Area Forecast Discussion
Issued by NWS Sterling, VA

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000 FXUS61 KLWX 230209 AFDLWX AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC 909 PM EST THU JAN 22 2015 .SYNOPSIS... HIGH PRESSURE BUILDS OVERHEAD TONIGHT. A LOW PRESSURE SYSTEM WILL INTENSITY OVER THE SOUTHEASTERN STATES FRIDAY NIGHT AND TRACK NORTHEAST JUST OFF THE DELMARVA COAST SATURDAY. A WEAKER LOW PRESSURE SYSTEM WILL CROSS THE AREA FROM THE WEST SUNDAY NIGHT THROUGH MONDAY. HIGH PRESSURE IS THEN EXPECTED THROUGH THE MIDWEEK. && .NEAR TERM /THROUGH FRIDAY/... AS OF 01Z...1033MB SFC HIGH CENTERED OVER SRN OHIO WITH A 140 KT WLY JET OVERHEAD AT H3 AND A SFC LOW OVER THE NRN GOM SOUTH OF LOUISIANA. HIGH CLOUDS FROM THE JET HAVE FILTERED THE STARS OUTSIDE...WITH SCT MID LEVEL CLOUDS WEST OF THE BLUE RIDGE FROM THE WLY FLOW OVER THE APPALACHIANS. THE HIGH WILL BE OVER THE CWA AT SUNRISE FRIDAY. HIGH CLOUDS WILL STILL BE OVER THE AREA FROM THE UPR RIDGE OVER THE TN VLY...BUT GOOD RADIATIONAL COOLING AND DECOUPLED SFC SHOULD ALLOW LOW TO MID 20S OVER THE AREA. SNOW PERSISTS OVER THE NRN SECTIONS OF THE CWA...WERE AN SPS HAS BEEN ISSUED FOR REFREEZE/BLACK ICE PATCHES. THE HIGH WILL MOVE OFFSHORE FRIDAY MORNING. CONTINUED OVERRUNNING WILL ALLOW FOR CLOUDS TO THICKEN/LOWER ACROSS THE CWA BY FRIDAY AFTERNOON. CHANGED PRECIP FOR FRIDAY AFTERNOON IN THE SWRN ZONES TO BE A WINTRY MIX AT HIGHER ELEVATIONS AND ON THE LEADING EDGE...PARTICULARLY TOWARD SUNSET. POPS A LITTLE AHEAD OF 18Z GUIDANCE DUE TO WARM AIR ADVECTION WHICH OFTEN COMES IN A LITTLE EARLIER THAN PROGGED. DUE TO UNCERTAINTY ON RAIN/WINTRY MIX LINE...WILL LET MIDNIGHT SHIFT LIFT THE EXPECTED WINTER WX ADVISORY. && .SHORT TERM /FRIDAY NIGHT THROUGH SATURDAY/... FOCUS OF FRI NIGHT-SAT WILL BE A DEVELOPING COASTAL PLAIN LOW AS IT CROSSES FROM ERN NC TO OFF THE SHORE AT THE NC/VA BORDER. THIS TRACK IS VERY FAVORABLE FOR PRECIPITATION ACROSS THE AREA. HOWEVER...THE PRESENCE OF THE NRN STREAM TROUGH NORTH OF THE GREAT LAKES IS LIMITING COLD AIR. THE COOL AIR THAT IS THERE ALONG WITH DYNAMICAL COOLING WILL BRING ADVISORY LVL SNOW/WINTRY MIX TO AREAS WEST OF THE I-95 CORRIDOR FRI NIGHT-SAT. DID HOURLY TEMPERATURES TO ACCOUNT FOR WARM AIR CROSSING SRN MD FRIDAY NIGHT WITH WARMING THROUGH THE NIGHT THERE. SHOULD SEE FRONTOGENESIS WITH SLIGHT COOLING FOR CNTRL/NERN MD. THIS IS WHERE A BAND/TROWAL WOULD SET UP WHICH COULD UP SNOW TOTALS ALONG AND NORTH OF A LINE FROM DC TO BALTIMORE SHOULD DYNAMICAL COOLING BE STRONG ENOUGH. WRAP AROUND PRECIP LOOKS TO CHANGE TO SNOW SATURDAY...BUT A WINTRY MIX COULD HOLD ON THROUGH MOST OF THE MORNING. FOR THE MOST PART SNOW TOTALS WERE LOWERED A BIT FROM THE DAY SHIFT AND ICE ACCUMULATION WAS INCREASED. PREVIOUS... SHORTWAVE OVER THE MOUNTAIN WEST TODAY WILL SWING THROUGH THE SOUTHERN US...WITH THE NORTHERN STREAM SWEEPING THE ENERGY UP ALONG THE EASTERN SEABOARD LATER SAT. AT THE SFC...ASSOCIATED DEVELOPING LOW OVER THE SOUTHEASTERN US NUDGES JUST OFF THE COAST OF THE CAROLINAS BY 12Z SAT...EVENTUALLY DEEPENING GREATLY WELL TO THE NORTH AND EAST OF THE REGION. THE EXACT PATH OF THIS LOW WILL BE A MAJOR PLAYER IN THE EVENT AS WE HAVE HIGH CONFIDENCE OF THE PCPN MOVING IN LATE FRI AFTN/EARLY EVENING...THEN OVERSPREADING THE ENTIRE MID ATLANTIC AREA BY 06Z SAT. P-TYPE HOWEVER IS STILL IN DEBATE WITH THE 12Z EURO NOW TRENDING THE LOW CLOSER TO SHORE...AND BRINGING IN WARMER TEMPS MUCH FURTHER WEST. 12Z NAM REMAINS THE COLDER SOLUTION...BUT IS TRENDING WARMER AS WELL. IF THE LOW TRACKS FURTHER EAST...WE WOULD SEE COLDER TEMPS...BUT IT WOULD ALSO TAKE THE AXIS OF HEAVIER PCPN TO THE EAST WHERE IT WOULD MORE LIKELY FALL AS RAIN. IF THE LOW TRACKS TO THE WEST...WE GET A WETTER SOLUTION...BUT AGAIN MORE IN THE FORM OF RAIN. SO FOR THE P-TYPE...SIDING WITH THE TREND OF THE WARMER SOLUTION...HAVE PREDOMINATELY A RAIN EVENT FOR SOUTHERN MD. FOR THE I-95 CORRIDOR...STARTING OFF WITH RAIN...WITH PSBL SLEET MIXING. HEADING NORTH AND WEST...BETTER CHC OF STARTING OFF SNOW/SLEET MIX. DECREASING CONFIDENCE FOR THE SECOND HALF OF THE NIGHT WITH UNCERTAINTY ON WHERE EXACTLY THE RAIN/SNOW LINE SETS UP. HOWEVER...WITH BOTH THE NAM AND GFS BUFKIT SOUNDINGS BECOMING ISOTHERMAL...HAVE REMOVED THE SLEET POTENTIAL. SFC TEMPS HOVERING IN THE UPPER 20S/LOWER 30S EXTENDING FROM NORTH OF BALTIMORE DOWN THROUGH NORTHERN VA INTO THE SHENANDOAH VALLEY COULD LEAD TO PERIODS OF FREEZING RAIN. HOWEVER...TEMPS COULD BE TOO LOW...ESPECIALLY IF THE TREND CONTINUES WITH WARMING TEMPS AND WITH NO BLOCKING HIGH TO THE NORTH USHERING IN THE COLDER TEMPS...THIS COULD VERY WELL END UP BEING ONLY A RAIN/SNOW MIX. BY DAYBREAK...WILL SEE MOSTLY RAIN EVENT EAST OF BLUE RIDGE...WITH SOME SNOWFLAKES MIXING IN...THEN LIGHT SNOW TO THE WEST. BEST FRONTOGENETIC FORCING FROM THE 12Z MODELS LINING UP BASICALLY ALONG THE BLUE RIDGE AND EAST AND AS SUCH HAVE THE HIGHEST SNOW TOTALS MAINLY SPREAD BETWEEN THE BLUE RIDGE AND THE I-95 CORRIDOR. AS THE LOW DEEPENS AND PUSHES NORTHEAST...PCPN WILL TAPER OFF FROM WEST TO EAST DURING THE DAY SAT. MOST 12Z SOLUTIONS ARE MOVING THE LOW THROUGH QUICKER NOW...AND AS SUCH...THE PCPN COULD VERY WELL TAPER OFF SOONER THAN CURRENTLY IN THE FORECAST. BY SAT NIGHT...DRY WX TO THE EAST...WITH UPSLOPE SNOWS TO THE ALLEGHENY FRONT. && .LONG TERM /SATURDAY NIGHT THROUGH THURSDAY/... AN ALBERTA CLIPPER LOW PRESSURE SYSTEM WILL MOVE ACROSS THE LOWER GREAT LAKES SUNDAY...SLIDE ACROSS OHIO AND PENNSYLVANIA SUNDAY NIGHT...BEFORE PUSHING OFFSHORE NEW JERSEY MONDAY. WITH THE STORM TRACK OF THIS SYSTEM TO THE NORTH OF OUR FORECAST REGION SUNDAY NIGHT AND MONDAY...A SOUTH TO SOUTHWESTERLY WIND WILL HAVE MORE OF AN INFLUENCE ON PRECIPITATION TYPE DUE TO SLIGHTLY MILDER AIR IN THE LOWER 5000 FEET OF THE ATMOSPHERE. CURRENT THINKING IS A CHANCE FOR OCCASIONAL LIGHT SNOW AT THE START AND MAINLY IN THE WEST SUNDAY. THEN AS THE SURFACE LOW AND SOME UPPER LEVEL FORCING PENETRATES THE REGION FROM THE WEST...A WINTRY MIX OF SNOW...SLEET AND RAIN COULD EVOLVE SUNDAY NIGHT. EXPECTED AMOUNTS APPEAR TO BE LIGHT. AS THE SURFACE LOW EXITS EAST AND THE UPPER LEVEL TROUGH OF LOW PRESSURE PIVOTS TO THE CHESAPEAKE BAY MONDAY...A WEST-NORTHWEST TO NORTHWEST FLOW WILL DEVELOP AND ANY LEFTOVER RAIN AND SNOW SHOWERS WILL BE ISOLATED AND MAYBE CONFINED TO THE HIGHER ELEVATIONS OF THE POTOMAC HIGHLANDS AND BLUE RIDGE DUE TO THE SQUASH OF THE DOWNSLOPING FLOW ON ANY PRECIPITATION. THESE SAME NORTHWEST WINDS COULD GUST 30 TO 40 MPH. ASIDE FROM SOME UPSLOPE SNOW IN THE HIGHER TERRAIN OF THE POTOMAC HIGHLANDS TUESDAY AND TUESDAY NIGHT...THEN AGAIN WEDNESDAY NIGHT AND THURSDAY...DRY AND COLD CONDITIONS WILL PREVAIL ACROSS THE REGION TUESDAY THROUGH THURSDAY. TEMPERATURES COULD BE ABOUT 10 DEGREES BELOW NORMAL. && .AVIATION /02Z FRIDAY THROUGH TUESDAY/... VFR CONDITIONS INTO FRIDAY AFTERNOON AS HIGH PRESSURE BUILDS OVERHEAD LATE TONIGHT (NWLY FLOW DECREASES TO CALM BY SUNRISE) AND LIGHT RETURN SLY FLOW AS HIGH PRESSURE MOVES OFFSHORE FRIDAY MORNING. SUB-VFR CONDITIONS LIKELY FRI NIGHT-SAT WITH PCPN OVERSPREADING THE REGION. INCREASING CHC OF IFR OR LOWER 06-15Z SAT. LOW CONFIDENCE ON P-TYPE...WITH I-95 CORRIDOR SITES MORE LIKELY ALL RAIN OR BRIEF SNOW/RAIN MIX SAT MORNING...WHILE HEADING WEST HAS INCREASING CHC OF WINTRY MIX. SNOW TOTALS AT THIS TIME 1 INCH OR LESS I-95 CORRIDOR...2-4 INCHES FURTHER WEST. A CHANCE OF A WINTRY MIX OF SNOW...SLEET AND RAIN COULD LEAD TO IFR CONDITIONS...MAINLY SUNDAY NIGHT INTO EARLY MONDAY. OTHERWISE...VFR CONDITIONS SUNDAY AND MIDDAY TO LATE MONDAY. WINDS SOUTH TO SOUTHWEST AND LESS THAN 5 KNOTS SUNDAY...BECOMING MAINLY SOUTHWEST AT 10 KNOTS SUNDAY NIGHT. WINDS WILL VEER WEST TO NORTHWEST AND BECOME GUSTY BY MONDAY AFTERNOON. WINDS MAY GUST 25 TO 30 KNOTS MONDAY AFTERNOON. && .MARINE... HIGH PRESSURE BUILDS IN OVERHEAD LATE TONIGHT WITH NWLY WIND DECREASING TO CALM BY SUNRISE FRIDAY. SUB-SCA CONDITIONS FRIDAY NIGHT WILL QUICKLY INCREASE SAT MORNING...WITH SCA MOST LIKELY DURING THE DAY. LINGERING GUSTS TO 20 KT IN THE EVENING...THEN DECREASING OVERNIGHT. PCPN LIKELY FRI NIGHT-SAT...WITH PERIODS OF HEAVY RAIN. LOW CHC OF FROZEN PCPN OVER THE WATERS. NO MARINE HAZARDS SUNDAY THROUGH MONDAY MORNING. SMALL CRAFT ADVISORIES MAY BE NEEDED MONDAY AFTERNOON FOR WIND GUSTS OF 25 TO 30 KNOTS. && .LWX WATCHES/WARNINGS/ADVISORIES... DC...NONE. MD...NONE. VA...NONE. WV...NONE. MARINE...NONE. && $$ SYNOPSIS...BAJ/SEARS/BPP NEAR TERM...BAJ/BPP SHORT TERM...SEARS LONG TERM...KLW AVIATION...BAJ/SEARS/BPP/KLW MARINE...BAJ/SEARS/BPP/KLW

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