Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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000
FXUS62 KRAH 301136
AFDRAH

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RALEIGH NC
636 AM EST FRI JAN 30 2015

.SYNOPSIS...FOLLOWING A COLD FRONT MOVING THROUGH CENTRAL NORTH
CAROLINA THIS MORNING AND OFFSHORE BY AFTERNOON...HIGH PRESSURE
BUILDS OVER THE REGION FROM THE NORTHWEST. THE HIGH MOVES OFFSHORE
SATURDAY NIGHT INTO SUNDAY. A LOW PRESSURE SYSTEM SHOULD MOVE INTO
THE REGION BY SUNDAY NIGHT.

&&

.NEAR TERM /THROUGH TODAY/...
AS OF 300 AM FRIDAY...

A COLD FRONT WAS SLOWLY MOVING ACROSS THE STATE EARLY THIS
MORNING...AND ALL OF THE GUIDANCE SUGGESTS STEADY PROGRESS WITH THE
FRONT AS IT MOVES THROUGH CENTRAL NORTH CAROLINA THIS MORNING AND
OFFSHORE BY EARLY AFTERNOON. JUST BEHIND THE FRONT...WATER VAPOR
IMAGERY SHOWS A GOOD DRY PUNCH MOVING ACROSS THE NORTH CAROLINA
MOUNTAINS...AS AN UPPER TROUGH EXTENDING FROM HUDSON BAY THROUGH THE
GREAT LAKES AND INTO THE OHIO VALLEY MOVES EAST. THIS MORNING...THE
NEAR-TERM GUIDANCE VARIES ON THE POTENTIAL FOR RENEWED PRECIPITATION
ACCOMPANYING THE FRONT AND THE LEFT-ENTRANCE REGION OF A 130KT 250MB
JET THAT WILL BE OVER OR NEAR SOUTHERN PARTS OF CENTRAL NORTH
CAROLINA THIS MORNING INTO THE AFTERNOON. BEHIND THE FRONT...850MB
THETA-E VALUES FALL SHARPLY AND K INDICES GO NEGATIVE...BUT WITH THE
FRONT THERE IS WEAK SPEED CONVERGENCE ON THE 295K SURFACE OF THE GFS
ESPECIALLY TOWARD THE SANDHILLS AND SOUTHERN COASTAL PLAIN. AS OF
THIS WRITING A FEW...FAINT ECHOES WERE NOTED ON THE KRAX WSR-88D
JUST EAST OF KGSO TOWARD KBUY...BUT BETTER SURFACE DEW POINTS WERE
OFF TO THE EAST AND SOUTHEAST TOWARD KETC...KFAY...AND KCTZ. PLAN TO
AT LEAST HAVE A SLIGHT CHANCE OF EARLY MORNING SHOWERS MAINLY ALONG
AND EAST OF ABOUT U.S. 1...WITH A CHANCE IN SOME LOCATIONS TOWARD
INTERSTATE 95 WHERE THE LOW-LEVEL MOISTURE WILL BE GREATER AS THE
FRONT MOVES THROUGH WITH THE UPPER SUPPORT.

SKIES SHOULD START TO CLEAR IN GENERAL BEHIND THE FRONT...THOUGH THE
NAM AND GFS BUFR SOUNDINGS ESPECIALLY FROM THE TRIANGLE NORTH AND
EAST SUGGEST A PERIOD OF BROKEN STRATOCU OR SHALLOW CU DURING THE
EARLY TO MID AFTERNOON AS THE TROUGH AXIS AND MODERATE VORTICITY
MOVE THROUGH CENTRAL NORTH CAROLINA. IN FACT...THE GFS BUFR
SOUNDINGS NEAR KRDU IN PARTICULAR WOULD SUGGEST ENOUGH LIFT...ALBEIT
SHALLOW...TO GET A PARCEL A LITTLE COLDER THAN -10C AND POSSIBLY
PROVIDE FOR VIRGA OR A SPRINKLE. WILL LEAVE THE AFTERNOON FORECAST
DRY...THOUGH SHOW A PERIOD OF GREATER CLOUD COVER FROM THE TRIANGLE
NORTH AND EAST DURING A PART OF THE AFTERNOON.

IN ADDITION...THE SURFACE GRADIENT TIGHTENS BEHIND THE FRONT WITH
850MB WINDS OF 30 TO 35KT AND 925MB WINDS DIMINISHING FROM NEAR 40KT
EARLY THIS MORNING TO AROUND 30KT BY 18Z. PURE LIFT FROM THE GFS
BUFR SOUNDINGS UP THE DRY ADIABAT WOULD SUGGEST WIND GUSTS ABOVE
30KT POSSIBLE...BUT THE NAM AND RAP SOUNDINGS SUGGEST A LITTLE LOWER
GUSTS AND MOMENTUM TRANSFER FIELDS FROM ALL THREE MODELS ON BUFKIT
CAP GUSTS AT 30KT. WILL KEEP THE GUSTS TO 30KT OR 35MPH IN THE
FORECAST WHILE ANTICIPATING A SPOT OR THREE TO BE BRIEFLY A LITTLE
ABOVE THAT. THICKNESSES IN MANY PARTS OF CENTRAL NORTH CAROLINA FALL
DURING THE DAY...AND 1000-850MB THICKNESSES WOULD SUGGEST A LEAN
TOWARD THE SLIGHTLY COOLER MET MOS FOR HIGHS TODAY. BASED ON CURRENT
READINGS AND EXPECTED SUN OFFSET BY COOL ADVECTION...WILL HAVE HIGHS
FROM THE MID 40S TO AROUND 50 AND SHADING TOWARD THE MET MOS.

&&

.SHORT TERM /TONIGHT THROUGH SUNDAY NIGHT/...
AS OF 300 AM FRIDAY...

WINDS WILL DIMINISH TONIGHT UNDER CLEAR SKIES. THERE SHOULD BE
ENOUGH OF A GRADIENT FOR AT LEAST A SLIGHT STIR TO THE WIND THROUGH
THE NIGHT...AS 925MB WINDS REMAIN TO 35KT. SURFACE DEW POINTS SHOULD
CONTINUE TO DRY...AND 1000-850MB THICKNESSES WOULD SUGGEST LOWS FROM
THE TEENS TO THE LOWER 20S. THIS WILL ESSENTIALLY BE THE FORECAST
FOR LOWS OVERNIGHT...19 TO 20 IN THE NORTHWEST PIEDMONT TO NEAR 25
TOWARD KFAY...CLOSE TO THE AVERAGE OF THE MET AND MAV MOS. ON
SATURDAY...925MB WINDS DIMINISH TO AROUND 15KT BY 18Z...AND BUFR
SOUNDINGS FROM BOTH THE NAM AND GFS SUGGEST A FEW WIND GUSTS IN THE
TEENS KNOTS WITH INITIAL MIXING BEFORE THE WINDS DIMINISH AS HIGH
PRESSURE CONTINUES TO BUILD IN FROM THE NORTHWEST.

SATURDAY AFTERNOON...A FLAT RIDGE AXIS ALOFT GETS CLOSE TO CENTRAL
NORTH CAROLINA AS SOME MID-LEVEL VORTICITY ADVECTION MOVES INTO AND
ACROSS CENTRAL NORTH CAROLINA DURING THE LATE AFTERNOON AND
NIGHTTIME HOURS...FORECAST BY BOTH THE GFS AND NAM. GFS AND NAM BUFR
SOUNDINGS SUGGEST INCREASING UPPER-LEVEL MOISTURE SUCH THAT
INCREASING HIGH CLOUDS SHOULD GRADUALLY OCCUR FROM SATURDAY
AFTERNOON INTO SATURDAY NIGHT. WITH MOST IF NOT ALL OF CENTRAL NORTH
CAROLINA EXPECTED TO BE MOSTLY CLOUDY BY THE MIDDLE OF THE NIGHT
SATURDAY...OVERNIGHT LOWS SHOULD BE WARMER...MID TO UPPER 20S IN THE
NORTHERN COASTAL PLAIN TO AROUND 30 ELSEWHERE. -DJF

MINOR MID-LEVEL IMPULSES EMANATING FROM THE UPPER TROUGH/CLOSED LOW
OVER THE SOUTHWEST US WILL GET KICKED EASTWARD...IN ADVANCE OF AN
AMPLIFYING NORTHERN STREAM OVER THE CENTRAL PLAINS...ON SUNDAY.
ASSOCIATED CYCLOGENESIS WILL TRACK EASTWARD ACROSS THE LOWER MS
VALLEY/TN VALLEY ON SUNDAY...THEN ACROSS THE CAROLINAS/VIRGINIA
SUNDAY NIGHT BEFORE MOVING OFF THE MID-ATLANTIC COAST MONDAY
MORNING.

NWP MODEL GUIDANCE CONTINUES TO EXHIBIT CONSIDERABLE SPREAD WITH THE
TRACK OF THE SURFACE LOW AS IT MOVES THROUGH THE REGION SUNDAY
NIGHT...WITH A DEFINITE NORTHWARD SHIFT OBSERVED IN THE LATEST
00Z/30 MODEL ITERATION. THIS RESULTS IN A SLIGHTLY SLOWER/DELAYED
ONSET OF PRECIP ACROSS THE AREA LATE SUNDAY AFTERNOON AND
EVENING...BUT IMPORTANTLY DISPLACES THE HEAVIER QPF NORTH OF THE
AREA.

AS SUCH...SUNDAY WILL END UP MOSTLY DRY ACROSS CENTRAL NC WITH
THICKENING CLOUD COVER THROUGH THE AFTERNOON WITH HIGHS RANGING FROM
MID 40S NORTH TO LOWER 50S SOUTH. RAIN CHANCES WILL QUICKLY RAMP UP
SUNDAY EVENING...WITH CATEGORICAL POPS SUNDAY NIGHT...CUTTING OFF
FROM WEST TO EAST MORNING MONDAY AS THE MID-LEVEL DRY SLOT RACES
EASTWARD. ESTIMATED QPF AMOUNTS NOW LOOK TO BE IN THE 0.25-0.50"
RANGE. WITH ONLY WEAK ELEVATED INSTABILITY AT BEST EXPECTED ACROSS
THE COASTAL PLAIN AND WITH THE SURFACE LOW NOW DISPLACED NORTH OF
THE AREA...WILL KEEP OUT THE MENTION OF ANY THUNDER ACROSS THE
EASTERN ZONES.

EXPECT A NON-DIURNAL TEMP TREND SUNDAY NIGHT...WITH LOWS OCCURRING
BEFORE MIDNIGHT...THEN TEMPERATURES WARMING OVERNIGHT OWING TO
STRONG WAA. LOWS SUNDAY NIGHT IN THE LOWER 40S NORTHWEST TO UPPER
40S SOUTHEAST. -CBL

&&

.LONG TERM /MONDAY THROUGH THURSDAY/...
AS OF 300 AM FRIDAY...

MONDAY THROUGH TUESDAY: AGGRESSIVE MID-LEVEL DRY AIR INTRUSION WILL
OVERTAKE THE AREA FROM THE WEST BETWEEN 12 TO 18Z MONDAY IN ADVANCE
OF THE PASSAGE OF THE NORTHERN STREAM TROUGH PASSAGE MONDAY
AFTERNOON. THIS WILL BRING AN ABRUPT END TO PRECIP ACROSS THE AREA
MONDAY MORNING...WITH RAIN/SHOWERS EXITING THE COASTAL PLAIN BY MID
TO LATE MORNING. EQUALLY IMPRESSIVE WILL BE STRONG POST-FRONTAL DRY
COLD AIR ADVECTION REGIME...WITH TEMPERATURES FALLING BY THE
AFTERNOON AS CONTINENTAL POLAR HIGH PRESSURE BUILDS INTO THE AREA
MONDAY NIGHT AND INTO THE DAY ON TUESDAY. IF PROJECTED LOW-LEVEL
THICKNESSES VERIFY AND WE DECOUPLE AS THE SURFACE HIGH MOVES
OVERHEAD... EXPECT LOWS TUESDAY MORNING IN THE UPPER TEENS TO LOWER
20S. UNDER FULL COMPLIMENTS OF SUN...TEMPS TUESDAY WILL STRUGGLE TO
WARM THROUGH THE 30S. HIGHS RANGING FROM MID/UPPER 30S NORTH TO
LOWER 40S SOUTH.

WEDNESDAY THROUGH THURSDAY: MODEL SPREAD REMAINS HIGH WITH THE
EVOLUTION OF THE SLOW MOVING UPPER LOW/TROUGH EJECTING EASTWARD FROM
MEXICO AND SUBSEQUENT DEVELOPMENT OF A LOW PRESSURE AREA TRACKING
ALONG THE SOUTHEAST COAST. IN A COMPLETE ROLE REVERSAL... THE GFS IS
NOW MORE PROGRESSIVE THAN THE EC WITH BRINGING PRECIP BACK INTO THE
AREA DURING THE DAY ON WEDNESDAY...WITH THE EC NEARLY 24 HOURS
SLOWER...DELAYING UNTIL THURSDAY. GIVEN LATER TIMING OF ONSET OF
PRECIP...LOW-LEVEL THICKNESSES CURRENTLY SUPPORT ALL RAIN. HOWEVER
IF FUTURE MODEL RUNS SPEED UP THE TIMING OF THE SYSTEM...ANY PRECIP
INTO THE AREA TUESDAY NIGHT/EARLY WEDNESDAY MORNING COULD BE OF THE
FROZEN VARIETY. WILL CONTINUE TO MONITOR TRENDS...BUT FOR NOW GIVEN
UNCERTAINTY WILL KEEP POPS AT SMALL CHANCE FOR WEDNESDAY AND
THURSDAY WITH A CONTINUATION OF BELOW NORMAL TEMPERATURES.

&&

.AVIATION /12Z FRIDAY THROUGH TUESDAY/...
AS OF 635 AM FRIDAY...

VFR CONDITIONS ARE EXPECTED TO CONTINUE THROUGH THE 12Z VALID TAF
PERIOD. A COLD FRONT MOVES THROUGH CENTRAL NORTH CAROLINA THIS
MORNING WHICH WILL RESULT IN RAPIDLY VEERING WINDS TO THE NORTHWEST
WITH SPEEDS INCREASING TO GUSTS AROUND 30KT BY LATE MORNING.
ALREADY...THE WIND HAD GUSTED TO 26KT AT KINT. WHILE THE GFS MODEL
SHOWS THE POTENTIAL FOR WIND GUSTS A LITTLE ABOVE THAT...THE NAM AND
RAP MODELS ARE LESS...AND MOMENTUM TRANSFER SPEEDS TOP OUT AT MOST
ABOUT 30KT ON ALL THREE WHICH WILL BE THE CAP FOR THE CENTRAL NORTH
CAROLINA TAFS. SHOWERS WERE MOVING AWAY FROM THE COASTAL PLAIN AND...
EXCEPT FOR KRWI INITIALLY...THE TAFS SHOW A DRY FORECAST.

WITH A STRONG MID-LEVEL DISTURBANCE MOVING THROUGH TODAY...THERE IS
THE POTENTIAL FOR SHALLOW CONVECTION...BROKEN VFR CLOUDS AND MAYBE A
LITTLE VIRGA KRDU AND EAST EARLY THIS AFTERNOON. WINDS DIMINISH THIS
EVENING DIURNALLY. HOWEVER...AVIATION INTERESTS SHOULD EXPECT
NORTHWEST WINDS AOA 30KT AT AND ABOVE 2000FT.

BEYOND THE 12Z VALID TAF PERIOD...VFR CONDITIONS CONTINUE INTO
SUNDAY...WITH AREAS OF HIGH CLOUDS MOVING IN SATURDAY NIGHT
GRADUALLY LOWERING SUNDAY. A CHANCE OF RAIN IN THE WESTERN PIEDMONT
SUNDAY AFTERNOON FOLLOWED BY BETTER CHANCES BY SUNDAY NIGHT ALONG
WITH THE POTENTIAL OF SUB-VFR CONDITIONS INTO MONDAY MORNING. VFR
CONDITIONS ARE EXPECTED TO RETURN BY MONDAY AFTERNOON ACCOMPANIED BY
BREEZY CONDITIONS ONCE AGAIN...WITH THE VFR CONDITIONS THEN
CONTINUING THROUGH TUESDAY.

&&

.FIRE WEATHER...
AS OF 300 AM FRIDAY...

WIND GUSTS TO 30KT TODAY...OR TO AROUND 35 MPH...ARE CERTAINLY
POSSIBLE AS THE SURFACE GRADIENT TIGHTENS BEHIND THE COLD FRONT.
SURFACE DEW POINTS WILL FALL BEHIND THE FRONT AS WELL...WITH THE
LOWEST GUIDANCE OF THE RAP SUGGESTING SOME DEW POINTS IN SINGLE
FIGURES LATE IN THE DAY IN THE NORTHWEST PIEDMONT. THE GFS IS
HIGHER...AND THE NAM IS MORE OF A COMPROMISE...WHICH IS CONSISTENT
WITH THE MOS GUIDANCE. BY 00Z SATURDAY...THE GRIDDED FORECAST WILL
SHOW A DEW POINT NEAR 10F IN THE TRIAD...BUT EVEN THERE THE MINIMUM
RELATIVE HUMIDITY IS IN THE UPPER 20S PERCENT. BASED THOSE DEW
POINTS...RECENT RAIN...AND EARLIER FORECAST SERVICE COORDINATION...
WILL FOR NOW HIGHLIGHT THE ADVERSE CONDITIONS OF THE WIND GUSTS IN
THE DISCUSSION OF THE FIRE WEATHER FORECAST.

&&

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

&&

$$

SYNOPSIS...DJF
NEAR TERM...DJF
SHORT TERM...DJF/CBL
LONG TERM...CBL
AVIATION...DJF
FIRE WEATHER...DJF


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