Area Forecast Discussion
Issued by NWS Sterling, VA

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000 FXUS61 KLWX 081706 AFDLWX AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC 106 PM EDT TUE JUL 8 2014 .SYNOPSIS... A COLD FRONT ACROSS THE GREAT LAKES AND MIDWEST WILL APPROACH THE REGION LATE TODAY AND TONIGHT...CROSS THE AREA EARLY WEDNESDAY...AND STALL OVER SOUTHERN VIRGINIA WEDNESDAY NIGHT INTO THURSDAY. HIGH PRESSURE THEN BUILDS OVER THE MID-ATLANTIC THURSDAY AND FRIDAY. && .NEAR TERM /THROUGH TONIGHT/... ...A SEVERE THUNDERSTORM WATCH IS IN FOR PORTIONS OF WESTERN MARYLAND AND EASTERN WEST VIRGINIA. THE PREVIOUS DISCUSSION FOLLOWS... HIGH PRESSURE WILL REMAIN OVER THE ATLANTIC WHILE A COLD FRONT MOVES INTO THE OHIO VALLEY THIS AFTERNOON. THE COLD FRONT WILL APPROACH THE NORTHWESTERN PORTION OF THE CWA TONIGHT. A SOUTHWEST FLOW AHEAD OF THE COLD FRONT WILL USHER IN MORE HOT AND HUMID CONDITIONS THIS AFTERNOON. MAX TEMPS WILL RANGE FROM THE UPPER 70S AND LOWER 80S ALONG THE RIDGES TO THE LOWER AND MIDDLE 90S ACROSS MOST OTHER LOCATIONS. THE HOT AND HUMID CONDITIONS WILL LEAD TO AN UNSTABLE ATMOSPHERE...AND WITH DEWPOINTS A BIT HIGHER TODAY INSTABILITY SHOULD TURN OUT TO BE HIGHER THAN MONDAY. THE MODIFIED 12Z KIAD RAOB SHOWS AROUND 1500 J/KG OF MLCAPE DEVELOPING THIS AFTERNOON. A FEW SHOWERS AND THUNDERSTORMS MAY DEVELOP ALONG A PRESSURE TROUGH THIS AFTERNOON...BUT THE PRIMARY SOURCE OF CONVECTION IS EXPECTED TO MOVE IN FROM THE OHIO VALLEY LATER THIS AFTERNOON AND EVENING. A BROKEN LINE OF SHOWERS AND THUNDERSTORMS WILL MOVE INTO THE POTOMAC HIGHLANDS DURING THE MIDDLE AFTERNOON HOURS AND IT WILL REACH THE WASHINGTON AND BALTIMORE METROPOLITAN AREAS EARLY THIS EVENING. GIVEN THE MODERATE AMOUNTS OF INSTABILITY AND FAVORABLE SHEAR PROFILES...SEVERE THUNDERSTORMS ARE POSSIBLE. THE BEST CHANCE FOR SEVERE THUNDERSTORMS WILL BE ACROSS NORTHERN MARYLAND INTO NORTHERN AND CENTRAL VIRGINIA AS WELL AS EASTERN WEST VIRGINIA. THIS IS WHERE THE HEIGHTS WILL BE LOWEST AND THE SHEAR PROFILES WILL BE STRONGEST. THE CONVECTION TREND SHOULD DECREASE OVERNIGHT DUE TO THE LOSS OF DAYTIME HEATING...BUT A SHOWER OR THUNDERSTORM CANNOT BE RULED OUT WITH THE COLD FRONT NEARBY. WARM AND HUMID CONDITIONS WILL PERSIST. && .SHORT TERM /WEDNESDAY THROUGH WEDNESDAY NIGHT/... NAM/GFS DIFFS...WHILE SUBTLE...MANIFEST THEMSELVES BY WED. BASED ON GFS/CONSENSUS SOLN...THE CWFA WL BE DRAPED ACRS CWFA BY WED MRNG...PUSHING MOST OF THE INSTBY S/E OF THE AREA. /NAM...ON THE OTHER HAND...STILL HAS FNT W OF AREA. THAT MAKES THE NAM SOLN MUCH WETTER THAN ALL OTHER GDNC./ THIS FNT WL STALL DURING THE DAY AS IT GETS TRAPPED W/IN THE TROF AXIS...TIL AN UPR S/WV ACTS AS A KICKER WED NGT. KEPT PTMC HIGHLANDS/OKV-MRB- HGR/FDK-W54 ALL DRY AS LWR DEWPTS ADVECT SEWD. MEANWHILE...PCPN WL BUBBLE NEAR THE SFC BNDRY BY MID- LT MRNG. WHILE THERE WL BE MODEST INSTBY AND AVBL SHEAR... THE DEEPER VALUES OF EACH WL BE S/E OF AREA. THEREFORE...DAY WL FEATURE SCT SHRA/TSRA...WHICH BE PUSHED SE OF AREA DURING THE EVNG. LIMITING FACTOR FOR TEMPS WED WL BE CLDCVR...WHICH MAY BE XTNSV. /THE CLDS WL PREVENT GREATER INSTBY AS WELL./ VALUES NEAR CLIMO. MIN-T ALSO CLOSE TO AVG...W/ DEWPTS DROPPING THRU THE 60S. THE MID-UPR 50S SHUD RETURN W OF THE BLURDG. && .LONG TERM /THURSDAY THROUGH MONDAY/... HIGH PRESSURE WILL BE MOVING INTO THE MID-ATLANTIC THURSDAY WHILE A COLD FRONT WILL BE NEAR DELMARVA EXTENDING SOUTH TO CENTRAL VA. CLOUDS WILL ACCOMPANY THE FRONT AS IT MOVES EASTWARD AS WELL AS SHOWERS AND THUNDERSTORMS IN THE AFTERNOON. AT THIS TIME THE PIEDMONT AND SRN MD AND SURROUNDING WATERS HAVE THE BEST CHANCE FOR ISO-SCT SHOWERS AND THUNDERSTORMS THURS AFTERNOON BUT ACTIVITY MAY STAY TO THE EAST AND OUT OF THE LOOKOUT AREA. FCST MAX TEMPS WILL REACH THE MID TO UPPER 80S ON THURSDAY. AN UPPER LEVEL TROUGH WILL CROSS THE REGION FRIDAY WHILE HIGH PRESSURE PERSISTS AT THE SURFACE. RETURN FLOW WILL SET UP AT THE SFC FRIDAY AFTERNOON AND SCT SHOWERS WILL BE POSSIBLE ALONG THE HIGHER ELEVATIONS DUE TO TERRAIN CIRCULATIONS. ANOTHER TROUGH WILL EJECT DOWN FROM THE GREAT LAKES REGION SATURDAY. HIGH PRESSURE WILL MOVE OFF THE NEW ENGLAND COAST AND RETURN FLOW WILL INCREASE. SHOWERS AND THUNDERSTORMS WILL BE POSSIBLE MAINLY WEST OF THE BLUE RIDGE SATURDAY AS THE TROUGH PASSES OVER THE REGION. LITTLE INSTABILITY AND A WEAK WIND PROFILE WILL LEAD TO NON-SVR CONVECTION. HIGH PRESSURE WILL MOVE FURTHER OFF THE EAST COAST SAT NIGHT AND SUNDAY AND SRLY FLOW WILL ADVECT WARM AND HUMID CONDITIONS INTO THE REGION SUNDAY. MULTIPLE DISTURBANCES WILL ROTATE AROUND A DEEP LOW IN NRN CANADA TO START THE WORK WEEK. SHOWERS AND THUNDERSTORMS WILL BE POSSIBLE SUN AND MONDAY WHILE A COLD FRONT APPROACHES FROM THE OHIO VALLEY. HEAVY RAIN AND STRONG THUNDERSTORMS WILL BE POSSIBLE MONDAY. && .AVIATION /17Z TUESDAY THROUGH SATURDAY/... VFR CONDITIONS ARE EXPECTED MOST OF THE TIME THROUGH THIS EVENING. SOUTHWEST WINDS WILL GUST AROUND 20 TO 25 KNOTS THIS AFTERNOON...BUT WINDS WILL DIMINISH AROUND SUNSET. SHOWERS AND THUNDERSTORMS WILL LIKELY PASS THROUGH THE TERMINALS...FIRST ACROSS THE WESTERN TERMINALS LATE THIS AFTERNOON AND THEN ACROSS THE EASTERN TERMINALS THIS EVENING. BRIEF SUBVFR CONDITIONS ARE EXPECTED IN THUNDERSTORMS...AND SOME THUNDERSTORMS WILL BE CAPABLE OF PRODUCING GUSTY WINDS AND HAIL. PCPN CVRG WL GRDLY DECR OVNGT...BUT CANNOT COMPLETELY RULE OUT LT NGT PCPN...EVEN LT NGT TSRA. BELIEVE VFR WL GNLY PREVAIL OUTSIDE OF ANY SHRA/TSRA...AND FLGT RESTRICTIONS W/IN MAINLY MVFR. CDFNT WL PUSH ACRS TERMINALS ELY WED AND THEN STALL. SCT TSRA SHUD DVLP ONCE AGN BY LT MRNG...BUT BEST CHCS E OF THE BLURDG. SCT CVRG AND INTENSITY NOT AS STRONG AS TUE. ANY SHRA/TSRA SHUD BE SE OF TERMINALS BY DARK. HIGH PRESSURE MOVES INTO THE MID-ATLANTIC THURSDAY AND FRIDAY. A UPPER LEVEL DISTURBANCE WILL CROSS SATURDAY AND TSRA WILL BE POSSIBLE MAINLY AT MRB. && .MARINE... THE GRADIENT WILL CONTINUE THIS THROUGH EARLY THIS EVENING. A SMALL CRAFT ADVISORY IS IN EFFECT FOR THE WATERS DURING THIS TIME. THE SMALL CRAFT ADVISORY CONTINUES THROUGH TNGT FOR THE MARYLAND CHESAPEAKE BAY AND LOWER TIDAL POTOMAC RIVER. SCT TSRA WL THREATEN THE WATERS...ESPECIALLY THIS EVENING. STRONG GUSTY WNDS AND LRG HAIL WL BNE PSBL W/IN ANY STORM...AND SPECIAL MARINE WRNGS WL BE PSBL. CDFNT WL BE NEAR THE WATERS BY WED...AND IT/LL STALL OUT FOR MUCH OF THE DAY. WITH THE FNT IN THE NEIGHBORHOOD...XPCT SCT SHRA/TSRA BUT THE GRADIENT OF TDA WL BE LACKING. SWLY WNDS AOB 10 KT WL VEER NWLY WED NGT. A COLD FRONT WILL STALL NEAR THE WATERS THURSDAY. HIGH PRESSURE MOVES INTO THE REGION THURSDAY NIGHT AND FRIDAY. SRLY WINDS INCREASE SATURDAY-MONDAY AND SCA WILL BE POSSIBLE ACROSS ALL THE WATERS. && .LWX WATCHES/WARNINGS/ADVISORIES... DC...NONE. MD...NONE. VA...NONE. WV...NONE. MARINE...SMALL CRAFT ADVISORY UNTIL 6 AM EDT WEDNESDAY FOR ANZ530>534- 537-539>541-543. SMALL CRAFT ADVISORY UNTIL 9 PM EDT THIS EVENING FOR ANZ535- 536-538-542. && $$ SYNOPSIS...HTS NEAR TERM...BJL/HTS SHORT TERM...HTS LONG TERM...HAS AVIATION...BJL/HAS/HTS MARINE...BJL/HAS/HTS

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