FXUS62 KRAH 031759
AFDRAH
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RALEIGH NC
100 PM EST THU DEC 03 2009
.SYNOPSIS...
HIGH PRESSURE WILL BUILD INTO THE REGION TODAY THROUGH FRIDAY. A
STRONG UPPER LEVEL DISTURBANCE WILL MOVE THROUGH THE REGION SATURDAY
AND SATURDAY NIGHT.
&&
.NEAR TERM /THROUGH TONIGHT/...
AS OF 945 AM THURSDAY...
SURFACE LOW IS LOCATED OVER UPSTATE NY THIS MORNING...WITH ITS MAIN
COLD FRONT NOW OFFSHORE. THE TRUE COLDER AIR IS STILL ALONG AND
WEST OF A SURFACE TROUGH HUGGING THE LEE OF THE APPALACHIANS. OTHER
THAN A LITTLE BIT OF MOISTURE ALONG THE 850MB TROUGH IN THE WEST AND
BELOW THE SUBSIDENCE INVERSION IN THE WAKE OF THE DEPARTING
SYSTEM...THE ATMOSPHERE IS MUCH DRIER WITH PWS FALLING BACK TO
0.5". A FEW FLAT CU POSSIBLE THIS AFTERNOON...AND WITH THE MAIN
UPPER JET AXIS STILL SW-NE ACROSS THE CAROLINAS...WE'LL SEE SOME
HIGH CLOUDS TRACKING ACROSS THE EASTERN HALF OF THE CWA THROUGH
EARLY AFTERNOON. AHEAD OF THE PREVIOUSLY MENTIONED SURFACE TROUGH
WINDS WILL REMAIN SWRLY...AND CONSIDERING A DECENT BUT WEAKENING
PRESSURE GRADIENT OVER THE AREA...A FEW 20KT GUSTS POSSIBLE MAINLY
IN THE E AND NE. HIGHS SHOULD REACH THE 60-65 RANGE ACROSS MUCH OF
THE CWA...BUT AS THE SURFACE TROUGH SHIFTS EAST TODAY...TEMPS MAY
BEGIN TO FALL BY EARLY AFTERNOON AS COLD ADVECTION KICKS IN.
CURRENT TEMPS FAIRLY WELL ON TRACK...AND THIS NON-DIURNAL TYPE TEMP
TREND MAY ONLY BE MARGINALLY NOTICEABLE LATE TODAY IN THE FAR WEST.
-SMITH
PREVIOUS DISCUSSION....
THE TRUE COLD FRONT(AIRMASS CHANGE) IS PROGGED TO EAST OF THE AREA
BY DAYBREAK...STALLING OUT OFFSHORE AS IT WILL PLAY A CRITICAL ROLE
IN THE WEEKENDS NEXT WEATHER SYSTEM. A SECONDARY LEE SIDE SURFACE
TROUGH WILL DEVELOP ACROSS THE FOOTHILLS LATER THIS MORNING...IN
RESPONSE TO 925-850MB WESTERLY DOWNSLOPE FLOW. SKIES WILL BE MOSTLY
SUNNY TODAY WITH HIGHS EXPECTED TO REACH UPPER 50S TO MID 60S
BEFORE COLD AIR ADVECTION GETS UNDERWAY AFTER 18Z...IN THE WAKE OF
THE 850 TROUGH PASSAGE. SKIES WILL REMAIN MOSTLY CLEAR OVERNIGHT
WITH MINS IN THE MID 30S NORTH TO AROUND 40 SE.
MUCH COOLER ON FRIDAY WITH WEAK HIGH PRESSURE DRAPED ACROSS SOUTHERN
NEW ENGLAND AND MID ATLANTIC STATES UNDER A LIGHT NORTHERLY FLOW
AND THICKENING HIGH AND MID LEVEL CLOUD COVER. HIGHS IN THE LOWER
50S NW TO MID-UPPER 50S SE.
&&
.SHORT TERM /FRIDAY NIGHT THROUGH SATURDAY/...
AS OF 330 AM THURSDAY...
THE AFOREMENTIONED STALLED SFC FRONT OFF THE SE COAST WILL BEGIN
TO UNDERGO CYCLOGENESIS FRIDAY NIGHT THROUGH SATURDAY IN RESPONSE TO
SIGNIFICANT H5 HEIGHT FALLS ACROSS THE SOUTHERN MS VALLEY AND GULF
COAST AS ANOTHER STRONG(2 TO 3 STANDARD DEVIATIONS BELOW NORMAL)
SOUTHERN STREAM UPPER VORTEX BARRELS EAST-NORTHEAST ACROSS THE
SOUTHERN APPALACHIANS. ATLANTIC MOISTURE FEED ATTENDANT TO THE
OFFSHORE BAROCLINIC FRONTAL ZONE WILL GET DRAWN BACK INTO THE AREA
FRIDAY NIGHT...SPREADING A COLD RAIN EAST TO WEST ACROSS THE AREA
WITH OVERNIGHT TEMPS IN THE UPPER 30S TO MID 40S ACROSS THE AREA.
HAVE INCREASED POPS FRIDAY NIGHT WITH LIKELY POPS IN THE EAST TO
SMALL CHANCE IN THE WEST.
GOOD ISENTROPIC ASCENT OF THIS ATLANTIC MOISTURE IN THE 285-295K
LAYER WILL MAKE FOR YET ANOTHER WET AND COOL DAY ACROSS CENTRAL
NC ON SATURDAY...WITH DAYTIME HIGHS REMAINING IN THE 40S...WITH
WESTERN AREAS STRUGGLING TO MAKE IT OUT OF THE UPPER 30S.
MODELS ARE IN EXCELLENT AGREEMENT WITH QPF ON SATURDAY...INDICATING
A WEST TO EAST GRADIENT OF ONE-QUARTER TO AS MUCH AS ONE INCH.
THE FORECAST BEGINS TO GET REALLY INTERESTING LATE SATURDAY AFTERNOON
AND SATURDAY EVENING WHEN MID-LEVEL CAA ASSOCIATED WITH THE UPPER
WAVE STARTS TO SPREAD INTO THE AREA FROM THE WEST...WITH CAA IN THE
LOW-LEVELS KICKING IN AT THE SAME TIME AS LIFTING OFFSHORE LOW
REINFORCES THE LOW-LEVEL NELY FLOW. A NARROW BAND OF HEAVIER PRECIP
IS POSSIBLE AS THE 850 LOW LIFTS ACROSS THE AREA...WITH MODELS
SHOWING STRONG 850-500MB FRONTOGENESIS ACROSS THE AREA. PROXIMITY OF
THE FRONT AND LOW TO THE COAST WILL BE A DETERMINING FACTOR IN BOTH
THE WESTWARD EXTENT OF PRECIP AND THE STRENGTH OF THE LOW-LEVEL CAA
SURGE...BUT MODELS ARE IN REMARKABLE AGREEMENT WITH SHOWING THE
ENTIRE COLUMN COOLING BELOW FREEZING ACROSS THE NORTHERN/NORTHWEST
PIEDMONT SATURDAY EVENING BETWEEN 21 TO 00Z...TRANSLATING EAST
ACROSS THE AREA THROUGH DAYBREAK SUNDAY. BUT AS IS ALWAYS THE
CASE...IT WILL BE A FINE LINE/NARROW WINDOW BEFORE THE INVADING
COLD/DRY AIR SURGE COMPLETELY DRYS THE DENDRITIC GROWTH ZONE. GFS IS
VERY QUICK TO DRY OUT THE COLUMN...WHILE THE NAM IS A LITTLE
SLOWER...MAINTAINING DEEP MOISTURE AND LIFT WELL ABOVE THE -15 TO
-18C LAYER. THIS FITS WELL WITH P-TYPE TRENDS AS WELL. IN
SHORT...AREAS ACROSS THE NORTHERN PIEDMONT AND NORTHERN COASTAL
PLAIN COULD SEE SOME MEASURABLE SNOWFALL SATURDAY EVENING AND
SATURDAY NIGHT.
HAVE WENT AHEAD AND INTRODUCED A BRIEF PERIOD OF SNOW ACROSS THE
NORTHERN TIER OF THE FORECAST BEGINNING AT 21 TO 00Z IN THE WEST AND
TRENDING EAST THROUGH DAYBREAK. BUT WITH THE GFS FASTER TO DRY THINGS
OUT...HAVE KEPT POPS IN LOW CHANCE RANGES. THIS WILL BE A SYSTEM
WE WILL NEED TO KEEP AN EYE ON...ESPECIALLY SINCE THE POTENTIAL
FOR BANDING COULD RESULT IN SOME ISLAND OF HEAVY PRECIP.
.LONG TERM/SUNDAY THROUGH WEDNESDAY/...
AS OF 245 AM THURSDAY...
SUNDAY THROUGH TUESDAY: A CHILLY SURFACE HIGH WILL DOMINATE THE
WEATHER ACROSS CENTRAL NORTH CAROLINA THROUGH THE BEGINNING OF NEXT
WEEK...WITH DRY AND PARTLY CLOUDY CONDITIONS EXPECTED. AFTER A
CHILLY START ON SUNDAY MORNING...HIGH TEMPS ARE ONLY EXPECTED TO
RISE INTO THE UPPER 40S TO LOW 50S AS THICKNESS VALUES WILL RANGE
BETWEEN 1300 AND 1310M. WITH MOSTLY CLEAR SKIES AND LIGHT
WINDS...LOWS ON MONDAY MORNING WILL FALL INTO THE LOWER 30S
AREAWIDE. THICKNESS VALUES WILL ONLY REBOUND SLIGHTLY ON MONDAY...SO
EXPECT ANOTHER DAY OF UPPER 40S TO LOWER 50S. THE HIGH WILL FINALLY
SLOWLY SHIFT OFF TO THE NORTHEAST BY EARLY NEXT WEEK...ALLOWING
TEMPS TO SLOWLY REBOUND...WITH LOWS IN THE MID TO UPPER 30S AND
HIGHS IN THE LOW TO MID 50S BY TUESDAY. CLOUDS WILL BE ON THE
INCREASE TUESDAY AHEAD OF OUR NEXT SYSTEM.
TUESDAY NIGHT THROUGH WEDNESDAY: MOISTURE WILL BEGIN TO INCREASE
TUESDAY AS THE HIGH MOVES OFFSHORE AND WINDS BECOME MORE SOUTHERLY.
RAIN CHANCES WILL ONCE AGAIN ENTER THE FORECAST BY TUESDAY NIGHT
AHEAD OF THE NEXT COLD FRONT. THE BEST CHANCE FOR PRECIP FOR NOW
LOOKS TO BE ON WEDNESDAY AS THE FRONT MOVES ACROSS THE REGION AND
CENTRAL NORTH CAROLINA IS UNDER THE RIGHT ENTRANCE REGION OF A
STRONG JET CORE (150+ KNOTS). FOR NOW WILL ONLY SHOW WIDESPREAD
CHANCE POPS AS THESE SYSTEMS TEND TO SLOW DOWN AS TIME PROGRESSES.
&&
AVIATION /18Z THURSDAY THROUGH MONDAY/...
AS OF 100 PM THURSDAY...
WITH DRIER AIR OVER CENTRAL NC IN THE WAKE OF THE DEPARTING COLD
FRONT...VFR CONDITIONS WILL PERSIST THROUGH MIDDAY FRIDAY...WITH
ONLY A FEW STRATOCU OBSERVED IN THE EAST..AND SCT HIGH CLOUDS
EXPECTED TO PASS OVERHEAD. A GENTLE NW BREEZE (WITH 15-20KT GUSTS
COMING TO AN END) WILL EVENTUALLY SWING AROUND TO MORE N-NERLY
OVERNIGHT...AS A SURFACE HIGH PRESSURE RIDGE EXTENDS EAST OVER THE
MID ATLANTIC. HIGH CLOUDS WILL INCREASE AND THICKEN AS AN UPPER
LEVEL TROUGH BEGINS TO APPROACH FROM THE W.
THE COMBINATION OF AN UPPER LEVEL DISTURBANCE AND A DEVELOPING
SURFACE LOW OFF THE CAROLINA COAST WILL BRING A CHANCE OF RAIN...
AND POTENTIALLY A CHANGE OVER TO A MIX OF RAIN AND SNOW BY SATURDAY
NIGHT. MVFR CONDITIONS...WITH PERIODS OF IFR...WILL BE POSSIBLE
BEFORE THE SYSTEM MOVES OUT OF THE AREA BY SUNDAY.
&&
.RAH WATCHES/WARNINGS/ADVISORIES...
NONE.
&&
$$
SYNOPSIS...CBL/SMITH
NEAR TERM...CBL/SMITH
SHORT TERM...CBL
LONG TERM...KRR
AVIATION...SMITH
