Area Forecast Discussion
Issued by NWS Sterling, VA

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000 FXUS61 KLWX 240900 AFDLWX AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC 400 AM EST WED DEC 24 2014 .SYNOPSIS...
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STRENGTHENING LOW PRESSURE WILL LIFT FROM THE DEEP SOUTH INTO THE GREAT LAKES TODAY AND TONIGHT. THAT WILL MOVE A COLD FRONT THROUGH OUR REGION TONIGHT. MILD SOUTHERN HIGH PRESSURE WILL MOVE IN FOR THE END OF THE WEEK. A WEAK COLD FRONT WILL PUSH IN FROM THE NORTHWEST SUNDAY. THEN LOW PRESSURE FROM THE DEEP SOUTH WILL RIDE UP ALONG THAT FRONT AND OVER THE REGION EARLY NEXT WEEK. COLDER HIGH PRESSURE WILL FOLLOW FOR MID WEEK.
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&& .NEAR TERM /THROUGH 6AM/...
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GENERALLY A QUARTER TO A HALF INCH OF RAIN HAS FALLEN ACROSS THE REGION AS OF 3 AM. FIRST BATCH IS MOVING OUT WITH NEXT AREA BEGINNING TO PUSH UP FROM THE SOUTHWEST.
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&& .SHORT TERM /TODAY THROUGH TONIGHT/...
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DYNAMIC AND MULTIFACETED STORM SYSTEM WILL AFFECT THE AREA THROUGH TONIGHT. SFC LOW PRESSURE WILL DEEPENS AS IT TRACKS FROM THE TN VALLEY TOWARD THE GREAT LAKES. A STRONG LLJ WILL TRANSPORT UNSEASONABLY HIGH ATMOSPHERIC MOISTURE CONTENT UP THE EASTERN SEABOARD...WITH NUMEROUS ROUNDS OF RAIN IN THE STRONG ISENTROPIC LIFT. ONE ROUND OF RAIN HAS PUSHED THROUGH MOST OF THE CWA. HI-RES MODELS INDICATING THE MIDDAY HOURS WILL BE THE FOCUS OF THE MOST WIDESPREAD RAIN...WITH SOME DRYING WORKING IN BEFORE THE FRONT PUSHES THROUGH THIS EVENING...ALTHOUGH SHOWERS MAY STILL EXIST. THEN A LINE OF SHOWERS MAY DEVELOP ALONG THE FRONT...POSSIBLY BECOMING MORE ORGANIZED EAST OF THE MOUNTAINS. WHILE NOT AN EXTREMELY FAVORABLE ENVIRONMENT...SOME POSTFRONTAL UPSLOPE RAIN AND SNOW SHOWERS MAY DEVELOP LATE TONIGHT ON THE WESTERN RIDGES. HIGH TEMPERATURES WILL BE MILD TODAY...WITH 60S MOST LIKELY ALONG AND EAST OF I-95. IT MAY BE DIFFICULT TO SCOUR OUT THE COOLER AIR WEST OF THE BLUE RIDGE...BUT 50S ARE STILL LIKELY FOR MOST. TEMPERATURES WILL ONLY GRADUALLY FALL BEHIND THE FRONT TONIGHT. IN TERMS OF POTENTIAL HAZARDS... FLOODING...CORRIDOR OF 1.5 INCH PWATS AND DEEP WARM CLOUD LAYERS WILL EXIST ALONG AND EAST OF I-95. FFG IS LOWEST IN THE METROS AND RIGHT ALONG I-95. QUESTION IS HOW MUCH OF THE QPF WILL BE REALIZED AT ONCE. THE GREATEST RISK WILL BE IF MULTIPLE CONVECTIVE ELEMENTS DEVELOP LATE AFTERNOON/EVENING...BUT DON/T HAVE CONFIDENCE IN THAT HAPPENING. WILL CONTINUE MENTION OF POSSIBLE MINOR/NUISANCE HIGH WATER IN THE HWO. SEVERE...SPC HAS TRIMMED MRGL RISK SOUTH OUT OF THE CWA. HOWEVER IF THERE IS A LOW END POTENTIAL...THE MOST FAVORED CORRIDOR WILL BE THE SAME AS ABOVE...WITH THE MUCH WARMER TEMPERATURES AND BOUNDARY LAYER MOISTURE. 00Z ARW AND NMM SHOW POSSIBLE LOW TOPPED CONVECTIVE LINE AHEAD OF THE FRONT...AND SHERB PARAMETER APPROACHES ONE. IF THIS OCCURS...SOME STRONGER GUSTS COULD MIX DOWN FROM ALOFT...EVEN WITH A LACK OF THUNDER. DID RAISE THE WX GRIDS TO CHANCE THUNDER IN THIS AREA GIVEN 00Z NAM CAPE PROFILE. WIND...INVERSION WILL LIKELY INHIBIT THE STRONG LLJ WINDS FROM REACHING THE SFC DURING THE DAY. HOWEVER AFTER THE FRONT PASSES...THE POTOMAC HIGHLANDS WILL HAVE A CHANCE TO SEE GUSTS ABOVE 40KT...MAINLY ABOVE 2500 FT. THEREFORE WILL START A WIND ADVISORY THERE AT 7 PM THIS EVENING.
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&& .LONG TERM /THURSDAY THROUGH TUESDAY/...
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WITH THE TRACK OF THE EXITING LOW MOVING N THRU THE GREAT LAKES INTO CANADA...THE SOURCE REGION FOR THE STRONG WINDS BEHIND OUR COLD FRONT IS THE MIDWEST AND PLAINS...NOT THE USUAL CANADIAN AIR. FURTHERMORE THE HIGH BUILDING IN IS MOVING UP FROM TEXAS AND THE SOUTH. COMBINE ALL THAT WITH A DOWNSLOPING WEST NORTHWEST WIND...AND TEMPS ON CHRISTMAS DAY WILL BE ABOVE NORMAL EVEN AFTER A STRONG COLD FRONTAL PASSAGE. IT WILL STILL FEEL COOL WITH THE WINDS. THE STRONG GRADIENT WITH THE COLD FRONT IS MORE INDICATIVE OF THE EXCEPTIONAL NATURE OF THE WARM AIR AHEAD OF IT THAN THE COOLER AIR BEHIND IT. HIGH PRES WILL PRODUCE A COUPLE OF MILD DAYS WITH A DECENT AMOUNT OF SUN FRI AND SAT. THEN BY SUN AND MON...A WEAK FRONT STALLS OVER THE AREA AND WAITS FOR LOW PRESSURE TO RIPPLE ALONG IT AND OVER THE REGION. ALL OF THAT SHOULD CLEAR OUT BY TUE AS COOLER MORE SEASONABLE AIR GETS PULLED IN BEHIND THE LOW.
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&& .AVIATION /09Z WEDNESDAY THROUGH SUNDAY/...
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IFR OR LOWER CIGS REMAIN POSSIBLE THROUGH THIS EVENING. VSBYS HAVE IMPROVED SOME OVERNIGHT...BUT MAY STILL HAVE PERIODS OF IFR...PARTICULARLY DURING PERIODS OF RAIN. LLWS WILL BE A CONCERN TODAY WITH A STRONG LOW LEVEL JET JUST ABOVE A SFC INVERSION. A COLD FRONT WILL PUSH THROUGH AROUND MIDNIGHT GIVE OR TAKE A FEW HOURS...SHIFTING WINDS TO THE WEST AND INCREASING IN SPEED. CIGS AND VSBYS WILL IMPROVE BEHIND THE FRONT...WITH ANY CHANCE OF SHOWERS COMING TO AN END. AS HIGH PRESSURE MOVES IN...GUSTY SFC WINDS OF 25 TO 32 KNOTS ARE EXPECTED THURSDAY DURING THE DAY. OTW...VFR CONDITIONS EXPECTED THU THRU SAT. WEAK FRONT HANGING UP ON THE REGION WITH AN AREA OF LOW PRESSURE MOVING ALONG IT EARLY NEXT WEEK SHOULD ALLOW FOR AT LEAST MVFR CONDITIONS SUN AND MON WITH THE POSS OF IFR. TUE AND WED VFR RETURNS WITH COOLER TEMPS.
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&& .MARINE...
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LIGHT AND VARIABLE WINDS WILL BECOME SOUTHERLY AND INCREASE THIS AFTERNOON TO SCA LEVELS. PERIODS OF RAIN WILL BE POSSIBLE WHICH COULD REDUCE THE VISIBILITY. A COLD FRONT WILL PASS THROUGH THIS EVENING AND SHIFT WINDS TO THE WEST...WITH GUSTS INCREASING BEHIND THE FRONT. DO NOT THINK GALES WILL BE REACHED TODAY OR TONIGHT DUE TO POOR MIXING. HOWEVER...STRONGER SHOWERS COULD BRING DOWN HIGHER GUSTS...WHICH COULD BE HANDLED WITH A SMW IF NEEDED. 20 TO 30 KT WIND GUSTS THU WILL KEEP A SMALL CRAFT ADV UP THROUGH THE DAY. THERE IS A POSSIBILITY OF NEEDING A GALE WARNING FOR MID MORNING THRU MID AFTERNOON THU. BUT THAT IS NOT THE EXPECTATION AT THIS POINT. WINDS SHOULD DIE OFF ENOUGH TO LOWER THE ADVISORY BY THU EVENING. AFTER THAT...NO MARINE ISSUES ANTICIPATED THROUGH EARLY NEXT WEEK.
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&& .TIDES/COASTAL FLOODING...
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ORNING HIGH TIDE IS THE LOWER TIDE TODAY AND SHOULD NOT BE A CONCERN. LAST EVENING...ANNAPOLIS WAS ABOUT 0.3 FEET BELOW MINOR FLOOD. ANOMALIES HAVE CONTINUED TO INCREASE AND WILL CONTINUE TO DO SO TODAY AS SOUTHERLY WINDS INCREASE. THEREFORE EVENING HIGH TIDE MAY BE CLOSE TO MINOR FLOOD AT SENSITIVE SITES. WILL ALLOW LATER SHIFTS TO MONITOR THE ANOMALIES TO SEE IF AN ADVISORY MAY BE NEEDED.
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&& .CLIMATE...
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IT HAS BEEN A RATHER CLOUDY DECEMBER. AT WASHINGTON AND BALTIMORE ONLY 2 DAYS...THE 7TH AND 17TH...HAVE HAD MORE SUN THAN CLOUDS.
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&& .LWX WATCHES/WARNINGS/ADVISORIES...
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DC...NONE. MD...WIND ADVISORY FROM 7 PM THIS EVENING TO 6 AM EST THURSDAY FOR MDZ501. VA...WIND ADVISORY FROM 7 PM THIS EVENING TO 6 AM EST THURSDAY FOR VAZ503-504. WV...WIND ADVISORY FROM 7 PM THIS EVENING TO 6 AM EST THURSDAY FOR WVZ501>503-505-506. MARINE...SMALL CRAFT ADVISORY FROM 1 PM THIS AFTERNOON TO 5 PM EST THURSDAY FOR ANZ530>534-537>543. SMALL CRAFT ADVISORY FROM 9 PM THIS EVENING TO 5 PM EST THURSDAY FOR ANZ535-536.
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&& $$ SYNOPSIS...CAS NEAR TERM...CAS SHORT TERM...ADS LONG TERM...CAS AVIATION...ADS/CAS MARINE...ADS/CAS TIDES/COASTAL FLOODING...ADS/CAS CLIMATE...CAS

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