AFDAKQ AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE WAKEFIELD VA 432 AM EDT SUN MAR 27 2011 .SYNOPSIS... LOW PRESSURE ORIENTED ALONG THE CAROLINA COAST WILL ACCELERATE OFF THE MID ATLANTIC COAST THROUGH THIS EVENING. CANADIAN HIGH PRESSURE BUILDS SOUTH ACROSS THE REGION EARLY NEXT WEEK. LOW PRESSURE APPROACHES FROM THE WEST WEDNESDAY. && .NEAR TERM /THROUGH TONIGHT/... LATEST WX ANALYSIS DEPICTS OLD STATIONARY BOUNDARY DRAPED ACROSS SE SC/N GA THIS MORNING...WITH A WEAK AREA OF SFC LOW PRESSURE MOVING ALONG THE FRONT JUST OFF THE SC COAST. TO OUR NORTH...HIGH PRESSURE OVER THE UPR GREAT LAKES/CANADIAN PRAIRIE PROVINCES IS RIDGING SE INTO THE MID-ATLANTIC REGION. BEST OVERRUNNING MOISTURE IN ASSN WITH SOUTHERN LOW PUSHING INTO TIDEWATER COUNTIES ATTM...AND SHOULD TRANSITION OFFSHORE BY MID MORNING. MEANWHILE...TO THE NORTH MOISTURE IN ASSN WITH UPR WAVE CROSSING APP MTNS PUSHING ACROSS THE NORTHERN TIER OF CWA THIS MORNING WITH SNOW NOW NOTED ACROSS MUCH OF OUR GOING WWA AREA. COLUMN /EVAPORATIVE/ COOLING HAS ALLOWED FOR SOME SN/SLEET TO MIX IN AS FAR SOUTH AS THE RICHMOND METRO AND WILLIAMSBURG AREAS. HOWEVER...ERY MORNING WV IMAGERY SHOWS DRIER AIR ALOFT PUSHING INTO NW ZONES...AND RUC/NAM SOUNDINGS SHOWING MOISTURE IN DENDRITIC GROWTH ZONE DIMINISHING QUICKLY AFTER 12Z OVER THE WEST...AND BY 16Z OVER MOST OF AKQ CWA. ACCORDINGLY...HV ADJUSTED SNOWFALL ACCUMULATIONS DOWN TO ~1 INCH (OR LESS) WEST OF THE CHES BAY WITH THIS PACKAGE. THINKING THAT RN WL REMAIN THE PREDOMINATE PCPN TYPE FOR THIS EVENT OVER THE RICHMOND METRO...WITH A BRIEF TRANSITION TO SNOW POSSIBLE BEFORE BEST MOISTURE SHIFTS EASTWARD AFTER 12Z. FARTHER EAST...APPEARS ARRIVING LLVL MOISTURE AND COLUMN COOLING WL PROVIDE BEST CHC AT ACCUMULATING SNOWFALL OVER AKQ CWA...WITH 1-2" FORECAST STILL LOOKING REASONABLE OVER THE EASTERN SHORE FROM NOW THROUGH MID- MORNING HOURS. AS NOTED PREVIOUSLY...MOISTURE IN CRITICAL DENDRITIC GROWTH ZONE DIMINISHES QUICKLY AFTER MID-MORNING INTO THE AFTN HOURS...WHICH DESPITE LINGERING LOW LEVEL MOISTURE AND NE FLOW SHOULD ALLOW FOR LTL MORE THAN INTERMITTENT PERIODS OF LGT RAIN/DRIZZLE THIS MORNING...DIMINISHING IN AREAL COVERAGE BY THE AFTN AS ISENTROPIC LIFT CEASES. MET NUMBERS ALREADY WAY OFF...SO HV GONE WITH A MIX OF PERSISTENCE AND MAV NUMBERS FOR TODAY...YIELDING HIGHS MAINLY IN THE L40S...WITH U30S COASTAL ZONES. && .SHORT TERM /TONIGHT THROUGH TUESDAY/... TONIGHT... OVC CONDITIONS SHOULD PERSIST OVERNIGHT AS WEDGE LOOKS TO REMAIN IN PLACE OVER CENTRAL/SOUTHERN ZONES. HV GONE A BIT COOLER OVER MD/NORTHERN NECK VA ZONES WITH LOWEST LLVL MOISTURE PORTENDING TO WHAT COULD BE AT LEAST PARTIAL CLEARING OVERNIGHT. WL GO WITH LOWS IN THE LOW 30S FOR MOST...U20S OVER NORTHERN TIER. MONDAY... AFOREMENTIONED CANADIAN HIGH BUILDS SE INTO THE RGN FROM THE N MONDAY AND TUE. MODELS CONTINUE TO CONVERGE TOWARDS BRINGING ACROSS WEAK SHORTWAVE ENERGY FROM THE TN VLY BY MONDAY MORNING. BEST RN CHCS LOOK TO REMAIN ORIENTED OVER SOUTHERN ZONES WHERE BEST LIFT AND LLVL MOISTURE CONVERGENCE INVOF WEDGE FRONT REMAINS IN PLACE. WL STICK WITH SCT/BKN CLOUD COVER IDEA FROM PVS SHIFT AND ADJUST MAXIMA ONLY SLIGHTLY...STILL BELOW SEASONAL VALUES RANGING THROUGH THE 40S. TUESDAY... SLOW WRMG TREND TUE AS SFC HIGH SLIDES OFFSHORE. HIGHS U40S/NR50 ALONG THE COAST TO M/U50S WELL INLAND. && .LONG TERM /TUESDAY NIGHT THROUGH SATURDAY/... COMPARED TO PREVIOUS RUNS...ECMWF/GFS ARE IN BETTER AGREEMENT WHEN IT COMES TO THE LATTER PORTION OF THE EXTENDED PERIOD (FRI-SAT). THE PREVIOUS (00Z) CANADIAN RUN IS MORE OF AN OUTLIER WITH THE MORE AMPLIFIED UPR PATTERN (DEEPER LOW) ACROSS THE ERN CONUS FRI-SAT. EARLIER IN THE PERIOD...LATEST ECMWF/GFS CONSENSUS LEADS TO HIGHER CONFIDENCE FOR A PERIOD OF WAA RAIN ON WED...WITH A LLVL CAD WEDGE IN PLACE AS A WEAK LOW TRAVERSES THE CAROLINAS. AT THIS POINT IT LOOKS LIKE A QUARTER-HALF INCH OF STRATIFORM RAINFALL...POTENTIALLY MORE OVER SRN AREAS DEPENDING ON PRESENCE OF ANY ELEVATED CONVECTION. HIGHS FROM THE 40S FAR N TO THE 50S S. NEXT CHANCE FOR WIDESPREAD RAIN COMES ON FRI...THOUGH AGAIN THE MODELS (PARTICULARLY THE CANADIAN) DIFFER ON THE DETAILS. THE GFS NO LONGER DEPICTS A DEEPENING LOW OFF THE MID ATLC COAST...INSTEAD SHOWS ANOTHER OVERRUNNING EVENT WITH A WEAK LOW TRACK S OF THE FCST AREA. THE ECMWF...WHICH AT 00Z WAS MUCH DRIER OVER OUR AREA FOR FRI...NOW SHOWS CYCLOGENESIS OFF THE MID ATLC AND NE COASTS THU NIGHT AND FRI. THIS SOLUTION STILL DOES NOT GIVE MUCH OF OUR REGION ANYTHING MORE THAN MINIMAL RAIN CHANCES (HIGHEST ALONG THE COAST)... HOWEVER...GIVEN THE SLIGHTLY WETTER TREND AND SOMEWHAT BETTER CONSISTENCY OF THE GFS...WILL MAINTAIN RAIN CHANCES ON FRI...ALBEIT FOR NOW MUCH LOWER THAN ON WED. && .AVIATION /08Z SUNDAY THROUGH THURSDAY/... AS OF 06Z...BEGINNING TO SEE CIGS/VSBYS DETERIORATE...ALTHOUGH THE MAIN TIMEFRAME FOR IFR CONDITIONS LOOKS TO BE 09Z-15Z. HAVE NOT CHANGED MUCH FROM PREV FCST...EITHER RASN OR SNPL AT RIC/SBY...KEEPING IT -RA ELSEWHERE (ALTHOUGH A BRIEF PERIOD OF -RASN CERTAINLY POSSIBLE AT ORF/PHF). OTHER ISSUE WILL BE A FAIRLY STRONG NE WIND AT ORF/ECG...15-20KT G25KT FROM ABOUT 10-16Z. BY AFTN...LINGERING LOW CLOUDS WILL BE SLOWEST TO LIFT AT ORF/PHF/ECG (CIGS AROUND 1 K FT) ALONG WITH DZ. SHOULD SEE CIGS LIFT TO MORE LIKE 2-3 K FT AT RIC/SBY AFTER 18Z...AND POSSIBLY SCATTER OUT TWDS 22-23Z (AND ELSEWHERE AFTER 00Z). MON-THU...INCREASING CLOUDS MON 12-18Z..BUT ONLY EXPECTING CIGS TO DROP CLOSE TO 1-2 K FT AT ECG...GNLY ABOVE 3K FT ELSEWHERE. DRY/QUIET MON NGT-TUE NGT. ANOTHER SYSTEM LOOKS TO BRING -RA AND POSSIBLY LOW CIGS/VBSYS WED. && .MARINE... SCA FLAGS IN EFFECT FOR ALL EXCEPT FAR NRN CSTL WATERS...A FAIRLY QUICK SHOT THOUGH AS SYSTEM RAPIDLY MOVES OFF THE SRN NC/SC COAST LATER THIS MORNING. GRADIENT W/ THIS SYSTEM IS TIGHTEST OVER SRN AREAS AND WEAKENS RAPIDLY FARTHER TO THE NORTH. THUS...STRONGEST WINDS (GUSTS TO 30 KT)...AND HIGHEST SEAS (BUILDING TO 6-7 FT) WILL BE OVER SRN CSTL WATERS...WITH MORE MARGINAL CONDS IN THE REMAINING AREAS. BY MID-LATE AFTN EXPECT TO BE ABLE TO DROP THE SCA FLAGS EXCEPT FOR LINGERING 5 FT SEAS OVER SRN CSTL WATERS. A BRIEF AND WEAK CAA SURGE WILL ALLOW WINDS TO INCREASE SLIGHTLY OVERNIGHT BUT SHOULD STAY BELOW SCA CRITERIA. ANOTHER WAVE OF LOW PRESSURE MOVES ACRS THE CAROLINAS AND OFF THE NC COAST MON...ALLOWING FOR ONE MORE MARGINAL INCREASE IN NLY WINDS MON NGT/ERLY TUE MRNG (HAVE THIS TREND IN THE FCST BUT EXPECT CONDS TO ONCE AGAIN STAY BELOW SCA CRITERIA). QUIET CONDITIONS PREVAIL TUE WITH ANOTHER DISTURBANCE FOR WED-THU. && .CLIMATE... VERY COLD HIGH TEMPERATURES EXPECTED TODAY/SUNDAY...COULD POSSIBLY TIE THE RECORD LOW MAX VALUE AT RIC (WILL BE TOO WARM AT ORF)... REC LOW MAX MAR 27TH / YEAR RICHMOND......41 F...../ 1947 (HAS HIT 41 F SO FAR THIS MRNG) NORFOLK.......38 F...../ 1894 (HAS HIT 41 F SO FAR THIS MRNG) && .AKQ WATCHES/WARNINGS/ADVISORIES... MD...WINTER WEATHER ADVISORY UNTIL 2 PM EDT THIS AFTERNOON FOR MDZ021>023. NC...NONE. VA...WINTER WEATHER ADVISORY UNTIL 2 PM EDT THIS AFTERNOON FOR VAZ048-049-061>064-074>076. MARINE...SMALL CRAFT ADVISORY UNTIL 6 PM EDT THIS EVENING FOR ANZ630>633. SMALL CRAFT ADVISORY UNTIL 7 PM EDT THIS EVENING FOR ANZ652- 654. SMALL CRAFT ADVISORY UNTIL 1 AM EDT MONDAY FOR ANZ656-658. && $$ SYNOPSIS...MAM