Area Forecast Discussion
Issued by NWS Jackson, KY

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FXUS63 KJKL 200241 AAA
AFDJKL

AREA FORECAST DISCUSSION...UPDATED
NATIONAL WEATHER SERVICE JACKSON KY
1041 PM EDT TUE MAY 19 2015

.UPDATE...
ISSUED AT 1041 PM EDT TUE MAY 19 2015

SOME OF THE MORE SHELTERED VALLEYS HAVE STARTED TO DECOUPLE...WITH
SOME SPOTS DOWN INTO THE MID 50S. GIVEN THE CURRENT TRENDS...EXPECT
UP TO ANOTHER 10 DEGREE DROP OR SO THROUGH THE REST OF THE NIGHT.
AS SUCH...DID NUDGE UP SOME OF THE READINGS...PARTICULARLY THE
RIDGETOPS AND BROADER VALLEYS...WHERE MIXING WILL BATTLE THE
RADIATIONAL COOLING. THIS WILL LIKELY KEEP MOST OF THESE SITES
ABOVE THE 50 DEGREE MARK...WHILE THE MORE SHELTERED LOCATIONS DIP
INTO THE 40S. UPDATES WILL BE SENT SHORTLY.

UPDATE ISSUED AT 809 PM EDT TUE MAY 19 2015

FLATTENED CUMULUS HAVE DISSIPATED AS WE HEAD TOWARDS SUNSET.
FORECAST LOWS LOOK REASONABLE AND WILL ONLY ALLOW FOR SOME TOUCH
UPS ON THE HOURLY TEMPERATURE AND DEW POINT CURVES TO ACCOUNT FOR
THE CURRENT TRENDS IN OBSERVATIONS.

&&

.SHORT TERM...(THIS EVENING THROUGH WEDNESDAY NIGHT)
ISSUED AT 314 PM EDT TUE MAY 19 2015

A COLD FRONT CONTINUES TO DEPART TO THE SOUTH AND EAST OF THE
REGION AS OF MID AFTERNOON WITH LOW LEVEL MOISTURE LEFT BEHIND
WEST OF THE CREST OF THE APPALACHIANS. SKIES HAVE CLEARED FROM
NEAR THE INTERSTATE 64 CORRIDOR NORTHWEST WHILE CU AND STRATOCU
REMAIN ACROSS THE REMAINDER OF THE AREA. DRIER AIR CONTINUES TO
GRADUALLY FILTER INTO THE REGION AS SFC HIGH PRESSURE CENTERED
OVER THE NORTHERN PLAINS REGION NOSES INTO THE LOWER OH VALLEY
REGION. AT MID LEVELS...A WEAK SHORTWAVE RIDGE WAS WORKING INTO
THE REGION AS WELL. MEANWHILE... FURTHER TO THE WEST...A MID LEVEL
SHORTWAVE WAS WORKING FROM THE ROCKIES INTO THE PLAINS STATES.

THROUGH THE PERIOD...THE SFC HIGH IS EXPECTED TO SHIFT SOUTH INTO
THE CENTRAL PLAINS WITH RIDGING EXTENDING EAST INT THE OH VALLEY
REGION. MEANWHILE...THE MID LEVEL WAVE IS EXPECTED TO MOVE EAST
THROUGH THE PERIOD AND APPROACH THE LOWER OH VALLEY AS IT MOVES
WITHIN A GENERALLY ZONAL PATTERN FROM THE ROCKIES INTO THE EASTERN
CONUS. THIS SHORTWAVE WILL WORK ACROSS THE REGION AT THE END OF
THE PERIOD INTO VERY EARLY IN THE LONG TERM PERIOD.

CU SHOULD CONTINUE TO LIFT AND MIX OUT FOR THE REMAINDER OF THE
AFTERNOON INTO THE EVENING HOURS. THE MID LEVEL RIDGING AND SFC
HIGH SHOULD BRING CLEAR OR MOSTLY CLEAR SKIES TO THE REGION
TONIGHT ALONG WITH SLACKENING WINDS. THIS WILL SET THE STAGE FOR A
SMALL TO POSSIBLY MODERATE RIDGE/VALLEY SPLIT...ESPECIALLY ACROSS
THE NORTH AND WESTERN PARTS OF THE REGION. WITH THE DRIER AIR
HAVING ALREADY ADVECTED INTO THE NORTHWESTERN PART OF THE REGION
AND THE DRIER AIR BEING SLOWER TO WORK INTO THE SOUTHEAST...IT
APPEARS THAT THE STAGE WILL LIKELY BE SET FOR SOME RIVER VALLEY
FOG IN THE NORTHWEST AND VALLEY FOG IN THE SOUTHEAST. SOME OF THE
VALLEY FOG IN THE SOUTHEAST COULD BE DENSE SINCE DEW POINTS ACROSS
MUCH OF THAT AREA ARE STILL IN THE UPPER 50S TO LOWER 60S. THE
COLDEST LOWS TONIGHT SHOULD BE IN VALLEY LOCATIONS GENERALLY NORTH
OF THE MTN PARKWAY...WHERE SOME LOW TO MID 40S WILL BE POSSIBLE...
WHILE FURTHER SOUTH VALLEY LOCATIONS SHOULD RANGE FROM THE MID 40S
TO AROUND 50. RIDGETOP LOCATIONS ARE EXPECTED TO REMAIN AROUND 50
OR IN THE LOWER 50S.

MID AND HIGH LEVEL MOISTURE WILL BEGIN TO INCREASE TOMORROW...
ESPECIALLY LATE IN THE DAY AHEAD OF THE APPROACHING SHORTWAVE
TROUGH. THE CLOUDS SHOULD THICKEN MORE QUICKLY ACROSS THE NORTH
AND WEST AND GIVEN A NORTH TO SOUTH GRADIENT IN 850 MB TEMPERATURES
IN THE ZONAL PATTERN...HIGHS ON WED ARE EXPECTED TO HAVE A GENERAL
NORTH TO SOUTH GRADIENT OF POSSIBLY MORE THAN 10
DEGREES...REACHING THE UPPER 60S TO AROUND 70 IN THE FAR NORTH
AND NEARING THE 80 DEGREE MARK NEAR THE TN BORDER.

THERE REMAINS MODEL DISAGREEMENT BETWEEN THE CONSTANTLY DRIER GFS
AND MUCH OF THE OTHER GUIDANCE SUCH AS THE NAM AND ECMWF FOR RAIN
CHANCES AS THE SHORTWAVE WORKS THROUGH THE AREA ON WED NIGHT. WITH
ALL THE NON GFS GUIDANCE STILL BRINGING IN SOME PRECIPITATION TO
THE REGION...THE SREF POPS RATHER HIGH...AND THE MODEL BLENDS
HIGHER THAN THE PREVIOUS FORECAST...POPS WERE RAISED TO ABOUT 40
PERCENT FOR WED NIGHT. IF THE GFS GUIDANCE ALSO FALLS IN LINE WITH
BEING A BIT WETTER POPS MAY NEED TO BE RAISED FURTHER. ATTM...THE
PRECIP TYPE WAS KEPT AS JUST SHOWERS AS INSTABILITY APPEARS TO LOW
FOR ANY CHANCES OF THUNDER. RAINFALL WHERE RAIN DOES OCCUR WITH
THIS SYSTEM SHOULD BE RATHER LIGHT...NO MORE THAN A TENTH TO
QUARTER OF AN INCH IF THAT. WITH CLOUDS AND RAIN CHANCES LOWS ON
WED NIGHT SHOULD BE IN GENERAL MORE UNIFORM ACROSS THE AREA AND
MILDER THAN TONIGHT.

.LONG TERM...(THURSDAY THROUGH TUESDAY)
ISSUED AT 250 PM EDT TUE MAY 19 2015

THE EXTENDED PERIOD STARTS WITH AN UPPER LEVEL TROUGH PASSING TO
OUR NORTH ON THURSDAY MORNING...BRINGING A CHANCE FOR PRECIP TO
OUR AREA. STILL SOME DIFFERENCES IN THE MODELS BUT NOW THE DRY GFS
IS THE OUTLIER...SO HAVE DECIDED TO TRANSITION OVER TO SLIGHT POPS
FROM WEST TO EAST INTO THURSDAY EVENING. HIGHER HEIGHTS THEN BUILD
INTO THE REGION ON FRIDAY AS A SFC AND UPPER LEVEL RIDGE TAKES
HOLD OF THE EASTERN US. THIS WILL ALLOW FOR BEAUTIFUL WEATHER FOR
THE FIRST HALF OF MEMORIAL DAY WEEKEND.

BY SUNDAY...SOUTHERLY FLOW SETS UP AHEAD OF A DEVELOPING SOUTHERN
PLAINS LOW PRESSURE SYSTEM. THIS RETURN FLOW INCREASES MOISTURE IN
THE REGION AND ALLOWS FOR DIURNALLY DRIVEN SHOWERS AND
THUNDERSTORMS EACH AFTERNOON THROUGH THE END OF THE PERIOD.

TEMPERATURES WILL GENERALLY HOVER AROUND THE 80 DEGREE MARK
THROUGH THE PERIOD WITH THE EXCEPTION OF THURSDAY AND FRIDAY WHERE
LOWS WILL BE IN THE UPPER 40S/LOW 50S AND AFTERNOON HIGHS WILL
REACH THE LOW TO MID 70S. OTHERWISE...OVERNIGHT LOWS WILL BE ON
THE MILD SIDE...IN THE LOWER 60S...SUNDAY ONWARD.

&&

.AVIATION...(FOR THE 00Z TAFS THROUGH 00Z WEDNESDAY EVENING)
ISSUED AT 809 PM EDT TUE MAY 19 2015

HIGH PRESSURE WILL BUILD IN ACROSS THE OHIO VALLEY TONIGHT...
ALLOWING FOR MAINLY VFR CONDITIONS. THERE WILL LIKELY BE SOME
PATCHY IFR OR WORSE FOG BETWEEN 06 AND 13Z...HOWEVER THIS WILL BE
RESTRICTED TO THE DEEPER RIVER VALLEYS. HIGH CLOUDS WILL BE ON THE
INCREASE DURING THE DAY ON WEDNESDAY...AS AN UPPER LEVEL
DISTURBANCE APPROACHES FROM THE NORTHWEST. WINDS WILL REMAIN IN
THE 5 TO 10 KT RANGE...GENERALLY FROM THE NORTHEAST.


&&

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

$$

UPDATE...GEOGERIAN
SHORT TERM...JP
LONG TERM...JVM
AVIATION...GEOGERIAN


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