Area Forecast Discussion
Issued by NWS Sterling, VA

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000
FXUS61 KLWX 011847 AAA
AFDLWX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC
244 PM EDT SAT AUG 1 2015

.SYNOPSIS...
HIGH PRESSURE WILL DOMINATE THE AREA THROUGH SUNDAY NIGHT. A WARM
FRONT WILL MOVE ACROSS THE AREA MONDAY. A COLD FRONT WILL MOVE INTO
THE AREA AND STALL TUESDAY. A WAVE OF LOW PRESSURE WILL DEVELOP
NEARBY ALONG THE FRONT WEDNESDAY AND THURSDAY BEFORE MOVING AWAY
FRIDAY.

&&

.NEAR TERM /THROUGH SUNDAY/...
TROUGH ALOFT WITH SURFACE REFLECTION IS CURRENTLY CROSSING THE
REGION. FORCING IS PRETTY WEAK...BUT SOME MOISTURE HAS RETURNED AS
EVIDENCED BY DEW POINTS CLIMBING BACK INTO THE MID 60S IN MANY
LOCALES. THE LATEST SPC MESOANALYSIS SHOWS A MAX OF CAPE SOUTH OF
DC...AND MESOSCALE GUIDANCE HAS BEEN DEPICTING A FEW SHOWERS
POPPING UP THIS AFTERNOON INTO EARLY EVENING IN THIS AREA AS WELL.
LATEST RADAR TRENDS SHOW THAT THIS APPEARS TO BE STARTING TO
HAPPEN...SO THEREFORE INCLUDED SOME ISOLATED SHOWERS IN THE
FORECAST IN THIS AREA. AN ISOLATED LIGHTNING STRIKE CANNOT BE
COMPLETELY RULED OUT EITHER. OTHERWISE...AND FOR THE MAJORITY OF
LOCATIONS AND MAJORITY OF TIME IN THE REST OF THE AREA...IT SHOULD
BE A DRY AND PLEASANT LATE AFTERNOON AND EVENING WITH TEMPS NEAR
TO SLIGHTLY BELOW NORMAL AND HUMIDITY WHICH IS STILL LOWER THAN
WHAT YOU WOULD EXPECT FOR EARLY AUGUST.

SURFACE HIGH PRESSURE BUILDS IN FROM THE WEST BEHIND THE TROUGH
TONIGHT AND PERSISTS THROUGH SUNDAY AS HEIGHTS RISE ALOFT AND THE
FLOW ALOFT BECOMES MORE WEST TO SOUTHWEST. THIS SHOULD PROMOTE
MOSTLY SUNNY SKIES AND A LACK OF PRECIPITATION. LIGHT WIND LATE
TONIGHT INTO EARLY SUNDAY MAY RESULT IN PATCHY FOG ACROSS INLAND
LOCALES AWAY FROM THE METRO...BUT THAT IS PRETTY MUCH ALL THERE IS
TO TALK ABOUT. HIGHS WILL BE NEAR NORMAL AGAIN BUT DEW POINTS WILL
DROP BACK INTO THE UPPER 50S SO OVERALL...SUNDAY SHOULD BE
SLIGHTLY MORE COMFORTABLE THAN TODAY.

&&

.SHORT TERM /SUNDAY NIGHT THROUGH TUESDAY/...
HIGH PRESSURE WILL MAINTAIN CONTROL SUNDAY NIGHT WITH MOSTLY CLEAR
SKIES...THOUGH DEW POINTS WILL BEGIN TO CREEP BACK UP. PATCHY FOG
WILL AGAIN BE A CONCERN IN THE SHELTERED INLAND LOCALES AWAY FROM
THE METRO WHERE RADIATIONAL COOLING SHOULD ALLOW TEMPS TO REACH
THE DEW POINT. WITH THE RISING DEW POINTS...LOWS SHOULD END UP A
BIT MILDER THAN TONIGHT.

MONDAY LOOKS TO BE QUITE HOT WITH GRADUALLY INCREASING HUMIDITY
AND 850 MB TEMPS INCREASING TO 19- 22 C. IT WILL BE THE FIRST DAY
WITH APPRECIABLE SOUTHERLY RETURN FLOW SO EXPECT DEW POINTS TO
REMAIN IN THE 60S...LEADING TO APPARENT TEMPERATURES IN THE MIDDLE
TO UPPER 90S DURING THE AFTERNOON.

A COLD FRONT WILL APPROACH FROM THE WEST LATE IN THE DAY...ALONG
WITH AN UPPER JET MAX AROUND 250 MB. THINKING THIS WILL FIRE
SHOWERS AND THUNDERSTORMS DURING THE AFTERNOON TO THE NORTHWEST OF
THE CWA...PROPAGATING INTO THE POTOMAC HIGHLANDS DURING THE
EVENING. MOST GUIDANCE IS IN AGREEMENT WITH MODERATE CAPE AND
SHORTWAVE FORCING...AS WELL AS MODEST SHEAR OVER THESE AREAS. AS
SUCH...SPC HAS THE NORTHWESTERN CORNER OF THE AREA IN A MARGINAL
RISK FOR SEVERE THUNDERSTORMS ON DAY 3/MONDAY. CANNOT RULE OUT A
STRONG STORM OR TWO ACCOMPANIED BY GUSTY WINDS. WENT WITH LIKELY
POPS/CHANCE THUNDER OVER THE HIGHLANDS IN THE EVENING...GRADUALLY
TAPERING OFF AS ACTIVITY MOVES EAST AND DIMINISHES OVERNIGHT WITH
THE LOSS OF HEATING. A POP UP THUNDERSTORM IS ALSO POSSIBLE IN A
ZONE OF ENHANCED CONVERGENCE AHEAD OF LEE SIDE PRESSURE TROUGH
OVER CENTRAL MD/BALTIMORE METRO AREA MONDAY AFTERNOON...SO HAVE
ISOLATED POPS FOR THESE AREAS AS WELL.

TUESDAY WILL BE ANOTHER VERY WARM DAY AS THE FRONT STALLS
NEAR/JUST SOUTH OF THE AREA. DEEP-LAYER WESTERLY FLOW
/DOWNSLOPING/ TAKES OVER ON TUESDAY AND WITH NO REAL FORCING
MECHANISM EXPECT RAIN CHANCES TO BE PRETTY MINIMAL...BUT THAT
COULD CHANGE IF THE FRONT STALLS FURTHER NORTH /KEEPING LOW-LEVEL
WINDS MORE SOUTHERLY AND MOIST/.

&&

.LONG TERM /TUESDAY NIGHT THROUGH SATURDAY/...
MEAN TROUGHING ALOFT WILL LINGER OVER THE NORTHEASTERN CONUS
DURING THE SECOND HALF OF THE WEEK. AT THE SURFACE...A FRONT WILL
REMAIN STALLED NEAR THE AREA. UNSETTLED CONDITIONS ARE LIKELY AT
TIMES...BUT PINPOINTING THE EXACT TIMING AT THIS TIME RANGE IS
DIFFICULT AT BEST. GEFS/EC MEAN SEEMS TO WANT TO HIGHLIGHT
WEDNESDAY NIGHT INTO THURSDAY WITH HIGHER POPS AS A WAVE OF LOW
PRESSURE MOVES ALONG THE FRONT...BUT TIMING/PLACEMENT/STRENGTH OF
SAID WAVE ARE ALL IN QUESTION.

THE PATTERN PERSISTS BUT WITH EVEN LESSER CERTAINTY IN DETAILS
THROUGH THE END OF THE WEEK.

&&

.AVIATION /18Z SATURDAY THROUGH THURSDAY/...
HIGH PRESSURE WILL KEEP VFR CIGS AND VIS WITH WINDS MAINLY BELOW
10 KNOTS THROUGH SUNDAY NIGHT. THE PROVERBIAL FLY IN THE OINTMENT
IS THAT SOME INLAND TERMINALS AWAY FROM THE METRO...I.E. MRB AND
CHO...MAY SEE SOME PATCHY FOG DEVELOP WITH IFR VIS/CIGS LATE
TONIGHT...AND AGAIN LATE SUNDAY NIGHT. THIS SHOULD NOT AFFECT THE
BUSIER TERMINALS IN THE METRO.

GENERALLY REMAINING VFR MON-WED...BUT SUB-VFR POSSIBLE ESPECIALLY
FOR MRB/CHO MON EVE...INITIALLY IN SHRA/SCTD TSRA...THEN LWR VSBYS
PSBL OVERNIGHT IN PATCHY FOG AS WINDS LIGHTEN W/ FRONT OVERHEAD.
SLY WINDS 10-15 KT MON BECOME WLY MON NIGHT-TUE AOB 10 KT. WIND
FORECAST BECOMES UNCERTAIN BY WED AND DEPENDS ON POSITIONING OF
FRONT/APPROACHING WAVE OF LOW PRESSURE.

&&

.MARINE...
WINDS HAVE STAYED BELOW SCA CRITERIA SO FAR TODAY AND AM NOT
EXPECTING THEM TO INCREASE AS MUCH AS SOME GUIDANCE HAS
SUGGESTED THEY MIGHT AS THE TROUGH PASSES. THEREFORE...KEPT WINDS
BELOW SCA LEVELS THROUGH EVENING. HIGH PRESSURE WILL KEEP WINDS
LIGHT TONIGHT THROUGH SUNDAY NIGHT.

SCA GUSTS LOOK LIKELY MONDAY AFTERNOON INTO MONDAY NIGHT IN
SOUTHERLY CHANNELING AHEAD OF AN APPROACHING COLD FRONT/LEE SIDE
PRESSURE TROUGH. GRADIENT WEAKENS AS FRONT MOVES OVERHEAD AND
WINDS TURN WESTERLY TUESDAY INTO WEDNESDAY.

&&

.TIDES/COASTAL FLOODING...
FULL MOON WILL CAUSE ASTRONOMICALLY HIGH TIDES TODAY. WHILE TIDES
WILL BE SLIGHTLY ABOVE NORMAL...AM NOT EXPECTING ANY FLOODING.
SOUTHERLY FLOW AHEAD OF THE NEXT FRONT WILL ALSO ELEVATE TIDES ON
MONDAY...BUT AT THIS POINT NOT EXPECTING MINOR FLOODING. THIS
POSSIBILITY WILL REQUIRE MONITORING HOWEVER.

&&

.LWX WATCHES/WARNINGS/ADVISORIES...
DC...NONE.
MD...NONE.
VA...NONE.
WV...NONE.
MARINE...NONE.

&&

$$
SYNOPSIS...RCM
NEAR TERM...RCM
SHORT TERM...RCM/DFH
LONG TERM...DFH
AVIATION...RCM/DFH
MARINE...RCM/DFH
TIDES/COASTAL FLOODING...KRW/RCM


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