Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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000 FXUS62 KRAH 171110 AFDRAH AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE RALEIGH NC 610 AM EST WED DEC 17 2014 .SYNOPSIS...HIGH PRESSURE WILL BUILD SLOWLY INTO THE AREA THROUGH FRIDAY. MEANWHILE...AN AREA OF LOW PRESSURE WILL TRACK EASTWARD ACROSS THE NORTHERN GULF AND THEN ALONG THE NC COAST OVER THE WEEKEND. && .NEAR TERM /THROUGH TONIGHT/... AS OF 223 AM WEDNESDAY... UPPER FLOW BECOMES ZONAL BEHIND THE DEPARTING UPPER TROUGH. AT THE SURFACE...HIGH PRESSURE OVER THE CENTRAL US WILL BE VERY SLOW TO BUILD EASTWARD WITH NEUTRAL TEMPERATURE ADVECTION AT 850MB NOTED. UNDER MOSTLY SUNNY SKIES...EXPECT SEASONABLE AFTERNOON HIGHS RANGING FROM LOWER TO MID 50S NORTH TO MID/UPPER 50S SOUTH. AN ACTIVE PACIFIC WAVE TRAIN MOVING ONSHORE ACROSS CALIFORNIA AND THEN THROUGH THE SOUTHWEST US WILL REINVIGORATE THE PACIFIC JET THAT EXTENDS ACROSS THE SOUTHERN CONUS. AN OPAQUE CIRRUS SHIELD WILL SPREAD EAST INTO THE AREA THIS EVENING AND OVERNIGHT WHICH SHOULD TEMPER MIN TEMPS A BIT. MOST AREA SHOULD BOTTOM OUT IN THE MID 30S...WITH SOME LOWER 30S IN SOME OUTLYING AREAS. && .SHORT TERM /THURSDAY AND THURSDAY NIGHT/... AS OF 223 AM WEDNESDAY... WEAK SHORTWAVE DISTURBANCES EMBEDDED IN THE VIGOROUS PACIFIC JET BRANCH THAT EXTENDS ACROSS THE SOUTHERN CONUS WILL RESULT IN AN EXTENSIVE CIRRUS SHIELD ACROSS THE AREA ON THURSDAY...AT LEAST THROUGH THE FIRST HALF OF THE DAY. THE GFS OVER THE PAST COUPLE OF DAYS HAS BEEN INSISTENT IN SPREADING A HUNDREDTH OR TWO OR QPF ACROSS THE NORTH/NORTHWEST PIEDMONT IN PROXIMITY TO THE WEAK DPVA/UPPER DIVERGENCE REGION...HOWEVER A DEEP DRY SUB-CLOUD LAYER ASSOCIATED WITH THE DRY AIR SURFACE RIDGE EXTENDING INTO THE AREA FROM THE NORTHWEST SHOULD PRECLUDE ANY SPRINKLES FROM REACHING THE GROUND AND THUS WILL KEEP FORECAST DRY. TEMPERATURES WILL INITIALLY STRUGGLE TO WARM UNDERNEATH THE MILKY SKIES...WITH A GOOD CHANCE THAT TEMPS MAY NOT HAVE ENOUGH TIME TO FULLY RECOVER AS WE APPROACH THE SHORTEST DAY OF THE YEAR(DEC 21). AS SUCH...HIGHS THURSDAY SEVERAL DEGREES COOLER THAN TODAY...RANGING FROM UPPER 40S NORTH TO MID 50S SOUTH. SKIES SHOULD REMAIN MOSTLY CLEAR THURSDAY NIGHT WITH LOWS IN THE LOWER TO MID 30S. && .LONG TERM /FRIDAY THROUGH TUESDAY/... AS OF 318 AM WEDNESDAY... FRIDAY...SFC RIDGE PROJECTED TO EXTEND NW-SE ACROSS THE REGION FROM A PARENT HIGH (1025MB +/-) OVER THE LOWER OH VALLEY. MEANWHILE ALOFT...WEAK S/W RIDGE WILL CROSS THE REGION. EXPECT THE DAY TO START OUT SUNNY/MOSTLY SUNNY BUT SHOULD SEE AN INCREASE IN HIGH LEVEL CLOUDINESS LATE IN THE DAY...ESPECIALLY WESTERN PIEDMONT...IN RESPONSE TO S/W TROUGH AND ATTENDANT SURFACE LOW DEVELOPING WELL TO OUR SW. LOW LEVEL THICKNESSES CLOSE TO NORMAL WHICH SUGGEST HIGH TEMPS AROUND 50 NORTH TO LOW-MID 50S SOUTH. FRIDAY NIGHT...CLOUDS WILL CONTINUE TO THICKEN/LOWER THROUGH THE NIGHT. ENOUGH ISENTROPIC UPGLIDE EXISTS SHORTLY BEFORE DAYBREAK TO INCLUDE A MENTION OF SPOTTY LIGHT RAIN OVER THE SW TWO-THIRDS OF THE CWA. PARTIAL THICKNESSES HOVERING IN VICINITY OF THE RAIN/FREEZING SECTOR OF THE WINTER P-TYPE NOMOGRAM OVER THE NW PIEDMONT. HOWEVER...MODEL GUIDANCE HAD BEEN TRENDING WARMER AND THE FREEZING LEVEL FAIRLY ELEVATED (6000-8000FT). WHILE SATURATION AND SIGNIFICANT LIFT NOTED IN THE FAVORED ICE NUCLEATION REGION OF THE ATMOSPHERE...LOW LEVEL AIR MASS CURRENTLY APPEARS TOO WARM FOR ANY WINTER P-TYPE AT THE ONSET OF THE PRECIP. WORSE CASE SCENARIO WOULD BE SOME WET SNOWFLAKES MIXING WITH THE RAIN WHEN THE PRECIP RATES ARE MODERATE/BRIEFLY HEAVY. MIN TEMPS GENERALLY MID 30S. SATURDAY...SFC DRY AIR RIDGE AND PARENT HIGH IN FAVORABLE LOCATION TO SUPPORT A COLD AIR DAMMING EVENT SATURDAY. THE NEAR SURFACE NE FLOW WILL ADVECT A COOL AIR MASS INTO OUR REGION. MEANWHILE 850- 700MB FLOW WILL PULL WARM GULF MOISTURE OVER THE COOL STABLE NEAR SURFACE AIR MASS RESULTING IN WIDESPREAD RAIN. LIFT APPEARS BEST IN THE MORNING THROUGH EARLY AFTERNOON WITH LIFT WANING IN THE WEST BY MID AFTERNOON. THE COOL SFC AIR MASS COMPOUNDED BY THE RAIN WILL HOLD TEMPS AT OR BELOW 40 DEGREES ACROSS THE NW PIEDMONT...AND IN THE 40S PRETTY MUCH ELSEWHERE. SATURDAY NIGHT...AREAS OF RAIN WILL GRADUALLY TAPER TO SPOTTY LIGHT RAIN WITH AREAS OF DRIZZLE AS MAIN LIFT MOVES AWAY FROM OUR REGION AS S/W DAMPENS TO OUR EAST. LOW LEVEL AIR MASS EXPECTED TO REMAIN NEARLY SATURATED SO WILL LIKELY KEEP LOW CLOUDS ALL NIGHT. MIN TEMPS MID-UPPER 30S. SUNDAY THROUGH TUESDAY...L/W TROUGH TO OUR WEST AMPLIFIES THIS PERIOD AS A SUBSTANTIAL S/W DIGS ON THE BACK SIDE OF THE TROUGH. THIS WILL MAINTAIN A SW FLOW ALOFT OVER CENTRAL NC. WITH A LACK OF A MECHANISM TO SCOUR OUR THE CAD AIR MASS AND CONTINUED SW FLOW ALOFT...COULD SEE A SET UP FOR A PERIOD OF CLOUDINESS SUNDAY THROUGH TUESDAY ACROSS CENTRAL CN WITH PATCHES OF LIGHT RAIN AND/OR DRIZZLE SUNDAY AND POSSIBLY INTO MONDAY. MAY SEE SOME IMPROVEMENT LATE MONDAY INTO TUESDAY THOUGH MAY BE TRADING IN LOW CLOUDS FOR A DECK OF MID-HIGH LEVEL CLOUDS. OVERALL EXPECT MORE CLOUDS THAN SUN THIS PERIOD. HIGH TEMPS WILL AVERAGE 3-5 DEGREES BELOW NORMAL WHILE MIN TEMPS WILL AVERAGE NEAR OR SLIGHTLY ABOVE NORMAL (TYPICAL FOR CLOUDY CONDITIONS). && .AVIATION /12Z WEDNESDAY THROUGH SUNDAY/...
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AS OF 610 AM WEDNESDAY... 24-HR TAF PERIOD: THERE IS HIGH CONFIDENCE OF VFR CONDITIONS THROUGH THE 24 TAF PERIOD AS WEAK HIGH PRESSURE EXTEND INTO THE AREA WITH A LIGHT WEST-NORTHWEST BREEZE. LOOKING AHEAD: SHORTWAVE DISTURBANCES EMBEDDED WITHIN THE VIGOROUS PACIFIC JET THAT EXTENDS ACROSS THE SOUTHERN CONUS MAY RESULT IN PERIODS OF BROKEN/OVERCAST MID/HIGH CLOUD DECK. OTHERWISE...A DRY AIR SURFACE RIDGE EXTENDING INTO THE CAROLINAS FROM THE NORTH/NORTHWEST WILL SECURE VFR CONDITIONS THROUGH FRIDAY. A LOW PRESSURE SYSTEM TRACKING FROM THE GULF OF MEXICO NORTHEASTWARD ALONG THE SOUTHEAST COAST WILL RESULT IN ADVERSE AVIATION CONDITIONS LATE FRIDAY AND INTO THE WEEKEND.
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&& .RAH WATCHES/WARNINGS/ADVISORIES... NONE. && $$ SYNOPSIS...CBL NEAR TERM...CBL SHORT TERM...CBL LONG TERM...WSS AVIATION...CBL

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