747 FXUS61 KCAR 202005 AFDCAR AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE CARIBOU ME 304 PM EST WED NOV 20 2002 .SYNOPSIS... HIGH PRESSURE OVER THE MARITIMES OVERNIGHT AND THURSDAY WILL GIVE WAY TO DEVELOPING LOW PRESSURE OVER THE MID ATLANTIC STATES THURSDAY NIGHT AND FRIDAY. THIS SHOULD RESULT IN MOSTLY CLOUDY SKIES THROUGH THURSDAY WITH RAIN GRADUALLY SPREADING NORTHEAST THROUGH THE REGION THURSDAY NIGHT. RAIN WILL CONTINUE FRIDAY AND FRIDAY NIGHT...OCCASIONALLY MIXING WITH SNOW OVER HIGHER TERRAIN OF NORTHERN MAINE...AS THE LOW SLOWLY MOVES NE OVER CAPE COD. BY SATURDAY...LOOK FOR RAIN TO CHANGE SNOW NORTH TO THE SOUTH ACROSS THE REGION...AS THE LOW INTENSIFIES OVER THE GULF OF MAINE... BRINGING SLIGHTLY COLDER AIR INTO THE REGION FROM QUEBEC. DISCUSSION... OVERALL PROGGED LONGWAVE PATTERN THROUGH DAY 7 FEATURES A GRADUALLY AMPLIFYING WRN NA RIDGE AND ERN NA UPPER TROF PATTERN. TWO MAJOR S/WV COMPLEXES HELP ESTABLISH THIS PATTERN. OPTED TO LEAN WITH THE AVN THRU DAY 4...WHICH HAS SHOWN THE GREATEST RUN TO RUN CONSISTENCY. THE FIRST MAJOR S/WV COMPLEX DIGGING SSE FROM CNTRL CAN RESULTS IN A CLOSED UPPER LOW OVR CNTRL APPALACHIA AS JET STREAK ENERGY BOTTOMS OUT OVR THE SE STATES NEAR 85 DEG W LON. THIS RESULTS IN THE UPPER FLOW BACKING OUT OF THE S AND OVERRUNNING RNFL OVR OUR FA LATE THU NGT THRU FRI EVE. DURING THIS TIME...SFC LOW PRES REMAINS DISORGANIZED IN THE VCNTY OF THE VA CAPE. SFC PRESURES ARE THEN PROGGED TO FALL FAIRLY RAPIDLY LATE FRI NGT INTO SAT OVR SE NEW ENG AND THE GULF OF ME AS THE UPPER LOW EJECTS NE OVR THE MID ATLC STATES AND MOVES NE INTO THE WRN GULF OF ME. PRIOR TO THIS RAPID DEEPENING...STRONG 925-700 MB WARM ADVCN WILL BRING SFC-850 MB SOUNDING TEMPS ABV ZERO EVEN ACROSS MOST OF THE N...RESULTING IN PRIMARILY RNFL THRU FRI NGT. AFTERWARDS...AS THE UPPER LOW APCHS FROM THE SW AND THE SFC LOW DEEPENS OVR THE GULF OF ME...LLVL COLD AVCN AS SFC WINDS SHIFT TO THE NNE AND PERHAPS DYNAMIC COOLING FROM ALF WILL ALLOW RN TO TRANSITION TO SN FROM N TO S ACROSS THE FA DURING THE DAY SAT. THE TIMING OF THE SCENARIO MAY OCCUR FASTER THAN THE 12Z OPERATIONAL AVN MODEL WHICH WAS ABOUT 6 TO 12 HRS SLOWER THAN THE ENSEMBLE MEAN IN EJECTING THE UPPER LOW. FOR THIS REASON...WE TAPERED THE PRECIP OFF SAT NGT FASTER THAN IMPLIED BY THE 12Z AVN RUN. ATTM...GIVEN THE UNCERTAINTY OF WHAT THE WINDOW OF OPPORTUNITY FOR SNFL WITH TIS EVENT...WE DO NOT HAVE ENOUGH CONFIDENCE TO ISSUE AN SPS FOR THE POTENTIAL OF SIG SNFL FOR ANY PTN OF THE FA SAT...ALTHOUGH IT IS POSSIBLE ANYWHERE N OF THE IMMEDIATE COAST DEPENDING ON THE SPEED AND TRACK OF THE UPPER LOW. BEHIND THIS SYSTEM...COLDER AIR SHOULD MOVE INTO THE FA SUN AND MON. THE NEXT OPPORTUNITY FOR PRECIP WILL BE TUE INTO WED WITH ANOTHER SERIES OF S/WVS SHARPENING THE UPPER TROF NEAR 90 DEG W. THIS SYSTEM COULD PRODUCE MORE IN THE FROZEN PRECIP THAN THE SYSTEM THIS WEEKEND...GIVEN MORE AVAILIABLE COLD AIR. COASTAL WATER: NO IMMEDIATE HEADLINES FOR COASTAL WATERS...WILL HIGHLIGHT THE POSSIBILITY OF GALES SAT EVE WITH THE N OR NW WINDS BEHIND THE LOW MOVING INTO THE MARITIMES. .CAR...NONE. VJN