Area Forecast Discussion
Issued by NWS Sterling, VA

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000
FXUS61 KLWX 031536 AAA
AFDLWX

AREA FORECAST DISCUSSION...UPDATED
NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC
1036 AM EST TUE MAR 3 2015

.SYNOPSIS...
HIGH PRESSURE WILL PERSIST OVER THE AREA BEFORE MOVING OFFSHORE
LATER TODAY. 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/...
VERY CHALLENGING FORECAST THIS AFTERNOON AND EVENING.

LIFT FROM WARM AIR ADVECTION IS BEGINNING TO INCREASE ACROSS THE
FORECAST AREA BUT PRECIPITATION IS HAVING A TOUGH TIME REACHING
THE GROUND DUE TO DRY AIR AT THE MID LEVELS. THE COLUMN WILL
GRADUALLY MOISTEN UP BUT PRECIPITATION WILL LIKELY START A BIT
LATER THAN PREVIOUSLY EXPECTED. THE LATER START TIME WILL ALLOW
FOR TEMPERATURES TO WARM A FEW DEGREES ESPECIALLY SOUTH OF THE
METRO AREAS. THIS MAKES THE FORECAST PROBLEMATIC WITH MILDER
TEMPERATURES...ESPECIALLY OVER CENTRAL AND SOUTHERN LOCALES.

AREAS OF HIGHEST CONFIDENCE FOR ICING CONCERNS LOOK TO BE SETTING
UP TO THE NORTH AND WEST OF THE BALTIMORE AND WASHINGTON DC METRO
AREAS AND PORTIONS OF THE SHENANDOAH VALLEY AND HIGHLANDS. SHALLOW
COLD AIR WILL LIKELY HOLD IN LONGEST AND POSE THE GREATEST CONCERN
FOR SLIPPERY TRAVEL LATER THIS AFTERNOON INTO THIS EVENING. AREAS
CLOSEST TO THE MASON DIXON LINE OVER NE MARYLAND MAY HOLD SUB
FREEZING AIR INTO THE LATE EVENING. STILL CANNOT RULE OUT SOME
ICING TO THE SOUTH WITH DEWPOINT DEPRESSIONS RUNNING 10 OR MORE
DEGREES AND DRY POCKET ALOFT. PRECIPITATION WILL COOL THE COLUMN
AT LEAST INITIALLY.

P-TYPES NOW LOOK TO BE MOSTLY FREEZING RAIN WITH SOME SLEET AT THE
START. LATER START TIMES LEND TO WARMING ALOFT WITH LESS POTENTIAL
FOR SNOW. PRECIP IN ALL AREAS WILL BE LIGHT.

TEMPERATURES RISE ABOVE FREEZING LATER TONIGHT FOR THE ENTIRE
AREA. RAIN RATES INCREASE OVER ALLEGHENIES LATE...WILL NEED TO BE
ON THE LOOKOUT FOR LOCALIZED FLOODING CONCERNS GIVEN EXPECTED
SNOWPACK MELT WITH HIGHLAND TEMPERATURES RISING INTO THE 40S.

&&

.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 /15Z TUESDAY THROUGH SATURDAY/...
LIGHT WINTRY MIX OVERSPREADS THE TERMINALS THROUGH THE AFTERNOON
AS A WARM FRONT APPROACHES. IFR CIGS EXPECTED LATE THIS AFTERNOON
INTO THE OVERNIGHT. LIGHT SLEET/FREEZING RAIN AT ONSET CHANGING
QUICKLY OVER TO FREEZING RAIN. WINTRY PRECIPITATION LIKELY TO
CHANGE OVER TO RAIN BY TONIGHT. IFR CONDITIONS EXPECTED.

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...
SMALL CRAFT ADVISORY NOW IN EFFECT FOR ALL OF THE WATERS THIS
AFTERNOON INTO THIS EVENING. HIGH PRESSURE WILL MOVE OFFSHORE AND
SOUTHERLY FLOW WILL INCREASE. WINDS ARE EXPECTED TO DIP BELOW
ADVISORY LEVEL TONIGHT. VSBY RESTRICTIONS EXPECTED.

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 UNTIL 10 PM EST THIS EVENING FOR
     DCZ001.
MD...WINTER WEATHER ADVISORY UNTIL 7 PM EST THIS EVENING FOR MDZ501-
     502.
     WINTER WEATHER ADVISORY UNTIL 10 PM EST THIS EVENING FOR
     MDZ003.
     WINTER WEATHER ADVISORY UNTIL 10 PM EST THIS EVENING FOR
     MDZ004>006-011-013-014-503>508.
     WINTER WEATHER ADVISORY UNTIL 7 PM EST THIS EVENING FOR
     MDZ016>018.
VA...WINTER WEATHER ADVISORY UNTIL 7 PM EST THIS EVENING FOR
     VAZ025>031-036>040-050-051-501>504-507-508.
     WINTER WEATHER ADVISORY UNTIL 10 PM EST THIS EVENING FOR
     VAZ053-054-505-506.
     WINTER WEATHER ADVISORY UNTIL 7 PM EST THIS EVENING FOR VAZ052-
     055>057.
WV...WINTER WEATHER ADVISORY UNTIL 7 PM EST THIS EVENING FOR WVZ050-
     055-501>506.
     WINTER WEATHER ADVISORY UNTIL 10 PM EST THIS EVENING FOR
     WVZ051>053.
MARINE...SMALL CRAFT ADVISORY UNTIL 8 PM EST THIS EVENING FOR
     ANZ530>543.

&&

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


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