Area Forecast Discussion
Issued by NWS Jackson, KY

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FXUS63 KJKL 291725 AAC
AFDJKL

AREA FORECAST DISCUSSION...UPDATED
NATIONAL WEATHER SERVICE JACKSON KY
125 PM EDT WED JUL 29 2015

.UPDATE...
ISSUED AT 115 PM EDT WED JUL 29 2015

THE LOW LEVEL CLOUDS OVER THE CUMBERLAND VALLEY CONTINUE TO
GRADUALLY LIFT AND MIX INTO CU. OVERALL...A WARM AND MOIST AIRMASS
IS IN PLACE...AND A COUPLE OF STRAY SHOWERS HAVE DEVELOPED OVER
THE FAR SOUTHEASTERN PART OF THE CWA. ADDITIONAL SHOWERS HAVE
DEVELOPED OVER CENTRAL KY. THROUGH MID TO LATE AFTERNOON...ADDITIONAL
ISOLATED TO SCATTERED SHOWERS AND THUNDERSTORMS SHOULD DEVELOP...BUT
THESE MAY WANE DURING THE EVENING. MODEL GUIDANCE CONTINUES TO
SUGGEST THE GREATEST COVERAGE OF CONVECTION AS THE COLD FRONT
MOVES INTO THE AREA DURING THE LATE EVENING INTO THE OVERNIGHT
HOURS. OVERALL... HOURLY GRIDS WERE FRESHENED UP BASED ON RECENT
OBSERVATIONS...WITH LITTLE ADDITIONAL CHANGE ATTM.

UPDATE ISSUED AT 1111 AM EDT WED JUL 29 2015

THE REGION IS IN THE WARM SECTOR AS AN AREA OF LOW PRESSURE TRACKS
ACROSS NORTHERN ONTARIO. A WARM AND RATHER MOIST AIRMASS REMAINS
IN PLACE ACROSS THE AREA. DEWPOINTS REMAIN IN THE UPPER 60S TO
MID 70S. HOWEVER...THE AIRMASS IS NOT QUITE AS MOIST THROUGH THE
ENTIRE COLUMN ACROSS THE CENTRAL AND EASTERN PART OF THE AREA
WITH PW THERE AROUND 1.6 INCHES. PW ACROSS THE WEST IS AROUND 1.8
TO 1.9 INCHES.

WITH DAYTIME HEATING...LOW CLOUDS SHOULD EVENTUALLY LIFT INTO CU
ACROSS THE SOUTHWEST PART OF THE AREA. THE AIRMASS SHOULD ALSO
DESTABILIZE WITH ML CAPES EXPECTED TO REACH THE 1000 TO 1500 J/KG
RANGE ACROSS THE WEST BY MID AFTERNOON. THE MOISTURE GRADIENT
ACROSS CENTRAL KY INTO THE WESTERN PART OF THE CWA MAY BE A FOCUS
FOR CONVECTIVE DEVELOPMENT LATER TODAY. ALSO...THE HIGHER TERRAIN
ALONG THE VA BORDER THAT IS GETTING PLENTY OF SUNSHINE ATTM AND
DIFFERENTIAL HEATING NEAR WHERE HEAVIER RAIN FELL ON TUESDAY MAY
ALSO BE POSSIBLE LOCATIONS FOR THE FIRST CELL DEVELOPMENT. SHEAR
IS RATHER WEAK TODAY...AND CELLS SHOULD MORE OR LESS PROPAGATE VIA
OUTFLOW BOUNDARIES. MORE ORGANIZED CONVECTION...AND POSSIBLE A
BROKEN LINE OF LINE SEGMENTS OF STORMS SHOULD NEAR THE REGION
AROUND SUNSET. ISOLATED TO SCATTERED POPS.

UPDATE ISSUED AT 805 AM EDT WED JUL 29 2015

MADE ONLY MINOR UPDATES FOR EARLY MORNING OBS.

&&

.SHORT TERM...(TODAY THROUGH THURSDAY)
ISSUED AT 411 AM EDT WED JUL 29 2015

ISOLATED SLOW MOVING SHOWERS HAVE PERSISTED DURING THE NIGHT IN
THE SOUTHEAST PART OF THE FORECAST AREA. FORECAST SOUNDINGS SHOW
THAT SOME ADDITIONAL DEVELOPMENT CAN NOT BE RULED OUT THIS
MORNING...BUT THE PROBABILITY AT ANY GIVEN LOCATION IS LOW.
ADDITIONAL DEVELOPMENT OF SHOWERS/THUNDERSTORMS IS MORE PROBABLE
BY THIS AFTERNOON AS HEATING OCCURS. MOST OF THEM SHOULD DIE OUT
AGAIN IN THE EVENING WITH LOSS OF HEATING. A COLD FRONT WILL PASS
LATE TONIGHT AND THURSDAY MORNING. A FEW SHOWERS MAY LINGER ALONG
AND AHEAD OF THE FRONT IN THE SOUTHEAST PART OF THE AREA ON
THURSDAY MORNING. HOWEVER...DRIER AIR ALOFT AND A POST FRONTAL
INVERSION WILL PUT AN END TO ANY LINGERING SHOWERS...WITH MOST OF
THURSDAY BEING DRY.

.LONG TERM...(THURSDAY NIGHT THROUGH TUESDAY)
ISSUED AT 354 AM EDT WED JUL 29 2015

WE WILL BE IN A POST FRONTAL REGIME TO START OFF THE EXTENDED
FORECAST AT 0Z FRIDAY. SURFACE HIGH PRESSURE WILL CONTINUE TO TAKE
HOLD THROUGH THE DAY FRIDAY WITH SLIGHTLY COOLER NRLY WINDS AT THE
SURFACE. MEANWHILE...A STRONG UPPER LEVEL LOW WILL BECOME NEARLY
STATIONARY ACROSS HUDSON BAY...ROTATING AROUND THE BAY FROM
FRIDAY THROUGH AT LEAST MONDAY. THIS WILL KEEP A LONGWAVE
TROUGHING PATTERN ACROSS MUCH OF THE MIDWEST AND EASTERN
CONUS...CONTINUING THE NW FLOW REGIME ACROSS THE OHIO RIVER
VALLEY. THIS NW FLOW WILL PROVIDE THE PERFECT SCENARIO FOR
SHORTWAVES TO TRACK SE ALONG THE TROUGH AND INTO THE OHIO VALLEY
AS IT ROUNDS THE BASE OF THE TROUGH. HOWEVER...HIGH PRESSURE WILL
HAVE HOLD AT THE SURFACE. THE QUESTION THROUGHOUT THE EXTENDED IS
WHETHER OR NOT THIS HIGH PRESSURE WILL BE STRONG ENOUGH TO SWAY
THE IMPACT OF THESE SHORTWAVES AS THEY MOVE THROUGH EASTERN KY.

THE FIRST OF THESE SHORTWAVES WILL MOVE THROUGH SATURDAY INTO
SUNDAY. AS OF 0Z FRIDAY...THE ACCOMPANYING SURFACE COLD FRONT IS
POSED TO BE LOCATED ACROSS THE NORTHERN PLAINS AND UPPER GREAT LAKES
REGION...AND WILL SHIFT SOUTHWARD THROUGHOUT THE DAY FRIDAY AS THE
SHORTWAVE NEARS. HOWEVER...THIS BOUNDARY WILL BE MOISTURE DEPRIVED
AND FAIRLY WEAK. LATEST MODELS ARE STILL SHOWING SOME DISAGREEMENT
ON IF THIS BOUNDARY WILL BE ABLE TO SUSTAIN DEEP MOISTURE AS IT
MOVES INTO THE OHIO RIVER VALLEY. JUST LIKE YESTERDAY...THE GFS IS
POINTING TOWARDS A FEW SCATTERED SHOWERS MAKING IT INTO THE
CWA...WHILE THE ECMWF IS KEEPING US DRY. MEANWHILE...DESPITE THE
PLAN VIEW GFS OUTPUT...THE GFS FORECAST SOUNDINGS ARE ONLY
POINTING AT A NARROW WINDOW OF MID LEVEL MOISTURE WITH ABUNDANT
DRY AIR NEAR THE SURFACE. THIS IS MORE CHARACTERISTIC OF SOME SCT
TO BKN CLOUD COVER RATHER THAN RAINFALL. AS SUCH...WILL CONTINUE
TO TREND TOWARD THE DRIER ECMWF.

THE NEXT SHORTWAVE AND SURFACE BOUNDARY WILL MOVE THROUGH TUESDAY
INTO WEDNESDAY AS WE FINISH OUT THE 7 DAY FORECAST. GRANTED...THIS
IS FAR OUT IN THE FORECAST...BUT MODELS ARE IN SURPRISINGLY GOOD
AGREEMENT IN THE UPPER LEVELS...SO CONFIDENCE IS A BIT HIGHER. THIS
PARTICULAR UPPER LEVEL SHORTWAVE WILL SHOW SIGNIFICANT DIGGING AS IT
NEARS THE OHIO VALLEY REGION...LENDING TO A STRONGER SURFACE
BOUNDARY. IF THIS PROVES TO BE TRUE...WE MAY SEE OUR NEXT BETTER
CHANCE FOR SHOWERS AND THUNDERSTORMS DURING THIS TIME.

AS FOR TEMPERATURES...

THE POST FRONTAL CONDITIONS AND DRIER NW FLOW WILL BRING IN SLIGHTLY
COOLER TEMPERATURES TO START OFF FRIDAY. HOWEVER...STRONG SURFACE
HIGH PRESSURE IN PLACE AND CLEAR SKIES WILL PROMOTE MAXIMUM DAYTIME
RADIATION...SO THE TEMP DROP WILL NOT BE THAT GREAT...STILL
MAINTAINING LOW TO MID 80S. PERHAPS MORE NOTICEABLE THAN THE SLIGHT
CHANGE IN TEMPERATURES WILL BE THE DECREASE IN HUMIDITY...AS LIGHT
WINDS AT THE SURFACE AND NW FLOW ALOFT WILL PROMOTE LOWER RH VALUES.
AS HIGH PRESSURE REMAINS IN PLACE THROUGH MUCH OF THE
EXTENDED...EXPECT TEMPS TO GRADUALLY WARM A DEGREE OR TWO EACH
DAY...STAYING IN THE MID 80S THROUGH THE WEEKEND AND INTO NEXT WEEK.
MEANWHILE...MAXIMUM RADIATIONAL COOLING DURING THE OVERNIGHT WILL
KEEP OVERNIGHT LOWS IN THE LOW TO MID 60S THROUGH THE BEGINNING OF
NEXT WEEK.

&&

.AVIATION...(FOR THE 18Z TAFS THROUGH 18Z THURSDAY AFTERNOON)
ISSUED AT 125 PM EDT WED JUL 29 2015

MVFR LINGERS WHERE THE EARLY MORNING FOG AND STRATUS HAS LIFTED
INTO CU. THIS SHOULD CONTINUE LIFTING...WITH VFR EXPECTED OUTSIDE
OF ANY SHRA AND TSRA BY 20Z. ISOLATED TO SCATTERED SHRA AND TSRA
SHOULD DEVELOP DURING THE FIRST 4 HOURS OF THE PERIOD...WITH A
POSSIBLE LULL IN ACTIVITY BEFORE MORE SCATTERED SHRA AND TSRA AS A
COLD FRONT MOVES INTO THE REGION AFTER 0Z. ANY HEAVIER SHRA OR
TSRA WILL BRING BRIEF IFR VIS AND OR CIGS. BEHIND THE FRONT...GENERALLY
AFTER THE 4Z TO 6Z PERIOD...ANOTHER PERIOD OF IFR TO MVFR IS
POSSIBLE. THESE LOW CIGS WOULD LIFT BEFORE THE END OF THE PERIOD.

&&

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

$$

UPDATE...JP
SHORT TERM...HAL
LONG TERM...JMW
AVIATION...JP


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