Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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FXUS62 KRAH 042009
AFDRAH

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RALEIGH NC
308 PM EST WED MAR 4 2015

.SYNOPSIS...A STRONG COLD FRONT WILL CROSS CENTRAL NC LATE TONIGHT
AND EARLY THURSDAY. ARCTIC HIGH PRESSURE WILL BUILD OVER THE REGION
BEHIND THE FRONT FRIDAY AND SATURDAY.

&&

.NEAR TERM /THROUGH THURSDAY NIGHT/...
AS OF 305 PM WEDNESDAY...

MODELS ARE IN RELATIVELY GOOD AGREEMENT IN THE TIMING OF SFC COLD
FRONT WITH AN INITIAL WEAK WAVE OF LOW PRESSURE INTO THE AREA
BETWEEN 06Z-12Z. SOUTHWESTERLY LOW TO MID LEVEL FLOW..BEHIND THE
COLD FRONT BISECTING THE AREA AT 12Z WILL SUPPORT ANA-FRONTAL PRECIP
BAND ON THE COOL SIDE OF THE BOUNDARY...ALONG A LINE FROM ALBEMARLE
TO SANFORD TO WILSON...MAKING FOR A MESSY MORNING COMMUTE FOR THE
TRIAD AND TRIANGLE. EXPECT QUITE A SHARP NORTH-SOUTH CONTRAST IN
TEMPERATURES...RANGING FROM LOWER 40S TO LOWER 60S.

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 /18Z WEDNESDAY THROUGH MONDAY/...
AS OF 1245 PM WEDNESDAY...

AVIATION CONDITIONS WILL CONTINUE TO IMPROVE EARLY THIS AFTERNOON
WITH VFR CONDITIONS HIGHLY PROBABLE FOR MOST SITES BY 20Z. A BREEZY
SW WIND WILL FREQUENTLY GUST AROUND 25 MPH.

A STRONG COLD FRONT CURRENTLY CROSSING THE TN VALLEY WILL PROGRESS
SLOWLY SEWD...CROSSING THE NORTHERN PIEDMONT AND NORTHERN COASTAL
PLAIN SHORTLY BEFORE DAYBREAK...AND THE SOUTHERN COUNTIES INCLUDING
KFAY AFTER DAYBREAK. SW WINDS THROUGH LATE THIS EVENING WILL VEER TO
A NORTH-NORTHEAST DIRECTION WITH THE PASSAGE OF THE FRONT. ALONG AND
IMMEDIATELY BEHIND THE FRONT...AREAS OF RAIN AND LOW STRATUS WILL
OCCUR WITH IFR/LIFR CEILINGS HIGHLY PROBABLE.

COLDER AIR WILL INFILTRATE THE LOWER LEVELS OF THE ATMOSPHERE DURING
THE DAY THURSDAY WITH TEMPS EXPECTED TO PLUMMET BELOW FREEZING BY
LATE THURSDAY AFTERNOON-EARLY THURSDAY EVENING MOST LOCATIONS. THIS
WILL CAUSE THE RAIN TO CHANGE OVER TO FREEZING RAIN OR A MIX OF
FREEZING RAIN AND SLEET BEFORE ENDING LATE THURSDAY NIGHT. THERE IS
AN INCREASING CHANCE FOR ICE ACCRUAL OVER THE NORTHERN COUNTIES
THURSDAY EVENING...AND POSSIBLY IN THE SANDHILLS AND SOUTHERN
COASTAL PLAIN BY MID-LATE THURSDAY EVENING.

AVIATION CONDITIONS ARE EXPECTED TO IMPROVE TO VFR BY EARLY FRIDAY
AS ARCTIC HIGH PRESSURE BUILDS INTO THE REGION. THIS WEATHER SYSTEM
WILL BRING AN EXTENDED PERIOD OF VFR CONDITIONS THAT SHOULD LAST
THROUGH MONDAY.

&&

.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...CBL
SHORT TERM...WSS
LONG TERM...MLM
AVIATION...WSS
CLIMATE...CBL


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