Area Forecast Discussion
Issued by NWS Sterling, VA

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000
FXUS61 KLWX 050735
AFDLWX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC
335 AM EDT WED AUG 5 2015

.SYNOPSIS...
HIGH PRESSURE WILL BUILD OVERHEAD THROUGH TONIGHT. A WAVE LOW
PRESSURE WILL PASS BY ALONG A STALLED BOUNDARY TO OUR SOUTH LATER
THURSDAY INTO FRIDAY. HIGH PRESSURE WILL RETURN FOR THE WEEKEND.

&&

.NEAR TERM /THROUGH TONIGHT/...
ANALYSIS EARLY THIS MORNING SHOWS A WEAK COLD FRONT DROPPING TO
OUR SOUTH. AN UPPER-LEVEL DISTURBANCE IN THE ZONAL FLOW ALOFT IS
PASSING THROUGH THE REGION...BRINGING SOME HIGH AND MID-LEVEL
CLOUDS. HIGH CLOUDS WILL DISSIPATE LATER THIS MORNING AS THE
UPPER-LEVEL DISTURBANCE MOVES OFF TO OUR EAST.

THE BOUNDARY WILL STALL TO OUR SOUTH TODAY WHILE HIGH PRESSURE
APPROACHES FROM THE WEST. A WEST TO NORTHWEST FLOW IS EXPECTED
BEHIND THE COLD FRONT...RESULTING IN DRIER CONDITIONS. MAX TEMPS
WILL BE SEVERAL DEGREES COOLER COMPARED TO TUESDAY DUE TO WEAK
COLD ADVECTION. HOWEVER...IT WILL STILL TURN OUT TO BE A WARM
AFTERNOON WITH MAX TEMPS IN THE MID TO UPPER 80S ACROSS MOST
AREAS...AND NEAR 90 IN DOWNTOWN WASHINGTON/BALTIMORE.

HIGH PRESSURE WILL BUILD OVER THE REGION TONIGHT AND A NORTHERLY
FLOW WILL ALLOW FOR NOTICEABLY COOLER AND DRIER CONDITIONS. MIN
TEMPS WILL RANGE FROM THE 50S IN THE ALLEGHENY AND POTOMAC
HIGHLANDS...TO THE LOWER AND MIDDLE 60S IN THE SUBURBS OF
WASHINGTON AND BALTIMORE...TO THE UPPER 60S/NEAR 70 IN DOWNTOWN
WASHINGTON AND BALTIMORE.

&&

.SHORT TERM /THURSDAY THROUGH FRIDAY NIGHT/...
A WAVE OF LOW PRESSURE WILL RIDE ALONG THE BOUNDARY...PASSING BY
TO OUR SOUTH LATE THURSDAY INTO FRIDAY. THERE IS STILL HIGH
UNCERTAINTY WITH THE TRACK AND STRENGTH OF THIS SYSTEM.
HOWEVER...LATEST GUIDANCE OVERALL HAS TRENDED TOWARD A WEAKER
SYSTEM THAT TRACKS FARTHER SOUTH. THIS MEANS THAT MOST OF THE AREA
WILL REMAIN ON THE COOL SIDE OF THE BOUNDARY WITH THE LOW BEING
SUPPRESSED TO THE SOUTH. WITH THE TRACK POSSIBLY BEING FARTHER
SOUTH...THE GRADIENT BETWEEN A SOAKING RAIN VS. LITTLE OR NO
RAINFALL WILL LIKELY SETUP OVER OUR CWA.

THE WAVE OF LOW PRESSURE WILL LIKELY APPROACH FROM THE OHIO AND
TENNESSEE VALLEYS THURSDAY BEFORE PASSING BY TO OUR SOUTH THURSDAY
NIGHT AND EVENTUALLY MOVING OFFSHORE DAY FRIDAY. RAIN IS MOST
LIKELY ACROSS CENTRAL VIRGINIA AND SOUTHERN MARYLAND DURING THIS
TIME WITH THE GRADIENT POSSIBLY SETTING UP ACROSS NORTHERN
VIRGINIA TOWARD WASHINGTON AND BALTIMORE LATER THURSDAY INTO EARLY
FRIDAY. THIS SEEMS TO BE IN LINE WITH MOST OF THE DETERMINISTIC
GUIDANCE ALONG WITH THEIR ENSEMBLE FIELDS. THE DETERMINISTIC 00Z
ECMWF IS A BIT STRONGER WITH THE LOW AND FARTHER NORTH WITH THE
RAIN. TWEAKED THE LATEST FORECAST TO TREND TOWARD THE MAJORITY OF
GUIDANCE...BUT DID ACCOUNT FOR POSSIBLE SHOWERS ACROSS NORTHERN
AREAS WHICH THE 00Z ECMWF STILL SHOWS. THURSDAY WILL BE NOTICEABLY
COOLER DUE TO RECENT DAYS DUE TO CLOUD COVER AND
RAINFALL..ESPECIALLY ACROSS CENTRAL VIRGINIA INTO SOUTHERN
MARYLAND. ANY LEFTOVER RAINFALL SHOULD END FROM NORTHWEST TO
SOUTHEAST FRIDAY BEFORE HIGH PRESSURE BUILDS IN FRIDAY NIGHT.
AGAIN TIMING IS UNCERTAIN. IF THE LOW IS WEAKER AND FARTHER
SOUTH...THEN MUCH OF FRIDAY MAY BE DRY. HOWEVER...IF IT IS A BIT
STRONGER THEN RAINFALL MAY HANG AROUND FOR MUCH OF THE
DAY...ESPECIALLY TO THE SOUTH AND EAST.


&&

.LONG TERM /SATURDAY THROUGH TUESDAY/...
SFC LOW PRESSURE WILL BE SITTING OFFSHORE BY 12Z
SAT...PROGRESSING TO THE NORTH AND EAST DURING THE DAY. HIGH
PRESSURE OVER SOUTHERN CANADA WILL SQUEEZE IN ACROSS THE EAST
COAST AS THIS LOW PIVOTS TO THE NE AND ANOTHER LOW TREKS INTO THE
GREAT LAKES SAT INTO SUN. 00Z MODEL SUITE STILL HINTING AT SLIGHT
CHC OF PCPN SAT WITH UPPER LVL TROUGH SWINGING THRU...WHICH
COMBINED WITH ENOUGH DAYTIME INSTABILITY...COULD GENERATE SHOWERS
AND TSTMS. HOWEVER...CONFIDENCE IS LOW OF OCCURRING SO THE
FORECAST HAS BEEN KEPT DRY. LOSS OF DAYTIME HEATING WILL DIMINISH
THE THREAT...AND HAVE GONE WITH A DRY FORECAST BY SAT NIGHT AND ON
INTO SUN.

NEXT LOW PRESSURE SYSTEM APPROACHES THE BEGINNING OF NEXT WEEK. SOME
DIFFERENCES ON THE PLACEMENT OF ASSOCIATED WARM FRONT WHICH COULD
SLOW THE ARRIVAL TIME OF THE PCPN SUN NIGHT INTO MON. INCRSG
COVERAGE OF CONVECTION MON AFTN AND OVERNIGHT AS COLD FRONT
APPROACHES AND MOVES THRU TUES. THE FRONT STALLS JUST OFFSHORE
MIDWEEK AS THE UPPER LVL PATTERN MAINTAINS A DEEPENING TROUGH OVER
THE EASTERN US...KEEPING THE CHC OF PCPN IN THE FORECAST.

&&

.AVIATION /07Z WEDNESDAY THROUGH SUNDAY/...
VFR CONDITIONS ARE EXPECTED THROUGH TONIGHT. WEST TO NORTHWEST
WINDS WILL GUST AROUND 15 TO 20 KNOTS THIS AFTERNOON.

A WAVE OF LOW PRESSURE WILL RIDE ALONG STALLED BOUNDARY TO OUR
SOUTH...POSSIBLY IMPACTING THE AREA THURSDAY INTO FRIDAY. THE BEST
CHANCE FOR RAIN AND SUBVFR CONDITIONS WILL BE ACROSS KCHO.
HOWEVER...RAIN MAY MAKE IT FARTHER NORTH INTO THE REST OF THE
TERMINALS BUT UNCERTAINTY REMAINS HIGH AT THIS TIME.

GENERALLY VFR CONDITIONS FOR THE WEEKEND. SUB-VFR
CONDITIONS PSBL AS EARLY AS SUN NIGHT...BCMG MORE LIKELY DURING
THE DAY MON WITH INCRSG COVERAGE OF PCPN.

&&

.MARINE...
HIGH PRESSURE WILL BUILD TOWARD THE WATERS TODAY. A DEEP MIXING
LAYER WILL ALLOW FOR WIND GUSTS AROUND SCA CRITERIA ACROSS THE
NORTHERN PORTION OF THE CHESAPEAKE BAY THIS AFTERNOON AND
EVENING.

HIGH PRESSURE WILL BUILD OVERHEAD TONIGHT INTO THURSDAY. A WAVE OF
LOW PRESSURE WILL PASS BY TO THE SOUTH THURSDAY NIGHT INTO FRIDAY
BEFORE MOVING OFFSHORE FRIDAY NIGHT. A SMALL CRAFT ADVISORY MAY BE
NEEDED FOR PORTIONS OF THE WATERS DURING THIS TIME.

SUB-SCA CONDITIONS THIS WEEKEND. PSBL SCA MON AHEAD OF
THE COLD FRONT...BUT CONFIDENCE IS LOW ATTM OF OCCURRING. SUB-SCA
CONDITIONS RETURN BY MID WEEK.

&&

.LWX WATCHES/WARNINGS/ADVISORIES...
DC...NONE.
MD...NONE.
VA...NONE.
WV...NONE.
MARINE...SMALL CRAFT ADVISORY FROM NOON TODAY TO 8 PM EDT THIS EVENING
     FOR ANZ530>532-538>540.

&&

$$
SYNOPSIS...BJL
NEAR TERM...BJL
SHORT TERM...BJL
LONG TERM...BJL/SEARS
AVIATION...BJL/SEARS
MARINE...BJL/SEARS


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