Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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000 FXUS62 KRAH 181138 AFDRAH AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE RALEIGH NC 638 AM EST THU DEC 18 2014 .SYNOPSIS...HIGH PRESSURE OVER THE MISSISSIPPI RIVER VALLEY WILL EXTEND EASTWARD INTO THE MID ATLANTIC AND CAROLINAS ON THROUGH FRIDAY. A LOW PRESSURE SYSTEM WILL DEVELOP ALONG THE TEXAS COAST ON FRIDAY AND TRACK EAST ALONG THE GULF COAST ON SATURDAY...THEN MOVE OFFSHORE THE SOUTHEAST COAST SATURDAY NIGHT INTO SUNDAY. && .NEAR TERM /THROUGH TONIGHT/... AS OF 245 AM THURSDAY... BRIEF S/W RIDGING WILL BUILD ACROSS THE AREA THIS MORNING INTO THE EARLY AFTERNOON... WITH A QUICK MOVING MID LEVEL S/W APPROACHING THE AREA TODAY AND CROSSING THE REGION TONIGHT IN ITS WAKE. THIS WILL ALLOW FOR AN INCREASE IN MID AND HIGH CLOUDS TODAY. GIVEN THE LOW AMPLITUDE OF THIS DISTURBANCE AND DRY LOW LEVELS WE DO NOT EXPECT ANY PRECIP FROM THE PASSING DISTURBANCE. HOWEVER... THE CLOUDS WILL LIKELY HAVE SOME IMPACT ON HIGH TEMPS TODAY. AFTERNOON LOW LEVEL THICKNESS VALUES ARE EXPECTED TO BE AROUND 10 TO 15 METERS LOWER THAN ON WEDNESDAY. THUS... GIVEN THE EXPECTED CLOUD COVER AND LOWER THICKNESS VALUES EXPECT WE SHOULD SEE HIGH TEMPS RUN A GOOD 6 TO 9 DEGREES COOLER TODAY. THIS YIELDS HIGH TEMPS RANGING FROM AROUND 50 NORTH TO THE MID 50S SOUTH. SKIES WILL BEGIN TO CLEAR OFF BY EARLY FRIDAY MORNING WITH THE PASSAGE OF THE AFOREMENTIONED MID LEVEL TROUGH. GIVEN A RATHER WEAK MSLP GRADIENT ACROSS THE AREA WITH SURFACE HIGH PRESSURE EXTENDING INTO THE AREA FROM THE WEST... WE SHOULD SEE LIGHT AND VARIABLE TO CALM WINDS OVERNIGHT. THIS COMBINED WITH CLEAR SKIES WILL ALLOW US TO COOL QUITE NICELY TONIGHT. EXPECT LOW TEMPS WILL RANGE FROM THE UPPER 20S TO AROUND 30 (WITH MAYBE EVEN A FEW MID 20S) IN THE USUAL RURAL COLD LOCATIONS TO THE LOWER 30S ELSEWHERE. && .SHORT TERM /FRIDAY AND FRIDAY NIGHT/... AS OF 310 AM THURSDAY... FRIDAY AND FRIDAY NIGHT: ANOTHER SOUTHERN STREAM DISTURBANCE IS EXPECTED TO APPROACH THE AREA ON FRIDAY. S/W ENERGY IS EXPECTED TO LIFT NORTHEASTWARD OUT OF THE SOUTHERN PLAINS ON FRIDAY. MEANWHILE CENTRAL NC WILL EXPERIENCE BRIEF S/W RIDGING AGAIN ON FRIDAY IN BETWEEN THE AFOREMENTIONED SYSTEM TONIGHT AND THE APPROACHING SYSTEM ON FRIDAY. THIS WILL YIELD MOSTLY SUNNY SKIES... POSSIBLY BECOMING PARTLY SUNNY BY LATE IN THE DAY AS HIGH LEVEL CLOUD COVER BEGINS TO STREAM NORTH AND EASTWARD IN ADVANCE OF THE NEXT SYSTEM. AFTERNOON LOW LEVEL THICKNESS VALUES ARE EXPECTED TO BE A BIT LOWER ON FRIDAY... AROUND 5 METERS OR SO. HOWEVER... WITH MORE SUN EXPECTED ON FRIDAY THINK WE WILL SEE SIMILAR HIGH TEMPS COMPARED TO TODAY. THUS... EXPECT HIGH TO RANGE FROM 50 TO 55. AS THE MID LEVEL DISTURBANCE SHIFTS NORTHEASTWARD TOWARDS OUR REGION FROM THE LOWER MS RIVER VALLEY ON FRIDAY EVENING/EARLY SATURDAY MORNING SURFACE LOW PRESSURE WILL DEVELOP ACROSS THE NORTHERN GULF OF MEXICO AND BEGIN TRACKING EASTWARD. AS THE SYSTEM APPROACHES MOISTURE WILL STREAM NORTHWARD ACROSS CENTRAL NC... WITH SHALLOW ISENTROPIC LIFT BEGINNING TO INCREASE ACROSS THE WESTERN AND SOUTHWESTERN PORTION OF THE CWA DURING THE EARLY MORNING HOURS OF SATURDAY. AT THE ONSET OF LIGHT PRECIP SPREADING INTO NORTHWEST PIEDMONT WE COULD SEE A BRIEF PERIOD OF SOME SLEET MIXED IN WITH THE LIGHT RAIN. HOWEVER... TEMPS ARE EXPECTED TO REMAIN ABOVE FREEZING ACROSS THE WESTERN/NORTHWESTERN PIEDMONT ON SATURDAY MORNING NO IMPACTS ARE EXPECTED. IN FACT WILL KEEP ANY MENTION OF SLEET OUT OF THE FORECAST FOR NOW.... AS ANY OCCURRENCE WOULD BE BRIEF AND OF NO IMPACT. LOW TEMPS SATURDAY MORNING WILL RANGE FROM THE UPPER 30S SOUTH/SOUTHWEST TO THE LOWER 30S NORTHEAST. && .LONG TERM /SATURDAY THROUGH WEDNESDAY/... AS OF 347 AM WEDNESDAY... SATURDAY...WHILE A SFC DRY AIR RIDGE AND PARENT HIGH ARE STILL IN A FAVORABLE LOCATION TO SUPPORT A COLD AIR DAMMING EVENT SATURDAY...THE LATEST MODEL GUIDANCE HAS TAKEN THE MID LEVEL S/W ON A MORE SLY TRAJECTORY THAN PREVIOUS MODEL RUNS AND PARENT HIGH A FEW MILLIBARS WEAKER THAN PREVIOUS MODEL RUNS. THIS STILL YIELDS A HYBRID DAMMING EVENT THOUGH PRECIP AMOUNTS APPEAR TO BE LIGHTER THAN EARLIER FORECASTS. S/W HAS RECENTLY ENTERED THE UPPER AIR RAWINSONDE NETWORK SO THE 12Z MODEL RUN SHOULD GIVE AN INDICATION OF EVENTUAL STRENGTH/TRACK OF THIS SYSTEM REGARDLESS...OVERCAST SKIES AND AREAS/WIDESPREAD LIGHT RAIN WILL RESULT IN A COLD DAMP DAY. MOS GUIDANCE APPEARS TOO WARM AND AM RELUCTANT TO RAISE MAX TEMPS SATURDAY FROM CURRENT FORECAST (NEAR 40 NW TO UPPER 40S FAR SE). IF RAIN COVERAGE ENDS UP BEING SPOTTY VERSUS WIDESPREAD...THEN COULD SEE AN ADJUSTMENT IN MAX TEMPS TO VALUES COMPARABLE TO THE NAM MOS (MID-UPPER 40S, NEAR 50 SE). SATURDAY NIGHT...SUBSIDENCE BEHIND THE EXITING S/W SHOULD AID TO DIMINISH LIGHT PRECIP WITH GREATEST THREAT FOR SPOTTY LIGHT PRECIP OVER THE SANDHILLS/SOUTHERN COASTAL PLAIN (AGAIN DUE TO THE MORE SLY TRACK OF THE S/W). OTHERWISE CONTINUED CONSIDERABLE CLOUDINESS WITH PATCHY DRIZZLE AND/OR LIGHT FOG. MIN TEMPS MID-UPPER 30S. SUNDAY THROUGH WEDNESDAY...A MAJOR STORM MAY AFFECT THE SE U.S. LATE TUESDAY INTO WEDNESDAY (INCLUDING CENTRAL NC) WITH POTENTIAL IMPACT ON TRAVEL DUE TO HEAVY RAIN AND STRONG GUSTY WINDS. MODEL GUIDANCE FLIP-FLOPPED A BIT FOR SUNDAY INTO MONDAY WITH GUIDANCE NOW INDICATING A NARROW DRY AIR SFC RIDGE ACROSS THE REGION SUNDAY WITH ANOTHER S/W IN THE SOUTHERN STREAM INITIATING ANOTHER AREA OF RAIN LATE SUNDAY INTO MONDAY. THIS SCENARIO HAS ALSO BEEN PICKED-UP BY THE LATEST ECMWF. PARTIAL THICKNESSES SUPPORT ALL LIQUID ACROSS THE PIEDMONT AT THIS TIME. DUE TO THE SHIFT...PLAN TO CONFINE POPS TO JUST CHANCE AT THIS TIME LATE SUNDAY INTO MONDAY. IF LATER MODEL RUNS MAINTAIN SOME CONSISTENCY...LIKELY POPS WARRANTED FOR OVERNIGHT SUNDAY INTO MONDAY MORNING. WILL CONTINUE BELOW NORMAL HIGH TEMPS SUNDAY INTO MONDAY...WITH MAX TEMPS MONDAY AS MUCH AS 7-8 DEGREES BELOW NORMAL IF RAIN MATERIALIZES. TUESDAY INTO WEDNESDAY...AMPLIFYING L/W TROUGH IN THE NORTHERN STREAM WILL TAP GULF MOISTURE AND STREAM IT NORTHWARD INTO THE CAROLINAS TUESDAY INTO TUESDAY NIGHT. MODEL GUIDANCE INDICATE A STRONG JET ROUNDING BASE OF TROUGH LATE TUESDAY NIGHT INTO WEDNESDAY MORNING CAUSING THE TROUGH TO BECOME NEGATIVELY TILTED ACROSS THE SE U.S. IF THIS HOLDS TOGETHER...COULD SEE A BAND OF HEAVY SHOWERS WITH A FEW STORMS CROSS CENTRAL NC OVERNIGHT TUESDAY NIGHT INTO EARLY WEDNESDAY. THE PARENT LOW DEEPENS SIGNIFICANTLY WEDNESDAY AND WEDNESDAY NIGHT WITH THE POTENTIAL FOR STRONG GUSTY WINDS ACROSS CENTRAL NC. A BRIEF BUMP UP IN TEMPS TUESDAY AHEAD OF THE STORM SYSTEM TUESDAY FOLLOWED BY ANOTHER ROUND OF BELOW NORMAL MAX TEMPS THOUGH TRULY FRIGID AIR NOT SEEN IN OUR REGION THROUGH CHRISTMAS. && .AVIATION /12Z THURSDAY THROUGH MONDAY/... AS OF 635 AM THURSDAY... 24-HOUR TAF PERIOD: HIGH CONFIDENCE THAT VFR CONDITIONS AND LIGHT AND VARIABLE WINDS WILL DOMINATE THE 24 HOUR TAF PERIOD AS HIGH PRESSURE EXTENDS INTO THE AREA FROM THE WEST. SCATTERED TO BROKEN MID AND HIGH CLOUDS WILL CONTINUE TO TRAVERSE THE AREA AS A MID LEVEL DISTURBANCE APPROACHES THE REGION FROM THE WEST AND MOVES ACROSS THE AREA TONIGHT. SKIES ARE EXPECTED TO CLEAR TONIGHT... GENERALLY IN THE EARLY MORNING HOURS OF FRIDAY. LOOKING AHEAD: VFR CONDITIONS ARE EXPECTED TO CONTINUE INTO SATURDAY MORNING. AVIATION CONDITIONS ARE EXPECTED TO DETERIORATE ON SATURDAY MID TO LATE MORNING INTO THE AFTERNOON AS A STORM SYSTEM IS EXPECTED TO FORM OVER THE TEXAS GULF COAST LATE FRIDAY...WITH LOW PRESSURE TRACKING EAST ACROSS THE SOUTHERN GULF STATES SATURDAY...TO ALONG OR JUST OFF THE SOUTHEAST COAST SAT NIGHT AND SUN. AREAS OF RAIN WITH SUB-VFR CONDITIONS APPEAR LIKELY FROM SATURDAY MID SATURDAY MORNING THROUGH SATURDAY NIGHT. VFR CONDITIONS ARE EXPECTED TO BRIEFLY RETURN FOR SUNDAY... BEFORE ANOTHER DISTURBANCE LIFTS NORTHEASTWARD OUT OF THE GULF... SPREADING RAIN INTO CENTRAL NC SUNDAY NIGHT INTO MONDAY... WITH SUB-VFR CONDITIONS. && .RAH WATCHES/WARNINGS/ADVISORIES... NONE. && $$ SYNOPSIS...BSD/VINCENT NEAR TERM...BSD SHORT TERM...BSD LONG TERM...WSS AVIATION...BSD/KC

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