000 FXUS62 KRAH 050807 AFDRAH AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE RALEIGH NC 307 AM EST SUN FEB 5 2012 .SYNOPSIS... AN UPPER LEVEL LOW PRESSURE SYSTEM OVER THE MID MISSISSIPPI VALLEY WILL DRIFT SLOWLY EAST TODAY THROUGH MONDAY...CROSSING THE CAROLINAS AND SOUTHERN VIRGINIA MONDAY NIGHT. THIS WEATHER SYSTEM WILL CAUSE UNSETTLED WEATHER CONDITIONS ACROSS OUR REGION DURING THIS PERIOD. && .NEAR TERM /THROUGH TONIGHT/... AS OF 305 AM SUNDAY... COMPLEX WEATHER PATTERN THROUGH TONIGHT. MINOR S/W ALOFT CROSSING WESTERN NC AT 2 AM AND SHOULD CONTINUE TO TRAVERSE EAST THROUGH THE EARLY MORNING HOURS. MEANWHILE SURFACE FRONT DRAPED WEST-TO-EAST ACROSS THE NORTHERN PIEDMONT-NORTHERN COASTAL PLAIN WILL CONTINUE TO DRIFT SOUTH AND SHOULD LIE SOUTH OF HIGHWAY 64 BY 7 AM. THE COMBINATION OF THE EASTWARD MOVING MID LEVEL S/W AND THE SURFACE FRONT WILL CAUSE WIDESPREAD RAIN ACROSS MUCH OF CENTRAL NC THROUGH THE REMAINDER OF THE OVERNIGHT...THEN THE FOCUS WILL SHIFT SOUTH INTO THE SANDHILLS AND COASTAL PLAIN LATER THIS MORNING. SINCE APPEARS BACKEDGE OF RAIN WILL BE IN THE VICINITY OF THE TRIAD BY DAYBREAK...WILL START POPS THERE IN THE CHANCE CATEGORY WITH POPS QUICKLY RAMPING UP INTO THE CATEGORICAL RANGE FARTHER EAST AND SOUTH. BY MIDDAY...EXPECT MAINLY SLIGHT CHANCE FOR MEASURABLE RAIN ACROSS THE NW WITH CHANCE POPS IN THE SE. LOW LEVEL NNE FLOW BEHIND THE SURFACE BOUNDARY WILL ADVECT COOLER AIR INTO THE REGION. WITH OVERCAST SKIES...COOL NLY FLOW AND SPOTTY LIGHT RAIN OR DRIZZLE EXPECTED LATER TODAY...TEMPS WILL STRUGGLE TO RECOVER WITH A DIURNAL TEMP VARIANCE OF NO MORE THAN 4-6 DEGREES EXPECTED. FAVORED THE COOLER NAM MOS GUIDANCE FOR MAX TEMPS WHICH HAS BEEN CONSISTENT THE PAST FEW MODEL RUNS. MAX TEMPS MID 40S NORTH TO MID/UPPER 50S (EARLY) FAR SOUTH. TONIGHT...SURFACE RIDGE WILL NOSE SOUTHWARD INTO OUR REGION BRINGING CHILLY AIR INTO THE REGION. WEAK LOW LEVEL FLOW COUPLED WITH PLENTIFUL MOISTURE IN THE LOWEST 6000FT OF THE ATMOSPHERE WILL SUPPORT AREAS OF FOG AND LOW CLOUDS. MAY SEE PATCHY LIGHT RAIN AND/OR DRIZZLE...ESPECIALLY OVER THE FAR SOUTH AND WEST WHERE WEAK ISENTROPIC UPGLIDE IS FAVORED. MIN TEMPS MID 30S NORTH TO NEAR 40 FAR SOUTH && .SHORT TERM /MONDAY THROUGH TUESDAY NIGHT/... AS OF 305 AM SUNDAY... MONDAY AND MONDAY NIGHT...DEEP UPPER LOW OVER THE LOWER MO VALLEY WILL DRIFT EAST TODAY..THEN OPEN UP AND MOVE A LITTLE QUICKER EASTWARD MONDAY AND MONDAY NIGHT AS IT ENCOUNTERS CONFLUENT FLOW. THIS FEATURE WILL BEGIN TO ENHANCE SLY FLOW OVER THE COOL STABLE AIR MASS ENTRENCHED AT THE SURFACE AFTER DAYBREAK MONDAY...MORE MONDAY AFTERNOON-MONDAY EVENING IN THE SOUTH AND EAST. THUS EXPECT A CONTINUATION OF THE UNSETTLED WEATHER PATTERN WITH CONSIDERABLE CLOUDINESS EXPECTED MONDAY ALONG WITH PATCHES OF LIGHT RAIN OR DRIZZLE IN THE MORNING..MAINLY OVER THE SOUTHWEST HALF. AS WEAKENING UPPER LEVEL LOW APPROACHES MONDAY AFTERNOON...EXPECT A FEW SHOWERS TO BECOME MORE PROBABLE ALONG AND EAST OF HIGHWAY 1 WITH HIGHEST THREAT OF RAIN OVER THE SOUTHERN COASTAL PLAIN AND EASTERN SANDHILLS (THIS REGION WILL BE IN CLOSEST PROXIMITY TO DEEPER MOISTURE). WILL CAP POPS AT 30-33 PERCENT IN THE SE MONDAY AFTERNOON-EVENING AT THIS TIME. MAX TEMPS DEPENDENT IN EXTENT OF PRECIP AND WHETHER ANY SIGNIFICANT BREAKS OCCUR IN THE OVERCAST. WENT WITH MAX TEMPS CLOSE TO MOS GUIDANCE THOUGH IF SKIES REMAIN OVERCAST AND AREAS OF RAIN A BIT MORE EXTENSIVE...POTENTIAL FOR MAX TEMPS TO BE 5-8 DEGREES COOLER...ESPECIALLY NW HALF. ONCE MID/UPPER LEVEL FEATURE SWINGS THROUGH LATE MONDAY NIGHT...WNW FLOW IN ITS WAKE WILL ADVECT DRIER AIR INTO OUR REGION. THIS CHANGE IN AIR MASS SHOULD AID TO DISSIPATE/DIMINISH CLOUD COVERAGE LATE MONDAY NIGHT. MIN TEMPS MID 30S NW TO LOWER 40S SE. TUESDAY AND TUESDAY NIGHT: WEAK HIGH PRESSURE WILL MOVE ACROSS THE REGION ALONG WITH WEAK S/W RIDGING ALOFT ON TUESDAY. THIS WILL RESULT IN PLEASANT WEATHER FOR TUESDAY... WITH MOSTLY SUNNY SKIES AND HIGH TEMPS REACHING TO AROUND 60 DEGREES/LOWER 60S AS AFTERNOON LOW LEVEL THICKNESS VALUES ARE EXPECTED TO TOP OUT IN THE 1330S TO 1340S. CLOUD COVER IS EXPECTED TO INCREASE ON TUESDAY NIGHT/WEDNESDAY MORNING IN ADVANCE OF THE NEXT S/W ENERGY ALOFT... WHICH IS EXPECTED TO CROSS THE REGION ON WEDNESDAY. DEPENDING ON THE AMOUNT OF CLOUD COVER AND HOW FAST THE CLOUD COVER MOVES INTO THE AREA ON TUESDAY... WILL PLAY A KEY ROLE ON OVERNIGHT LOWS. GIVEN THE EXPECTED INCREASE IN CLOUD IN A GENERALLY SOUTHWEST/WEST TO NORTHEAST/EAST FASHION OVERNIGHT... WILL FORECAST LOW TEMPS RANGING FROM THE LOWER TO MID 30S NORTHEAST TO UPPER 30S WEST/SOUTHWEST. -BSD && .LONG TERM /WEDNESDAY THROUGH SATURDAY/... AS OF 305 AM SUNDAY... MEDIUM RANGE MODELS CONTINUE TO STRUGGLE WITH THE AMPLIFICATION OF THE UPPER FLOW PATTERN ACROSS THE EASTERN HALF OF THE COUNTRY MID-LATE NEXT WEEK INTO THE WEEKEND... AND IF A CUT OFF LOW NEAR THE BAJA WILL TRANSLATE EASTWARD AND BE ABSORBED BY THE DEEP CYCLONIC FLOW OVER THE EASTERN HALF TO TWO-THIRDS OF THE COUNTRY LATE NEXT WEEK (POSSIBLY SENDING UNSETTLED WEATHER IN OUR DIRECTION FOR LATE NEXT WEEK INTO THE WEEKEND). WHAT THIS MEANS FOR CENTRAL NORTH CAROLINA IS GENERALLY DRY CONDITIONS FOR THE REGION WEDNESDAY THROUGH FRIDAY (WITH A FEW MOISTURE STARVED S/W`S ALOFT MOVING THROUGH THE AREA)... WITH A SLIGHT CHANCE OF LIGHT RAIN FOR SOME OF OUR FAR EASTERN COUNTIES LATE THURSDAY INTO FRIDAY. HOWEVER... MODELS CONTINUE TO STRUGGLE WITH HOW FAR OFFSHORE A POSSIBLE SURFACE LOW WILL TRACK/DEVELOP AND THUS HOW FAR INLAND PRECIP WILL REACH. GIVEN THE FORECAST IS DRY NOW... AND THE CONTINUED POOR RUN TO RUN CONTINUITY OF THE MEDIUM RANGE MODELS... WILL KEEP THE FORECAST DRY FOR THE WEDNESDAY THROUGH FRIDAY TIME FRAME. CRITICAL THICKNESS VALUES... IF WE WERE TO SEE ANY PRECIP... INDICATE THIS WOULD BE AN ALL RAIN EVENT FOR LATE THURSDAY INTO FRIDAY MORNING. AS THE POLAR VORTEX AMPLIFIES LATE NEXT WEEK ACROSS THE EASTERN HALF/TWO THIRDS OF THE COUNTRY EXPECT AN ARCTIC COLD FRONT WILL MOVE THROUGH THE AREA FRIDAY NIGHT INTO SATURDAY. MODELS STILL DIFFER IN IF ANY PRECIP WILL ACCOMPANY THE AMPLIFICATION OF THE TROUGH AND COLD FRONT. THE GFS IS CURRENTLY DEEPER WITH ITS TROUGH AND ABSORBS THE BAJA LOW HELPING TO PULL MOISTURE NORTH/NORTHEASTWARD AND PRODUCE SHOWERS ACROSS THE AREA FOR FRIDAY NIGHT INTO SATURDAY. HOWEVER... THE ECMWF IS NOT AS DEEP WITH ITS TROUGH AND DOES NOT FULLY ABSORB THE LOW AND THUS... HAS DRY CONDITIONS ACCOMPANYING THE COLD FRONTAL PASSAGE. HPC CONTINUES TO PREFER A BLEND OF THE 00Z ECMWF AND ITS OWN ENSEMBLE MEAN. THUS... WILL MAINTAIN A DRY FORECAST. EXPECT TEMPS DURING THE WEDNESDAY THROUGH FRIDAY TIME FRAME TO CONTINUE TO BE NEAR TO SLIGHTLY ABOVE NORMAL FOR THIS TIME OF YEAR... WITH THE TRUE COLD AIR REMAINING ACROSS THE NORTHERN PLAINS/UPPER MIDWEST/GREAT LAKES REGIONS. TEMPS ARE EXPECTED TO FALL BACK TO NEAR OR SLIGHTLY BELOW NORMAL VALUES FOR SATURDAY BEHIND THE ARCTIC FRONT. HOWEVER... IT APPEARS THIS WILL ONLY BE A GLANCING BLOW AS MODELS INDICATE LOW LEVEL THICKNESS VALUES BOUNCING BACK QUICKLY LATE NEXT WEEKEND INTO THE NEXT WEEK... ALTHOUGH A LOT COULD CHANGE THAT FAR OUT. && .AVIATION /06Z SUNDAY THROUGH THURSDAY/... AS OF 1234 AM SUNDAY... WIDESPREAD IFR/LIFR WILL OCCUR OVERNIGHT INTO THE FIRST HALF OF SUNDAY AS AN AREA OF LOW PRESSURE DRIFTS ESE FROM WESTERN NC INTO UPSTATE SC. THIS FEATURE WILL DROP A COLD FRONT SOUTHWARD ACROSS CENTRAL NC OVERNIGHT THROUGH EARLY SUNDAY. WIDESPREAD RAIN WILL PERSIST ACROSS THE REGION UNTIL 4 AM...THEN GRADUALLY TAPER OFF WEST-TO-EAST THROUGH 10 AM. SUNDAY AFTERNOON SHOULD SEE CEILINGS GRADUALLY LIFT INTO THE LOW END OF MVFR. EXPECT A STEADY NNE SURFACE FLOW BETWEEN 7-12 KTS. LATEST MODEL GUIDANCE SUGGEST THAT PLENTIFUL LOW LEVEL MOISTURE SHOULD SUPPORT THE EXISTENCE OF LOW CLOUDS AND FOG SUNDAY NIGHT INTO EARLY MONDAY...SUGGESTING A POTENTIAL FOR WIDESPREAD IFR/LIFR CONDITIONS. EXPECT CEILINGS TO LIFT INTO THE HIGH END OF MVFR OR LOW END VFR...ESPECIALLY IN THE WEST. THE APPROACH AND PASSAGE OF A LOW PRESSURE SYSTEM OVER OUR REGION LATE MONDAY AND MONDAY NIGHT MAY CAUSE AREAS OF SHOWERS TO OCCUR...CAUSING PERIODS OF MVFR VISIBILITY. IMPROVING WEATHER CONDITIONS TUESDAY WITH VFR CONDITIONS HIGHLY PROBABLE. THE PASSAGE OF YET ANOTHER LOW PRESSURE SYSTEM MAY CAUSE A PERIOD OF SUB VFR CONDITIONS WEDNESDAY AND WEDNESDAY NIGHT. A RETURN TO VFR CONDITIONS EXPECTED ON THURSDAY. && .RAH WATCHES/WARNINGS/ADVISORIES... NONE. && $$ SYNOPSIS...WSS NEAR TERM...WSS SHORT TERM...WSS/BSD LONG TERM...BSD AVIATION...WSS
NWS RAH Office Area Forecast Discussion