Area Forecast Discussion
Issued by NWS Sterling, VA

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000 FXUS61 KLWX 291342 AAA AFDLWX AREA FORECAST DISCUSSION...UPDATED NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC 942 AM EDT WED JUL 29 2015 .SYNOPSIS... WEAK HIGH PRESSURE PERSISTS OVER THE AREA INTO TONIGHT. A COLD FRONT MOVES THROUGH THE REGION THURSDAY FROM THE WEST. HIGH PRESSURE THEN PERSISTS OVER THE AREA THROUGH THE WEEKEND. && .NEAR TERM /THROUGH TONIGHT/... 12Z IAD RAOB SHOWS MOISTURE EXTENDS DEEPER TODAY UP TO 600 MB AND PWAT VALUES ARE UP TO 1.75 INCHES. EXTENSIVE LOW CLOUDS AND FOG THIS MORNING MAY DELAY ONSET OF SHOWERS AND T-STORMS BY A COUPLE OF HOURS THIS AFTERNOON. STEERING FLOW IS A LITTLE STRONGER AND BETTER DEFINED TODAY SUGGESTING STORMS WILL MOVE A LITTLE FASTER BUT MOISTURE IS DEEPER WHICH MAY STILL POSE A THREAT OF HEAVY RAINFALL. HEAT INDICES APPEAR WILL GET AWFUL CLOSE TO HEAT ADVISORY CRITERIA THIS AFTERNOON. SFC DEWPOINTS ARE RUNNING 2-3F HIGHER THAN 24 HRS AGO. A BIT MORE CLOUD COVER TODAY SHOULD KEEP TEMPS A DEG OR TWO COOLER THAN YDAY KEEPING HEAT INDICES JUST BELOW 105F. WILL MONITOR OBS CLOSELY AND ISSUE A HEAT ADVISORY IF NECESSARY. && .TONIGHT...COLD FRONT (NOW STRUNG OUT FROM THE PARENT LOW OVER ONTARIO) CROSSES THE MID-ATLANTIC WITH PREFRONTAL THUNDERSTORM CHANCES REACHING THE CENTRAL APPALACHIANS AFTER MIDNIGHT. OTHERWISE INCREASING CLOUDS WITH MIN TEMPS LOW TO MID 70S. && .SHORT TERM /THURSDAY THROUGH THURSDAY NIGHT/... THURSDAY...COLD FRONT CROSSES THE CWA THROUGH THE DAY. POPS INCREASE AHEAD OF THE FRONT THROUGH THE DAY PER DIURNAL TRENDS. FRONT IS A BIT MORE PROGRESSIVE THAN PREVIOUS...COMES IN QUICKER WITH AFTERNOON LIKELY POPS FOR BALT-WASH METRO THUNDERSTORMS. MAX TEMPS LOW TO POSSIBLY MID 90S AHEAD OF THE FRONT. SHOULD IT PUSH THROUGH SOONER...TEMPS WOULD BE MODERATED. DEWPOINTS IN THE LOW 70S RESULT IN HEAT INDICES AROUND 100F. THURSDAY NIGHT...COLD FRONT CLEARS THE SERN ZONES THURSDAY EVENING WITH COOLER AIR TRAILING. MIN TEMPS 60S WEST OF I-95...LOW 70S EAST. && .LONG TERM /FRIDAY THROUGH TUESDAY/... FAIRLY TRANQUIL WEATHER PATTERN FOR LAST DAY OF JULY THROUGH THE FIRST FEW DAYS OF AUGUST...AS HIGH PRESSURE BUILDS IN FROM THE WEST BEHIND DEPARTING COLD FRONT. FRONT WILL HAVE MOVED THROUGH THE CWA BY 8 AM FRIDAY...THOUGH THERE COULD BE A FEW LINGERING SHOWERS OVER SOUTHERN MARYLAND. NOT MUCH OF A TEMPERATURE CHANGE WITH THIS FRONT...AS TEMPERATURES EXPECTED TO REMAIN IN THE U80S/L90S. BUT DEWPOINTS DROP AT LEAST TEN DEGREES...AND GENERALLY REMAIN AOB 65F THROUGH THE LONG TERM. SLOW WARMING TREND THROUGH TUESDAY...WITH TEMPS REMAINING A FEW DEGREES ABOVE NORMAL. PRECIP CHANCES THROUGH THE PERIOD ARE VERY LOW...WITH NO DECENT SOURCE OF LIFT AND QUALITY LOW-LEVEL MOISTURE SHUNTED OFF TO OUR SOUTHEAST. WHILE LOW...BEST CHANCES FOR PRECIP OCCUR MONDAY IN OUR SOUTHERN AND EASTERN ZONES AS MOISTURE RETURN SLOWLY COMMENCES. && .AVIATION /14Z WEDNESDAY THROUGH SUNDAY/... IFR VSBYS/POSSIBLE CIGS THROUGH SUNRISE UNDER WEAK FLOW AND CLEAR SKIES...PARTICULARLY WHERE IT RAINED LATE TUESDAY. VFR THEN PREVAILS INTO TONIGHT OUTSIDE OF LOW CHANCES FOR TSTMS...PARTICULARLY NEAR KCHO THIS AFTERNOON. WEAK COLD FRONT CROSSES TERMINALS THURSDAY WITH LIKELY THUNDERSTORMS IN THE AFTERNOON FOR DC METROS. VFR CONDITIONS EXPECTED FRIDAY THROUGH THE REMAINDER OF THE PERIOD UNDER HIGH PRESSURE. && .MARINE... SCA FOR SLY CHANNELING THIS EVENING SOUTH OF SANDY PT. OTHERWISE HIGH PRESSURE. WEAK COLD FRONT CROSSES WATERS THURSDAY AFTERNOON. WINDS EXPECTED TO BE SUB-SCA FRIDAY THROUGH THE REMAINDER OF THE PERIOD UNDER HIGH PRESSURE. LOW CHANCE FOR AFTERNOON THUNDERSTORMS OVER THE WATERS MONDAY AS LOW LEVEL MOISTURE SLOWLY INCREASES. && .LWX WATCHES/WARNINGS/ADVISORIES... DC...NONE. MD...NONE. VA...NONE. WV...NONE. MARINE...SMALL CRAFT ADVISORY FROM 6 PM THIS EVENING TO 3 AM EDT THURSDAY FOR ANZ532>534-537-540-541-543. && $$ SYNOPSIS...BAJ/MSE NEAR TERM...LFR SHORT TERM...BAJ LONG TERM...MSE AVIATION...BAJ/MSE MARINE...BAJ/MSE

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