Area Forecast Discussion
Issued by NWS Sterling, VA

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000 FXUS61 KLWX 160814 AAA AFDLWX AREA FORECAST DISCUSSION...UPDATED NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC 414 AM EDT SAT AUG 16 2014 .SYNOPSIS... HIGH PRESSURE WILL MOVE OFF THE COAST TODAY AND AN UPPER-LEVEL DISTURBANCE WILL PASS THROUGH THE REGION SUNDAY. A STRONGER DISTURBANCE AND ITS ASSOCIATED SURFACE LOW WILL PASS THROUGH THE AREA LATER MONDAY INTO TUESDAY. THE COLD FRONT ASSOCIATED WITH THIS LOW WILL STALL OUT NEAR THE AREA DURING THE MIDDLE PORTION OF NEXT WEEK. && .NEAR TERM /THROUGH TONIGHT/... A COUPLE OF WEAK EMBEDDED SHORTWAVES HAVE BEEN SWINGING AROUND THE BASE OF A LARGE UPPER TROUGH FROM THE GREAT LAKES TO THE MID-ALTC COAST. THE CLOSEST SHORTWAVE HAS HELPED KICK-OFF A HANDFUL OF SHOWERS ALONG THE SRN PERIPHERY OF THE CWA FROM N CNTRL VA ALONG THE TIDAL PTMC AND LOWER SRN MD. THIS ACTIVITY IS MOVING OVER SRN PORTIONS OF THE MD BAY...THE LAST EXPECTED PRECIP FOR THE REGION UNTIL EARLY SUN W/ THE ARRIVAL OF A COLD FRONT. UNTIL THE ARRIVAL OF THE FRONT...HIGH PRESSURE WILL ROLL ACROSS THE AREA AND OFF THE COAST AHEAD OF THE COLD FRONT. THE SFC HIGH ITSELF IS A FAIRLY WEAK AND ELONGATED FEATURE...STRETCHED ACROSS THE ERN SEABOARD STATES AND THE CENTER HOVERING OVER THE SRN APLCNS. THE POSITION OF THE HIGH WILL ALLOW FOR A WEAK SWLY SFC WIND LATER THIS AFTN THAT WILL HELP ADVECT RELATIVELY WARMER AND MORE MOIST AIR BACK INTO THE REGION THAN WE RECEIVED ON FRIDAY. AFTER ANOTHER COOL OVERNIGHT PERIOD...TEMPS WILL RISE BACK INTO THE 70S AND L80S TOWARD THE LATE MRNG HRS TODAY. HIGHS FOR MUCH OF THE AREA WILL REACH THE L80S...W/ A FEW M80S ALONG AND NEAR THE I-95 CORRIDOR/DC-BALT METRO AREA...UNDER MOSTLY CLEAR SKIES. BASE MAV VALUES SEEMED A BIT HIGH...THOUGH THE BIAS-CORRECTED VALUES ARE MORE REASONABLE. FORECAST HIGHS ARE A BLEND OF THE BC-MAV/ADJ-MET AND COUPLE OF WRF DERIVATIVES. A DEWPOINT GRADIENT WILL ALSO BE STATIONED ALONG AND E OF THE I-95 CORRIDOR...LEADING TO SOME WEAK CONVERGENCE AREAS LATER THIS AFTN. S-SW FLOW INTO THE ZONE COULD LEAD TO SOME ISOLATED SHOWER ACTIVITY DEVELOPING ACROSS AND/OR EAST OF THE CHES BAY THIS AFTN. RECENT MESOANALYSIS INDICATES A WEAK SFC LOW OVER THE NRN NECK WHICH IS EXPECTED TO DRIFT NE ACROSS THE DELMARVA PENINSULA OVER THE NEXT SEVERAL HRS...POTENTIALLY PROVIDING THE LIFT/CONVERGENCE FOR SOME ISOLATED SHOWERS AND PATCHY MID STRATUS DECKS. A BRIEF PERIOD OF ZONAL UPPER FLOW TOWARD THE END OF TODAY WILL QUIET DOWN WX ACROSS THE REGION EVEN FURTHER...CLEARING SKIES OUT AND DROPPING WINDS BACK DOWN TO NEAR-CALM CONDITIONS. THE GRADUAL INCREASE IN DEWPOINTS WILL TEMPER OVERNIGHT LOWS...KEEPING THEM LOCKED IN THE L-M60S FOR MUCH OF THE AREA. && .SHORT TERM /SUNDAY THROUGH SUNDAY NIGHT/...
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BY SUNRISE...A COLD FRONT WILL ALREADY BE ON THE NRN DOORSTEP OF THE CWA. THE FRONT WILL BE CONNECTED TO A LOW THAT WILL BE QUICKLY SWEPT ACROSS THE NRN NEW ENGLAND STATES OVER THE COURSE OF THE DAY. THE UPPER FLOW WILL CARRY THE SYSTEM AND MUCH OF THE DYNAMICS WELL OFF TO OUR NORTH...W/ NOT MUCH LEFT TO PUSH THE COLD FRONT STEADILY ACROSS OUR AREA. SOME LIGHT SHOWER ACTIVITY WILL PUSH INTO THE CNTRL APLCNS DURING THE FIRST HALF OF THE DAY...W/ SOME FRACTIONS OF THE ACTIVITY MOVING TOWARD THE BLUE RIDGE AND EAST...BUT MAINLY JUST CLOUD DEBRIS WILL COVER THE METRO AREAS AND EAST W/ LITTLE MORE THAN A BRIEF SHOWER. THE INCREASING CLOUD COVER MAY TEMPER THE EXPECTED HIGHS FOR SUNDAY WHICH ARE M-U80S. THE FRONT ITSELF IS NOT EXPECTED TO NECESSARY CLEAR THE AREA BUT INSTEAD BECOME STATIONARY AS THE SFC LOW EXITS OFF TO THE NE AND AN INCOMING LOW FROM THE WEST BEGINS TO STRENGTHEN THE PRE-STORM WARM FRONTAL REGION ACROSS THE UPPER MIDWEST. THE LACK OF AN ACTUAL PASSAGE AND THE MODIFYING OF THE AIRMASS WILL ALLOW TEMPS TO CLIMB BACK INTO THE 80S AND AN LIKELY EVEN TOP-OUT A COUPLE OF DEGREES HIGHER THAN ON SAT. AN INCREASE IN THE LOW LEVEL MOISTURE PROFILE WILL ALSO INCREASE THE HUMIDITY AND THEREFORE THE HEAT INDICES - WHICH MAY APPROACH OR BARELY EXCEED THE 90-DEG MARK SUN AFTN. A SHORTWAVE WILL MOVE OFF TO OUR EAST SUNDAY NIGHT AND A COLD FRONT WILL REMAIN STALLED OUT OVER THE AREA. ANY EVENING CONVECTION SHOULD DISSIPATE AND MOST AREAS ARE EXPECTED TO TURN OUT DRY SUNDAY NIGHT DUE TO SUBSIDENCE BEHIND THE SHORTWAVE. HOWEVER...THERE WILL BE SOME CLOUDS THAT REMAIN OVER THE CENTRAL AND SOUTHWESTERN PORTIONS OF THE CWA AS ANOTHER DISTURBANCE APPROACHES FROM THE WEST.
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&& .LONG TERM /MONDAY THROUGH FRIDAY/... THE BOUNDARY OVERHEAD WILL SHIFT NORTH AND DISSIPATE MONDAY...ALLOWING FOR SOUTHERLY WINDS TO BRING MORE WARM AND HUMID CONDITIONS. AN UPPER-LEVEL DISTURBANCE AND ITS ASSOCIATED SURFACE LOW WILL TRACK THROUGH THE OHIO VALLEY DURING THIS TIME. MOST OF THE FORCING WILL REMAIN TO OUR WEST...BUT THE WARM AND HUMID ATMOSPHERE SHOULD PROVIDE ENOUGH INSTABILITY TO TRIGGER SOME SHOWERS AND THUNDERSTORMS...ESPECIALLY ACROSS THE POTOMAC HIGHLANDS AND CENTRAL VIRGINIA...WHERE MOISTURE WILL BE DEEPEST. THE UPPER-LEVEL DISTURBANCE AND ITS ASSOCIATED LOW WILL PASS THROUGH THE AREA MONDAY NIGHT INTO TUESDAY...BRINGING A BETTER CHANCE FOR SHOWERS AND POSSIBLE THUNDERSTORMS. GUIDANCE STILL DIVERGES IN ITS FORECASTED INTENSITY OF THIS SYSTEM...AND THAT WILL HAVE A SIGNIFICANT IMPACT ON THE FORECAST. IF THIS SYSTEM IS STRONGER LIKE THE GFS AND NAM SUGGEST...THEN THE FORCING WILL COMBINE WITH TROPICAL MOISTURE TO BRING HEAVY RAINFALL TO THE AREA DURING THIS TIME. HOWEVER...IF THE DISTURBANCE IS WEAKER AND FARTHER SOUTH LIKE THE EURO AND CMC SUGGEST...THEN SHOWERS ARE LIKELY BUT THE HEAVY RAIN THREAT WOULD NOT BE AS SIGNIFICANT. GIVEN THE DEEP MOISTURE THAT WILL BE IN PLACE DURING THIS TIME...EVEN A LITTLE FORCING WOULD INDICATE A THREAT FOR HEAVY RAIN AND THIS WILL BE COVERED IN THE HWO FOR NOW. HOWEVER...CERTAINTY IN THE COVERAGE OF HEAVY RAINFALL AND EXACTLY HOW HEAVY RAIN WILL BE REMAINS LOW AT THIS TIME. THIS SYSTEM WILL MOVE AWAY FROM THE AREA LATER TUESDAY...BUT A BOUNDARY WILL REMAIN STALLED OUT OVER THE AREA. A NORTHWEST FLOW ALOFT WILL DEVELOP DURING THE MIDDLE AND LATTER PORTIONS OF THE WEEK AS A RIDGE BUILDS OVER THE CENTRAL CONUS. SEVERAL UPPER-LEVEL DISTURBANCES MOVING OVERHEAD ALONG WITH THE BOUNDARY NEARBY SUGGESTS THAT UNSETTLED CONDITIONS WILL OCCUR. && .AVIATION /08Z SATURDAY THROUGH WEDNESDAY/...
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A WEAK SFC LOW NEAR THE MD CHES BAY HELPING TO DEVELOP SOME PATCHES OF MID-LEVEL STRATUS ACROSS THE REGION WHICH WILL DISSIPATE AND MOVE EAST TOWARD THE PREDAWN HRS. HIGH PRESSURE WILL MOVE OFF THE COAST LATER TODAY...BUT STILL KEEPING MUCH OF THE AREA CLEAR AND BRINGING IN A LIGHT SW FLOW BY MID AFTN. SOLID VFR CONDITIONS THRU THE CURRENT TAF PERIOD...W/ MID CLOUD DECKS AND A FEW SHOWERS ACROSS THE WEST ARRIVING TOWARD THE END OF THE PERIOD...A PREVIEW OF THE COMING ROUTINE CYCLE. VFR CONDITIONS ARE EXPECTED SUNDAY EVENING...BUT PATCHY FOG IS POSSIBLE OVERNIGHT SUNDAY INTO EARLY MONDAY. LOW PRESSURE WILL APPROACH THE TERMINALS MONDAY BEFORE PASSING THROUGH MONDAY NIGHT INTO TUESDAY. THERE IS A BETTER CHANCE FOR SHOWERS AND THUNDERSTORMS DURING THIS TIME. THERE IS A POTENTIAL FOR LOCALLY HEAVY RAINFALL DURING THIS TIME...BUT CERTAINTY REMAINS LOW. SUBVFR CIGS/VSBYS ARE POSSIBLE IN SHOWERS AND THUNDERSTORMS. THE LOW WILL MOVE AWAY FROM THE AREA TUESDAY...BUT A STALLED BOUNDARY WILL REMAIN OVERHEAD...BRINGING THE CHANCE FOR CONVECTION THROUGH WEDNESDAY.
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&& .MARINE...
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A FEW SHOWERS MOVING OVER THE BAY WILL EXIT SHORTLY. LIGHT WINDS OVER MUCH OF THE BAY AND TP RVR OVERNIGHT...THOUGH A FEW 10-15KT BREEZES ONGOING OVER THE SRN MD BAY. HIGH PRESSURE WILL KEEP THE LIGHT WINDS OVER THE WATERS THRU MUCH OF THE DAY. A COLD FRONT WILL ARRIVE ON SUN MRNG...BUT WINDS ARE EXPECTED TO REMAIN BELOW SCA LEVELS THROUGHOUT THE DAYTIME HRS. NO MARINE HEADLINES ARE EXPECTED SUNDAY NIGHT INTO MONDAY. LOW PRESSURE WILL APPROACH THE WATERS LATER MONDAY BEFORE PASSING THROUGH MONDAY NIGHT INTO TUESDAY. THERE IS A BETTER CHANCE FOR SHOWERS AND THUNDERSTORMS DURING THIS TIME. THE LOW WILL MOVE AWAY FROM THE WATERS LATER TUESDAY...BUT A BOUNDARY WILL REMAIN NEARBY BRINGING UNSETTLED CONDITIONS.
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&& .TIDES/COASTAL FLOODING...
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POSITIVE TIDAL ANOMALIES OVER THE LOWER MD BAY ARE STILL HOVERING BETWEEN 1/2 AND 3/4 FT ABOVE NORMAL...WHILE THE MIDDLE AND NRN BAY ARE A BIT LOWER - MAINLY BELOW A 1/2 FT. HOWEVER...STILL COMING OUT OF THE LATEST FULL MOON CYCLE AND WINDS OVER THE BAY AT TIMES SHOWING AN ELY COMPONENT...LEVELS CLOUD INCREASE FURTHER HEADING INTO THE NEXT COUPLE OF H.T. CYCLES. THE ARRIVAL OF A COLD FRONT ON SUN MRNG AND SUBSEQUENT WLY FLOW SHOULD BEGIN TO CHOP AWAY AT HIGHER ANOMALIES DURING THE DAY.
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&& .LWX WATCHES/WARNINGS/ADVISORIES... DC...NONE. MD...NONE. VA...NONE. WV...NONE. MARINE...NONE. && $$ SYNOPSIS...BJL NEAR TERM...GMS SHORT TERM...BJL/GMS LONG TERM...BJL AVIATION...BJL/GMS MARINE...BJL/GMS TIDES/COASTAL FLOODING...GMS

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