Area Forecast Discussion
Issued by NWS Sterling, VA

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000 FXUS61 KLWX 250928 AAA AFDLWX AREA FORECAST DISCUSSION...UPDATED NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC 528 AM EDT FRI JUL 25 2014 .SYNOPSIS... HIGH PRESSURE WILL REMAIN OVER THE REGION THROUGH TONIGHT BEFORE MOVING OFF THE COAST SATURDAY. AN UPPER-LEVEL DISTURBANCE WILL PASS THROUGH THE AREA SUNDAY AND A POTENT COLD FRONT WILL MOVE THROUGH MONDAY. HIGH PRESSURE WILL RETURN FOR THE MIDDLE PORTION OF NEXT WEEK. && .NEAR TERM /THROUGH TONIGHT/... UPDATE...CANCELLED SMALL CRAFT ADVISORY FOR THE MIDDLE/LOWER BAY AND LOWER TP RVR. PREV DISC.... AFTER THE POST-FRONTAL REPRIEVE YESTERDAY...OUR TEMPS WILL MAKE A SLIGHT TURN BACK TOWARD THE WARMER SIDE THAT WILL GRADUALLY INCREASE OVER THE NEXT FEW DAYS. HOWEVER...DEWPOINTS WILL TAKE A SLIGHT DOWNWARD TURN TODAY ...LEVELING-OFF THE TEMP INCREASE AND MAKING TODAY LESS HUMID THAN YESTERDAY. THE METRO AREAS WILL SEE HIGHS TOP-OUT IN THE M80S...WHILE L80S WILL BE COMMON ACROSS THE REST OF THE CWA. WATER VAPOR IMAGERY ATTM SHOWS OUR REGION AS THE "DRIEST" IN THE COUNTRY - AT THE MID-LEVELS OF THE ATMOS. THIS REGIONAL-SIZED AREA OF SUBSIDENCE WILL EVENTUALLY MIX DOWN SOME OF THE DRIER AIR THRU THE BOUNDARY LAYER AS THE SFC HIGH ROLLS OVER THE AREA AND TOWARD THE MID ATLC COAST. AS THIS FEATURE MOVES EAST LATER TONIGHT...WINDS WILL TURN BACK TOWARD SLY AND AGAIN BEGIN THE LOW-LEVEL MOISTURE INCREASE. DEWPOINTS LATER TONIGHT WILL CLIMB BACK INTO THE L60S FROM THE SHEN VLY TOWARD THE EAST OVER TIME. NO SUBSTANTIAL WX-CHANGE FROM THIS RETURN FLOW OVERNIGHT BUT IT WILL SET-UP THE AREA HEADING INTO THE WEEKEND FOR A RETURN TO THE WARMER/HUMID CONDITIONS - AND AN ACTIVE ATMOS TO START THE COMING WEEK. && .SHORT TERM /SATURDAY THROUGH SATURDAY NIGHT/... HIGH PRESSURE WILL MOVE OUT INTO THE ATLANTIC SATURDAY THROUGH SATURDAY NIGHT. A SOUTHERLY FLOW WILL ALLOW FOR WARMER AND MORE HUMID CONDITIONS TO RETURN. MAX TEMPS SATURDAY WILL RANGE FROM THE 70S IN THE MOUNTAINS TO THE UPPER 80S/NEAR 90 IN THE WASHINGTON AND BALTIMORE METROPOLITAN AREAS. THE HEAT AND HUMIDITY WILL LEAD TO AN UNSTABLE ATMOSPHERE SATURDAY AFTERNOON AND EVENING. A FEW SHOWERS AND THUNDERSTORMS ARE POSSIBLE...BUT WITH THE LACK OF A STRONG LIFTING MECHANISM...CONVECTION COVERAGE WILL BE ISOLATED OR WIDELY SCATTERED. A POTENT SHORTWAVE IN THE WESTERLY FLOW ALOFT WILL APPROACH THE AREA SATURDAY NIGHT. MOST OF THE FORCING SHOULD REMAIN TO THE WEST...BUT A SURFACE TROUGH WILL STRENGTHEN A BIT OVER THE AREA. THEREFORE...A FEW SHOWERS AND THUNDERSTORMS WILL REMAIN POSSIBLE SATURDAY NIGHT. MIN TEMPS WILL RANGE FROM THE 60S IN THE MOUNTAINS TO THE MIDDLE 70S IN DOWNTOWN WASHINGTON AND BALTIMORE...AND IT WILL FEEL NOTICEABLY MORE HUMID. && .LONG TERM /SUNDAY THROUGH THURSDAY/... THE POTENT SHORTWAVE WILL PASS THROUGH THE REGION SUNDAY IN THE WESTERLY FLOW ALOFT. THE FORCING FROM THE SHORTWAVE WILL COMBINE WITH SOME INSTABILITY FROM A WARM AND HUMID AIRMASS TO BRING A BETTER CHANCE FOR SHOWERS AND THUNDERSTORMS. SHEAR PROFILES DO SUPPORT THE POSSIBILITY OF SEVERE THUNDERSTORMS...BUT THERE IS A QUESTION REGARDING THE COVERAGE BECAUSE PLENTY OF HIGH AND MID- LEVEL CLOUDS MAY LIMIT INSTABILITY. AS OF NOW...THERE IS AT LEAST AN ISOLATED THREAT FOR LOCALLY DAMAGING WIND GUSTS. LOCALLY HEAVY RAINFALL IS MORE LIKELY IN SHOWERS AND THUNDERSTORMS SUNDAY. WITH PWATS OVER 2 INCHES AND THE POSSIBILITY FOR TRAINING CONVECTION...THIS DOES POSE A THREAT FOR FLASH FLOODING. AGAIN...THE EXTENT OF FLASH FLOODING WILL BE DEPENDENT ON HOW MUCH INSTABILITY CAN DEVELOP. THE SHORTWAVE WILL MOVE OFF TO THE EAST SUNDAY NIGHT...BUT AN EVEN STRONGER SHORTWAVE AND ITS ASSOCIATED COLD FRONT WILL APPROACH FROM THE OHIO VALLEY. MORE SHOWERS AND THUNDERSTORMS ARE POSSIBLE SUNDAY NIGHT AHEAD OF THIS SYSTEM. THE COLD FRONT WILL PASS THROUGH THE REGION MONDAY...BRINGING THE CHANCE FOR SHOWERS AND THUNDERSTORMS. IF THIS SYSTEM IS SLOW ENOUGH...THEN THERE WILL BE ENOUGH HEATING FOR SEVERE THUNDERSTORMS SINCE SHEAR PROFILES WILL BE EXTREMELY FAVORABLE. DAMAGING WIND GUSTS AND LARGE HAIL WOULD BE THE PRIMARY THREATS. DETAILS ARE STILL UNCERTAIN DUE TO THE HIGH UNCERTAINTY WITH THE TIMING OF THE FRONT. HIGH PRESSURE WILL BUILD IN BEHIND THE FRONT FOR THE MIDDLE PORTION OF NEXT WEEK...BRINGING NOTICEABLY COOLER AND DRIER CONDITIONS. && .AVIATION /10Z FRIDAY THROUGH TUESDAY/... LIGHT NW FLOW PERSISTS OVER THE AREA INTO THE OVERNIGHT HRS. SOME CALM OB SITES AND THE TYPICAL FOG-PRONE NRN VA VLY LOCATIONS W/ THE PATCHY DENSE GROUND FOG/LOW STRATUS. THE KCHO AREA PARTICULARLY UNDER THE MOST FOG PRONE CONDITIONS TONIGHT AFTER THE LONGER PERIOD OF RAIN SHOWERS FROM YESTERDAY`S ACTIVITY. CONFIDENT THAT MOST AREAS WILL REMAIN IN SOLID VFR W/ ONLY THE KCHO AREA WAVERING W/ THE RECENT RAINFALL...LOW-LEVEL WINDS DECOUPLING AND TERRAIN-INDUCED VLY FOG. POST-SUNRISE THE LEFTOVER GROUND FOG WILL MIX-OUT AND TEMPS WILL STAY AT A REASONABLE L-M80S FOR HIGHS. ONLY SCATTERED BATCH OF CLOUDS TODAY AND AGAIN QUIET HEADING INTO THE OVERNIGHT HRS. PATCHY BR IS POSSIBLE SATURDAY MORNING...ESPECIALLY ACROSS THE WESTERN TERMINALS. OTHERWISE...VFR CONDITIONS ARE EXPECTED WITH A SOUTH-SOUTHWEST FLOW. A FEW SHOWERS AND THUNDERSTORMS ARE POSSIBLE SATURDAY AFTERNOON AND SATURDAY NIGHT...BUT COVERAGE WILL BE LIMITED. PATCHY BR IS POSSIBLE OVERNIGHT SATURDAY INTO EARLY SUNDAY. A POTENT UPPER-LEVEL DISTURBANCE WILL PASS THROUGH THE TERMINALS SUNDAY INTO SUNDAY EVENING...BRINGING A BETTER CHANCE FOR SHOWERS AND THUNDERSTORMS. THUNDERSTORMS MAY CONTAIN GUSTY WINDS AND LOCALLY HEAVY RAINFALL THAT COULD REDUCE CIGS/VSBYS TO IFR LEVELS AT TIMES. A POTENT COLD FRONT WILL APPROACH THE TERMINALS SUNDAY NIGHT AND PASS THROUGH MONDAY. MORE SHOWERS AND THUNDERSTORMS ARE POSSIBLE AHEAD OF THE FRONT. HIGH PRESSURE WILL RETURN FOR TUESDAY WITH A NORTHWEST FLOW. && .MARINE... MARGINAL SCA CONDITIONS APPEARING IN OBS OVERNIGHT FROM THE WEAK NLY CHANNELING OVER THE MAIN STEM OF THE MD BAY. THESE WINDS WILL LIKELY SWITCH TOWARD SLY OVERNIGHT TONIGHT AS THE SFC HIGH ROLLS OVER THE REGION AND THE OFF THE COAST. SOUTHERLY WINDS ARE EXPECTED AROUND HIGH PRESSURE OVER THE ATLANTIC FOR SATURDAY AND SUNDAY. WINDS MAY GUSTS PAST SCA CRITERIA OVER PORTIONS OF THE WATERS SATURDAY NIGHT INTO SUNDAY. A COLD FRONT WILL PASS THROUGH THE WATERS MONDAY AND NORTHWEST WINDS MAY GUST PAST SCA CRITERIA BEHIND THE FRONT MONDAY NIGHT AND TUESDAY. SHOWERS AND THUNDERSTORMS ARE POSSIBLE SATURDAY THROUGH MONDAY. AS OF NOW...IT APPEARS THAT THE BEST CHANCE FOR THUNDERSTORMS WILL SUNDAY AND MONDAY. THUNDERSTORMS MAY CONTAIN GUSTY WINDS AND LOCALLY HEAVY RAINFALL THAT COULD REDUCE VSBYS BELOW A MILE AT TIMES. && .CLIMATE... 59 DEGREES IS THE FORECAST FOR BWI EARLY THIS MORNING. THE RECORD LOW FOR THE THREADED BALTIMORE CLIMATE RECORD IS 59...SET IN 2008... 1976...1973...AND 1876. && .LWX WATCHES/WARNINGS/ADVISORIES... DC...NONE. MD...NONE. VA...NONE. WV...NONE. MARINE...NONE. && $$ UPDATE...GMS PREV DISCUSSION...GMS/BJL

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