Area Forecast Discussion
Issued by NWS Sterling, VA

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000 FXUS61 KLWX 281420 AFDLWX AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC 1020 AM EDT THU APR 28 2016 .SYNOPSIS... A COLD FRONT WILL REMAIN STALLED TO THE SOUTH THROUGH FRIDAY. WAVES OF LOW PRESSURE WILL RIDE ALONG THE BOUNDARY DURING THIS TIME. THE BOUNDARY WILL DROP FARTHER SOUTH SATURDAY...BUT IT WILL THEN LIFT NORTHWARD CLOSER TO THE REGION AGAIN SUNDAY AND MONDAY AS ANOTHER WAVE OF LOW PRESSURE MOVES ALONG IT. && .NEAR TERM /THROUGH TONIGHT/... LTL SYNOP CHG TO FCST THIS MRNG. STALLED SFC BOUNDARY STILL LOCATED NEAR NC...SNAKING TO VERTICALLY STACKED LOW PRESSURE OVER IOWA. MARITIME FLOW DOMINATES WITH PLENTY OF CLOUD COVER. A SWATH OF SHRA STRETCHES FM THE PTMC HIGHLANDS ACRS METRO DC TO SRN MD. BEHIND THIS ACTIVITY...FAIRLY SUBSTANTIAL DRY SLOT IS NOTED IN WATER VAPOR IMAGERY. THIS WILL LIKELY LEAD TO RAPIDLY DIMINISHING COVERAGE OF SHOWERS DURING THE AFTERNOON. HOWEVER...WITH ADDITIONAL WEAK SHORTWAVE ENERGY AND CONTINUED OVERRUNING...SOME LIGHT SHOWERS OR SPRINKLES WILL REMAIN POSSIBLE. IN ADDITION...BL HEATING WILL TAKE PLACE S/W OF THE CWA IN AN ENVIRONMENT OF MODERATE DEEP LAYER SHEAR. SOME OF THIS THUNDERSTORM ACTIVITY MAY PUSH INTO THE POTOMAC HIGHLANDS AND ALONG THE SOUTHERN CWA BORDER THIS AFTERNOON. HV MADE TIMING ADJUSTMENTS IN DATABASE TO ACCNT FOR THIS THINKING AND LTST RADAR TRENDS. ON THE WHOLE...PREV THOUGHT PROCESS REMAINS VALID. CONSIDERING CURRENT RAFL AND LTST LAMP...HV ADJUSTED TEMPS DOWN ARND MUCH OF MD AND ADJACENT VA. AM NOT TOUCHING CENTRAL FOOTHILLS/CENTRAL SHEN VLY AS TEMPS CUD JUMP THERE QUITE QUICKLY. THE OPENED LOW WILL BE NEAR PA TONIGHT. THUS THE HIGHEST POPS WILL BE IN THE NORTHERN CWA. LOW LEVELS WILL BE SATURATED ACROSS THE ENTIRE AREA THOUGH...SO HAVE INTRODUCED PATCHY DRIZZLE AND FOG TO THE FORECAST. LOWS WILL RANGE FROM THE MID 40S TO MID 50S. && .SHORT TERM /FRIDAY THROUGH SATURDAY NIGHT/... WEAK SFC LOW WILL STILL BE NEAR THE AREA ON FRIDAY WITH CAD WEDGE FRONT NEARLY UNCHANGED. HOWEVER...TREND IN 00Z GUIDANCE IS TO KEEP SHORTWAVE TROUGH FARTHER TO THE NORTH. SO SEE LITTLE REASON TO CHANGE POPS...CAPPING IN THE CHANCE CATEGORY WITH HIGHEST NEAR PA BORDER. THE LOW MAY DRAW SOME WARMER AIR INTO CENTRAL VA...BUT HIGHS WILL REMAIN IN THE MID 50S NEAR THE PA BORDER. ANY CHANCE OF MEASURABLE PRECIP WILL END FRIDAY EVENING AS THE DEPARTING LOW DRAGS THE FRONT SOUTH AND HIGH PRESSURE BUILDS. THERE WILL STILL BE LOW LEVEL OVERRUNNING...SO COULD SEE SOME LINGERING DRIZZLE. THE FIRST HALF OF SATURDAY SHOULD BE DRY AS SHORTWAVE RIDGING MOVES OVERHEAD. HOWEVER...THE TREND HAS BEEN FASTER WITH ISENTROPIC LIFT AHEAD OF THE NEXT LOW OVER THE PLAINS...WITH RAIN POSSIBLE ACROSS WESTERN AREAS BY AFTERNOON AND ACROSS MOST OF THE AREA OVERNIGHT. HIGHS MAY GET A BOOST FROM MIDDAY SUN BREAKS...POTENTIALLY REACHING THE 60S IN MOST AREAS. && .LONG TERM /SUNDAY THROUGH WEDNESDAY/... GUIDANCE THROUGH MONDAY IS IN REASONABLE...IF ROUGH...AGREEMENT. THE STATIONARY BOUNDARY TO OUR SOUTH WILL START TO LIFT NORTH AS ANOTHER WAVE OF LOW PRESSURE TRACKS EASTWARD FROM THE CENTRAL PLAINS AND OHIO VALLEY. THE WEDGE OF COOLER AIR WILL BE HARD TO DISLODGE AND WHILE SOME MILDER AIR MAY TRY TO ENTER THE CWA LATE SUNDAY OR MONDAY...MOST OF THE REGION WILL PROBABLY STAY ON THE COOL SIDE OF THE BOUNDARY. AFTER THE TROUGH AXIS ALOFT PASSES THROUGH LATE MONDAY...GUIDANCE DIFFERS IN THE POTENTIAL FOR ANOTHER WAVE TO MOVE NORTHEASTWARD UP THE COAST...SO WE MAINTAIN A CHANCE OF SHOWERS. OTHER THAN THE BRIEF CHANCE OF A WARM INTERLUDE WITH THE PASSING WAVE LATE SUNDAY INTO MONDAY...TEMPERATURES WILL BE ON THE COOL SIDE OF NORMAL. && .AVIATION /14Z THURSDAY THROUGH MONDAY/... OVERALL THEME OF FORECAST DOES NOT CHANGE APPRECIABLY THROUGH FRIDAY NIGHT AS THE REGION WILL REMAIN ENTRENCHED IN MARITIME FLOW/CAD WEDGE. MAIN ISSUE WILL BE TIMING IN IFR RESTRICTION (MORE LIKELY OVERNIGHT THAN DURING DAY). FOG...SHOWERS...AND DRIZZLE COULD REDUCE VSBY AT TIMES...BUT CLOUDS WILL BE THE BIGGER ISSUE. BEST CHANCE AT POTENTIALLY MODERATE RAIN WILL CROSS THE AREA DURING THE MID MORNING HOURS (QUICKER THAN PREVIOUS FORECASTS). ANY AFTERNOON THUNDERSTORMS SHOULD STAY SOUTH OF CHO. COULD SEE A RISE TO SOLID VFR CONDITIONS ON SATURDAY...BUT ADDITIONAL RAIN AND LOW CLOUDS WILL ARRIVE SATURDAY NIGHT AND CONTINUE THROUGH MONDAY IF NOT LONGER. && .MARINE... ONSHORE FLOW WILL CONTINUE THROUGH SATURDAY. GENERALLY EXPECTING 5- 10 KT WITH OCCASIONAL INCREASES TO 15 KT. SOME GUIDANCE INDICATES PERIODIC FLIRTING WITH SCA-LEVEL GUSTS THIS AFTERNOON...BUT LACK OF CONSISTENT SIGNAL PRECLUDES A HEADLINE FOR NOW. SAME GOES FOR FRIDAY AFTERNOON. WINDS MAY TURN MORE TO THE SE SATURDAY NIGHT BUT REMAIN SUB-SCA. BETTER CHANCE OF SCA CONDITIONS SUNDAY AND MONDAY WITH A MORE POTENT LOW PRESSURE SYSTEM MOVING THROUGH. && .TIDES/COASTAL FLOODING... WATER LEVELS REMAIN ANOMALOUSLY HIGH DUE TO EASTERLY FLOW ALONG THE WESTERN SHORE OF THE CHESAPEAKE BAY AND PORTIONS OF THE TIDAL POTOMAC. WITH MINOR FLOODING OCCURRING ALONG THE CHESAPEAKE...WILL KEEP COASTAL FLOOD ADVISORIES IN PLACE INTO THE EARLY AFTERNOON...EXCEPT ST MARYS COUNTY WHERE HIGH TIDE HAS PASSED AND WATER LEVELS ARE DROPPING. HAVE ALSO ISSUED ADVISORIES ALONG THE TIDAL POTOMAC IN THE DC METRO AREA WITH MINOR FLOODING FORECAST THIS AFTERNOON. WITH OUR AREA EXPECTED TO REMAIN ON THE NORTH SIDE OF THE FRONT WITH PERSISTENT EASTERLY FLOW...MINOR FLOODING WILL REMAIN A CONCERN FOR THE NEXT SEVERAL DAYS. && .LWX WATCHES/WARNINGS/ADVISORIES... DC...COASTAL FLOOD ADVISORY UNTIL 4 PM EDT THIS AFTERNOON FOR DCZ001. MD...COASTAL FLOOD ADVISORY UNTIL NOON EDT TODAY FOR MDZ018. COASTAL FLOOD ADVISORY UNTIL 3 PM EDT THIS AFTERNOON FOR MDZ011-014. VA...COASTAL FLOOD ADVISORY UNTIL 4 PM EDT THIS AFTERNOON FOR VAZ054. WV...NONE. MARINE...NONE. && $$ SYNOPSIS...RCM NEAR TERM...ADS/HTS SHORT TERM...ADS LONG TERM...RCM AVIATION...ADS/RCM MARINE...ADS/RCM TIDES/COASTAL FLOODING...MJM/RCM

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