AFDLWX AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC 415 AM EDT TUE APR 19 2011 .SYNOPSIS... A NEARLY STATIONARY BOUNDARY WILL REMAIN CLOSE TO OR JUST NORTHWEST OF THE REGION THROUGH TONIGHT. A COLD FRONT WILL MOVE ACROSS THE AREA WEDNESDAY...BRINGING A CHANCE OF THUNDERSTORMS. HIGH PRESSURE DOMINATES WEDNESDAY NIGHT THROUGH THURSDAY NIGHT...WITH A WARM FRONT CROSSING ON FRIDAY. && .NEAR TERM /THROUGH TONIGHT/... AT 4AM...A STATIONARY FRONT IS STILL ANALYZED NEAR THE MASON-DIXON LINE. WITH THE DEVELOPING LOW IN ADVANCE OF THIS FRONT BACK OVER OKLAHOMA...LITTLE FORCING WILL BE WITH THIS FRONT. COOL AIR GENERALLY WINS IN STATIONARY FRONT SITUATIONS...SO THE BOUNDARY IS EXPECTED TO SAG SOUTH AS A COLD FRONT INTO CENTRAL MARYLAND/BALTIMORE TODAY. ENELY FLOW NORTH OF THE FRONT WILL KEEP MAX TEMPS IN THE UPPER 60S...WHILE SLY FLOW SOUTH OF THE FRONT WILL DRAW LOW 80S INTO N-CNTRL VA...AND UPR 70S ACROSS THE DC METRO. INCREASING CLOUDS THROUGH THE DAY. A VORT LOBE RIDING EAST ALONG THE OH VLY PORTION OF THIS FRONT IS SETTING OFF THUNDERSTORMS INVOF THE CNTRL OH RIVER. THESE ARE EXPECTED TO CONTINUE PUSHING ENE THROUGH THE DAY. THE MAJORITY SHOULD BE BEHIND THE FRONT IN SRN PA...THOUGH ACTIVITY ALONG THE FRONTAL ZONE WOULD BRING THUNDERSTORMS TO THE NRN SHEN VLY AND CENTRAL MD. WENT WITH CATEGORICAL POPS ALONG THE MASON-DIXON...WITH CHANCES FOR THE NRN DC METRO AND BALTIMORE. STRONG THUNDERSTORMS ARE POSSIBLE WITH BULK SHEAR 40 TO 50 KT AND CAPE UP TO 500 J/KG. IN FACT A FEW SUPERCELLS ARE POSSIBLE...KEEP AN EYE ON THE WEATHER TODAY... TONIGHT...THE QUICK MOVING SFC LOW FROM THE CENTRAL PLAINS PUSHES INTO THE EASTERN GREAT LAKES WITH THE CNTRL MID ATLANTIC FULLY IN THE WARM SECTOR AS THE COLD FRONT MOVES NORTH. A LULL IN SHOWERS/TSTM ACTIVITY FOR THE OVERNIGHT...MIN TEMPS AROUND 60F...MID 50S UP ALONG THE MASON-DIXON. MOSTLY CLOUDY. && .SHORT TERM /WEDNESDAY THROUGH WEDNESDAY NIGHT/... SOUTHERLY LOW LEVEL JET WILL USHER IN WARM AND MOIST ATMOSPHERE INTO MID-ATLANTIC WEDNESDAY. MAXIMA SHOULD REACH WELL INTO 80S...POSSIBLY WITHIN 5F OF DAILY RECORDS. WITH SURFACE DEWPOINTS IN LOWER 60S AND PWAT VALUES IN EXCESS OF 1 INCH...SCATTERED SHOWERS AND THUNDERSTORMS SHOULD DEVELOP ALONG A COLD FRONT THAT WILL MOVE THROUGH DURING THE AFTERNOON. QUICK MOVEMENT AND LIMITED AREAL COVERAGE OF CONVECTION PRECLUDES ALL BUT VERY LOCALIZED FLOOD THREAT...HOWEVER...VARIOUS PARAMETERS INDICATE THREAT FOR SEVERE WEATHER WEDNESDAY AFTERNOON. THESE INCLUDE 50KT BULK SHEAR...SBCAPE AROUND 1000 J/KG...STEEP MID-LEVEL LAPSES...AND PLENTY OF LIFT. DAMAGING WINDS APPEAR TO BE PRIMARY THREAT...WITH LARGE HAIL ALSO POSSIBLE. COLD FRONT MAY BE APPROACHING BLUE RIDGE DURING MAXIMUM DIURNAL HEATING...SO THREAT COULD BE GREATEST ALONG AND EAST OF BLUE RIDGE. CONVECTION SHOULD QUICKLY EXIT SOUTH AND EAST OF AREA AFTER SUNSET...WITH DRY AND COOLER CONDITIONS DEVELOPING OVER MID-ATLANTIC. MINIMA WILL STILL BE ABOVE NORMAL...40S WEST OF BLUE RIDGE AND NORTHERN MARYLAND...WITH LOW TO MID 50S ELSEWHERE. && .LONG TERM /THURSDAY THROUGH MONDAY/... SHORTWAVE RIDGE CROSSES THURSDAY AND THURSDAY NIGHT...THOUGH MID AND UPPER FLOW TURNS SOUTHERLY AND MOISTURE INCREASES BY FRIDAY MORNING. WARM FRONT CROSSES FRIDAY...COMBINING WITH MOIST SOUTHEASTERLY LOW LEVEL FLOW TO LIKELY BRING SHOWERS TO THE REGION. WITH ANTECEDENT CONDITIONS QUITE MOIST...WILL HAVE TO WATCH FOR SIGNIFICANT QPF/FLOOD POTENTIAL. FRONT STALLS MAINLY JUST NORTH OF AREA BY SATURDAY...WHEN UPPER DISTURBANCE CROSSES THE REGION BRINGING CHANCE FOR THUNDERSTORMS. POPS CONTINUE INTO EARLY NEXT WEEK AS BOUNDARY REMAINS IN VICINITY OF MID-ATLANTIC. && .AVIATION /08Z TUESDAY THROUGH SATURDAY/... A WEAK COLD FRONT WILL SAG SOUTH INTO CENTRAL MARYLAND TODAY. ENERGY MOVING EAST ALONG THIS FRONT IS EXPECTED TO TRIGGER THUNDERSTORMS ACROSS PA...WITH CHANCES FOR BALTIMORE AND JUST NORTH OF DC...MAINLY THIS AFTERNOON/EVENING. SLY FLOW SOUTH OF THIS FRONT WILL GUST TO AROUND 20 KT...WHILE ENELY FLOW NORTH OF THE FRONT WILL BE AROUND 15 KT. VFR CONDITIONS SHOULD PREVAIL INTO FRIDAY. HOWEVER...SCATTERED SHOWERS AND THUNDERSTORMS...SOME SEVERE...ARE POSSIBLE WEDNESDAY AFTERNOON. PREVAILING SUB-VFR VISIBILITY AND CEILINGS MAY IMPACT TERMINALS ON FRIDAY AS A WARM FRONT LIFTS THROUGH THE REGION. && .MARINE... SLY FLOW WILL INCREASE ACROSS THE BAY AND TIDAL POTOMAC THROUGH THE DAY TODAY AS A COLD FRONT SAGS SOUTH ACROSS THE NORTHERN PORTION OF THE MD BAY. ENELY FLOW WILL INCREASE NORTH OF THE FRONT...WITH 18 KT GUSTS POSSIBLE. THEREFORE...THE SMALL CRAFT ADVISORY FOR THE AFTERNOON WAS EXPANDED TO INCLUDE ALL OF THE MD PORTION OF THE BAY. ALLOWED THE UPPER TIDAL POTOMAC ZONE TO DROP OFF FOR THE OVERNIGHT...THOUGH SHOULD THE COLD FRONT SAG FAR ENOUGH SOUTH...GUSTY NELY FLOW COULD OVERSPREAD DC. PERHAPS BRIEF MORNING LULL IN 20 KNOT GUSTS WEDNESDAY MORNING...BUT TIGHTENING PRESSURE GRADIENT IN ADVANCE OF COLD FRONT WILL LEAD TO INCREASING SOUTHERLY WINDS BY NOON. SMALL CRAFT ADVISORY EXPANDED TO ALL OF WATERS INTO WEDNESDAY EVENING. SCATTERED SHOWERS AND THUNDERSTORMS ARE EXPECTED AS THE COLD FRONT MOVES THROUGH WEDNESDAY AFTERNOON AND EVENING. THIS ACTIVITY MAY BRING LARGE AND AND DAMAGING WINDS. WINDS WILL SHIFT TO NORTHWEST WEDNESDAY NIGHT...THOUGH GUSTS IN EXCESS OF SMALL CRAFT ADVISORIES MAY PERSIST INTO THURSDAY NIGHT. WINDS BECOME SOUTHEASTERLY FRIDAY...AND A SMALL CRAFT ADVISORY MAY BE NEEDED FRIDAY AND SATURDAY. && .HYDROLOGY... RIVER LEVELS CONTINUE TO DROP ACROSS THE SHENANDOAH AND POTOMAC BASINS. MINOR FLOODING WILL END ON THE POTOMAC BELOW POINT OF ROCKS THIS MORNING...WITH LITTLE FALLS EXPECTED TO SAY ABOVE THE ACTION STAGE OF 5 FT THROUGH THE REST OF THE WORK WEEK. PLEASE SEE FLSLWX OR THE AHPS PAGE ON WEATHER.GOV FOR LATEST DETAILS. && .TIDES/COASTAL FLOODING... THE CURRENT DC AND ARLINGTON/ALEXANDRIA COASTAL FLOOD WARNING SHOULD BE ALLOWED TO EXPIRE AT NOON. THE POTOMAC AT LITTLE FALLS WILL DECREASE FROM AROUND 10.5 FT AT 4AM TO AROUND 9 FT BY 3PM TODAY. THE WISC AVE GAGE SHOULD SEE A LOW TIDE AT 4AM OF AROUND 7FT /THE MODERATE FLOOD THRESHOLD/ WITH A SLIGHT INCREASE THROUGH THE HIGH TIDE AT 10AM...THEN A DECREASE TO BELOW 7FT THROUGH THE AFTERNOON. THE WASHINGTON CHANNEL AND ALEXANDRIA GAGES SHOULD SEE ONLY MINOR COASTAL FLOODING THROUGH THE MORNING HIGH TIDE...THOUGH WITH LITTLE FALLS STILL IN FLOOD...THE COASTAL FLOOD WARNING WILL REMAIN UP FOR THE VA SIDE. NO COASTAL FLOOD HEADLINE AT THIS TIME FOR THE HIGH TIDE LATE THIS EVENING. HOWEVER...LITTLE FALLS WILL STILL BE AROUND 8 FT AROUND HIGH TIDE...AND SLY FLOW COULD AT LEAST PREVENT WATER LEVELS FROM DROPPING AS QUICKLY. A COASTAL FLOOD ADVISORY MAY BE NECESSARY. && .LWX WATCHES/WARNINGS/ADVISORIES... DC...COASTAL FLOOD WARNING UNTIL NOON EDT TODAY FOR DCZ001. MD...NONE. VA...COASTAL FLOOD WARNING UNTIL NOON EDT TODAY FOR VAZ054. WV...NONE. MARINE...SMALL CRAFT ADVISORY FROM 2 PM THIS AFTERNOON TO 8 PM EDT WEDNESDAY FOR ANZ530>532-536-538>542. SMALL CRAFT ADVISORY UNTIL 8 PM EDT WEDNESDAY FOR ANZ533-534- 537-543. SMALL CRAFT ADVISORY FROM 2 PM THIS AFTERNOON TO 8 PM EDT THIS EVENING FOR ANZ535. SMALL CRAFT ADVISORY FROM 10 AM TO 8 PM EDT WEDNESDAY FOR ANZ535. && $$ SYNOPSIS...BAJ/SBK