Area Forecast Discussion
Issued by NWS Sterling, VA

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000 FXUS61 KLWX 021414 AFDLWX AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC 1014 AM EDT TUE SEP 2 2014 .SYNOPSIS...
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BERMUDA HIGH WILL PERSIST TODAY AHEAD OF A WEAK COLD FRONT THAT WILL CROSS THE AREA TONIGHT. HIGH PRESSURE WILL THEN BUILD FROM THE MIDWEST THROUGH WEDNESDAY THEN PERSIST OFFSHORE THURSDAY INTO THE WEEKEND. A COLD FRONT WILL ENTER THE REGION IN THE SATURDAY NIGHT TIME FRAME.
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&& .NEAR TERM /THROUGH TONIGHT/...
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VERY WARM AND MOIST AIR MASS REMAINS OVER THE CWA TODAY. THIS WILL LIKELY HELP FUEL THUNDERSTORMS FROM MID OR LATE AFTERNOON INTO THE EVENING. BEFORE THEN...CWA SHOULD BE DRY SAVE FOR A PASSING/STRAY SHOWER CLIPPING THE ALLEGHENY HIGHLANDS. SUNSHINE THIS MORNING WILL EVENTUALLY BE REPLACED BY INCREASING CLOUDS THIS AFTERNOON. SUNSHINE...TOASTY 850 MB TEMPS AND A W/SW FLOW WILL HELP BOOST SURFACE TEMPERATURES AOA 90 DEG F FOR MOST AREAS THIS AFTERNOON. COMBINE THE HUMIDITY AND IT MAY FEEL MORE LIKE MID TO UPPER 90S EAST OF THE BLUE RIDGE. PRE-FRONTAL CONVECTION OVER THE OHIO VALLEY HAS BEEN WEAKENING WITH TIME. WHATEVER IS LEFT OF IT WILL LIKELY MAKE IT TO THE POTOMAC HIGHLANDS BY MID-AFTERNOON...AND THEN UNDERGO A RE-INTENSIFICATION FURTHER DOWNSTREAM IN WHAT MAY BE A MODERATELY UNSTABLE /MODIFIED 12Z KIAD SOUNDING REVEALS 3000 J/KG CAPE/ AND MOIST AIR MASS. IN ADDITION...PRESENCE OF A SURFACE TROUGH /SORT OF PARALLELLING I-95/ WOULD ALSO SUPPORT CONVECTION. GIVEN THE EXPECTED BUOYANCY...A FEW THUNDERSTORMS MAY BE ABLE TO PRODUCE STRONG TO DAMAGING WIND GUSTS AS THEY MOVE EASTWARD ACROSS THE CWA THROUGH THIS EVENING. A HIGH PRECIPITABLE WATER ENVIRONMENT ALSO SUPPORTS HEAVY RAINFALL HOWEVER STORM MOTION MAY BE SUFFICIENT ENOUGH TO PRECLUDE FLASH FLOODING /UNLESS TRAINING OCCURS/. POP/WX GRIDS HAVE BEEN UPDATED TO REFLECT A LITTLE MORE DETAIL IN TIMING OF CONVECTION...HWO MENTIONS DAMAGING WIND GUSTS. EVENTUALLY...COLD FRONT CATCHES UP TO THE TROUGH LATER THIS EVENING AND THEN PUSHES OFFSHORE. THIS WILL EFFECTIVELY END THE CHANCE FOR SHOWERS AND THUNDERSTORMS OVERNIGHT.
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&& .SHORT TERM /WEDNESDAY THROUGH WEDNESDAY NIGHT/... DRY AND STABLE ON WED. NO POPS IN THE FORECAST. ANOTHER WARM AND RELATIVELY HUMID DAY...AS HIGHS WILL AGAIN APPROACH THE 90F DEG MARK ACROSS MUCH OF THE AREA. DEWPOINTS WILL STILL BE IN THE L-M60S...CREATING HEAT INDICES RIGHT AROUND THE AMBIENT TEMP LEVELS/SLIGHTLY HIGHER. WEDNESDAY NIGHT...HIGH PRESSURE CENTER OVER THE AREA SHIFTS OFFSHORE WITH A RETURN FLOW DEVELOPING IN THE OVERNIGHT HOURS. DEWPOINTS QUICKLY RAISE BACK TO NEAR 70F...MIGHT AS WELL GET AREAS OF FOG WORDING IN THE GRIDS. WITH THE HIGH PERSISTING OFFSHORE...AN UNSTABLE GULF AIRMASS BRINGS THE MID-ATLANTIC RIGHT BACK INTO AN ACTIVE PATTERN BY THURSDAY. CHANCES FOR DIURNAL DRIVEN SCATTERED THUNDERSTORMS. SHOULD LOW LEVEL FLOW BE MORE SELY THAN SLY...TERRAIN ENHANCEMENT WOULD ALSO BE A FACTOR IN THUNDERSTORM DEVELOPMENT. SIMILAR PATTERN FOR FRIDAY WITH THE NEXT COLD FRONT. MAX TEMPS THURSDAY AND FRIDAY AROUND 90F THOUGH CLOUD COVER WILL BE A FACTOR. && .LONG TERM /THURSDAY THROUGH MONDAY/... ANOTHER WEAK COLD FRONT APPROACHES FRIDAY NIGHT. LIKELY POPS FOR THUNDERSTORMS WEST FROM THE BLUE RIDGE SATURDAY AS THERE IS GOOD CONSENSUS BETWEEN THE 00Z GFS AND 00Z ECMWF. QUESTION IS HOW QUICKLY THE FRONT PUSHES THROUGH THE AREA. THE ECMWF LINGERS THE COLD FRONT OVER SERN ZONES THROUGH SUNDAY. && .AVIATION /13Z TUESDAY THROUGH SATURDAY/...
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MAIN ISSUE WILL BE SHRA/TSRA AFFECTING THE TERMINALS THIS AFTERNOON/EVENING. AT THE HUBS...LATEST RUNS OF THE HRRR/WRF-ARW HIGHLIGHT 21Z-01Z AS THE PRIMARY WINDOW OF CONCERN. COLD FRONT ACCELERATES TO A TROUGH AND THEN MOVES OFFSHORE BY LATE EVENING. PREVAILING/SYNOPTIC WIND SHIFT LIKELY OCCURS 02Z-05Z. NAM/GFS BOTH SUGGEST SOME FOG TONIGHT. LOW LEVEL MOISTURE DOES LINGER INTO THE OVERNIGHT...BUT WITH WIND SHIFT TO NW WILL LEAN TOWARD A MORE OPTIMISTIC APPROACH ATTM. HIGH PRESSURE OVERHEAD WEDNESDAY AND WEDNESDAY NIGHT. WITH LIGHT/CALM WINDS MAY HAVE SOME FOG WED NIGHT. LIGHT SLY RETURN FLOW THURSDAY AND FRIDAY WITH MAINLY AFTERNOON CHANCES FOR THUNDERSTORMS. COLD FRONT ENTERS THE AREA LATE SATURDAY WITH THUNDERSTORMS AHEAD OF IT.
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&& .MARINE...
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SW FLOW CONTINUES TODAY AHEAD OF A COLD FRONT. WIND SHIFT TO NW OCCURS LATE THIS EVENING BEHIND THE FRONT BUT NW PUSH/GRADIENT APPEAR WEAK ENOUGH FOR WINDS TO REMAIN BELOW SCA. MAIN CONCERN WILL BE THUNDERSTORMS LATE THIS AFTERNOON AND EVENING WHICH COULD PRODUCE STRONG WINDS THAT WOULD PROMPT SMW/S. WED WILL SEE HIGH PRES BUILD INTO THE REGION AND DROP WIND SPEEDS DOWN EVEN FURTHER. LIGHT AND VARIABLE FLOW WEDNESDAY EVENING GIVES WAY TO SLY FLOW AS HIGH PRESSURE MOVES OFFSHORE. WILL HAVE TO WATCH FOR CHANNELING AGAIN (PROBABLY THURSDAY EVENING) BUT AS OF NOW THERE ARE NO SCA HEADLINES EXPECTED. COLD FRONT APPROACHES THE WATERS SATURDAY WITH GOOD CHANCES FOR THUNDERSTORMS.
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&& .LWX WATCHES/WARNINGS/ADVISORIES... DC...NONE. MD...NONE. VA...NONE. WV...NONE. MARINE...NONE. && $$ SYNOPSIS...BPP/BAJ NEAR TERM...BPP SHORT TERM...GMS LONG TERM...BAJ AVIATION...BPP/BAJ MARINE...BPP/BAJ

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