Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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000
FXUS62 KRAH 270559
AFDRAH

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RALEIGH NC
100 AM EST THU NOV 27 2014

.SYNOPSIS...AN UPPER LEVEL DISTURBANCE AND ASSOCIATED LOW PRESSURE
SYSTEM WILL TRACK EAST ACROSS THE REGION EARLY THIS MORNING. HIGH
PRESSURE WILL BUILD INTO THE REGION FROM THE WEST THIS AFTERNOON AND
TONIGHT THEN SETTLE OVER THE CAROLINAS ON FRIDAY AND SATURDAY.

&&

.NEAR TERM /THROUGH THURSDAY/...
AS OF 1040 PM WEDNESDAY...

REMARKABLE CHANGES OF THE THERMODYNAMIC PROFILE OBSERVED AT KGSO
DURING THE PAST 12 HOURS...SUCH THAT THE DEEP NEAR FREEZING
ISOTHERMAL LAYER FROM THE SURFACE TO 550 MB THIS MORNING HAS BEEN
REPLACED BY MUCH STEEPER LAPSE RATES IN THE SAME LAYER THIS
EVENING...INCLUDING A 12 HR 500 MB CHANGE OF 15 DEGREES. LAPSE RATES
WILL CONTINUE TO STEEPEN OVERNIGHT...MOST NOTABLY ACROSS THE
NORTHERN PIEDMONT...AS A SERIES OF MID-UPPER LEVEL VORTICITY MAXIMA
AND ASSOCIATED COLDER TEMPERATURES ALOFT - INCLUDING MINUS 30 C AT
KBNA AT 00Z - ROUND THE BASE OF A MEAN TROUGH AND CROSS NC. THE
STEEPENING OF THE LAPSE RATES...AND RE-MOISTENING/RE-SATURATION OF
THE LOWEST 3-4 KM OWING TO THE APPROACH AND PASSAGE OF STRONG QG-
FORCING ACCOMPANYING BOTH THE VORTICITY MAXIMA ALOFT AND A BRIEF LOW
LEVEL WAA REGIME IN ASSOCIATION WITH ELONGATED 850 MB LOW PRESSURE
FROM THE MID-MS VALLEY TO THE SOUTHERN APPALACHIANS...WILL CAUSE AN
AREA OF MIXED CHARACTER RAIN/SHOWERS TO FURTHER BLOSSOM IN THE LEE
OFF THE APPALACHIANS...AND ACROSS THE NORTHERN NC PIEDMONT...
TONIGHT.

ALTHOUGH TEMPERATURES HAVE RADIATIONALLY COOLED BRIEFLY TO
NEAR FREEZING OVER PORTIONS OF THE PIEDMONT...THE INCREASING
CLOUDINESS ACCOMPANYING THE INCOMING PRECIPITATION WILL CAUSE
SURFACE TEMPERATURES TO CREEP UP (FROM DOWNWARD L/W RADIATION) INTO
THE MIDDLE TO UPPER 30S - SIMILAR TO WHAT WAS OBSERVED AT KBUY AND
K5W8 FROM 02-03Z - SUCH THAT ALL RAIN IS EXPECTED. IN FACT...RECENT
AMDAR DATA FROM RDU INDICATES A WARM LAYER WITH A MAXIMUM
TEMPERATURE OF AROUND 5 DEGREES IS PRESENT BETWEEN A 3-5 THOUSAND FT
FREEZING LEVEL...AND THE AFOREMENTIONED NEAR FREEZING TEMPERATURE
RIGHT AT THE SURFACE - MUCH TOO DEEP AND WARM FOR SNOW. WHILE IT IS
POSSIBLE FOR A FEW LIGHTNING STRIKES TO OCCUR WITH THE PRECIPITATION
TONIGHT...OVER THE NW PIEDMONT WHERE LAPSE RATES WILL BE STEEPEST
AND TOTAL TOTALS AND K-INDICES ARE FORECAST TO PEAK AROUND 55 AND
NEAR 30 C...RESPECTIVELY...THE RELATIVE BETTER (BUT STILL LOW
PROBABILITY) WILL BE WITH DIURNAL HEATING/BENEATH THE COLD POOL
ALOFT ON THU.  -MWS


PREVIOUS DISCUSSION THROUGH THU FOLLOWS:
AS OF 315 PM WEDNESDAY...

THE COASTAL LOW CURRENTLY SITS JUST OFF THE NRN OUTER BANKS OF NC...
MOVING STEADILY NORTHWARD. THE MID LEVEL VORTICITY MAX RIDING NE ON
THE SW SIDE OF THE BROAD RIDGE ALOFT CONTINUES TO SHEAR AND WEAKEN
AS IT MOVES THROUGH CENTRAL NC/VA... AND THIS DWINDLING FORCING FOR
ASCENT COUPLED WITH WANING UPPER DIVERGENCE AND LOWER PW FROM WEST
TO EAST ARE RESPONSIBLE FOR THE DOWNTURN IN BOTH COVERAGE AND
INTENSITY OF RAINFALL... AS WELL AS THE INCREASING SUNSHINE ACROSS
THE WRN AND SRN CWA. THIS TREND SHOULD CONTINUE... WITH RAIN CHANCES
DECREASING RAPIDLY OVER THE NEXT FEW HOURS... YIELDING LITTLE OR NO
RAIN CHANCES IN CENTRAL NC AFTER 6 PM OR 7 PM OR SO. BUT ATTENTION
IMMEDIATELY TURNS TO THE POTENT SHORTWAVE TROUGH NOW MOVING RAPIDLY
THROUGH THE MID MISS VALLEY... EXPECTED TO MOVE EAST THROUGH THE
CAROLINAS TONIGHT THROUGH MIDDAY THU... ACCOMPANIED BY SURFACE LOW
PRESSURE EXPECTED TO MOVE EASTWARD ACROSS CENTRAL/SRN NC. LATEST
SHORT-RANGE HI-RES MODEL GUIDANCE HAS SPED UP THE ONSET OF LIGHT
RAIN OVER OUR FORECAST AREA...AND BASED ON EXTRAPOLATION OF UPSTREAM
PRECIP...THIS LOOKS VERY REASONABLE. WILL BRING IN SLIGHT CHANCES OF
LIGHT SHOWERS OVER THE WRN PIEDMONT BY MID-LATE EVENING...THEN
FOLLOWING THE CONSENSUS OF LATEST MODEL OUTPUT...WILL SPREAD 20-50%
RAIN CHANCES ACROSS THE NRN PIEDMONT AND NRN COASTAL PLAIN LATER
TONIGHT... CONTINUING THROUGH THU MORNING... FOLLOWED BY AN EXIT OF
THE PRECIP OUT OF THE NORTHEAST CWA DURING THE EARLY AFTERNOON
HOURS. THIS PRECIP SHOULD BE MOSTLY SHOWERY IN NATURE...GIVEN THE
POTENTIAL FOR WEAK INSTABILITY ALOFT AS 850-500 MB LAPSE RATES ARE
STILL PROJECTED TO BE 7.0-7.5 C/KM. AS SUCH...WOULDN`T BE SURPRISED
TO SEE A FEW LIGHTNING STRIKES...ESPECIALLY GIVEN THE DYNAMIC
CONTRIBUTION TO LIFT FROM THE INCOMING VORTICITY MAX AND IMPROVING
UPPER DIVERGENCE DUE TO WIND ACCELERATION OVER SC AND SRN NC. TOTAL
RAINFALL AMOUNTS WITH THIS SYSTEM SHOULD BE SMALL... GENERALLY A
TENTH OF AN INCH OR LESS... ALTHOUGH TRENDS WOULD SUGGEST THAT THE
VA BORDER COUNTIES COULD SEE A COUPLE TENTHS... AS FORECAST
SOUNDINGS SHOW GREATER SATURATION IN THE LOW LEVELS AS COMPARED TO
YESTERDAY. CONSENSUS OF STATISTICAL GUIDANCE SUPPORTS LOWS TONIGHT
OF 34-37. THERE IS STILL A SMALL CHANCE THAT WE COULD SEE A FEW WET
SNOWFLAKES LATE TONIGHT INTO THU MORNING MAINLY NEAR THE VA
BORDER... BUT FORECAST SOUNDINGS AND SREF PLUMES AT DANVILLE SUGGEST
A THREAT TOO LOW TO MENTION... AND ANYTHING THAT FELL WOULD GENERATE
NO IMPACT. EXPECT IMPROVING SUNSHINE LATE IN THE DAY... WITH MORE
OVERALL INSOLATION SOUTH THAN NORTH... BUT STILL ANTICIPATE COOL
HIGHS RANGING FROM 48 NORTH TO 55 FAR SOUTH. -GIH

&&

.SHORT TERM /THURSDAY NIGHT THROUGH FRIDAY NIGHT/...
AS OF 320 PM WEDNESDAY...

THU NIGHT: THE VORTICITY MAX AND ACCOMPANYING SURFACE LOW SHOULD BE
HEADING EAST OFF THE COAST BY THU EVENING... AS HIGH PRESSURE BEGINS
TO BUILD IN FROM THE WEST... WITH GRADUALLY RISING HEIGHTS OVERNIGHT
AS THE SHORTWAVE TROUGH LIFTS OUT. EXPECT CLEARING SKIES EARLY WITH
DECREASING WINDS. LOWS AT THE MID RANGE OF GUIDANCE... 25-30... WITH
GOOD RADIATIONAL COOLING CONDITIONS EXPECTED. -GIH

FRIDAY AND FRIDAY NIGHT: SURFACE HIGH PRESSURE WILL BUILD IN FROM
THE DEEP SOUTH ON FRIDAY AS THE UPPER LEVEL TROUGH MOVES OFF OF THE
COAST. FOR THE FIRST PART OF THE DAY...CENTRAL NC WILL REMAIN ON THE
EAST SIDE OF THE HIGH...IN WEAK NORTHERLY FLOW BUT BY LATE AFTERNOON
THE HIGH WILL MOVE DIRECTLY OVERHEAD...CALMING ANY REMAINING WIND.
CLOUD COVER LEFT OVER FROM THE DEPARTING SYSTEM WILL FILTER OUT TO
THE NORTHEAST. THUS EXPECT LOWEST TEMPS IN THE NE AND HIGHEST IN THE
SW. COOLEST DAY OF THE WEEK WITH HIGHS IN THE MID 40S TO NEAR 50
DEGREES. FRIDAY NIGHT WILL SEE TEMPERATURES DROP INTO THE MID TO
UPPER 20S WITH FEW CLOUDS AND CALM WINDS. -ELLIS

&&

.LONG TERM /SATURDAY THROUGH WEDNESDAY/...
AS OF 245 PM WEDNESDAY...

SATURDAY THROUGH MONDAY NIGHT: THE FIRST PART OF THE LONG TERM WILL
FEATURE A SIGNIFICANT WARMING TREND AS SURFACE HIGH PRESSURE MOVES
EAST OF THE AREA SETTING UP RETURN FLOW OVER CENTRAL NC. THIS WILL
BE THE MAIN DRIVER AS UPPER LEVEL FLOW REMAINS VERY ZONAL. ALTHOUGH
BOTH THE GFS AND THE ECMWF AGREE THAT IT WILL BE WARMER...THE
QUESTION REMAINS HOW MUCH? WITH FEW TO SCATTERED CLOUDS OVER THE
AREA...RISING THICKNESSES AND WARM AIR ADVECTION THROUGH
SOUTHWESTERLY FLOW...CANT SEE HOW TEMPERATURES WONT RISE
SIGNIFICANTLY. THEREFORE HAVE GONE TO THE HIGH SIDE OF GUIDANCE
WHICH IN THIS CASE IS MORE IN LINE WITH THE LONG RANGE ECMWF NUMBERS
FOR MAX TEMPS THROUGH MONDAY. SPECIFICALLY MID TO UPPER 50S
SATURDAY...MID TO UPPER 60S SUNDAY...AND UPPER 60S TO LOWER 70S
MONDAY. LOWS WILL ALSO WARM THROUGH THE WEEKEND BUT MORE
MODESTLY...UPPER 30S INCREASING TO MID 40S SUNDAY NIGHT BEFORE
FALLING SLIGHTLY BACK INTO THE LOWER 40S ON TUESDAY AHEAD OF A COLD
FRONT DRAPED TO OUR NORTHWEST.

TUESDAY THROUGH WEDNESDAY: THE LAST PART OF THE LONG TERM INTRODUCES
A FAIR AMOUNT OF UNCERTAINTY IN THE HANDLING OF THE AFOREMENTIONED
COLD FRONT AS THE PARENT LOW IS IS QUICKLY HAULED AWAY TO THE
NORTHEAST BY THE NORTHERN STREAM JET...LEAVING A WEAKLY DEFINED
FRONTAL ZONE JUST TO THE NORTHWEST OF THE CWA. ANY PRECIPITATION
ASSOCIATED WITH TEH FRONT SHOULD HOLD OFF UNTIL TUESDAY MORNING WHEN
A FAIRLY STRONG 1040 MB HIGH PRESSURE SYSTEM MOVES THROUGH QUEBEC.
THIS LOCATION IS FURTHER NORTH THAN THE PREVIOUS MODEL RUNS AND IS
NOT QUITE AS IDEAL FOR A CLASSICAL/HYBRID COLD AIR DAMMING EVENT AS
IT WAS YESTERDAY. STILL THINK SOME FORM OF A WEAK CAD IS POSSIBLE
AND THUS KEEPING HIGHS ON TUESDAY FAIRLY LOW AS WE SHOULD BE
OVERCAST WITH NORTHEASTERLY WINDS. MAX TEMPS IN THE LOW TO UPPER 50S
BUT STILL COULD BE LOWER IN THE TRIAD IF WEDGE DEVELOPS. THIS HIGH
WILL NOT REMAIN IN PLACE FOR VERY LONG AS IT IS QUICKLY MOVES OUT TO
SEA BY A DEVELOPING LOW OVER NORTHERN ONTARIO AND A DEEPENING UPPER
LEVEL TROUGH OVER THE MIDWEST. THIS WILL SET UP A SLIGHTLY WARMER
DAY ON WEDNESDAY IN THE WARM AIR ADVECTION REGIME AHEAD OF THE FRONT
AS LONG AS THE WEDGE DISSIPATES. MID 50S TO MID 60S NW TO SE. PRECIP
CHANCES AND AMOUNTS STILL FAIRLY UNCERTAIN AT THIS POINT BUT WILL
CARRY SLIGHT CHANCE POPS TUESDAY AND WEDNESDAY. LOWS DURING THIS
TIME IN THE UPPER 30S TO LOWER 40S.

&&

.AVIATION /06Z THURSDAY THROUGH MONDAY/...
AS OF 100 AM THURSDAY...

A STRONG UPPER LEVEL DISTURBANCE WILL CROSS CENTRAL NC EARLY THIS
MORNING...EXITING OUR REGION BY THIS AFTERNOON. PROCEEDING THIS
SYSTEM...THERE WILL BE A PERIOD OF MVFR/LOW END VFR CEILINGS ALONG
WITH PATCHES OF LIGHT RAIN. THESE CEILINGS AND PRECIP WILL BE MOST
PROMINENT ACROSS THE NORTHERN TERMINALS AND LESS LIKELY AT KFAY.

AFTER 14Z...WEST TO NW SFC WINDS WILL BE BLUSTERY WITH GUSTS 18-23
KTS LIKELY. THE GUSTS WILL BECOME LESS LIKELY AFTER 22Z...THOUGH A
STEADY NW WIND AROUND 10KTS EXPECTED WELL INTO TONIGHT.

HIGH PRESSURE WILL BUILD INTO CENTRAL NC TONIGHT AND SETTLE OVERHEAD
FRIDAY THROUGH SATURDAY...PROVIDING A PERIOD OF VFR CONDITIONS WITH
SFC WINDS LESS THAN 10KTS.

THE HIGH WILL SHIFT OFFSHORE SUNDAY. THE RESULTING SOUTH-SOUTHWEST
LOW LEVEL FLOW WILL ADVECT MOISTURE INTO OUR REGION BY LATE SUNDAY-
SUNDAY NIGHT LEADING TO THE POTENTIAL FOR AREAS OF MVFR FOG OR IFR
CEILINGS IN STRATUS BY EARLY MONDAY.

&&

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

&&

$$

SYNOPSIS...WSS
NEAR TERM...MWS/HARTFIELD
SHORT TERM...HARTFIELD/ELLIS
LONG TERM...ELLIS
AVIATION...WSS



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