Area Forecast Discussion
Issued by NWS Jackson, KY

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000 FXUS63 KJKL 281138 CCA AFDJKL AREA FORECAST DISCUSSION...CORRECTED NATIONAL WEATHER SERVICE JACKSON KY 738 AM EDT TUE JUL 28 2015 .UPDATE... ISSUED AT 738 AM EDT TUE JUL 28 2015 ONLY MINOR NEAR TERM CHANGES WERE MADE BASED ON LATEST OBSERVATIONS. && .SHORT TERM...(TODAY THROUGH WEDNESDAY) ISSUED AT 400 AM EDT TUE JUL 28 2015 THE PERIOD WILL BE DOMINATED BY AN ATMOSPHERE WITH ONLY VERY WEAK FEATURES AND LIGHT FLOW ALOFT IN OUR REGION...WITH AN UPPER LEVEL HIGH CENTERED TO OUR SW. CONDITIONS WILL BE VERY SIMILAR TO YESTERDAY...EXCEPT FOR A SLIGHTLY WARMER ATMOSPHERIC COLUMN. WILL EXPECTED SCATTERED CONVECTION TO REDEVELOP AFTER HEATING BOTH TODAY AND WEDNESDAY. IT SHOULD GRADUALLY DIE THIS EVENING WITH LOSS OF HEATING. WITH LIGHT FLOW AND SLOW MOVEMENT OF THUNDERSTORMS...ISOLATED HEAVY RAINFALL MAY OCURR. .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 12Z TAFS THROUGH 12Z WEDNESDAY MORNING) ISSUED AT 738 AM EDT TUE JUL 28 2015 MAINLY IFR AND MVFR CONDITIONS ARE ANTICIPATED AT THE START OF THE PERIOD...ON THE MOVE TOWARD VFR BY LATE MORNING. SCATTERED SHOWERS AND THUNDERSTORMS ARE EXPECTED TO DEVELOP THIS AFTERNOON...BRINGING LOCALIZED SUB-VFR CONDITIONS. THE CONVECTION SHOULD DIMINISH TOWARD SUNSET. FOG WILL DEVELOP AGAIN DURING THE NIGHT...FIRST IN VALLEYS...BUT THEN SPREADING OUT AND GROWING IN DEPTH TO BRING IFR TO MOST PLACES BEFORE THE END OF THE PERIOD. && .JKL WATCHES/WARNINGS/ADVISORIES... NONE. && $$ UPDATE...HAL SHORT TERM...HAL LONG TERM...JMW AVIATION...HAL

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