Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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000 FXUS62 KRAH 151115 AFDRAH AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE RALEIGH NC 715 AM EDT MON SEP 15 2014 .SYNOPSIS...WEAK HIGH PRESSURE WILL EXTEND SOUTHWARD INTO CENTRAL NC TODAY THEN DRIFT EAST TONIGHT. A COLD FRONT WILL DRIFT SOUTHEAST ACROSS CENTRAL NC ON TUESDAY. COOL HIGH PRESSURE WILL BUILD INTO THE REGION ON WEDNESDAY. && .NEAR TERM /THROUGH TONIGHT/... AS OF 325 AM MONDAY... CHALLENGING FORECAST IN THE NEAR TERM. MOIST STABLE LOW LEVEL AIR MASS CURRENTLY IN PLACE WITH WEAK SURFACE HIGH RIDGING SOUTHWARD INTO THE CAROLINAS FROM A WEAK PARENT HIGH (1024MB) CENTERED OVER SOUTHERN NEW ENGLAND. THIS FEATURE PROJECTED TO DRIFT EAST TODAY. UPSTAIRS...WLY FLOW ALOFT WILL ADVANCE A VORT MAX CURRENTLY CROSSING THE SOUTHERN PLAINS EARLY THIS MORNING ACROSS THE TN VALLEY THIS AFTERNOON AND INTO OUR REGION TONIGHT. THIS FEATURE PROJECTED TO SLOWLY WEAKEN AS IT GETS CLOSER TO OUR AREA. WHEN IT ARRIVES...IT WILL HAVE ENOUGH MOISTURE TO WORK WITH AS PRECIPITABLE WATER VALUES SHOULD RANGE 1.3/1.4 INCHES ACROSS THE NORTH TO 1.75 INCHES ACROSS THE SOUTH. ASIDE FROM THE MID/UPPER LEVEL DISTURBANCE...FORCING IS WEAK IN THE LOWER HALF OF THE ATMOSPHERE. THUS...CANNOT SEE POP ANY HIGHER THAN ABOUT 1-IN-3 CHANCE...AND MAINLY ACROSS THE WEST AND SOUTH SECTIONS DURING THE EVENING HOURS. SO...EXPECT WIDESPREAD CLOUDINESS THIS MORNING WITH AN ISOLATED SHOWER POSSIBLE SOUTH HALF. BY MID AFTERNOON...EXPECT SOME PARTIAL SUNSHINE. THIS HEATING MAY FUEL A FEW MORE SHOWERS AND POSSIBLY A THUNDERSTORM...AGAIN MAINLY ACROSS THE SOUTH. THE APPROACH OF THE UPPER LEVEL DISTURBANCE FROM TEH WEST SHOULD MAINTAIN A THREAT FOR A FEW SHOWERS AND POSSIBLY A THUNDERSTORM...MAINLY ACROSS THE WEST AND SOUTH...WITH THE THREAT DECREASING FROM THE NW WELL AFTER MIDNIGHT. TEMPS TODAY DEPENDENT UPON WHEN/IF CLOUDS DIMINISH TO ALLOW SOME SUN. USED A BLEND OF MOS GUIDANCE WITH A SLIGHT ADJUSTMENT TOWARD THE COOLER END. MAX TEMPS UPPER 70S NORTH TO LOWER 80S SOUTH. MIN TEMPS TONIGHT MID-UPPER 60S. && .SHORT TERM /TUESDAY AND TUESDAY NIGHT/... AS OF 325 AM MONDAY... WHILE MID LEVEL DISTURBANCE CROSSES OUR REGION LATE TONIGHT...ANOTHER (THOUGH STRONGER) S/W WILL BE CROSSING THE GREAT LAKES INTO SOUTHERN NEW ENGLAND. THIS FEATURE WILL PROPEL A SURFACE COLD FRONT ACROSS CENTRAL NC TUESDAY. DUE TO WEAK SUBSIDENCE IN THE WAKE OF THE DEPARTING INITIAL DISTURBANCE...FORCING ALONG THE SURFACE COLD FRONT IS RELATIVELY WEAK. THUS...EXPECT ANY CONVECTION ASSOCIATED WITH THE COLD FRONT TO BE NO WORSE THAN SCATTERED...MAINLY OCCURRING ACROSS THE SOUTH HALF OF THE FORECAST AREA. PASSAGE OF A MID LEVEL TROUGH TUESDAY NIGHT WILL MAINTAIN A SLIGHT CHANCE POP TUESDAY NIGHT ACROSS THE FAR SOUTH. DOWNSLOPE FLOW IN THE WAKE OF THE DEPARTING INITIAL DISTURBANCE WILL AID TO MIX OUT ANY LOW LEVEL CLOUDINESS AND RESULT IN SOME SUBSIDENCE WARMING. MOS GUIDANCE APPEARS TOO WARM BY ABOUT A CATEGORY AS CLOUDINESS MAY HOLD ON LONGER THAN PROJECTED BY THE MODELS PLUS DOWNSLOPE FLOW RATHER WEAK. FAVOR MAX TEMPS 2-4 DEGREES COOLER THAN GUIDANCE (LOW-MID 80S). MIN TEMPS TUESDAY NIGHT NEAR 60 FAR NORTH-NW TO THE MID 60S SOUTH. && .LONG TERM /WEDNESDAY THROUGH SUNDAY/... AS OF 330 AM MONDAY... THE MEDIUM RANGE WILL FEATURE A LONGWAVE TROUGH THAT WILL AMPLIFY OVER THEN MOVE OFFSHORE THE EAST COAST MID-LATE WEEK. THE TROUGH WILL THEN LIFT OUT AND YIELD BRIEFLY TO A FLAT SUB-TROPICAL RIDGE FORECAST TO BUILD EAST FROM THE SOUTHERN PLAINS AND LOWER MS VALLEY EARLY THIS WEEKEND...BEFORE RENEWED TROUGHING AMPLIFIES FROM CENTRAL CANADA TO THE EAST COAST SUN-MON. MEANWHILE AT THE SFC...A LEAD SFC HIGH WILL BUILD FROM THE OH VALLEY TO THE MIDDLE ATLANTIC COAST WED...THEN BE OVERWHELMED BY A STRONGER (1028-1030 MB) ONE FORECAST TO BUILD FROM CENTRAL CANADA TO THE CANADIAN MARITIMES...AND RIDGE SOUTH/SOUTHWESTWARD IN A DAMMING ORIENTATION EAST OF THE APPALACHIANS...THU THROUGH THE WEEKEND. THE RESULT WILL BE A RELATIVELY PROLONGED PERIOD OF EAST TO NORTHEAST LOW LEVEL FLOW AND ASSOCIATED BELOW NORMAL TEMPERATURES...TEMPERED FURTHER BY PERIODS OF BKN MULTI-LAYERED CLOUD COVER. THE RELATIVE GREATEST CLOUD COVERAGE WILL OCCUR WED-THU...WHEN A SLIGHT-LOW CHANCE OF SHOWERS WILL ALSO BE INTRODUCED...AS WEAK DISTURBANCES RIPPLE THROUGH THE AFOREMENTIONED LONGWAVE TROUGH AMPLIFYING OVER THE EASTERN STATES. IN FACT...WED MAY WELL BE A RATHER DREARY DAY THROUGH AT LEAST EARLY AFTERNOON...AS ISENTROPIC LIFT IN RETURN FLOW AROUND A 925-850 MB RIDGE ALONG THE COASTAL CAROLINAS AUGMENTS THE WEAK FORCING ATTENDING THE PASSING MID LEVEL DISTURBANCES. SOME PARTIAL CLEARING FROM THE WEST WILL BE POSSIBLE BY MID LATE AFTERNOON...WHEN THE FLOW BECOMES INCREASINGLY WESTERLY/DOWNSLOPE AS THE AFOREMENTIONED LOW LEVEL ANTICYCLONE DRIFTS OFFSHORE. AS SUCH...HIGH TEMPERATURES SHOULD CLIMB ONLY INTO THE 69 TO 76 DEGREE RANGE...COOLEST OVER THE NE PIEDMONT AND NORTHERN COASTAL PLAIN. OTHERWISE...THE INCREASING INFLUENCE OF THE RIDGING AT THE SFC AND ALOFT SHOULD PROMOTE DRY CONDITIONS FRI-SUN...THOUGH WITH TEMPERATURES MODERATING ONLY SLOWLY THROUGH THE 70S. && .AVIATION /12Z MONDAY THROUGH FRIDAY/... AS OF 715 AM MONDAY... WIDESPREAD MVFR CEILINGS WILL PERSIST ACROSS CENTRAL NC THIS MORNING...AND MAY LAST UNTIL MID-AFTERNOON. BETWEEN 12Z-16Z...MAY SEE POCKETS OF IFR CEILING. BETWEEN 19Z-21Z...MVFR CEILINGS MAY GRADUALLY SCATTER OUT....BUT MVFR CEILINGS MAY RETURN BY 00Z TUESDAY. SURFACE WINDS WILL BE LIGHT (LESS THAN 10KTS)...AND SLOWLY VEER FROM THE CURRENT EAST-NORTHEAST TO A SOUTH-SOUTHEAST DIRECTION BY 22Z. LATE TONIGHT INTO EARLY TUESDAY MORNING...AREAS OF LOW CLOUDS AND FOG MAY DEVELOP WITH CEILINGS 500-1000FT HIGHLY PROBABLE WITH POCKETS OF 200-500FT POSSIBLE. VISIBILITY 3-5SM EXPECTED WITH AREAS OF 1-2 MILES PROBABLE. A COLD FRONT WILL DRIFT ACROSS CENTRAL NC TUESDAY. THIS SYSTEM MAY CAUSE AREAS OF MVFR CEILING ALONG WITH SCATTERED SHOWERS AND ISOLATED THUNDERSTORMS. THE ISOLATED THUNDERSTORM THREAT WILL BE HIGHEST IN VICINITY OF KFAY. COOL HIGH PRESSURE WILL BUILD INTO CENTRAL NC FROM THE NORTHWEST. NE LOW LEVEL FLOW MAY MAINTAIN MOISTURE IN THE LOWEST 8K FT...RESULTING IN PERIODS OF MVFR CEILINGS AND POSSIBLY PATCHY LIGHT RAIN WEDNESDAY...AND POSSIBLY THURSDAY. VFR CONDITIONS ANTICIPATED FRIDAY. && .RAH WATCHES/WARNINGS/ADVISORIES... NONE. && $$ SYNOPSIS...WSS NEAR TERM...WSS SHORT TERM...WSS LONG TERM...MWS AVIATION...WSS

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