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-- Discussion containing changed information from previous version are highlighted. --
000
FXUS62 KRAH 301802
AFDRAH

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RALEIGH NC
100 PM EST FRI JAN 30 2015

.SYNOPSIS...BREEZY NORTHWESTERLY WINDS TODAY WILL GIVE WAY TO HIGH
PRESSURE BUILDING IN FROM THE WEST OVER THE WEEKEND.  A LOW PRESSURE
SYSTEM WILL THEN CROSS THE REGION LATE SUNDAY AND MONDAY.

&&

.NEAR TERM /THROUGH TODAY/...
AS OF 1030 AM FRIDAY...

AN UPPER TROUGH IS CURRENTLY SWINGING ACROSS THE AREA WITH A COLD
FRONT DEPARTING TO THE EAST. STRONG POST-FRONTAL COLD ADVECTION IS
SETTING UP ACROSS THE AREA THIS MORNING WITH THE 12Z KGSO RAOB
SHOWING AN ALREADY DEEP MIXED LAYER UP TO 5000 FT AND A GUST TO 38KT
AT KGSO.  NORTHWESTERLY WINDS ARE STEADILY INCREASING AND GUSTS ARE
STARTING TO REACH THE UPPER 20S TO AROUND 30KT AREAWIDE. IT APPEARS
THE GUSTS WILL PEAK LATE THIS MORNING AND VERY EARLY AFTERNOON...AS
MUCH AS 30-35KT IN SOME AREAS...BEFORE THE PRESSURE GRADIENT BEGINS
TO SLOWLY WEAKEN.  MEANWHILE...REGIONAL VIS SHOWS A FEW STREAMS OF
MOISTURE (JUST ABOVE 850MB PER KGSO/KRNK RAOBS) SPILLING EAST ACROSS
THE NORTHERN CWA.  THE STRONG INVERSION JUST ABOVE AND STRENGTHENING
SUBSIDENCE BEHIND THE UPPER TROUGH WILL KEEP THIS MOISTURE TRAPPED
AND THE STRATOCU FAIRLY SHALLOW...SO WE MAINLY EXPECT SKIES VARYING
FROM PARTLY CLOUDY SOUTHWEST TO A PERIOD OF MOSTLY CLOUDY NORTHEAST.
 DRY ADIABATIC MIXING TO 850MB WHILE ACCOUNTING FOR SOME DOWNSLOPE
WARMING YIELDS HIGHS IN THE 43-50 RANGE...ONLY ABOUT 3-4 DEGREES OFF
CURRENT READINGS.  -BLS



 &&

.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 /18Z FRIDAY THROUGH WEDNESDAY/...
-- Changed Discussion --
AS OF 100 PM FRIDAY...

STRONG NORTHWESTERLY WIND GUSTS (CROSSWINDS FOR MANY RUNWAYS) OF
ANYWHERE FROM 25KT TO 35KT ARE OCCURRING ACROSS CENTRAL NC THIS
MORNING IN THE WAKE OF A DEPARTING COLD FRONT.  THESE GUSTS WILL
CONTINUE THIS AFTERNOON AND MAY LINGER INTO THE EVENING HOURS BEFORE
SUBSIDING AFTER MIDNIGHT. SCATTERED STRATOCU WILL BE MOSTLY
CONCENTRATED FROM KRDU NORTH AND EAST BUT REMAIN ABOVE 5000 FT THIS
AFTERNOON. OTHERWISE...HIGH PRESSURE WILL BUILD IN FROM THE WEST
THROUGH SATURDAY AND VFR CONDITIONS ARE EXPECTED TO PREVAIL.

BEYOND THE 12Z VALID TAF PERIOD... VFR CONDITIONS WILL CONTINUE
THROUGH EARLY SUNDAY.  A LOW PRESSURE SYSTEM WILL CROSS THE CENTRAL
APPALACHIANS SUNDAY NIGHT...WITH A CHANCE OF RAIN AND SUB-VFR
CONDITIONS FROM LATE SUNDAY AFTERNOON THROUGH MONDAY AFTERNOON.
HIGH PRESSURE AND VFR CONDITIONS WILL RETURN FOR TUESDAY...WITH
ANOTHER SYSTEM TO APPROACH THE REGION ON WEDNESDAY.
-- End Changed Discussion --

&&

.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/BLS
SHORT TERM...DJF/CBL
LONG TERM...CBL
AVIATION...BLS
FIRE WEATHER...DJF