AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE RALEIGH NC 749 AM EDT SUN MAR 16 2014 .SYNOPSIS... A WEAK COLD FRONT WILL SETTLE SOUTH THROUGH THE CAROLINAS TONIGHT. MEANWHILE...AN AREA OF LOW PRESSURE WILL DEVELOP OVER THE SOUTHERN PLAINS AND THEN TRACK EASTWARD ALONG THE NORTHERN GULF COAST STATES AND COASTAL CAROLINAS SUNDAY AND SUNDAY NIGHT. && .NEAR TERM /TODAY/... AS OF 300 AM SUNDAY... TODAY: SURFACE OBSERVATIONS AND REGIONAL VWP WINDS INDICATE THE COLD FRONT STRETCHED AT 07Z ALONG A NC OUTER BANKS-GOLDSBORO-STATESVILLE- ASHEVILLE ARC. NEAR TERM NWP GUIDANCE SUGGESTS THE BOUNDARY WILL DRIFT SOUTH OF THE BORDER...TO THE SAVANNAH BASIN...THROUGH MIDDAY. MEANWHILE...AN AREA OF LOW PRESSURE OVER THE CENTRAL PLAINS WILL TRACK EASTWARD ALONG THE NORTHERN GULF COAST STATES TODAY...WITH A PRECEDING STRENGTHENING LOW-MID LEVEL WAA REGIME SUPPORTING THE DEVELOPMENT AND NORTHEASTWARD EXPANSION OF RAIN ACROSS CENTRAL NC...THOUGH A FEW HOURS LATER THAN EARLIER FORECAST BASED ON RECENT RADAR AND NWP GUIDANCE TRENDS. AFTER INITIALLY FALLING IN THE FORM OF VIRGA FROM MIXED PHASE MID LEVEL CLOUDS...THE RAIN SHOULD SUBSEQUENTLY BEGIN TO REACH THE GROUND FROM SOUTHWEST TO NORTHEAST OVER THE SOUTHERN/WESTERN PIEDMONT AND SANDHILLS DURING THE MIDDAY HOURS...THEN NORTHWARD ACROSS THE REMAINDER OF THE PIEDMONT AND COASTAL PLAIN THIS AFTERNOON. DESPITE 10-15 MPH OF NE TO ENE SURFACE FLOW...THE SLOWER ARRIVAL OF PRECIPITATION AND DEEPER LAYER CLOUD COVER SUGGESTS TEMPERATURES WILL BE ABLE TO WARM INTO THE 49 TO 57 DEGREE RANGE PRIOR TO THE DEEPER OVERCAST AND RAIN. THE RAIN WILL BECOME MODERATE IN INTENSITY WITH THE ARRIVAL OF THE H85 WARM FRONT THIS AFTERNOON INTO THIS EVENING. && .SHORT TERM /TONIGHT THROUGH TUESDAY/... AS OF 320 AM SUNDAY... ...WINTER WEATHER ADVISORY FOR MAINLY MINOR ACCUMULATIONS OF FREEZING RAIN WILL BE ISSUED FOR MIDNIGHT TO NOON MONDAY FOR LOCATIONS NEAR AND NORTH OF INTERSTATE 85... DIFFICULT FORECAST DURING THIS PERIOD AS THERE CONTINUES TO BE SOME SIGNIFICANT DIFFERENCES IN THE NWP GUIDANCE...ESPECIALLY FOR THE MONDAY INTO TUESDAY TIME FRAME. THE END RESULT IS A COMPLEX AND BUSY FORECAST WITH DIFFERING IMPACTS...MOST OF WHICH WILL BE MINOR TO MODERATE. WIDESPREAD RAIN WILL BE ONGOING THIS EVENING AT THE START OF THE SHORT TERM PERIOD AS A SURGE IN LOW LEVEL WARM ADVECTION PRECIPITATION ENHANCED BY THE RIGHT ENTRANCE REGION OF A 125KT UPPER LEVEL JET ACROSS THE MID ATLANTIC. AT THE SAME TIME A BACK DOOR COLD FRONT WILL PUSH SOUTH INTO CENTRAL NC WITH A PUSH OF CONSIDERABLY COLDER AND DRIER AIR AT THE SURFACE. PRECIPITATION COVERAGE AND INTENSITY WILL WANE CONSIDERABLY LATE IN THE EVENING AND OVERNIGHT AS THE BEST FORCING LIFTS NORTHEAST OF THE AREA AND AS THE MID/UPPER LEVELS DRY OUT. LIGHT QPF AMOUNTS ON THE ORDER OF .10 INCHES WEST TO .15 INCHES EAST ARE EXPECTED AFTER MIDNIGHT. GUIDANCE DIFFERS WITH THE STRENGTH OF THE SURFACE BASED COLD AIR OVER CENTRAL NC. THE NAM IS CONSIDERABLY COLDER...LIKELY AS A RESULT OF THE SLIGHTLY STRONGER AND FURTHER SOUTH PLACEMENT OF THE MODERATELY STRONG SURFACE HIGH WHICH PROVIDES A CLOSER COLD AIR SOURCE REGION AND WHICH DEVELOPS A SLIGHTLY STRONGER PRESSURE GRADIENT TO PUSH THE COLD/DRY AIR FURTHER SOUTH. USED A BLEND OF GFS/ECMWF GUIDANCE TO PRODUCE SURFACE TEMPERATURES WHICH FALL TO FREEZING AT AROUND 3 TO 4 AM NEAR THE VA BORDER. THE NAM GIVES A SFC TEMP OF 26 AT KGSO AT 8AM WHILE THE GFS GIVES A COLD BUT MORE REASONABLE 29. THE 32 DEGREE SFC TEMP LINE REACHES AS FAR SOUTH AS LOUISBURG....DURHAM AND HIGH POINT MONDAY MORNING WITH SUBFREEZING TEMPS FURTHER NORTH. MOST OF THE PRECIPITATION SHOULD FALL AS FREEZING RAIN OR FREEZING DRIZZLE WITH A BRIEF PERIOD OF SLEET POSSIBLE WHEN MOISTURE IS STILL SUFFICIENTLY DEEP ENOUGH FOR ICE ALOFT. WITH THIS IN MIND...WILL ISSUE A WINTER WEATHER ADVISORY FROM MIDNIGHT THROUGH NOON MONDAY FOR OUR NORTHERN TIER OF COUNTIES...MAINLY NORTH OF INTERSTATE 95. SURFACE TEMPERATURES RECOVER A BIT ON MONDAY AS PRECIP EBBS AND THE SURGE OF COLD/DRY AIR SUBSIDES. IN ADDITION...IT IS DIFFICULT TO GET MEANINGFUL ICE ACCRUAL WITH FREEZING RAIN DURING THE DAYTIME HOURS IN MID MARCH AT OUR LATITUDE. SO EXPECT MOST OF THE FREEZING RAIN AND DRIZZLE TO FALL BETWEEN 4AM AND 9AM WITH ACCUMULATIONS GENERALLY CONFINED TO ELEVATED SURFACES SUCH AS TREE TOPS IN THE COLDER AIR ALOFT AND REMOVED FROM THE GROUND WHICH SHOULD BE RADIATING SOME HEAT. LOWS MONDAY MORNING WILL RANGE FROM NEAR 30 AT THE VA BORDER TO THE UPPER 30S TOWARD THE SC BORDER. EXPECT PRECIPITATION TO BE RATHER LIGHT AND INTERMITTENT LATE MONDAY AND MONDAY AFTERNOON AS DRYING ALOFT MOVES IN AND CENTRAL NC IS IN A REGION OF WEAK RIDGING BETWEEN SYSTEMS. SENSIBLE WEATHER IS BEST CHARACTERIZED AS CLOUDY SKIES WITH PERIODS OF LIGHT RAIN OR DRIZZLE WITH POPS IN THE 30-40 PERCENT RANGE. TEMPERATURES SHOULD RECOVER SLIGHTLY WITH THE ABSENCE OF WIDESPREAD RAIN AND SOME INSOLATION THROUGH THE CLOUD COVER. HIGHS WILL RANGE IN THE 34 NEAR THE VA BORDER TO THE LOWER 40S NEAR THE SC BORDER. ANOTHER SURGE OF COLD AIR IS EXPECTED ON MONDAY NIGHT WITH SURFACE TEMPERATURES GETTING EVEN COLDER THAN MONDAY MORNING. BOTH THE GFS/ECMWF DRIVE THE WET BULB FREEZING LINE EVEN FURTHER SOUTH ACROSS THE WESTERN PIEDMONT WITH THE ORIENTATION OF THE WBZ LINE SHIFTING FROM WEST-EAST ON MONDAY MORNING TO MORE SOUTHWEST-NORTHEAST BY TUESDAY MORNING. THE NAM REMAINS AN OUTLIER DURING THIS PERIOD AS IT APPEARS TO GO BONKERS BY DEVELOPING AN INTENSE SURFACE LOW NEAR SAVANNAH AND DRIVES THE LOW NORTHEAST ALONG THE CAROLINA COAST. THERE IS ANOTHER PERIOD OF FREEZING RAIN AND EVEN SOME SLEET POSSIBLE MONDAY NIGHT WITH THE ULTIMATE IMPACT DRIVEN NOT ONLY BY THE MOUNT OF COLD AIR BUT MORE IMPORTANTLY BY THE QPF. GUIDANCE DIFFERS WITH THE AMOUNT AND TIMING OF PRECIPITATION DURING THE PERIOD BUT THERE WILL LIKELY BE AROUND 0.10 TO POSSIBLY 0.20 INCHES OF LIQUID EQUIVALENT THAT FALLS ACROSS THE COLDER AND POTENTIALLY WINTRY WEATHER AREA. LOWS TUESDAY MORNING SHOULD RANGE FROM NEAR 27 ACROSS THE FAR NORTHERN PARTS OF THE TRIAD TO MID 30S ACROSS THE SOUTHEAST. CONTINUED CLOUDY AND UNSETTLED ON TUESDAY AS BOTH THE GFS/ECMWF PUSH A SURFACE WAVE AWAY FROM THE MID ATLANTIC WHILE THE NAM APPEARS LOST BY DRIVING AN INTENSIFYING SURFACE WAVE INTO THE CHESAPEAKE BAY. TEMPERATURES SHOULD RECOVER A BIT AND CLIMB ABOVE FREEZING EVERYWHERE BY MID MORNING BEFORE HIGHS EVENTUALLY REACH THE 40-45 DEGREE RANGE. THE GREATEST CHANCE OF PRECIPITATION WILL OCCUR ACROSS THE SOUTHEAST AHEAD OF THE SOUTHERN STREAM SHORT WAVE AND CLOSER TO THE SURFACE WAVE. THREE-DAY QPF VALUES RANGE FROM AROUND AN INCH NEAR THE VA BORDER TO 1.5 INCHES NEAR THE SC BORDER ALTHOUGH SOME GUIDANCE...ESPECIALLY THE NAM/SREF ARE CONSIDERABLY HIGHER. MUCH OF THAT PRECIPITATION ARRIVES SUNDAY AFTERNOON AND EVENING WITH GENERALLY LIGHTER AMOUNTS EXPECTED FOR MONDAY AND TUESDAY. THESE AMOUNTS ARE LIKELY INSUFFICIENT FOR A FLASH FLOOD OR AERIAL FLOOD WATCH. SEE THE HYDROLOGY SECTION BELOW FOR MORE DETAILS. -BLAES && .LONG TERM /TUESDAY NIGHT THROUGH SATURDAY/... AS OF 300 AM SUNDAY... A LOT OF UNCERTAINTY STILL EXISTS IN THE LONG TERM. A SERIES OF SHORTWAVES ARE EXPECTED TO MOVE THROUGH THE AREA AND THE GFS AND ECMWF HANDLE THEM DIFFERENTLY WITH RESPECT TO TIMING...AMPLITUDE... AND PRECIPITATION. IN GENERAL...THE ECMWF IS SLOWER...WETTER...AND COOLER THAN THE GFS. ALTHOUGH THERE IS A DESCENT CHANCE THAT PRECIPITATION WILL LINGER THROUGH THE DAY WEDNESDAY...IT SHOULD BE ALL LIQUID AND FAIRLY LIGHT. GIVEN THE MODEL DISCREPANCIES AND RESULTANT UNCERTAINTY...WILL MAINTAIN A MAINLY DRY FORECAST WEDNESDAY NIGHT THROUGH SUNDAY...WITH THE EXCEPTION OF A SLIGHT CHANCE FOR RAIN WITH THE FROPA ON SATURDAY. IN THE LOW LEVELS...THE COLD AIR WEDGE...PRESENT IN BOTH MODELS OVER THE NORTHWEST...SHOULD WEAKEN AS A FRONTAL BOUNDARY APPROACHES FROM THE WEST THURSDAY. A WEAK SURFACE HIGH WILL MOVE THROUGH THE AREA BEHIND THE FRONT ON FRIDAY...AHEAD OF THE NEXT FRONTAL SYSTEM TO THE WEST. BOTH MODELS INDICATE THE COLD FRONT WITH THIS SYSTEM WILL PROGRESS THROUGH CENTRAL NC SATURDAY EVE/NIGHT...ALTHOUGH THE SPEED AND ORIENTATION DIFFER BETWEEN THE MODELS. HIGH PRESSURE IS AGAIN EXPECTED TO BUILD IN BEHIND THE FRONT. HIGH TEMPERATURES WILL GENERALLY INCREASE THROUGH SATURDAY...LOWEST IN THE NORTHWEST AND HIGHEST IN THE SOUTHEAST. && .AVIATION /12Z SUNDAY THROUGH THURSDAY/... AS OF 745 AM SUNDAY... VFR CONDITIONS WILL CONTINUE THIS MORNING...AS CONTINENTAL POLAR HIGH PRESSURE RIDGES SOUTHWARD FROM SOUTHERN CANADA. WARM AND MOIST AIR FROM THE SOUTH WILL ASCEND THE HIGH PRESSURE AND ASSOCIATED NORTHEASTERLY FLOW AT THE SURFACE AND RESULT IN THE DEVELOPMENT/ NORTHEASTWARD EXPANSION OF RAIN AND MVFR-IFR CONDITIONS BETWEEN 15- 21Z TODAY. ENE TO NE SURFACE WINDS WILL GRADUALLY INCREASE INTO THE 10-15 KT RANGE...AND BECOME GUSTY TO AROUND 20 KTS THIS AFTERNOON AND TONIGHT...AS THE PRESSURE GRADIENT TIGHTENS BETWEEN THE SURFACE HIGH AND LOW PRESSURE TRACKING ALONG THE COAST OF THE CAROLINAS. MARGINAL LOW LEVEL WIND SHEAR CONDITIONS WILL ALSO BE POSSIBLE FOR A BRIEF TIME AT KFAY THIS EVENING...WHERE WINDS AT 2000 FT MAY BRIEFLY BECOME SOUTHEASTERLY AT 35 KTS (ATOP NORTHEASTERLY SURFACE FLOW). PERIODS OF RAIN AND DRIZZLE - AND CONTINUED MVFR-IFR CONDITIONS - WILL TRANSITION TO FREEZING RAIN AND FREEZING DRIZZLE BETWEEN 06Z- 09Z AT TRIAD TERMINALS...AND THIS CHANGEOVER WILL NEAR KRDU BY 12Z MON...WITH CONTINUED LIQUID ELSEWHERE. THESE POOR AVIATION CONDITIONS WILL THEN LIKELY CONTINUE THROUGH EARLY WED...AS ANOTHER AREA OF LOW PRESSURE LIFTS UP THE SOUTHEAST COAST AND MAINTAINS THE COLD AIR DAMMING REGIME OVER CENTRAL NC. && .HYDROLOGY... AS OF 420 AM SUNDAY... THREE-DAY QPF VALUES WILL RANGE FROM AROUND AN INCH NEAR THE VA BORDER TO 1.5 INCHES NEAR THE SC BORDER ALTHOUGH SOME GUIDANCE SUGGESTS THAT AMOUNTS COULD BE CONSIDERABLY HIGHER. MUCH OF THE PRECIPITATION WILL ARRIVE TODAY AND TONIGHT WITH GENERALLY LIGHTER AMOUNTS EXPECTED FOR MONDAY AND TUESDAY. FLASH FLOOD GUIDANCE FOR A SIX HOUR PERIOD RANGES FROM 2.8 TO 4.1 INCHES WITH THE HIGHER VALUES ACROSS THE SOUTHEASTERN PART OF THE HSA WHERE THE HEAVIER RAIN IS EXPECTED. PROJECTED RAINFALL APPEARS INSUFFICIENT FOR A FLASH FLOOD WATCH WITH THE POTENTIAL FOR AERIAL FLOODING ALSO LIMITED. BASED ON THE QPF NOTED ABOVE...SIGNIFICANT RISES ARE EXPECTED ON THE MAIN STEM RIVERS. IT APPEARS THAT THE GREATEST POTENTIAL FOR MINOR FLOODING WILL BE ALONG WITH NEUSE RIVER...ESPECIALLY AT SMITHFIELD AND POSSIBLY CLAYTON. SIGNIFICANT RISES ARE POSSIBLE ON THE TAR RIVER BUT THE POTENTIAL FOR FLOODING IS MUCH LESS. -BLAES && .CLIMATE... THE RECORD LOW MAXIMUM TEMPERATURES FOR MARCH 17 ARE... KGSO...38 DEGREES FROM 2005. KRDU...32 DEGREES FROM 1892. KFAY...39 DEGREES FROM 2005. && .RAH WATCHES/WARNINGS/ADVISORIES... WINTER WEATHER ADVISORY FROM MIDNIGHT TONIGHT TO NOON EDT MONDAY FOR NCZ007>009-021>023. &&
Posted on: Sun, 16 Mar 2014 12:39:54 +0000