AFDLWX AREA FORECAST DISCUSSION...UPDATED NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC 1023 PM EDT SUN APR 17 2011 .SYNOPSIS... HIGH PRESSURE WILL MOVE OFF THE SOUTHEAST COAST BY EARLY MONDAY. LOW PRESSURE WILL MOVE ACROSS THE NORTHERN MID ATLANTIC LATE MONDAY...WITH A WEAK FRONT STALLING NEAR THE MASON DIXON LINE THROUGH TUESDAY. A COLD FRONT WILL MOVE THROUGH THE REGION ON WEDNESDAY...THEN STALL JUST SOUTH OF THE AREA THROUGH THE REST OF THE WORK WEEK. && .NEAR TERM /UNTIL 6 AM MONDAY MORNING/... THE MULTITUDE OF HAZARDS LEFTOVER FROM YESTERDAYS STORM SYSTEM BEGINNING TO TAPER OFF INTO RESIDUAL FLOODING /COASTAL AND RIVER/. NUMEROUS FLOOD WARNINGS REMAIN IN EFFECT FOR THE RIVERS ACROSS THE SHENANDOAH VLY...N AND S BRANCH POTOMAC BASINS AS WELL. SEE WBCFLSLWX FOR FURTHER DETAILS OR THE AHPS PAGE LINKED ON OUR WEB PAGE WEATHER.GOV/LWX. AS FOR CURRENT CONDITIONS...WHAT WILL BE A TREND OVER THE NEXT 2-3 DAYS HAS ALREADY BEGUN. A WEAK EMBEDDED SHORTWAVE SWINGING AROUND THE BASE OF THE PARENT LOW PRESSURE SYSTEM /NOW MOVING OFF NEW ENGLAND/ IS SLIDING ACROSS THE OHIO VLY AND INTO THE CNTRL APLCNS. A LOW LEVEL JET MAX ASSOCIATED W/ THE SHORTWAVE ALSO MAKING AN ENTRANCE ACROSS THESE AREAS...WILL CONTINUE TO MOVE OVER THE POTOMAC HIGHLANDS AND ACROSS THE MASON-DIXON LINE OVERNIGHT. THIS WILL BE THE FIRST OF SEVERAL SUCH FEATURES TO MOVE OVER THIS SAME REGION MON-TUE-INTO WED PART OF THE FAST-FLOW ZONAL REGIME TAKING SHAPE. THE LOW LEVELS ARE DRY W/ A GOOD INVERTED-V SOUNDING FOR KLWX THIS EVE. ENOUGH MOISTURE IS STREAMING INTO THE AREA IN THE 700-600MB LAYER /FROM THE OHIO VLY/ THAT THERE IS CONCERN THE ISOLATED SHOWERS WILL PUSH STRONG WINDS GUSTS TO THE SFC IN LOCALIZED AREAS. THEREFORE...A SHORT-TERM SPS IS IN EFFECT FOR THE POTOMAC HIGHLANDS HIGHLIGHTING THIS ACTIVITY. && .SHORT TERM /6 AM MONDAY MORNING THROUGH TUESDAY NIGHT/... HIGH PRESSURE WILL CONTINUE MOVE OFFSHORE OVERNIGHT AND A DEFINITE CHANGE IN THE SFC WIND FIELD WILL BE APPARENT OVER THE NEXT SEVERAL HRS. A BACKDOOR PSEUDO-COLD FRONT WILL PUSH SWD OVER THE CWA INTO THE PREDAWN HRS...DROPPING WIND SPEEDS TO NEAR CALM AS IT PROGRESSES. THIS BOUNDARY WILL BECOME STATIONARY TEMPORARILY DURING THE MORNING HRS AND BEGIN TO MOVE BACK NWD - SLOWLY - OVER THE COURSE OF THE DAY ON MONDAY. PUSHING THIS BOUNDARY TO THE NORTH WILL BE MORE GUSTY WINDS FROM THE SOUTH...THOUGH MAINLY A 15-25MPH GUST RANGE INSTEAD OF THE 30-40MPH GUSTS FROM EARLIER THIS AFTN. && .LONG TERM /WEDNESDAY THROUGH SUNDAY/... COLD FRONT EXPECTED TO MOVE THROUGH THE MID ATLANTIC ON LATE WEDNESDAY/EARLY THURSDAY. ATMOS EXPECTED TO DESTABILIZE...WITH THE POTENTIAL FOR SEVERE THUNDERSTORMS. HIGH PRESSURE SETTLES OVER THE REGION FOR THURSDAY...BUT MOVES OFFSHORE FOR FRIDAY. THE NEXT STORM SYSTEM EXPECTED FOR THE WEEKEND. && .AVIATION /02Z MONDAY THROUGH FRIDAY/... VFR CONDITIONS WILL CONTINUE OVERNIGHT AND TOMORROW. ANY CIGS WELL ABOVE 5 KFT. WINDS WILL REMAIN OUT OF THE SW OVERNIGHT AND GUSTY THROUGH SUNSET. NOT EXPECTING WINDS TO COMPLETELY DECOUPLE OVERNIGHT...BUT REMAIN AOB 10 KT W/ A FEW RANDOM GUSTS NEAR 20KT ACROSS NRN MD/WV PANHANDLE. WINDS WILL SHIFT TO THE SE TOMORROW AFTERNOON AND THEN SOUTHERLY OVERNIGHT. WINDS EXPECTED TO STAY SOUTHERLY THROUGH WEDNESDAY. COLD FRONT WILL MOVE THROUGH LATE WEDNESDAY/EARLY THURSDAY...WITH A WIND SHIFT TO THE NW AND SUB VFR CIGS/VSBYS IN TSRA. && .MARINE... SMALL CRAFT CONDITIONS WILL WEAKEN OVER THE NEXT FEW HRS...SUBSIDING BELOW 10KT INTO THE PREDAWN HRS. WINDS WILL THEN COME BACK AROUND FROM THE SOUTH AND INCREASE BACK INTO SCA BY LATE MORNING-EARLY AFTN. SOUTHERLY WINDS WILL CONTINUE THROUGH WEDNESDAY AHEAD OF A COLD FRONT. SMALL CRAFT CONDITIONS ARE POSSIBLE TUESDAY AND WEDNESDAY. BEHIND THE FRONT...NW WINDS MAY ALSO REACH SMALL CRAFT CRITERIA ON THURSDAY. && .HYDROLOGY... AREAL FLOOD WARNINGS CONTINUE FOR PORTIONS OF THE NORTHERN SHENANDOAH VALLEY AND EASTERN PANHANDLE OF WEST VIRGINIA THROUGH TODAY. MANY ROAD CLOSURES CONTINUE. MINOR TO MODERATE FLOODING CONTINUES ALONG THE SHENANDOAH...RAPPAHANNOCK...MONOCACY AND PORTIONS OF THE POTOMAC RIVERS. && .TIDES/COASTAL FLOODING... THE POTOMAC RVR THRU THE DC CHANNEL/ALEXANDRIA IS COMING OUT OF ITS EVE HIGH TIDE CYCLE - WHICH STILL MANAGED TO GET TO MINOR COASTAL FLOODED. LEVELS WERE AIDED A BIT BY THE FRESH-WATER FLOODING COMING DOWNSTREAM BUT LEVELS ARE IMPROVING LATE TONIGHT AND AFTER MIDNIGHT ALL AREAS SHOULD BE OUT OF MINOR FLOODING. A COMBINATION OF FRESHWATER RUN AND INCREASING SLY WINDS CHANNELING UP THE TIDAL POTOMAC ON MON AFTN MAY AGAIN INCREASE WATER LEVELS IN THE DC-CHANNEL POTOMAC COASTAL AREAS. THE EARLY MORNING HIGH TIDE CYCLE MAY ESCAPE MINOR FLOODING LEVELS BUT THE EVE/NIGHT CYCLE MAY NEED ANOTHER COASTAL FLOOD ADVISORY. IN ADDITION...THE POTENTIAL FOR MINOR COASTAL FLOODING WILL EXIST ACROSS THE ENTIRE TIDAL POTOMAC AND MARYLAND WESTERN SHORE OF THE CHESAPEAKE BAY TUESDAY INTO WEDNESDAY WITH PROLONGED SOUTHERLY WINDS. && .LWX WATCHES/WARNINGS/ADVISORIES... DC...COASTAL FLOOD ADVISORY UNTIL MIDNIGHT EDT TONIGHT FOR DCZ001. MD...NONE. VA...COASTAL FLOOD ADVISORY UNTIL MIDNIGHT EDT TONIGHT FOR VAZ054. WV...NONE. MARINE...SMALL CRAFT ADVISORY UNTIL 4 AM EDT MONDAY FOR ANZ530>534- 537>543. SMALL CRAFT ADVISORY FROM 1 PM TO 11 PM EDT MONDAY FOR ANZ530>543. && $$ UPDATE...GMS