FXUS62 KRAH 240809
AFDRAH
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RALEIGH NC
307 AM EST THU DEC 24 2009
.SYNOPSIS...
HIGH PRESSURE WILL EXTEND INTO THE REGION FROM THE NORTH THROUGH
TODAY. A STORM SYSTEM WILL APPROACH FROM THE SOUTHWEST THIS EVENING
AND AFFECT THE AREA CHRISTMAS EVE THROUGH CHRISTMAS DAY AND
CHRISTMAS NIGHT. A DRY AND MILD AIR MASS WILL MOVE IN SATURDAY...
THEN COOL HIGH PRESSURE WILL BUILD IN FOR SUNDAY THROUGH MONDAY...
RETURNING TEMPERATURES TO SEASONAL NORMALS.
&&
.NEAR TERM /THROUGH TONIGHT/...
AS OF 245 AM THURSDAY...
THE THICKER CIRRUS REMAIN WELL TO THE WEST OVER MIDDLE TENNESSEE
THIS MORNING AND ONLY A FEW THIN CIRRUS HAVE BEEN MOVING ACROSS
THE AREA. THE CIRRUS WILL GRADUALLY THICKEN MOVING IN FROM THE
WEST LATER THIS AFTERNOON. THE GFS BRINGS THE HIGH LEVEL MOISTURE
IN AROUND 18Z-21Z WHEREAS THE NAM HOLDS OFF ON THICKENING THE CIRRUS
UNTIL THIS EVENING. WILL KEEP SKIES PARTLY CLOUDY FOR TODAY WITH
JUST THE THIN CIRRUS EXPECTED. 1000-850 MB THICKNESSES RE ONLY 3-5
METERS COOLER THAN YESTERDAY SO WILL STICK CLOSER TO THE WARMER
NAM GUIDANCE WHICH IS JUST A DEGREE COOLER THAN LOCAL TIHCKENESS
SCHEMES. HIGHS TODAY WILL RANGE FROM NEAR 50 IN THE TRIAD TO MID
50S IN THE SOUTHEAST.
MODELS ARE IN DECENT AGREEMENT WITH THE TIMING OF THE MOISTURE
STREAMING IN FROM THE SOUTH TONIGHT AND EARLY SATURDAY. ISENTROPIC
LIFT WILL BE ON THE INCREASE TONIGHT AS WINDS AT 850
MILLIBARS INITIALLY AT TEN TO THIRTY KNOTS INCREASES TO THIRTY-
FIVE TO FIFTY KNOTS OVERNIGHT. THIS WILL MEAN AN INCREASE IN LOW
CLOUDS IN THE EVENING BEFORE MIDNIGHT. THE RAIN WILL HOLD OFF A
LITTLE LONGER AND SHOULD SPREAD OVER THE WESTERN SANDHILLS AND NW
PIEDMONT A FEW HOURS BEFORE DAWN AND BECOME LIKELY IN THE TRIANGLE
AND GOLDSBORO AREA AROUND SUNRISE FRIDAY. THOUGH MODELS HAVE
WARMED THE LAST COUPLE OF RUNS THEY ARE STILL CONSISTENT IN
SHOWING A SMALL RISK FOR LIGHT FREEZING RAIN IN THE NORTHWEST
BEFORE SUNRISE. IT APPEARS ONLY TREES AND RAISED METAL SURFACES
ARE AT RISK FOR A MINIMAL GLAZE LASTING JUST A FEW HOURS. WITH ANY
ICE MELTING AFTER SUNRISE AS WARM AIR ADVECTION CONTINUES ALOFT
AND TEMPERATURES INCH UPWARD AT THE SURFACE. OVERNIGHT LOWS NEAR
FREEZING IN THE NORTHWEST... OTHERWISE MID 30S... TO LOWER 40S IN
THE EXTREME SOUTH.
&&
.SHORT TERM /FRIDAY THROUGH SATURDAY NIGHT/...
AS OF 250 AM THURSDAY...
FOR CHRISTMAS DAY/NIGHT: THE MID LEVEL VORTEX OVER THE LOWER MISS
VALLEY ROTATES NORTHWARD AND BECOMES ABSORBED BY THE STRONGER LOW
DROPPING INTO THE MIDWEST. THE SURFACE FRONT IS STILL EXPECTED TO
SHIFT FROM THE GULF COAST STATES NORTHEASTWARD INTO THE WESTERN
CAROLINAS FRIDAY MORNING... WITH TRIPLE POINT DEVELOPMENT OVER
WESTERN SC WHICH THEN TRACKS NORTHEAST THROUGH CENTRAL NC INTO
EASTERN VA LATE FRIDAY NIGHT. MODEL PROJECTIONS OF SURFACE WET BULB
TEMPS SHOW THE ZERO LINE OVER THE FAR NORTHWEST PIEDMONT AT 12Z
RAPIDLY SHIFTING NORTHWARD BY 15Z. DESPITE THE DRY SURFACE AIR TO
OUR NORTH... CONSIDERING THAT THE SURFACE RIDGE AND ITS UPPER
SUPPORT WILL BE QUICKLY MOVING TO THE NORTHEAST... CUTTING OFF ANY
FURTHER LOW LEVEL DRY AIR ADVECTION THAT MIGHT PROLONG THE FREEZING
RAIN THREAT... AND CONSIDERING THE SELF-LIMITING PROCESS OF LATENT
HEAT RELEASE... DO NOT EXPECT ANY ADDITIONAL NOTABLE ICING AFTER
SUNRISE FRIDAY. THE MODELS CONTINUE TO SLOW DOWN THE ARRIVAL OF
PRECIP INTO CENTRAL NC. THE WRF... WHICH HAS BEEN AMONG THE SLOWER
MODELS FOR A FEW DAYS NOW... LOOKS TO HAVE A GOOD HANDLE ON THE
CURRENT PRECIP OVER THE SOUTHERN PLAINS AND LOWER MISS VALLEY AND IS
GENERALLY PREFERRED. HAVE SLIGHTLY SLOWED THE EXISTING FORECAST A
BIT MORE... BRINGING CATEGORICAL POPS INTO THE SOUTHWEST CWA FRIDAY
MORNING AND SPREADING SHOWERS ACROSS THE ENTIRE AREA TOWARD MIDDAY
INTO THE EARLY AFTERNOON WITH THE ONSET OF STRONG AND DEEPENING
MOIST UPGLIDE. THE RISK OF SEVERE STORMS REMAINS QUESTIONABLE AS
FORECAST INSTABILITY IS UNIMPRESSIVE... JUST A FEW HUNDRED J/KG OF
MUCAPE BRUSHING THE EXTREME SOUTHERN AND EASTERN CWA FRIDAY
AFTERNOON/EVENING. DYNAMIC FORCING FOR ASCENT IS ALSO LIMITED WITH
MINIMAL DPVA AND THE BULK OF UPPER DIVERGENCE (ASSOCIATED WITH THE
STRENGTHENING GULF COAST JET) HEADING TO OUR NORTHWEST AND EAST. THE
WIND FIELDS DO FAVOR AN ORGANIZED CONVECTIVE LINE OR BOWING
SEGMENTS... WITH A 50-60 KT LOW LEVEL JET AND 50 KTS OF 0-6 KM BULK
SHEAR... BUT DISCRETE CELLS ARE UNLIKELY TO SURVIVE IN THIS STRONGLY
SHEARED ENVIRONMENT. HAVE KEPT ISOLATED THUNDER MAINLY ALONG AND
EAST OF THE HIGHWAY 1 CORRIDOR... ALONG AND EAST OF THE TRIPLE POINT
LOW TRACK... FRIDAY AFTERNOON INTO THE EVENING... AND WILL MENTION
IN THE HAZARDOUS WEATHER OUTLOOK THE POSSIBILITY OF STRONG WIND
GUSTS WITH ANY INTENSE SHOWERS OR STORMS. THIS RISK OF STRONG
DOWNBURST WINDS MAY BE HEIGHTENED IF THE MID LEVEL DRY PUNCH ARRIVES
EARLIER... AS THE GFS SUGGESTS. WILL TAPER OFF POPS SOUTHWEST TO
NORTHEAST FRIDAY NIGHT. EXPECT TOTAL RAINFALL OF ONE TO ONE AND A
HALF INCHES... GIVEN THAT PRECIPITABLE WATER VALUES EXCEED ONE INCH
OVER MOST OF THE AREA AND APPROACH 1.5 INCHES OVER THE SOUTHEAST
WITH INTENSE LOW LEVEL THETA-E ADVECTION. LOW LEVEL THICKNESSES
SURGE OVER 1360 M OVER MOST OF THE AREA FRIDAY AFTERNOON AND HAVE
ADJUSTED HIGHS UP AND SHIFTED THE TIGHT GRADIENT FURTHER NORTHWEST.
EXPECT HIGHS FROM THE MID 40S IN THE TRIAD TO UPPER 50S IN THE
TRIANGLE TO LOWER-MID 60S IN THE FAR SOUTHEAST. WITH THE
SOUTHWESTERLY MID LEVEL FLOW HAVING LITTLE CROSS-FRONTAL COMPONENT
AND THE LACK OF AN IMMEDIATE UPSTREAM COLD AIR MASS TO PROPEL THE
COLD FRONT ACROSS CENTRAL NC FRIDAY NIGHT... IT SHOULD TAKE SOME
TIME FOR THE COOLER AIR TO ARRIVE... WHICH IS REFLECTED IN THE NAM'S
SLOWER DROP IN THICKNESSES. HAVE RAISED LOWS A BIT TO 37-52 WEST TO
EAST.
FOR SATURDAY/SATURDAY NIGHT: FORECAST SOUNDINGS SHOW A SUBSTANTIAL
LOW LEVEL INVERSION DEVELOPING WITH QUITE A BIT OF NEAR-SURFACE
MOISTURE SATURDAY MORNING... AND THIS ALONG WITH A CONTINUOUS STREAM
OF HIGH CLOUDS WITH FAST UPPER LEVEL FLOW SHOULD KEEP PARTLY TO
MOSTLY CLOUDY SKIES IN THE MORNING WITH INCREASING SUNSHINE AS
MIXING COMMENCES BY MIDDAY. AS NOTED ABOVE... LOW LEVEL THICKNESSES
DO NOT DROP OFF DRASTICALLY UNTIL SATURDAY NIGHT... AND ABOVE-NORMAL
VALUES SATURDAY INDICATE HIGHS OF 52-62... A SLIGHT UPTICK FROM
PREVIOUS FORECAST HIGHS. EXPECT MOSTLY CLEAR SKIES SATURDAY NIGHT
WITH MODIFIED HIGH PRESSURE BUILDING IN FROM THE SOUTHWEST...
ALTHOUGH LIGHT WINDS AND ANY RESIDUAL GROUND MOISTURE COULD LEAD TO
PATCHY FOG DEVELOPMENT LATE. LOWS 28-34. -GIH
&&
.LONG TERM /SUNDAY THROUGH WEDNESDAY/...
AS OF 255 AM THURSDAY...
FOR SUNDAY THROUGH MONDAY: THE MID LEVEL LOW TRACKS FROM NEAR
CHICAGO ACROSS NORTHERN IN/OH TO PA AND OFF THE NEW ENGLAND COAST
DURING THIS PERIOD. PASSAGE OF A REINFORCING SURFACE COLD FRONT LATE
SUNDAY AFTERNOON WILL PULL IN EVEN CHILLIER AIR FOR SUNDAY NIGHT
THROUGH MONDAY... AND EXPECT SLIGHTLY BELOW NORMAL HIGHS OF 46-54
SUNDAY TO RUN WELL BELOW NORMAL MONDAY -- 43-48 -- AS THICKNESSES
PLUMMET TO 1280-1290 M. SKIES SHOULD BE NO WORSE THAN PARTLY CLOUDY
WITH THE NORTHWEST FLOW MOISTURE LOCKED ON THE WEST SIDE OF THE
MOUNTAINS AND DRYING TERRAIN DOWNGLIDE OVER THE PIEDMONT.
FOR MONDAY NIGHT THROUGH WEDNESDAY: HIGH PRESSURE CONTINUES TO BUILD
INTO THE EASTERN US. THE POLAR LOW SITS AND SPINS OVER QUEBEC
THROUGH TUESDAY... KEEPING A NORTHWEST MID LEVEL FLOW OVER NC...
BEFORE THE LOW LIFTS NORTHEAST AND THE SOUTHERN STREAM ONCE AGAIN
STARTS TO PREVAIL OVER THE TX/GULF COAST/SOUTHEAST STATES INTO
MIDWEEK. A MID LEVEL LOW WHICH TRAVERSES SOUTHERN CA AND THE
NORTHERN BAJA LATE MONDAY IS EXPECTED TO DAMPEN AS IT HEADS OVER
TX/LA BY WEDNESDAY AND PICKS UP GULF MOISTURE. THE ECMWF HAS BEEN
FAIRLY CONSISTENT IN TAKING THE SURFACE RIDGE TO OUR NORTHEAST WITH
INCREASING SOUTHEAST FLOW INTO THE CAROLINAS AND A CHANCE OF RAIN
VERY LATE WEDNESDAY. AS CONFIDENCE IS TYPICALLY VERY LOW IN TIMING
FEATURES IN THIS SORT OF PATTERN THIS FAR OUT IN TIME... WILL KEEP
THE FORECAST DRY FOR NOW. TEMPS SHOULD HOLD NEAR OR JUST UNDER
SEASONAL NORMALS. -GIH
&&
.AVIATION /08Z THURSDAY THROUGH MONDAY/...
AS OF 130 PM THURSDAY...
VFR CONDITIONS WILL CONTINUE THROUGH THE 24 TAF PERIOD.
HIGH PRESSURE OVER SOUTHERN CANADA WILL NOSE DOWN INTO NORTH
CAROLINA THROUGH THURSDAY. WITH THE SURFACE RIDGE AXIS
DIRECTLY OVERHEAD...EXPECT MOSTLY CALM WINDS OVERNIGHT...PICKING UP
TO 5 TO 10KTS FROM THE NORTHEAST ON THURSDAY.
CEILINGS WILL BEGIN TO LOWER THURSDAY EVENING AS A STORM SYSTEM
APPROACHES NORTH CAROLINA FROM THE WEST SOUTHWEST. IFR TO MVFR
CONDITIONS ARE EXPECTED BY DAYBREAK FRIDAY WITH WIDESPREAD RAIN
OVERSPREADING THE AREA MOVING SW TO NE. CEILINGS WILL LIKELY BE
IFR BY DAYBREAK AT INT AND GSO AND BECOME IFR FURTHER EAST AT RDU
BETWEEN 12-15Z. KINT AND KGSO COULD SEE A BRIEF PERIOD OF
FREEZING RAIN FRIDAY MORNING...BEFORE SWITCHING OVER TO ALL RAIN.
THERE IS ALSO THE POTENTIAL FOR LOW LEVEL WIND SHEAR CONDITIONS
THURSDAY NIGHT AND FRIDAY MORNING FROM A 40 TO 45 KNOT
SOUTHEASTERLY LOW LEVEL JET. VFR CONDITIONS RETURN SATURDAY AFTER
SUNRISE AS THE STORM SYSTEM EXITS THE AREA AND CONTINUE INTO
MONDAY.
&&
.RAH WATCHES/WARNINGS/ADVISORIES...
NONE.
&&
$$
SYNOPSIS...HARTFIELD
NEAR TERM...JO
SHORT TERM...HARTFIELD
LONG TERM...HARTFIELD
AVIATION...JO
