Area Forecast Discussion
Issued by NWS Sterling, VA

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000 FXUS61 KLWX 260704 AFDLWX AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC 304 AM EDT TUE MAY 26 2015 .SYNOPSIS... HIGH PRESSURE WILL REMAIN OFFSHORE THIS WEEK. A SOUTHERLY FLOW WILL BRING WARM HUMID CONDITIONS TO THE MID ATLANTIC THROUGH SATURDAY. SHOWERS AND THUNDERSTORMS WILL BE POSSIBLE EACH AFTERNOON AND EVENING. A COLD FRONT WILL APPROACH THE AREA EARLY NEXT WEEK. && .NEAR TERM /THROUGH TONIGHT/... AN UPPER-LEVEL RIDGE WILL SLIDE OFF THE MID-ATLANTIC COAST TODAY WHILE HIGH PRESSURE REMAINS OVER THE ATLANTIC OCEAN. THE SURFACE HIGH AND UPPER-LEVEL RIDGE WILL REMAIN OVER THE ATLANTIC OCEAN TONIGHT. A SOUTHWEST FLOW FROM THE SURFACE THROUGH THE UPPER- LEVELS OF THE ATMOSPHERE WILL USHER IN MORE MOISTURE DURING THIS TIME. MAX TEMPS TODAY ARE FORECAST TO RANGE FROM THE 70S IN THE MOUNTAINS...TO THE LOWER AND MIDDLE 80S WEST OF THE BLUE RIDGE MOUNTAINS...TO THE MID AND UPPER 80S EAST OF THE BLUE RIDGE MOUNTAINS. TEMPS HAVE BEEN TWEAKED DOWN A COUPLE DEGREES DUE TO A BKN/OVC DECK OF HIGH AND MID-LEVEL CLOUDS THAT WILL OVERSPREAD THE AREA EARLY THIS MORNING AND REMAIN IN PLACE THROUGH THIS AFTERNOON. THE INCREASED MOISTURE WILL LEAD TO A FEW SHOWERS AND THUNDERSTORMS THIS AFTERNOON AND EVENING. COVERAGE SHOULD REMAIN ISOLATED TO SCATTERED FOR MOST AREAS SINCE THERE WILL NOT BE A STRONG LIFTING MECHANISM. HOWEVER...THE HEAT AND HUMIDITY ALONG WITH LOWER HEIGHTS BEHIND THE DEPARTING RIDGE SHOULD BE ENOUGH TO COMBINE WITH WEAK SHORTWAVE ENERGY FOR CONVECTION TO DEVELOP. THE BEST CHANCE FOR CONVECTION WILL BE NORTH AND WEST OF INTERSTATE 95 AND FOR LOCATIONS WEST OF THE BLUE RIDGE MOUNTAINS. LOWER HEIGHTS AND MORE SHORTWAVE ENERGY WILL BE OVER THESE AREAS. LATEST GUIDANCE ALSO SHOWS A THETA E RIDGE SETTING UP FOR LOCATIONS JUST NORTH AND WEST OF INTERSTATE 95. SHEAR PROFILES WILL REMAIN RELATIVELY WEAK AND INSTABILITY SHOULD BE MARGINAL DUE TO HIGH AND MID-LEVEL CLOUDS. THEREFORE...THE THREAT FOR SEVERE WEATHER IS LOW THIS AFTERNOON AND EVENING. HOWEVER...ANY THUNDERSTORMS THAT DO DEVELOP MAY PRODUCE LOCALLY HEAVY RAIN AND GUSTY WINDS. A SOUTHWEST FLOW WILL CONTINUE TONIGHT...CAUSING WARM AND HUMID CONDITIONS. A FEW SHOWERS ARE POSSIBLE DUE TO THE COPIOUS AMOUNTS OF MOISTURE...ESPECIALLY NEAR THE ALLEGHENY HIGHLANDS WHERE MOISTURE WILL BE DEEPEST 500MB HEIGHTS WILL BE LOWEST FURTHER AWAY FROM THE UPPER-LEVEL RIDGE. && .SHORT TERM /WEDNESDAY THROUGH WEDNESDAY NIGHT/... A SIMILAR SYNOPTIC SETUP IS EXPECTED WEDNESDAY THROUGH WEDNESDAY NIGHT WITH AN UPPER-LEVEL RIDGE AND SURFACE HIGH OVER THE ATLANTIC OCEAN. IN FACT...A COLD FRONT IS EXPECTED TO SLIDE THROUGH THE GREAT LAKES DURING THIS TIME. THIS SHOULD WEAKEN THE RIDGE A BIT MORE...ALLOWING FOR LOWER HEIGHTS OVER OUR AREA. WARM AND HUMID CONDITIONS WILL CONTINUE THANKS TO A SOUTHWEST FLOW AROUND THE SURFACE HIGH OVER THE ATLANTIC. A BKN/OVC DECK OF HIGH AND MID-LEVEL CLOUDS WILL CONTINUE TO MOVE THROUGH THE AREA ALONG WITH MORE SHORTWAVE ENERGY IN THE SOUTHWEST FLOW ALOFT. THE WARM AND HUMID CONDITIONS ALONG WITH THE SHORTWAVE ENERGY WILL LEAD TO MORE SHOWERS AND THUNDERSTORMS. COVERAGE MAY BE MORE WIDESPREAD COMPARED TO TUESDAY DUE TO LOWER HEIGHTS. SHEAR PROFILES MAY BE A BIT STRONGER...BUT STILL RELATIVELY WEAK. HOWEVER...LATEST GUIDANCE CONTINUES TO SUGGEST THAT THERE WILL BE A MAX IN INSTABILITY NEAR AND EAST OF THE BLUE RIDGE MOUNTAINS...ESPECIALLY NEAR THE WASHINGTON AND BALTIMORE METROPOLITAN AREAS INTO NORTH- CENTRAL MARYLAND. THIS IS LIKELY DUE TO DIFFERENTIAL HEATING. MID AND HIGH-LEVEL CLOUDS ARE FORECAST TO BE THICKER TO THE WEST WITH MORE BREAKS OF SUNSHINE FURTHER EAST ACROSS THESE AREAS. SHOULD THIS DEVELOP...THEN INSTABILITY HAS THE POTENTIAL TO BE HIGH WHICH WOULD INCREASE THE CHANCE FOR SEVERE THUNDERSTORMS. AS OF NOW...CERTAINTY IS TOO LOW TO MENTION IN THE FORECAST BUT THIS WILL HAVE TO BE MONITORED. MOST CONVECTION SHOULD DISSIPATE OVERNIGHT WEDNESDAY...BUT IT WILL REMAIN WARM AND QUITE HUMID THANKS TO THE SOUTHWESTERLY FLOW. && .LONG TERM /THURSDAY THROUGH MONDAY/... SFC LOW IN SE CANADA WILL DRAG AN ASSOCIATED COLD FRONT THROUGH THE NORTHEAST ON THURSDAY. THE FRONT BECOMES NEARLY STATIONARY LATE THURS INTO FRI MORNING...EVENTUALLY DISSIPATING BY SAT MORNING AS EMBEDDED SHORTWAVE TROUGH RIDING THE FLOW ALOFT IS PUSHED OFF TO THE NORTH AND EAST AS THE RIDGE TAKES CONTROL YET AGAIN OF THE EASTERN US. MAINTAINING UPPER END CHC POPS THRU THESE TWO DAYS TO ACCOUNT FOR TSTM POTENTIAL...SFC HIGH SITTING OFFSHORE WILL KEEP WARM AIR AND MOISTURE ADVECTION OVER THE REGION...RESULTING IN DECENT INSTABILITY VALUES. SHEAR ON THE LIGHTER SIDE...AND AS SUCH THINK ANY SVR THREAT WILL BE MINIMAL. WHILE CONFIDENCE EXISTS THAT TSTMS WILL DEVELOP...ESP DURING THE AFTN/EVENING HOURS...TRYING TO PINPOINT LOCATION AND TIMING STILL TOO EARLY SO WILL KEEP SCT WORDING FOR NOW. HAVE ONLY ISO SHOWERS IN THURS/FRI NIGHT WITH THE LOSS OF DIURNAL HEATING. THE NEXT COLD FRONT APPROACHES SAT...NEARING THE WESTERN AREAS BY LATE SAT. COULD SEE SHOWERS/TSTMS POP UP AHEAD OF THE FRONT IN THE WARM/MOIST ATMO...BUT NOT EXPECTING ANYTHING REALLY ORGANIZED AT THIS TIME. THE FRONT BECOMES NEARLY STATIONARY AS WELL NEAR THE MASON-DIXON WITH THE LOSS YET AGAIN OF ANY UPPER LVL FLOW. MODEL DIVERGENCE IN THE 00Z SOLUTIONS WITH THE HANDLING OF THIS FRONT...WITH THE GFS DEVELOPING A MORE DEFINED SFC LOW ALONG THE FRONT AND TRACKING IT INTO THE OH RIVER VALLEY. AS SUCH WILL KEEP CHC POPS IN...THOUGH WITH THE PAST COUPLE OF RUNS HINTING AT THE FRONT STALLING IN THE VICINITY...IT IS LOOKING MORE LIKELY WE WILL SEE PCPN OCCURRING SUN-MON WITH THIS BOUNDARY. TEMPS ABV NORMAL THRU THE EXTENDED PERIOD...WITH 850MB TEMPS HOVERING BETWEEN 10 AND 15 DEGREES CELSIUS. DESPITE THE WARMER TEMPS..EXPECTING ONLY ISOLATED SPOTS TO REACH 90 DUE TO ON GOING PCPN/CLOUD COVER. LOWS WILL REMAIN MILD IN THE 60S AND 70S. && .AVIATION /07Z TUESDAY THROUGH SATURDAY/... VFR CONDITIONS ARE EXPECTED MOST OF THE TIME THROUGH THIS EVENING. A COUPLE THUNDERSTORMS ARE EXPECTED THIS AFTERNOON AND EVENING. COVERAGE WILL REMAIN SCATTERED DUE TO A LACK OF A STRONG LIFTING MECHANISM SO MUCH OF THE TIME WILL BE DRY. HOWEVER...BRIEF SUBVFR CONDITIONS ARE POSSIBLE ALONG WITH LOCALLY GUSTY WINDS IN ANY THUNDERSTORM THAT MOVES OVER A TERMINAL. PATCHY FOG IS POSSIBLE LATE TONIGHT INTO WEDNESDAY MORNING. MORE SHOWERS AND THUNDERSTORMS ARE POSSIBLE LATER WEDNESDAY INTO WEDNESDAY EVENING. COVERAGE MAY BE MORE WIDESPREAD DUE TO LOWER HEIGHTS BEHIND A DEPARTING RIDGE OVER THE ATLANTIC OCEAN. PATCHY FOG IS POSSIBLE AGAIN LATE WEDNESDAY NIGHT. VARYING CONDITIONS THROUGH THIS WEEKEND...WITH PERIODS OF MVFR OR LOWER PSBL WITH ANY SHOWER/TSTM. ANY TSTM COULD PRODUCE GUSTY WINDS...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 WEDNESDAY NIGHT. A SOUTH TO SOUTHWEST FLOW IS EXPECTED DURING THIS TIME. A SMALL CRAFT ADVISORY REMAINS IN EFFECT THROUGH THIS EVENING FOR THE MARYLAND CHESAPEAKE BAY SOUTH OF POOLES ISLAND AND THE LOWER TIDAL POTOMAC RIVER. A SMALL CRAFT ADVISORY IS IN EFFECT LATE TONIGHT THROUGH WEDNESDAY FOR THE MARYLAND CHESAPEAKE BAY SOUTH OF SANDY POINT AND THE LOWER TIDAL POTOMAC RIVER...AND A SMALL CRAFT ADVISORY MAY BE NEEDED FOR PORTIONS OF THE WATERS WEDNESDAY NIGHT. WILL HAVE TO WATCH THE GRADIENT WIND TODAY FOR THE UPPER TIDAL POTOMAC AND NORTHERN CHESAPEAKE BAY. SOUTHWEST WINDS WILL APPROACH SCA CRITERIA...BUT THE FORECAST HAS WINDS CAPPED AT 15 KNOTS FOR NOW DUE TO A WEAKER PRESSURE GRADIENT COMPARED TO MONDAY. THUNDERSTORMS ARE POSSIBLE...ESPECIALLY THIS AFTERNOON AND EVENING...AND AGAIN WEDNESDAY AFTERNOON AND EVENING. COVERAGE TODAY SHOULD BE ISOLATED TO SCATTERED. THERE MAY BE A BETTER CHANCE FOR THUNDERSTORMS WEDNESDAY AFTERNOON AND EVENING DUE TO LOWER HEIGHTS BEHIND A DEPARTING UPPER-LEVEL RIDGE. ANY THUNDERSTORMS THAT DO DEVELOP MAY PRODUCE GUSTY WINDS AND LOCALLY HEAVY RAINFALL THAT CAN BRIEFLY REDUCE VSBYS BELOW ONE MILE AT TIMES. EXPECTING SUB-SCA CONDITIONS THURS AND FRI FOR MOST OF THE ZONES WITH WEAKENING PRESSURE GRADIENT. MID CHESAPEAKE BAY COULD SEE GUSTS TO 20 KTS EACH AFTN THRU FRI DUE TO SOUTHERN CHANNELING. 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. && .LWX WATCHES/WARNINGS/ADVISORIES... DC...NONE. MD...NONE. VA...NONE. WV...NONE. MARINE...SMALL CRAFT ADVISORY UNTIL MIDNIGHT EDT TONIGHT FOR ANZ531-538- 539. SMALL CRAFT ADVISORY UNTIL 6 PM EDT WEDNESDAY FOR ANZ532>534- 537-540>543. && $$ SYNOPSIS...BJL NEAR TERM...BJL SHORT TERM...BJL LONG TERM...SEARS AVIATION...BJL/SEARS MARINE...BJL/SEARS

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