AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE RALEIGH NC 948 AM EST SUN DEC 21 2014 .SYNOPSIS...WEAK LOW PRESSURE WILL MOVE OFF THE SOUTHEAST COAST TONIGHT...AS HIGH PRESSURE REMAINS OVER THE AREA THROUGH SUNDAY. ANOTHER LOW PRESSURE SYSTEM WILL MOVE ALONG THE CAROLINA COAST MONDAY. && .NEAR TERM /THROUGH TONIGHT/... AS OF 325 AM SUNDAY... TODAY...A STREAM OF DRIER AIR IS MOVING INTO THE SOUTHERN PART OF THE STATE AS EVIDENT ON THIS MORNINGS WATER VAPOR IMAGERY. THAT IS THE STORY WITH THE UPPER LEVEL...BUT THE LOWER LEVELS STILL HANGING ONTO A LOT OF MOISTURE AS BROKEN MVFR CEILINGS PREVAIL OVER MUCH OF THE CWA. FORECAST SOUNDINGS SHOW THIS LOW LEVEL MOISTURE WAINING A LITTLE BIT LATE THIS MORNING INTO THE EARLY AFTERNOON BUT THE DEGREE OF CLEARING THAT WE WILL SEE...IF ANY...REMAINS TO BE SEEN. THE CLOUD DECK WILL CERTAINLY GET THINNER BUT WHETHER OR NOT WE SEE SOME BREAKS IS THE REAL QUESTION. THE UPSHOT WILL BE A HINDERANCE TO INSOLATION AND THEREFORE FAIRLY UNIFORM TEMPERATURES SHOULD PREVAIL ACROSS THE AREA TODAY. UPPER 40S TO LOW 50S IF WE SEE SOME DEGRADATION IN THE CLOUD COVER...OTHERWISE HIGH TEMPS COULD TOP OUT IN THE MID TO UPPER 40S...AND RIGHT NOW AM LEANING TOWARDS THIS SCENARIO AND MAY ADJUST TEMPERATURES DOWN FOR THE NOON UPDATE. WITH MOISTURE REMAINING SUPPRESSED ACROSS THE SOUTH...PRECIPIATION IS UNLIKELY TODAY. -ELLIS LATE THIS AFTERNOON-TONIGHT...MODEL GUIDANCE IN GOOD AGREEMENT IN ITS DEPICTION OF A SOUTHERN STREAM S/W PROJECTED TO CROSS THE LOWER MS VALLEY AND INDUCE WEAK SFC WAVE DEVELOPMENT OFF THE SC COAST BY EARLY MONDAY. WHILE THE DRY AIR SFC RIDGE WILL MAINTAIN A PRESENCE OVER CENTRAL NC...DEVELOPING SLY FLOW A FEW THOUSAND FEET ALOFT WILL INITIATE AN OVERRUNNING EVENT...LEADING TO A CLASSICAL OR HYBRID COLD AIR DAMMING EVENT. AS SLY FLOW STRENGTHENS OVERNIGHT...EXPECT RAIN TO OVERSPREAD THE REGION FROM THE SOUTH...LOCKING IN THE CAD AIR MASS. SPOTS OF LIGHT PRECIP MAY BREAK OUT PRIOR TO SUNSET ACROSS THE FAR SOUTH BUT BEST LIFT EXPECTED TO OCCUR AFTER MID-LATE EVENING IN THE SOUTH...AND AFTER MIDNIGHT ACROSS THE NORTH. PLAN TO ADJUST POPS IN THIS DIRECTION...WITH LIKELY POPS ACROSS THE FAR SOUTH BY 01Z-02Z WITH SLIGHT CHANCE ACROSS THE NORTH...BECOMING CATEGORICAL BY EARLY MONDAY ACROSS THE SOUTH AND LIKELY ACROSS THE NORTH. MODEL PRECIP AMOUNTS NOT AS ROBUST AS 24-36 HOURS AGO WITH AMOUNTS THROUGH SUNDAY NIGHT-EARLY MONDAY ABOUT A TENTH OF A INCH OR LESS. INCREASING/THICKENING CLOUDS OVERNIGHT WILL AID TO MODERATE TEMPS SO EXPECT MIN TEMPS TO OCCUR AROUND OR SHORTLY AFTER MIDNIGHT WITH STEADY TEMPS THEREAFTER. MIN TEMPS 35-40. -WSS && .SHORT TERM /MONDAY AND MONDAY NIGHT/... AS OF 325 AM SUNDAY... MONDAY...BEST LIFT ASSOCIATED WITH THE SOUTHERN STREAM S/W WILL AFFECT OUR REGION MONDAY MORNING THEN LIFT NEWD OUT OF OUR AREA MONDAY AFTERNOON. THUS...WILL ADVERTISE HIGHEST POPS IN THE MORNING WITH DECREASING POPS IN THE AFTERNOON. AGAIN MODEL CONSENSUS HAS DECREASED EXPECTED RAINFALL AMOUNTS COMPARED TO 24 HOURS AGO BUT STILL EXPECT AROUND A QUARTER OF AN INCH. THE WIDESPREAD RAIN EARLY IN THE DAY WILL AID TO LOCK IN THE CAD AIR MASS AND ASSOCIATED LOW CLOUDS. THIS WILL RESULT IN MAX TEMPS JUST 5-8 DEGREES WARMER THAN EXPECTED MIN TEMPS. MAX TEMPS NEAR 40 NW TO NEAR 50 FAR SE. MONDAY NIGHT...CAD AIR MASS EXPECTED TO PERSIST MAINTAINING EXTENSIVE CLOUDINESS WITH AREAS OF DRIZZLE OR SPOTTY LIGHT RAIN. TEMPS USUALLY DO NOT DISPLAY MUCH DIURNAL CHANGE IN THIS TYPE OF AIR MASS SO MIN TEMPS EXPECTED TO RANGE FROM THE MID 30S NW TO THE LOW- MID 40S SE. && .LONG TERM /TUESDAY THROUGH SATURDAY/... AS OF 215 AM SUNDAY... ...WARM... WET AND RATHER WINDY SYSTEM TO AFFECT OUR REGION TUESDAY NIGHT THROUGH CHRISTMAS EVE... THEN WINDY AND COOLER CHRISTMAS DAY... THERE IS HIGH CONFIDENCE OF A WARM... WET AND WINDY SYSTEM WILL AFFECT OUR REGION MID WEEK. MODELS AND ENSEMBLES AGREE IN GENERAL IN THAT A THE MAIN SURFACE STORM TRACK WILL BE FROM THE GULF OF MEXICO NORTHWARD THROUGH THE TENNESSEE AND OHIO VALLEY REGIONS TUE NIGHT INTO WEDNESDAY NIGHT. THE OPERATIONAL GFS IS SLOWER/A BIT WEAKER WITH THE MAIN SURFACE WAVE... DEPICTING A 997 MB SURFACE LOW OVER KY 18Z/WED... WHILE THE AVERAGE OF THE ENSEMBLES SUGGEST AROUND A 992 LOW OVER OR NEAR NW OHIO 12Z/WED. REGARDLESS... WITH THE STORM HEADING UP THE WEST SIDE OF THE APPALACHIANS... OUR REGION WILL HAVE TO DEAL WITH RESIDUAL COLD AIR DAMMING... A RETREATING WEDGE/WARM/COASTAL FRONT... AND THEN THE MAIN COLD FRONT. TIMING OF THESE WILL BE CRITICAL TO THE SENSIBLE WEATHER FORECASTS. THIS FAR OUT... THESE DETAILS WILL HAVE TO BE REFINED AS THE EVENT EVOLVES. AT THIS POINT WE WILL MAINTAIN CONTINUITY FROM OUR PREVIOUS FORECASTS AND BLEND IN THE LATEST ENSEMBLE MEANS TO GIVE IT OUR BEST SHOT AT EACH OF THESE FEATURES. ONE THING FOR SURE... CONFIDENCE IS 100 PERCENT IN ALL RAIN. TUESDAY AND TUESDAY NIGHT... LINGERING COLD AIR DAMMING IS EXPECTED TO BE IN PLACE OVER A GOOD PORTION OF THE PIEDMONT DAMMING REGION 12Z/TUESDAY. AN INITIAL WEAK SURFACE WAVE SHOULD BE TRACKING OFF THE DELMARVA COAST WITH A TRAILING COASTAL FRONT INTO SE GEORGIA. THIS COASTAL FRONT APPEARS THAT IT WILL HAVE A DIFFICULT TIME COMING INLAND INITIALLY GIVEN THAT THE MAIN STORM TRACK AND DYNAMICS WILL BE LIFTING NORTH (WEST OF THE MOUNTAINS) INSTEAD OF COMING EAST OR NORTHEAST ACROSS THE MOUNTAINS. THE PRESSURE GRADIENT WILL BE LACKING TUESDAY. HOWEVER... THE WAA PATTERN WILL INCREASE LATER TUESDAY INTO TUESDAY NIGHT AS THE SURFACE WAVE STRENGTHENS OVER THE TENNESSEE VALLEY AND LIFTS TOWARD OHIO BY 12Z/WED. WAA RAINS WILL BE AIDED BY WARM FRONTAL LIFT FROM THE SOUTHEAST LATE TUESDAY NIGHT INTO EARLY WEDNESDAY. SOME OF THE LATEST GUIDANCE SUGGESTS THE HEAVIEST RAINS MAY FALL OVER THE WESTERN PIEDMONT INTO THE MOUNTAINS ALONG AND NEAR THE RETREATING WARM/COASTAL FRONT. IT IS STILL DIFFICULT TO FORECAST EXACTLY WHERE THE WARM FRONT WILL BE LOCATED 12Z/WED... BUT WHEN CLIMATOLOGY IS APPLIED TO THE GIVEN STORM TRACK AND STRENGTH ALONG WITH THE LINGERING CAD (RETREATING SURFACE HIGH OF 1030 MB OFF NEW ENGLAND)... THE WARM FRONT MOST LIKELY WILL BE VERY NEAR THE SE PIEDMONT FROM CHARLOTTE TO RALEIGH EARLY IN THE DAY WED. THE FRONT SHOULD LIFT INTO VIRGINIA DURING THE AFTERNOON. THIS WILL LIKELY LEAD TO A LULL IN THE WARM FRONTAL RAINS AS THEY LIFT INTO VIRGINIA WEDNESDAY AFTERNOON. THE MAIN COLD FRONT SHOULD ARRIVE BETWEEN 00Z/06Z THURSDAY (WEDNESDAY NIGHT)... ACCOMPANIED BY ADDITIONAL SHOWERS AND POSSIBLY A FEW THUNDERSTORMS (IF THE LOW LEVELS CAN DESTABILIZE ENOUGH WHICH IS IN DOUBT - GIVEN THE TIME OF YEAR. HOWEVER... SURFACE DEW POINTS WEDNESDAY AFTERNOON IN THE WARM SECTOR SHOULD REACH 60 OR EVEN 65 SE. BREEZY TO WINDY SW FLOW AT 10-25 MPH CAN BE EXPECTED WITH TEMPS INTO THE 65-72 RANGE. THIS WOULD STILL ONLY YIELD MUCAPES OF 100 TO 200 J/KG. IN ADDITION... THE STRONGEST LOW LEVEL JET IS EXPECTED TO PUSH NORTHWARD INTO VA/MD BY EARLY WEDNESDAY AFTERNOON ALONG THE RETREATING WARM FRONT. WITH THE MAIN DYNAMICS PASSING OVER THE GREAT LAKES... THESE FACTORS WILL GREATLY LIMIT ANY SEVERE POTENTIAL WITH THIS STORM FOR CENTRAL NC. SENSIBLE WEATHER TUESDAY THROUGH WEDNESDAY... COOL AND CLOUDY TUESDAY WITH SOME LIGHT DRIZZLE. THEN A CHANCE OF RAIN AGAIN IN TEH AFTERNOON IN THE SW. HIGHS IN THE MID 40S TO MID 50S (PROBABLY NOT UNTIL TUESDAY EVENING). PERIODS OF RAIN... SOME HEAVY TUESDAY NIGHT INTO WEDNESDAY MORNING. RAIN ENDING FROM THE SOUTH BY AFTERNOON. THEN SHOWERS AND A SLIGHT CHANCE OF THUNDERSTORMS AGAIN IN THE MID TO LATE AFTERNOON (NW)... LATE AFTERNOON AND EVENING ELSEWHERE. BECOMING WINDY AND WARMER FROM THE SOUTH TUESDAY NIGHT INTO WEDNESDAY (NW ZONES LATEST TO SEE WARMING). TEMPS RISING LATE WITH READINGS MID 50S TO MID 60S BY 12Z/WED NW TO SE. HIGHS WEDNESDAY IN THE MID 60S TO LOWER 70S. SHOWERS TAPER OFF QUICKLY FROM THE WEST WEDNESDAY NIGHT. CLOUDY WITH LOWS IN THE 40S TO LOWER 50S. THURSDAY THROUGH SATURDAY... THE PRESSURE GRADIENT WILL REMAIN TIGHT THURSDAY WITH A GUSTY W-NW WIND AT 15-25 MPH. HIGHS GENERALLY IN THE 50S WITH PARTLY TO MOSTLY SUNNY SKIES. FRIDAY SHOULD BE DRY WITH ANOTHER COLD FRONT EXPECTED TO AFFECT THE REGION BY LATE FRIDAY NIGHT AND SATURDAY WITH A CHANCE OF RAIN SHOWERS. LOWS 35-40. HIGHS 55-62. && .AVIATION /12Z SUNDAY THROUGH THURSDAY/... AS OF 635 AM SUNDAY... WIDESPREAD MVFR/LOW END VFR CEILINGS WILL PERSIST THROUGH MID-LATE MORNING ACROSS MUCH OF THE PIEDMONT AND SANDHILLS. OVER THE COASTAL PLAIN...PARTIAL CLEARING MAY OCCUR. THE KRWI IS ON THE EDGE OF THE THIS CLEARING WHICH MAY LEAD TO PERIODS OF VFR/HIGH END MVFR CEILINGS. MODEL GUIDANCE SO FAR THIS MORNING HAS NOT VERIFIED WELL WITH THE CURRENT STRATOCU DECK OVER THE REGION. THIS LEADS TO LOW CONFIDENCE THAT WE WILL SEE APPRECIABLE CLEARING LATER THIS MORNING-THIS AFTERNOON. CURRENT THINKING IS THAT A BROKEN DECK OF STRATOCU WILL PERSIST INTO THE AFTERNOON WITH CEILINGS 3500-4500 FT. ANY CLEARING THAT OCCURS WILL LIKELY BE SHORT-LIVED. A DEVELOPING LOW PRESSURE SYSTEM OVER THE NORTHERN GULF WILL BEGIN TO LIFT NE ALONG THE GA-SC COAST TONIGHT. THIS WEATHER SYSTEM WILL SPREAD ADDITIONAL MOISTURE INTO CENTRAL NC LATER TODAY AND TONIGHT. THIS WILL LEAD TO A DETERIORATION OF AVIATION CONDITIONS WITH WIDESPREAD MVFR/IFR CEILINGS AND AN EXPANDING AREA OF LIGHT RAIN. THE ADVERSE AVIATION WEATHER CONDITIONS WILL PERSISTS INTO MONDAY MORNING. THE RAIN WILL DIMINISH MONDAY AFTERNOON-MONDAY NIGHT THOUGH EXTENSIVE CLOUDINESS EXPECTED TO PERSIST.WILL LIKELY SEE WIDESPREAD IFR CONDITIONS MONDAY NIGHT DUE TO LOW CLOUDS AND FOG/DRIZZLE. ANOTHER LOW PRESSURE SYSTEM WILL AFFECT CENTRAL NC LATE TUESDAY INTO WEDNESDAY...BRINGING A ROUND OF HEAVY SHOWERS AND POSSIBLY A FEW THUNDERSTORMS. IMPROVING SKY/WEATHER CONDITIONS CHRISTMAS DAY BEHIND AN EXITING COLD FRONT. SFC WINDS WILL BECOME BREEZY WEDNESDAY THROUGH CHRISTMAS DAY WITH WIND GUSTS 30-35KTS PROBABLE. && .RAH WATCHES/WARNINGS/ADVISORIES... NONE. &&
Posted on: Sun, 21 Dec 2014 15:29:33 +0000
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