Area Forecast Discussion
Issued by NWS Sterling, VA

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000 FXUS61 KLWX 141919 AFDLWX AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC 219 PM EST SUN DEC 14 2014 .SYNOPSIS... HIGH PRESSURE WILL BUILD OVERHEAD THROUGH TONIGHT BEFORE SLOWLY MOVING TO OUR EAST MONDAY THROUGH MONDAY NIGHT. A COLD FRONT WILL PASS THROUGH THE AREA LATER TUESDAY INTO TUESDAY NIGHT AND HIGH PRESSURE WILL RETURN FOR THE WEDNESDAY THROUGH FRIDAY. LOW PRESSURE MAY IMPACT THE AREA NEXT WEEKEND. && .NEAR TERM /THROUGH MONDAY/...
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SURFACE HIGH PRESSURE REMAINS ACROSS WEST VIRGINIA...EASTERN KY/TN AND FURTHER SOUTH THIS AFTERNOON. NW FLOW AROUND THE HIGH WILL CONTINUE THROUGH THE AFTERNOON. BOUNDARY LAYER GOES UP TO ABOUT 900MB...WITH A STRONG INVERSION RIGHT ABOVE IT. LOW LEVEL MOISTURE TRAPPED BELOW THE INVERSION IS KEEPING A STRATUS DECK OVER ALL OF MD...THE ERN WV PANHANDLE AND NORTHERN VA. UNDERNEATH THE CLOUDS...TEMPS ARE IN THE 40S WITH A FEW SPOTS IN THE LOW 50S. FURTHER SOUTH...CLEAR SKIES HAVE ALLOWED TEMPS TO REACH THE MID AND UPPER 50S. THERES ALSO PLENTY OF WIND BELOW THE INVERSION FOR GUSTS UP TO 20-25 KTS ACROSS THE NORTHERN HALF OF THE FORECAST AREA. THE HIGH WILL GRADUALLY BUILD INTO THE WESTERN HALF OF THE FORECAST AREA TONIGHT. FORECAST SOUNDINGS INDICATE CLOUDS ALREADY IN PLACE WILL PERSIST BENEATH THE INVERSION OVERNIGHT. RADIATIONAL COOLING WILL BE MORE EFFECTIVE FURTHER SOUTH...WHERE LOW TEMPS WILL DROP TO NEAR FREEZING. SLIGHTLY WARMER UNDER THE CLOUDS OVER THE NORTHERN HALF OF THE CWA...WHERE LOWS ARE EXPECTED TO BE IN THE MID TO UPPER 30S. FOR LOCATIONS ALONG AND WEST OF THE ALLEGHENY FRONT...THERE IS SOME POTENTIAL FOR FREEZING DRIZZLE TONIGHT. BOUNDARY LAYER WILL BE A LITTLE BIT DRYER HOWEVER...AND LOW TEMPS WILL BE A FEW DEGREES WARMER THAN LAST NIGHT. NOT ENOUGH CONFIDENCE TO ISSUE A FREEZING RAIN ADVISORY TONIGHT.
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&& .SHORT TERM /MONDAY NIGHT THROUGH TUESDAY NIGHT/...
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HIGH PRESSURE WILL WEAKEN AND MOVE OFF OF THE COAST MONDAY NIGHT AS LOW PRESSURE CROSSES THE SOUTHERN GREAT LAKES REGION. THE SURFACE LOW WILL BEGIN TO GRADUALLY FILL MONDAY NIGHT AND CONTINUE THROUGH THE DAY TUESDAY AS THE UPPER LEVEL LOW WEAKENS FROM A CUT-OFF LOW TO A SHORTWAVE TROUGH AND LIFTS NORTHEASTWARD THROUGH THE PERIOD. THE COLD FRONT ASSOCIATED WITH THIS SURFACE LOW WILL FOLLOW SUIT IN WEAKENING AS IT APPROACHES THE WESTERN PART OF THE CWA BEGINNING EARLY TUESDAY MORNING. WEAK WAA IN THE LOWER LEVELS AND A BLANKET OF CLOUDS WILL ENSURE THAT LOWS MONDAY NIGHT REMAIN ABOVE FREEZING AND ALL PRECIP SHOULD FALL AS RAIN. THE HIGHEST RAIN AMOUNTS SHOULD OCCUR ACROSS THE NORTHWESTERN PORTION OF THE CWA DUE TO THE PROXIMITY OF THE LOW AND THE STRUGGLE OF THE RAIN TO SURVIVE ACROSS THE APPALACHIAN CREST. THE METRO AREAS WILL SEE THEIR HIGHEST PRECIP CHANCES AROUND MIDDAY...THOUGH THE SHOWERS WILL MAINLY BE OF THE LIGHT/NUISANCE VARIETY. OUR ENTIRE AREA IS HIGHLIGHTED IN THE GENERAL THUNDER PORTION OF THE SPC DAY THREE OUTLOOK...WITH AROUND A 10 PERCENT CHANCE OF THUNDER. WHILE IT IS NOT TOTALLY IMPOSSIBLE FOR SOME THUNDER IN THE STRONGEST SHOWERS...DUE TO VERY SMALL AMOUNTS OF INSTABILITY IDEALLY LOCATED IN THE MIXED PHASE LAYER...THE OVERALL THREAT IS TOO SMALL TO INCLUDE IN THE FORECAST AT THIS TIME. GUSTY...SUB SEVERE WINDS COULD ALSO REACH THE SURFACE IN SHOWERS TUESDAY THANKS TO A MODERATELY STRONG MID/UPPER-LEVEL PREFRONTAL JET. RAIN SHOWERS SHOULD WRAP UP FROM WEST TO EAST AS THE FROPA OCCURS THROUGH THE EVENING TUESDAY...WITH RAIN CHANCES ONLY REMAINING OVER THE BAY BY MIDNIGHT. THE ARRIVAL OF A REINVIGORATING UPPER LEVEL SHORTWAVE TO THE LOW PRESSURE OVER NEW ENGLAND WILL ZONALLY ELONGATE THE SURFACE LOW TUESDAY NIGHT. WHILE THIS WILL HAVE LITTLE EFFECT ON OUR AREA IN TERMS OF PRECIP...IT WILL RESULT IN MORE WESTERLY POSTFRONTAL WINDS...WHICH WILL LIMIT THE POSTFRONTAL CAA. HOWEVER...UPSLOPING ALONG THE ALLEGHENY FRONT WILL KEEP POPS IN THE FORECAST THROUGH THE NIGHT TUESDAY FOR THE POTOMAC HIGHLANDS AND DOWNSLOPING ACROSS THE REST OF THE AREA WILL RESULT IN BREEZY WINDS AND DRY AIR.
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&& .LONG TERM /WEDNESDAY THROUGH SATURDAY/... AN UPPER LEVEL DISTURBANCE OVER THE GREAT LAKES WILL SHIFT TO THE EAST WEDNESDAY AND WEDNESDAY NIGHT BEFORE PIVOTING ACROSS THE MID ATLANTIC THURSDAY. MUCH OF THE REGION SHOULD BE DRY WITH EXCEPTION TO A CHANCE FOR SNOW SHOWERS IN THE HIGHER ELEVATIONS OF THE POTOMAC HIGHLANDS WEDNESDAY AND WEDNESDAY NIGHT. HIGH PRESSURE WILL BUILD LATE THURSDAY THROUGH FRIDAY. AS HIGH PRESSURE SLIDES TO THE DELMARVA PENINSULA AND EAST COAST LATE FRIDAY AND FRIDAY NIGHT...AN UPPER LEVEL DISTURBANCE WILL MOVE EAST ACROSS THE LOWER GREAT LAKES AND OHIO VALLEY. ENERGY AHEAD OF THE MAIN UPPER LEVEL LOW WILL COMBINE WITH SOME INCREASING MID LEVEL MOISTURE FRIDAY NIGHT INTO SATURDAY TO BRING A CHANCE OF A MIX OF LIGHT RAIN OR LIGHT SNOW. THERE ARE STILL SOME UNCERTAINTIES IN THE TRACK...INTENSITY...AND TIMING OF THE MAIN UPPER LEVEL STORM. COMPUTER MODELS ARE INDICATING THAT A SURFACE LOW COULD FORM NEAR THE COAST OF NORTH CAROLINA IN AFFILIATION WITH THIS UPPER LEVEL DISTURBANCE SOMETIME SATURDAY. SHOULD THIS COASTAL LOW DEVELOP...WE LEFT A CHANCE FOR SOME LIGHT SNOW ACROSS THE CWA FOR SATURDAY NIGHT. BY SUNDAY...THE MAIN DISTURBANCE WILL BE ACROSS NEW ENGLAND WITH A SURFACE LOW MOVING GRADUALLY OUT TO SEA. HIGH PRESSURE WILL WORK ITS WAY INTO THE REGION...RESULTING IN DRIER CONDITIONS. SOME UPSLOPE RAIN OR SNOW SHOWERS ARE POSSIBLE IN THE POTOMAC HIGHLANDS WITH A CHANCE OF SOME LINGERING RAIN OR SNOW SHOWERS IN THE NORTH AND EAST WITH RESPECT TO THE DEPARTING LOW PRESSURE. && .AVIATION /19Z SUNDAY THROUGH FRIDAY/...
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VFR CONDITIONS THROUGH TONIGHT. BALTIMORE/WASHINGTON TERMINALS WILL CONTINUE TO BE BENEATH A STRATUS CLOUD DECK WITH CIGS AROUND 035-040. SOME CHANCE THAT CIGS MAY DROP TO MVFR TONIGHT...BUT NOT ENOUGH CONFIDENCE TO INCLUDE IN TAFS. WINDS THIS AFTERNOON HAVE BEEN GUSTY FROM THE NW AT KIAD/KMRB...UP TO 25KTS AT TIMES. POTENTIAL STILL EXISTS FOR SOME GUSTS AT KDCA/KBWI...BUT MAY BE SPORADIC. THE WINDS WILL DIMINISH AROUND SUNSET THIS EVENING....WITH 10KT OR LESS FROM THE NW OVERNIGHT. VFR CONDITIONS AND LIGHT WINDS EXPECTED MONDAY WITH HIGH PRESSURE OVERHEAD. MVFR AND IFR CONDITIONS CAN BE EXPECTED TUESDAY WITH SHOWERS AND POSSIBLY LOW CLOUD DECKS AS A COLD FRONT APPROACHES THE AREA. SOUTHERLY WINDS 10K OR LESS. VFR CONDITIONS WEDNESDAY AND WEDNESDAY NIGHT. WINDS WEST TO NORTHWEST 10 TO 20 KNOTS WITH HIGHER GUSTS BUT DIMINISHING WEDNESDAY NIGHT. VFR CONDITIONS THURSDAY. WINDS NORTHWEST AROUND 10 KNOTS.
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&& .MARINE...
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CANCELLED SMALL CRAFT ADVISORY FOR THE NORTHERN CHESAPEAKE BAY AND SURROUNDING WATERS...INCLUDING BALTIMORE HARBOR. SMALL CRAFT ADVISORY REMAINS EFFECT FOR THE REST OF THE WATERS THIS AFTERNOON. GUSTS HAVE BEEN SLOW TO DEVELOP DUE TO CLOUD COVER AND COOL WATER TEMPS...BUT GIVEN UPWARD TREND IN GUSTS OVER THE POTOMAC RIVER AND THE LOWER HALF OF THE BAY...WILL KEEP THE SCA GOING FOR NOW. WITH NW FLOW ALOFT...MODELS INDICATE A MODEST SURGE OF COOLER AIR ALOFT AFTER SUNSET WHICH MAY ALSO KEEP GUSTS GOING INTO THE NIGHT...SO WILL KEEP SCA IN EFFECT FOR ALL ZONES EXCEPT THE NORTHERN TIDAL POTOMAC AND CHESAPEAKE BAY NORTH OF SANDY POINT TONIGHT. LIGHT WINDS EXPECTED MONDAY AND MONDAY NIGHT WITH HIGH PRESSURE OVERHEAD. GUSTY PREFRONTAL SOUTHERLY WINDS WILL LIKELY REQUIRE A SMALL CRAFT ADVISORY BEGINNING LATE MORNING TUESDAY...ESPECIALLY FOR AREAS PRONE TO SOUTHERLY CHANNELING. BREEZY DOWNSLOPING WINDS BEHIND THE FRONT MAY REQUIRE A SMALL CRAFT ADVISORY CONTINUING THROUGH TUESDAY NIGHT. SMALL CRAFT ADVISORIES MAY BE NEEDED WEDNESDAY WITH GUSTS TO 20 KNOTS. NO MARINE HAZARDS WEDNESDAY NIGHT AND THURSDAY.
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&& .LWX WATCHES/WARNINGS/ADVISORIES...
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DC...NONE. MD...NONE. VA...NONE. WV...NONE. MARINE...SMALL CRAFT ADVISORY UNTIL 6 AM EST MONDAY FOR ANZ532>534-537- 540-541-543. SMALL CRAFT ADVISORY UNTIL 6 PM EST THIS EVENING FOR ANZ535- 536-542.
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&& $$ SYNOPSIS...KCS NEAR TERM...KCS SHORT TERM...CEB LONG TERM...KLW AVIATION...KCS/CEB/KLW MARINE...KCS/CEB/KLW

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