-- Discussion containing changed information from previous version are highlighted. --
000
FXUS62 KRAH 230608
AFDRAH

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RALEIGH NC
208 AM EDT THU MAY 23 2013

.SYNOPSIS...
-- Changed Discussion --
A TROUGH ALOFT AND ACCOMPANYING PRE-FRONTAL SURFACE PRESSURE TROUGH
WILL MOVE INTO CENTRAL NC TODAY...FOLLOWED BY THE PASSAGE OF A COLD
FRONT TONIGHT. CANADIAN HIGH PRESSURE WILL THEN EXPAND ACROSS OUR
REGION THROUGH THE HOLIDAY WEEKEND.
-- End Changed Discussion --

&&

.NEAR TERM /THROUGH TONIGHT/...
AS OF 1010 PM WEDNESDAY...

ANY SHOWERS AND THUNDERSTORMS FROM THIS AFTERNOON AND EVENING
ASSOCIATED WITH THE SEA BREEZE AND OUTFLOW ACROSS THE EASTERN
TWO-THIRDS OF THE AREA HAVE DISSIPATED WITH THE LOSS OF DAYTIME
HEATING AND RESULTANT STABILIZING BOUNDARY LAYER. CONVECTION THAT
FIRED ACROSS THE HIGHER TERRAIN TODAY... HAS GENERALLY STAYED TO THE
WEST OF THE REGION WITH A 15 TO 20 KT SOUTH-SOUTHWESTERLY MEAN
STEERING FLOW. HOWEVER... A WEST-NORTHWESTERLY OUTFLOW... GENERATED
FROM THESE CLUSTERS OF SHOWERS AND STORMS THAT ORIGINATED ALONG THE
HIGHER TERRAIN... HAS FINALLY ALLOWED FOR THE DEVELOPMENT OF SHOWERS
AND STORMS ACROSS OUR FAR NORTHWESTERN REACHES OF OUR CWA... ALONG
THE OUTFLOW. THINK THIS OUTFLOW SHOULD SUPPORT AT LEAST SCATTERED
SHOWERS AND ISOLATED THUNDERSTORMS ACROSS OUR WESTERN PIEDMONT
THROUGH 06/07Z... GIVEN 500 TO 1000 J/KG OF SURFACE BASED CAPE.
THEREAFTER... EXPECT BOUNDARY LAYER COOLING SHOULD YIELD A TREND TO
ISOLATED SHOWERS AT BEST. ANY SIGNIFICANT S/W ENERGY ROTATING
THROUGH THE CYCLONIC FLOW ALOFT FROM THE APPROACHING MID LEVEL
TROUGH WELL TO THE WEST OF THE AREA... INVOF THE MS RIVER THIS
EVENING... IS EXPECTED TO PASS TO THE WEST AND NORTH OF THE REGION
THUS... PLAN TO TRIM POPS TO SLIGHT CHANCE BY EARLY THURSDAY MORNING
ACROSS THE ENTIRE CWA. THIS IS SUPPORTED BY THE LATEST HRRR.
HOWEVER... ITS WORTH NOTING THE LATEST HRRR DOES SHOW SOME SHOWERS
CURRENTLY OFF THE CAROLINA COAST MOVING ONSHORE OVERNIGHT ACROSS THE
COASTAL PLAIN. CURRENT HI-RES MODELS GENERALLY SHOW THIS PRECIP
REMAINING JUST TO THE EAST OF OUR AREA. THUS... WILL KEEP ONLY
SLIGHT CHANCE POPS ACROSS OUR EAST AS WELL. OVERNIGHT LOWS IN THE
MID TO UPPER 60S ARE STILL EXPECTED... WITH GENERALLY PATCHY FOG
(FOG... AT LOCATIONS THAT ARE PICKING UP DECENT SHOWERS/STORMS
ACROSS THE TRIAD NOW) AND WIDESPREAD LOW STATUS.

&&

.SHORT TERM /THURSDAY AND THURSDAY NIGHT/...
AS OF 300 PM WEDNESDAY...

A COLD FRONT WILL APPROACH CENTRAL NC FROM THE WEST ON FRIDAY. AS A
DEEP 500 MB TROUGH DIGS SOUTHWARD THROUGH THE OHIO VALLEY. AS FAR AS
TIMING IS CONCERNED...SHOWERS AND THUNDERSTORMS AHEAD OF FRONT WILL
BEGIN TO AFFECT THE TRIAD BY LATE THURSDAY MORNING AND CONTINUE TO
PROGRESS SLOWLY EASTWARD ACROSS THE CWA BY AFTERNOON/EVENING. SEVERE
POTENTIAL WITH THIS SYSTEM WILL BE GREATER THAN THE PAST COUPLE OF
DAYS BUT STILL LOOKS VERY LOW. EFFECTIVE SHEAR WILL BE ABOUT 20
KNOTS SUGGESTING MORE LINEAR THUNDERSTORMS. THIS IS SUPPORTED BY THE
STRAIGHT HODOGRAPHS SHOWN BY NAM FORECAST SOUNDINGS. MID LEVEL LAPSE
RATES WILL BE WEEK ALTHOUGH 1000 ML CAPE OF THE TALL AND SKINNY
VARIETY COULD BE REALIZED BY AFTERNOON. LATER IN THE EVENT DYNAMICS
IMPROVE AS A 30 KNOT 850MB APPROACHES THE NORTHWEST. IT IS UNCLEAR
AT THIS TIME WHETHER OR NOT CONVECTION WILL BE TOO FAR TO THE EAST
TO TAKE ADVANTAGE OF THE INCREASED SHEAR. STORMS LINGERING BACK
TOWARDS THE WEST MAY BE ABLE TO TAKE ADVANTAGE OF AN INCREASED AXIS
OF DCAPE EXPECTED TO MOVE THROUGH THE CWA JUST AFTER 00Z FRIDAY.
THEREFORE IF WE DO ENCOUNTER SEVERE WEATHER TOMORROW...IT WILL MOST
LIKELY BE DAMAGING WINDS AND NOT HAIL. FOR NOW SPC HAS KEPT THE
RALEIGH AREA OUT OF THE SLIGHT RISK AREA FOR TOMORROW. PRECIPITABLE
WATERS WILL BE SIMILAR TO TODAY NEAR 1.5 INCHES BUT QPF WITH FRONTAL
PASSAGE IS ONLY EXPECTED TO BE BETWEEN A QUARTER AND A HALF OF AN
INCH WITH LOCALLY HEAVIER AMOUNTS POSSIBLE IN THUNDERSTORMS.
LOCALIZED FLOODING COULD BE AN ISSUE...ESPECIALLY IN URBAN AREAS
UNDER SLOW MOVING OR TRAINING THUNDERSTORMS. CLOUD COVER SHOULD
OVERSPREAD THE AREA FAIRLY EARLY TOMORROW AND THUS WILL TREND
TOWARDS THE COOLER MET GUIDANCE WITH HIGH TEMPERATURES. UPPER 70S IN
THE NORTHWEST TO LOW 80S SOUTHEAST. AS THE LOWER ATMOSPHERE BEGINS
TO DRY OUT LOW TEMPERATURES IN THE TRIAD SHOULD DIP INTO THE UPPER
50S IN THE NORTHWEST FOR THE FIRST TIME IN SEVERAL DAYS BUT FURTHER
TO THE SOUTHEAST LOWS WILL REMAIN IN THE MIDDLE 60S AS THE FRONT IS
EXPECTED TO FULLY MOVE THROUGH THE EAST UNTIL CLOSER TO 6Z ON FRIDAY.

&&

.LONG TERM /FRIDAY THROUGH WEDNESDAY/...
AS OF 310 PM WEDNESDAY...

FRIDAY THROUGH SATURDAY NIGHT...

A DEEP UPPER LEVEL TROUGH WILL SWING ACROSS CENTRAL NC FRIDAY AND
EXIT THE REGION FRIDAY NIGHT. MAY SEE A FEW INSTABILITY SHOWERS
WITH THE PASSAGE OF THIS SYSTEM HOWEVER MODEL RH CROSS SECTIONS
DEPICT THE AIR MASS DRYING OUT APPRECIABLY ABOVE 5000-8000FT BY
EARLY AFTERNOON. FOR NOW WILL LIMIT POPS TO SLIGHT CHANCE. OTHERWISE
BRISK NW FLOW WILL ADVECT COOLER MORE STABLE AIR INTO THE REGION.
SUSTAINED NW WINDS 10-15 MPH WITH GUSTS AROUND 25 MPH PROBABLE. THE
ARRIVAL OF THIS AIR MASS WILL RESULT IN COOLER CONDITIONS WITH
AFTERNOON MAX TEMPS IN THE LOWER 70S NORTH TO UPPER 70S FAR SE.

FRIDAY NIGHT...SKIES WILL CLEAR EARLY THOUGH A STEADY NW SFC WIND
WILL BE SLOW TO SUBSIDE. LOW LEVEL THICKNESSES CLUSTERING AROUND
1340M. HISTORICALLY...THIS SUGGEST MIN TEMPS NEAR 40-LOWER 40S.
FAVOR THE HIGH END OF THIS REGION DUE TO EXPECTED MIXING WELL INTO
THE NIGHT. MIN TEMPS 45-50.

SATURDAY INTO SATURDAY NIGHT...CANADIAN HIGH PRESSURE OVER THE LOWER
GREAT LAKES WILL BUILD/EXTEND INTO OUR REGION SATURDAY INTO SATURDAY
NIGHT. THIS WEATHER SYSTEM WILL RESULT IN A DRY WEATHER PATTERN WITH
BELOW NORMAL TEMPS. AFTERNOON THICKNESSES PROJECTED TO BE ABOUT 35M
BELOW NORMAL...SUPPORTIVE OF TEMPS CLOSE TO 10 DEGREES BELOW NORMAL.
ALLOWING FOR WARMTH FROM LATE MAY SUN...EXPECT AFTERNOON HIGH TEMPS
IN THE MID-UPPER 70S. MOS GUIDANCE LIKELY TRENDING TOWARD
CLIMATOLOGY BY SATURDAY NIGHT. WITH SFC RIDGE OVERHEAD AND CORE OF
LOW LEVEL DRY ACROSS THE REGION...TEMPS SHOULD COOL QUICKLY INT EH
EVENING THEN STABILIZE. MODEL RH CROSS SECTIONS HINT AT INCREASING
MID-HIGH LEVEL CLOUDS OVERNIGHT INTO EARLY SUNDAY. FIRST GLANCE
SUGGEST THAT CLOUD COVERAGE MAY INITIALLY BE THIN AND SPOTTY SO
COULD SEE DECENT NOCTURNAL COOLING. FAVOR MIN TEMPS A FEW DEGREES
COOLER THAN PREVIOUS FORECAST WITH MIN TEMPS IN THE MID-UPPER 40S.

SUNDAY INTO MONDAY...DEEP UPPER LEVEL LOW OVER NORTHERN NEW
ENGLAND-CANADIAN MARITIME PROVINCES WILL MAINTAIN A NW FLOW OVER THE
FORECAST AREA SUNDAY. WEAK PERTURBATIONS IN THIS FLOW ALOFT WORKING
WITH AVAILABLE MOISTURE WILL LIKELY CAUSE AN INCREASE IN MID-HIGH
LEVEL CLOUDINESS SUNDAY INTO SUNDAY NIGHT...MORE SO ACROSS OUR WEST
AND SOUTH SECTIONS AND LEAST IN THE NE. A MODIFYING AIR MASS WILL
LEAD TO SLIGHTLY WARMER CONDITIONS WITH AFTERNOON TEMPS IN THE
MID-UPPER 70S...AND AND MIN TEMPS IN THE MID 50S. 00Z ECMWF SUGGEST
THAT THERE MAY BE ENOUGH AMPLITUDE TO AN APPROACHING MID LEVEL
TROUGH TO WARRANT A SLIGHT-SMALL CHANCE POP ACROSS CENTRAL NC MONDAY
AFTERNOON-MONDAY EVENING.

TUESDAY INTO WEDNESDAY...AN AMPLIFYING MID-UPPER LEVEL RIDGE OVER
THE EASTERN HALF OF THE U.S. WILL PLACE CENTRAL NC BACK INTO A
SUMMER-LIKE PATTERN WITH A SFC HIGH ANCHORED OFFSHORE BUT EXTENDING
WESTWARD INTO THE SE U.S. THIS SUGGEST A RETURN TO WARM AND SLIGHTLY
HUMID CONDITIONS WITH AFTERNOON TEMPS IN THE LOW-MID 80S AND MIN
TEMPS 60-65. CONVECTION APPEARS TO BE DIURNALLY DRIVEN...ADDED BY A
SEABREEZE TO SE AND  NW FLOW ALOFT SENDING CONVECTION OFF THE HIGHER
TERRAIN INTO THE WESTERN PIEDMONT. POPS NO HIGHER THAN SLIGHT
CHANCE-SMALL CHANCE AT THIS TIME...CONFINED TO THE AFTERNOON-EVENING
HOURS.

&&

.AVIATION /06Z THURSDAY THROUGH MONDAY/...
-- Changed Discussion --
AS OF 205 AM THURSDAY...

A LINE OF SHOWERS AND ISOLATED STORMS THAT EARLIER AFFECTED THE
TRIAD TERMINALS WILL CONTINUE TO MOVE SLOWLY EASTWARD AT AROUND 10
MPH...AFFECTING THE KRDU AREA BETWEEN 8-10Z. A GRADUAL
WEAKENING/DISSIPATING TREND SHOULD OCCUR AS THE AIR MASS CONTINUES
TO STABILIZE WITH NOCTURNAL COOLING...HOWEVER...SO CONFIDENCE OF THE
CONVECTION REACHING THE KFAY AND KRWI AREAS IS LOW. OTHERWISE...A
CONTINUED MOIST AIR MASS WILL PROMOTE A HIGH CHANCE OF LIFR-IFR
CEILINGS THIS MORNING...THOUGH WITH RELATIVE LOWEST CHANCES - AROUND
60 PERCENT - AT TRIAD TERMINALS. THESE CEILINGS WILL LIFT AND
SCATTER TO VFR WITH HEATING THROUGH MIDDAY. HEATING OF THE MOIST AIR
MASS WILL ALSO CAUSE SCATTERED TO NUMEROUS SHOWERS AND STORMS TO
DEVELOP THIS AFTERNOON...AND THESE WILL LIKELY CONTINUE UNTIL A COLD
FRONT SWEEPS ACROSS CENTRAL NC FROM WEST TO EAST BETWEEN 04-06Z AT
TRIAD TERMINALS...TO 09-12Z AT EASTERN ONES. AREAS O FOG OR LOW
STRATUS WILL ALSO BE POSSIBLE AHEAD OF THE COLD FRONT...MOST LIKELY
AT KFAY AND KRWI BETWEEN 06-12Z.

VFR CONDITIONS WILL OTHERWISE PREVAIL IN CANADIAN HIGH PRESSURE
THROUGH THE HOLIDAY WEEKEND.
-- End Changed Discussion --

&&

.CLIMATE...
MORNING LOW TEMPERATURES ON THE 25TH AND 26TH ARE EXPECTED TO BE A
FEW DEGREES SHY OF RECORD MIN TEMPS FOR THE DATE.

RECORD MIN TEMP/YEAR SET      MAY 25TH            MAY 26TH

RDU                           43 / 1967           43 / 1979

GSO                           43 / 1956           42 / 1930


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

&&

$$

SYNOPSIS...MWS
NEAR TERM...BSD
SHORT TERM...ELLIS
LONG TERM...WSS
AVIATION...MWS
CLIMATE...RAH