Area Forecast Discussion
Issued by NWS Sterling, VA

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000 FXUS61 KLWX 251318 AFDLWX AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC 918 AM EDT MON MAY 25 2015 .SYNOPSIS... HIGH PRESSURE WILL REMAIN OVER THE ATLANTIC OCEAN THROUGH NEXT WEEKEND. A SOUTHWEST FLOW WILL USHER IN WARMER AND MORE HUMID CONDITIONS DURING THIS TIME. THE HEAT AND HUMIDITY WILL INCREASE THE RISK OF THUNDERSTORMS STARTING TUESDAY AND CONTINUING THROUGH THE REMAINDER OF THE WEEK. && .NEAR TERM /THROUGH TONIGHT/... SUNNY CONDITIONS ACROSS THE REGION THIS MORNING. TEMPS ALREADY AROUND 70 DEGREES THIS MEMORIAL DAY. PREVIOUS DISCUSSION... HIGH PRESSURE WILL REMAIN OVER THE ATLANTIC OCEAN THROUGH TONIGHT AND AN UPPER-LEVEL RIDGE CENTERED OFF THE SOUTHEAST COAST WILL EXTEND NORTHWEST INTO THE MID-ATLANTIC DURING THIS TIME. THE UPPER-LEVEL RIDGING ALONG WITH A SOUTHWEST FLOW WILL USHER IN WARMER AND SLIGHTLY MORE HUMID CONDITIONS TODAY. LEANED TOWARD THE WARMER SIDE OF GUIDANCE DUE TO THE SUBSIDENCE EXPECTED WITH THE RIDGE AXIS OVERHEAD AND PLENTY OF SUNSHINE. MAX TEMPS ARE FORECAST TO RANGE FROM THE 70S IN THE MOUNTAINS TO THE MID AND UPPER 80S ACROSS MOST OTHER LOCATIONS. A SOUTHERLY FLOW WILL CONTINUE TONIGHT AROUND THE HIGH CENTERED TO OUR EAST. THEREFORE...WARMER CONDITIONS ARE EXPECTED. THE UPPER- LEVEL RIDGE AXIS WILL START TO SHIFT OFF THE MID-ATLANTIC COAST TONIGHT...ALLOWING FOR HIGH AND MID-LEVEL CLOUDS TO INCREASE OVERNIGHT. MOST AREAS WILL REMAIN DRY...BUT A COUPLE SHOWERS CANNOT BE RULED OUT ACROSS EXTREME WESTERN AREAS WELL AFTER MIDNIGHT. && .SHORT TERM /TUESDAY THROUGH TUESDAY NIGHT/... THE UPPER-LEVEL RIDGE WILL REMAIN CENTERED TO OUR EAST WHILE SURFACE HIGH PRESSURE REMAINS OVER THE ATLANTIC TUESDAY THROUGH TUESDAY NIGHT. A SOUTHWEST FLOW FROM THE SURFACE THROUGH THE UPPER-LEVELS OF THE ATMOSPHERE WILL USHER IN MORE MOISTURE DURING THIS TIME. MAX TEMPS TUESDAY ARE FORECAST TO RANGE FROM THE 70S IN THE MOUNTAINS TO THE MID AND UPPER 80S ACROSS MOST OTHER LOCATIONS. DID TWEAK TEMPS A COUPLE DEGREES FROM CONTINUITY DUE TO A BKN/OVC DECK OF HIGH AND MID-LEVEL CLOUDS EXPECTED. THE INCREASED MOISTURE WILL LEAD TO THE CHANCE FOR SHOWERS AND THUNDERSTORMS. THE BEST CHANCE FOR CONVECTION WILL BE DURING THE AFTERNOON AND EVENING HOURS DURING PEAK HEATING. ASIDE FROM WEAK SHORTWAVE ENERGY...THERE WILL NOT BE A STRONG LIFTING MECHANISM TO ENHANCE CONVECTION COVERAGE IS EXPECTED TO BE SCATTERED ACROSS MOST AREAS. SHEAR PROFILES REMAIN RELATIVELY WEAK AND INSTABILITY WILL BE MARGINAL DUE TO THE CLOUD COVER SO THE THREAT FOR SEVERE THUNDERSTORMS WILL BE LOW. WILL CONTINUE WITH THE CHANCE FOR SHOWERS/ISOLATED THUNDERSTORMS OVERNIGHT DUE TO SHORTWAVE ENERGY SWINGING THROUGH AND DEEP MOISTURE. MIN TEMPS WILL RANGE FROM THE LOWER 60S IN PORTIONS OF THE POTOMAC HIGHLANDS TO THE MID 70S IN DOWNTOWN WASHINGTON AND BALTIMORE. IT WILL ALSO FEEL QUITE HUMID. && .LONG TERM /WEDNESDAY THROUGH SUNDAY/... MULTIPLE ROUNDS OF UNSETTLED WX EXPECTED IN THE EXTENDED WITH MULTIPLE BOUNDARIES NEARING AND STALLING CLOSE TO THE REGION. WHILE CONFIDENCE EXIST THAT EACH DAY WILL BRING A CHC FOR TSTM ACTIVITY...THERE REMAINS SOME MODEL DISCREPANCIES ON THE PLACEMENT OF THE BOUNDARIES AND AS SUCH TRYING TO FINE TUNE WHERE AND WHEN THE PCPN OCCURS STILL HAS SOME UNCERTAINTY. AS SUCH...HAVE CAPPED POPS THROUGH THE PERIOD AS HIGH END CHC. WELL ABOVE NORMAL TEMPS WILL PERSIST THRU THE PERIOD...WITH HIGHS AND LOWS REACHING OVER 10 DEGREES ABV NORMAL EACH DAY. PLEASE REFER TO THE CLIMATE SECTION FOR RECORD INFORMATION FOR THE COMING WEEK. SFC LOW PUSHING NORTH THRU THE GREAT LAKES WED MORNING WILL DRAG ITS ASSOCIATED COLD FRONT TO JUST WEST OF THE REGION. SFC HIGH PRESSURE PERSISTING OFFSHORE WILL COUNTER THE PROGRESSION OF THE FRONT WHILE RIDGING ALOFT NUDGES THE APPROACHING UPPER LVL TROUGH OFF WELL NORTH OF THE REGION. GENERALLY EXPECTING WITH THIS SYNOPTIC SETUP FOR THE FRONT TO PUSH INTO THE OHIO RIVER VALLEY...THEN STALLING/WEAKENING WED INTO THURS. THIS STALLED BOUNDARY WILL BE THE TRIGGERING MECHANISM FOR SCT-NUM TSTM ACTIVITY WED AFTN-FRI. GOOD MOISTURE ADVECTION ON THE SWLY FLOW COMBINING WITH TEMPS IN THE 80S WILL ENABLE DECENT INSTABILITY TO FORM BY WED AFTN. SOME QUESTION AS TO HOW MUCH INSTABILITY WITH MORNING CLOUD COVER NEEDING TO SCATTER TO ENABLE THE BEST DIURNAL HEATING. SHEAR IS MORE ON THE WEAKER SIDE WITH MAINLY UNIDIRECTIONAL FLOW AROUND 20 KTS. THINKING MOST LIKELY WILL END UP SEEING A STRONG SHEAR/WEAKER INSTABILITY WEST OF THE BLUE RIDGE...AND STRONGER INSTABILITY/WEAKER SHEAR EAST OF THE BLUE RIDGE WITH THE BETTER CHC OF HAVING BREAKS IN THE CLOUDS. MODELS ARE ALREADY HINTING AT SOME SORT OF LINEAR FORMATION...PSBL OVER THE OH RIVER VALLEY...CARRYING THEN SOUTH THRU CENTRAL MD AND INTO MD. MANY SVR PARAMETERS ON THE WEAKER SIDE...BUT ITS DEFINITELY NOT OUT OF THE QUESTION FOR GUSTY TO STRONGER WINDS TO FORM WITH SOME OF THE STORMS LATE WED AFTN/DURING THE EVENING. WITH PWATS NEAR 1.8 INCHES...ANY STORM COULD ALSO RESULT IN BRIEF HEAVY RAINFALL...ESP ALONG THE I-95 CORRIDOR. ISO-SCT SHOWERS WILL REMAIN PSBL WED NIGHT. THE FRONTAL BOUNDARY SINKS FURTHER INTO THE MID ATLANTIC ON THURS...RESULTING IN YET ANOTHER ROUND OF SHOWERS AND TSTMS...ESPECIALLY OVER EASTERN AREAS WITH THE AXIS OF THE HIGHER INSTABILITY ALIGNING FROM DC TO BALTIMORE. DESPITE THE HIGHER INSTABILITY VALUES...SHEAR JUST CONTINUES TO LACK THOUGH THERE IS MORE DIRECTIONAL SHEAR AS WINDS BACK TO THE SE. WOULD EXPECT TO SEE TSTMS SCT IN NATURE THROUGHOUT THE DAY...THOUGH WITH MUCH LESS OF A SVR POTENTIAL THAN THE PREVIOUS DAYS. MUCH OF THE SAME STORY FOR FRIDAY. ANOTHER LOW TRACKING THROUGH SOUTHERN CANADA WILL DRAG ITS ASSOCIATED COLD FRONT INTO THE MID ATLANTIC SAT...WITH SOME QUESTION THEN HOW LONG THIS BOUNDARY REMAINS STALLED IN THE VICINITY. THE GFS AND ECMWF HAVE TWO VERY DIFFERENT SLNS IN THE HANDLING OF THE RIDGE ALOFT AND THUS THE MOVEMENT OF THE FRONT. WITH THE AREA STILL ON THE WESTERN PERIPHERY OF THE OFFSHORE HIGH HOWEVER...EXPECT PLENTY OF WARM AIR AND MOISTURE ADVECTION ON THE SWLY FLOW OVER THE WEEKEND TO KEEP THE POTENTIAL FOR SCT SHOWERS AND TSTMS...ESP EACH AFTN. && .AVIATION /13Z MONDAY THROUGH FRIDAY/... VFR CONDITIONS ARE EXPECTED THROUGH TONIGHT. SOUTH TO SOUTHWEST WINDS WILL GUST AROUND 20 TO 25 KNOTS LATE THIS MORNING AND AFTERNOON. WINDS SHOULD DIMINISH AFTER SUNSET THIS EVENING. A FEW THUNDERSTORMS ARE POSSIBLE TUESDAY AFTERNOON INTO TUESDAY NIGHT. HOWEVER...COVERAGE WILL REMAIN SCATTERED DUE TO A LACK OF A STRONG LIFTING MECHANISM. THEREFORE...MUCH OF THE TIME MAY END UP PRECIPITATION FREE. THE THREAT FOR SEVERE THUNDERSTORMS IS LOW...BUT BRIEF GUSTY WINDS AND SUBVFR CONDITIONS ARE POSSIBLE. VARYING CONDITIONS THROUGH THIS WEEKEND...WITH PERIODS OF MVFR OR LOWER PSBL WITH ANY SHOWER/TSTM. STRONGER TSTMS PSBL WED AFTN...WITH GUSTY WINDS AND HEAVY RAINFALL. WED COULD ALSO SEE OCNL GUSTS UP TO 20 KTS OUTSIDE OF ANY PCPN...WITH WINDS GENERALLY 10 KTS OR LESS OUTSIDE OF PCPN THE REMAINDER OF THE EXTENDED. && .MARINE... HIGH PRESSURE WILL REMAIN OVER THE ATLANTIC OCEAN THROUGH TUESDAY NIGHT. SOUTH TO SOUTHWEST WINDS ARE EXPECTED DURING THIS TIME. THE GRADIENT WILL BE STRONGEST TODAY SO A SMALL CRAFT ADVISORY IS IN EFFECT FOR ALL OF THE WATERS INTO THIS EVENING. A SMALL CRAFT ADVISORY IS IN EFFECT FOR MIDDLE PORTIONS OF THE MARYLAND CHESAPEAKE BAY AND LOWER TIDAL POTOMAC RIVER LATE TONIGHT THROUGH TUESDAY. THE SMALL CRAFT ADVISORY MAY HAVE TO BE EXTENDED FARTHER NORTH TUESDAY...BUT CONFIDENCE IS LOW AT THIS TIME DUE TO A SLIGHTLY WEAKER GRADIENT AND RELATIVELY COOLER WATERS. SOUTHERLY WINDS ARE EXPECTED TO CHANNEL UP THE BAY AND LOWER TIDAL POTOMAC RIVER TUESDAY NIGHT. A SMALL CRAFT ADVISORY MAY BE NEEDED FOR THESE AREAS. INCREASED MOISTURE WILL LEAD TO A CHANCE FOR THUNDERSTORMS...MAINLY TUESDAY AFTERNOON AND EVENING. COVERAGE SHOULD REMAIN SCATTERED AT BEST SINCE THERE WILL NOT BE A STRONG LIFTING MECHANISM. THE THREAT FOR SEVERE THUNDERSTORMS IS LOW...BUT BRIEF GUSTY WINDS AND REDUCED VISIBILITIES FROM RAIN ARE POSSIBLE IN ANY THUNDERSTORMS THAT DO DEVELOP. SCA CONDITIONS PSBL ON WED...ESP ON THE CHESAPEAKE BAY...WITH A TIGHTENING PRESSURE GRADIENT AND SLY CHANNELING. AS THE PRESSURE GRADIENT SLACKENS BY WED NIGHT...EXPECTING SUB-SCA CONDITIONS THEN THURS AND FRI FOR MOST OF THE ZONES. MID CHESAPEAKE BAY COULD SEE GUSTS TO 20 KTS EACH AFTN THRU FRI. A TIGHTENING PRESSURE GRADIENT YET AGAIN WITH THE NEXT COLD FRONT ON SAT WILL INCREASE WINDS...WITH PSBL SCA CONDITIONS ON ALL WATERS SAT- SAT NIGHT. OUTSIDE OF THE SYNOPTIC FLOW...EACH DAY WILL BRING A CHC FOR SHOWERS AND TSTMS...WHICH COULD ALSO RESULT IN GUSTY WINDS. && .CLIMATE... UNUSUALLY WARM TEMPERATURES FOR THIS EARLY IN THE YEAR ARE FORECAST DURING MUCH OF THE UPCOMING WEEK. BELOW IS A LIST OF RECORD DAILY WARM TEMPERATURES FOR THE UPCOMING WEEK. CURRENT FEELING IS THAT HIGH AND MID-LEVEL CLOUDS WILL PREVENT RECORD- BREAKING HIGH TEMPERATURES THIS WEEK...BUT SHOULD WE GET MORE SUNSHINE THEN EXPECTED SOME OF THESE RECORDS COULD BE CHALLENGED. SOME OF THE RECORD HIGH MIN TEMPS COULD BE CHALLENGED. ....RECORD WARM TEMPERATURES FOR DCA........ DATE...RECORD HIGH...........RECORD HIGH MIN... 5/25...94 (1880).............71 (2012)......... 5/26...96 (1880).............74 (1991)......... 5/27...95 (1965/1914/1880)...75 (1991)......... 5/28...97 (1941).............75 (1991)......... 5/29...97 (1991/1969)........74 (1991)......... 5/30...98 (1991).............74 (1991)......... ....RECORD WARM TEMPERATURES FOR BWI........ DATE...RECORD HIGH...........RECORD HIGH MIN... 5/25...94 (1991).............70 (1936)......... 5/26...94 (1914).............74 (1880)......... 5/27...95 (1965/1941)........75 (1880)......... 5/28...97 (1941).............78 (1941)......... 5/29...97 (1969).............71 (1908)......... 5/30...98* (2011/1991).......72 (1895)......... *ALSO HIGHEST OBSERVED MAY MONTHLY TEMPERATURE ....RECORD WARM TEMPERATURES FOR IAD........ DATE...RECORD HIGH...........RECORD HIGH MIN... 5/25...92 (1991).............67 (2004)......... 5/26...92 (2007).............70 (1991)......... 5/27...92 (2010/1965)........69 (2008/1991).... 5/28...90 (2012/1991)........70 (1991)......... 5/29...97* (1969)............69 (2012)......... 5/30...95 (2006/1991/1987)...70 (2011)......... *ALSO HIGHEST OBSERVED MAY MONTHLY TEMPERATURE BELOW IS THE LONGEST STRETCH OF CONSECUTIVE DAYS AT OR ABOVE 90 F DURING THE MONTH OF MAY. DCA...7 DAYS (05/25-05/31/1991) BWI...7 DAYS (05/25-05/31/1991) IAD...7 DAYS (05/25-05/31/1991) && .LWX WATCHES/WARNINGS/ADVISORIES... DC...NONE. MD...NONE. VA...NONE. WV...NONE. MARINE...SMALL CRAFT ADVISORY UNTIL 6 AM EDT TUESDAY FOR ANZ531-538-539. SMALL CRAFT ADVISORY UNTIL 6 PM EDT TUESDAY FOR ANZ540-542. SMALL CRAFT ADVISORY UNTIL 6 PM EDT TUESDAY FOR ANZ532>534-537- 541-543. SMALL CRAFT ADVISORY UNTIL 2 AM EDT TUESDAY FOR ANZ530-535-536. && $$ SYNOPSIS...BJL NEAR TERM...BJL/HAS SHORT TERM...BJL LONG TERM...SEARS AVIATION...BJL/SEARS MARINE...BJL/SEARS CLIMATE...

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