Area Forecast Discussion
Issued by NWS Jackson, KY

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FXUS63 KJKL 221126
AFDJKL

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE JACKSON KY
726 AM EDT MON SEP 22 2014

.UPDATE...
ISSUED AT 712 AM EDT MON SEP 22 2014

A MID AND UPPER LEVEL DISTURBANCE CONTINUES TO PUSH ACROSS THE LOWER
GREAT LAKES. IN RESPONSE...A LARGE AREA OF CLOUDS DEVELOPED IN THIS
REGION...AND HAS SINCE FOLLOWED THE GENERAL WIND FLOW S TO SE INTO
THE FAR EASTERN OHIO RIVER VALLEY. UPDATED THE SKY GRIDS BASED ON THE
THE CURRENT VISIBLE SATELLITE TRENDS...AS WELL AS SOME OF THE HI RES
MODEL GUIDANCE. EXPECT THAT WITH DAYTIME HEATING...THESE CLOUDS WILL
BEGIN TO LIFT. AND AS DRY AIR CONTINUES TO PULL INTO THE REGION FROM
THE NORTH AND WEST...THESE CLOUDS SHOULD EVENTUALLY THIN OUT AND
DISSIPATE BY EARLY THIS AFTERNOON. OTHER FORECAST PARAMETERS SEEMED
TO BE WELL IN ORDER. LOADED IN THE LATEST OBSERVATIONAL GUIDANCE TO
MAKE SURE THE NEAR TERM FORECAST MATCHED UP WELL WITH ONGOING CONDITIONS.

&&

.SHORT TERM...(TODAY THROUGH TUESDAY)
ISSUED AT 402 AM EDT MON SEP 22 2014

SUBSTANTIAL DRY AIR HAS MOVED IN ACROSS MUCH OF EASTERN KY AFTER A
DEPARTING COLD FRONT FROM EARLIER IN THE DAY. HOWEVER...A
DISTURBANCE CURRENTLY MOVING ACROSS THE UPPER GREAT LAKES REGION HAS
CAUSED A BROAD DECK OF 2 TO 3 KFT CLOUDS. ACCORDING TO THE LATEST
IMAGERY...THESE CLOUDS ARE CONTINUING TO PUSH SSE-WARD AND ARE
EXPECTED TO ENTER INTO EASTERN KY OVER THE NEXT SEVERAL HOURS. THE
LEADING EDGE OF THIS CLOUD DECK IS ALREADY PUSHING INTO SJS
OBSERVATION SITE IN THE FAR EASTERN PORTION OF THE CWA. THE LATEST
OBSERVATIONS UPSTREAM...ALONG WITH THE LATEST MODEL SOUNDINGS AND
LAMP GUIDANCE...ALL POINT AT THIS CLOUD DECK REMAINING MVFR.

DURING THE DAY TODAY...STRONG SUBSIDENCE WILL TAKE HOLD ACROSS THE
REGION UNDER SURFACE HIGH PRESSURE AND RISING UPPER LEVEL HEIGHTS AS
A LONGWAVE TROUGH DEPARTS EAST FROM THE AREA. THIS WILL LEAD TO A
THINNING OF CLOUDS THROUGHOUT THE MORNING AND AN INFLUX OF COLD DRY
CANADIAN AIR. WINDS WILL REMAIN OUT OF THE NORTH BOTH AT THE SURFACE
AND UPPER LEVELS AS THE STRONGLY DISPLACED NORTHERN JET CONTINUES
MOVE EASTWARD ACROSS THE REGION FOLLOWING THE LONGWAVE PATTERN.
EXPECT HIGHS TODAY TO BE MUCH LOWER THAN THAT OF YESTERDAY...ONLY
REACHING THE UPPER 60S IN MOST LOCATIONS. SIMILARLY...WITH THE LOSS
OF DAYTIME HEATING...RADIATIONAL COOLING WILL BE AT A MAXIMUM UNDER
MOSTLY CLEAR SKIES. THIS WILL ALLOW FOR TEMPS TO DROP WELL BELOW
NORMAL...INTO THE LOW TO MID 40S ACROSS THE REGION FOR LOWS. SOME OF
THE DEEPEST RIVER VALLEYS WILL LIKELY SEE FOG DEVELOPMENT AS THE DEW
POINTS REMAIN HIGHER IN THESE LOCATIONS.

THE NORTHERN JET WILL PUSH OFF EAST OF THE AREA BY TUESDAY/TOMORROW.
WHILE WINDS WILL REMAIN NORTHERLY...THEY WILL NOT BE QUITE AS STRONG
IN THE MID AND UPPER LEVELS. CONTINUED SUNSHINE ACROSS THE AREA WILL
ALSO WORK TO MODIFY TEMPS SLIGHTLY HIGHER AS STRONG HIGH PRESSURE
REMAINS OVERHEAD. DAYTIME HIGHS ARE EXPECTED TO REACH THE LOW 70S IN
SOME LOCATIONS...WHILE SOME OF THE HIGHER ELEVATIONS MAY CONTINUE TO
SEE UPPER 60S.

.LONG TERM...(TUESDAY NIGHT THROUGH SUNDAY)
ISSUED AT 410 AM EDT MON SEP 22 2014

THE MODEL CONSENSUS IS FOR AN UPPER LEVEL RIDGE TO EXTEND FROM THE
DESERT SOUTHWEST EAST INTO THE LOWER MS VALLEY AND THEN NORTH INTO
THE LOWER OH VALLEY AND CENTRAL GREAT LAKES REGION TO START THE
PERIOD. AN UPPER LEVEL LOW/TROUGH IS EXPECTED TO LINGER ALONG THE
EASTERN SEABOARD WITH ANOTHER UPPER LOW OVER THE NORTHERN PLAINS
REGION...AS THE MAIN BAND OF WESTERLIES WILL BE DISPLACED WELL NORTH
OF THE US/CANADIAN BORDER AT THE START OF THE PERIOD. AT THAT
POINT...CORRESPONDING SFC HIGH PRESSURE IS EXPECTED TO BE CENTERED
OVER QUEBEC WITH RIDGING SOUTH INTO THE OH VALLEY AND MS VALLEY
REGIONS. FROM TUESDAY NIGHT INTO THE WEEKEND...A TROUGH IS EXPECTED
TO WORK INTO THE WESTERN CONUS...BUT THERE ARE SOME MODEL
DIFFERENCES IN TIMING AND DETAILS. THE UPPER LEVEL RIDGE INITIALLY
CENTERED OVER THE SOUTHWESTERN CONUS IS EXPECTED TO BUILD NORTH INTO
HE NORTHERN PLAINS/UPPER MIDWEST REGION AND BECOME CENTERED OVER
THAT REGION BY FRI...BEFORE SHIFTING EAST INTO THE GREAT LAKES
REGION. MUCH OF THE CENTRAL AND EASTERN CONUS WILL BE TO SOME DEGREE
INFLUENCED BY UPPER LEVEL RIDGING FROM MID TO LATE THIS WEEK...BUT
THERE WILL ALSO BE SOME WEAKNESS IN THE RIDGE AS WELL...THAT THE GFS
AND ECMWF HAVE HAD SOME DIFFERENCES IN PLACEMENT AND DETAILS WITH FROM
RUN TO RUN AND MODEL TO MODEL FOR THE PAST FEW DAYS.

OVERALL...THE PATTERN SHOULD BE RATHER BENIGN. THE MODEL CONSENSUS
IS THAT RATHER DRY AIR WILL PERSIST ACROSS MUCH OF THE OHIO RIVER
VALLEY...THROUGH AT LEAST WED NIGHT OR THU. THE 0Z ECMWF IS MORE
MOIST IN THE LOW LEVELS FROM THU THROUGH THE END OF THE PERIOD AS
COMPARED TO THE 0Z GFS AND EVEN THE 12Z ECMWF FOR THAT MATTER AS IT
KEEPS A WEAKNESS IN THE RIDGE OVER THE REGION OR CLOSE TO THE
REGION. AS NOTED BY THE PREVIOUS FORECASTER...THE LOSS OF NORTHERLY
FLOW AT BOTH THE SURFACE AND ALOFT...ESPECIALLY THE LOWEST LEVELS
AND MORE OF A WEAK EASTERLY FLOW WILL LEAD TO GRADUAL AIR MASS
MODIFICATION...WITH INCREASES IN MAX AND MIN TEMPERATURES FROM DAY
TO DAY AND A GRADUAL INCREASE IN DEWPOINTS FROM MID TO LATE WEEK.

MODELS REMAIN IN NOT VERY GOOD AGREEMENT OVER THE WEEKEND AT THE END
OF THE PERIOD AND THUS CONFIDENCE IS LOWER THAN AVERAGE. RATHER
SHALLOW WEAK SOUTHEAST FLOW AS IS IN THE 0Z ECMWF WOULD LIMIT
PRECIPITATION THREAT TO POSSIBLY DIURNALLY DRIVEN ON SUNDAY OR
POSSIBLY EARLIER UNTIL THE WEAKNESS THAT THE 0Z MODELS AGREE ON OVER
THE CENTRAL AND SOUTHERN PLAINS AT THE START OF THE WEEKEND LIFTS ON
OUT TO THE NORTH AND NORTHEAST. THE 0Z GFS IS QUICKER TO BRING THIS
FEATURE NORTH AND NORTHEAST AT THE END OF THE PERIOD THAN THE 0Z
ECMWF BUT DOES NOT BRING DEEPER MOISTURE TO THE AREA UNTIL AFTER THE
PERIOD. THE MODEL CONSENSUS BLEND GRID LOAD HAD SLIGHT CHANCES IN THE
SOUTHWEST CWA BEFORE THE END OF THE PERIOD WHICH WAS IN LINE WITH
THE PREVIOUS FORECAST AND DID NOT CHANGE THIS ATTM. PRECIPITATION
CHANCES MAY BE A BIT HIGHER EARLY NEXT WEEK JUST PAST THE END OF THE
PERIOD IF A PATTERN CLOSER TO THE 0Z GFS ENSEMBLE MEAN OR 0Z ECMWF
WERE TO VERIFY.

&&

.AVIATION...(FOR THE 06Z TAFS THROUGH 06Z MONDAY NIGHT)
ISSUED AT 725 AM EDT MON SEP 22 2014

A DISTURBANCE CURRENTLY MOVING EASTWARD OVER THE LOWER GREAT LAKE
REGION HAS RESULTED IN AN AREA OF MVFR CLOUDS. WITH GENERALLY
NW TO SE FLOW...THESE CLOUDS CONTINUE TO EXPAND SOUTHWARD INTO
APPALACHIAN REGION...INCLUDING EASTERN KY. UNFORTUNATELY...MODELS DO
NOT HAVE A GOOD HANDLE ON THESE CLOUDS...ESPECIALLY IN REGARDS TO HOW
LONG AND TO WHAT EXTENT THEY WILL AFFECT THE TAF SITES. EXPECT THAT
THEY MAY MISS KLOZ AND KSME...OR ONLY IMPACT THEM FOR A BRIEF TIME.
WITH DAYTIME HEATING...THESE CLOUDS SHOULD SLOWLY LIFT AND
DISSIPATE...BUT THE TIMING OF SUCH ACTIONS IS UNCERTAIN. TRIED TO
TREND TO BETWEEN 15 AND 19Z IN THE TAFS...BUT THIS MAY NEED TO BE
UPDATED WITH THE LATEST TRENDS. OTHERWISE...HIGH PRESSURE SHOULD KEEP
CALM AND DRY CONDITIONS ACROSS THE TAF SITES THROUGH THE AFTERNOON
AND EVENING. THERE IS THE THREAT OF SOME VALLEY FOG DEVELOPING
OVERNIGHT...POSSIBLY INFLUENCING THE TAF SITES NEAR DAYBREAK AS IT
BEGINS TO LIFT. TRIED TO TREND TOWARDS LOWERING VIS...BUT UNCERTAINTY
THIS FAR OUT LED TO KEEPING A MORE OPTIMISTIC MVFR APPROACH FOR RIGHT
NOW.

&&


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

$$

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





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