000 FXUS61 KLWX 101032 AAA AFDLWX AREA FORECAST DISCUSSION...UPDATED NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC 532 AM EST FRI FEB 10 2012 .SYNOPSIS... HIGH PRESSURE OVER THE REGION THIS MORNING WILL SHIFT OFF THE EAST COAST THIS AFTERNOON. LOW PRESSURE WILL DEVELOP ALONG THE SOUTHEAST COAST THIS EVENING AND TRACK NORTHEASTWARD OFF THE EAST COAST THIS WEEKEND. A COLD FRONT TRACKING SOUTHEAST FROM CANADA WILL BRING COLDER AIR TO THE REGION FOR THE WEEKEND INTO EARLY NEXT WEEK. MODERATING TEMPERATURES ARE EXPECTED BY THE MIDDLE OF NEXT WEEK AS HIGH PRESSURE MOVES OFF THE COAST. && .NEAR TERM /THROUGH TONIGHT/... ERY MRNG SFC ANALYSIS SHOWS A BROAD AREA OF HIPRES OVER THE MID- ATLANTIC REGION. ASIDE FROM A LLVL STRATOCU DECK ONLY IMPACTING THE POTOMAC HIGHLANDS ERY THIS MRNG...THIN CI WILL STREAM IN FROM THE W-SW IN ADVANCE OF A THE NEXT STORM SYSTEM. HIPRES WILL SHIFT OFF THE EAST COAST THIS AFTN...WHICH WILL MARK THE BEGINNING OF AN ACTIVE WX PATTERN. A LEADING SRN STREAM TROUGH WILL INTERACT WITH A MUCH STRONGER NRN STREAM TROUGH THAT IS DIGGING INTO THE MIDWEST AND GREAT LAKES REGIONS LATER TODAY INTO TNGT. SWLY FLOW DEVELOPING OUT AHEAD OF BOTH SYSTEMS WILL ADVECT MILDER AIR INTO THE MID ATLANTIC TDA. DESPITE INCREASING CLOUD COVER LATE THIS AFTN...MAX TEMPS SHOULD RISE WELL INTO THE 40S AND EVEN LOW 50S ACROSS CENTRAL VA AND SRN MD...EXCEPT FOR THE COOLER RIDGE TOPS OF THE POTOMAC HIGHLANDS. ISENTROPIC LIFT IN THE LLVLS INCREASE LATE THIS AFTN AHEAD OF THE APPROACHING TROUGH. HAVE MADE MINOR UPWARD ADJUSTMENTS TO THE POPS THIS AFTN FROM THE BLUE RIDGE-WWD. GIVEN THE WARM TEMPS IN THE BOUNDARY LAYER...PRECIP SHOULD BE RAIN EVERYWHERE EXCEPT FOR A RA-SN MIX ACROSS THE FAR WRN RIDGES ABOVE 2 KFT. NUMERICAL MODEL GUIDANCE CONTINUES TO SHOW A COMPLEX WEATHER PATTERN SHAPING UP FOR TNGT. AN ARCTIC COLD FRONT ASSOCIATED WITH THE NRN STREAM TROUGH WILL PROGRESS EWD TOWARD THE WRN SIDE OF THE APPALACHIANS TNGT...WHILE THE WEAKER SRN STREAM SYSTEM MOVES ACROSS THE SE STATES. AS THESE TWO SYSTEMS START TO PHASE...A SECONDARY LOW DEVELOPS NEAR THE CAROLINA COAST THIS EVE. IT APPEARS THESE TWO SYSTEMS DO NOT TRULY PHASE UNTIL THE COASTAL LOW PASSES TO OUR NORTH AND EAST. THEREFORE...THE COASTAL LOW IS EXPECTED TO TAKE A MORE OFFSHORE TRACK THAT KEEPS THE HEAVIEST PRECIP EAST OF THE CHSPK BAY. MODELS DUE SHOW WEAK FORCING VIA ISENTROPIC LIFT AND LLVL FRONTOGENESIS OVER THE CWA AS MOISTURE STREAMS NWD AHEAD BOTH SYSTEMS. THEREFORE...LGT PRECIP IS EXPECTED ACROSS THE AREA. PRECIP IS EXPECTED TO START OFF AS RAIN THIS EVE...BEFORE MIXING WITH AND EVENTUALLY TRANSITIONING TO ALL SNOW FROM NW TO SE TNGT. SIMILAR TO THE EVENT ON WED...SFC TEMPERATURES START OUT FAIRLY WARM. ATTM...EXPECT THE RA/SN LINE TO BE NEAR THE BLUE RIDGE BY MIDNIGHT...WITH SNOW OVER POTOMAC HIGHLANDS/ERN WV/WRN MD AND RAIN ALONG THE I-95 CORRIDOR. PRECIP IS THEN FORECASTED TO CHANGE OVER TO SNOW LATE TNGT ACROSS THE NRN/WRN SUBURBS OF DC AND BALTIMORE. THE HIGHEST SNOWFALL ACCUMULATIONS WILL BE WELL NORTH AND WEST OF THE CITIES. GIVEN THE LGT QPF TNGT AND MARGINAL SFC TEMPS...GENERALLY NOT MUCH MORE THAN AN INCH TO PERHAPS TWO INCHES IN THE POTOMAC HIGHLANDS AND NEAR THE MASON-DIXON LINE IS POSSIBLE. THE LIKELIHOOD FOR TWO INCHES OF SNOW IS NOT HIGH ENOUGH TO ISSUE A SECOND PERIOD ADVISORY. PRECIP MAY CHANGE OVER TO A WET SNOW IN THE CITIES...BUT THE GROUND WILL LIKELY BE TOO WARM FOR SNOW TO ACCUMULATE. && .SHORT TERM /SATURDAY THROUGH SUNDAY NIGHT/... UPPER TROUGH INITIALLY OVER THE GREAT LAKES AND OHIO VALLEY SAT MORNING WILL PROGRESS EWD AND REACH THE CWA BY SAT EVENING. AS THE TROUGH APPROACHES...LOW PRESSURE WILL DEVELOP OFFSHORE EAST OF THE HAMPTON ROADS REGION AND RAPIDLY STRENGTHEN AS IT TRAVERSES THE GULF STREAM WATERS. PRIMARY DIFFERENCES IN MODELS AT THIS TIME ARE HOW QUICKLY THE LOW ORGANIZES SAT MORNING AND HOW MUCH PRECIPITATION WRAPS AROUND THE BACK SIDE OF THE LOW. GENERAL CONSENSUS IS THAT MOST PRECIP DIRECTLY ASSOCIATED WITH THE SURFACE LOW WOULD FALL ACROSS SERN VA AND EAST OF CHESAPEAKE BAY...BUT THERE MAY BE ENOUGH LIFT ASSOCIATED WITH THE UPPER TROUGH TO GENERATE PRECIP WEST OF THE BAY AS WELL. AS THIS POINT...LIMITING POPS TO CHANCE OVER MOST OF THE CWA EAST OF THE MOUNTAINS...EXCEPT SOME AREAS NEAR CHES BAY IN THE MORNING WHERE LIKELY POPS ARE FORECAST. UNCERTAINTY OVER TEMPERATURES ALSO LIMITS CONFIDENCE IN P-TYPE...BUT GENERAL TREND INDICATES RAIN/SNOW MIX POTENTIAL EAST OF THE BLUE RIDGE IN THE MORNING...THEN CHANGING TO RAIN...THEN BACK TO A MIX LATE IN THE DAY. FURTHER WEST OVER THE POTOMAC HIGHLANDS...STRONG NORTHWESTERLY WINDS DEVELOP DURING THE DAY ENHANCING POTENTIAL FOR ACCUMULATING UPSLOPE SNOWFALL. FORECAST SOUNDINGS INDICATE STEEP LAPSE RATES DEVELOPING AT LOW LEVELS. WIND DIRECTION SHOULD BE FAVORABLE FOR ADVECTING MOISTURE FROM THE GREAT LAKES. AT THIS POINT...SNOWFALL SHOULD BE LESS THAN WINTER STORM WARNING CRITERIA...BUT THIS WILL NEED TO BE EVALUATED WITH ADDITIONAL MODEL RUNS FOR POTENTIAL OF HIGHER SNOW AMOUNTS. SIGNIFICANT ARCTIC AIR ENTERS THE MID-ATLANTIC BEHIND THIS SYSTEM. THE LOW WILL PUSH FARTHER OFFSHORE SATURDAY NIGHT WITH DRY WEATHER EXPECTED...EXCEPT POSSIBLY OVER THE POTOMAC HIGHLANDS WHERE UPSLOPE SNOW MAY LINGER. TEMPS DROP INTO THE TEENS TO LOW 20S OVER MOST OF THE REGION...WITH POTENTIAL FOR SINGLE-DIGIT LOWS IN HIGHER ELEVATIONS. GUSTY WINDS ARE EXPECTED MOST OF THE NIGHT...WITH POTENTIAL FOR SINGLE-DIGIT WIND CHILLS OVER LOWER ELEVATIONS AND SUB-ZERO WIND CHILLS OVER HIGHER ELEVATIONS. SOME RIDGE TOPS MAY EVEN SEE WIND CHILLS BELOW -10 AT TIMES EARLY SUNDAY MORNING. && .LONG TERM /MONDAY THROUGH THURSDAY/... HIGH PRESSURE RETURNS MONDAY AND MONDAY NIGHT...WITH DRY WEATHER AND DIMINISHING WINDS EXPECTED. DOWNSLOPE FLOW MONDAY WILL HELP TEMPS RETURN TO NORMAL. NEXT OPPORTUNITY FOR PRECIP WILL BE MONDAY NIGHT OVER WESTERN PORTIONS OF THE CWA...THEN TUESDAY AND TUESDAY NIGHT FOR THE REMAINDER...WITH THE POTENTIAL FOR WEAK LOW PRESSURE PASSING THROUGH THE REGION. && .AVIATION /10Z FRIDAY THROUGH TUESDAY/... VFR CONDITIONS AND LGT SLY FLOW TDA. CLOUD COVER WILL INCREASE THIS AFTN...THEN CIGS WILL LOWER THIS EVE AS A COLD FRONT APPROACHES FROM THE WEST. PRECIP WILL INITIALLY BE RA THIS EVE. HOWEVER...COLDER AIR MOVING IN FROM THE WEST WILL CAUSE RA TO MIX WITH SNOW. A TRANSITION TO ALL SNOW IS LIKELY AT MRB AROUND MIDNIGHT AND IAD/BWI SOMETIME DURING THE ERY MRNG. THE TIMING OF A CHANGE OVER IS STILL A LITTLE UNCERTAIN ATTM. IFR CIGS/VSBYS ARE LIKELY WITH SNOW. PERIODS OF SUB-VFR CONDS PSBL SATURDAY WITH RAIN OR A RAIN/SNOW MIX. GUSTY WINDS DVLP BY SAT AFTERNOON...WITH POTENTIAL FOR GUSTS EXCEEDING 30 KTS LATE AFTERNOON INTO THE EVENING. VFR LIKELY SUNDAY WITH GUSTY NW WINDS CONTINUING. VFR LIKELY MONDAY WITH LIGHT WINDS. OCCASIONAL SUB-VFR PSBL TUESDAY. && .MARINE... SLY WINDS TDA WILL BE LGT...EXCEPT FOR CHANNELED FLOW LEADING TO HIGHER GUSTS UPWARDS OF 15 KT IN THE MAIN STEM OF THE MD CHSPK BAY. A COASTAL LOW WILL DEVELOP ALONG THE CAROLINA COAST THIS EVE BEFORE TRACKING NEWD AND WELL OFF THE DELMARVA COAST LATE TNGT. PRECIP WILL OVERSPREAD THE AREA AS A RESULT. SMALL CRAFT ADVISORY CONDITIONS WILL START BY SATURDAY MORNING AS LOW PRESSURE STRENGTHENS OVER THE ATLANTIC JUST OFFSHORE. GALES WILL BE LIKELY OVER PORTIONS OF THE WATERS BY SATURDAY AFTERNOON AND CONTINUING INTO SUNDAY WITH GUSTY NW FLOW BEHIND THE SYSTEM. CONDITIONS IMPROVE GRADUALLY SUNDAY NIGHT...BUT SCA GUSTS WILL BE POSSIBLE INTO MONDAY MORNING. THEN SUB-SCA CONDITIONS BY MONDAY AFTERNOON AND CONTINUING THROUGH TUESDAY WITH HIGH PRESSURE OVER THE WATERS. && .LWX WATCHES/WARNINGS/ADVISORIES... DC...NONE. MD...NONE. VA...NONE. WV...NONE. MARINE...SMALL CRAFT ADVISORY FROM 8 AM TO 6 PM EST SATURDAY FOR ANZ530>543. && $$ UPDATE...KLEIN PREVIOUS DISCUSSION...KLEIN/KCS