Area Forecast Discussion
Issued by NWS Sterling, VA

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000
FXUS61 KLWX 041908
AFDLWX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC
308 PM EDT SAT JUL 4 2015

.SYNOPSIS...
LOW PRESSURE RIDING ALONG A STATIONARY FRONT OVER THE AREA WILL
PUSH EAST TONIGHT. THE FRONT MOVES SOUTH AS A COLD FRONT ON SUNDAY
WITH HIGH PRESSURE BRIEFLY BUILDING INTO THE REGION. HIGH PRESSURE
MOVES OFF THE COAST SUNDAY EVENING. AN UPPER LEVEL DISTURBANCE
IMPACTS THE AREA SUNDAY NIGHT THROUGH TUESDAY BRINGING UNSETTLED
WEATHER.

&&

.NEAR TERM /THROUGH SUNDAY NIGHT/...
LATEST SURFACE ANALYSIS AS OF ABOUT 18Z INDICATED A LOW PRESSURE
EAST OF THE DELMARVA MOVING EAST...AND A WEAKER LOW OVER
NORTHWESTERN PENNSYLVANIA MOVING NORTHEAST. A WARM FRONT WAS
STRETCHED BETWEEN THE TWO LOWS...CROSSING OUR CWA APPROXIMATELY
BETWEEN WASHINGTON AND BALTIMORE. TO THE SOUTH AND WEST OF THE
FRONT...THE SUN HAS BROKEN THROUGH THE CLOUDS AND RESULTED IN
SIGNIFICANT INSTABILITY. HOWEVER...THIS IS FIGHTING AGAINST AN
INCREASING PUSH OF DRY AIR ALOFT. THIS WILL MOST LIKELY LIMIT THE
HEIGHT OF THUNDERSTORM TOWERS AND KEEP THEM BELOW SEVERE LIMITS
THIS AFTERNOON AND EVENING DESPITE A DECENT AMOUNT OF SHEAR.
HOWEVER...AN ISOLATED STRONG WIND GUST FROM THE STORMS IS NOT OUT
OF THE QUESTION.

TROUGH ALOFT WHICH IS HELPING TO SPARK OFF THE STORMS WILL SLIDE
EAST TONIGHT ALONG WITH THE WEAKENING SURFACE FRONT...WHICH WILL
MOVE BACK SOUTH AS WHAT WILL TECHNICALLY BE CALLED A COLD FRONT.
STORMS SHOULD BE MOSTLY DONE BY ABOUT 9PM AND COMPLETELY OVER WITH
BY MIDNIGHT AS THEY MOVE OFF TO THE EAST AND WEAKEN. LINGERING
MOISTURE WILL LIKELY RESULT IN PATCHY FOG OVERNIGHT INTO EARLY
SUNDAY MORNING...ESPECIALLY IN THE SHELTERED VALLEYS NORTH AND
WEST OF I-95. LOWS WILL DROP INTO THE 60S.

HIGH PRESSURE WILL DOMINATE SUNDAY WITH PARTLY TO MOSTLY SUNNY
SKIES FOR MUCH OF THE DAY ESPECIALLY OVER THE METRO.
HOWEVER...FURTHER SOUTHWEST...A NEW CLOSED LOW WILL DEVELOP ALOFT
TONIGHT OVER THE TENESSEE VALLEY AND MOVE NORTHEAST TOWARD OUR
REGION. CLOUDS WILL BEGIN INCREASING AGAIN...AND SHOWERS AND
THUNDERSTORMS ARE EXPECTED TO DEVELOP AND ADVECT NORTHEASTWARD
STARTING IN OUR SOUTHWESTERN ZONES DURING THE AFTERNOON. THESE
WILL OVERSPREAD MOST OF THE CWA BY LATER SUNDAY NIGHT. AFTER HIGHS
IN THE 80S SUNDAY...LOWS WILL DROP BACK INTO THE 60S ON SUNDAY
NIGHT.

&&

.SHORT TERM /MONDAY THROUGH TUESDAY/...
MID/UPPER LEVEL DISTURBANCE THAT IS CUTOFF FROM THE MAIN BELT OF
WESTERLIES TO THE NORTH BEGINS TO IMPACT THE AREA IN EARNEST
DURING THE DAY MON. COMBINATION OF SFC WARM FRONT MOVING NORTH
OVER AREA...UPPER LEVEL DIFFLUENCE...AND VERY MOIST DEEP LAYER
WITH PWATS PROGGED TO BE NEAR 2 INCHES SUGGEST THE POTENTIAL FOR
EFFICIENT RAIN PRODUCERS WITH MODERATE TO HEAVY RAIN POSSIBLE.
SHEAR REMAINS WEAK (0-6 KM EBS AOB 20 KTS) AND INSTABILITY COULD
BE LIMITED DUE TO EXTENSIVE CLOUD COVER...WHICH WOULD LIMIT
OVERALL STORM ORGANIZATION/INTENSITY. TEMPS MIGHT NEED TO BE
ADJUSTED A LITTLE FURTHER DOWNWARD IN SUBSEQUENT FORECASTS...AS
AFOREMENTIONED CLOUD COVER COULD LIMIT INSOLATION.

BULK OF ACTIVITY SHOULD MOVE AWAY FROM THE AREA DURING THE
OVERNIGHT MONDAY AS THE DISTURBANCE IS ENGULFED INTO THE NORTHERN
STREAM. LIKELY A PERIOD OF SUBSIDENCE BEHIND DISTURBANCE PROVIDING
SOME CLEARING DURING THE EARLY PART OF TUE. LITTLE IN THE WAY OF
FORCING MECHANISM TUE...THOUGH COULD GET SOME ACTIVITY MOVING EAST
OFF HIGHER TERRAIN OR ALONG LEE TROUGH. STARTS GETTING A LITTLE
WARMER TUE...WITH TEMPS GETTING BACK TO NEAR NORMAL (U80S).

&&

.LONG TERM /TUESDAY NIGHT THROUGH SATURDAY/...
DISTURBANCE LINGERS IN THE AREA TUES NIGHT INTO WED AS A COLD
FRONT APPROACHES LATE ON WED. COLD FRONT SLOWLY DRIFTS SOUTH OVER
THE CWA AND LINGERS THROUGH THE END OF THE WEEK...DRIER CONDITIONS
ARRIVE FOR THE WEEKEND. UNCERTAINTY ON LOCATION OF THE FRONT MAY
AFFECT POPS...BUT DIURNAL EFFECTS ALLOWS FOR THE RISK OF
ISOLATED/SCATTERED SHOWERS AND/OR TSTMS EACH DAY. HIGH TEMPS WILL
BE IN THE 80S...LOW TEMPS IN THE 70S FOR MOST OF THE CWA...AND IN
THE MID TO UPR 60S AT HIGHER ELEVATIONS.

&&

.AVIATION /18Z SATURDAY THROUGH THURSDAY/...
LOW CIGS HAVE MOSTLY LIFTED...SO MAIN CONCERN HAS BECOME SCATTERED
SHOWERS AND ISOLATED THUNDERSTORMS FOR THE REMAINDER OF THE
AFTERNOON INTO EARLY EVENING. ANY STORM MAY PRODUCE BRIEF IFR
CIGS/VIS DUE MAINLY TO HEAVY RAIN...OR MAYBE A GUST TO 25 KNOTS.
STORMS WILL DISSIPATE/MOVE EAST THIS EVENING...BUT PATCHY FOG WITH
IFR VIS IS A CONCERN LATE TONIGHT AND EARLY SUNDAY ESPECIALLY AT
CHO AND MRB. SUNDAY AFTER ANY FOG BREAKS SHOULD BE MOSTLY
VFR...THOUGH LATE IN THE DAY ANOTHER ROUND OF STORMS LOOKS TO MOVE
INTO CHO AND THEN NORTHEAST TOWARD THE REST OF THE TERMINALS
SUNDAY NIGHT...WITH MORE CONCERNS ABOUT GUSTY WINDS AND REDUCED
VIS. OUTSIDE OF STORMS...WINDS SHOULD REMAIN BELOW 10 KNOTS
THROUGH SUNDAY NIGHT.

IFR CIGS APPEAR POSSIBLE THROUGH THE DAY MON IN MODERATE/HEAVY
RAIN SHWRS AND STORMS. IMPROVING TO MVFR LATE MON AND VFR BY
TUESDAY MORNING AS UPPER LEVEL DISTURBANCE PULLS AWAY FROM THE
AREA.

VFR CONDITIONS EXPECTED FOR TUES NIGHT AND WED. SUB-VFR DUE TO
PSBL SHOWERS AND TSTMS WED AFTN.

&&

.MARINE...
SCA REMAINS IN EFFECT FOR MIDDLE PORTIONS OF THE BAY AND SOME
ADJACENT WATERS DUE TO WINDS IN THE WAKE OF THE DEPARTING LOW
PRESSURE SYSTEM. THESE SHOULD END EARLY THIS EVENING AND SUB-SCA
WINDS ARE EXPECTED THROUGH SUNDAY NIGHT. ANY STORMS THIS EVENING
COULD PRODUCE REDUCED VISIBILITY IN HEAVY RAIN OR A WIND GUST TO
25 KNOTS...WHILE MORE STORMS EXPECTED SUNDAY NIGHT MAY DO
LIKEWISE.

WINDS EXPECTED TO REMAIN LIGHT AND VARIABLE MON....BUT COULD
STRENGTHEN SOME ON TUE DUE TO CHANNELING SRLY FLOW. COULD BE SOME
ISOLATED TSTMS MON AND AGAIN TUE AFTERNOON.

SUB-SCA CONDITIONS EXPECTED FOR TUES NIGHT AND WED. PSBL SHOWERS
AND TSTMS ACROSS THE WATERS ON WED AFTN.

&&

.TIDES/COASTAL FLOODING...
LOW PRESSURE DEPARTING EASTWARD ALLOWING WINDS TO TURN MORE
NORTHERLY SHOULD PREVENT ANY ADDITIONAL TIDAL FLOODING. ALL
ADVISORIES WERE ALLOWED TO EXPIRE AT NOON.

&&

.LWX WATCHES/WARNINGS/ADVISORIES...
DC...NONE.
MD...NONE.
VA...NONE.
WV...NONE.
MARINE...SMALL CRAFT ADVISORY UNTIL 6 PM EDT THIS EVENING FOR ANZ533-
     534-537-543.

&&

$$
SYNOPSIS...MSE
NEAR TERM...RCM
SHORT TERM...MSE/RCM
LONG TERM...IMR
AVIATION...IMR/MSE/RCM
MARINE...IMR/MSE/RCM
TIDES/COASTAL FLOODING...RCM



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