Area Forecast Discussion
Issued by NWS Sterling, VA

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000 FXUS61 KLWX 041908 AFDLWX AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC 308 PM EDT SAT JUL 4 2015 .SYNOPSIS... LOW PRESSURE RIDING ALONG A STATIONARY FRONT OVER THE AREA WILL PUSH EAST TONIGHT. THE FRONT MOVES SOUTH AS A COLD FRONT ON SUNDAY WITH HIGH PRESSURE BRIEFLY BUILDING INTO THE REGION. HIGH PRESSURE MOVES OFF THE COAST SUNDAY EVENING. AN UPPER LEVEL DISTURBANCE IMPACTS THE AREA SUNDAY NIGHT THROUGH TUESDAY BRINGING UNSETTLED WEATHER. && .NEAR TERM /THROUGH SUNDAY NIGHT/... LATEST SURFACE ANALYSIS AS OF ABOUT 18Z INDICATED A LOW PRESSURE EAST OF THE DELMARVA MOVING EAST...AND A WEAKER LOW OVER NORTHWESTERN PENNSYLVANIA MOVING NORTHEAST. A WARM FRONT WAS STRETCHED BETWEEN THE TWO LOWS...CROSSING OUR CWA APPROXIMATELY BETWEEN WASHINGTON AND BALTIMORE. TO THE SOUTH AND WEST OF THE FRONT...THE SUN HAS BROKEN THROUGH THE CLOUDS AND RESULTED IN SIGNIFICANT INSTABILITY. HOWEVER...THIS IS FIGHTING AGAINST AN INCREASING PUSH OF DRY AIR ALOFT. THIS WILL MOST LIKELY LIMIT THE HEIGHT OF THUNDERSTORM TOWERS AND KEEP THEM BELOW SEVERE LIMITS THIS AFTERNOON AND EVENING DESPITE A DECENT AMOUNT OF SHEAR. HOWEVER...AN ISOLATED STRONG WIND GUST FROM THE STORMS IS NOT OUT OF THE QUESTION. TROUGH ALOFT WHICH IS HELPING TO SPARK OFF THE STORMS WILL SLIDE EAST TONIGHT ALONG WITH THE WEAKENING SURFACE FRONT...WHICH WILL MOVE BACK SOUTH AS WHAT WILL TECHNICALLY BE CALLED A COLD FRONT. STORMS SHOULD BE MOSTLY DONE BY ABOUT 9PM AND COMPLETELY OVER WITH BY MIDNIGHT AS THEY MOVE OFF TO THE EAST AND WEAKEN. LINGERING MOISTURE WILL LIKELY RESULT IN PATCHY FOG OVERNIGHT INTO EARLY SUNDAY MORNING...ESPECIALLY IN THE SHELTERED VALLEYS NORTH AND WEST OF I-95. LOWS WILL DROP INTO THE 60S. HIGH PRESSURE WILL DOMINATE SUNDAY WITH PARTLY TO MOSTLY SUNNY SKIES FOR MUCH OF THE DAY ESPECIALLY OVER THE METRO. HOWEVER...FURTHER SOUTHWEST...A NEW CLOSED LOW WILL DEVELOP ALOFT TONIGHT OVER THE TENESSEE VALLEY AND MOVE NORTHEAST TOWARD OUR REGION. CLOUDS WILL BEGIN INCREASING AGAIN...AND SHOWERS AND THUNDERSTORMS ARE EXPECTED TO DEVELOP AND ADVECT NORTHEASTWARD STARTING IN OUR SOUTHWESTERN ZONES DURING THE AFTERNOON. THESE WILL OVERSPREAD MOST OF THE CWA BY LATER SUNDAY NIGHT. AFTER HIGHS IN THE 80S SUNDAY...LOWS WILL DROP BACK INTO THE 60S ON SUNDAY NIGHT. && .SHORT TERM /MONDAY THROUGH TUESDAY/... MID/UPPER LEVEL DISTURBANCE THAT IS CUTOFF FROM THE MAIN BELT OF WESTERLIES TO THE NORTH BEGINS TO IMPACT THE AREA IN EARNEST DURING THE DAY MON. COMBINATION OF SFC WARM FRONT MOVING NORTH OVER AREA...UPPER LEVEL DIFFLUENCE...AND VERY MOIST DEEP LAYER WITH PWATS PROGGED TO BE NEAR 2 INCHES SUGGEST THE POTENTIAL FOR EFFICIENT RAIN PRODUCERS WITH MODERATE TO HEAVY RAIN POSSIBLE. SHEAR REMAINS WEAK (0-6 KM EBS AOB 20 KTS) AND INSTABILITY COULD BE LIMITED DUE TO EXTENSIVE CLOUD COVER...WHICH WOULD LIMIT OVERALL STORM ORGANIZATION/INTENSITY. TEMPS MIGHT NEED TO BE ADJUSTED A LITTLE FURTHER DOWNWARD IN SUBSEQUENT FORECASTS...AS AFOREMENTIONED CLOUD COVER COULD LIMIT INSOLATION. BULK OF ACTIVITY SHOULD MOVE AWAY FROM THE AREA DURING THE OVERNIGHT MONDAY AS THE DISTURBANCE IS ENGULFED INTO THE NORTHERN STREAM. LIKELY A PERIOD OF SUBSIDENCE BEHIND DISTURBANCE PROVIDING SOME CLEARING DURING THE EARLY PART OF TUE. LITTLE IN THE WAY OF FORCING MECHANISM TUE...THOUGH COULD GET SOME ACTIVITY MOVING EAST OFF HIGHER TERRAIN OR ALONG LEE TROUGH. STARTS GETTING A LITTLE WARMER TUE...WITH TEMPS GETTING BACK TO NEAR NORMAL (U80S). && .LONG TERM /TUESDAY NIGHT THROUGH SATURDAY/... DISTURBANCE LINGERS IN THE AREA TUES NIGHT INTO WED AS A COLD FRONT APPROACHES LATE ON WED. COLD FRONT SLOWLY DRIFTS SOUTH OVER THE CWA AND LINGERS THROUGH THE END OF THE WEEK...DRIER CONDITIONS ARRIVE FOR THE WEEKEND. UNCERTAINTY ON LOCATION OF THE FRONT MAY AFFECT POPS...BUT DIURNAL EFFECTS ALLOWS FOR THE RISK OF ISOLATED/SCATTERED SHOWERS AND/OR TSTMS EACH DAY. HIGH TEMPS WILL BE IN THE 80S...LOW TEMPS IN THE 70S FOR MOST OF THE CWA...AND IN THE MID TO UPR 60S AT HIGHER ELEVATIONS. && .AVIATION /18Z SATURDAY THROUGH THURSDAY/... LOW CIGS HAVE MOSTLY LIFTED...SO MAIN CONCERN HAS BECOME SCATTERED SHOWERS AND ISOLATED THUNDERSTORMS FOR THE REMAINDER OF THE AFTERNOON INTO EARLY EVENING. ANY STORM MAY PRODUCE BRIEF IFR CIGS/VIS DUE MAINLY TO HEAVY RAIN...OR MAYBE A GUST TO 25 KNOTS. STORMS WILL DISSIPATE/MOVE EAST THIS EVENING...BUT PATCHY FOG WITH IFR VIS IS A CONCERN LATE TONIGHT AND EARLY SUNDAY ESPECIALLY AT CHO AND MRB. SUNDAY AFTER ANY FOG BREAKS SHOULD BE MOSTLY VFR...THOUGH LATE IN THE DAY ANOTHER ROUND OF STORMS LOOKS TO MOVE INTO CHO AND THEN NORTHEAST TOWARD THE REST OF THE TERMINALS SUNDAY NIGHT...WITH MORE CONCERNS ABOUT GUSTY WINDS AND REDUCED VIS. OUTSIDE OF STORMS...WINDS SHOULD REMAIN BELOW 10 KNOTS THROUGH SUNDAY NIGHT. IFR CIGS APPEAR POSSIBLE THROUGH THE DAY MON IN MODERATE/HEAVY RAIN SHWRS AND STORMS. IMPROVING TO MVFR LATE MON AND VFR BY TUESDAY MORNING AS UPPER LEVEL DISTURBANCE PULLS AWAY FROM THE AREA. VFR CONDITIONS EXPECTED FOR TUES NIGHT AND WED. SUB-VFR DUE TO PSBL SHOWERS AND TSTMS WED AFTN. && .MARINE... SCA REMAINS IN EFFECT FOR MIDDLE PORTIONS OF THE BAY AND SOME ADJACENT WATERS DUE TO WINDS IN THE WAKE OF THE DEPARTING LOW PRESSURE SYSTEM. THESE SHOULD END EARLY THIS EVENING AND SUB-SCA WINDS ARE EXPECTED THROUGH SUNDAY NIGHT. ANY STORMS THIS EVENING COULD PRODUCE REDUCED VISIBILITY IN HEAVY RAIN OR A WIND GUST TO 25 KNOTS...WHILE MORE STORMS EXPECTED SUNDAY NIGHT MAY DO LIKEWISE. WINDS EXPECTED TO REMAIN LIGHT AND VARIABLE MON....BUT COULD STRENGTHEN SOME ON TUE DUE TO CHANNELING SRLY FLOW. COULD BE SOME ISOLATED TSTMS MON AND AGAIN TUE AFTERNOON. SUB-SCA CONDITIONS EXPECTED FOR TUES NIGHT AND WED. PSBL SHOWERS AND TSTMS ACROSS THE WATERS ON WED AFTN. && .TIDES/COASTAL FLOODING... LOW PRESSURE DEPARTING EASTWARD ALLOWING WINDS TO TURN MORE NORTHERLY SHOULD PREVENT ANY ADDITIONAL TIDAL FLOODING. ALL ADVISORIES WERE ALLOWED TO EXPIRE AT NOON. && .LWX WATCHES/WARNINGS/ADVISORIES... DC...NONE. MD...NONE. VA...NONE. WV...NONE. MARINE...SMALL CRAFT ADVISORY UNTIL 6 PM EDT THIS EVENING FOR ANZ533- 534-537-543. && $$ SYNOPSIS...MSE NEAR TERM...RCM SHORT TERM...MSE/RCM LONG TERM...IMR AVIATION...IMR/MSE/RCM MARINE...IMR/MSE/RCM TIDES/COASTAL FLOODING...RCM

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