Area Forecast Discussion
Issued by NWS Sterling, VA

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000 FXUS61 KLWX 220101 AFDLWX AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC 901 PM EDT THU MAY 21 2015 .SYNOPSIS...
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LOW PRESSURE PASSES EAST OF THE REGION OVERNIGHT. A COLD FRONT CROSSES THE AREA FRIDAY. HIGH PRESSURE BUILDS IN FOR THE WEEKEND WITH COOL WEATHER TO START FOLLOWED BY NOTICEABLE WARMING LATER ON. AS A SUMMER-LIKE AIR MASS ENTERS THE REGION EARLY NEXT WEEK...HOT TEMPERATURES AND AN INCREASED RISK OF THUNDERSTORMS WILL BECOME THE MAIN STORY.
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&& .NEAR TERM /UNTIL 6 AM FRIDAY MORNING/...
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LOPRES REMAINS OFF CAPE HATTERAS THIS EVNG. MUCH OF CWFA REMAINS IN THE VOID BETWEEN THIS LOW...A 2NDRY AREA OF LOPRES OVER SC... AND THE LEADING EDGE OF NW FLOW ENTERING THE MTNS. IN THE CNVGNC ZONE TO THE WEST...ADDTL SHRA/SPRINKLES HV DVLPD AND MVD EAST TO THE PTMC HIGHLANDS. GDNC SUGGESTING THAT CVRG WL BE SPARCE... LOCATION SHUDNT OUTRUN BLURDG...AND DURATION SHUDNT EXCEED MIDNGT. HV UPDTD DATABASE FOCUSED ON THESE PRINCIPLES. OTRW...LOW CLDS WL BE CLEARING OVNGT...SPCLY ONCE NW WINDS ARRIVE. IF CLDS MANAGE TO BREAK PRIOR TO THAT...THEN A WINDOW OF OPPORTUNITY EXISTS FOR FOG TO DVLP. ATTM WL DOWNPLAY THAT PSBLTY BUT WONT OUTRIGHT IGNORE IT. TEMPS WL BE FAIRLY LVL THRU THE NGT...PSBLY DROPPING SLGTLY ONCE STRONG CAA ARRIVES.
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&& .SHORT TERM /6 AM FRIDAY MORNING THROUGH SUNDAY/... MAINLY DRY PERIOD TO END THE WEEK AS HIGH PRESSURE BUILDS ACROSS THE REGION. A QUICK MOVING COLD FRONT WILL PUSH THROUGH FRIDAY BEFORE THE HIGH COMPLETELY TAKES HOLD OF THE REGION. EXPECTING MAINLY A DRY PASSAGE WITH MOISTURE LACKING. COULD SEE ISO SHOWERS OVER NORTHWEST CORNER OF THE CWA MAINLY DUE TO ANY TERRAIN CIRCULATIONS ON THE NW FLOW. TIGHTENING PRESSURE GRADIENT BETWEEN THE DEPARTING...DEEPENING SFC LOW AND APPROACHING HIGH WILL LEAD TO GUSTS UP INTO THE 20S DURING THE DAY FRIDAY...DIMINISHING BY FRI EVENING. HIGHS ON FRI NEAR SEASONAL...HAVING GONE A DEGREE OR TWO HIGHER THAN THE GUIDANCE TO ACCOUNT FOR DOWNSLOPING EFFECTS...WHICH PUSHES MOST AREAS INTO THE UPPER 60S TO LOWER 70S. CLEARING SKIES...LIGHT WINDS AND CAA WILL DROP LOWS FRI NIGHT BLW NORMAL. SOME SPOTS OF FAR WESTERN POTOMAC HIGHLANDS COULD EVEN SEE TEMPS FALLING INTO THE MID 30S...HAVE INCLUDED PATCHY FROST TO ACCOUNT FOR THIS THOUGH LIMITED MOISTURE ON SUCH A DRY PATTERN MIGHT LIMIT ANY DEVELOPMENT DESPITE THE TEMP. BY SATURDAY MORNING...HIGH PRESSURE WILL BE CENTERED OVER THE UPPER OHIO VALLEY WITH LIGHT WINDS AND MOSTLY CLEAR SKIES ACROSS THE CWA. AFTER A COOL START FOR LATE MAY...TEMPERATURES WILL REBOUND INTO THE LOWER 70S ACROSS MOST OF THE REGION WITH LIGHT WINDS. ALTHOUGH STILL A BIT BELOW NORMAL...PLENTIFUL SUNSHINE WILL HELP MAKE IT A VERY NICE DAY...IF STILL TOO COOL TO REALLY BE CONSIDERED A BEACH DAY. DURING SATURDAY NIGHT HIGH PRESSURE WILL SLIDE OFF THE COAST INTO THE WESTERN ATLANTIC. WINDS WILL GRADUALLY SHIFT TOWARDS THE SOUTHWEST...BUT THE RETURN OF WARMTH AND MOISTURE WILL NOT HAVE REALLY STARTED JUST YET SATURDAY NIGHT SO ANOTHER GOOD RADIATIONAL NIGHT IS EXPECTED WITH MOSTLY CLEAR SKIES...LIGHT WINDS...AND TEMPS IN THE 40S OUTSIDE OF THE CITIES. HIGH PRESSURE WILL CONTINUE ITS SLOW SLIDE EAST ON SUNDAY...BUT THE RETURN FLOW WILL BE MORE NOTICEABLE WITH TEMPERATURES RISING BACK ABOVE NORMAL. LOW 80S WILL BE COMMON ACROSS THE CWA. COMBINED WITH THE EXPECTED DEWPOINTS RISE OF OVER 20 DEGREES (SATURDAY`S READINGS IN THE 30S VERSUS SUNDAY`S IN THE 50S)...AND IT WILL FEEL MUCH MORE SUMMERLIKE ON SUNDAY VERSUS SATURDAY. WHILE THIS INCREASED WARMTH AND MOISTURE WILL SIGNAL A RETURN OF CONVECTION NEXT WEEK...IT SHOULD NOT OCCUR JUST YET ON SUNDAY WITH THE RIDGE AXIS ALOFT STILL WEST OF THE REGION. && .LONG TERM /SUNDAY NIGHT THROUGH THURSDAY/... ECMWF 500 MB RIDGE OVER MID ATLANTIC REGION WILL ASSUME A NORTHEAST TO SOUTHWEST ORIENTATION AND WEAKEN DURING THE WORKWEEK. STRONGEST PVA WILL STAY WEST AND NORTH OF AREA. SURFACE WARM FRONT WILL CROSS AREA SUNDAY NIGHT THROUGH MONDAY AFTERNOON. ALTHOUGH BEST CHANCES OF SHOWERS AND THUNDERSTORMS LOOKS TO OCCUR MONDAY...INCREASED MOISTURE... TEMPERATURES AND WEAK PVA WILL SUPPORT SCATTERED CONVECTIVE ACTIVITY EACH DAY. && .AVIATION /01Z FRIDAY THROUGH TUESDAY/...
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MVFR-IFR CIGS DOMINATE...ALTHO A FEW VFR BINOVC WL BE PSBL THIS EVNG. XPCT CLDS TO SCATTER OUT BTWN 03-05 UTC...ALTHO TIMING A LTL UNCERTAIN. ALTHO MOST RECENT GDNC SUGGESTING IMPVMNT WL COME ON THE BACK EDGE OF THAT RANGE...MOST RECENT MTR DATA HINTING THAT TIMING WL ACTUALLY BE ERLR. VFR CONDS AND NW WINDS WL PREVAIL OVERNIGHT INTO THE MRNG PUSH FRI. NW FLOW WILL INCREASE...WITH GUSTS 20-25 KTS BEGINNING AROUND 13-14Z AND LASTING INTO FRI EVENING. VFR CIGS AND VIS THROUGH THE WEEKEND WITH LIGHT WINDS AS HIGH PRESSURE REIGNS SUPREME. THE THREAT OF THUNDERSTORMS WILL BEGIN TO INCREASE ON MEMORIAL DAY AS THE HIGH MOVES EAST AND A WARMER AND MORE HUMID AIR MASS ADVECTS INTO THE REGION.
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&& .MARINE...
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GREATLY SIMPLIFIED SCA FOR WATERS THRU FRI. ALTHO WINDS REALLY NOT VERIFYING ATTM...XPCT THEY WL OVERNIGHT AS CAA REACHES WATERS. ATTM ADVY ONLY FOR DRUM PT-SMITH PT/TANGIER SOUND...BUT THAT WL EXPAND AT 3AM TO INCL MOST OF THE MD BAY /POOLES ISL SWD/ AS WELL AS THE MOUTH OF THE PTMC. BHD REINFORCING CDFNT FRI...WINDS WL PICK UP TO FREQUENT 20-25 KT GUSTS AT THAT TIME. THIS IS THE PLACE WHERE ADVY EXPANDED TO INCL ALL WATERS...AS GDNC SUPPORTS GOOD MIXING AND SCA GUSTS AVBL W/IN MIXED LYR. ADVY POKES INTO FRI EVNG BEFORE DIURNAL TRENDS AND DIMINISHING P-GRAD SHUD IMPEDE MIXED POTL. WINDS SHOULD STAY BELOW SCA LEVELS THROUGH THE WEEKEND WITH HIGH PRESSURE IN CONTROL. NO PRECIPITATION IS EXPECTED. THE THREAT OF SHOWERS AND THUNDERSTORMS WILL INCREASE NEXT WEEK AS A WARMER AND MORE HUMID AIR MASS MOVES INTO THE AREA.
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&& .CLIMATE...
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UNUSUALLY COOL HIGH TEMPERATURES WERE OBSERVED TODAY...MAY 20TH. BELOW IS A LIST OF DAILY RECORD LOW MAXIMUM TEMPERATURES FOR TODAY`S DATE. SITE...RECORD LOMX... DCA....52 (1895)..... BWI....52 (1895)..... IAD....59 (2002).....
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&& .LWX WATCHES/WARNINGS/ADVISORIES...
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DC...NONE. MD...NONE. VA...NONE. WV...NONE. MARINE...SMALL CRAFT ADVISORY FROM 10 AM TO 11 PM EDT FRIDAY FOR ANZ530- 535-536-538-539. SMALL CRAFT ADVISORY FROM 3 AM TO 11 PM EDT FRIDAY FOR ANZ531>533-537-540>542. SMALL CRAFT ADVISORY UNTIL 11 PM EDT FRIDAY FOR ANZ534-543.
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&& $$ SYNOPSIS...HTS/SEARS/RCM NEAR TERM...HTS SHORT TERM...SEARS/RCM LONG TERM...CEM AVIATION...HTS/SEARS/RCM MARINE...HTS/RCM CLIMATE...DH

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