Area Forecast Discussion
Issued by NWS Sterling, VA

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000 FXUS61 KLWX 191835 AFDLWX AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC 235 PM EDT TUE AUG 19 2014 .SYNOPSIS... LOW PRESSURE WILL MOVE AWAY FROM THE AREA TODAY...BUT A BOUNDARY WILL REMAIN STATIONARY OVER THE REGION. THE BOUNDARY WILL REMAIN OVERHEAD THROUGH THURSDAY BEFORE SLOWLY DROPPING SOUTH AS A COLD FRONT FRIDAY INTO THE WEEKEND. && .NEAR TERM /THROUGH WEDNESDAY/... LOW PRESSURE IS LOCATED OFF THE VA TIDE WATER/OBX COAST THIS AFTERNOON WHILE A STATIONARY FRONT IS DRAPED ACROSS THE POTOMAC HIGHLANDS AND STRETCHED ACROSS CENTRAL VA. LOW PRESSURE IS ALSO LOCATED ACROSS LAKE SUPERIOR WITH A COLD FRONT STRETCHED BACK ACROSS THE NRN PLAINS. E-NE FLOW ACROSS THE REGION TODAY HAS LED TO LOW CLOUDS ACROSS MOST OF THE REGION. THIS WILL CONTINUE TODAY AND TONIGHT AS LOW PRESSURE NEAR THE NORFOLK COAST SLOWLY MOVES EASTWARD. A FEW BREAKS OF SUN WILL BE POSSIBLE ACROSS NE MD AS DRIER AIR FROM THE NORTHEAST ADVECTS SOUTH. CLOSER TO THE SFC LOW...AROUND 500 J/KG OF MUCAPE EXISTS AND SHOWERS HAVE FORMED NEAR THE HIGHER PWATS AND CONVERGENCE AROUND THE LOW. THESE SHOWERS SHOULD MOVE SOUTH AND EAST THIS AFTERNOON BEFORE MOVING OFF THE COAST BY TONIGHT. FURTHER WEST...CONVERGENCE ALONG THE STATIONARY FRONT ACROSS THE ALLEGHENY FRONT WILL LEAD TO DIURNAL SHOWER AND ISO THUNDERSTORM DEVELOPMENT. ANY ACTIVITY WILL WANE THIS EVENING. EASTERLY FLOW BECOMES SOUTHERLY AND LIGHT TONIGHT. AN UPPER LEVEL DISTURBANCE CURRENTLY ACROSS IL WILL MOVE ACROSS THE REGION WEDNESDAY. SHOWERS ARE EXPECTED TO MOVE FROM WEST TO EAST THROUGHOUT THE DAY REACHING THE I-95 CORRIDOR BY LATE AFTERNOON AND EVENING. MINIMAL CAPE AND SHEAR ARE PROGGED AND THEREFORE CHANCE OF THUNDER IS LOW. PWATS ARE EXPECTED TO REACH NEAR 1.8 INCHES AND THEREFORE SHOWERS MAY BE LOCALLY HEAVY. && .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/... 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 AFORE MENTIONED 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. && .AVIATION /18Z TUESDAY THROUGH SUNDAY/... EASTERLY FLOW WILL KEEP THE CHANCE OF MVFR CLOUDS AT THE TERMINALS THIS AFTERNOON. -SHRA POSSIBLE AT CHO-DCA THIS AFTERNOON. EASTERLY FLOW BECOMES SOUTHERLY BY WED MORNING AND MVFR CIGS WILL BE POSSIBLE LATE TONIGHT. IFR VSBY IS POSSIBLE AT CHO 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. && .MARINE... EASTERLY WINDS WILL CONTINUE ACROSS THE WATERS THIS AFTERNOON. LOW PRESSURE TO THE SOUTH HAS LED TO EASTERLY WINDS 10-15KTS WITH GUSTS UP TO 20KTS THIS AFTERNOON. WINDS SHOULD SUBSIDE THIS EVENING AS THE LOW MOVES AWAY FROM THE NORFOLK AREA. WINDS WILL BECOME SOUTHERLY WEDNESDAY AND THURSDAY AND SHOULD 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. && .TIDES/COASTAL FLOODING... AN ONSHORE FLOW WILL CONTINUE THROUGH TONIGHT...BUT IT WILL REMAIN WEAK. TIDAL ANOMALIES AROUND ONE-HALF FOOT ABOVE NORMAL WILL LIKELY PERSIST THROUGH TONIGHT. MINOR TIDAL FLOODING IS NOT EXPECTED WITH THE LOWER OF THE TWO HIGH TIDES THIS AFTERNOON. WATER LEVELS WILL BE CLOSE TO MINOR FLOODING THRESHOLDS DURING THE HIGH TIDE CYCLE LATE TONIGHT...BUT CURRENT THINKING IS THAT WATER LEVELS WILL REMAIN BELOW MINOR FLOODING THRESHOLDS SINCE THE ONSHORE FLOW IS WEAK. && .LWX WATCHES/WARNINGS/ADVISORIES... DC...NONE. MD...NONE. VA...NONE. WV...NONE. MARINE...SMALL CRAFT ADVISORY UNTIL 6 PM EDT THIS EVENING FOR ANZ533- 534-537-541-543. && $$ SYNOPSIS...HAS NEAR TERM...HAS SHORT TERM...HAS LONG TERM...CEB AVIATION...HAS/CEB MARINE...HAS/CEB TIDES/COASTAL FLOODING...

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