Issued by NWS Sterling, VA
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-- Discussion containing changed information from previous version are highlighted. --000 FXUS61 KLWX 231508 AFDLWX AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC 1008 AM EST MON NOV 23 2009 .SYNOPSIS...-- Changed Discussion --LOW PRESSURE WILL TRACK UP THE MID-ATLANTIC COAST THIS AFTERNOON AND TOWARDS LONG ISLAND TONIGHT. HIGH PRESSURE WILL BUILD IN BEHIND THIS SYSTEM TUESDAY AND TUESDAY NIGHT. A STORM SYSTEM WILL APPROACH FROM THE NORTHWEST WEDNESDAY. A STRONGER SYSTEM WILL MOVE ACROSS THE AREA THANKSGIVING AND FRIDAY.-- End Changed Discussion --&& .NEAR TERM /UNTIL 6 PM THIS EVENING/...-- Changed Discussion --CURRENT ANALYSIS SHOWS LOW PRESSURE OFF THE NORTH CAROLINA COAST THIS MORNING. HIGH PRESSURE OVER EASTERN CANADA EXTENDS INTO NEW ENGLAND. A SERIES OF WEAK UPPER-LEVEL DISTURBANCES EXTEND FROM NEW JERSEY THROUGH THE MID-ATLANTIC AND INTO THE OHIO VALLEY. THE SURFACE LOW OFF THE CAROLINA COAST WILL CONTINUE TO SLOWLY TRACK UP THE MID-ATLANTIC COAST THIS AFTERNOON. WITH HIGH PRESSURE TO THE NORTH...A LOW-LEVEL EASTERLY FLOW WILL USHER IN PLENTY OF MOISTURE FROM THE ATLANTIC OCEAN. THE WARMER AND MORE MOIST AIR AT THE LOW-LEVELS WILL OVERRUN THE COOL AIR AT THE SURFACE...RESULTING IN PLENTY OF CLOUDS ALONG WITH PERIODS OF RAIN. WEAK MID-LEVEL FORCING WILL KEEP THE STEADIEST RAIN ACROSS THE VIRGINIA PIEDMONT INTO LOWER SOUTHERN MARYLAND...WHERE RAINFALL AMOUNTS AROUND ONE QUARTER TO ONE HALF INCH ARE EXPECTED. FURTHER NORTH AND WEST...RAINFALL AMOUNTS WILL BE CLOSER TO ONE TENTH OF AN INCH...WITH EVEN LIGHTER AMOUNTS NEAR THE MASON DIXON LINE. MAX TEMPERATURES THIS AFTERNOON WILL BE SEVERAL DEGREES COOLER COMPARED TO RECENT DAYS DUE TO THE CLOUD COVER AND RAIN. MAX TEMPS WILL 40S IN THE SHENANDOAH VALLEY TO THE LOWER 50S IN WASHINGTON AND BALTIMORE.-- End Changed Discussion --&& .SHORT TERM /6 PM THIS EVENING THROUGH 6 AM TUESDAY/... TNGT THE LOW WL BE TRACKING NE OF THE AREA. WL HV CAT POPS IN THE XTRM NE CORNER OF THE CWA FOR THE EVE HRS...DROPPING TO CHC EVERYWHERE AFTR MDNGT. SKIES WL RMN CLDY. AGN LTL MODERATION W/ THE TEMPS - XPCT THE LOWS TNT TO RANGE FM A40 IN THE HIGHLANDS TO A50 ALONG THE BAY. && .LONG TERM /TUESDAY THROUGH SUNDAY/... WEAK HIPRES WILL BUILD OVER THE AREA BEHIND THE DEPARTING LOW OFF THE NEW ENGLAND COAST. DESPITE HIPRES OVRHD...CLDY CONDITIONS WILL CONT MIDWEEK AS LLVL MOISTURE REMAINS TRAPPED BELOW SUBSIDENCE INVERSION. CANNOT RULE OUT PATCHY DRIZZLE WITH LGT SLY FLOW AT LLVLS SUPPORTING WEAK ISENTROPIC LIFT IN SHALLOW MOIST LAYER. LEADING UPPER SHORTWAVE ENERGY EMBEDDED IN C CONUS LONGWAVE TROUGH WILL TRACK OVER THE MIDWEST TUE AND THE GREAT LAKES WED. ALTHOUGH THIS WEAKENING SYSTEM SHOULD TRACK WELL NW OF THE AREA...ENOUGH LIFT AIDED BY DPVA/WAA WILL DEVELOP TO MENTION LOW CHANCES FOR SHOWERS WED/WED NGT. THE TRAILING SHORTWAVE TROUGH DROPS SEWD WHILE AMPLIFYING ACROSS THE C CONUS THU. WITH STRENGTHENING HGT FALLS AHEAD OF THE CUTOFF LOW...SFC DEVELOPMENT IS FCST TO OCCUR SOMEWHERE ALONG THE SE COAST. BEST CWFA-WIDE CHANCE FOR RAIN OR SHOWERS APPEARS TO BE THU AFTN INTO THU NGT WITH THE SFC LOW TRACKING THRU THE MID ATLANTIC REGION. WITH THE THERMAL GRADIENT TIGHTENING...STRONG CAA WILL ENSUE BEHIND THE SFC LOW ONCE THE ATTENDANT COLD FRONT CROSSES THE APPALACHIANS LATE THU INTO FRI. 00Z GFS BUFKIT SOUNDINGS SUPPORT A RA/SN MIX FOR THE HIGHER ELEVATIONS IN THE POTOMAC HIGHLANDS THU NGT AND FRI. CYCLONIC WLY FLOW AROUND THE UPPER LOW WILL LEAD TO SEASONABLY COLD TEMPERATURES ACROSS THE ENTIRE AREA WHILE PROLONGING THE CHANCES FOR UPSLOPE SN SHOWERS ACROSS THE WRN SLOPES OF THE ALLEGHENY FRONT AND POTOMAC HIGHLANDS THRU SAT. HIPRES BUILDS BACK INTO THE AREA SUN. && .AVIATION /15Z MONDAY THROUGH FRIDAY/...-- Changed Discussion --LOW CLOUDS WILL CONTINUE TO AFFECT THE TERMINALS THROUGHOUT THE AFTERNOON. RAIN WILL ALSO OVERSPREAD THE TERMINALS. MVFR CIGS ACROSS MOST OF THE AIRPORTS THIS MORNING WILL DROP TO IFR LEVELS ONCE THE RAIN BEGINS. MVFR/IFR VSBYS ARE ALSO EXPECTED IN AREAS OF RAIN. MORE IFR CIGS ARE EXPECTED TONIGHT WITH MVFR/IFR VSBYS. PERIODS OF SUB-VFR CIGS AND DZ POSSIBLE THRU MIDWEEK AS MARINE MOISTURE REMAINS TRAPPED AT THE LLVLS. A STORM SYSTEM WILL TRACK NW OF THE TERMINALS WED BUT CLOSE ENOUGH TO BRING CHANCES FOR SHRA. A STRONGER DISTURBANCE IS EXPECTED TO MOVE THRU THU INTO ERY FRI.-- End Changed Discussion --&& .MARINE...-- Changed Discussion --WILL CONTINUE WITH A SMALL CRAFT ADVISORY THIS AFTERNOON FOR THE CHESAPEAKE BAY AND LOWER TIDAL POTOMAC. THE PRESSURE GRADIENT WILL STRENGTHEN A BIT RESULTING IN WIND GUSTS PAST SCA CRITERIA. ACROSS THE UPPER TIDAL POTOMAC...WIND GUSTS AROUND 15 KNOTS ARE EXPECTED THIS AFTERNOON. WINDS WILL TURN MORE TOWARD THE NORTH TONIGHT AS THE LOW PRESSURE TRACKS TOWARD LONG ISLAND. MORE SCA WIND GUSTS ARE EXPECTED ACROSS THE CHESAPEAKE BAY AND LOWER TIDAL POTOMAC. WINDS WILL BE LGT DURING THE MIDDLE PART OF THE WEEK WITH HIPRES OVRHD. THE PRESSURE GRADIENT WILL TIGHTEN LATE IN THE WEEK AS DEVELOPING LOPRES TRACKS UP THE MID ATLANTIC COAST. SCA CONDITIONS APPEARS POSSIBLE THU AFTN AND NGT AS THE LOW TRACKS OVER THE REGION. STRONG CAA BEHIND THE LOW AND ASSOCIATED COLD FRONT WILL ALLOW FOR WIDESPREAD SCA CONDITIONS TO CONT INTO THE FIRST HALF OF THE WEEKEND.-- End Changed Discussion --&& .TIDES/COASTAL FLOODING...-- Changed Discussion --TIDAL ANOMALIES CURRENTLY ARE RUNNING ABOUT ONE HALF TO ONE FOOT ABOVE NORMAL THIS MORNING. AS LOW PRESSURE TRACKS UP THE MID-ATLANTIC COAST THIS AFTERNOON AND TOWARDS LONG ISLAND TONIGHT...A PERSISTENT ONSHORE FLOW WILL CONTINUE. TIDAL ANOMALIES MAY INCREASE AS THE LOW PRESSURE PASSES BY TO THE EAST LATE THIS AFTERNOON INTO TONIGHT. LATEST CBOFS AS WELL AS EXTRA TROPICAL MODELS CONTINUE TO KEEP WATER LEVELS BELOW THRESHOLDS FOR MINOR COASTAL FLOODING. WILL CONTINUE TO MONITOR THE TIDAL ANOMALIES THIS AFTERNOON...WITH MAX HIGH TIDE EXPECTED TONIGHT ANY INCREASE IN TIDAL ANOMALIES MAY WARRANT A COASTAL FLOOD ADVISORY.-- End Changed Discussion --&& .LWX WATCHES/WARNINGS/ADVISORIES... DC...NONE. MD...NONE. VA...NONE. WV...NONE. MARINE...SMALL CRAFT ADVISORY UNTIL 5 AM EST TUESDAY FOR ANZ531>534-537- 539>541-543. SMALL CRAFT ADVISORY UNTIL 8 PM EST THIS EVENING FOR ANZ530- 538-542. && $$ PRODUCTS...LASORSA/WOODY!/JRK
