Area Forecast Discussion
Issued by NWS Sterling, VA

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000 FXUS61 KLWX 221433 AFDLWX AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC 1033 AM EDT TUE APR 22 2014 .SYNOPSIS... A COLD FRONT WILL PASS THROUGH THE AREA THIS AFTERNOON AND EVENING. HIGH PRESSURE RETURNS FOR WEDNESDAY AND THURSDAY BEFORE MOVING OFF THE COAST FRIDAY. A COLD FRONT IS EXPECTED TO PASS THROUGH THE AREA SATURDAY. && .NEAR TERM /THROUGH TONIGHT/...
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SFC COLD FRONT WAS ANALYZED OVER THE ERN GREAT LAKES AND OH VLY AT 13Z. THIS FRONT IS ASSOCIATED WITH A 1000 MB SFC LOW NEAR THE SRN ONTARIO-QUEBEC BORDER. PRE-FRONTAL CLOUDS AND SHOWERS ARE CURRENTLY MOVING INTO THE MTS THIS MRNG IN ASSOCIATION WITH A LEADING MID-LVL SHORTWAVE TROUGH. UPSTREAM RADAR AND THE LATEST HI-RES MODEL GUIDANCE SUPPORT DECREASING POPS WITH THE FCST FOR TDA WITH COVERAGE OF SHOWERS NOT EXPECTED TO BE WIDESPREAD. THIS WOULD MAKE SENSE GIVEN THE BEST FORCING ASSOCIATED WITH THE UPPER SHORTWAVE TROUGH/JET STREAK AND SFC LOW REMAINING TO OUR NORTH. 12Z IAD RAOB REVEALED AN IMPRESSIVE LLVL INVERSION WITH THE WARM NOSE OF 19C AT 950 MB. IT WILL NOT TAKE MUCH TO MIX DOWN THIS WARMER AIR. THEREFORE INCREASED MAX TEMPS FOR TDA ACROSS THE ENTIRE AREA EVEN WITH THE CLOUD COVER TO CONTEND WITH. TEMPS THIS AFTN COULD REACH THE LOWER 80S ALONG AND EAST OF I-95 WHERE STRONG HEATING THIS MRNG WILL PRECEDE ARRIVAL OF DENSER CLOUDS THIS AFTN. LLVL WINDS ARE FCST TO VEER MORE OUT OF THE WEST THIS AFTN BEHIND A PRE-FRONTAL TROUGH. EXPECT LOWER DEWPOINTS EAST OF THE MTS THAN WHAT MODELS ARE INDICATING JUST PRIOR TO FROPA DUE TO DOWNSLOPING FLOW. RAOB SOUNDINGS MODIFIED FOR A SFC TEMP NEAR 80F AND DEWPOINT NEAR 50F REVEAL MARGINAL INSTABILITY (SBCAPE AOB 500 J/KG) OWING TO THIS LIMITED MOISTURE RETURN AND WEAK MID-LVL LAPSE RATES AHEAD OF THE FRONT. THIS WILL FAVOR COVERAGE OF TSTMS ISOLATED AND TSTM INTENSITY WEAK. THE OPPORTUNITY FOR TSTMS APPEAR TO BE LIMITED TO ALONG OR JUST AHEAD OF THE FRONT FOR A 2-4 HR WIND THIS AFTN IN THE MTS AND DURING THE LATE AFTN/ERY EVE TOWARD THE I-95 AND THE CHSPK BAY. AS THE VORT MAX FROM THE GREAT LAKES REGION NEARS THE AREA LATE TONIGHT...SOME OF THE GUSTIER PARTS OF THE LOW LEVEL JET WILL GET MIXED DOWN TO THE SFC AND NW WINDS WILL SWEEP ACROSS THE AREA W/ GUSTS IN THE 20-30MPH RANGE FOR MUCH OF THE NIGHTTIME HRS. DEWPOINTS WILL DROP BACK DOWN INTO THE 30S AND TEMPS WILL DROP BACK INTO THE 40S FOR OVERNIGHT LOWS...W/ LOWER WIND CHILLS FROM THE GUSTY AND DRY NW WINDS.
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&& .SHORT TERM /WEDNESDAY THROUGH WEDNESDAY NIGHT/... LOW PRESSURE WILL INTENSIFY OFF THE NEW ENGLAND COAST WEDNESDAY WHILE HIGH PRESSURE BUILDS TOWARD THE REGION FROM THE GREAT LAKES. THE PRESSURE GRADIENT BETWEEN THESE SYSTEMS WILL CAUSE GUSTY NORTHWEST WINDS...AND MAX TEMPS WILL BE BELOW CLIMO DUE TO THE COLD ADVECTION ASSOCIATED WITH THE NORTHWEST FLOW. MAX TEMPS WILL RANGE FROM THE 40S ALONG THE ALLEGHENY HIGHLANDS...TO THE LOWER AND MIDDLE 60S NEAR WASHINGTON AND BALTIMORE...TO THE UPPER 60S IN THE VIRGINIA PIEDMONT. A DEEP MIXING LAYER AND STRONG PRESSURE GRADIENT WILL CAUSE NORTHWEST WINDS TO GUST FREQUENTLY BETWEEN 30 AND 40 MPH. HIGH PRESSURE WILL BUILD OVERHEAD WEDNESDAY NIGHT...CAUSING DRY AND CHILLY CONDITIONS. WINDS WILL DIMINISH AROUND SUNSET. MIN TEMPS WEDNESDAY NIGHT WILL RANGE FROM NEAR 30 IN THE POTOMAC HIGHLANDS TO THE LOWER AND MIDDLE 40S IN DOWNTOWN WASHINGTON AND BALTIMORE. && .LONG TERM /THURSDAY THROUGH MONDAY/... HIGH PRESSURE WILL REMAIN OVER THE REGION THURSDAY...BRINGING DRY CONDITIONS ALONG WITH SUNSHINE. THE HIGH WILL MOVE OFF THE COAST THURSDAY NIGHT AHEAD OF AN APPROACHING COLD FRONT FROM THE WEST. THE COLD FRONT WILL PASS THROUGH THE AREA FRIDAY...BRINGING MORE CLOUDS ALONG WITH THE LIKELIHOOD FOR SHOWERS. ANOTHER COLD FRONT WILL APPROACH THE AREA SATURDAY BEFORE PASSING THROUGH SATURDAY NIGHT. A WESTERLY DOWNSLOPING FLOW AHEAD OF THE COLD FRONT SHOULD ALLOW FOR MILD CONDITIONS SATURDAY. A COUPLE SHOWERS CANNOT BE RULED OUT AHEAD OF THE FRONT FOR LOCATIONS NEAR THE MASON-DIXON LINE...BUT MOST OF THE TIME WILL TURN OUT DRY SINCE LITTLE MOISTURE WILL BE ASSOCIATED WITH THE BOUNDARY. THE BOUNDARY WILL STALL TO OUR SOUTH SUNDAY AND MONDAY. WAVES OF LOW PRESSURE WILL DEVELOP ALONG THE BOUNDARY...POSSIBLY BRINGING UNSETTLED CONDITIONS TO THE AREA NEXT WEEK. && .AVIATION /14Z TUESDAY THROUGH SATURDAY/...
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MID AND HI CLOUDS HAVE BEEN STREAMING IN FROM THE WEST THIS MRNG AHEAD OF A COLD FRONT. BRIEF PERIOD OF SHRA BEFORE 16Z AT MRB/CHO AND BETWEEN 16-18Z FARTHER EAST. NO FLIGHT RESTRICTIONS EXPECTED WITH THESE LEADING SHRA. ANOTHER AREA OF SHRA AND ISO TSRA POSSIBLE BETWEEN 18-21Z IN THE WRN TERMINALS AND 21-00Z FROM IAD EWD. BRIEF/LOCAL FLIGHT RESTRICTIONS POSSIBLE WITH THIS ACTIVITY. WINDS WILL STAY OUT OF THE SOUTH UNTIL LATER THIS AFTN WHEN A COLD FRONT SLIDES THRU AND TURNS WINDS BACK TO THE NW AND HIGHER GUSTS IN THE 20-30KT RANGE APPEAR FOR THE LATE EVE/OVERNIGHT HRS. CONDITIONS WILL DRY OUT TONIGHT BUT WINDS WILL STAY BREEZY INTO WED MRNG. GUSTY NORTHWEST WINDS AROUND 30 TO 35 KNOTS ARE EXPECTED WEDNESDAY BEHIND A COLD FRONT. HIGH PRESSURE WILL BUILD OVER THE TERMINALS WEDNESDAY NIGHT AND THURSDAY. WINDS WILL DIMINISH AROUND SUNSET WEDNESDAY EVENING. A COLD FRONT WILL PASS THROUGH THE TERMINALS FRIDAY...LIKELY TRIGGERING A FEW SHOWERS. CIGS/VSBYS MAY APPROACH MVFR LEVELS DURING THIS TIME. ANOTHER COLD FRONT WILL APPROACH THE TERMINALS SATURDAY...BUT MOST PLACES WILL END UP DRY WITH VFR CONDITIONS.
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&& .MARINE... SLY FLOW WILL LAST FOR MUCH OF THE DAYTIME HRS...W/ SOME MINOR CHANNELING BUT SUB-SCA UNTIL THIS AFTN. SHOWERS WILL CARRY ISOLATED HIGHER WIND GUSTS THIS AFTN/EVE...THEN THE PRESSURE GRADIENT WILL BRING MORE WIDESPREAD GUSTY WINDS LATER THIS EVE. A FEW HEAVIER SHOWERS AND ISOLATED TSTMS POSSIBLE LATER TODAY...SO THE POTENTIAL FOR HIGHER LOCALIZED WINDS EXISTS UNTIL A COLD FRONT PUSHES THRU LATE TONIGHT...SPREADING MORE WIDESPREAD AND NW WINDS OVER THE WATERS FOR MOST OF THE OVERNIGHT HRS...WELL INTO SCA RANGE. GUSTY NORTHWEST WINDS ARE EXPECTED BEHIND A COLD FRONT WEDNESDAY. A GALE WARNING IS IN EFFECT FOR THE WATERS. WINDS WILL GRADUALLY DIMINISH WEDNESDAY NIGHT...BUT A SMALL CRAFT ADVISORY WILL LIKELY BE NEEDED FOR PORTIONS OF THE WATERS. THE SMALL CRAFT ADVISORY MAY ALSO BE NEEDED FOR PORTIONS OF THE WATERS ON THURSDAY. A COLD FRONT WILL PASS THROUGH THE WATERS FRIDAY...LIKELY TRIGGERING A FEW SHOWERS. ANOTHER COLD FRONT WILL APPROACH THE WATERS SATURDAY BEFORE PASSING THROUGH SATURDAY NIGHT. A SMALL CRAFT ADVISORY MAY BE NEEDED FOR PORTIONS OF THE WATERS SATURDAY. && .FIRE WEATHER...
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FUEL MOISTURE REMAINS LOW THIS MORNING. THERE WILL BE A FEW SHOWERS AROUND TODAY AHEAD OF A COLD FRONT...BUT RAINFALL AMOUNTS SHOULD AVERAGE TO BE LESS THAN ONE-QUARTER INCH ACROSS MOST AREAS. THE COLD FRONT WILL PASS THROUGH THE AREA TONIGHT AND GUSTY NORTHWEST WINDS ARE EXPECTED BEHIND THE COLD FRONT WEDNESDAY. A DEEP MIXING LAYER WILL ALLOW FOR DRIER AIR TO MIX DOWN...CAUSING LOW RELATIVE HUMIDITY VALUES DURING THE LATE MORNING THROUGH THE AFTERNOON. THE COMBINATION OF GUSTY WINDS...LOW FUEL MOISTURE AND LOW RELATIVE HUMIDITY WILL ENHANCE THE THREAT FOR THE SPREAD OF WILDFIRES WEDNESDAY. DAY SHIFT HAS COORDINATE WITH STATE CONTACTS ABOUT FUEL MOISTURE. A FIRE WEATHER WATCH MAY BE NECESSARY FOR TOMORROW AND WOULD BE ISSUED THIS AFTN.
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&& .TIDES/COASTAL FLOODING...
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A SOUTHERLY FLOW HAS CAUSED TIDAL ANOMALIES TO BE AROUND THREE- QUARTERS OF A FOOT ABOVE THE ASTRONOMICAL NORM. THE TIDAL ANOMALIES SHOULD NOT CHANGE MUCH THIS AFTN AS THE FLOW GRADUALLY SHIFTS WEST OF SOUTH. THIS WILL KEEP TIDAL LEVELS BELOW THRESHOLDS FOR MINOR COASTAL FLOODING. GUSTY NORTHWEST WINDS WILL DEVELOP TONIGHT AND CONTINUE THROUGH WEDNESDAY. BLOWOUT TIDES ARE EXPECTED WEDNESDAY.
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&& .LWX WATCHES/WARNINGS/ADVISORIES...
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DC...NONE. MD...NONE. VA...NONE. WV...NONE. MARINE...SMALL CRAFT ADVISORY UNTIL 6 AM EDT WEDNESDAY FOR ANZ530>543. GALE WARNING FROM 6 AM TO 6 PM EDT WEDNESDAY FOR ANZ530>543.
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&& $$ SYNOPSIS...BJL NEAR TERM...JRK/GMS SHORT TERM...BJL LONG TERM...BJL AVIATION...JRK/BJL MARINE...JRK/BJL FIRE WEATHER...BJL/JRK TIDES/COASTAL FLOODING...JRK

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