Area Forecast Discussion
Issued by NWS Sterling, VA

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000 FXUS61 KLWX 241833 AFDLWX AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC 233 PM EDT MON AUG 24 2015 .SYNOPSIS... A COLD FRONT APPROACHING FROM THE WEST WILL CROSS THE MID ATLANTIC STATES TONIGHT. HIGH PRESSURE WILL GRADUALLY BUILD INTO THE AREA DURING THE MIDDLE OF THE WEEK AND BECOME CENTERED OVER THE AREA FOR THE START OF THE WEEKEND. && .NEAR TERM /THROUGH TUESDAY/... SOUTHERLY FLOW AHEAD OF THE APPROACHING FRONT HAS ALLOWED DEW POINTS TO RETURN TO NEAR 70F ACROSS OUR AREA ALONG WITH WARMER 850 MB AIR. ADDING IN THE DAYTIME HEATING HAS ALLOWED ML CAPE VALUES TO RISE PAST 1000 J/KG. COMBINED WITH LOWERING HEIGHTS IN ADVANCE OF THE TROUGH...A WEAK JETSTREAK...AND THE CONVERGENCE AHEAD OF THE APPROACHING FRONT...AND WE HAVE CONDITIONS RIPE FOR SHOWER AND THUNDERSTORM DEVELOPMENT. THIS HAS BEEN ONGOING FOR THE LAST HOUR OR TWO AND SHOULD CONTINUE TO EXPAND OVER THE NEXT FEW HOURS AS THE ACTIVITY PROGRESSES EASTWARD. SHEAR IS WEAK AND CAPE IS NOT EXCESSIVE...SO DO NOT EXPECT MUCH IN THE WAY OF A SEVERE THREAT...BUT A FEW PULSE STORMS COULD CAUSE A STRONG WIND GUST HERE OR THERE. THE FRONT WILL CROSS THE REGION TONIGHT. SHOWERS OR STORMS MAY LINGER IN THE CHESAPEAKE BAY AND SOUTHERN MARYLAND UNTIL AFTER MIDNIGHT BUT SHOULD CLEAR MOST OF THE CWA BEFORE MIDNIGHT. NORTHWEST WINDS WILL BRING MUCH DRIER AIR INTO THE AREA BEHIND THE FRONT WITH DEW POINTS LOWERING INTO THE UPPER 40S AND LOWER 50S IN MUCH OF THE AREA BY DAWN TUESDAY. LOWS WILL NOT BE TOO MUCH LOWER COMPARED TO SUNDAY NIGHT MAINLY DUE TO MIXING WITH THE NEW AIR MASS ADVECTING IN. HIGH PRESSURE SLOWLY BUILDS IN ON TUESDAY AS THE FRONT STALLS TO OUR SOUTHEAST. SOME PATCHY CLOUDS WILL BE AROUND BUT FOR THE MOST PART SUN WILL PREVAIL...AND DEW POINTS SHOULD REMAIN VERY LOW... IN THE LOW-MID 50S FOR THE MOST OF THE REGION. HIGH TEMPERATURES WILL ALSO BE COOLER WITH A TROUGH OF LOW PRESSURE CENTERED NEARBY ALOFT...WITH MOST READINGS 5-8 DEGREES BELOW THE HIGHS WE WILL REACH TODAY. OVERALL...A VERY NICE LATE AUGUST DAY. && .SHORT TERM /TUESDAY NIGHT THROUGH WEDNESDAY NIGHT/... HIGH PRESSURE PERSISTS ACROSS THE UPPER MID-WEST INTO THE MID- ATLANTIC TUESDAYS NIGHT THROUGH WEDNESDAY NIGHT. LIGHT NRLY FLOW WILL PERSIST AT THE SURFACE RESULTING IN DRY CONDITIONS WITH TEMPS BARELY REACHING THE UPPER 70S AT HIGHER ELEVATIONS ALONG AND WEST OF THE BLUE RIDGE AND IN THE LOW 80S NEAR THE METROS ON WEDNESDAY. && .LONG TERM /THURSDAY THROUGH MONDAY/... SFC HIGH PRESSURE DOMINATES THE WEATHER PATTERN THROUGH THE LONG TERM...WITH LITTLE DAY-TO-DAY VARIABILITY IN SENSIBLE WEATHER AND LITTLE-TO-NO CHANCE OF MEANINGFUL PRECIPITATION. FULL LATE SUMMER INSOLATION WILL LEAD TO A SLOW INCREASE IN TEMPERATURES EACH DAY AS AIRMASS MODIFIES...WITH TEMPERATURES AOA NORMAL BY SATURDAY AND A FEW DEGREES WARMER...U80S/L90S...ACROSS THE ENTIRE CWA BY SUNDAY. DEWPOINTS REMAIN RELATIVELY LOW THROUGH THE END OF THE WEEK WITH L/M50S ACROSS THE CWA...WHICH WILL KEEP NIGHTTIME TEMPERATURES IN 50S/L60S...THOUGH THERE COULD BE A FEW ISOLATED SPOTS IN OUR FAR WEST WITH LOWS IN THE M/U40S FRIDAY MORNING. WEAK RETURN FLOW BEGINS OVER THE WEEKEND...BUT WITH QUALITY MOISTURE SHUNTED WELL SOUTH AND EAST OF OUR AREA...DEWPOINTS EXPECTED TO ONLY INCREASE INTO THE L60S...SO EVEN WITH TEMPERATURES IN L90S...HEAT INDICES WILL REMAIN AOB 85. ESSENTIALLY NO CHANCE OF PRECIP THURSDAY OR FRIDAY. SFC HIGH WEAKENS ITS GRIP SLIGHTLY OVER THE WEEKEND AND WITH WEAK MOISTURE RETURN...COULD BE A FEW SHOWERS/STORMS AROUND...THOUGH COVERAGE SHOULD BE ISOLATED AND MAINLY CONFINED TO HIGHER TERRAIN. && .AVIATION /18Z MONDAY THROUGH SATURDAY/... SUB-VFR CONDITIONS POSSIBLE AT ALL TERMINALS THIS AFTERNOON AND EVENING AS SCATTERED SHOWERS AND THUNDERSTORMS MOVE THROUGH WITH A COLD FRONT. WINDS WILL BE SOUTHERLY 5-10 KNOTS BEFORE FRONTAL PASSAGE...SHIFTING WEST TO NORTHWEST AT SIMILAR SPEEDS BEHIND THE FRONT LATER TONIGHT AND TUESDAY. OTHERWISE...VFR THROUGH THE REMAINDER OF THE PERIOD UNDER HIGH PRESSURE. && .MARINE... SOUTHERLY CHANNELING STILL HAS POTENTIAL TO PRODUCE A FEW GUSTS TO 20 KNOTS OR SO LATE THIS AFTERNOON AND THIS EVENING...WITH POSSIBLE PRESSURE SURGE GUSTS BEHIND THE FRONT OVERNIGHT...SO SMALL CRAFT ADVISORY REMAINS IN EFFECT FOR PARTS OF THE BAY AND A FEW ADJACENT WATERS. SHOWERS AND THUNDERSTORMS ARE ALSO EXPECTED TO IMPACT THE WATERS TONIGHT AS THE FRONT MOVES THROUGH. WINDS EXPECTED TO REMAIN SUB-SCA THROUGH THE REMAINDER OF THE FORECAST PERIOD UNDER HIGH PRESSURE. && .TIDES/COASTAL FLOODING... STILL WATCHING TIDAL ANOMALIES CLOSELY WITH POTENTIAL FOR MINOR FLOODING WITH THE SOUTHERLY UP-BAY FLOW. GUIDANCE IS STILL SUGGESTING MINOR FLOODING AT ANNAPOLIS LATER TONIGHT THOUGH SOME QUESTION EXISTS REGARDING THE EXPECTED WIND SHIFT BEFORE THEN AND HOW IT MIGHT AFFECT ANOMALIES. THIS IS SOMETHING WE WILL BE WATCHING CLOSELY THIS EVE. A COASTAL FLOOD ADVISORY IS POSSIBLE. && .LWX WATCHES/WARNINGS/ADVISORIES... DC...NONE. MD...NONE. VA...NONE. WV...NONE. MARINE...SMALL CRAFT ADVISORY FROM 6 PM THIS EVENING TO 1 AM EDT TUESDAY FOR ANZ531-541-543. SMALL CRAFT ADVISORY UNTIL 6 AM EDT TUESDAY FOR ANZ533-534-537. SMALL CRAFT ADVISORY UNTIL 1 AM EDT TUESDAY FOR ANZ532. && $$ SYNOPSIS...RCM NEAR TERM...RCM SHORT TERM...HAS LONG TERM...MSE AVIATION...HAS/MSE/RCM MARINE...HAS/MSE/RCM TIDES/COASTAL FLOODING...RCM

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