Issued by NWS Sterling, VA
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-- Discussion containing changed information from previous version are highlighted. --000 FXUS61 KLWX 222216 AAA AFDLWX AREA FORECAST DISCUSSION...UPDATED NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC 516 PM EST SUN NOV 22 2009 .SYNOPSIS... HIGH PRESSURE WILL CONTINUE TO RETREAT TO THE NORTH TONIGHT WHILE AN AREA OF LOW PRESSURE DEVELOPS OFF THE SOUTHEAST COAST. THIS LOW WILL TRACK UP THE MID-ATLANTIC COAST MONDAY AND TOWARDS NEW ENGLAND MONDAY NIGHT INTO TUESDAY. HIGH PRESSURE WILL BUILD IN BEHIND THIS SYSTEM LATER TUESDAY AND WEDNESDAY. A COLD FRONT WILL PASS THROUGH THURSDAY BRINGING UNSETTLED CONDITIONS. AN UPPER-LEVEL LOW WILL CONTINUE TO IMPACT THE REGION LATE IN THE WEEK. && .NEAR TERM /UNTIL 6 AM MONDAY MORNING/... CURRENT ANALYSIS SHOWS HIGH PRESSURE CENTERED OVER NEW ENGLAND THIS AFTERNOON. A SURFACE LOW CONTINUES TO TRACK ALONG THE GULF COAST STATES. THE UPPER-LEVEL LOW ASSOCIATED WITH THE SURFACE LOW IS TRACKING TOWARD THE TENNESSEE VALLEY. SURFACE HIGH WILL CONTINUE TO RETREAT TO THE NORTHEAST TONIGHT WHILE THE SURFACE LOW REDEVELOPS ALONG THE SOUTHEAST COAST. THE UPPER-LEVEL LOW ASSOCIATED WITH THIS SYSTEM WILL TRACK THROUGH THE TENNESSEE VALLEY TONIGHT AND TOWARD SOUTHWESTERN VIRGINIA BY MONDAY MORNING. A LOW-LEVEL EAST-SOUTHEAST FLOW AROUND THE DEPARTING HIGH AND THE LOW PRESSURE SYSTEM WILL BRING INCREASING AMOUNTS OF MOISTURE OFF THE ATLANTIC OCEAN. THE MOISTURE INCREASE COMBINED WITH ISENTROPIC LIFT WILL RESULT IN INCREASING LOW CLOUDS LATER THIS EVENING INTO THE OVERNIGHT HOURS. WITH THE ACTUAL STORM SYSTEM REMAINING WELL TO THE SOUTH...DRY CONDITIONS ARE EXPECTED THROUGH THIS EVENING. HOWEVER...RAIN AHEAD OF THE STORM SYSTEM WILL BEGIN TO OVERSPREAD THE REGION FROM SOUTH TO NORTH LATE. && .SHORT TERM /6 AM MONDAY MORNING THROUGH 6 PM MONDAY/... THE SURFACE LOW WILL CONTINUE TO TRACK UP THE MID-ATLANTIC COAST WHILE THE UPPER-LEVEL LOW SHEARS APART AS IT TRACKS ACROSS OUR REGION. A LOW-LEVEL EASTERLY FLOW COMBINED WITH ISENTROPIC LIFT WILL RESULT IN LOW CLOUDS ALONG WITH OCCASIONAL RAIN. RAINFALL AMOUNTS SHOULD BE ON THE LIGHT SIDE DUE TO THE LACK OF STRONG DYNAMICS WITH THIS SYSTEM. MAX TEMPS WILL BE SEVERAL DEGREES COOLER THAN RECENT DAYS DUE TO THE RAINFALL...RANGING FROM THE MID AND UPPER 40S ACROSS THE POTOMAC HIGHLANDS INTO THE SHENANDOAH VALLEY...TO NEAR 50 IN WASHINGTON AND BALTIMORE...TO THE LOWER AND MIDDLE 50S ACROSS LOWER SOUTHERN MARYLAND. && .LONG TERM /MONDAY NIGHT THROUGH SUNDAY/... ANY PCPN LINGERING MON NGT WUD BE AS A RSLT OF THE DEF AXIS ACRS CWFA. HWVR...LOPRES RATHER WEAK...AND FAR OFFSHORE...SO DONT THINK THAT PCPN WUD BE PLENTIFUL. WUD BE MORE CONCERNED ABT DZ...BUT SFC WNDS NLY NOT NE/ELY. HIPRES BRIEFLY BLDS TUE-TUE NGT. BUT IT SHUD BE A DIRTY RDG AS AMPLE LLVL MSTR STILL LINGERS. SUNSHN SHUD BE LMTD...ASSUMING IT CAN BRK THRU MARINE STRATUS. BASED ON TKNS OF MARINE DECK ON MDL TIME-HGTS...THAT/LL BE A BIG ASSUMPTION. SUSPECT LLVL CLDS WL BE SUFFICIENT FOR DZ TO DVLP TUE NGT...SPCLY SINCE SFC HIGH WEDGED A LA CAD AND H9-8 FLOW BCMG SLY. CMPLX SCENARIO SETTING UP FOR MID WK...AS S/WV ENERGY DROPS INTO CNTRL PLAINS...CUTTING OFF H5 LOW BY TUE. ADDTL VORTS CARVE OUT A 2ND LOW...WHICH WL DEEPEN LOW OVR GRTLKS BY THU. LCLLY...CWFA WL RECEIVE ISENT LIFT...THEN GLANCING BLOW OF PVA WED. THUS...CLDS GOING NOWHERE...AND CHC SHRA RETURNS. SOME MIXING CUD PUNCH HOLES IN THE CLD DECK BHD VORT LT WED-WED NGT. TEMPS FAIRLY TEMPERATE THRU THE PD. NOT MUCH SPREAD IN MOS TEMPS TMRW NGT-TUE...AND A SLGTLY LRGR SPREAD TUE NGT. CONSIDERING CLDS...STAYED AWAY FM BIG DIURNAL SWINGS-- WARM SIDE OF MEAN FOR MIN-T BUT COOLER SIDE FOR MAXT. XTNDD...DP H5 TROF AXIS/CUTOFF LOW TO PIVOT ACRS CWFA THU-FRI. THIS CYCLE...GDNC - SPCLY GFS - NOW TRANSFERRING ENERGY TO DVLPG CSTL SYSTM LT THU NGT-ELY FRI MRNG. BUT EVEN THE MORE STBL ECMWF TRENDING TWD GFS. EITHER WAY THE END RSLT WL BE SIMLR...FVRBL SUPPORT FOR PCPN...AND SIGNALS THAT HIER ELEVS CUD RECEIVE SNW. WL INCR POPS THU-THU NGT...AND STICK W/ MTN SNW/MIX ONCE CAA UPON US THU PM. NW FLOW PTTN THRU SAT. WL ENHANCE UPSPL PCPN THRU THAT TIME. && .AVIATION /22Z SUNDAY THROUGH FRIDAY/... VFR CONDITIONS ARE EXPECTED THROUGH EARLY THIS EVENING WITH INCREASING HIGH CLOUDS. AS LOW PRESSURE DEVELOPS OFF THE SOUTHEAST COAST...AN ONSHORE FLOW WILL RESULT IN LOW CLOUDS LATE THIS EVENING AND OVERNIGHT. RAIN AND DRIZZLE WILL OVERSPREAD THE TERMINALS MONDAY MORNING WHILE A NORTHEAST FLOW CONTINUES TO USHER IN PLENTY OF LOW-LEVEL MOISTURE FROM THE ATLANTIC. CIGS WILL LIKELY DROP TO IFR LEVELS LATE TONIGHT AND LAST THROUGH MONDAY. VSBYS WILL DROP MAINLY TO MVFR LEVELS LATE TONIGHT...BUT IFR VSBYS ARE POSSIBLE ONCE THE RAIN BEGINS. FLGT RESTRICTIONS PSBL THRU MUCH OF WK AS UNSTTLD CONDS ABOUND. IF THERE WERE A BRK IT WUD COME TUE AFTN/EVE...BUT LOW CLDS/DZ LKLY TO RTN TUE NGT. && .MARINE...-- Changed Discussion --PRESSURE GRADIENT APPEARS TO BE SHARPENING SLGTLY EARLIER THAN DEPICTED IN PREV GRIDS...MAINLY LWR PORTIONS OF MD CHSPK BAY AND LWR TIDAL POTOMAC. HAVE ADJUSTED START TIME OF SMALL CRAFT ADZY TO PRESENT TIME FOR THESE ZONES..WHERE 17-20 KT GUSTS COMMON AND XPCD TO PERSIST. RMNDR OF ADZY WILL BGN AT MIDNIGHT AS PREVLY ISSUED. PREV DISCUSSION FOLLOWS... LOW PRESSURE WILL DEVELOP OFF THE SOUTHEAST COAST TONIGHT. A STRENGTHENING PRESSURE GRADIENT DUE TO THE LOW WILL BRING SCA WIND GUSTS ACROSS THE CHESAPEAKE BAY AND LOWER TIDAL POTOMAC OVERNIGHT. AS LOW PRESSURE TRACKS UP THE MID- ATLANTIC COAST MONDAY...MORE SCA CONDITIONS ARE EXPECTED ACROSS THE LOWER TIDAL POTOMAC AND CHESAPEAKE BAY. HAVE CAPPED WIND GUSTS MONDAY AROUND 15 KNOTS ACROSS THE UPPER TIDAL POTOMAC...BUT WITH FASTER WINDS LESS THAN A THOUSAND FEET FROM THE SURFACE...ANY MIXING WOULD BRING STRONGER WIND GUSTS LATER MONDAY MORNING/AFTERNOON. THIS WILL HAVE TO BE MONITORED BY LATER SHIFTS. G20KT LKLY TO CONT INTO TMRW NGT DUE TO NLY FLOW...SPCLY FOR MAIN CHANNEL BAY BLO POOLES ISL AND FOR LWR PTMC. WL INCL BIG INLETS BUT NOT BALT HARBOR/PAX RIVER. HIPRES RDG SHUD DECR WNDS TUE-WED...ALTHO LOW CLDS SHUD BE PLENTIFUL AND RA A PSBLTY BY WED.-- End Changed Discussion --&& .TIDES/COASTAL FLOODING... WITH HIGH PRESSURE WELL TO OUR NORTH...AN ONSHORE FLOW HAS DEVELOPED THIS AFTERNOON. THE FLOW IS WEAK AND TIDAL ANOMALIES RANGE FROM NEAR NORMAL TO ABOUT ONE HALF FOOT ABOVE NORMAL. LOW PRESSURE IS EXPECTED TO DEVELOP OFF THE SOUTHEAST COAST TONIGHT AND THE GRADIENT IS EXPECTED TO TIGHTEN BETWEEN THESE TWO SYSTEMS OVERNIGHT AND MONDAY. AS THE LOW TRACKS UP THE MID-ATLANTIC COAST MONDAY INTO MONDAY NIGHT...THIS WILL CAUSE TIDAL ANOMALIES TO INCREASE DURING THIS TIME. LATEST CBOFS AND EXTRATROPICAL MODELS CONTINUE TO INDICATE THAT WATER LEVELS WILL REMAIN BELOW THRESHOLDS FOR MINOR COASTAL FLOODING. THE ASTRONOMICAL NORMS FOR WATER LEVELS ARE ALSO ON THE LOWER SIDE DUE TO THE LUNAR CYCLE APPROACHING THE FIRST QUARTER PHASE. HAVE NOT ISSUED AN ADVISORY FOR THESE TWO REASONS...BUT THIS WILL HAVE TO BE MONITORED BY LATER SHIFTS. && .LWX WATCHES/WARNINGS/ADVISORIES...-- Changed Discussion --DC...NONE. MD...NONE. VA...NONE. WV...NONE. MARINE...SMALL CRAFT ADVISORY FROM MIDNIGHT TONIGHT TO 5 AM EST TUESDAY FOR ANZ531>533-539>541. SMALL CRAFT ADVISORY FROM MIDNIGHT TONIGHT TO 8 PM EST MONDAY FOR ANZ530-538-542. SMALL CRAFT ADVISORY UNTIL 5 AM EST TUESDAY FOR ANZ534-537-543.-- End Changed Discussion --&& $$ UPDATE...KRAMAR PREV DISCUSSION...LASORSA/HTS
