Area Forecast Discussion
Issued by NWS Wilmington, NC

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000
FXUS62 KILM 280537
AFDILM

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE WILMINGTON NC
1237 AM EST SAT FEB 28 2015

.SYNOPSIS...
HIGH PRESSURE WILL WEDGE DOWN THE COAST THIS WEEKEND. DRY BUT CHILLY
WEATHER IS EXPECTED ON SATURDAY. RAIN CHANCES WILL INCREASE SUNDAY
AS TEMPERATURES MODERATE. A COLD FRONT WILL CROSS THE AREA MONDAY
ACCOMPANIED BY SHOWERS. SEASONABLE WEATHER IS EXPECTED TUESDAY
BEFORE THIS FRONT LIFTS NORTH AS A WARM FRONT WEDNESDAY...BRINGING
ONE DAY OF WELL ABOVE NORMAL TEMPERATURES. ANOTHER COLD FRONT WILL
APPROACH WEDNESDAY NIGHT OR THURSDAY.

&&

.NEAR TERM /UNTIL 6 AM SATURDAY MORNING/...
AS OF 945 PM FRIDAY...SUBTROPICAL JET STREAM MOISTURE CONTINUES OVER
THE COASTAL CAROLINAS...WITH UPSTREAM SATELLITE TRENDS INDICATING
THE WESTERN EDGE OF THIS CLOUD DECK MAY NOT DRIFT OFFSHORE AFTER
ALL. NORTHEAST WINDS ARE FIRMLY ESTABLISHED AT THE SURFACE...
ALTHOUGH WIND SPEEDS HAVE YET TO RAMP UP WITH THE COLD AIR SURGE
EXPECTED TO BEGIN AROUND MIDNIGHT. RECENT RUC AND HRRR MODEL TRENDS
HAVE BEEN UPWARD WITH LOW TEMPERATURES TONIGHT AND I HAVE MADE
UPWARD TWEAKS AT MOST LOCATIONS: 27-31 ACROSS SE NORTH CAROLINA AND
29-32 OVER NE SOUTH CAROLINA...WARMEST AT THE COAST. DISCUSSION FROM
630 PM FOLLOWS...

ONLY MINOR CHANGES MADE TO THE NEAR TERM FORECAST THIS EVENING. THE
LEADING EDGE OF A NE SURGE CURRENTLY DROPPING SOUTH ACROSS THE
CHESAPEAKE BAY WILL REACH OUR AREA AFTER MIDNIGHT. THE BIGGEST
QUESTION REMAINS HOW MUCH (IF ANY) LOW CLOUDINESS DEVELOPS IN THE
NORTHEASTERLY LOW-LEVEL FLOW BEHIND THE SURGE? 18Z NAM AND GFS MODEL
OUTPUT SHOW ENOUGH MOISTURE IN THE LOWEST 1000 FEET OF THE
ATMOSPHERE DEVELOPING OVERHEAD BETWEEN 09-12Z (4-7 AM) TO PRODUCE
LOW CLOUDS. A LOCAL RULE OF THUMB IS TO LOOK AT
CONVERGENCE/DIVERGENCE WITHIN THE MOISTURE-BEARING LAYER TO HELP
DIAGNOSE THE POTENTIAL FOR LOW CLOUDINESS -- AND ALL MODELS SHOW
DIVERGENCE ON THE 1000 MB SURFACE TONIGHT. FOR THIS REASON I HAVE
REDUCED THE AMOUNT OF FORECAST CLOUDINESS LATE TONIGHT...
ANTICIPATING MAINLY 300 MB CIRRUS MOISTURE.

&&

.SHORT TERM /6 AM SATURDAY MORNING THROUGH SUNDAY NIGHT/...
AS OF 3 PM FRIDAY...DEVELOPING COLD WEDGE THIS WEEKEND WILL KEEP
SKIES CLOUDY AND HOLD HIGHS 10 TO 20 DEGREES BELOW CLIMO. WEAKLY
AMPLIFIED MID LEVEL PATTERN WILL CONTINUE TO PUMP MOISTURE INTO THE
SOUTHEAST. SOUTHWEST FLOW ALOFT COMBINED WITH LOW LEVEL NORTHEAST
FLOW WILL MAINTAIN WEAK ISENTROPIC LIFT FOR MUCH OF THE PERIOD BUT
LOW LEVEL DRY AIR HOLDING ON SAT AND MOST OF SAT NIGHT WILL KEEP THE
REGION DRY FOR THE FIRST HALF OF THE WEEKEND. LOW LEVELS MOISTEN UP
SUN MORNING WITH LIGHT RAIN SPREADING OVER THE AREA AS COASTAL
TROUGH DEVELOPS OFFSHORE. LATER SUN MID LEVEL RIDGE EXPANDING NORTH
FROM THE GULF OF MEXICO STARTS TO WEAKEN THE WEDGE...LESSENING
ISENTROPIC LIFT. WEDGE COMPLETELY BREAKS DOWN SUN NIGHT WITH LIGHT
WESTERLY FLOW DEVELOPING AFTER MIDNIGHT. ALTHOUGH NORTHERLY FLOW
CONTINUES AT THE SURFACE DURING SUN THERE WILL BE SOME MODEST WARM
ADVECTION JUST ABOVE THE BOUNDARY LAYER. THIS WILL HELP PUSH HIGHS
ON SUN CLOSER TO CLIMO...THOUGH TEMPS WILL ULTIMATELY FALL 5 TO 10
DEGREES SHORT. CLOUD COVER WILL HELP KEEP LOWS NEAR FREEZING SAT
NIGHT. WARM ADVECTION ALONG WITH CLOUDS WILL KEEP LOWS NEAR CLIMO
SUN NIGHT.

&&

.LONG TERM /MONDAY THROUGH FRIDAY/...
AS OF 330 PM FRIDAY...COLD FRONT WILL MAKE ITS WAY OFF SHORE MONDAY
AS HIGH PRESSURE BUILDS DOWN FROM THE NORTHWEST TO NORTH. DEEPER
WESTERLY FLOW EARLY MONDAY WILL BECOME NW AS SHORTWAVE MOVES OFF TO
THE E-NE THROUGH LATE MONDAY. THEREFORE...INITIALLY THE DOWNSLOPE
FLOW AND SOME BREAKS OF SUNSHINE SHOULD PUSH TEMP UP AROUND 60 ON
MONDAY. BY LATER ON MONDAY A DEEPER NW FLOW WILL INCREASE CAA
BRINGING 850 TEMPS FROM CLOSE TO 10C EARLY MON DOWN TO 4 C BY TUES
MORNING. THE WINDS WILL SHIFT AROUND BECOMING MORE NORTHERLY
OVERNIGHT AND MORE ON SHORE BY TUES AFTN.  INCREASING CLOUD COVER
AND WINDS MON NIGHT SHOULD KEEP TEMPS ABOVE NORMAL.

A RIDGE IN THE MID TO UPPER LEVELS WILL PUSH UP FROM THE GULF MON
NIGHT INTO TUES AND WILL SHARPEN AS TROUGH DIGS DOWN THROUGH THE MID
WEST BY WED. AT THE SAME TIME THE SFC HIGH TO THE NORTH WILL MOVE
OFF SHORE THROUGH TUES AND RIDGE TO THE SOUTH WILL HELP PUSH COLD
FRONT BACK NORTH AS WARM FRONT. A BRIEF WEDGE WILL DEVELOP WITH
INCREASING ISENTROPIC LIFT AS WARM FRONT MOVES NORTH INTO SHALLOW
RELATIVELY COOLER AIR IN PLACE ON TUES. EXPECT CLOUDS AND CHC OF PCP
ON TUES AS WARM FRONT LIFTS NORTH. WILL KEEP A LARGER TEMP RANGE IN
TIGHTENED GRADIENT BETWEEN COOL TEMPS TO THE NORTH AND WARMER TEMPS
TO THE SOUTH ON TUES BEFORE WARM FRONT LIFTS BY END OF DAY. TUES
NIGHT WILL HAVE NEAR STEADY OR RISING TEMPS IN WAA BEHIND FRONT.

COASTAL CAROLINAS WILL BE IN WARM AND MOIST AIR MASS ON WED AHEAD OF
APPROACHING COLD FRONT. TEMPS SHOULD SOAR INTO THE 70S MOST PLACES
EXCEPT CLOSER TO THE COAST WHERE COOLER OCEAN TEMPS WILL KEEP THE
AIR COOLER. ALTHOUGH CLOUDS WILL LIMIT WARMING...SOME BREAKS MAY
PUSH TEMPS HIGHER IN A FEW PLACES. ECMWF IS MUCH SLOWER WITH COLD
FRONT WHILE GFS BRINGS IT THROUGH BY MIDNIGHT WED NIGHT. FOR NOW
WILL HEDGE TOWARD SLOWER FROPA AND KEEP TEMPS WARMER WED NIGHT AND
WILL BRING FRONT THROUGH EARLIER ON THURS WITH TEMPS COOLING IN CAA
THROUGH THURS INTO FRI. IF FRONT COMES EARLIER THAN SHOWERS WILL BE
MORE WIDESPREAD ON WED AFTN AND EVENING. OVERALL EXPECT INCREASING
SHOWERS AHEAD OF FRONT. EXPECT TEMPS BELOW NORMAL AGAIN LATE THURS
INTO FRI AS COLD AND DRY HIGH PRESSURE BUILDS IN.

&&

.AVIATION /06Z SATURDAY THROUGH WEDNESDAY/...
AS OF 06Z...VFR EXPECTED THROUGH THE VALID TAF PERIOD AS HIGH
PRESSURE CONTINUES TO BUILD IN...WITH POSSIBLE MVFR ALONG THE COAST
TOWARDS THE END OF THE PERIOD.

LATEST SATELLITE IMAGERY DEPICTS A SWATH OF SCT HIGH CLOUDS ACROSS
THE AREA. THIS WILL PERSIST THROUGH THE OVERNIGHT HOURS AND ALLOW
FOR VFR TO PREVAIL WITH LIGHT NORTHEAST WINDS. AFTER
DAYBREAK...EXPECT A GRADUAL TIGHTENING OF THE PRESSURE GRADIENT
WHICH WILL BRING AN INCREASE IN NORTHEAST WINDS...SUSTAINED AOB 15
KTS AND GUSTS UP TO AROUND 20 KTS. MOISTURE WITHIN THE ATMOSPHERIC
COLUMN IS FORECAST TO INCREASE AS WELL YIELDING INCREASING MID TO
HIGH CLOUDS DURING THE DAYLIGHT HOURS TODAY. INTO THE EVENING
HOURS...THERE IS THE POSSIBILITY OF LOWERING CIGS ALONG THE COAST
WHICH COULD CREATE MVFR.

EXTENDED OUTLOOK...MVFR/IFR POSSIBLE LATE SUNDAY THROUGH TUESDAY AS
A WEDGE SETS UP. WINDY WEDNESDAY WITH POSSIBLE SHOWERS WEDNESDAY
NIGHT. OTHERWISE EXPECT VFR.

&&

.MARINE...
.NEAR TERM /THROUGH TONIGHT/...
AS OF 945 PM FRIDAY...WINDS AND SEAS ARE RAMPING UP MORE SLOWLY THAN
ANTICIPATED...DELAYING THE ONSET OF SMALL CRAFT ADVISORY CONDITIONS.
UPSTREAM OBSERVATIONS ACROSS THE OUTER BANKS AND NORTHEASTERN NORTH
CAROLINA CONTINUE TO SUPPORT THE IDEA OF STRONGER WINDS MOVING INTO
THE AREA OVER THE NEXT FEW HOURS. THERE IS LITTLE SPREAD IN MODEL
GUIDANCE LENDING HIGH CONFIDENCE THAT WE WILL EVENTUALLY SEE THESE
DETERIORATING CONDITIONS DEVELOP. DISCUSSION FROM 630 PM FOLLOWS...

NO SIGNIFICANT CHANGES ARE NEEDED TO THE FORECAST WITH THIS
EARLY-EVENING UPDATE. FORECAST WIND SPEEDS HAVE BEEN REDUCED BY 3-5
KNOTS BASED ON OBSERVATIONS THROUGH THE EVENING...WITH INCREASING
SPEEDS EXPECTED OVERNIGHT AS THE PRESSURE GRADIENT TIGHTENS UP ON
THE SOUTH EDGE OF HIGH PRESSURE.

SHORT TERM /SATURDAY THROUGH SUNDAY NIGHT/...
AS OF 3 PM FRIDAY...SURFACE HIGH WEDGING DOWN THE EAST COAST WILL
MAINTAIN A PINCHED GRADIENT OVER THE WATERS SAT AND SAT NIGHT.
NORTHEAST FLOW WILL BE SOLIDLY IN THE 20 TO 25 KT RANGE WITH SEAS 4
TO 8 FT SAT. ONLY EXCEPTION WILL BE LOCATIONS WHERE NORTHEAST FLOW
IS OFFSHORE. IN THESE LOCATIONS NEAR SHORE SEAS WILL RUN 1 TO 3 FT.
GRADIENT STARTS TO RELAX LATE SAT NIGHT AS COASTAL TROUGH TAKES
SHAPE AND HIGH STARTS TO WEAKEN. WINDS DROP UNDER 20 KT EARLY SUN
MORNING AND BY AFTERNOON WILL BE 10 KT OR LESS. REDUCTION IN
NORTHEAST FLOW WILL ALLOW SEAS TO DROP AND BY DAYBREAK SUN SEAS
SHOULD BE 3 TO 5 FT AND 2 TO 4 FT BY THE END OF THE PERIOD.

LONG TERM /MONDAY THROUGH TUESDAY/...
AS OF 300 AM FRIDAY...A COLD FRONT WILL DROP TOWARDS...AND THEN
ACROSS...THE WATERS DURING MONDAY PRODUCING VARIABLE WINDS THAT WILL
VEER FROM SW EARLY MONDAY...TO NE BY TUESDAY MORNING. THE GRADIENT
REMAINS RATHER WEAK DURING THIS TIME HOWEVER...SO SPEEDS WILL BE
LESS THAN 15 KTS THROUGH THE DAY. THIS FRONT WILL STALL SOUTH OF THE
WATERS THE FIRST HALF OF TUESDAY...MAINTAINING THE NE WINDS...BEFORE
LIFTING RAPIDLY BACK NORTH AS A WARM FRONT LATE TUESDAY. WINDS WILL
AGAIN VEER THROUGH HALF THE COMPASS...BECOMING SW AND RISING TO
15-20 KTS LATE. SEAS OF 2-4 FT WILL BE COMMON MONDAY AND THE FIRST
HALF OF TUESDAY...ALTHOUGH COMPRISED BY A VARIETY OF WIND WAVES
WHICH WILL FOLLOW THE PRIMARY WIND DIRECTION. THIS WILL LIKELY
CREATE PERIODS OF CONFUSED WAVE STATES DURING MONDAY AND TUESDAY.
LATE TUESDAY SEAS BUILD TOWARDS 6 FT...AND AN SCA MAY BE REQUIRED AT
THE END OF THE PERIOD.

&&

.ILM WATCHES/WARNINGS/ADVISORIES...
SC...NONE.
NC...NONE.
MARINE...SMALL CRAFT ADVISORY FROM 10 PM THIS EVENING TO 5 AM EST
     SUNDAY FOR AMZ250-252-254-256.

&&

$$

NEAR TERM...TRA
SHORT TERM...III
LONG TERM...RGZ
AVIATION...SGL/31






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