Area Forecast Discussion
Issued by NWS Sterling, VA

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000 FXUS61 KLWX 241030 AAA AFDLWX AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC 630 AM EDT WED SEP 24 2014 .SYNOPSIS... HIGH PRESSURE WILL EXIT OFF THE NEW ENGLAND COAST TODAY...AS LOW PRESSURE APPROACHES FROM THE ATLANTIC COAST. THIS SYSTEM WILL MOVE ALONG THE ATLANTIC COASTLINE...ACROSS THE MID-ATLANTIC REGION AND THEN OFF THE COAST INTO EARLY THURSDAY. HIGH PRESSURE IS ON TAP FOR THIS WEEKEND. && .NEAR TERM /THROUGH TONIGHT/... HEADLINE UPDATE...ADDED THE MIDDLE PORTIONS OF THE MD CHES BAY TO THE CURRENT SCA. HIGHER GUSTS ARE BEGINNING TO SPREAD FURTHER NWD AHEAD OF THE APPROACHING LOW PRES SYSTEM. A FLOOD WATCH IS IN EFFECT FOR MUCH OF THE WASHINGTON AND BALTIMORE METRO AREAS FROM THIS EVENING THRU THE OVERNIGHT HOURS TONIGHT. SEE HYDROLOGY SECTION BELOW FOR FURTHER DETAILS. THE LOW PRES SYSTEM OVER THE SRN ATLC STATES IS STILL GEARING UP TO MAKE ITS NWD JOG BUT WILL FIND IN THE COMING HRS A FAIRLY OPEN PATH DUE NORTH FROM THE CAROLINAS. HIGH PRESSURE THAT HAS GIVEN OUR AREA A VERY FALL-LIKE START TO THE SEASON WILL ROLL OFF THE NEW ENGLAND COAST...OPENING UP THE PATH FOR THE LOW TO TRACK UP ACROSS THE I-95 CORRIDOR. A CUT-OFF UPPER LOW POWERING THE SYSTEM WILL REMAIN ON THE WRN FRINGE OF THE SFC SYSTEM...ALSO DRIFTING NWD UP THE SPINE OF THE APLCNS. LIGHT SHOWERS ARE ALREADY SPREADING UP ACROSS SERN VA...LARGELY DISSIPATING UPON ARRIVING TO THE SRN CWA BORDER. THIS WILL CONTINUE INTO THE MID MRNG HRS...WHEN MORE OF THE DRY BOUNDARY LAYER BECOMES SATURATED. THE 00Z KRNK SOUNDING SHOWS A VERY DRY LEVEL BETWEEN 600-850MB...ESSENTIALLY DRYING OUT THE INCOMING ACTIVITY. THIS DRY POCKET WILL MOVE ITS WAY UP ACROSS OUR REGION OVER THE NEXT SEVERAL HRS...PREVENTING MUCH PRECIP FROM AFFECTING THE AREA FOR THE FIRST HALF OF THE DAY BUT WILL EVENTUALLY BE OVERCOME LATER THIS AFTN. MORE STEADY SHOWERS WILL BEGIN TO ARRIVE OVER SRN MD AND NRN VA INTO THE LATE AFTN HRS...THEN ON TOWARD THE METRO AREAS AND JUST INTO THE SHEN VLY LATER THIS EVE. THE HEAVIER ACTIVITY IS EXPECTED TO BEGIN LATE TONIGHT...AFTER SUNSET AND INTO THE EARLY MRNG HRS. POCKETS OF EMBEDDED HEAVY RAIN WILL FORM ALONG CONFINED REGIONS OF STRONG LIFT...LIKE WHAT IS OCCURRING OVER THE NC OUTER BANKS ATTM. BREEZY WINDS WILL ALSO BEGIN TO ARRIVE INTO THE EARLY MRNG HRS...SURROUNDING THE INCOMING SFC LOW. THE LOW ITSELF WILL STAY MAINLY TO OUR SOUTH AND EAST...BUT THE STRONGEST WINDS AND HEAVIEST RAIN WILL BE STATIONED ALONG AN EAST/WEST AXIS JUST NORTH OF THE LOW AND W/ THE NOSE OF IT POKING INTO THE CWA FROM DELMARVA. THE TIMING OF ALL OF THIS HAS BECOME PROGRESSIVELY SLOWER W/ RECENT NAM/EURO RUNS WHICH HAVE BEEN THE MOST CONSISTENT AND PERSISTENT W/ THE DEPICTION OF THE LOW`S TRACK/INTENSITY. && .SHORT TERM /THURSDAY/... AS THE LOW BEGINS TO DRIFT BACK OFF THE DELMARVA COAST INTO THU...WINDS WILL DROP OFF WHILE TURNING NELY. THIS WILL BEGIN TO DISSIPATE THE LEFTOVER PRECIP - THOUGH THE DENSE LOW CLOUDS WILL STICK AROUND FOR MUCH OF THE DAY. HIGH PRESSURE WILL PROVIDE GOOD SUBSIDENCE IN THE WESTERN HALF OF THE REGION. && .LONG TERM /THURSDAY NIGHT THROUGH TUESDAY/... UPPER TROUGH/LOW PRESSURE WILL GRADUALLY PULL AWAY FROM THE MIDDLE ATLANTIC REGION THURSDAY NIGHT AND THE FIRST PART OF FRIDAY. STEADY RAIN IS EXPECTED TO END BY THURSDAY NIGHT BUT A FEW LINGERING SHOWERS COULD STILL HOLD ON FROM THE BALTIMORE METRO AREA AND POINTS NORTH INTO EARLY FRIDAY. IF THE SYSTEM SLOWS DOWN OR UPPER ENERGY HANGS BACK LONGER FUTURE SHIFTS MAY NEED TO EXTEND POPS FURTHER OUT IN TIME. HIGH PRESSURE WILL BUILD INTO THE MIDDLE ATLANTIC REGION LATER FRIDAY AND REMAIN IN PLACE THROUGHOUT THE UPCOMING WEEKEND. TEMPERATURES ARE EXPECTED TO MODERATE BACK INTO THE MIDDLE TO UPPER 70S WITH LOWS GENERALLY RUNNING IN THE 40S WEST TO 50S TO NEAR 60 EAST. THE NEXT TROUGH OF LOW PRESSURE COULD APPROACH THE MIDDLE ATLANTIC LATE MONDAY OR TUESDAY OF NEXT WEEK BRINGING INCREASING CLOUDS AND A CHANCE FOR SHOWERS. && .AVIATION /12Z WEDNESDAY THROUGH SUNDAY/... VFR CONDS EARLY THIS MRNG AND INTO THE AFTN HRS. LOWER CIGS AND SHOWERS WILL ARRIVE LATE THIS EVE ACROSS MUCH OF THE AREA. SUB VFR CIGS AND RESTRICTED VSBYS IN LIGHT RAIN/SHOWERS WILL LINGER INTO THURSDAY NIGHT. CONDITIONS ARE EXPECTED TO IMPROVE BY FRIDAY AND VFR CONDITIONS ARE EXPECTED SATURDAY THROUGH MONDAY. THE NEXT LOW PRESSURE SYSTEM COULD BRING A CHANCE FOR SHOWERS AND LOWERED CIGS BY LATE MONDAY INTO TUESDAY OF NEXT WEEK. && .MARINE... WINDS HAVE ALREADY BEEN GUSTY OVER THE SRN MD BAY...SO A SCA IS IN EFFECT FOR THESE AREAS THRU MID-MRNG. WINDS WILL INCREASE OVER THE REMAINDER OF THE AREA WATERS LATER THIS AFTN...AS LOW PRESSURE APPROACHES FROM THE SOUTH. SCA BEGINS 10 AM WEDNESDAY FOR ALL THE WATERS AND CONTINUES INTO THE OVERNIGHT HRS WHILE THE LOW IS APPROACHING AND PASSING BY JUST TO THE SE OF THE BAY. PERIODS OF RAIN LATE THIS AFTN/EVE. SCA CONDITIONS WILL GRADUALLY DIMINISH THURSDAY NIGHT. HIGH PRESSURE WILL BUILD OVER THE WATERS LATER FRIDAY AND CONTINUE INTO MONDAY OF NEXT WEEK. DURING THIS TIME...WINDS ARE EXPECTED TO REMAIN BELOW SCA LEVELS. && .HYDROLOGY... EURO/NAM NEAR-TERM GUIDANCE CONTINUE TO SHOW THE ERN...AND PARTICULARLY THE EXTREME NERN SECTIONS OF THE AREA UNDER THE BEST COMBINATION OF THE MOISTURE...LIFT AND SHEAR FOR PERSISTENT MODERATE TO HEAVY RAIN. MOISTURE-RICH AIR WILL BE LOCALIZED TO THE AXIS OF HIGHEST LIFT ALONG/NEAR THE COASTLINE. NAM 250MB WINDS SHOW A NORTH/SOUTH UPPER JET DIRECTLY OVER THE ERN HALF OF THE CWA FOR GOOD UPPER DIVERGENCE. MORE IMPRESSIVE IS THE EXPECTED LOW LEVEL JET MAX W/ A DUE ELY ONSHORE FLOW OVERNIGHT THAT CREATES A THIN BUT PRONOUNCED AXIS. A SOLID 1-2 INCHES POSSIBLE ALONG THE WRN SHORE COUNTIES OF THE BAY - STORM-TOTAL - INTO EARLY THU...LOCALLY HIGHER. THESE AMOUNTS WILL TAPER OFF TO THE WEST...ALSO W/ LOCALLY HIGHER AMOUNTS EXPECTED. && .TIDES/COASTAL FLOODING... CURRENT WATER LEVELS ARE RIGHT AT OR JUST BELOW NORMAL...BUT ARE THERE BECAUSE THEY HAVE BEEN RISING FROM OVER A HALF-FOOT BELOW NORMAL OVER A DAY AGO. A SLOW/STEADY INCREASE WILL CONTINUE THRU THE DAY TODAY...THOUGH MINOR FLOODING NOT ANTICIPATED FOR UPCOMING H.T. CYCLE. WINDS WILL INCREASE LATER THIS AFTN/EVE AHEAD OF A STRENGTHENING LOW PRES SYSTEM TO OUR SOUTH. STEADY 15-25KT WINDS WILL THEN QUICKLY INCREASE WATER LEVELS ALONG THE MD CHES BAY WRN SHORE LOCALES. THE POTENTIAL FOR MINOR CF WILL INCREASE SHARPLY WHERE THE ELY WINDS BANK UP STRONGEST/LONGEST LATE TONIGHT. AS THE LOW DRIFTS NE OF THE AREA ON THU...THE WIND FIELD WILL TURN MORE NLY AND ALLOW WATER TO PUSH BACK DOWN THE BAY AND DECREASE FLOODING POTENTIAL OVER THE COURSE OF THE DAY. && .LWX WATCHES/WARNINGS/ADVISORIES... DC...FLOOD WATCH FROM 6 PM EDT THIS EVENING THROUGH LATE TONIGHT FOR DCZ001. MD...FLOOD WATCH FROM 6 PM EDT THIS EVENING THROUGH LATE TONIGHT FOR MDZ006-007-009>011-013-014. VA...FLOOD WATCH FROM 6 PM EDT THIS EVENING THROUGH LATE TONIGHT FOR VAZ053-054. WV...NONE. MARINE...SMALL CRAFT ADVISORY FROM 10 AM THIS MORNING TO 6 AM EDT THURSDAY FOR ANZ535-536. SMALL CRAFT ADVISORY UNTIL 2 PM EDT THURSDAY FOR ANZ532-540. SMALL CRAFT ADVISORY UNTIL 6 AM EDT THURSDAY FOR ANZ533-534- 537-541>543. SMALL CRAFT ADVISORY FROM 10 AM THIS MORNING TO 2 PM EDT THURSDAY FOR ANZ530-531-538-539. && $$ UPDATE...GMS PREV DISCUSSION...GMS/KRW

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