Area Forecast Discussion
Issued by NWS Sterling, VA

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000 FXUS61 KLWX 260144 AFDLWX AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC 844 PM EST SUN JAN 25 2015 .SYNOPSIS... HIGH PRESSURE BUILDS INTO THE MID ATLANTIC STATES BRIEFLY TODAY. LOW PRESSURE OVER IOWA WILL TRACK ACROSS SOUTHERN VIRGINIA TONIGHT...STRENGTHENING AS IT MOVES UP THE COAST MONDAY AND TUESDAY. HIGH PRESSURE IS THEN EXPECTED THROUGH MIDWEEK. && .NEAR TERM /THROUGH MONDAY/... SFC LOPRES 1005 MB BTWN SDF AND LWX. HWVR...THE WATER VAPOR LOOP DEPICTS AN IMPRESSIVELY ROBUST SYSTEM...EVEN CRANKING OUT A BIT OF LTNG ACRS DIXIE. ITLL STILL BE SVRL HRS THOUGH BEFORE THE CATALYST FOR ANY SGFNT PCPN WL REACH CWFA. TIL THEN...ANY PCPN SHUD BE REAL LGT...IE SPRINKLES OR FLURRIES. SINCE CLDS HV OVERSPREAD AREA...TEMPS NOT DROPPING MUCH. BELIEVE EVAP COOLING WL BE THE TRIGGERING FACTOR FOR THAT TO HPPN. WITH THAT IN MIND...WL BE MAKING A FEW SMALL TWEAKS TO THE FCST. WL BE PADDING SNW ACCUM TO THE CENTRAL SHEN VLY/BLURDG...TO ACCT FOR DYNAMICAL COOLING/PCPN PRODUCTION INVOF PVA. THAT WUD PROVIDE SUFFICIENT ACCUMS TO ADD THE CENTRAL VA BLUE RIDGE ZONE TO A WINTER WX ADVY. WL ALSO BE BUMPING MIN-T UPWD BY A DEGF OR TWO FM CHO-DCA-NAK. NO CHGS TO THE SYNOPTIC EVOLUTION AS DESCRIBED PREVIOUSLY. WL LEAVE THAT PART OF THE DSCN BELOW. CONCERNING THE SENSIBLE WEATHER...PCPN PUSHES EAST INTO THE AREA...FOLLOWING THE MASON DIXON LINE AS A SHORTWAVE LIFTS NORTH. TIMED THE PCPN FOLLOWING A BLEND OF THE HIRES ARW/NMM...WHICH KEEPS THE PCPN THIS EVENING MAINLY NORTH OF THE DC/BALTIMORE METROS. AS THE LOW NEARS OVERNIGHT AND THE TROUGH BEGINS TO ROTATE HEADING TO THE NEGATIVE TILT...THE PCPN OVERSPREADS THE AREA...COMING FROM A SOUTH AND WEST POSITION. TEMPS INITIALLY IN THE UPPER 30S/LOWER 40S THIS EVENING WOULD SUGGEST ALL RAIN...WITH SOME SNOWFLAKES MIXING IN. AS THE BETTER DYNAMICALLY FORCING MOVES THROUGH...WILL SEE THE PCPN CHANGING TO ALL SNOW FROM A N TO S PATH. 12Z NAM AND SREF BUFKIT SOUNDINGS ARE THE COLDER SOLUTIONS...BUT REALLY LAG THE CHANGE OVER. THE 12Z GFS...A MUCH WARMER SOLUTION...HOLDS ONTO THE RAIN FOR MANY PORTIONS OF THE AREA WELL INTO MONDAY BEFORE THE CAA REALLY TAKES HOLD. WAS INITIALLY IMPRESSED WITH 850MB TEMPS A COUPLE DAYS AGO DROPPING TO -7 DEGREES CELSIUS...BUT NOW GFS/ECMWF AND NAM ALL KEEP AROUND -2 DEGREES CELSIUS THRU MONDAY. THE THINKING IS IT WILL TAKE THE HEAVIER QPF AMTS TO RESULT IN AN ALL SNOW SOLUTION AND AS SUCH HAVE TIME THE CHANGE OVER TO CORRESPOND AS THE HEAVIER PCPN MOVES IN. QPF AMTS WERE TRICKY...WITH GFS ON THE HIGHER END AND THEN THE ECMWF AND NAM ON THE LOWER SIDE. TOOK A BLEND OF THE GFS/ECMWF TO ACCOUNT FOR THE SPREAD. WHEN CALCULATING SNOW TOTALS...KEPT WITH A 10:1 RATIO FOR TONIGHT. WOULD LIKE TO STRESS THAT THE TIMING OF THE CHANGEOVER WILL BE CRUCIAL TO THE SNOW TOTALS FOR TONIGHT...WITH SOME AREAS MAYBE GETTING NOTHING...AND SOME SEEING AN ADDITIONAL 1-2 INCHES. THE LOW PUSHES OFFSHORE WITH THE UPPER LVL TROUGH BCMG NEGATIVELY TILTED DURING THE DAY. AS THE LOW MOVES EAST...AN EASTERLY FLOW SET UP WILL KEEP PLENTY OF MOISTURE BEING INJECTED IN OVER THE AREA THROUGHOUT THE DAY. ON GOING PCPN DURING THE PERIOD AS THE UPPER LVL ENERGY SHIFTS FROM THE WESTERN PORTIONS OF THE CWA AND ALIGNS ALONG A LINE PARALLEL TO THE CHESAPEAKE BAY. HAVE TIMED OUT THE HEAVIEST PCPN CORRESPONDING TO THE BETTER FRONTOGENETIC FORCING...WHICH HAS THE LINE OF HEAVIEST PCPN LINING THE BLUE RIDGE IN THE MORNING. 12Z NAM AND GFS HAVE CAPTURED THIS WITH THE ECMWF HINTING AT IT. CONTINUED TO USE A BLEND OF THE GFS AND ECMWF FOR QPF TOTALS THROUGHOUT THE DAY MONDAY. AS FOR PCPN TYPES...EXPECTING TO SEE ACTUALLY A LITTLE WARMING IN THE MORNING...THEN SHOULD SEE DECREASING TEMPS HEADING INTO THE AFTN AS THE COLDER AIR IS USHERED ON THE BACKSIDE OF THE DEEPENING LOW...NOW OFFSHORE. THINKING THE TYPICALLY COLDER AREAS OF BALTIMORE METRO EXTENDING TO THE SOUTH AND WEST OF DC METRO WILL STAY COLDER DURING THE TIME AS A NORTHEAST FLOW SETS UP. SO WILL KEEP THEM ALL SNOW...WITH RAIN/SNOW MIX TO THE SOUTH...OR POSSIBLY EVEN A PERIOD OF ALL RAIN IN THE MORNING. AS THE TEMPS COOL IN THE AFTN...EXPECTING EVERYWHERE BUT SOUTHERN MD TO BECOME SNOW. AGAIN...SHOULD BE NOTED...ANY DIFFERENCE IN P-TYPE WILL CHANGE THE SNOW TOTALS...ESP CONSIDERING THAT AS THE DAY PROGRESSES AND WE GET COLDER AIR...SHOULD EXPECT TO SEE INCREASING SNOW RATIOS. && .SHORT TERM /MONDAY NIGHT THROUGH TUESDAY NIGHT/... OFFSHORE LOW PRESSURE STRENGTHENS RAPIDLY MONDAY NIGHT...WHILE AN UPPER LOW MOVES ACROSS THE CWA INTO THE ATLANTIC OCEAN. ENOUGH MOISTURE OVER THE AREA...COMBINED WITH TEMPS BELOW FREEZING OVER MOST OF THE CWA...WILL RESULT IN CONTINUED SNOW. MAIN QUESTION FOR MONDAY NIGHT PERIOD WILL BE WHETHER AN AXIS OF HEAVIER SNOW WILL SET UP WEST OF CHESAPEAKE BAY BEFORE LIFTING OFF TO THE NORTHEAST. A WINTER STORM WATCH HAS BEEN ISSUED FOR THE MARYLAND COUNTIES ALONG THE WESTERN SHORE OF CHESAPEAKE BAY. WL BE AWAITING 00Z GDNC. MAY MAKE SOME DECISION AT THAT TIME IF SUFFICIENT CONSISTENCY DISPLAYED ON WHERE THE BACK EGDE OF THE PCPN SHIELD WL RESIDE. FURTHER WEST...ANOTHER INCH OR SO OF SNOW IS LIKELY ACROSS NORTH CENTRAL MD...THE EASTERN WV PANHANDLE...THE WASHINGTON DC METRO AND NORTHERN VA. REFRAINED FROM EXTENDING THE WINTER WX ADVISORY AT THIS TIME DUE TO THE LIKELIHOOD THAT ADDITIONAL SNOW WOULD TAKE PLACE AFTER EVENING RUSH HOUR...AND END BEFORE THE TUESDAY MORNING RUSH. THE LOW WILL CONTINUE TO PUSH TO THE NORTHEAST TUESDAY...ALTHOUGH GFS AND ECMWF DIFFER ON WHETHER IT PROGRESSES FARTHER THAN LONG ISLAND. BEST CHANCE FOR ADDITIONAL SNOW ACCUMULATION CONTINUES TO BE ALONG THE WESTERN SHORE OF CHESAPEAKE BAY...WITH SNOW OTHERWISE ENDING FROM WEST TO EAST ACROSS THE CWA. COLD AIR WILL ADVECT INTO THE REGION WITH NORTHERLY FLOW AROUND THE BACK SIDE OF THE LOW...WITH GUSTY WINDS LIKELY, HIGH TEMPS TUESDAY WITH BE IN THE 30S. COMBINATION OF STRONG HIGH PRESSURE TO THE WEST AND THE OFFSHORE LOW EAST OF NEW ENGLAND WILL CONTINUE BRING IN VERY COLD AIR FROM CANADA TUESDAY NIGHT. LOW TEMPS WILL DROP INTO THE TEENS OVER MUCH OF THE CWA...WITH LOW 20S ALONG AND EAST OF I-95. ANY REMAINING PRECIP COMES TO AN END TUESDAY NIGHT...EXCEPT POTENTIAL UPSLOPE SNOW OVER THE POTOMAC HIGHLANDS. && .LONG TERM /WEDNESDAY THROUGH SUNDAY/... HIGH PRESSURE WILL BUILD ACROSS THE REGION WEDNESDAY AND WEDNESDAY NIGHT. DRY CONDITIONS EXPECTED WITH HIGH AND LOW TEMPERATURES ABOUT 10 DEGREES BELOW NORMAL. HIGH PRESSURE WILL MOVE EAST THURSDAY TO ALLOW FOR A GREAT LAKES LOW PRESSURE SYSTEM TO DRAG A COLD FRONT ACROSS THE REGION LATE THURSDAY AND THURSDAY NIGHT. THERE WILL LIKELY BE A PERIOD OF LIGHT RAIN AND LIGHT SNOW ALONG THE LOW`S WARM FRONT AND AHEAD OF THE LOW PRESSURE SYSTEM. AS WE VENTURE INTO THURSDAY NIGHT AND THE LOW PASSES OVERHEAD WITH A TRAILING COLD FRONT...SNOW SHOWERS ARE EXPECTED AND COULD LEAD TO A SMALL ACCUMULATION. ADDITIONAL AND HIGHER ACCUMULATIONS ARE EXPECTED ALONG THE WESTERN RIDGES IN THE POTOMAC HIGHLANDS DUE TO UPSLOPE WIND. TEMPERATURES WILL REMAIN BELOW NORMAL BY ABOUT 3 TO 5 DEGREES. THERE IS A CHANCE FOR LINGERING SNOW SHOWERS FRIDAY...MAINLY IN THE WEST AND NORTH AS AN UPPER LEVEL TROUGH OF LOW PRESSURE PIVOTS ACROSS THE REGION. A DOWNSLOPING WIND OFF OF THE POTOMAC HIGHLANDS AND BLUE RIDGE SHOULD SUPPRESS A LOT OF THE SNOW SHOWERS. HIGH PRESSURE WILL BUILD INTO THE REGION LATE FRIDAY THROUGH SUNDAY...ALLOWING FOR DRIER AND MORE PEACEFUL WEATHER CONDITIONS. TEMPERATURES SHOULD REMAIN BELOW NORMAL. && .AVIATION /02Z MONDAY THROUGH FRIDAY/... VFR CONDS PREVAIL ACRS THE TERMINALS ATTM. ANTICIPATE FLGT CONDS DROPPING BEFORE MRNG PUSH AS PCPN ARRIVES. HV PUSHED LIFR BACK INTO MID MRNG. AM CONCERNED THAT PCPN PRIOR TO THAT WL EITHER BE LGT OR HV A HEALTHY CONTRIBUTION FM RA /OUTSIDE OF MRB/. ONCE AOB IFR CONDS ARRIVE...THEY WL LKLY LAST THRU MON MORNING WITH PERIODS OF HEAVIER SNOW. PCPN TYPE QUESTIONABLE AS PSBL RAIN/SNOW MIX OR ALL RAIN AT KDCA/KBWI/KCHO AT FIRST...THEN BCMG ALL SNOW AFTR 12Z. OTHER TERMINALS MORE LIKELY ONLY A BRIEF PERIOD OF RAIN/SNOW MIX BCMG ALL SNOW OVERNIGHT. ONGOING PCPN MONDAY WITH SNOW...IFR OR LOWER CONDITIONS LIKELY. ANOTHER ROUND OF HEAVIER PCPN (ALL SNOW) MON NIGHT INTO TUES KEEPS IFR OR LOWER CONDITIONS IN PLACE. SUB-VFR CONDITIONS LIKELY WITH LIGHT SNOW MONDAY NIGHT. HEAVIER MAY DEVELOP MONDAY NIGHT OR TUESDAY MORNING NEAR KBWI/KMTN WITH N-NW WINDS GUSTING 20-25KT. SNOW MAY CONTINUE AT KBWI/KMTN TUESDAY. ANY LEFTOVER SNOW AT THE OTHER TERMINALS SHOULD END. GUST NW WINDS EXPECTED ACROSS THE REGION...AROUND 20-25KT...WITH SOME 30KT GUSTS PSBL. VFR TUES NIGHT. GUSTY NW WINDS CONTINUE. VFR CONDITIONS WEDNESDAY. HOWEVER...NORTHWEST WINDS WILL BE GUSTING 20 TO 30 KNOTS. IFR OR PERHAPS LIFR CONDITIONS COULD DEVELOP THURSDAY WITH PERIODS OF LIGHT RAIN AND LIGHT SNOW NEAR THE TERMINALS WITH AN APPROACHING LOW PRESSURE SYSTEM. && .MARINE... SUB-SCA CONDITIONS CONTS THIS EVNG. WINDS WL BE INCRSG OVNGT...HWVR THE BEST CHC FOR GUSTS TO 20 KTS LOOKS TO BE TWD DAWN...AND ESPECIALLY THEN DURING THE DAY MONDAY. GUSTY N-NW WINDS EXPECTED ACROSS THE WATERS MONDAY NIGHT AS LOW PRESSURE STRENGTHENS OFFSHORE. WL EXPAND GLW TO INCL THE ENTIRE CHSPK BAY. MID-UPR PTMC A BIT TOO FAR WEST...AND AM NOT CERTAIN HOW FAR WEST THE P-GRAD WUD EXTEND. GALE MAY NEED TO BE EXPANDED BY TUESDAY MORNING AS COLDER AIR ALOFT ALLOWS BETTER MIXING. SMALL CRAFT ADVISORIES ARE LIKELY WEDNESDAY MORNING AS NORTHWEST WINDS GUST 20 TO 30 KNOTS. SMALL CRAFT ADVISORIES MAY BE NEEDED WEDNESDAY AFTERNOON...DEPENDING ON HOW FAST NORTHWEST WINDS DIMINISH INTO THE OVERNIGHT. && .LWX WATCHES/WARNINGS/ADVISORIES... DC...WINTER WEATHER ADVISORY FROM 2 AM TO 6 PM EST MONDAY FOR DCZ001. MD...WINTER WEATHER ADVISORY UNTIL 6 PM EST MONDAY FOR MDZ004>006- 011-503>508. WINTER STORM WARNING UNTIL 6 PM EST MONDAY FOR MDZ003. WINTER WEATHER ADVISORY FROM 2 AM TO 6 PM EST MONDAY FOR MDZ013-014. WINTER STORM WATCH FROM MONDAY EVENING THROUGH TUESDAY AFTERNOON FOR MDZ006-011-014-017-018-507-508. WINTER STORM WARNING UNTIL 6 PM EST MONDAY FOR MDZ501-502. VA...WINTER WEATHER ADVISORY UNTIL 6 PM EST MONDAY FOR VAZ025>027- 029>031-040-501-503>508. WINTER STORM WARNING UNTIL 6 PM EST MONDAY FOR VAZ028. WINTER WEATHER ADVISORY FROM 2 AM TO 6 PM EST MONDAY FOR VAZ039-051>054-502. WV...WINTER WEATHER ADVISORY UNTIL 6 PM EST MONDAY FOR WVZ505-506. WINTER STORM WARNING UNTIL 6 PM EST MONDAY FOR WVZ051>053. WINTER STORM WARNING UNTIL 6 PM EST MONDAY FOR WVZ050-055- 501>504. MARINE...SMALL CRAFT ADVISORY UNTIL 6 PM EST MONDAY FOR ANZ530>534- 537>543. GALE WARNING FROM 6 PM MONDAY TO 6 AM EST TUESDAY FOR ANZ530>534-537>543. SMALL CRAFT ADVISORY UNTIL 6 AM EST TUESDAY FOR ANZ535-536. && $$ SYNOPSIS...SEARS/KCS NEAR TERM...HTS/SEARS SHORT TERM...HTS/KCS LONG TERM...KLW AVIATION...HTS/SEARS/KCS/KLW MARINE...HTS/SEARS/KCS/KLW

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