Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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FXUS62 KRAH 270644 CCA
AFDRAH

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RALEIGH NC
244 AM EDT MON OCT 27 2014

.SYNOPSIS...
BENEATH BUILDING HEIGHTS ALOFT...HIGH PRESSURE WILL DRIFT OVERHEAD
THIS MORNING AND OFFSHORE BY THIS EVENING. THE HIGH PRESSURE WILL
DRIFT EAST INTO BERMUDA-HIGH POSITION THROUGH MID-WEEK AND RESULT IN
WARM SOUTHWEST FLOW UNTIL A COLD FRONT CROSSES CENTRAL NC WED INTO
WED EVENING.

&&

.NEAR TERM /THROUGH MONDAY NIGHT/...
AS OF 1000 PM SUNDAY...

AFTERNOON TEMPS SOARED WELL INTO THE 70S TO THE LOWER 80S ACROSS THE
SOUTH UNDER SUNNY SKIES. AIR MASS VERY DRY (EVEN FOR THIS TIME OF
YEAR) AS DEWPOINTS GOT AS LOW AS THE MID 20S IN THE TRIAD
REGION...RESULTING IN MINIMUM RH VALUES BELOW 20 PERCENT.

THIS DRY AIR MASS AND A LIGHT/CALM WIND REGIME THIS EVENING HAS
ALLOWED TEMPS TO DROP INTO THE 50S WITH A FEW 40S ALREADY OCCURRING
BEFORE 10 PM AT THE NORMALLY COLDER LOCATIONS. MIN TEMPS FORECAST
APPEARS ON TARGET (40-45 DEGREES WITH UPPER 30S IN THE NORMALLY
COLDER LOCATIONS).

MONDAY AND MONDAY NIGHT...MID-UPPER LEVEL RIDGE BUILDS INTO THE SE
U.S. FROM THE LOWER MS VALLEY. 00Z 850MB TEMP ANALYSIS DEPICTS TEMPS
1-2 DEG C WARMER THAN PROJECTED BY THE MODELS OVER THE MID SOUTH-
LOWER MS VALLEY (20 DEG C AT LITTLE ROCK). FLOW AROUND THE 850MB
ANTI-CYCLONE SHOULD ADVECT THIS AIR MASS INTO NC MONDAY. MODEL
THICKNESS PROJECTED TO BE 10-12M HIGHER THAN THIS AFTERNOON THANKS
TO THIS WARMER LAYER. HOWEVER MODEL SOUNDINGS SUGGEST THAT LOW-MID
LAYER INVERSION WILL LIMIT MIXING OF THIS WARMER AIR TO THE SURFACE.
THUS EXPECT MAX TEMPS IN THE 70S WITH LOWER 80S ONCE AGAIN ACROSS
THE SOUTH. WITH HIGH PRESSURE AT THE SURFACE AND ALOFT MONDAY
NIGHT...EXPECT ANOTHER DRY AND SEASONABLY COOL NIGHT. MIN TEMPS IN
THE 40S TO AROUND 50.

&&

.SHORT TERM /TUESDAY THROUGH WEDNESDAY NIGHT/...
AS OF 210 PM SUNDAY...

A WARM AND DRY TUESDAY AS THE UPPER LEVEL RIDGE AXIS GRADUALLY
PUSHES TO OUR EAST DURING THE DAY RESULTING IN INCREASING SW FLOW
ALOFT. THE SURFACE HIGH WILL BE WELL OFFSHORE WITH A GOOD SW RETURN
FLOW EXPECTED. LOW LEVEL THICKNESSES AND NEARLY FULL SUN AND SW FLOW
SUGGEST HIGHS NEAR THE WARMEST MOS STATISTICAL GUIDANCE (MES). THE
NEXT COLD FRONT IS EXPECTED TO APPROACH LATE TUESDAY NIGHT AND EARLY
WEDNESDAY. THE PRESSURE GRADIENT IS EXPECTED TO TIGHTEN ENOUGH THAT
WAA SHOULD BEGIN BEFORE DAWN WEDNESDAY ALLOWING THE TEMPERATURES TO
REMAIN MILDER THAN AVERAGE. IN ADDITION... INCREASING LOW LEVEL
MOISTURE WILL LEAD TO DEW POINTS IN THE 50S... KEEPING IT MILDER AS
WELL.

THE COLD FRONT IS SLATED TO MOVE ACROSS THE STATE WEDNESDAY. DEEP
MOISTURE AND INSTABILITY WILL BE LACKING. A VERY NARROW AXIS OF
MARGINAL LIFT AND MOISTURE SUGGESTS ANY SHOWERS WILL REMAIN
SCATTERED WITH LIGHT QPF. THERE IS EXPECTED TO BE PLENTY OF MID AND
HIGH LEVEL CLOUDINESS IN A NARROW AXIS WITH THE FRONT ITSELF. THIS
WILL TEND TO KEEP THE TEMPERATURES IN CHECK. THE CAA IS EXPECTED TO
BE LAGGING WELL BEHIND THE FRONT AND NOT ARRIVE UNTIL LATER IN THE
DAY. HIGHS SHOULD TOP OUT IN THE 70S EXCEPT AROUND 80 IN THE SE. THE
CHANCE OF SHOWERS WILL LINGER INTO THE EVENING AND OVERNIGHT IN THE
SOUTHERN AND EASTERN ZONES. RESIDUAL CLOUDINESS AND GOOD MIXING WITH
CAA (WIND SHIFT TO THE N-NE) WILL PRECLUDE RADIATIONAL COOLING. CAA
SHOULD LEAD TO LOWS IN THE 40S BY THURSDAY MORNING.

&&

.LONG TERM /WEDNESDAY THROUGH SUNDAY/...
AS OF 245 AM MONDAY...

...FIRST POSSIBLE FROST OF THE SEASON THIS WEEKEND...

WEDNESDAY THROUGH THURSDAY: A FRONTAL SYSTEM WILL APPROACH THE AREA
ON WEDNESDAY ASSOCIATED WITH A LOW PRESSURE SYSTEM OVER WESTERN
QUEBEC. THE UPPER LEVEL RIDGE THAT HAD BROUGHT US THE UNSEASONABLY
WARM WEATHER WILL MOVE OFFSHORE...REPLACED BY AN EASTERN CONUS
TROUGH THAT WILL SET THE STAGE FOR A COOLING TREND FOR THE END OF
THE WEEK. TIMING IS GENERALLY GOOD FOR A FRONTAL PASSAGE WEDNESDAY
EVENING OR EARLY THURSDAY MORNING. THE CURRENT RUN OF THE GFS IS
SLIGHTLY FASTER THAN THE ECMWF. THERE IS NOT A LOT OF MOISTURE WITH
THIS SYSTEM AND EVEN LESS INSTABILITY. SHEAR VALUES WILL BE DECENT
IN THE 0-6 KM RANGE...BUT THE UPPER LEVEL JET DYNAMICS ARE FAIRLY
WEAK FOR THIS TIME OF YEAR. THEREFORE ONLY EXPECTING LIGHT SHOWERS
WITH THE FRONTAL PASSAGE WITH QPF VALUES PLUS OR MINUS A TENTH OF AN
INCH. TEMPERATURES WEDNESDAY SHOULD STILL ACHIEVE MID 70S TO LOW 80S
AS FROPA WILL BE LATER IN THE DAY. WITH CLOUDS STILL AROUND
WEDNESDAY NIGHT EXPECT LOWS TO ONLY MAKE IT DOWN TO THE MID 40S NW
TO MID 50S SE. THESE COULD EVEN BE HIGHER IF THE SLOWER TIMING OF
THE ECMWF VERIFIES. THE FRONT WILL CONTINUE SOUTHEASTWARD ON
THURSDAY AND GRADUAL CLEARING WILL OCCUR BEHIND THE FRONT. COLD AIR
ADVECT WILL BEGIN IN EARNEST WITH MAX TEMPS ONLY REACHING THE LOW
60S NORTH TO UPPER 60S SOUTH.

THURSDAY NIGHT THROUGH SUNDAY: A COLD AND DRY PERIOD WILL BEGIN
THURSDAY NIGHT AS THE UPPER LEVEL TROUGH BEGINS TO DEEPEN AND A
STRONG UPPER LEVEL LOW MOVES THROUGH THE GREAT LAKES AND INTO
WESTERN NY. AS COLD AIR ADVECTION CONTINUES AND THICKNESS VALUES
DROP...MAX TEMPERATURES WILL SUFFER...5-10 DEGREES BELOW NORMAL IN
THE NORTH TO NEAR NORMAL HIGHS IN THE SOUTH (LOW TO UPPER 60S). LOWS
WILL DROP INTO THE UPPER 30S TO LOW 40S BY SATURDAY MORNING. AS THE
AXIS OF THE UPPER LEVEL TROUGH APPROACHES NC...A SURFACE HIGH TO THE
WEST OF THE APPALACHIANS WILL SET UP NORTHERLY SURFACE FLOW AND HELP
TO DROP TEMPS FURTHER THIS WEEKEND WITH HIGHS ONLY IN THE 50S AND
THE FIRST FROST OF THE SEASON VERY POSSIBLE ON SUNDAY MORNING. WHILE
SKIES WILL CLEAR...THE SURFACE WINDS MAY HELP TO KEEP TEMPERATURES
UP SLIGHTLY FROM POTENTIAL LOWS SUGGESTED BY THICKNESS VALUES WITH
OPTIMAL RADIATIONAL COOLING CONDITIONS. EXPECT LOW TO MID 30S OVER
MUCH OF THE AREA SUNDAY MORNING.

&&

.AVIATION /06Z MONDAY THROUGH FRIDAY/...
AS OF 200 AM SUNDAY...

UNDER THE INFLUENCE OF DRY AND SUBSIDENT RIDGING ALOFT AND AT THE
SURFACE...VFR CONDITIONS WILL PREVAIL THROUGH THE TAF PERIOD. CALM
TO LIGHT AND VARIABLE WINDS WILL GRADUALLY VEER TO SSW BY THIS
AFTERNOON...PARTICULARLY AT WESTERN SITES...IN RETURN FLOW AROUND
THE OFFSHORE-DRIFTING SURFACE HIGH.

OUTLOOK: SHALLOW MOISTURE JUST ABOVE THE SURFACE...IN STRENGTHENING
SSW FLOW AHEAD OF AN APPROACHING COLD FRONT...WILL RESULT IN A
CHANCE OF LOW STRATUS EARLY WED MORNING. THEN THE COLD FRONT...AND
ACCOMPANYING CHANCE OF SHOWERS AND SUB-VFR CONDITIONS...WILL MOVE
EAST ACROSS CENTRAL NC WED...INTO WED EVENING AT EASTERN SITES.

&&

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

&&

$$

SYNOPSIS...MWS
NEAR TERM...WSS
SHORT TERM...PWB
LONG TERM...ELLIS
AVIATION...MWS



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