Area Forecast Discussion
Issued by NWS Sterling, VA

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000
FXUS61 KLWX 231811
AFDLWX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC
211 PM EDT SAT AUG 23 2014

.SYNOPSIS...
A WEAK COLD FRONT WILL PUSH SOUTH AND WEST THROUGH THE
APPALACHIANS THIS EVENING. HIGH PRESSURE WILL BUILD FROM THE
CANADIAN MARITIMES DOWN THE COAST...REACHING THE DELMARVA BY
SUNDAY...AND REMAINING THROUGH THE MIDDLE OF NEXT WEEK.

&&

.NEAR TERM /THROUGH TONIGHT/...
LATEST ANALYSIS SHOWS HIGH PRESSURE EXTENDING THROUGH NEW ENGLAND.
A WEAK COLD FRONT IS LOCATED NEAR THE APPALACHIAN MOUNTAINS AND
AN EASTERLY FLOW BEHIND THE BOUNDARY HAS CAUSED MOISTURE TO MOVE
IN FROM THE ATLANTIC.

THE EASTERLY FLOW WILL CONTINUE ACROSS MOST OF THE AREA THIS
AFTERNOON AND EVENING AS THE COLD FRONT SLOWLY MOVES SOUTH AND
WEST THROUGH THE APPALACHIAN MOUNTAINS. PLENTY OF MOISTURE REMAINS
OVERHEAD DUE TO THE ONSHORE FLOW. ALSO...THE FRONT IS RELATIVELY
SHALLOW WHICH MEANS THE 850 MB FRONT IS STILL OVERHEAD. THIS IS
PROVIDING ENOUGH FORCING FOR SHOWERS...DESPITE DRIER AIR MOVING IN
ALOFT. SHOWERS ARE LIKELY FOR THE REST OF THIS AFTERNOON INTO THIS
EVENING AS THE 850MB BOUNDARY REMAINS OVERHEAD. THERE IS SOME
CONCERN FOR LOCALLY HEAVY RAINFALL. PWATS ARE DROPPING A BIT AS
DRIER AIR MOVES IN ALOFT...BUT PLENTY OF LOW-LEVEL MOISTURE
REMAINS. ALSO...WARM RAIN PROCESSES ARE EXPECTED WITH THE LOW-
TOPPED CONVECTION. DO NOT FEEL THE THREAT IS WIDESPREAD ENOUGH TO
WARRENT A FLASH FLOOD WATCH AT THIS TIME SINCE ANY HEAVY RAIN WILL
BE LOCALIZED AND FLASH FLOOD GUIDANCE REMAINS HIGH ACROSS MOST
AREAS.

THE COLD FRONT WILL MOVE WEST OF OUR AREA TONIGHT AND THE SURFACE
HIGH OVER NEW ENGLAND WILL PUSH FARTHER SOUTH AND WEST INTO OUR
AREA. DRIER AIR WILL MOVE IN FROM THE NORTH AND EAST...CAUSING THE
PRECIPITATION SHIELD TO SHIFT WEST INTO CENTRAL VIRGINIA AND THE
POTOMAC HIGHLANDS. DRIER CONDITIONS ARE EXPECTED ACROSS THE
WASHINGTON AND BALTIMORE METROPOLITAN AREAS. LOW CLOUDS AND AREAS
OF FOG ARE EXPECTED AS LOW-LEVEL MOISTURE GETS TRAPPED UNDERNEATH
THE NOCTURNAL INVERSION. MIN TEMPS WILL RANGE FROM THE UPPER 50S
AND LOWER 60S IN THE MOUNTAINS TO THE MIDDLE 60S IN DOWNTOWN
WASHINGTON AND BALTIMORE.

&&

.SHORT TERM /SUNDAY THROUGH WEDNESDAY/...
HIGH PRESSURE WILL CONTINUE TO BUILD INTO THE AREA
SUNDAY...ALLOWING FOR DRIER AIR TO MOVE IN FROM THE NORTH AND
EAST. A FEW MORNING SHOWERS ARE POSSIBLE ACROSS CENTRAL VIRGINIA
INTO THE POTOMAC HIGHLANDS...BUT EVEN ACROSS THESE AREAS SUNDAY
AFTERNOON SHOULD TURN OUT DRY. MAX TEMPS WILL RANGE FROM THE UPPER
60S AND LOWER 70S IN THE MOUNTAINS TO NEAR 80 IN WASHINGTON AND
BALTIMORE.

NICE STRETCH OF WEATHER COMING UP SUNDAY NIGHT THROUGH WEDNESDAY AS
POSITIVELY TILTED UPPER RIDGE DOMINATES THE UPPER PATTERN OVERHEAD.
SURFACE HIGH PRESSURE BUILDING IN BEHIND BACKDOOR COLD FRONT...AND
PWATS UNDER ONE INCH WILL RESULT IN LOW HUMIDITY WITH LIGHT WINDS
AND BELOW NORMAL TEMPERATURES THROUGH EARLY WEEK. TEMPS AND HUMIDITY
BEGIN TO MODERATE BY WEDNESDAY AS UPPER RIDGE NUDGES EASTWARD.

&&

.LONG TERM /WEDNESDAY NIGHT THROUGH SATURDAY/...
NICE STRETCH OF WEATHER COMING UP SUNDAY NIGHT THROUGH WEDNESDAY AS
POSITIVELY TILTED UPPER RIDGE DOMINATES THE UPPER PATTERN OVERHEAD.
SURFACE HIGH PRESSURE BUILDING IN BEHIND BACKDOOR COLD FRONT...AND
PWATS UNDER ONE INCH WILL RESULT IN LOW HUMIDITY WITH LIGHT WINDS
AND BELOW NORMAL TEMPERATURES THROUGH EARLY WEEK. TEMPS AND HUMIDITY
BEGIN TO MODERATE BY WEDNESDAY AS UPPER RIDGE NUDGES EASTWARD.

TROUGH PROGRESSING ACROSS THE NORTHERN CONUS LATE IN THE WEEK IS NOW
SLOWER THAN PREVIOUS RUNS WHICH BRINGS THE TRACK OF TROPICAL SYSTEM
FARTHER WEST ON BACKSIDE OF MID-LEVEL UPPER RIDGE FLOW. CURRENT
TRACK IS STILL WELL OFFSHORE TO THE SOUTHEAST OF THE MID-ATLANTIC
LATE IN THE WEEK BUT UNCERTAINTY EXISTS ATTM. AFOREMENTIONED UPPER
TROUGH WILL THEN DRAG A SURFACE COLD FRONT EASTWARD ACROSS THE
REGION NEXT WEEKEND WITH DEEP LAYER SHEAR AND INSTABILITY PROFILES
LOOKING FAVORABLE FOR SOME ORGANIZED CONVECTION. FROPA TIMING
DIFFERENCE STILL PRESENT BETWEEN EXTENDED MODELS HOWEVER...WITH THE
EURO MUCH LESS PROGRESSIVE. TEMPERATURES WILL CLIMB BACK TO NEAR
NORMAL AHEAD OF THE THIS FRONT AS RETURN FLOW SETS IN THURSDAY AND
FRIDAY.

&&

.AVIATION /18Z SATURDAY THROUGH THURSDAY/...
SHOWERS ARE LIKELY THIS AFTERNOON INTO THIS EVENING WITH MVFR
CIGS FOR MOST OF THE TIME. BRIEF IFR CONDITIONS CANNOT BE RULED
OUT IN HEAVIER SHOWERS. AN EASTERLY FLOW IS EXPECTED TONIGHT...BUT
SOME DRIER AIR WILL PUSH IN AS HIGH PRESSURE BUILDS INTO OUR AREA.
LOW CLOUDS AND AREAS OF FOG ARE EXPECTED UNDERNEATH THE NOCTURNAL
INVERSION FOR THE WESTERN TERMINALS. THE LOW CLOUDS MAY MAKE IT
INTO THE EASTERN TERMINALS...BUT CONFIDENCE IS LESS. ANY LOW
CLOUDS AND FOG WILL BURN OFF SUNDAY MORNING.

HIGH PRESSURE WILL PREVAIL THROUGH MID WEEK BEFORE A
COLD FRONT APPROACHES FRIDAY.

&&

.MARINE...
A PRESSURE SURGE IS EXPECTED BEHIND A COLD FRONT TONIGHT. THIS
WILL CAUSE WIND GUSTS AROUND SCA CRITERIA FOR THE MARYLAND
CHESAPEAKE BAY SOUTH OF POOLES ISLAND AND THE LOWER TIDAL POTOMAC
RIVER. A SMALL CRAFT ADVISORY IS IN EFFECT TONIGHT UNTIL 10 AM
SUNDAY MORNING FOR THESE AREAS. ELSEWHERE...WIND GUSTS HAVE BEEN
CAPPED AT 10 TO 15 KNOTS.

HIGH PRESSURE WILL THEN BUILD ACROSS THE AREA THROUGH MID
WEEK BEFORE A COLD FRONT APPROACHES FRIDAY. WINDS LOOK TO STAY BELOW
SCA LEVELS.

&&

.TIDES/COASTAL FLOODING...
A PERSISENT ONSHORE FLOW HAS CAUSED TIDAL ANOMALIES TO RISE TO
AROUND ONE FOOT ABOVE NORMAL. THE PM TIDE TODAY IS THE LOWER OF
THE TWO ASTRONOMICALLY...BUT WITH THE FCST WATER LVL INCREASE
SHOULD END UP BEING SIMILAR TO THE MRNG TIDE...IF NOT A PINCH
HIGHER. THE CONCERN COMES LATE TNGT INTO SUN MRNG...WHEN
DEPARTURES OF A FOOT WL CAUSE WATER TO APPROACH MINOR THRESHOLDS
FOR SENSITIVE LOCATIONS ON THE WESTERN SHORE AND UPPER TIDAL
POTOMAC. A COASTAL FLOOD ADVISORY IS IN EFFECT DURING THIS TIME.

THE EASTERLY FLOW WILL CONTINUE INTO MONDAY. THE HIGH TIDE CYCLE
LATE SUNDAY NIGHT INTO MONDAY MORNING MAY CAUSE MORE MINOR TIDAL
FLOODING FOR SENSITIVE LOCATIONS.

&&

.LWX WATCHES/WARNINGS/ADVISORIES...
DC...COASTAL FLOOD ADVISORY FROM MIDNIGHT TONIGHT TO 10 AM EDT
     SUNDAY FOR DCZ001.
MD...COASTAL FLOOD ADVISORY FROM MIDNIGHT TONIGHT TO 10 AM EDT
     SUNDAY FOR MDZ011-014-017-018.
VA...COASTAL FLOOD ADVISORY FROM MIDNIGHT TONIGHT TO 10 AM EDT
     SUNDAY FOR VAZ054.
WV...NONE.
MARINE...SMALL CRAFT ADVISORY FROM 8 PM THIS EVENING TO 10 AM EDT
     SUNDAY FOR ANZ531>534-537-539>541-543.

&&

$$
SYNOPSIS...BJL
NEAR TERM...BJL
SHORT TERM...AEB
LONG TERM...AEB
AVIATION...BJL/AEB
MARINE...BJL/AEB
TIDES/COASTAL FLOODING...BJL








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