Area Forecast Discussion
Issued by NWS Sterling, VA

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000 FXUS61 KLWX 221732 AFDLWX AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC 1232 PM EST SAT NOV 22 2014 .SYNOPSIS... HIGH PRESSURE OVER EASTERN NORTH CAROLINA WILL SHIFT OFFSHORE THIS AFTERNOON. A DEEPENING LOW PRESSURE SYSTEM OVER THE GREAT LAKES WILL LIFT A WARM FRONT THROUGH THE AREA SUNDAY NIGHT. AN ASSOCIATED COLD FRONT IS EXPECTED TO MOVE THROUGH MONDAY NIGHT. THE FRONT STALLS JUST OFFSHORE AS HIGH PRESSURE BUILDS ACROSS THE AREA TUESDAY. && .NEAR TERM /THIS AFTERNOON/... HIGH PRES HAS MIGRATED TO ERN N CAROLINA. BRILLIANT SUNSHINE OVR THE MID ATLC AS A RESULT. IT IS INTERESTING TO LOOK AT THE 12Z IAD SNDGS YDA AND THIS MRNG. BOTH WERE VERY DRY. FRI MRNG`S 24 HR TEMPS CHG WAS NEUTRAL AT THE SFC THEN MARKEDLY COLDER THRU 600 MB W/ A NEAR NRML LAPSE RATE THRU 800 MB THEN ISOTHERMAL TO 500 MB. THIS MRNG SHOWED MUCH COLDER TEMPS AT THE SFC THEN STRONG WRMG THRU 600 MB. THE TEMP PROFILE SHOWED A STRONG RADIATIONAL INVERSION AT THE SFC. HIGHS IN THE U40S/L50S LOOK GOOD. && .SHORT TERM /TONIGHT THROUGH SUNDAY/... RDGG WL PROTECT CWFA TNGT AS WELL. WL HV DISTURBANCES ALONG THE NWRN PERHIPHERY AS WELL AS APPROACHING FM THE S. SHUD HV CLDS NAK/DCA/SHD NWD...BUT OTRW NONE OF THIS WL AFFECT AREA. WL BE ABLE TO RADIATE AFDK...BUT SUSPECT WE/LL KEEP A PINCH OF SWLY FLOW AS WELL...SO IT WONT BE ABLE TO GET ALL THAT COLD /SPCLY ON THE RDGTOPS/. CHGS FM GOING FCST NOT THAT SGFNT. BY SUN...PVA FM SRN STREAM WL BEGIN TO AFFECT AREA...SPCLY DURING THE AFTN HRS. WL START THE DAY MOSUN...BUT CLDS WL OVERSPREAD HRS MIDDAY/ELY AFTN AND WL BRING PCPN NEWD AFT 18Z. AM MOST CONFIDENT ON RA TWD/AFTER SUNSET DUE TO CONTD INFLUENCE OF SFC RDGG AND NEED TO SATURATE LLVLS FIRST. MAXT ONCE AGN A BLEND OF MOS. && .LONG TERM /SUNDAY NIGHT THROUGH FRIDAY/... WARM FRONT WILL MOVE THROUGH THE FORECAST AREA SUNDAY NIGHT INTO EARLY MONDAY MORNING. MODELS CONTINUE TO INDICATE VERY STRONG LLJ MOVING ACROSS THE REGION...ON THE ORDER OF 50-70KTS AT 850MB. ISENTROPIC LIFT...THE LLJ AND PWATS PEAKING AROUND 1.5 INCHES WILL SUPPORT A PERIOD OF MODERATE TO HEAVY RAINFALL FOR MOST OF THE AREA...WITH OTHERWISE STEADY LIGHT RAIN. BASIN WIDE QPF EXPECTED TO BE LESS THAN AN INCH...BUT LOCALLY HIGHER AMOUNTS OF RAIN POSSIBLE. LOW TEMPS SUNDAY NIGHT WILL BE IN THE 40S...WITH LOW 50S IN SOME SPOTS ALONG AND EAST OF I-95. WARM FRONT IS EXPECTED TO BE ACROSS PA BY 12Z MONDAY MORNING...WITH A COLD FRONT APPROACHING FROM THE OHIO VALLEY. PRESSURE GRADIENT BOTH SURFACE AND ALOFT WILL BE STRONG ENOUGH FOR A BREEZY DAY...WITH S-SW WINDS GUSTING TO AROUND 20-25 MPH. SOME MODEL OUTPUT SUGGESTS SCATTERED OR ISOLATED SHOWERS OVER PORTIONS OF THE AREA...BUT KEPT POPS CORRESPONDINGLY LOW. WARM AIRMASS WILL BRING A BRIEF RETURN TO MILD TEMPERATURES...WITH HIGHS AROUND 70 EAST OF THE BLUE RIDGE AND IN THE MID TO UPPER 60S ACROSS THE VALLEYS WEST OF THE BLUE RIDGE. COLD FRONT MOVES THROUGH MONDAY EVENING. 00Z NAM SUGGESTS POTENTIAL FOR ORGANIZED SHOWERS...BUT IS NOT SUPPORTED BY GFS OR ECMWF. WINDS WILL SHIFT TO THE NW BEHIND THE FRONT. LOWS PRIMARILY IN THE 40S...WITH SOME 30S IN THE SHENANDOAH VALLEY AND HIGHLANDS. CONFIDENCE DECREASES WITH SYNOPTIC SETUP FROM TUESDAY ONWARD. GENERAL SCENARIO IS THAT HIGH PRESSURE ATTEMPS TO BUILD IN FROM THE WEST...BUT A COASTAL LOW DEVELOPS OFF THE CAROLINA COAST AND MOVES THROUGH THE OFFSHORE WATERS. 00Z GFS AND ECMWF DIFFER IN TIMING...LOCATION AND STRENGTH OF THE LOW. FCST AT THIS POINT CALLS FOR POTENTIAL SHOWERS TUESDAY EAST OF I-95...FOLLOWED BY LIGHT RAIN OR A RAIN/SNOW MIX TUESDAY NIGHT. PRECIPITATION POTENTIAL INCLUDES MOST OF THE CWA WEDNESDAY INTO WEDNESDAY NIGHT. HIGH TEMPS WEDNESDAY SHOULD BE IN THE 40S...SO ANY PRECIP SHOULD BE LIQUID. WEDNESDAY NIGHT TEMPS START ABOVE FREEZING AND DROP BELOW LATE AT NIGHT FOR MOST OF THE CWA...SO A PERIOD OF SNOW OR A RAIN/SNOW MIX POSSIBLE. HOWEVER...WITH CWA BEING ON THE BACKSIDE OF THE LOW...PRECIP AMOUNTS WILL BE HIGHLY DEPENDENT ON THE EXACT TRACK OF THE STORM. BY LATE WEEK...MODEL DIVERGENCE INCREASES WITH ECMWF FAVORING AN UPPER LOW DROPPING INTO THE GREAT LAKES WHILE GFS FAVORS THE UPPER LOW FURTHER NORTH AND A COLD FROPA ACROSS THE MID-ATLANTIC. HIGH PRESSURE BUILDS IN FOR THE START OF THE WEEKEND. && .AVIATION /18Z SATURDAY THROUGH THURSDAY/... VFR TDA-TNGT. WL HV LWRG CIGS SUN AFTN AS PCPN APPROACHES. NO RESTRICTIONS XPCTD DURING MOST OF THE DAY...BUT DETERIORATING CONDS WL BE APPRCHG FM THE SW...POTENTIALLY AFFECTING AFTN PUSH. MVFR/IFR CONDITIONS EXPECTED SUNDAY NIGHT WITH RAIN...WITH POTENTIAL FOR A PERIOD OF HEAVY RAIN. CONDITIONS IMPROVE TO VFR MONDAY MORNING...WITH GUSTY S-SW WINDS. FLIGHT CONDITIONS UNCERTAIN MIDWEEK WITH POTENTIAL FOR SOME PRECIPITATION FROM A COASTAL SYSTEM. && .MARINE... GIVEN HV SEEN MULTIPLE GUSTS A20 KT AT VARIOUS CSTL LOCATIONS AN SCA WAS ISSUED INTO THE EARLY EVENG HRS. SMALL CRAFT CONDITIONS LIKELY SUNDAY NIGHT THROUGH MONDAY AS A WARM FRONT MOVES THROUGH...FOLLOWED BY A COLD FRONT MONDAY EVENING. GUSTY WINDS POSSIBLE MIDWEEK WITH A COASTAL LOW...BUT STRENGTH AND TRACK OF THE SYSTEM IS UNCERTAIN AT THIS TIME. && .LWX WATCHES/WARNINGS/ADVISORIES... DC...NONE. MD...NONE. VA...NONE. WV...NONE. MARINE...SMALL CRAFT ADVISORY UNTIL 7 PM EST THIS EVENING FOR ANZ530>543. && $$ UPDATE...WOODY! PRVS...HTS/KCS

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