FXUS62 KRAH 070255
AFDRAH
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RALEIGH NC
948 PM EST SUN DEC 6 2009
.SYNOPSIS...
HIGH PRESSURE WILL DRIFT OFF THE MID ATLANTIC COAST TONIGHT... ONLY
TO BE REPLACED BY ANOTHER MONDAY NIGHT AND TUESDAY. MOISTURE WILL
INCREASE LATE TUESDAY THROUGH WEDNESDAY AHEAD OF A POWERFUL STORM
SYSTEM TO THE WEST.
&&
.NEAR TERM /THROUGH MONDAY/...
AS OF 948 PM SUNDAY...
NO CHANGES ARE NEEDED TO THE CURRENT FORECAST AS PLENTY OF
CIRRUS/CIRROSTRATUS CONTINUE TO FLOW OVERHEAD IN THE STRONG DEEP
WESTERLY FLOW ALOFT. THERE IS AN INCREASE IN MID CLOUDS UPSTREAM
OVER TN (PER UPPER AIR SOUNDINGS... SURFACE OBSERVATIONS... AND IR
SATELLITE DATA). SOME OF THIS MOISTURE WILL BE MOVING OVER OUR
REGION LATER TONIGHT. EXPECT A CONTINUATION OF MOSTLY CLOUDY SKIES
THROUGH THE NIGHT WITH ENOUGH THIN SPOTS AND BREAKS TO PROVIDE FAIR
RADIATIONAL COOLING.
THE MID EVENING TEMPERATURES RANGED FROM 30 AT ROXBORO AND
WINSTON-SALEM TO 37 AT CLINTON. LOWS IN THE UPPER 20S TO LOWER 30S
APPEAR VERY REASONABLE. THERE HAVE BEEN A FEW PATCHY LIGHT
REFLECTIVITY RETURNS ACROSS WESTERN NC THIS EVENING. SOME LIGHT SNOW
FLAKES WERE REPORTED AT HICKORY EARLIER. SINCE THE AIR MASS IS VERY
DRY... EXPECT THAT WE WILL NOT SEE ANY FLAKES OVER THE WESTERN
PIEDMONT TONIGHT. -BADGETT
MONDAY: THE NWP MODELS TO VARYING DEGREES HAVE DEPICTED THE ARRIVAL
FROM SC OF ISENTROPIC LIFT/WAA IN THE LOWEST ~5 THOUSAND FT (285-295
K LAYER) FROM JUST BEFORE SUNRISE OVER THE SANDHILLS TO ALONG AND
EAST OF I-95 DURING THE DAY MONDAY. THE ISENTROPIC LIFT IS
MANIFESTED AS THE AGEOSTROPHIC LOW LEVEL RETURN BRANCH OF THE
THERMALLY INDIRECT CIRCULATION WITHIN A ~125 KT JET EXIT REGION AT
200-150 MB FORECAST TO NOSE ACROSS THE CAROLINAS BETWEEN 09Z AND
21Z. GIVEN THE SHALLOWNESS OF THE SATURATION... WHICH IS EXPECTED TO
REMAIN CONFINED BELOW 6-7 THOUSAND FT AND AT TEMPERATURES ABOVE
0C... DO NOT EXPECT MUCH IF ANY MEASURABLE RAIN. THE CLOUD COVER
SHOULD... HOWEVER... HOLD TEMPERATURES DOWN... PARTICULARLY IN THE
EAST. HIGHS GENERALLY UPPER 40S TO LOWER 50S... WARMEST SOUTHWEST
AND COOLEST NORTHWEST AND EAST. -MWS
&&
.SHORT TERM /MONDAY NIGHT THROUGH TUESDAY/...
AS OF 255 PM SUNDAY...
ONCE THE ISENTROPIC LIFT ATOP THE FIRST SURFACE RIDGE THAT WAS OVER
THE VIRGINIAS TODAY PIVOTS OFFSHORE BY MONDAY EVENING ... ANOTHER
SURFACE HIGH (~1025 MB) WILL FOLLOW AND RIDGE SOUTHWARD INTO NC
MONDAY NIGHT THROUGH TUESDAY. STRONG ISENTROPIC LIFT -- AHEAD OF A
POWERFUL STORM SYSTEM EXPECTED TO LIFT NORTHEASTWARD FROM THE FOUR
CORNERS MONDAY NIGHT TO THE GREAT LAKES BY WEDNESDAY -- WILL RESULT
IN AN INCREASING CHANCE OF RAIN FROM THE SOUTHWEST TUESDAY
AFTERNOON... RANGING FROM SLIGHT CHANCE NORTHEAST TO LIKELY WEST.
&&
.LONG TERM /TUESDAY NIGHT THROUGH SUNDAY/...
AS OF 245 PM...
TUESDAY NIGHT THROUGH WEDNESDAY NIGHT
SEVERE THREAT TUESDAY NIGHT IF ANY... LIKELY KEYING ON WARM FRONT
PASSAGE AFTER MIDNIGHT TUESDAY NIGHT AND ROUGHLY ALONG AND EAST OF A
WADESBORO... DURHAM... HENDERSON LINE. HOWEVER CONFIDENCE IN AN
EVENT IS VERY LOW AT THIS TIME AND WILL OMIT FROM OUTLOOK PRODUCTS
AT THIS TIME.
WINDS OF 50 TO 60 KNOTS BELOW 5000 FEET EXPECTED AS ABOVE MENTIONED
WARM FRONT LIFTS NORTH FROM SOUTH CAROLINA. STRONG HELICITY IN THE
VICINITY OF THE FRONT WOULD MAKE FOR A RISK OF TORNADOES WHILE
MOST RESIDENTS ARE IN BED... IF SUFFICIENT INSTABILITY WERE
PRESENT. WITH RAINS STABILIZING THE LOWEST LAYERS CURRENT THINKING
IS ANY CONVECTION WOULD BE ELEVATED AND UNABLE TO PUNCH THROUGH TO
THE SURFACE... AND THIS THINKING WILL BE FOLLOWED AT THIS TIME.
THE MARGIN FOR ERROR IS THIN AND THE SEVERE THREAT WILL OBVIOUSLY
CONTINUE TO BE EVALUATED AS THE EVENT NEARS.
RAIN LOOKS UNAVOIDABLE TUESDAY NIGHT INTO WEDNESDAY MORNING WITH
STRONG OVERRUNNING MOIST FLOW DEVELOPING TUESDAY NIGHT AS A STRONG
SURFACE LOW CLOSELY ASSOCIATED WITH AN UPPER TROUGH LIFTS
NORTHEAST TOWARD LAKE MICHIGAN. EVENT RAINFALL TOTALS IN EXCESS
OF ONE INCH FORECAST AT THIS TIME. SOME DRYING OF THE LOW LEVEL
AIR MASS BEGINS BEHIND THE WARM FRONT AND AHEAD OF THE COLD FRONT
TO THE WEST AND RAINFALL AMOUNTS AFTER SUNRISE WEDNESDAY PERHAPS
NO MORE THAN ONE QUARTER INCH...PERHAPS MUCH LESS... WITH THE
COLD FRONT ITSELF RELATIVELY DRY.
WEDNESDAY COULD BE QUITE BREEZY ONCE TEMPERATURES WARM AND STRONG
WINDS ALOFT MIX TO THE SURFACE. CURRENT FORECAST GUSTS TO 35 MPH
WEDNESDAY ACCEPTED.
ASSUMING THE LOW LEVEL DRYING OCCURS... WEDNESDAY NIGHT SHOULD BE
DRY... THOUGH IF THERE IS ANY RISK FOR MEASURABLE RAIN IT WOULD BE
EARLY AND EAST OF INTERSTATE 95. MOST OF THE NIGHT WILL BE PARTLY
CLOUDY TO MOSTLY CLEAR.
THE PARADE OF FRONTS WILL MAKE FOR A ROLLER COASTER RIDE FOR
TEMPERATURES. TEMPERATURES IN THE MID 40S TO LOW 50S TUESDAY EVENING
WILL RISE INTO THE 60S IN THE SOUTHEAST TOWARD SUNRISE WITH THE
PASSAGE OF THE WARM FRONT. TEMPERATURES CONTINUE TO WARM WEDNESDAY
AHEAD OF THE COLD FRONT IN GUSTY SOUTHWEST WINDS... WITH SOME 70S
IN THE EAST... AND THE NORTHWEST PIEDMONT PERHAPS TO 60 DEGREES
AHEAD OF THE COLD FRONT. TEMPERATURES QUICKLY DIVE IN COLD
ADVECTION BEHIND THE FRONT... REACHING THE MID 30S NORTHWEST...
AND MID 40S SOUTHEAST BY SUNRISE THURSDAY.
THURSDAY THROUGH SUNDAY
SURFACE HIGH PRESSURE OVER THE MIDWEST THURSDAY WILL SLOWLY ADVANCE
EAST AND CONTROL NORTH CAROLINA WEATHER INTO FRIDAY. THE ECMWF AND
GFS ARE IN ROUGH AGREEMENT IN DEVELOPING A SURFACE WAVE SATURDAY IN
THE NORTHERN GULF OF MEXICO AND DRIVING IT EAST INTO THE ATLANTIC.
HOWEVER THE 00Z RUN OF THE ECMWF IS MUCH SLOWER WITH THE SURFACE LOW
STILL SOUTH OF WILMINGTON AT SUNRISE SUNDAY. THE 12Z ECMWF HUGS A
SURFACE LOW TO THE NORTH CAROLINA COAST EARLY SUNDAY MORNING.
CONFIDENCE IN THE SURFACE FEATURES IN THE EXPECTED FAST FLOW
PATTERN IS LOW... BUT 48 HOURS OF CHANCES FOR MEASURABLE RAIN
UNLIKELY. WILL FOLLOW THE FASTER GFS AND HAVE BEST RAIN CHANCES
SATURDAY... BUT WITH LOW CONFIDENCE... AND LEAVE SUNDAY DRY.
AFTERNOON HIGHS MOSTLY IN THE 50S DURING THIS PERIOD... WITH SOME
UPPER 40S IN THE NORTH. THURSDAY NIGHT LOOKS TO BE THE COLDEST OF
THIS PERIOD AT 25 TO 30... WITH THE SURFACE HIGH NEAR AND THE AIR
MASS DRY. LOWS IN THE 30S FRIDAY AND SATURDAY NIGHTS.
&&
.AVIATION /00Z MONDAY THROUGH FRIDAY/...
AS OF 630 PM SUNDAY...
HIGH CLOUDS AHEAD OF A SOUTHERN STREAM SYSTEM WILL CONTINUE TO
STREAM OVER CENTRAL NORTH CAROLINA...HOWEVER VFR CONDITIONS WILL
PREVAIL THROUGH MUCH OF THE OVERNIGHT HOURS. DEVELOPING OVERRUNNING
CONDITIONS WILL LEAD TO A GRADUAL LOWERING OF CLOUD BASES OVER
PORTIONS OF THE REGION BY SUNRISE AND INTO THE AFTERNOON HOURS. THE
LOWEST BASES AND HIGHEST LIKELIHOOD OF BROKEN TO OVERCAST CEILINGS
ARE EXPECTED ALONG AND EAST OF THE INTERSTATE 95 CORRIDOR...
INCLUDING KFAY AND KRWI. LIGHT RAIN OR DRIZZLE ARE ALSO POSSIBLE IN
THESE AREAS...BUT NO ASSOCIATED VISIBILITY RESTRICTIONS ARE EXPECTED
GIVEN THE LIGHT NATURE AND ALSO THE LOW PROBABILITY OF ANY
PRECIPITATION.
AFTER A RETURN TO AREA WIDE VFR CONDITIONS FOR MONDAY NIGHT AND MOST
OF TUESDAY... EXPECT LIFR/IFR CONDITIONS AND A RAIN TO ONCE AGAIN
DEVELOP TUESDAY EVENING THROUGH WEDNESDAY... IN ASSOCIATION WITH
STRONG LIFT-INDUCING ISENTROPIC UPGLIDE AHEAD OF A POWERFUL MS
VALLEY STORM SYSTEM.
&&
.RAH WATCHES/WARNINGS/ADVISORIES...
NONE.
&&
$$
NEAR TERM...MWS/BADGETT
SHORT TERM...MWS
LONG TERM...RLH
AVIATION...KRR/MWS
