Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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000 FXUS62 KRAH 021432 AFDRAH AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE RALEIGH NC 1030 AM EDT TUE SEP 2 2014 .SYNOPSIS...AN AREA OF HIGH PRESSURE WILL EXTEND OVER THE REGION TODAY. A WEAK SURFACE FRONT WILL SETTLE SOUTHWARD ACROSS CENTRAL NC ON WEDNESDAY. HIGH PRESSURE WILL BUILD BACK OVER THE AREA FOR THE REMAINDER OF THE WORK WEEK. && .NEAR TERM /THROUGH TONIGHT/...
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AS OF 1030 AM TUESDAY... LITTLE CHANGE REQUIRED TO NEAR TERM FORECAST BASED ON UPPER AIR AND SATELLITE ANALYSIS. MID-UPPER RIDGE REMAINS ANCHORED OVER THE SE U.S. WITH THE 850MB AND 700 MB ANTI-CYCLONE CENTERED OVER THE SAVANNAH RIVER VALLEY. THE POSITION OF THIS HIGH AND STRENGTH (322-323DM) SUPPORT AFTERNOON TEMPS WELL INTO THE 90S ACROSS CENTRAL NC. THESE HOT TEMPERATURES COMBINED WITH THE HUMIDITY WILL CREATE HEAT INDICES IN THE 100-104 DEGREE RANGE FOR LOCATIONS GENERALLY ALONG AND EAST OF HIGHWAY 1 WITH THE HIGHEST VALUES EXPECTED IN THE SANDHILLS. IN ADDITION...THE HOT AND HUMID AIR MASS WILL YIELD MODERATE INSTABILITY. THIS SHOULD INITIATE/SUPPORT ISOLATED CONVECTION PRETTY MUCH ANYWHERE IN THE FORECAST AREA. THE CHANCES FOR CONVECTION WILL LIKELY INCREASE TOWARD SUNSET AS A S/W IN THE NORTHERN STREAM PASSES TO OUR NORTH...DRAGGING A WEAK SURFACE BOUNDARY TOWARD OUR NORTHERN COUNTIES. THIS FEATURE INTERACTING WITH AVAILABLE LOW LEVEL MOISTURE/INSTABILITY SHOULD MAINTAIN A FEW SHOWERS/STORMS THIS EVENING ACROSS THE NORTHERN PIEDMONT...AND POSSIBLY WELL PAST MIDNIGHT OVER THE REST OF THE FORECAST AREA. A STRONG OR SEVERE STORM MAY OCCUR LATE THIS AFTERNOON AS LOW LEVEL LAPSE RATES WILL BE IN THE 9-10 DEGREE RANGE...SUPPORTIVE OF A LOCALIZED DOWNBURST. THE BIG STORY MAY BE THE AMOUNT OF LIGHTNING ASSOCIATED WITH THE STORMS. DUE TO PROJECTED PARAMETERS ALOFT...A STORM OR TWO MAY PRODUCE FREQUENT TO EXCESSIVE AMOUNT OF LIGHTING STRIKES...ESPECIALLY ACROSS THE SOUTHERN PIEDMONT AND SANDHILLS.
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&& .SHORT TERM /WEDNESDAY THROUGH WEDNESDAY NIGHT/... AS OF 330 AM TUESDAY... THE WEAK FRONTAL ZONE...MAINLY JUST SURFACE TROUGH...WILL SETTLE OVER CENTRAL ON WEDNESDAY AS ITS PRIMARY SHORTWAVE LIFTS WELL OFF TO THE NORTHEAST. THE AXIS OF HIGHER PW NEAR 2 INCHES WILL SHIFT SOUTH ACROSS THE SOUTHERN TIER OF THE AREA. WEAK WESTERLY FLOW ALOFT MAY CONTAIN A DISTURBANCE OR TWO TO HELP TRIGGER SCATTERED SHOWERS AND STORMS...MAINLY ALONG AND SOUTH OF THE SURFACE TROUGH WHERE MODERATE INSTABILITY WILL DEVELOP. THE AIRMASS WONT CHANGE MUCH ON WEDNESDAY BUT H85 TEMPS ARE KNOCKED BACK A DEGREE OR TWO...AND ADDITIONAL CLOUD COVER SHOULD ALSO HELP TO KEEP HIGHS IN THE LOWER 90S. OVERNIGHT LOWS IN THE UPPER 60S AND LOWER 70S. && .LONG TERM /THURSDAY THROUGH MONDAY/... AS OF 325 AM TUESDAY... THE SUB-TROPICAL RIDGE WILL BRIEFLY EXPAND NORTHWARD...INTO THE OH VALLEY AND MIDDLE ATLANTIC...THROUGH FRI. MEANWHILE...A MID LEVEL SHEAR AND MOIST AXIS...THE TAIL END OF A TROUGH ALOFT FORECAST TO CROSS THE NORTHEAST US AND SOUTHEAST CANADA...WILL REMAINS DRAPED ACROSS THE CAROLINAS THROUGH THE MIDDLE OF THIS WEEK. MEDIUM RANGE ENSEMBLE GUIDANCE SUGGESTS THE SUB-TROPICAL RIDGE WILL THEN WEAKEN AND BECOME SUPPRESSED...IN PROGRESSIVE FLOW ALOFT...BY ANOTHER TROUGH FORECAST TO CROSS THE NE US AND SE CANADA THIS WEEKEND... BEFORE YET ANOTHER ESTABLISHMENT OF THE RIDGE ACROSS THE SOUTHEAST THROUGH THE MIDDLE OF NEXT WEEK. THE EBB AND FLOW OF THE PATTERN ALOFT...AND ASSOCIATED PERIODIC RELAXATION OF THE SUB-TROPICAL RIDGE...WILL ALLOW A SFC COLD FRONT TO SETTLE INTO THE CAROLINAS SUN-MON. THE FAVORED ECMWF ENSEMBLE MEAN SOLUTION SUGGESTS THE FRONT WILL SETTLE SOUTH THROUGH CENTRAL NC SUN AND SUN NIGHT...THEN STALL INVOF THE EASTERN CAROLINAS/ ADJACENT GULF STREAM WATERS...AS IT MEETS RESISTANCE FROM RENEWED SUB-TROPICAL RIDGING EXPANDING FROM THE SW ATLANTIC TO THE GOM EARLY NEXT WEEK. THU: THE PRESENCE OF THE AFOREMENTIONED MID LEVEL SHEAR/MOIST AXIS THROUGH THU WILL PROVIDE FOR A DEEPLY MOIST ENVIRONMENT...ONE CHARACTERIZED BY PWAT VALUES BETWEEN ONE AND THREE QUARTERS AND TWO INCHES...WHICH SHOULD SUPPORT SHOWER AND THUNDERSTORM GROWTH IN A MODERATELY UNSTABLE AND WEAKLY INHIBITED REGIME OVER OUR REGION. WITH CONSIDERABLE MID AND HIGH CLOUDS ACCOMPANYING THE SHEAR AXIS ALOFT...AND CONVECTION...TEMPERATURES ARE APT TO CLIMB SHORT OF WHAT CONTINUED WARM H85 TEMPS OF AROUND 18C WOULD SUPPORT - HIGHS AROUND 90. IF MORE SUNSHINE WERE REALIZED...HIGHS WOULD BE A CATEGORY WARMER. FRI-SAT NIGHT: A PATTERN OF WEAK SYNOPTIC-SCALE ASCENT FRI-SAT NIGHT...AHEAD OF THE AFOREMENTIONED COLD FRONT...WILL THEN FAVOR NEAR CLIMO PROBABILITIES OF DIURNALLY; PIEDMONT TROUGH, AND SEA BREEZE-DRIVEN CONVECTION...WITH HIGHS EDGING INTO THE LOWER 90S BENEATH THE BRIEFLY BUILDING SUB-TROPICAL RIDGE. SUN-MON: THE BEST CHANCE OF SHOWERS AND STORMS DURING THE LONG TERM PERIOD WILL ACCOMPANY THE ARRIVAL/PASSAGE OF THE COLD FRONT SUN-SUN NIGHT...WITH LESSENING PROBABILITIES/DRYING FROM NW TO SE...ON MON. COOLER INVOF AND BEHIND THE FRONT...WITH HIGHS GENERALLY IN THE LOWER TO MIDDLE 80S. && .AVIATION /12Z TUESDAY THROUGH SATURDAY/... AS OF 740 AM TUESDAY... STRATUS HAS SPREAD INLAND FROM THE KILM AREA TOWARD KCTZ...AND MAY REACH KFAY BEFORE SCATTERING OUT BY 14Z. HAVE INCLUDED A TEMPO THE LIFR CEILINGS AT KFAY. OTHERWISE...JUST A FEW LOCATIONS ARE REPORTING MVFR VSBY...WHICH WILL RAPIDLY IMPROVE TO VFR...AND VFR WILL PREVAIL THROUGH MUCH OF THE TAF PERIOD. MODELS ARE INDICATING THAT CONVECTION UPSTREAM OF THE MOUNTAINS...AS WELL AS CONVECTION THAT FORMS ALONG THE EAST SLOPES OF THE MOUNTAINS...WILL MOVE EAST INTO THE PIEDMONT THIS EVENING AHEAD OF A WEAK FRONTAL ZONE TO SETTLE INTO THE AREA OVERNIGHT. CONFIDENCE IS STILL BELOW AVERAGE AT THIS TIME...BUT THE BEST TIME FRAME FOR A SHOWER OR STORM AND LOCALIZED IMPACTS WOULD ROUGHLY BE BETWEEN 23Z AND 05Z FROM WEST TO EAST. LATER...AS THE FRONTAL ZONE SLIPS INTO THE AREA FROM THE NORTH...LIGHT WINDS AND LITTLE CHANGE IN LOW-LEVEL MOISTURE MAY LEAD TO SOME PATCHY FOG/STRATUS PRIOR TO 12Z. OUTLOOK...TYPICAL SUMMERTIME CONDITIONS ARE EXPECTED TO PERSIST THROUGH THE PERIOD...FEATURING DIURNAL CONVECTION EACH AFTERNOON/EVENING AND PATCHY FOG/LOW CLOUDS DURING THE PRE-DAWN MORNING HOURS. && .RAH WATCHES/WARNINGS/ADVISORIES... NONE. && $$ SYNOPSIS...WSS NEAR TERM...WSS SHORT TERM...BLS LONG TERM...MWS AVIATION...KRD/BLS

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