERRITORY FOR THURSDAY PROPER. THE BOUNDARY WILL SAG SOUTHEAST
BEHIND THE DEPARTING SFC LOW AND DISSIPATE BY THE WEEKEND...ALLOWING
FOR MAINLY DRY WEATHER. MEAN EASTERN CONUS TROUGH WILL AMPLIFY AGAIN
ACROSS THE OHIO VALLEY BY EARLY TO MID NEXT WEEK...BRINGING ANOTHER
FRONTAL ZONE WITH ASSOCIATED WEATHER THROUGH THE AREA AND TO OUR
SOUTH.

&&

.AVIATION...(FOR THE 00Z TAFS THROUGH 00Z WEDNESDAY EVENING)
ISSUED AT 840 PM EDT TUE AUG 4 2015

A STALLED FRONT REMAINS IN PLACE ACROSS KY. THIS WILL SERVE AS A
FOCUS FOR ISOLATED TO SCATTERED THUNDERSTORMS THROUGH AT LEAST
4Z...AND POSSIBLY LATER TONIGHT TOWARD 12Z AND THEN RUNNING
THROUGH THE END OF THE PERIOD AS A SERIES OF DISTURBANCE MOVE
THROUGH THE EASTERN CONUS TROUGH AND INTERACT WITH THE BOUNDARY.
WITH THE LOSS OF DAYTIME HEATING...CONFIDENCE IN ANY SPECIFIC TAF
SITE BEING DIRECTLY IMPACTED BY A THUNDERSTORM IS LOW AND ONLY
HAVE VCTS AT THE START OF THE PERIOD. FOG IS EXPECTED TO DEVELOP
THROUGH 8Z..REDUCING VISIBILITY TO IFR OR WORSE...POSSIBLY BELOW
AIRPORT MINS IN SOME AREAS UNTIL AROUND 13Z. OUTSIDE OF ANY
THUNDERSTORMS OR FOG...VFR CONDITIONS WILL PREVAIL.


&&

.JKL WATCHES/WARNINGS/ADVISORIES...
FLASH FLOOD WATCH FROM WEDNESDAY EVENING THROUGH LATE THURSDAY
NIGHT FOR KYZ044-050>052-058>060-068-069-079-080-088-104-106>120.

&&

$$

UPDATE...JP
SHORT TERM...SBH
LONG TERM...RAY
AVIATION...JP


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