Area Forecast Discussion
Issued by NWS Jackson, KY

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000
FXUS63 KJKL 210024
AFDJKL

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE JACKSON KY
824 PM EDT SUN JUL 20 2014

.UPDATE...
ISSUED AT 709 PM EDT SUN JUL 20 2014

QUICK UPDATE FOR THE UPTICK IN SHOWER ACTIVITY ACROSS THE AREA LATE
THIS AFTERNOON/EARLY THIS EVENING. SHORT WAVE CURRENTLY DROPPING
SOUTHEASTWARD INTO THE MID OHIO VALLEY REGION IN COMBINATION WITH
FAVORABLE DIURNAL HEATING IS RESPONSIBLE FOR THE LATE DAY INCREASE.
ONE PARTICULAR CLUSTER OF SHOWERS OVER THE BLUEGRASS HAS MANAGED TO
STRENGTHEN INTO THUNDERSTORMS. IN ADDITION...CLUSTERS HAVE MANAGED TO
PRODUCE A FEW OUTFLOW BOUNDARIES ACROSS THE AREA THAT ARE KICKING OFF
ADDITIONAL SHOWERS. INCREASED POPS LATE THIS AFTERNOON AND EARLY THIS
EVENING TO LINE UP WITH CURRENT RADAR TRENDS. TWEAKED GRIDS FOR
HOURLY OBS AS WELL. WITH EXTREMELY ISOLD NATURE OF THUNDER LEFT
MENTION OF OUT OF THE ZONE PACKAGE...PREFERRING TO MENTION IN OUR
GRAPHICAL-NOWCAST PRODUCTS.

&&

.SHORT TERM...(THIS EVENING THROUGH MONDAY NIGHT)
ISSUED AT 319 PM EDT SUN JUL 20 2014

A WEAK LOW PRESSURE CENTER JUST OFF TO OUR SOUTH HAS CONTROLLED
TODAY/S WEATHER...BRINGING MOIST CONDITIONS WITH LOW CLOUDS AND
DRIZZLE/LIGHT RAIN SHOWERS THROUGH THE FIRST PART OF THE DAY. DURING
THE AFTERNOON...SHOWERS FINALLY BEGAN PUSHING TO THE NE...WHILE
SMALL ISOLATED/SCATTERED SHOWERS STARTED POPPING UP ACROSS PORTIONS
OF EASTERN KY. THE LOW...CURRENTLY OVER MIDDLE TN...WILL QUICKLY
DROP SOUTHWARD LATE THIS AFTERNOON...PULLING THE BEST INSTABILITY
AND MOISTURE WITH IT. EXPECT ISOLATED TO SCATTERED SHOWERS TO
CONTINUE INTO THE LATE AFTERNOON...BEFORE TAPERING OFF BY EVENING.
BASED ON THE CURRENT LACK OF INSTABILITY AND THUNDERSTORM
DEVELOPMENT...WENT AHEAD AND REMOVED ANY MENTION OF THUNDER FROM THE
FORECAST FOR THE REMAINDER OF TODAY AND THIS EVENING.

THOUGH CLOUD COVER COULD LINGER IN SOME LOCATIONS OVERNIGHT...OTHERS
CAN EXPECT SOME DECENT CLEARING. LOWS WILL REGULATE AROUND
NORMAL...IN THE LOW TO MID 60S ACROSS THE REGION. GIVEN THE AMOUNT OF
LOW LEVEL MOISTURE ACROSS THE AREA...AND THE EXPECTATION OF ANOTHER
STRONG SUBSIDENCE INVERSION SETTING UP OVERNIGHT...FOG SHOULD ONCE
AGAIN BE THE MAIN CONCERN OVERNIGHT TONIGHT. INCLUDED PATCHY FOG
ACROSS THE ENTIRE CWA...WITH AREAS OF FOG IN THE RIVER VALLEYS. THERE
IS THE POTENTIAL THAT SOME OF THESE LOCATIONS COULD SEE DENSE
FOG...ESPECIALLY AREAS THAT RECEIVED RAINFALL DURING THE DAY TODAY.

THEN FOR TOMORROW...EXPECT A MORE TYPICAL SUMMER TIME DIURNAL
PATTERN TO TAKE OVER. AIR MASS MODIFICATION /ALONG WITH SOME CLEARING
DURING THE DAY/ WILL ALLOW FOR TEMPS TO RISE INTO THE UPPER 80S.
CONVECTION WILL THEN BE POSSIBLE DURING THE AFTERNOON
HOURS...ESPECIALLY IN THE SE. WINDS WILL BE VERY LIGHT...WITH LITTLE
FORCING. CHOSE TO KEEP ONLY ISOLATED THUNDER WORDING IN THE FORECAST
FOR THE AFTERNOON...GIVEN THE LACK OF A GOOD WIND
PROFILE...INSTABILITY...AND A DECENT MID LEVEL INVERSION ON THE
LATEST FORECAST SOUNDING. EXPECT CONVECTION TO DIE OUT IN THE EVENING
WITH THE LOSS OF DIURNAL HEATING. WITH MORE CLEARING EXPECTED
OVERNIGHT MONDAY NIGHT...TEMPS SHOULD DROP BACK DOWN INTO THE MID AND
UPPER 60S...WHICH IS STILL A FEW DEGREES WARMER THAN WHAT IS EXPECTED
FOR TONIGHT.

.LONG TERM...(TUESDAY THROUGH SUNDAY)
ISSUED AT 420 PM EDT SUN JUL 20 2014

THE LONG TERM PERIOD WILL BEGIN WITH RIDGING CENTERED OVER THE
SOUTHERN ROCKIES WITH ANOTHER RIDGE CENTERED OFF THE SOUTHEAST US
COAST. IN BETWEEN AN UPPER LEVEL LOW IS EXPECTED TO BE OVER THE
SOUTHEAST US. A SHORTWAVE OR SERIES OF SHORTWAVES IS EXPECTED TO BE
WORKING FROM THE US CANADIAN BORDER/UPPER MS VALLEY TOWARD THE GREAT
LAKES AT THAT TIME.

THROUGH TUE NIGHT...INTO WED...THE PATTERN IS STILL EXPECTED TO
AMPLIFY A BIT AROUND MIDWEEK WITH THE RIDGE STRENGTHENING A BIT OVER
THE WESTERN CONUS AND THE INITIAL SHORTWAVE TREKKING ACROSS THE GREAT
LAKES AND INTO THE NORTHEAST. ANOTHER SHORTWAVE SHOULD ROTATE AROUND
A CLOSED LOW OVER CANADA ACROSS SOUTHERN CANADA AND THE GREAT LAKES
REGION. DURING THIS PERIOD...THE SOUTHEAST UPPER LEVEL LOW SHOULD
MEANDER SLOWLY WEST. THIS SCENARIO SHOULD LEAD TO A PERIOD OF WEST
NORTHWEST TO NORTHWEST FLOW ALOFT ACROSS PARTS OF THE EASTERN CONUS
FROM WED NIGHT INTO FRI. THIS SHOULD COMBINATION SHOULD SEND A COLD
FRONT TOWARD THE REGION ON WED INTO AND THEN ACROSS THE AREA WED
NIGHT INTO THU. THE GFS RUNS CONTINUE TO PUSH THE BOUNDARY FURTHER
SOUTHEAST AND FASTER THAN THE ECMWF RUNS. THIS LEADS TO A BIT OF
UNCERTAINTY IN AMOUNT OF MOIST AND PRECIP CHANCES FROM THU NIGHT INTO
FRI. ALSO FROM THU INTO THE WEEKEND...THE PATTERN SHOULD BEGIN TO
FLATTEN OUT AGAIN AS A RATHER ROBUST UPPER LOW IS EXPECTED TO WORK
FROM THE PACIFIC NORTHWEST GRADUALLY EAST NEAR THE US/CANADIAN
BORDER THROUGH THE START OF THE WEEKEND. THEN LATE IN THE PERIOD...
THIS UPPER LOW IS PROGGED TO APPROACH THE GREAT LAKES REGION WITH THE
PATTERN AGAIN AMPLIFYING OR RETURNING TO A WESTERN CONUS RIDGE AND
EASTERN CONUS TROUGH.

PRECIPITATION CHANCES INITIALLY SHOULD BE GENERALLY DIURNALLY DRIVEN
WITH WEAK DISTURBANCES WORKING AROUND THE SOUTHEASTERN CONUS UPPER
LOW POSSIBLY ENHANCING CHANCES ACROSS PARTS OF THE SOUTH OR
SOUTHEAST. THEN AS THE SHORTWAVES APPROACH AND SEND THE COLD FRONT
TOWARD AND THEN ACROSS THE REGION...UNSETTLED WEATHER IS ANTICIPATED
FORM WED AFTERNOON INTO THU EVENING. HIGH CHANCE TO LIKELY POPS WERE
USED DURING THIS PERIOD AS THE PREFRONTAL AIR MASS AND THE UPPER
SUPPORT SHOULD COMBINE WITH THE BOUNDARY FOR GOOD CONVERGE OF
CONVECTION. THE MODEL CONSENSUS BLEND WAS USED FOR POPS ON THU NIGHT
INTO FRI. THE GFS MODEL RUNS IN GENERAL ARE DRIER THROUGH THIS PERIOD...
WHILE THE ECMWF IS WETTER AS IT HAS THE BOUNDARY CLOSER TO THE AREA
THAT PERIOD.

DIURNALLY DRIVEN ISOLATED CONVECTION APPEARS POSSIBLE TO START THE
WEEKEND ON SATURDAY AS THE FLOW BECOMES MORE WESTERLY...BUT ANY
PASSING DISTURBANCE COULD INTERACT WITH DAYTIME HEATING. THEN AS THE
TROUGH BEGINS TO DEVELOP LATE IN THE PERIOD...COVERAGE OF CONVECTION
SHOULD INCREASE ALONG WITH THE CHANCES FOR CONVECTION AT NIGHT.

TEMPERATURES WILL AVERAGE A BIT ABOVE NORMAL FOR TUE INTO WED...BUT
BEHIND THE BOUNDARY DROP A FEW DEGREES BELOW NORMAL FOR THU INTO SAT.
THE BIGGEST DEPARTURES OF ABOUT 5 TO 8 DEGREES WILL OCCUR WITH DAYTIME
HIGHS ON THU...AND IN HIGHS IN GENERAL.

&&

.AVIATION...(FOR THE 00Z TAFS THROUGH 00Z MONDAY EVENING)
ISSUED AT 824 PM EDT SUN JUL 20 2014

UPPER LEVEL DISTURBANCE AND DAYTIME HEATING HAS KICKED OFF SHOWER
ACTIVITY ACROSS THE AREA. MOST OF THE ACTIVITY HAS BEEN GENERALLY
EITHER SIDE OF A LINE FROM KEKQ TO KSYM. LONDON AND JACKSON HAD
SHOWERS PASS OVER THE TERMINALS. CONSIDERING TIME OF OCCURRENCE AND
THE FACT THAT WE ARE WELL INTO THE EARLY EVENING NOW...EXPECT FOG
MAY FORM A BIT EARLIER THAN MODEL GUIDANCE MIGHT SUGGEST AT LONDON
AND JACKSON. MODEL GUIDANCE TAKES ALL AIRPORTS DOWN INTO LIFR
TERRITORY THROUGH THE EARLY MORNING HOURS MONDAY DUE TO FOG. WITH
RECENT RAINFALL ACROSS PORTIONS OF THE AREA AND SIGNIFICANT INCREASE
IN BOUNDARY LAYER MOISTURE...SEE NO REASON TO DOUBT MODEL GUIDANCE
THROUGH THE FIRST 8 TO 12 HOURS OF THE FORECAST. ONCE FOG BURNS OFF
THROUGH THE MID TO LATE MORNING TIMEFRAME MONDAY...VFR CONDITIONS
SHOULD RETURN THROUGH THE REMAINDER OF THE TAF PERIOD. A FEW DIURNAL
SHOWERS AND THUNDERSTORMS COULD BE POSSIBLE AFTER 18Z TOMORROW...
MAINLY OVER THE HIGHER TERRAIN TO OUR SOUTHEAST. WINDS WILL BE LIGHT.

&&

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

&&

$$

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






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