Area Forecast Discussion
Issued by NWS Sterling, VA

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000 FXUS61 KLWX 101437 AFDLWX AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC 1037 AM EDT THU JUL 10 2014 .SYNOPSIS... A TROUGH OF LOW PRESSURE WILL LINGER ACROSS THE MID-ATLANTIC THROUGH THE END OF THE WEEK. WEAK HIGH PRESSURE BUILDS IN OVER THE WEEKEND. A COLD FRONT WILL THEN APPROACH EARLY NEXT WEEK. && .NEAR TERM /THROUGH FRIDAY/...
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CURRENT ANALYSIS SHOWS A SURFACE TROUGH OVER SOUTHERN MARYLAND THIS MORNING. AN UPPER-LEVEL TROUGH IS APPROACHING FROM THE OHIO VALLEY AND AN UPPER-LEVEL DISTURBANCE IS MOVING THROUGH IN THE SOUTHWEST FLOW ALOFT. THE SURFACE TROUGH IS EXPECTED TO RETROGRADE BACK TO THE WEST THIS AFTERNOON INTO TONIGHT. AN EASTERLY FLOW BEHIND THE SURFACE TROUGH WILL ALLOW FOR MOISTURE TO RETURN DURING THIS TIME. THERE SHOULD BE ENOUGH BREAKS IN MID-LEVEL CLOUDS FOR MAX TEMPS TO REACH THE MIDDLE 80S ACROSS MOST LOCATIONS. THE INCREASED MOISTURE WILL ALLOW FOR AN UNSTABLE ATMOSPHERE TO DEVELOP ONCE AGAIN THIS AFTERNOON. THE MODIFIED 12Z KIAD SHOWS AROUND 1000 TO 1500 J/KG OF MLCAPE. THE UPPER-LEVEL TROUGH WILL ALSO MOVE OVERHEAD DURING THIS TIME ALONG WITH THE RIGHT ENTRANCE OF THE UPPER-LEVEL JET. THE FORCING FROM THE UPPER-LEVEL JET AND TROUGH ALONG WITH THE SURFACE TROUGH WILL ALLOW FOR MORE SHOWERS AND THUNDERSTORMS TO DEVELOP THIS AFTERNOON. DEEP LAYER SHEAR WILL REMAIN SUFFICIENT ENOUGH TO COMBINE WITH THE INSTABILITY FOR THE THREAT OF SEVERE THUNDERSTORMS. LOCALLY DAMAGING WIND GUSTS AND LARGE HAIL WOULD BE THE PRIMARY THREATS. DO FEEL THAT THE SEVERE THREAT WILL BE LOCALIZED SIMILAR TO WEDNESDAY AND NOT AS WIDESPREAD AS TUESDAY OF THIS WEEK. ANOTHER CONCERN IS FOR HEAVY RAINFALL. THE SHEAR VECTORS INDICATE THAT STORMS WILL TRAIN OVER THE SAME AREAS...AND WITH THE RETURN OF MOISTURE PWATS WILL RETURN TO AROUND 1.75 TO 2.00 INCHES. THE SURFACE TROUGH WILL ALSO BE SLOWLY MOVING AND THE SHEAR VECTORS ARE NEARLY PARALLEL TO THAT. THEREFORE...FLASH FLOODING IS A CONCERN...ESPECIALLY FROM THE SHENANDOAH VALLEY/NORTH-CENTRAL MARYLAND EASTWARD LATE THIS AFTERNOON INTO TONIGHT. DID NOT ISSUE A FLASH FLOOD WATCH AT THIS TIME DUE TO LOW CONFIDENCE...BUT WILL COVER THE THREAT IN THE HAZARDOUS WEATHER OUTLOOK FOR NOW. THE UPPER LEVEL TROUGH WILL SHIFT TOWARD THE MID-ATLANTIC COAST LATE TONIGHT AND SHOWERS AND THUNDERSTORMS WILL MOVE OFF TO THE EAST BY FRIDAY MORNING. THE TROUGH AXIS WILL REMAIN NEAR THE MID- ATLANTIC COAST FRIDAY. AN ISOLATED SHOWER OR THUNDERSTORM CANNOT BE RULED OUT...BUT MOST AREAS WILL END UP DRY SINCE WE WILL BE ON THE SUBSIDENCE SIDE OF THE TROUGH.
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&& .SHORT TERM /FRIDAY NIGHT THROUGH SATURDAY/... ANY CONVECTION FROM FRIDAY AFTERNOON SHOULD DISSIPATE DURING THE EVENING...WITH CLEARING SKIES PROMOTING PATCHY FOG DEVELOPMENT OVERNIGHT. FRONTAL BOUNDARY REMAINS SOUTH OF THE CWA ON SATURDAY...AND IN CONJUNCTION WITH FLAT RIDGING ALOFT MAY HELP TO INHIBIT THUNDERSTORM DEVELOPMENT HOWEVER CAN/T RULE OUT A FEW TERRAIN-INDUCED DIURNAL STORMS AND THIS IS WHERE LOW CHANCE POPS RESIDE. && .LONG TERM /SATURDAY NIGHT THROUGH WEDNESDAY/... FRONTAL BOUNDARY /OR WHAT IS LEFT OF IT/ LOOKS TO LIFT BACK TO THE NORTH AS A WARM FRONT ON SUNDAY. MOISTURE WILL BE BETTER AND WITH SOME AFTERNOON INSTABILITY THERE WILL BE A CHANCE OF THUNDERSTORMS BACK FOR THE ENTIRE CWA. CONVECTIVE CHANCES LIKELY INCREASE FURTHER EARLY NEXT WEEK WITH DEEPER MOISTURE AND DECENT INSTABILITY ALONG WITH LOWER HEIGHTS FROM AN UPPER TROUGH AND ALSO A SURFACE TROUGH ON MONDAY FOLLOWED BY A COLD FRONT ON TUESDAY. THIS COLD FRONT IS EXPECTED TO MOVE THROUGH BY TUESDAY NIGHT...ALLOWING FOR DRIER AIR TO MOVE IN FOR WEDNESDAY. && .AVIATION /14Z THURSDAY THROUGH MONDAY/...
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VFR CONDITIONS ARE EXPECTED MOST OF THE TIME THROUGH THIS EVENING. SHOWERS AND THUNDERSTORMS WILL INCREASE IN COVERAGE LATER THIS AFTERNOON AND EVENING. A FEW THUNDERSTORMS WILL BE CAPABLE OF PRODUCING GUSTY WINDS AND HAIL ALONG WITH LOCALLY HEAVY RAINFALL THAT CAN REDUCE CIGS/VSBYS TO IFR LEVELS. FOG/BR IS EXPECTED LATE TONIGHT. A FRONTAL BOUNDARY REMAINS TO THE SOUTH INTO SATURDAY THEN LIFTS BACK NORTH SUNDAY. COLD FRONT THEN WILL AFFECT THE AREA EARLY NEXT WEEK WITH A CHANCE OF THUNDERSTORMS.
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&& .MARINE...
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WINDS WILL TURN TO THE SOUTHEAST THIS AFTERNOON THROUGH TONIGHT...BUT SPEEDS WILL REMAIN BELOW SCA CRITERIA. SHOWERS AND THUNDERSTORMS ARE POSSIBLE LATE THIS AFTERNOON WELL INTO TONIGHT. SOME THUNDERSTORMS WILL BE CAPABLE OF PRODUCING GUSTY WINDS AND HAIL ALONG WITH LOCALLY HEAVY RAINFALL THAT MAY REDUCE VSBYS BELOW ONE MILE AT TIMES. RELATIVELY WEAK GRADIENT SHOULD PRECLUDE SCA CONDITIONS INTO THE FIRST PART OF THE WEEKEND. WILL HAVE TO WATCH SOUTHERLY FLOW BY SUNDAY AS MARGINAL SCA CONDITIONS MAY BE POSSIBLE UP THE BAY BY EVENING AND POSSIBLY CONTINUING INTO EARLY NEXT WEEK AHEAD OF A COLD FRONT.
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&& .LWX WATCHES/WARNINGS/ADVISORIES... DC...NONE. MD...NONE. VA...NONE. WV...NONE. MARINE...NONE. && $$ SYNOPSIS...BPP/HAS NEAR TERM...BJL/HAS SHORT TERM...BPP LONG TERM...BPP AVIATION...BJL/BPP/HAS MARINE...BJL/BPP/HAS

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