-- Discussion containing changed information from previous version are highlighted. --
000
FXUS62 KRAH 050539
AFDRAH

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RALEIGH NC
1238 AM EST THU MAR 5 2015

.SYNOPSIS...A STRONG COLD FRONT WILL PUSH SOUTHWARD THROUGH CENTRAL
NORTH CAROLINA TODAY. A WAVE OF LOW PRESSURE TRACK EASTWARD ALONG
THE FRONT ACROSS NORTHERN SOUTH CAROLINA LATER TODAY... THEN
OFFSHORE TONIGHT. ARCTIC HIGH PRESSURE WILL BUILD OVER THE REGION
BEHIND THE FRONT TONIGHT THROUGH SATURDAY.

&&

.NEAR TERM /THROUGH TONIGHT/...
AS OF 1230 AM THURSDAY...

CONSIDERING A WINTER WEATHER ADVISORY FOR A CHANGEOVER TO FREEZING
RAIN AND SLEET ACROSS THE NORTHERN TIER OF NC COUNTIES FOR MID TO
LATE AFTERNOON INTO THE EARLY EVENING. RAIN ELSEWHERE.

AS FAR AS THE POTENTIAL WINTER WEATHER ADVISORY ALONG AND NORTH OF
THE TRIAD AND TRIAGLE... A CONCERN AT THE CURRENT TIME FOR THE
CHANGEOVER IS THAT THE PARENT ARCTIC SURFACE HIGH PRESSURE IS FAR
REMOVED FROM THE IDEAL PLACEMENT FOR THE QUICK DELIVERY OF LOW LEVEL
ARCTIC AIR INTO CENTRAL NC. THE HIGH PRESSURE CENTER WAS CURRENTLY
LOCATED OVER THE NORTHERN PLAINS AND NOT THE GREAT LAKES OR NEW
ENGLAND. EVEN DURING THE DAY... THE HIGH PRESSURE IS FORECAST TO
MOVE TO IOWA AT 12Z... THEN ILLINOIS BY 00Z/THIS EVENING. CURRENTLY
THE MAIN ARCTIC FRONT WAS LOCATED WEST OF THE APPALACHIANS (TRUE
ARCTIC AIR IS BLOCKED BY THE MOUNTAINS). NOTE THAT THE DEW POINTS AT
MIDNIGHT WERE STILL AROUND 40 IN THE DCA AREA. THE COLD AIR IN THIS
SET UP WILL HAVE TO BUILD EAST ACROSS OH INTO PA AND MD OVERNIGHT...
THEN SURGE SOUTHWARD THROUGH VA... TAKING A LONG ROUTE INTO NORTHERN
NC. SINCE THIS PROCESS HAS YET TO BEGIN... THE LATEST NAM/GFS
FORECASTS OF DELAYING THE CHANGEOVER BY A FEW HOURS FROM THE CURRENT
FORECAST ALONG OUR NORTHERN TIER MAY BE ON TARGET. ON THE FLIP
SIDE... THE ARCTIC AIR IS VERY COLD AND DENSE... AND AT TIMES THE
MODELS ARE NOT QUICK ENOUGH WITH THE COLD AIR SURGE AT THE SURFACE
(EVEN IN SCENERIES IN WHICH THE ARCTIC AIR IS BLOCKED BY THE
APPALACHIANS AND HAS TO TAKE THE LONGER ROUTE TO GET HERE.

MUCH TO CONSIDER AS THE NEW MODELS AND DATA ROLL IN.

BADGETT

PREVIOUS DISCUSSION FROM 305 PM WEDNESDAY:
THURSDAY AND THURSDAY NIGHT:

THE GFS AND NAM HAVE COME INTO BETTER WITH THE TIMING OF THE COLD
AIR SURGING SOUTH INTO THE AREA...WITH THE GFS TRENDING TOWARDS THE
SLOWER/LESS AGGRESSIVE NAM.

P-TYPE: LOW-LEVEL COLD AIR SURGING SOUTHWARD OUT OF VIRGINIA WILL
INITIALLY SUPPORT A CHANGEOVER FROM RAIN TO A FREEZING RAIN/SLEET
MIX AS MID-LEVEL COOLING(STRONG WARM NOSE)LAGS BEHIND. THEN AS THE
MID-LEVEL COOLS AND A SUBSTANTIAL/DEEP LOW-LEVEL COLD NOSE DEVELOPS
(-6C)...PRECIP COULD END AS MOSTLY SLEET WITH MODELS INDICATING A
.10 TO .20 INCHES OF LIQUID EQUIVALENT CENTERED OVER THE CENTRAL
PIEDMONT-NORTHERN AND CENTRAL COASTAL PLAIN BETWEEN 05/00Z AND
05/06Z. ICE AMOUNTS ARE ALWAYS DIFFICULT TO ASCERTAIN ANYTIME THERE
IS A LONG DURATION IN THE MIXED SLEET/FREEZING RAIN REGIONS OF THE
NOMOGRAM. ULTIMATELY THE PREDOMINATE P-TYPE IN THIS EVENT COULD
LARGELY BE DETERMINED BY PRECIP RATES...WITH MORE SLEET IN THE
HEAVIER PRECIP BANDS PROMOTING ENHANCED COOLING ALOFT. COULD SEE AS
MUCH AS 0.10 TO 0.15 OF AN INCH OF FREEZING RAIN ALONG AND NORTH OF
HIGHWAY 64 IS POSSIBLE...WITH SLEET AMOUNTS OF AROUND 0.50"
POSSIBLE. ANY ICE ACCRUAL WILL BE CONFINED MAINLY TO ELEVATED
SURFACES OWING TO WARM PAVEMENT TEMPERATURES FROM TODAYS +70 DEGREE
READINGS.

TIMING: USING A BLEND OF THE GFS AND NAM...THE CHANGE-OVER FROM RAIN
TO FREEZING RAIN/SLEET LOOKS TO OCCUR BETWEEN 21Z NEAR THE VIRGINIA
BORDER TO 00Z ACROSS THE CENTRAL PIEDMONT/COASTAL PLAIN(ROUGHLY
ALONG AND NORTH OF HIGHWAY 64). WHILE THE CHANGE-OVER SHOULD
CONTINUE TO SURGE SOUTHWARD INTO THE SANDHILLS/SOUTHERN
PIEDMONT/SOUTHERN COASTAL PLAIN BETWEEN 00 TO 06Z...SUFFICIENT
COOLING TO SUPPORT FROZEN PRECIP APPEARS TO SHORT TO ALLOW ANY
APPRECIABLE ACCRUAL BEFORE PRECIP ENDS.

SINCE ANY P-TYPE CONCERNS WILL BE DURING LATE 2ND/EARLY 3RD
PERIOD...PREFERENCE IS TO HOLD OFF ON ISSUING ANY ADVISORIES AT THIS
TIME SO THAT FURTHER MODEL TRENDS CAN BE EVALUATED WITH THE 00Z/05
MODEL PACKAGE.

CLEARING FROM NW TO SE AND INTRUSION OF ARCTIC AIR INTO THE AREA
WILL SUPPORT COLD OVERNIGHT LOWS IN THE 20S WHICH WILL LIKELY LEAD
TO BLACK ICE DEVELOPMENT ACROSS THE AREA THURSDAY NIGHT/FRIDAY
MORNING. A WINTER WEATHER ADVISORY MAY BE NEEDED FOR BLACK ICE

&&

.SHORT TERM /FRIDAY THROUGH SATURDAY NIGHT/...
AS OF 305 PM WEDNESDAY...

LOW LEVEL COLD AIR ADVECTION FRIDAY WILL RESULT IN ANOTHER DAY OF
WELL BELOW NORMAL TEMPS. THICKNESSES AVERAGE CLOSE TO 50M BELOW
NORMAL...SUGGESTIVE OF MAX TEMPS CLOSE TO 20 DEGREES BELOW NORMAL.
WITH PLENTY OF SUN AND AN INCREASING SUN ANGLE SHOULD SEE TEMPS
RECOVER AT LEAST 15-18 DEGREES FROM MORNING LOWS INSPITE OF THE LOW
LEVEL CAA. FAVOR THE COOLER MET GUIDANCE WHICH SUPPORTS MAX TEMPS IN
THE MID-UPPER 30S.

COLDEST NIGHT EXPECTED MOST LOCATIONS FRIDAY NIGHT AS 850MB THERMAL
TROUGH CROSSES REGION IN THE EVENING AND SFC RIDGE SETTLES DIRECTLY
OVERHEAD. MIN TEMPS 15-20 DEGREES FROM RDU AND AREAS NORTH AND
EAST...TO THE LOWERS 20S FAR WEST-SW.

MILDER CONDITIONS ANTICIPATED SATURDAY AS SFC RIDGE DRIFTS SLOWLY
EAST. WITH PLENTY OF DRY AIR AND A DEVELOPING LOW LEVEL WEST-SW
FLOW...SHOULD SEE A DIURNAL TEMP RECOVER OF 30-35 DEGREES ACROSS THE
AREA. MAX TEMPS NEAR 50 FAR NE TO THE MID 50S SW. POTENTIAL FOR MAX
TEMPS TO BE A FEW DEGREES WARMER...AS 850MB WLY FLOW HAS A TENDENCY
TO WARM US UP GREATER THAN EXPECTED IN THESE DRY AIR MASSES.

SATURDAY NIGHT...WLY FLOW ALOFT MAY FILTER SOME HIGH CLOUDS OVER THE
REGION BUT THE LOWER LEVELS WILL REMAIN DRY. A LINGERING LIGHT SW
SFC FLOW WILL AID TO KEEP TEMPS FROM FREE-FALLING AFTER SUNSET. MIN
TEMPS NEAR 30 NORTH TO LOWER 30S SOUTH.

&&

.LONG TERM /SUNDAY THROUGH WEDNESDAY/...
AS OF 305 PM WEDNESDAY...

MODERATING TEMPERATURES WILL CONTINUE INTO EARLY NEXT WEEK AS MILD
HIGH PRESSURE BUILDS EAST ACROSS THE SOUTHERN OHIO VALLEY.
MEANWHILE...FAST...CONFLUENT...NEAR ZONAL FLOW ALOFT WILL MAINTAIN
SEPARATION BETWEEN THE NORTHERN AND SOUTHERN STREAMS...WITH THE MORE
MOISTURE LADEN SOUTHERN STREAM SUPPRESSED ACROSS THE DEEP SOUTH.
THIS WILL RESULT IN MOSTLY SUNNY SKIES SUNDAY AND MONDAY. HIGHS
SUNDAY WILL REACH MAINLY MID 50S. ON MONDAY...AFTER A MORNING LOW
AROUND 40...HIGHS WILL CLIMB TO NEAR NORMAL...WITHIN A DEGREE OR SO
OF 60.

SLOW EJECTION OF A SOUTHERN STREAM SHORT WAVE ACROSS THE SOUTHERN
CONUS/NORTHERN GULF IS EXPECTED EARLY NEXT WEEK. AS THIS WAVE MOVES
EAST...THE GRADUAL DEEPENING OF A MID LEVEL TROF OVER THE MIDWEST
WILL INITIALLY BEGIN TO BULGE THE SOUTHERN STREAM NORTHWARD INTO THE
SOUTH ATLANTIC STATES MONDAY NIGHT. THUS EXPECT INCREASING MID/HIGH
CLOUDINESS MONDAY NIGHT WHICH WILL OFFSET RADIATION TO MAINTAIN
HIGHS OF AROUND 60 ON TUESDAY IN A WEAK CAD CONFIGURATION DESPITE
THE MODESTLY BUILDING HEIGHTS ALOFT.

HAVE LOW CONFIDENCE IN THE DETAILS IN THE LONGER RANGE GIVEN POOR
MODEL CONSENSUS AS TO WHEN AND WHERE WE MIGHT EXPECT SURFACE
DEVELOPMENT AND ATTENDANT MOISTURE ADVECTION INTO THE AREA. THE GFS
SOLUTION IS MUCH FASTER...WITH STRONG OVERRUNNING AS EARLY AS
TUESDAY NIGHT...WHILE THE ECMWF DELAYS DEVELOPMENT OF A SURFACE LOW
UNTIL THURSDAY. AT THIS POINT WILL MAINTAIN ONGOING SLIGHT LOW
CHANCES OF RAIN TUESDAY AND WEDNESDAY WITH HIGHS IN THE LOW TO MID
60S AS WE WAIT FOR BETTER MODEL CONSENSUS. THE HIGH TEMPERATURES
WILL BE HEAVILY DEPENDENT ON THE POTENTIAL IN-SITU DAMMING...AND THE
EARLIER GFS SOLUTION WOULD RESULT IN HIGHS BEING CONSIDERABLY
COOLER...ESPECIALLY ON TUESDAY.

&&

.AVIATION /06Z THURSDAY THROUGH MONDAY/...
AS OF 1237 AM THURSDAY...

MAINLY VFR CONDITIONS...IN CONTINUED SOUTHWESTERLY FLOW AHEAD OF AN
APPROACHING COLD FRONT...WILL BECOME MVFR-IFR FROM NORTH TO SOUTH
WITH THE PASSAGE OF THE COLD FRONT BETWEEN 10-14Z AT NORTHERN TAF
SITES...TO BETWEEN 15-19Z AT KFAY. TWO EXCEPTIONS TO THE OTHERWISE
PRECEDING VFR CONDITIONS WILL BE A TEMPORARY MVFR CEILING AT
KINT/KGSO FOR A BRIEF TIME THIS EVENING...AND A MEDIUM CHANCE OF IFR
VISIBILITY RESTRICTIONS AND/OR CEILINGS AT KFAY OVERNIGHT...WHERE
THE COMBINATION OF RADIATIONAL COOLING DURING TIMES OF LIGHTER TO
OCCASIONALLY NEAR CALM WIND...WITH A RELATIVE MAXIMUM IN SURFACE
DEWPOINTS OVER SE NC...WILL SUPPORT THE DEVELOPMENT OF AREAS OF
FOG/LOW STRATUS.

ONCE SURFACE WINDS LESSEN AND QUIT GUSTING AREA-WIDE WITHIN THE NEXT
COUPLE OF HOURS IN ASSOCIATION WITH THE DEVELOPMENT OF A NOCTURNAL
INVERSION...LOW LEVEL WIND SHEAR WILL ALSO BECOME PROBABLE OWING TO
THE DEVELOPMENT OF A 40-50 KT LOW LEVEL JET JUST ABOVE THE SURFACE.
THE PASSAGE OF THE AFOREMENTIONED SURFACE COLD FRONT WILL END THE
THREAT OF LOW LEVEL WIND SHEAR...AND INSTEAD RESULT IN A STRONG POST-
FRONTAL NORTHEASTERLY WIND BETWEEN 10-15 KTS...WITH GUSTS AROUND 20
KTS.

WIDESPREAD RAIN AND ASSOCIATED MVFR-IFR CONDITIONS TRAILING THE
PASSING COLD FRONT WILL CONTINUE THROUGHOUT THU...BEFORE RAIN
CHANGES TO FREEZING RAIN AND SLEET FROM NORTH TO SOUTH THU AFTERNOON
AND EVENING.

OUTLOOK: AFTER LINGERING LIGHT SLEET AND MVFR CONDITIONS
KRDU/KFAY/KRWI THU EVENING...PERSISTING LONGEST INTO THU NIGHT AT
KFAY...VFR CONDITION ARE ANTICIPATED FOR THE NEXT SEVERAL DAYS.

&&

.CLIMATE...
                            RDU           GSO         FAY

03/06:  RECORD LOW MAX    32-1901       34-1960     34-1960
               MIN        11-1960        5-1960     19-1960

&&

.RAH WATCHES/WARNINGS/ADVISORIES...
NONE.

&&

$$

SYNOPSIS...RAH
NEAR TERM...BADGETT/HARTFIELD/CBL
SHORT TERM...WSS
LONG TERM...MLM
AVIATION...BADGETT
CLIMATE...CBL