Area Forecast Discussion
Issued by NWS Sterling, VA

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000
FXUS61 KLWX 030855
AFDLWX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC
355 AM EST TUE MAR 3 2015

.SYNOPSIS...
HIGH PRESSURE WILL PERSIST OVER THE AREA THIS MORNING. A WARM FRONT
WILL LIFT THROUGH THE AREA THIS AFTERNOON AND EVENING. A COLD FRONT
WILL MOVE INTO THE REGION WEDNESDAY FOLLOWED BY HIGH PRESSURE FOR
THURSDAY LASTING INTO THE WEEKEND.

&&

.NEAR TERM /THROUGH TONIGHT/...
AS OF 08Z...1031MB SFC HIGH CENTERED OVER E-CNTRL PA WITH
1030MB PRESSURE OVER MOST OF LWX. SFC WINDS EITHER DECOUPLED OR
LIGHT OUT OF THE NORTH. TRANSLUCENT CI HAS OVERSPREAD THE AREA...
WILL THICKEN REST OF THE NIGHT...LIMITING MIN TEMPS A DEGREE OR TWO.
MOST AREAS TO START THE MORNING IN THE LOW TO MID 20S. PRECIP FOR
TODAY/TONIGHT IS ADVANCING EAST OVER IL/IN...AHEAD OF AN UPR TROUGH
MOVING EAST FROM THE NRN PLAINS. CLOUDS SHOWING UP ON RADAR WEST
FROM SRN SHEN VLY. WITH DRY SFC CONDITIONS...NO PRECIP IS EXPECTED
OUT THERE FOR A FEW MORE HOURS.

TODAY...PRECIP ONSET CONSENSUS TO BE LATE MORNING FOR WRN/NWRN
SECTION OF THE CWA...AFTER NOON FOR MUCH OF THE REST OF THE AREA
INCLUDING DC. THEREFORE...PUSHED BACK THE WINTER WEATHER ADVISORY
BEGINNING TIMES TO 10 AM FOR SHEN VLY AND N-CNTRL VA AND NOON FOR
GREATER BALT-WASH AND SRN MD. WITH WARM AIR RETURN NOT DELAYED...
THE WINDOW FOR FROZEN/FREEZING PRECIP IS SHORTER FOR AREAS LIKE SRN
MD. HOWEVER... THE NRN TIER SHOULD SEE SNOW/SLEET ACCUMS OF PERHAPS
HALF AN INCH BEFORE GETTING ICE ACCRETION. LEFT HEADLINES UP FOR ALL
AREAS CONSIDERING THE FREEZING RAIN THRESHOLD IS JUST A TRACE.

THIS EVENING...TYPICAL AREAS IN THE NRN SHEN VLY/WRN MD AND NRN MD
SEE FREEZING RAIN THE LONGEST. MAY NEED TO EXTEND UNTIL MIDNIGHT OR
SO FOR NRN TIER OF MD COUNTIES ALONG THE MASON-DIXON LINE FOR TEMPS
LINGERING NEAR FREEZING.

TEMPERATURES RISE OVERNIGHT WITH PLAIN RAIN BY MIDNIGHT FOR THE
ENTIRE AREA. RAIN RATES INCREASE OVER ALLEGHENIES LATE...WILL NEED
TO BE ON THE LOOKOUT FOR FLOODING CONCERNS GIVEN EXPECTED SNOWPACK
MELT WITH HIGHLANDS TEMPERATURES IN THE 40S. ONE TO TWO TENTHS QPF
EAST OF THE ALLEGHENY FRONT AND HALF INCH OR MORE WEST.

&&

.SHORT TERM /WEDNESDAY THROUGH THURSDAY/...
WEDNESDAY...COLD FRONT ENTERS CWA FROM THE WEST IN THE MORNING
AND DRIFTS EAST. WARMEST AIR IN NEARLY A MONTH (60F AT KIAD ON FEB
8) AHEAD OF THE FRONT WITH LOW 50S (A LITTLE LOWER THAN PREVIOUS
FORECASTS) EXPECTED GIVEN WIDESPREAD RAIN OVER THE AREA AT THE TIME.
QPF QUARTER TO HALF INCH OF RAIN OVER THE AREA WEDNESDAY. MOST OF
THE AREA LOOKS TO BE BETWEEN SHORTWAVES IN THE AFTERNOON...REDUCING
RAIN RATES.

WEATHER IMPACTS WILL INCREASE WEDNESDAY NIGHT. SFC BOUNDARY MAY HAVE
PUSHED A GOOD PART OF THE WAY THROUGH DURING THE EVENING...AS A WEAK
SFC WAVE IS PROJECTED TO CROSS THE CAROLINAS OVERNIGHT. HOWEVER...
COLDER TEMPS...ESPECIALLY ALOFT...WILL BE SLOW TO WORK SOUTHWARD.
PER COORDINATION WITH WPC...A GFS/ECMWF SOLUTION IS FAVORED...WHICH
ALLOWS THERMAL PROFILES TO COOL A BIT MORE QUICKLY AMONGST THE MODEL
SUITE. THIS ALSO GIVES A MORE DEFINITIVE RAIN-TO-SNOW TRANSITION VS
A MORE PRONOUNCED WARM NOSE IN THE NAM (LIKELY DUE TO A STRONGER SSW
LLJ IM THE 850-600MB LAYER) AND MORE MIXED PRECIP. CANNOT RULE OUT A
PERIOD OF IP/FZRA...BUT DID NOT HAVE ENOUGH CONFIDENCE ON
TIMING/PLACEMENT TO INCLUDE IN THE FORECAST AT THIS TIME. ON THE
WHOLE THOUGH...THERE WAS A SLIGHT SLOWING TREND OVERALL IN THE
TIMING OF PRECIP THROUGHOUT THE EVENT. ALL AREAS ARE FORECAST TO BE
SNOW BY THURSDAY MORNING...WITH PRECIP ENDED NW-SE DURING THE DAY.
TEMPERATURES WILL HOLD STEADY OR FALL.

SNOWFALL AMOUNT FORECASTS WILL BE CHALLENGING GIVEN THE
UNCERTAINTIES WITH PTYPES...TIMING...AND HOW MUCH MOISTURE FALLS IN
THE COLD AIR. THERE WILL BE TREMENDOUS MOISTURE TRANSPORT WITH
THE LLJ AS WELL AS LIFT ASSOCIATED WITH UPPER JET...BUT THE AXIS
OF HIGHEST QPF WILL LIKELY BE VERY NEAR THE TRANSITION ZONE...WITH
POTENTIAL FOR COLDER BUT DRIER AIR TO BEGIN WORKING INTO THE BACK
SIDE. NOT MUCH CHANGE TO CURRENT FORECAST OVER PREVIOUS. IF THE
QPF INDEED FALLS AFTER THE TRANSITION TO SNOW...OUR CURRENT
FORECAST IS ON THE CONSERVATIVE SIDE. HOWEVER FEEL THERE IS STILL
TOO WIDE OF A SPREAD IN SOLUTIONS TO GO HIGHER. SEE OUR WEBPAGE
FOR THE PROB RANGES. WILL ALLOW DAYSHIFT TO DECIDE ON POTENTIAL
FOR WATCHES. HIGHEST CONFIDENCE IN LARGER SNOW TOTALS ARE OVER THE
HIGHLANDS AT THIS TIME.

&&

.LONG TERM /THURSDAY NIGHT THROUGH MONDAY/...
ARCTIC HIGH PRESSURE WILL QUICKLY BUILD IN THURSDAY NIGHT. THERE MAY
BE A PERIOD OF UPSLOPE SNOW SHOWERS IN THE EVENING. NAM INDICATES
SNOW SHOWERS WILL BE POSSIBLE EAST OF THE MOUNTAINS AS WELL AS A
VORT MAX PASSES...BUT HAVE NOT INCLUDED THIS IN THE FORECAST NOW.
TEMPERATURES HAVE TRENDED COLDER...SINGLE DIGITS EXCEPT IN THE
METROS/NEAR THE BAY AND BELOW ZERO IN THE HIGHLANDS. IF GRADIENT
DOES NOT RELAX...WIND CHILL ADVISORIES MAY BE NEEDED IN THE
HIGHLANDS.

THE HIGH WILL SLIDE EAST ACROSS THE AREA THROUGH SATURDAY. FRIDAY
WILL STILL BE QUITE COLD BUT TEMPERATURES BEGIN TO MODERATE
SATURDAY. MOISTURE STARVED COLD FRONTS TRAILING LOW PRESSURE CENTERS
WELL TO THE NORTH WILL MAKE RUNS AT THE AREA SATURDAY NIGHT AND
AGAIN MONDAY. FOR NOW HAVE ONLY INCLUDED POPS IN THE UPSLOPE AREAS.
THERE ALSO WILL BE LITTLE EFFECT ON TEMPERATURES...WITH READINGS
SLIGHTLY BELOW NORMAL EXPECTED.

&&

.AVIATION /09Z TUESDAY THROUGH SATURDAY/...
VFR THIS MORNING UNDER HIGH PRESSURE. LIGHT WINTRY MIX
OVERSPREADS THE TERMINALS LATE THIS MORNING (KMRB AND KCHO) THROUGH
THE AFTERNOON (DC METROS) AS A WARM FRONT APPROACHES. HIGH CLOUDS
THICKEN AND LOWER TO MVFR CIGS BY MIDDAY...IFR CIGS EXPECTED LATE
THIS AFTERNOON INTO THE OVERNIGHT. LIGHT SLEET/SNOW AT ONSET
CHANGING QUICKLY OVER TO FREEZING RAIN. PLAIN RAIN SPREADS NORTH
OVER THE AREA THIS AFTERNOON AND EVENING. RAIN INTENSITY PICKS UP
LATE TONIGHT WITH IFR CONDS POSSIBLE AND PARTICULARLY FOR WEDNESDAY
MORNING WHEN IFR CONDS ARE MORE LIKELY IN MODERATE RAIN.

RAIN IS FORECAST TO CHANGE TO SNOW THURSDAY NIGHT. VSBY/CIG
REDUCTIONS WILL CONTINUE AND MAY DROP TO LIFR IF MODERATE/HEAVY SNOW
DEVELOPS. THE SNOW WILL END ON THURSDAY. NO AVIATION HAZARDS
EXPECTED THEREAFTER.

&&

.MARINE...
LIGHT NLY FLOW UNTIL SUNRISE WHEN HIGH PRESSURE CENTERS OVER
THE CHESAPEAKE BAY REGION. WARM FRONT APPROACHES THIS
MORNING...LIFTING NORTH OVER THE MD PART OF THE BAY THIS AFTERNOON
AND EVENING. SLY FLOW THIS EVENING EXPECTED TO GET TO 15 KT...HELD
OFF ON SCA FOR NOW THOUGH SOME 18 KT GUSTS POSSIBLE. COLD FRONT
APPROACHES WEDNESDAY WITH WIDESPREAD RAIN.

A COLD FRONT WILL PASS THROUGH THE WATERS WEDNESDAY NIGHT. RAIN WILL
CHANGE TO SNOW BY THURSDAY MORNING. SCA CONDITIONS ARE POSSIBLE FROM
LATE WEDNESDAY NIGHT THROUGH THURSDAY NIGHT BEHIND THE FRONT. WINDS
WILL SUBSIDE THEREAFTER UNDER HIGH PRESSURE.

&&

.HYDROLOGY...
LIQUID PRECIP FCST FROM WPC WEDNESDAY AND WEDNESDAY NIGHT AREA ONE
TO ONE AND A HALF INCHES. WITH TEMPERATURES EXPECTED TO RISE INTO
THE 50S ON WEDNESDAY...THERE WILL BE SOME...POSSIBLY A LOT
OF...MELTING OF THE EXISTING SNOWPACK...WHICH COMPUTER MODELS AND
OBSERVATIONS INDICATE CONTAINS ANYWHERE FROM 3/4 INCH TO 2 INCHES
OF SNOW WATER EQUIVALENT. THIS COMBINATION MAY LEAD TO MINOR
FLOODING AS THE RAIN FALLS ON WEDNESDAY. FURTHER COMPLICATING THIS
FORECAST IS AN EXPECTED CHANGEOVER TO SNOW WEDNESDAY NIGHT FOR
MUCH OF THE AREA.

ALTHOUGH RIVER ICE IS NOT ESPECIALLY THICK...IT WILL HAVE TO BE
MONITORED FOR POTENTIAL ROLE IN AFFECTING RUNOFF. ALSO...PLOWED SNOW
IS LIKELY COVERING SOME OF THE DRAINS OUT THERE...WHICH COULD CAUSE
MORE POOR DRAINAGE FLOODING THAN WOULD OTHERWISE USUALLY BE
EXPECTED.

&&

.LWX WATCHES/WARNINGS/ADVISORIES...
DC...WINTER WEATHER ADVISORY FROM NOON TODAY TO 10 PM EST THIS
     EVENING FOR DCZ001.
MD...WINTER WEATHER ADVISORY FROM 7 AM THIS MORNING TO 7 PM EST
     THIS EVENING FOR MDZ501-502.
     WINTER WEATHER ADVISORY FROM NOON TODAY TO 10 PM EST THIS
     EVENING FOR MDZ004>006-011-013-014-503>508.
     WINTER WEATHER ADVISORY FROM 10 AM THIS MORNING TO 10 PM EST
     THIS EVENING FOR MDZ003.
     WINTER WEATHER ADVISORY FROM NOON TODAY TO 7 PM EST THIS
     EVENING FOR MDZ016>018.
VA...WINTER WEATHER ADVISORY FROM 7 AM THIS MORNING TO 7 PM EST
     THIS EVENING FOR VAZ503-504.
     WINTER WEATHER ADVISORY FROM 10 AM THIS MORNING TO 7 PM EST
     THIS EVENING FOR VAZ025>031-036>040-050-051-501-502-507-
     508.
     WINTER WEATHER ADVISORY FROM NOON TODAY TO 10 PM EST THIS
     EVENING FOR VAZ053-054-505-506.
     WINTER WEATHER ADVISORY FROM NOON TODAY TO 7 PM EST THIS
     EVENING FOR VAZ052-055>057.
WV...WINTER WEATHER ADVISORY FROM 7 AM THIS MORNING TO 7 PM EST
     THIS EVENING FOR WVZ050-055-501>506.
     WINTER WEATHER ADVISORY FROM 10 AM THIS MORNING TO 10 PM EST
     THIS EVENING FOR WVZ051>053.
MARINE...NONE.

&&

$$
SYNOPSIS...BAJ/ADS
NEAR TERM...BAJ
SHORT TERM...BAJ/ADS
LONG TERM...ADS
AVIATION...BAJ/ADS
MARINE...BAJ/ADS
HYDROLOGY...LWX


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