Area Forecast Discussion
Issued by NWS Sterling, VA

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000 FXUS61 KLWX 230819 AAA AFDLWX AREA FORECAST DISCUSSION...UPDATED NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC 419 AM EDT WED JUL 23 2014 .SYNOPSIS... A COLD FRONT FROM THE GREAT LAKES WILL SLOWLY APPROACH THE REGION THROUGH TONIGHT. THE BOUNDARY WILL SLOWLY PASS THROUGH THE AREA THURSDAY INTO THURSDAY NIGHT AND HIGH PRESSURE WILL RETURN FOR FRIDAY. HIGH PRESSURE WILL MOVE OFF THE COAST DURING THE WEEKEND AND A COLD FRONT WILL PASS THROUGH THE AREA EARLY NEXT WEEK. && .NEAR TERM /THROUGH TONIGHT/... A CUT-OFF UPPER LOW OVER THE GULF COAST AND A STALLED UPPER TROUGH JUST OFF THE CAROLINA COAST...WHILE A LARGE UPPER TROUGH IS SLOWLY DIGGING DOWN TOWARD THE AREA - READY FOR A PASSAGE IN THE NEXT DAY OR SO. TODAY WILL BE THE WARMEST DAY OF THE STRETCH...NOT ONLY IN AMBIENT TEMPS BUT CONSIDERING REL HUMIDITIES AS WELL. DEWPOINTS WON`T STRAY FAR FROM THE L70S ALL-DAY AND EVEN INTO THE OVERNIGHT HRS TONIGHT. THIS WILL BE AMPLE NEAR-SFC MOISTURE FOR THE QUICK DEVELOPMENT OF UPDRAFTS GIVEN A PRE-EXISTING OR INCOMING SFC BOUNDARY LATER TODAY. BY ITSELF...THE INSTABILITY FROM DAYTIME HEATING MAY NOT BE ENOUGH FOR INITIATION...EVEN W/ TEMPS REACHING THE L90S DURING THE MID-AFTN. DURING THE FIRST HALF OF THE DAY...A WARM NOSE IN THE 10-15KFT REGION OVERHEAD MAY KEEP UNFAVORABLE LAPSE RATES IN PLACE...EVEN AS THE LOW LEVEL CAPPING INVERSION IS BEING BROKEN. LACK OF SHEAR WILL BE THE OTHER ISSUE IN TERMS OF CONVECTIVE INITIATION. A WEAK COLUMN EXISTS OVERHEAD...W/ OUR AREA STILL ON THE WRN PERIPHERY OF THE BERMUDA HIGH AND LITTLE/NO DYNAMIC FEATURES NEARBY. A SERIES OF WEAK PRE-FRONTAL TROUGHS ARE MAKING THEIR WAY DOWN ACROSS THE UPPER MIDWEST ATTM...BUT WILL ONLY GRADUALLY WORK THEIR WAY TOWARD THE CNTRL APLCNS AND EVENTUALLY OVER OUR AREA LATER THIS EVE/TONIGHT. THE COLD FRONT ITSELF WILL ALSO BE SLOW-MOVING AND WON`T ARRIVE UNTIL DURING THE OVERNIGHT HRS. BEFORE THEN...INSTABILITY WILL GRADUALLY INCREASE DURING THE AFTN HRS W/ AMPLE SUNSHINE TO START THE DAY BUT A CUMULUS FIELD WILL QUICKLY DEVELOP AND DAYTIME BOUNDARY LAYER MIXING WILL START TO CREATE THE TYPICAL BAY BREEZE AND LAND BREEZE BOUNDARIES. LOCAL HI-RES WRF GUIDANCE SUGGESTING THAT A MID-AFTN INITIATION OF DISCRETE SHOWERS/TSTMS WILL DEVELOP ALONG OR W/IN A COUNTY OF THE NRN VA BLUE RIDGE - LIKELY W/ A PRE-FRONTAL LEE TROUGH AXIS. THE ACTIVITY WOULD THEN DRIFT SE OVER TIME AND POTENTIALLY DEVELOP NEW OUTFLOW-DRIVEN CELLS FURTHER EAST/SE. CHANCES FOR PRECIP BEFORE 18Z ARE SLIM BUT A BOUNDARY SUCH AS A LOW LEVEL TROUGH MAY HELP QUICKLY ELEVATE THE RISK OF TSTMS. HOWEVER...STILL NOT A STRONG SIGNAL TOWARD THIS...ESPEC W/ MINIMAL SHEAR - ONLY ABOUT 15KT BULK IN THE MID LEVELS AND POSSIBLY 5KT IN THE LOW LEVELS...TOUGH TO SUSTAIN UPDRAFTS IN THAT ENVIRONMENT. HEADING INTO THE LATE AFTN/EVE HRS...AS SHEAR SLOWLY BUT SURELY BEGINS TO ARRIVE FROM THE NW...THE POTENTIAL WILL INCREASE. HEATING WILL CONTINUE THROUGHOUT THE EVE - STILL BEING LATE JULY W/ THE LONGER DAYTIME PERIOD. DEWPOINTS WILL STAY HIGH...SO THE POTENTIAL FOR STRONG AND EVEN A FEW SEVERE STORMS WILL BE POSSIBLE AS MORE DYNAMIC SHEAR ARRIVES AND BEGINS TO SHAPE ONGOING ACTIVITY. DAMAGING WINDS WOULD BE THE MAIN THREAT...W/ THE PROFILE NOT AS FAVORABLE FOR HAIL W/ SUCH SHORT-LIVED AND WEAKLY FORCED UPDRAFTS. TONIGHT...BEFORE THE COLD FRONT ARRIVES FROM THE NORTH...TEMPS WILL STILL BE FAIRLY WARM. 80S WILL STILL DOT THE MAP WELL AFT SUNSET BUT AS THE FRONT MOVES IN FROM THE NW...TEMPS WILL SLOWLY DROP OVER THE NWRN PART OF THE AREA AS DRIER NW WINDS TAKE DOWN TEMPS AND DEWPOINTS. && .SHORT TERM /THURSDAY THROUGH FRIDAY/...
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AN UPPER-LEVEL TROUGH WILL REMAIN OVER THE REGION THURSDAY THROUGH FRIDAY. A COLD FRONT WILL SLOWLY PASS THROUGH THE AREA THURSDAY INTO EVENING. MORE SHOWERS AND THUNDERSTORMS ARE POSSIBLE AHEAD OF THE FRONT...ESPECIALLY ACROSS CENTRAL AND SOUTHERN PORTIONS OF THE CWA WHERE MOISTURE WILL BE DEEPER. DRIER AIR WILL WORK ITS WAY INTO MOST AREAS OVERNIGHT THURSDAY. HIGH PRESSURE WILL BUILD OVER THE REGION FRIDAY. A SCT TO BKN CU DECK SHOULD DEVELOP DURING THE AFTERNOON DUE TO THE UPPER-LEVEL TROUGH OVERHEAD. TERRAIN CIRCULATION COULD LEAD TO AN ISOLATED SHOWER WEST OF THE BLUE RIDGE MOUNTAINS...BUT THE FORECAST REMAINS DRY FOR NOW THINKING THAT LOW-LEVEL DRY AIR SHOULD SUPPRESS CONVECTION FOR MOST AREAS. MAX TEMPS WILL BE NEAR CLIMO...RANGING FROM THE 70S IN THE MOUNTAINS TO THE MID AND UPPER 80S ACROSS MOST OTHER LOCATIONS...AND IT WILL FEEL NOTICEABLY LESS HUMID COMPARED TO RECENT DAYS.
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&& .LONG TERM /FRIDAY NIGHT THROUGH TUESDAY/... HIGH PRESSURE WILL SLOWLY MOVE OFF THE COAST FRIDAY NIGHT INTO SATURDAY AND IT WILL REMAIN OVER THE ATLANTIC OCEAN FOR SUNDAY. A RETURN SOUTHERLY FLOW WILL ALLOW FOR THE HUMIDITY TO RETURN DURING THE WEEKEND. A COUPLE SHOWERS AND THUNDERSTORMS ARE POSSIBLE SATURDAY AFTERNOON AND EVENING...BUT CONVECTION SHOULD BE LIMITED IN COVERAGE DUE TO THE LACK OF A STRONG LIFTING MECHANISM. HOWEVER...A POTENT SHORTWAVE IS EXPECTED TO DIG THROUGH THE GREAT LAKES AND INTO NEW ENGLAND SUNDAY. THIS WILL INCREASE SHEAR PROFILES AND CARVE OUT A TROUGH OF LOW PRESSURE BOTH AT THE UPPER LEVELS AND LOWER LEVELS OF THE ATMOSPHERE. SHOWERS AND THUNDERSTORMS MAY INCREASE IN COVERAGE FOR THESE REASONS SUNDAY. A POTENT COLD FRONT WILL LIKELY PASS THROUGH THE REGION MONDAY...BRINGING THE CHANCE FOR MORE SHOWERS AND THUNDERSTORMS BEFORE COOLER AND DRIER AIR MOVES INTO THE REGION DURING THE MIDDLE PORTION OF NEXT WEEK. && .AVIATION /08Z WEDNESDAY THROUGH SUNDAY/...
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AN UPPER RIDGE KEEPING THE AIRMASS OVERHEAD WILL KEEP THE AREA UNDER MOIST AND HUMID CONDITIONS THROUGHOUT THE DAY. THE TYPICAL TERRAIN CIRCULATIONS OCCURRING OVER THE APLCNS TO THE WEST OF THE METRO AREAS...WHEN THERE IS A LARGE OFFSHORE HIGH AS THERE IS CURRENTLY. THE MTNS RECEIVE PERIODS OF LOW LEVEL CONVERGENCE W/ MOISTURE...HELPING TO MAKE SCATTERED BATCHES OF MID-LEVEL DECKS. MOSTLY CLEAR FURTHER EAST...AS IT WILL REMAIN SO IN THE COMING HRS. ONLY THE DAYTIME HEATING OF THE MID-LATE MRNG WILL BEGIN DEVELOPING SCATTERED CUMULUS CLOUD DECKS ACROSS THE REGION AND EVENTUALLY HELP W/ ISOLATED SHOWERS/TSTMS AS THE DAY PROGRESSES. THE CONVECTIVE POTENTIAL INCREASES LATER TODAY...AS THE WINDS IN THE COLUMN INCREASE - ALBEIT SLIGHTLY AND SLOWLY. INCOMING 20-30KT LOW LEVEL SHEAR SHOULD BE ENOUGH TO CREATE INCREASED CONVECTIVE POTENTIAL OVER MORE OF THE AREA LATER TONIGHT. A COLD FRONT WILL SLOWLY ARRIVE OUT OF THE NW LATE TONIGHT AND INTO THE OVERNIGHT...TURNING SFC FLOW OUT OF THE NW AND NORTH...THOUGH STILL FAIRLY LIGHT. THIS WILL ALSO SLOWLY END THE CONVECTIVE POTENTIAL...MAKING ONGOING ACTIVITY TURN INTO SHOWERS. SUBVFR CIGS AND VSBYS ARE POSSIBLE FROM PATCHY LOW CLOUDS AND FOG THURSDAY MORNING. A COLD FRONT WILL SLOWLY PASS THROUGH THE TERMINALS THURSDAY INTO THURSDAY EVENING. SHOWERS AND THUNDERSTORMS ARE POSSIBLE AHEAD OF THE FRONT...WITH THE MOST WIDESPREAD COVERAGE BEING ACROSS THE CENTRAL AND SOUTHERN TERMINALS. SUBVFR CONDITIONS ARE POSSIBLE IN ANY SHOWERS AND THUNDERSTORMS. DRIER AIR WILL MOVE IN BEHIND THE COLD FRONT THURSDAY NIGHT THROUGH FRIDAY. PATCHY BR MAY CAUSE SUBVFR VSBYS EARLY FRIDAY MORNING...ESPECIALLY ACROSS KCHO WHERE DRIER AIR WILL BE LOWER TO MOVE IN. HIGH PRESSURE WILL BUILD OVERHEAD FRIDAY INTO FRIDAY NIGHT BEFORE MOVING OFF THE COAST DURING THE WEEKEND. A SOUTHERLY FLOW WILL CAUSE MORE MOISTURE TO RETURN ALONG WITH AN INCREASED CHANCE FOR SHOWERS AND THUNDERSTORMS...ESPECIALLY SUNDAY AFTERNOON AND EVENING.
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&& .MARINE...
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LIGHT WINDS OVER THE WATERS ATTM...W/ ONLY SOME SLY CHANNELING ACROSS THE MID-BAY REGION. THIS REGIME WILL STAY IN PLACE FOR MUCH OF THE DAY...EVEN AS PRES GRADIENT INCREASES. A FEW NEAR-SCA GUSTS MAY APPEAR LATER THIS AFTN. WINDS WILL SHIFT TO THE NORTHWEST BEHIND A SURFACE TROUGH TONIGHT. WINDS WILL BE BELOW SCA CRITERIA...10-15KT OR LESS. THUNDERSTORMS ARE POSSIBLE THIS AFTERNOON AND EVENING ACROSS THE WATERS. THUNDERSTORMS WILL BE CAPABLE OF PRODUCING GUSTY WINDS AND HAIL. A COLD FRONT WILL SLOWLY PASS THROUGH THE WATERS THURSDAY INTO THURSDAY EVENING. SHOWERS AND THUNDERSTORMS ARE POSSIBLE DURING THIS TIME...ESPECIALLY ACROSS THE MIDDLE PORTION OF THE BAY AND THE LOWER TIDAL POTOMAC RIVER. A PRESSURE SURGE BEHIND THE FRONT MAY CAUSE NORTHERLY WINDS TO GUST NEAR SCA CRITERIA OVERNIGHT THURSDAY INTO FRIDAY MORNING ACROSS THE MARYLAND PORTION OF THE CHESAPEAKE BAY AND THE LOWER TIDAL POTOMAC RIVER. HIGH PRESSURE WILL BUILD OVER THE WATERS FRIDAY AND WINDS WILL WEAKEN AND PERHAPS EVEN TURN ONSHORE DURING THE AFTERNOON. HIGH PRESSURE WILL MOVE OFF THE COAST SATURDAY AND SUNDAY AND A SOUTHERLY FLOW WILL RETURN DURING THIS TIME. THE SOUTHERLY FLOW WILL BRING MORE MOISTURE...INCREASING THE CHANCE FOR SHOWERS AND THUNDERSTORMS...ESPECIALLY SUNDAY. A POTENT COLD FRONT WILL MOVE TOWARD THE WATERS MONDAY...BRINGING THE CHANCE FOR MORE THUNDERSTORMS.
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&& .TIDES/COASTAL FLOODING... A SOUTHERLY FLOW HAS CAUSED TIDAL ANOMALIES TO BE AROUND ONE-HALF TO THREE QUARTERS OF A FOOT ABOVE NORMAL. THE MAX HIGH TIDE WILL BE EARLY THIS MORNING...BUT WATER LEVELS SHOULD REMAIN JUST BELOW MINOR FLOODING THRESHOLDS. THE POSITIVE ANOMALIES WILL CONTINUE THIS AFTERNOON AND EVENING...BUT THE HIGH TIDE WILL BE THE LOWER OF THE TWO SO MINOR FLOODING IS NOT EXPECTED. THE FLOW WILL TURN OFFSHORE BEHIND A SURFACE TROUGH LATE TONIGHT INTO THURSDAY...SO ANOMALIES ARE EXPECTED TO DECREASE DURING THIS TIME. && .LWX WATCHES/WARNINGS/ADVISORIES... DC...NONE. MD...NONE. VA...NONE. WV...NONE. MARINE...NONE. && $$ SYNOPSIS...BJL NEAR TERM...GMS SHORT TERM...BJL LONG TERM...BJL AVIATION...BJL/GMS MARINE...BJL/GMS TIDES/COASTAL FLOODING...

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