Area Forecast Discussion
Issued by NWS Sterling, VA

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000 FXUS61 KLWX 200132 AFDLWX AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC 932 PM EDT TUE AUG 19 2014 .SYNOPSIS...
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LOW PRESSURE WILL CONTINUE TO DRIFT EAST FROM NORTHEASTERN NORTH CAROLINA THROUGH TONIGHT...WITH AN ONSHORE FLOW PERSISTING INTO THURSDAY NIGHT. A COLD FRONT WILL MOVE THROUGH THE AREA FROM THE NORTHWEST FRIDAY WITH MORE ONSHORE FLOW FRIDAY NIGHT INTO NEXT WEEK.
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&& .NEAR TERM /THROUGH WEDNESDAY/...
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AS OF 01Z...1009MB SFC LOW IS OFFSHORE FROM THE VA/NC BORDER AND DRIFTING EAST. A LIGHT ONSHORE/SELY FLOW IS ACROSS THE CENTRAL MID-ATLANTIC. UPSTREAM...A SHORTWAVE IS MOVING EAST THROUGH THE MIDWEST STATES WITH AN MCS PUSHING EAST OVER LAKE ERIE (CURRENTLY NEAR CLEVELAND). WILL NEED TO MONITOR DEVELOPMENT ALONG THE SOUTHERN END OF THE MCS (CURRENTLY OVER COLUMBUS)...FOR DOWNSTREAM AREAS LIKE CUMBERLAND MD OVERNIGHT. HOWEVER...THE LOW IS OCCLUDED AND EASTWARD PROGRESS SHOULD BE SOMEWHAT LIMITED. THE 22Z HRRR SUGGEST A SUPPLEMENTAL VORT LOBE SHIFTS ACTIVITY EAST INTO NWRN PARTS OF THE CWA WEDNESDAY MORNING. TOOK THIS APPROACH IN THE GRIDS WITH CHANCE POPS ENTERING THE NORTHWEST AFTER 6 AM. SHEAR INCREASES OVER THE AREA WEDNESDAY AHEAD OF THE LOW THAT WILL CONTINUE DRIFTING EAST ACROSS THE GREAT LAKES. TIMING OF VORT MAX/TROUGH PASSAGE EAST FROM THE SHENANDOAH VALLEY SHOULD BE CLOSE TO PRIME DIURNAL HEATING...SO MORE ACTIVITY IS EXPECTED THAN RECENT DAYS. HOWEVER...THE ONSHORE FLOW SHOULD CONTINUE TO LIMIT STORMS EAST FROM THE BLUE RIDGE. MAINTAINED LIKELY POPS FOR LATE AFTERNOON/EARLY EVENING FOR NRN SECTIONS OF THE CWA...MAINLY WEST OF I-95. MAX TEMPS MID TO UPR 80S DEPENDING ON MID LEVEL CLOUD COVER CLEARING.
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&& .SHORT TERM /WEDNESDAY NIGHT THROUGH THURSDAY/... THE DISTURBANCE WILL MOVE OFF THE COAST LATE WEDNESDAY NIGHT AND SHOWERS MAY LINGER EAST OF THE BLUE RIDGE INTO THURSDAY. NORTHWEST FLOW ALOFT WILL ALLOW A UPPER LOW TO APPROACH THE REGION AND MOVE ACROSS THE NORTHEAST THURSDAY. THUNDERSTORMS ARE POSSIBLE THURSDAY AFTERNOON WEST OF THE BLUE RIDGE AS THE EXIT REGION OF AN UPPER LEVEL JET APPROACHES. SFC FLOW IS LIGHT AND WESTERLY WHICH WILL KEEP DEWPTS IN THE LOW TO MID 60S THURSDAY. INSTABILITY WILL BE BASED ON CLOUD COVER WHICH IS HARD TO SAY RIGHT NOW BUT THE MORE BREAKS THE GREATER THE INSTABILITY. MARGINAL SHEAR OF 25 KTS IS EXPECTED AT THIS TIME. AT THIS TIME...SVR STORM POTENTIAL IS LOW. && .LONG TERM /THURSDAY NIGHT THROUGH TUESDAY/...
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AN UPPER LEVEL LOW RIDING AROUND THE EAST SIDE OF A DEVELOPING SUBTROPICAL RIDGE WILL CROSS JUST NORTH OF THE AREA THURSDAY NIGHT AND FRIDAY. MANY LOCATIONS...PARTICULARLY IN MARYLAND...COULD SEE PERIODS OF HEAVY RAIN AND AN ISOLATED THUNDERSTORM THROUGH THE NIGHT THURSDAY. THE COLLOCATION OF ENHANCED LIFT FROM THE LEFT EXIT REGION OF A JET STREAK ROUNDING THE SOUTHWESTERN SIDE OF THE UPPER LEVEL LOW LATE THURSDAY NIGHT AS WELL AS A STALLED BOUNDARY AT THE SURFACE WILL FURTHER ENHANCE THE POTENTIAL FOR RAINFALL ACROSS THE AREA. OVERALL HAVE HIGHEST POPS ACROSS MARYLAND WITH SHOWERS AND ISOLATED THUNDERSTORMS THURSDAY NIGHT AND INTO FRIDAY MORNING. THE AFOREMENTIONED SURFACE BOUNDARY WILL REMAIN NEAR THE AREA THROUGH FRIDAY AFTERNOON AS A COASTAL LOW FORMS OFF OF CAPE HATTERAS. WITH MODEST MOISTURE ADVECTION OCCURRING IN THE LOW AND MID LEVELS...SHOWERS AND ISOLATED THUNDERSTORMS REMAIN POSSIBLE FRIDAY EVENING...ESPECIALLY OVER THE EASTERN HALF OF THE CWA. OVERALL RAINFALL COVERAGE SHOULD BE SIGNIFICANTLY LESS FRIDAY EVENING THAN THURSDAY NIGHT. HIGH PRESSURE WILL RIDGE DOWN INTO THE AREA BEGINNING FRIDAY NIGHT. THIS WILL WORK WITH THE LOW PARKED OFF THE SOUTHEAST COAST TO BRING ONSHORE FLOW INTO THE AREA. THIS MARINE AIRMASS WILL KEEP MOST OF THE AREA...PARTICULARLY EAST OF THE BLUE RIDGE...CLOUDY HUMID AND COOL THROUGH THE WEEKEND AND LIKELY INTO THE BEGINNING OF NEXT WEEK. THUNDERSTORMS ARE UNLIKELY WITH THIS AIRMASS...BUT ISOLATED LIGHT RAIN WILL BE POSSIBLE MOSTLY SATURDAY...PARTICULARLY IN AREAS WHERE THERE IS AN UPSLOPE COMPONENT TO THE FLOW. EXPECT MORE BREAKS IN THE CLOUDS WEST OF THE BLUE RIDGE...THOUGH LIGHT RAIN REMAINS POSSIBLE SATURDAY AND SUNDAY THERE AS WELL. HIGH PRESSURE EXTENDING DOWN THE EAST COAST WILL WEAKEN EARLY NEXT WEEK AS A COLD FRONT APPROACHES FROM THE WEST. THIS WILL LIKELY SIGNAL THE RETURN OF SOUTHERLY FLOW AND TEMPERATURES BECOMING MORE SEASONABLE. OVERALL THE COOLER THAN NORMAL TREND OF THE SUMMER WILL CONTINUE THROUGH THE LONG TERM WITH HIGHS MOSTLY IN THE UPPER 70S AS THE COOL MARINE AIRMASS COVERS THE AREA FOR THE WEEKEND AND MONDAY. TUESDAY WILL SEE HIGHS IN THE LOWER 80S AS WEAK WARM AIR ADVECTION BEGINS OVER THE REGION.
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&& .AVIATION /01Z WEDNESDAY THROUGH SUNDAY/...
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ONSHORE FLOW CONTINUES AND MVFR/IFR CIGS EXPECTED LATE TONIGHT. IFR CIGS/VSBYS MOST LIKELY AT CHO AND MRB WEDNESDAY MORNING. A DISTURBANCE MOVES ACROSS THE REGION WEDNESDAY AND SHRA AND VCTS ARE POSSIBLE. AT THIS TIME...THREAT OF TS IS LOW AND THEREFORE NOT IN THE TAFS. ANOTHER DISTURBANCE APPROACHES THURSDAY AND SHRA AND TSRA IS POSSIBLE IN THE AFTERNOON. PERIODS OF LOW CEILINGS ARE EXPECTED AS AN UPPER LEVEL DISTURBANCE CROSSES THE AREA THURSDAY NIGHT AND THEN AGAIN OVER THE WEEKEND AND INTO EARLY NEXT WEEK AS A MARINE AIRMASS SETTLES INTO THE AREA.
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&& .MARINE...
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LIGHT ONSHORE FLOW CONTINUES THROUGH THURSDAY AND WILL STAY BELOW SCA CRITERIA. SHOWERS AND ISOLATED THUNDERSTORMS ARE POSSIBLE WEDNESDAY AFTERNOON AND EVENING AND AGAIN THURSDAY AFTERNOON. CONFIDENCE IS LOW IN THE OCCURRENCE OF ANY MARINE HAZARDS THROUGH THE LONG TERM.
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&& .TIDES/COASTAL FLOODING...
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AN ONSHORE FLOW WILL CONTINUE THROUGH TONIGHT...BUT IT WILL REMAIN WEAK. TIDAL ANOMALIES AROUND ONE-HALF FOOT ABOVE NORMAL WILL PERSIST THROUGH TONIGHT. WATER LEVELS WILL BE CLOSE TO MINOR FLOODING THRESHOLDS DURING THE HIGH TIDE CYCLE LATE TONIGHT BUT EXPECTATION IS THAT WATER LEVELS WILL REMAIN BELOW MINOR FLOODING THRESHOLDS SINCE THE ONSHORE FLOW IS WEAK.
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&& .LWX WATCHES/WARNINGS/ADVISORIES...
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DC...NONE. MD...NONE. VA...NONE. WV...NONE. MARINE...NONE.
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&& $$ SYNOPSIS...BAJ/HAS NEAR TERM...BAJ SHORT TERM...HAS LONG TERM...CEB AVIATION...BAJ/HAS/CEB MARINE...BAJ/HAS/CEB TIDES/COASTAL FLOODING...LWX

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