Area Forecast Discussion
Issued by NWS Jackson, KY

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FXUS63 KJKL 280721
AFDJKL

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE JACKSON KY
321 AM EDT TUE JUL 28 2015

.UPDATE...
ISSUED AT 1015 PM EDT MON JUL 27 2015

RAIN SHOWERS AND ISOLATED THUNDERSTORMS HAVE BEEN QUITE PERSISTENT
ALONG AND NORTH OF I64 TONIGHT. THESE HAVE LIKELY BEEN RELATED TO
SOME DEEP MOISTURE CONVERGENCE AND ALSO FIRING UP ALONG A NEAR A
WEAK FRONTAL BOUNDARY. RIGHT NOW STILL EXPECTING MUCH OF THIS TO
WEAKEN AND DIE OFF THROUGH THE NIGHT. IN THE MEAN TIME THESE
SHOWERS AND STORMS HAVE BEEN PRODUCING QUITE THE RAINFALL ACROSS
PORTIONS OF THE REGION WITH 3 HOUR RADAR ESTIMATES OF 2 PLUS
INCHES IN SOME AREAS. UPDATED GRIDS TO BETTER HANDLE OVERALL
CONVECTION AND ADJUSTED TEMPS/DEW POINTS/WINDS TO LATEST OBS.

UPDATE ISSUED AT 810 PM EDT MON JUL 27 2015

CONTINUING TO SEE CONVECTION THIS EVENING ACROSS THE NORTH AND
NEAR THE TN BORDER...WHILE MUCH OF THE CENTRAL PORTIONS OF THE
REGION REMAINS DRY. THE CONVECTION CONTINUES TO SHOW A OVERALL
WEAKENING TREND BASED ON WSR-88D RADAR AND IR SAT. ALSO MANY OF
THE CONVECTIVE MODELS WOULD SUGGEST A OVERALL WEAKENING TREND WITH
LOSS OF DAYTIME HEATING. THEREFORE DO SHOW THAT AS WE GOING INTO
THE LATER EVENING HOURS. THE ISSUE TONIGHT WILL BE HOW MUCH FOG
PRODUCTION DO WE SEE...DO THINK VALLEY LOCATIONS AND AREAS THAT
SAW RAIN WILL HAVE THE BEST CHANCES FOR FOG OVERNIGHT. UPDATED
GRIDS TO REFLECT LATEST RADAR TRENDS AND ALSO UPDATED WITH LATEST
OBS.

&&

.SHORT TERM...(THIS EVENING THROUGH TUESDAY NIGHT)
ISSUED AT 321 PM EDT MON JUL 27 2015

CURRENT CONDITIONS ACROSS THE AREA FEATURE A WEAK BOUNDARY ACROSS
SOUTHERN OH AND INTO NORTHERN KY...THIS COMBINED WITH A VERY MOIST
AND UNSTABLE ATMOSPHERE HAS RESULTED IN SOME SHOWER AND
THUNDERSTORM ACTIVITY THROUGH THE AREA THIS AFTERNOON AND INTO
THIS EVENING. THIS ACTIVITY SHOULD QUICKLY WANE WITH THE LOSS OF
DAYTIME HEATING. THE CHALLENGING PART OF THE FORECAST WILL BE
LATER TONIGHT WITH THE LEFTOVER CLOUD COVER FROM THE DAYS
CONVECTION. THIS WILL SLOWLY DISSIPATE THROUGH THE NIGHT ALLOWING
FOR SOME FOG DEVELOPMENT. HOWEVER...SOUTHERLY FLOW DEVELOPING IN
THE LOWER LEVELS ALONG WITH ANOTHER CLUSTER OF CONVECTION TO THE
NORTHWEST MOVING IN...WILL ALLOW FOR ADDITIONAL CLOUD COVER
MOVING INTO THE AREA. THIS MAY HINDER FOG DEVELOPMENT TONIGHT.
THERE WILL BE A PERIOD OF CLEARING SKIES BUT WITH THE SATURATED
BOUNDARY LAYER IN PLACE...FOG MAY DEVELOP TONIGHT
REGARDLESS...ESPECIALLY WITH LIGHT WINDS EXPECTED.

THE SOUTHERLY MOIST FLOW MOVING INTO THE CENTRAL APPALACHIANS AND
INTO EASTERN KENTUCKY WILL ALLOW FOR AMPLE MOISTURE AND
INSTABILITY. THIS COMBINED WITH THE WEAK DISTURBANCES MOVING OVER
THE RIDGE AND INTO THE AREA WILL ALLOW FOR SHOWER AND THUNDERSTORM
DEVELOPMENT INTO THE DAY ON TUESDAY. MODEL SOUNDINGS SEEM TO HAVE
A WEAKER CAP IN PLACE THAN PREVIOUS RUNS AND THIS WILL MAKE FOR
RATHER EASY DEVELOPMENT ACROSS THE AREA WITH SOME HEAVY RAINFALL
AMOUNTS POSSIBLE IN SOME OF THE CELLS. TOWARDS THE END OF THE
DAY...THE MID LEVEL RIDGE AXIS WILL SHIFT OVER THE AREA BRINGING
AN END TO ANY CONVECTION AND ALLOWING SOME CLEARING FOR TUESDAY
NIGHT BEFORE THE NEXT FRONT BEGINS TO MOVE INTO THE AREA.
OVERALL...THE VERY WARM AND MOIST AIR MASS CONTINUES TO IMPACT
THE AREA WITH THE POTENTIAL FOR SHOWER AND THUNDERSTORM
DEVELOPMENT THROUGH MUCH OF THE SHORT TERM.

.LONG TERM...(WEDNESDAY NIGHT THROUGH MONDAY)
ISSUED AT 320 AM EDT TUE JUL 28 2015

WHILE BROAD RIDGING WILL BE IN PLACE ACROSS MUCH OF THE SOUTHERN
CONUS...INCLUDING THE OHIO RIVER VALLEY REGION...TO START THE
PERIOD...A FAST MOVING UPPER LEVEL LOW WILL BE TRAVERSING FROM WEST
TO EAST ACROSS SOUTHERN CANADA. THIS LOW WILL HAVE MADE IT TO
CENTRAL ONTARIO BY 0Z THURSDAY...AND WILL THEN CHANGE COURSE TOWARDS
THE NE. AS IT CONTINUES ON THIS TRACK...UPPER LEVEL HEIGHTS WILL
BEGIN FALLING ACROSS OUR REGION AS THE RIDGE GETS PUSHED FARTHER
BACK AND EAST. THE LOW WILL THEN BECOME STALLED OVER HUDSON
BAY...KEEPING THE BROAD TROUGH IN PLACE ACROSS MUCH OF THE EASTERN
AND MIDWEST CONUS...WHILE CONTINUING TO PUSH THE RIDGE FARTHER
WESTWARD TOWARDS THE 4 CORNER STATES BY FRIDAY AFTERNOON. EXPECT
THIS TROUGHING PATTERN TO CONTINUE THROUGH THE WEEKEND AND EVEN INTO
NEXT WEEK...WITH HEIGHTS OSCILLATING FROM HIGHER TO LOWER AS THE LOW
ROTATES BACK AND FORTH AROUND THE HUDSON BAY AREA.

AS IT RELATES TO OUR CWA...THIS LOWERING OF HEIGHTS AND INCOMING
TROUGH WILL TRANSLATE TO NW FLOW ALOFT THROUGH MUCH OF THE PERIOD.
MULTIPLE SHORTWAVES ARE EXPECTED TO TRAVERSE THE
TROUGH...HOWEVER...HIGH PRESSURE AT THE SURFACE MAY BE ENOUGH TO
WARD OFF ANY PRECIP CHANCES AS THESE WAVES/BOUNDARIES NEAR THE
REGION.

THE MAIN CONCERN FOR SHOWERS AND THUNDERSTORMS WILL COME AT THE
START OF THE PERIOD...AS THE CLOSED LOW MOVES ACROSS
ONTARIO...PULLING A STRONG SURFACE LOW PRESSURE SYSTEM WITH IT. A
COLD FRONT WILL EXTEND SOUTHWARD FROM THE SURFACE LOW...ACROSS
MUCH OF THE MISSISSIPPI RIVER VALLEY AT 0Z THURSDAY. IT WILL
QUICKLY SWIPE EASTWARD AND ACROSS KY THROUGH THE OVERNIGHT HOURS
WEDNESDAY NIGHT AND INTO THE DAY THURSDAY. INSTABILITY PARAMETERS
WEDNESDAY NIGHT ARE LACKING...WITH VERY LITTLE CAPE AND A STRONG
SURFACE INVERSION...SO NOT EXPECTING MORE THAN A FEW RUMBLES OF
THUNDER THROUGH 12Z. BETWEEN 12 AND 18Z...INSTABILITY IMPROVES
WITH DAYTIME HEATING...HOWEVER THE SURFACE INVERSION WILL LIFT TO
THE MID LEVELS. STORMS WOULD NEED TO OVERCOME THIS INVERSION TO
PRODUCE ANY STRONG TO SEVERE ACTIVITY. AND GIVEN THE VERY FAST
NATURE OF THIS FRONTAL BOUNDARY...DON/T EXPECT TRAINING OR
LINGERING OF HEAVY RAINING STORMS TO BE OF MUCH CONCERN.

MODELS START TO LOSE CONTINUITY ON SURFACE SOLUTIONS AFTER THIS
INITIAL FRONTAL BOUNDARY MOVES THROUGH FRIDAY AND ONWARD...THOUGH
THEY STILL MAINTAIN AGREEMENT IN THE UPPER LEVELS. ANOTHER SHORTWAVE
AND FRONTAL BOUNDARY IS EXPECTED TO MOVE THROUGH SOMETIME DURING THE
DAY SATURDAY. HOWEVER...WITH DRIER NW FLOW IN PLACE IN THE UPPER
LEVELS...AND HIGH PRESSURE OVER THE REGION IN THE LOWER LEVELS...THE
ECMWF KEEPS OUT ANY MOISTURE CHANCES WITH THE FRONTAL ZONE
WEAKENING BEFORE MAKING IT INTO THE OHIO RIVER VALLEY...WHILE THE
GFS SHOWS THE PRECIP WEAKENING BUT STILL MAINTAINS SOME SLIGHT
CHANCES ACROSS OUR CWA. A SIMILAR SCENARIO PLAYS OUT FOR ANOTHER
SHORTWAVE EXPECTED TO MOVE THROUGH SOMETIME SUNDAY NIGHT INTO
MONDAY. THE QUESTION WILL BE IF SURFACE HIGH PRESSURE WILL BE
STRONG ENOUGH TO KEEP THESE BOUNDARIES FROM AFFECTING EASTERN KY.
AS IT STANDS NOW...MODEL BLENDS ACTUALLY COME UP WITH GENERALLY
SUB SLIGHT CHANCES DURING BOTH OF THESE SYSTEMS...SO DECIDED TO
CONTINUE TO EXCLUDE MENTION OF ANY PRECIP CHANCES FOR THE
REMAINDER OF THE EXTENDED.

AFTER THE INITIAL COLD FRONT TUESDAY MORNING...NW FLOW WILL BRING IN
SLIGHTLY COOLER TEMPERATURES. HOWEVER...STRONG SURFACE HIGH PRESSURE
IN PLACE AND CLEAR SKIES WILL PROMOTE MAXIMUM DAYTIME RADIATION...SO
THE TEMP DROP WILL NOT BE THAT GREAT...ONLY A FEW DEGREES FROM THE
DAY BEFORE. 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 EACH DAY...STAYING IN THE MID AND UPPER 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 WEEKEND.

&&

.AVIATION...(FOR THE 06Z TAFS THROUGH 06Z TUESDAY NIGHT)
ISSUED AT 307 AM EDT TUE JUL 28 2015

CONDITIONS WERE LARGELY MVFR AT THE START OF THE PERIOD...WITH
SOME IFR AND VFR PRESENT AS WELL. AN OVERALL DETERIORATION IS
EXPECTED OVERNIGHT...WITH MAINLY IFR EXPECTED BY DAWN. IMPROVEMENT
TO VFR IS EXPECTED EARLY ON TUESDAY MORNING AFTER SUNRISE.
SCATTERED SHOWERS AND THUNDERSTORMS ARE EXPECTED TO DEVELOP ON
TUESDAY AFTERNOON...BRINGING LOCALIZED SUB-VFR CONDITIONS. THEY
SHOULD DIMINISH BY SUNSET.


&&

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

$$

UPDATE...DJ
SHORT TERM...SHALLENBERGER
LONG TERM...JMW
AVIATION...HAL


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