Area Forecast Discussion
Issued by NWS Sterling, VA

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000 FXUS61 KLWX 231846 AFDLWX AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC 246 PM EDT THU OCT 23 2014 .SYNOPSIS... LOW PRESSURE EAST OF THE DELMARVA WILL SLOWLY TRACK EAST OF LONG ISLAND TODAY. HIGH PRESSURE WILL RETURN TO THE MID ATLANTIC TONIGHT AND REMAIN OVER THE AREA INTO THE FIRST PART OF NEXT WEEK. && .NEAR TERM /THROUGH TONIGHT/...
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OFFSHORE LOW PRESSURE CONTINUES TO PULL AWAY FROM THE AREA...WHILE HIGH PRESSURE BUILDS IN OVER THE OHIO VALLEY. STRONG PRESSURE GRADIENT REMAINS OVER THE REGION...WITH NWLY WINDS GUSTING 20-30KT. CLOUD SHIELD PERSISTS OVER ERN MD AND PORTIONS OF NRN VA/WASHINGTON DC METRO...AND OVER THE POTOMAC HIGHLANDS WHERE UPSLOPE CONDITIONS ARE PRESENT. SOME UPSLOPE SHOWERS ARE POSSIBLE...BUT OTHERWISE DRY WEATHER EXPECTED THROUGH THE REST OF THE AFTERNOON. HIGH TEMPS IN THE 60S OVER MOST LOCATIONS LATE THIS AFTERNOON. TIME OF PARTIAL ECLIPSE - 5:50 TO 6;15 PM. APPROX 1/4 OF SUN WL BE COVERED IN THE SWRN SKY. CLDS SHOULD BE DIMINISHING DURG THIS TIME...EXCEPT OVER NORTHERN AND EASTERN PORTIONS OF THE FORECAST AREA. BEST CHCS FOR VIEWING WL MOST LKLY BE IN THE WRN PART OF THE CWA AND CENTRAL SHEN VLLY. LOW PRESSURE CONTINUES TO PULL AWAY TONIGHT WHILE HIGH PRESSURE BUILDS EASTWARD...REACHING EASTERN WV BY EARLY MORNING. GUSTS EXPECTED TO END AFTER SUNSET AS BOUNDARY LAYER DECOUPLES. HIGH PRESSURE SHOULD BE CLOSE ENOUGH TO THE WESTERN COUNTIES OF THE CWA TO ALLOW FOR A PERIOD OF GOOD RADIATIONAL COOLING. THIS WILL RESULT IN LOWS NEAR FREEZING IN THE POTOMAC HIGHLANDS AND SOME UPPER 30S IN THE SHELTERED VALLEYS. LOWS WILL BE IN THE 40S ELSEWHERE.
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&& .SHORT TERM /FRIDAY THROUGH SATURDAY NIGHT/...
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HIGH PRESSURE CONTINUES TO BUILD IN FROM THE WEST FRIDAY. THERE WILL BE SOME LEFTOVER PRESSURE GRADIENT FROM THE COASTAL LOW...WHICH WILL BE REACHING THE MARITIMES BY THE END OF THE DAY...SO NW WINDS WILL GUST TO AROUND 20KT IN THE LATE MORNING AND AFTERNOON. WITH MORE SUNSHINE...SLIGHTLY HIGHER 1000-500MB THICKNESS AND A PARTIAL DOWNSLOPE WIND COMPONENT...HIGHS WILL BE A FEW DEGREES WARMER THAN THURSDAY. MID TO UPPER 60S EXPECTED EAST OF THE BLUE RIDGE AND IN THE SHENANDOAH VALLEY...AND MID 50S TO LOW 60S AT HIGHER ELEVATIONS. HIGH PRESSURE PERSISTS TO THE SOUTH AND WEST FRIDAY NIGHT THROUGH SATURDAY. WEAK COLD FRONT MOVES THROUGH SATURDAY NIGHT...BUT WILL HAVE LIMITED MOISTURE. DRY FRONTAL PASSAGE EXPECTED...EXCEPT POSSIBLY SOME UPSLOPE RAIN OVER THE POTOMAC HIGHLANDS SATURDAY NIGHT. HIGHS GENERALLY MID TO UPPER 60S FRIDAY...AND UPPER 60S TO AROUND 70 IN SOME SPOTS SATURDAY. LOWS IN THE 40S FRIDAY NIGHT IN THE METRO AREAS...AND IN THE MID TO UPPER 30S IN AREAS THAT RADIATE WELL FRIDAY NIGHT. SATURDAY NIGHT LOWS GENERALLY IN THE 40S.
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&& .LONG TERM /SUNDAY THROUGH WEDNESDAY/...
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MOST OF THE LONG TERM PERIOD WILL FEATURE A RATHER BENIGN PATTERN...WITH DEEP-LAYER RIDGING ANCHORED ALONG THE EAST COAST FOR THE FIRST HALF OF NEXT WEEK. THERE ARE A FEW FEATURES OF NOTE...1- A PRESSURE SURGE/SECONDARY COLD FRONT SUNDAY ACCOMPANIED BY GUSTY WINDS AND FALLING TEMPERATURES BUT NO PRECIPITATION ON SUNDAY...2- A COLD FRONT ON WEDNESDAY...AND 3- A POTENTIAL APPROACHING TROUGH LATER IN THE WEEK. ALL GUIDANCE IS IN VERY GOOD AGREEMENT THROUGH THE MIDDLE OF NEXT WEEK...BUT THEN DIVERGES AFTER THAT. DEEP-LAYER /DRY/ NORTHWESTERLY FLOW WILL PREVENT APPRECIABLE MOISTURE FROM MOVING OVER THE REGION ON SUNDAY AS AN UPPER-LEVEL TROUGH SWINGS BY TO THE NORTH OVER NEW ENGLAND. THUS THE REFLECTION AT THE SURFACE IN THE FORM OF A COLD FRONT WILL NOT BE ACCOMPANIED BY ANY PRECIPITATION. WINDS WILL INCREASE THROUGH THE DAY AFTER THE FRONT MOVES THROUGH AND COULD BE GUSTY. THESE GUSTY WINDS WILL USHER IN A COOLER AIRMASS SUNDAY NIGHT...WITH LOW TEMPERATURES DROPPING TO FREEZING OVER PORTIONS OF THE WESTERN SLOPES. RIGHT NOW THE AREAS THAT ARE MOST LIKELY TO FALL TO FREEZING HAVE ALREADY HAD THEIR GROWING SEASON ENDED BY A FREEZE EARLIER THIS WEEK...BUT IF WINDS DIE OFF QUICKER THAN CURRENTLY FORECAST DURING THE EVENING MORE WIDESPREAD FROST/FREEZE CONDITIONS WILL BE POSSIBLE OVER THE HIGHLANDS. THE AIRMASS WILL REBOUND QUICKLY EARLY NEXT WEEK AS HIGH PRESSURE SETS UP JUST OFF THE SOUTHEAST COAST...SETTING UP A SOUTHWESTERLY RETURN FLOW. MODELS/ENSEMBLES ARE IN VERY GOOD AGREEMENT REGARDING THE TIMING OF A COLD FRONT WEDNESDAY AFTERNOON...WHICH MAY BRING RAIN SHOWERS TO THE AREA. HOWEVER THE BEST UPPER-LEVEL FORCING PASSES OVER THE WESTERN GREAT LAKES SO AT THE MOMENT PRECIPITATION WOULD LIKELY BE OF THE MORE SCATTERED VARIETY. BEYOND THIS TIME IS WHEN THE MODELS DIVERGE...WITH NON-NCEP GUIDANCE DEPICTING A FLAT SHORTWAVE APPROACHING THE EAST COAST...WHILE THE GFS/SEVERAL GEFS MEMBERS HAVE A MUCH DEEPER TROUGH AND IMPENDING CYCLOGENESIS NEAR THE MID-ATLANTIC BY THE END OF NEXT THURSDAY. THE UNCERTAINTY STEMS FROM SPREAD IN HOW GUIDANCE HANDLES A LARGE UPPER-LEVEL LOW MOVING OUT OF THE GULF OF ALASKA...WITH THE GFS SLOWER/DEEPER RESULTING IN WEST COAST RIDGING/DEEPER EAST COAST TROUGHING...AND THE NON-NCEP GUIDANCE A LITTLE QUICKER BRINGING THE UPPER LOW CLOSER TO THE NORTHWEST COAST AND FLATTENING OUT THE DOWNSTREAM FLOW RESULTING IN A LESS AMPLIFIED PATTERN IN OUR NECK OF THE WOODS. THE MAJORITY OF THE GUIDANCE AND TELECONNECTIONS WOULD TEND TO FAVOR A LESS AMPLIFIED PATTERN AT THE MOMENT BUT THAT STRAYS FROM THE PATTERN WE HAVE SEEN OVER THE LAST SEVERAL WEEKS. TIME WILL BE THE BEST INDICATOR AS TO WHETHER OR NOT THE PATTERN IS READY FOR A CHANGE OR IF THE MID-ATLANTIC IS IN STORE FOR ANOTHER LARGE AND SLOW-MOVING AREA OF LOW PRESSURE AND STORMINESS LATE NEXT WEEK.
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&& .AVIATION /18Z THURSDAY THROUGH TUESDAY/...
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VFR THIS AFTERNOON WITH NW WINDS GUSTING 20-30KT. GUSTS END AFTER SUNSET THIS EVENING...WITH NW FLOW AROUND 10KT...LIGHTER AT KCHO. VFR CONTINUES FRIDAY WITH NW WINDS 10-15KT...GUSTING TO 20KT LATE MORNING THROUGH AFTERNOON. VFR FRIDAY NIGHT THROUGH SATURDAY NIGHT WITH LIGHTER WINDS. VFR CONDITIONS EXPECTED SUN-MON NIGHT. GUSTY NW FLOW SUN UP TO 25 KTS POSSIBLE...DIMINISHING SUN NIGHT INTO MON AROUND 10 KTS OR LESS.
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&& .MARINE...
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SMALL CRAFT ADVISORY REMAINS IN EFFECT FOR ALL WATERS...WITH GUSTS 20 TO 30KT. MODELS ARE ALSO POINTING TO A POTENTIAL BRIEF INCREASE IN GUSTS EARLY THIS EVENING...SO WILL CONTINUE TO MONITOR THAT POSSIBILITY. SCA EXPIRES AT MIDNIGHT FOR NORTHERN TIDAL POTOMAC AND CHESAPEAKE BAY ZONES...BUT RENEWS FRIDAY MORNING AS GUSTS AROUND 20KT ARE EXPECTED MID MORNING THROUGH THE AFTERNOON. LIGHTER WINDS FRI NIGHT THROUGH SAT NIGHT UNDER HIGH PRESSURE. A PRESSURE SURGE BEHIND A DRY COLD FRONT WILL LIKELY LEAD TO SOLID SMALL CRAFT ADVISORY CONDITIONS OVER THE WATERS DURING THE DAY ON SUNDAY INTO SUNDAY EVENING. WINDS/SEAS SUBSIDE MONDAY INTO MONDAY NIGHT...BEFORE SOUTHERLY CHANNELING BETWEEN OFFSHORE HIGH PRESSURE AND A COLD FRONT APPROACHING FROM THE OHIO VALLEY COULD RESULT IN SMALL CRAFT ADVISORY CONDITIONS TUESDAY INTO WEDNESDAY.
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&& .LWX WATCHES/WARNINGS/ADVISORIES... DC...NONE. MD...NONE. VA...NONE. WV...NONE. MARINE...SMALL CRAFT ADVISORY UNTIL MIDNIGHT EDT TONIGHT FOR ANZ530-531- 535-536-538>540-542. SMALL CRAFT ADVISORY FROM 9 AM TO 6 PM EDT FRIDAY FOR ANZ530- 531-535-536-538>540-542. SMALL CRAFT ADVISORY UNTIL 6 PM EDT FRIDAY FOR ANZ532>534-537- 541-543. && $$ SYNOPSIS...KCS NEAR TERM...KCS SHORT TERM...KCS LONG TERM...DFH AVIATION...KCS/DFH MARINE...KCS/DFH

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