Area Forecast Discussion
Issued by NWS Sterling, VA

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000 FXUS61 KLWX 191853 AFDLWX AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC 253 PM EDT SUN OCT 19 2014 .SYNOPSIS...
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HIGH PRESSURE WILL BRIEFLY PASS BY THE AREA TO THE SOUTH... USHERING IN CALM WINDS AND CLEAR SKIES THROUGH EARLY MONDAY. AN UPPER LEVEL TROUGH WILL QUICKLY DIVE DOWN THROUGH THE UPPER MIDWEST...BUT SLOW DOWN AND RESIDE OVER THE MID-ATLANTIC AND NEW ENGLAND REGIONS THROUGH MUCH OF THE COMING WEEK.
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&& .NEAR TERM /THROUGH TONIGHT/...
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HEADLINE UPDATE...FREEZE WATCH REPLACED W/ FREEZE WARNING FOR PORTIONS OF THE CNTRL APLCNS COUNTIES - HIGHLAND/PENDLETON/W GRANT. A FROST ADVISORY IS NOW IN EFFECT FOR THE SHENANDOAH VALLEY...THE POTOMAC HIGHLANDS...AND NORTH CENTRAL MARYLAND. BOTH PRODUCTS FROM 2-9AM OVERNIGHT/EARLY MON MORNING. A MAJORITY OF THE FORCING AND LOW LEVEL MOISTURE THAT CONTINUED TO BUILD THE EARLIER STRATUS DECKS HAVE MOVED OFF THE COAST ALONG W/ THE UPPER TROUGH AXIS. THE WINDS WILL BE THE NEXT TO GO BUT WILL LINGER FOR AT LEAST ANOTHER FEW HRS UNTIL CLOSER TO SUNSET THIS EVE. THE TOP-END GUSTS HAVE DROPPED OFF FROM THE UPPER 20KT RANGE DOWN INTO LOWER 20S...SO MORE OF A STEADY BREEZE THAN WINDY. SEVERAL HRS OF THESE WINDS HAVE HELD-DOWN TEMPS ACROSS THE REGION...BARELY INTO THE U50S FOR MUCH OF THE AREA W/ A FEW L60S ACROSS THE I-95 CORRIDOR/NEAR-COASTAL ZONES. CLEAR SKIES WILL HELP THESE CONDITIONS SLIDE A DEGREE-OR-TWO HIGHER W/IN THE NEXT COUPLE OF HRS. DEWPOINTS ACROSS THE AREA ARE SHOWING AT LEAST A COUPLE DEG OR SLIGHTLY MORE - LESS THAN MOST MODELS...EVEN THE ADJ VALUES OR HAVE DIFFERENT AREAL PLACEMENT OF THE LOWER VALUES. THE DRY AFTN CONDITIONS AND LACK OF CLOUD COVER HEADING INTO THE NIGHTTIME HRS WILL SET MOST OF THE REGION UP FOR POTENTIAL FROST DEVELOPMENT. AS THE UPPER TROUGH CONTINUES TO DRAG THE ASSOCIATED TURBULENCE W/ IT AND SFC HIGH PRESSURE ROLLS BY JUST TO OUR SOUTH...GOOD RATIONAL COOLING IS EXPECTED FOR MUCH OF THE AREA. TEMPS NOT EXPECTED TO DROP FAR ENOUGH E OF THE BLUE RIDGE FOR MUCH MORE THAN PATCHY FROST - BUT ALONG/NEAR THE MASON DIXON LINE...DOWN ACROSS THE SHEN VLY AND WRN APLCNS VLYS - MORE WIDESPREAD AREAS OF FROST WILL BE POSSIBLE. A BRIEF PERIOD OF SUB-FREEZING TEMPS ALSO EXPECTED ACROSS THE HIGHER ELEVATION COUNTIES...IN THE VLYS...SO A FREEZE WRNG IN EFFECT WHILE STILL IN LATE STAGES OF THE GROWING SEASON. SOME UNCERTAINTY FOLLOWS THIS BECAUSE OF THE EXPECTED TIMING OF INCOMING CLOUD COVER FROM THE UPPER MIDWEST. A HIGH CIRRUS SHIELD COULD POTENTIALLY LIMIT THE AMOUNT AND COVERAGE OF FROST DEVELOPMENT...THOUGH WINDS SHOULD SUBSIDE ENOUGH AND THE TEMP/DEWPOINTS CONTINUITY IS FAVORABLE ACROSS THESE AREAS.
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&& .SHORT TERM /MONDAY THROUGH MONDAY NIGHT/...
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A ONE-DAY REPRIEVE FROM THE FALL-LIKE CONDITIONS AS THE SFC HIGH ROLLING ACROSS THE CAROLINAS MAKES AN EXIT OFF THE COAST AND BRINGS IN RETURN SLY FLOW. THIS WIND REGIME WILL ALLOW FOR A MINOR WARM-UP RELATIVE TO TODAY`S CONDITIONS. AS WINDS SWITCH OUT OF THE SOUTH FOR MUCH OF THE DAY...A FAST-MOVING CLIPPER-LIKE FEATURE WILL DIVE DOWN TOWARD THE AREA FROM N OF THE GREAT LAKES. AS THE APEX OF THE UPPER SHORTWAVE REACH NRN NY MON EVE...THE SYSTEM AS A WHOLE WILL DECELERATE AND BEGIN TO CUT-OFF FROM THE MAIN UPPER JET STREAM. MOISTURE WILL RETURNS FROM THE TOP-DOWN AS THE SHORTWAVE APPROACHES. THICKER MID-UPPER LEVEL CLOUD DECKS WILL ARRIVE LATE MON AFTN/EVE ON THE ERN FRINGE OF THE INCOMING UPPER WAVE. FALLING PRECIP WILL HAVE A SIZABLE AMOUNT OF DRY AIR TO OVERCOME BEFORE REACHING THE SFC...BUT THIS WILL BECOME MORE PROBABLE FROM WEST TO EAST DURING THE LATE NIGHT HRS. INCREASE POPS FOR THE CNTRL APLCNS LATE MON AND KEPT A LOW CHANCE FURTHER EAST TO THE BLUE RIDGE. THE SFC TROUGH CROSSES THE CWA MONDAY NIGHT. THE LOW CROSSES THE CWA TUESDAY NIGHT. LOW CHANCES FOR LIGHT RAIN ACROSS THE CWA AS DOWNSLOPING FLOW WILL GREATLY LIMIT THE COVERAGE OF RAIN. TEMPERATURES NEAR NORMAL WITH DOWNSLOPING FLOW COUNTERACTING CLOUD COVER FROM KEEPING TEMPERATURES TOO LOW.
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&& .LONG TERM /TUESDAY THROUGH SUNDAY/...
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AN UPPER LEVEL TROUGH WILL DIG ACROSS THE EASTERN UNITED STATES THROUGH THE FIRST HALF OF THE WORKWEEK. LOW PRESSURE ASSOCIATED WITH THIS TROUGH WILL JUMP SOUTHWARD FROM OVER THE GREAT LAKES TO THE MID-ATLANTIC THROUGH THE FIRST PART OF THE WORKWEEK AS HIGH PRESSURE MOVES OFFSHORE. THE LOW WILL LOOSE SOME OF ITS ORGANIZATION...LIKELY DUE TO THE PASSAGE OVER THE MOUNTAINS...BUT POPS WILL ENTER THE HIGH END CHANCE RANGE BEGINNING TUESDAY. PRECIP TYPE SHOULD MOSTLY BE LIGHT RAIN WITH LIMITED INSTABILITY. THE UPPER LEVEL LOW WILL OCCLUDE FROM THE BACKGROUND WESTERLIES AS THE ASSOCIATED SURFACE LOW DEEPENS OFF OF THE NORTHEAST COAST THROUGH THE DAY WEDNESDAY. OPERATIONAL EURO AND GFS ARE IN PRETTY GOOD AGREEMENT IN THE HIGHEST QPF ASSOCIATED WITH THIS SYSTEM BEING IN THE SOUTHEASTERN QUADRANT OF THE LOW WELL OFF OF THE COAST...BUT LIGHT PRECIPITATION COULD CONTINUE LOCALLY THROUGH WEDNESDAY AFTERNOON. COOL AND BREEZY NORTHERLY FLOW WILL FILL IN AS THE LOW SLOWLY MOVES UP THE COAST THROUGH THE SECOND HALF OF THE WORKWEEK. THIS WILL LEAD TO CLEARING SKIES AND TEMPS 5 TO 10 DEGREES BELOW NORMAL THURSDAY AND FRIDAY. HIGH PRESSURE WILL SETTLE OVERHEAD FOR THE WEEKEND ALLOWING TEMPS TO BEGIN TO SLOWLY REBOUND TOWARD NORMAL.
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&& .AVIATION /18Z SUNDAY THROUGH FRIDAY/...
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VFR CONDS THROUGH THE TAF PERIOD...THROUGH GUSTY NW WINDS WILL BE A CONCERN JUST THRU THE 22-23Z TIME FRAME - THEN THE SFC AND LOW LEVEL WINDS WILL START TO DROP OFF SUBSTANTIALLY. HIGH PRESSURE PASSING JUST TO OUR SOUTH WILL HELP TAKE WINDS TO NEAR CALM LEVELS OVERNIGHT AND IT`S OWN EXIT OFF THE COAST ON MON WILL STEER WINDS BACK TO A MORE SLY DIRECTION FOR THE DAYTIME HRS. CONFIDENCE IS LOW IN THE OCCURRENCE OF AVIATION HAZARDS THROUGH THE LONG TERM PERIOD.
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&& .MARINE...
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A SMALL CRAFT ADVISORY REMAINS IN EFFECT FOR ALL OF THE WATERS INTO THE EVE HRS. THE TOP-END GUSTS ARE DROPPING DOWN INTO THE L20KT RANGE AND WILL KEEP DISSIPATING IN THE COMING HRS...AS THE RESPONSIBLE UPPER LEVEL LOW MOVES OFFSHORE. WINDS DIMINISH LATE TONIGHT AS HIGH PRESSURE CENTER CROSSES THE BAY LATE IN THE NIGHT. A SMALL CRAFT ADVISORY MAY BE NEEDED FOR PORTIONS OF THE CHESAPEAKE BAY AND LOWER TIDAL POTOMAC IN GUSTY NORTHERLY WINDS AS LOW PRESSURE MOVES UP THE NORTHEAST COAST BEGINNING WEDNESDAY MORNING AND CONTINUING THROUGH FRIDAY NIGHT.
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&& .LWX WATCHES/WARNINGS/ADVISORIES...
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DC...NONE. MD...FROST ADVISORY FROM 2 AM TO 9 AM EDT MONDAY FOR MDZ003>005-501- 502. VA...FROST ADVISORY FROM 2 AM TO 9 AM EDT MONDAY FOR VAZ025>031. FREEZE WARNING FROM 2 AM TO 9 AM EDT MONDAY FOR VAZ503-504. WV...FROST ADVISORY FROM 2 AM TO 9 AM EDT MONDAY FOR WVZ050>053-055- 502>504. FREEZE WARNING FROM 2 AM TO 9 AM EDT MONDAY FOR WVZ501-505-506. MARINE...SMALL CRAFT ADVISORY UNTIL MIDNIGHT EDT TONIGHT FOR ANZ531>534- 537-539>541-543. SMALL CRAFT ADVISORY UNTIL 8 PM EDT THIS EVENING FOR ANZ530- 535-536-538-542.
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&& $$ SYNOPSIS...GMS NEAR TERM...GMS SHORT TERM...GMS LONG TERM...CEB AVIATION...GMS/CEB MARINE...GMS/CEB

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