Area Forecast Discussion
Issued by NWS Sterling, VA

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000 FXUS61 KLWX 141935 AFDLWX AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC 335 PM EDT MON APR 14 2014 .SYNOPSIS...
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HIGH PRESSURE WILL REMAIN OFF THE EAST COAST THIS EVENING. A COLD FRONT WILL CROSS THE APPALACHIANS LATE TONIGHT AND MOVE THROUGH THE AREA TUESDAY. HIGH PRESSURE WILL BUILD EAST INTO THE NORTHERN MID-ATLANTIC WEDNESDAY AND REMAIN OVER THE AREA THROUGH FRIDAY. LOW PRESSURE MAY IMPACT THE REGION ON SATURDAY.
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&& .NEAR TERM /THROUGH TUESDAY/...
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A POWERFUL SPRING STORM SYSTEM HAS BEEN SWINGING ACROSS A BETTER PART OF THE CONUS YESTERDAY INTO TODAY. A DEEP AND COLD UPPER TROUGH HAS SPENT MUCH OF TODAY PUSHING DOWN THE LENGTH OF THE PLAINS FROM CNTRL CANADA...DOWN TO THE TX GULF COAST. TO GET A FEEL FOR WHAT`S ON THE WAY...EVEN IF THE EFFECTS AREN`T SIMILAR - THE COLD FRONT HAS BEEN DROPPING TEMPS A SOLID 20-30F DEG IN JUST A FEW HRS ALONG MUCH OF THE BOUNDARY. THE PRECIP AMOUNTS W/ THIS LARGE-SCALE HAVEN`T BEEN TOO TERRIBLY HIGH...MAINLY OVER THE GULF COAST STATES WHERE MOST OF THE MOISTURE FETCH REMAINS BUT THIS WILL PLAY INTO OUR AREA GETTING MODERATE AMOUNTS OF QPF ON TUE. THE SFC LOW PRESSURE SYSTEM RESPONSIBLE FOR THE INITIAL PUSH OF COLD AIR YESTERDAY AND TODAY WILL ESSENTIALLY TAKE-OFF TOWARD THE NE TONIGHT AND LARGELY AWAY FROM OUR AREA INTO THE OVERNIGHT HRS. THE SFC LOW HERE IN THE MID AFTN HRS IS ALREADY MOVING UP THE NRN SIDE OF THE ST. LAWRENCE CHANNEL. THE COLD FRONT ASSOCIATED W/ THIS STORM SYSTEM WILL ALSO BE TAKEN AWAY W/ THE PARENT SFC LOW LATER TONIGHT...UNTIL ANOTHER SECONDARY SFC LOW DEVELOPS OVER THE CNTRL APLCNS OVERNIGHT. THIS FEATURE...IN CONCERT W/ YET ANOTHER SFC LOW DEVELOPING OVER SRN APLCNS EARLY TUE WILL THEN BRING A REJUVENATED COLD FRONT ACROSS OUR REGION MIDDAY TUE...BRINGING A NOTICEABLE AND SWIFT TANKING OF TEMPS TOMORROW. BEFORE THE SHARP TEMP DROP...WE`LL HAVE PERIODS OF RAIN MOVING ACROSS THE AREA - STARTING LATE TONIGHT FROM WEST TO EAST. THE MEAN LAYER SHEAR IS SWLY...WHICH WILL CAUSE THE INITIAL WAVES OF LIGHT TO MODERATE RAIN FROM SW-TO-NE ACROSS THE HIGHER TERRAIN AND PARTS OF THE SHENANDOAH VLY TONIGHT. AREAS EAST OF THE BLUE RIDGE TO THE COAST WILL BE THE LAST TO GET PRECIP MOVING IN...MORE TOWARD MIDNIGHT OR LATER. MOST OF THE ACTIVITY AFFECTING THE AREA FROM LATE TONIGHT INTO THE OVERNIGHT WILL BE SCATTERED...SHORT-LIVED...AND FAIRLY LIGHT. TOWARD THE PREDAWN HRS TUE...MORE WIDESPREAD SHIELD OF RAIN WILL MAKE THEIR WAY FROM THE SW AND OVER THE CWA...SPREADING GENERALLY LIGHT TO MODERATE RAIN OVER THE AREA UNDER TEMPS IN THE 50S AND 60S. THE GUSTY S-SWLY WINDS WILL CONTINUE TO SQUEEZE UP THE ERN SEABOARD AHEAD OF THE STRENGTHENING LOW PRES SYSTEM...EVEN BRINGING SOME AREAS OF THE I-95 CORRIDOR AND EAST INTO THE L70S BY DAWN. THIS WILL MAXIMIZE THE CONVECTIVE POTENTIAL DURING THE EARLY MRNG HRS. LOW CAPE VALUES IN THE COUPLE-FEW HUNDREDS WILL BE AVAILABLE FOR MUCH OF THE AREA - ESPEC THE SERN SECTION OF THE CWA...ALONG W/ A POTENT 40-50KT LOW LEVEL JET I-95 AND EAST FOR AMPLE LINEAR SUPPORT. THE CONVECTIVE NATURE OF THE PRECIP WILL THEN LIKELY TURN INTO A MORE STABLE AND STRATIFORM RAIN AS THE COLD FRONT BEGINS TO BARREL ACROSS THE AREA FROM THE POTOMAC HIGHLANDS TOWARD THE METRO AREAS LATE MRNG/EARLY AFTN. WINDS WILL BE GUSTY ANYWAY...BUT THEY`LL TURN FROM A WARM SLY BREEZE TO DRY AND COLD NW FLOW DIRECTLY BEHIND THE FRONT. TEMPS WILL START TO DROP SEVERAL DEGREES EACH HR THRU THE AFTN...DROPPING WELL INTO THE 30S/40S OVER THE WRN ZONES AND INTO THE 40S/50S E OF THE MTNS.
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&& .SHORT TERM /TUESDAY NIGHT THROUGH THURSDAY/...
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COLD FRONT MOVES OFFSHORE THROUGH THE EARLY EVENING HOURS ON TUESDAY. STRONG COLD AIR ADVECTION CONTINUES TO SUPPORT FALLING TEMPERATURES. FOLLOWED SREFS FOR POPS DECREASING FROM WEST TO EAST THROUGH EARLY EVENING. IF COLD AIR CAN CATCH UP TO THE BACK EDGE OF PRECIP QUICKLY ENOUGH...A FEW WET SNOWFLAKES COULD OCCUR BUT THE BULK OF THE PRECIP WILL END AS RAIN. FOCUS THEN TURNS TO THE COLD AIR. WITH COLD ADVECTION...MOMENTUM TRANSFER WILL KEEP GUSTY NORTHWEST WINDS GOING INTO THE NIGHT. BUT ITS THESE NORTHWEST WINDS THAT ARE BRINGING IN A MUCH COLDER AIR MASS AND DESPITE THE WIND TEMPERATURES HAVE THE POTENTIAL TO DROP BELOW FREEZING BY DAYBREAK ESPECIALLY IN THE SUBURBS. THE GROWING SEASON WILL BEGIN APRIL 15TH EAST OF THE BLUE RIDGE...WHICH MEANS THESE AREAS WILL BE CANDIDATES FOR FROST/FREEZE HEADLINES. CONSIDERING FORECAST MINIMA...WILL BE ISSUING A FREEZE WATCH FOR TUESDAY NIGHT/WEDNESDAY MORNING. HIGH PRESSURE BUILDS IN FOR WEDNESDAY. SUNSHINE WILL RETURN BUT MAXIMA MAY STRUGGLE TO REACH 50. HIGH PRESSURE WEDNESDAY NIGHT WILL ALSO PAVE THE WAY FOR ANOTHER COLD NIGHT WITH RADIATIONAL COOLING IN PLAY. ADDITIONAL FREEZE HEADLINES MAY BECOME NECESSARY WEDNESDAY NIGHT INTO THURSDAY MORNING. MODERATING TREND SHOULD BEGIN THURSDAY WITH HIGH PRESSURE MOVING OFF THE COAST.
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&& .LONG TERM /THURSDAY NIGHT THROUGH MONDAY/...
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SURFACE HIGH PRESSURE WILL DEPART INTO THE NORTH ATLANTIC THURSDAY NIGHT...LEAVING BEHIND A SURFACE RIDGE AXIS WEDGED AGAINST THE EASTERN SLOPES OF THE APPALACHIANS. THIS WILL RESULT IN A CONTINUED ONSHORE FLOW THROUGH FRIDAY. AN UPPER-LEVEL TROUGH AND SURFACE LOW PRESSURE APPROACH THE AREA FROM THE WEST LATE FRIDAY NIGHT INTO SATURDAY. THE LATEST GUIDANCE SHOWS A WIDE SPREAD IN THE DEPTH OF THE APPROACHING TROUGH AND STRENGTH OF LOW PRESSURE AT THE SURFACE. RAIN IS LIKELY FOR AT LEAST PART OF THE AREA SATURDAY...BUT THERE IS A MODERATE TO HIGH LEVEL OF UNCERTAINTY IN INTENSITY/COVERAGE. WEAK RIDGING AND MILDER WEATHER LOOKS TO BUILD INTO THE AREA LATE IN THE WEEKEND INTO EARLY NEXT WEEK.
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&& .AVIATION /19Z MONDAY THROUGH SATURDAY/...
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WE`RE STILL UNDER A HIGH PRESSURE REGIME...BUT THE STRENGTH OF A POWERFUL STORM SYSTEM OVER THE PLAINS AND UPPER MIDWEST IS CAUSING SLY WINDS AROUND THE BACKSIDE OF THE HIGH TO REMAIN GUSTY...WELL INTO THE 20-30KT RANGE. SUSTAINED SFC WINDS ARE ALSO RELATIVELY HIGH...A SIGN THAT THE LOW LEVELS ARE - AND WILL REMAIN - GUSTY THROUGHOUT THE REST OF THE DAY AND INTO THE OVERNIGHT. THE STORM SYSTEM TO OUR WEST WILL MAKE A COUPLE OF LARGE-SCALE TRANSITIONS BEFORE MOVING ACROSS THE REGION EARLY TUE - BUT ONCE IT DOES...A STRONG COLD FRONT WILL MOVE THRU AREA REGION FROM LATE MRNG INTO EARLY AFTN...W/ PERIODS OF RAIN OUT AHEAD OF AND ALONG W/ THE FRONT. WINDS WILL ALSO SHIFT FROM SLY TO NWLY W/ THE SAME POTENCY OF GUSTS IN THE 25-30KT RANGE. HIGH PRESSURE BUILDS IN FOR LESS WIND WEDNESDAY. NO SIGNIFICANT WX EXPECTED TO END THE WEEK.
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&& .MARINE...
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WINDS IN SOLID SCA RANGE THIS AFTN WILL ESSENTIALLY STAY IN THE 20-30KT RANGE THROUGHOUT THE EVE AND OVERNIGHT HRS OUT OF THE SOUTH. A STRONG COLD FRONT WILL THEN SWING ACROSS THE WATERS BY LATE AFTN TUE...SPREADING NEAR GALE GUSTS ON TUE AFTN. HIGHEST CONFIDENCE IN GALES IS BEHIND THE FRONT WITH A NORTHWEST SURGE AND GALE WARNING HAS BEEN ISSUED FOR THIS PERIOD. HIGH PRESSURE BUILDS IN FOR WEDNESDAY. SMALL CRAFT ADVISORY LEVEL WIND GUSTS ARE POSSIBLE FOR PARTS OF THE WATERS THURSDAY NIGHT...AND AGAIN OVER THE WEEKEND DEPENDING ON THE EVOLUTION OF LOW PRESSURE MOVING NEAR THE AREA.
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&& .TIDES/COASTAL FLOODING...
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POSITIVE TIDAL ANOMALIES REMAIN IN THE 1/2-3/4 FOOT RANGE FOR THE WRN SHORES OF THE MD CHSPK BAY. THE STEADY AND GUSTY SLY WINDS WILL KEEP THESE LEVELS STEADY INTO THE OVERNIGHT HRS AND THRU EARLY TUESDAY MRNG. A FULL MOON UPCOMING...LIKELY HELPING WATER LEVELS TO APPROACH MINOR FLOOD CRITERIA AT THE MORE SENSITIVE LOCATIONS AROUND TIMES OF THE HIGHER HIGH TIDES EARLY TUESDAY MRNG. CBOFS GUIDANCE HOWEVER FCSTS TIDAL LVLS BELOW MINOR COASTAL FLOODING THRESHOLDS AT ALL SITES.
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&& .CLIMATE... UNUSUALLY WARM CONDITIONS WERE OBSERVED ACROSS THE AREA EARLY THIS MORNING. LOW TEMPERATURES WERE AROUND 20 DEGREES ABOVE NORMAL. DEPENDING ON HOW LOW TEMPERATURES GET THIS EVENING...RECORD DAILY HIGH MINIMUM TEMPERATURES COULD BE TIED OR BROKEN AT DCA...BWI AND IAD. BELOW IS A TABLE OF RECORDS FOR THE DAY AND LOW TEMPERATURES OBSERVED SO FAR. SITE...PREVIOUS RECORD...LOW SO FAR... DCA....63 F IN 1896......65 F......... BWI....62 F IN 1896......62 F......... IAD....58 F IN 1972......63 F......... && .LWX WATCHES/WARNINGS/ADVISORIES...
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DC...FREEZE WATCH FROM LATE TUESDAY NIGHT THROUGH WEDNESDAY MORNING FOR DCZ001. MD...FREEZE WATCH FROM LATE TUESDAY NIGHT THROUGH WEDNESDAY MORNING FOR MDZ004>007-009>011-013-014-016. VA...FREEZE WATCH FROM LATE TUESDAY NIGHT THROUGH WEDNESDAY MORNING FOR VAZ036>040-042-050>057-501-502. WV...NONE. MARINE...SMALL CRAFT ADVISORY UNTIL 6 PM EDT TUESDAY FOR ANZ530>543. GALE WARNING FROM 6 PM TUESDAY TO 6 AM EDT WEDNESDAY FOR ANZ530>543.
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&& $$ SYNOPSIS...BPP NEAR TERM...GMS SHORT TERM...BPP LONG TERM...DFH AVIATION...GMS/BPP/DFH MARINE...GMS/BPP/DFH TIDES/COASTAL FLOODING...GMS CLIMATE...DFH

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