Area Forecast Discussion
Issued by NWS Sterling, VA

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000
FXUS61 KLWX 101437
AFDLWX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC
1037 AM EDT THU JUL 10 2014

.SYNOPSIS...
A TROUGH OF LOW PRESSURE WILL LINGER ACROSS THE MID-ATLANTIC
THROUGH THE END OF THE WEEK. WEAK HIGH PRESSURE BUILDS IN OVER THE
WEEKEND. A COLD FRONT WILL THEN APPROACH EARLY NEXT WEEK.

&&

.NEAR TERM /THROUGH FRIDAY/...
CURRENT ANALYSIS SHOWS A SURFACE TROUGH OVER SOUTHERN MARYLAND
THIS MORNING. AN UPPER-LEVEL TROUGH IS APPROACHING FROM THE OHIO
VALLEY AND AN UPPER-LEVEL DISTURBANCE IS MOVING THROUGH IN THE
SOUTHWEST FLOW ALOFT.

THE SURFACE TROUGH IS EXPECTED TO RETROGRADE BACK TO THE WEST THIS
AFTERNOON INTO TONIGHT. AN EASTERLY FLOW BEHIND THE SURFACE TROUGH
WILL ALLOW FOR MOISTURE TO RETURN DURING THIS TIME. THERE SHOULD
BE ENOUGH BREAKS IN MID-LEVEL CLOUDS FOR MAX TEMPS TO REACH THE
MIDDLE 80S ACROSS MOST LOCATIONS. THE INCREASED MOISTURE WILL
ALLOW FOR AN UNSTABLE ATMOSPHERE TO DEVELOP ONCE AGAIN THIS
AFTERNOON. THE MODIFIED 12Z KIAD SHOWS AROUND 1000 TO 1500 J/KG OF
MLCAPE. THE UPPER-LEVEL TROUGH WILL ALSO MOVE OVERHEAD DURING THIS
TIME ALONG WITH THE RIGHT ENTRANCE OF THE UPPER-LEVEL JET. THE
FORCING FROM THE UPPER-LEVEL JET AND TROUGH ALONG WITH THE
SURFACE TROUGH WILL ALLOW FOR MORE SHOWERS AND THUNDERSTORMS TO
DEVELOP THIS AFTERNOON. DEEP LAYER SHEAR WILL REMAIN SUFFICIENT
ENOUGH TO COMBINE WITH THE INSTABILITY FOR THE THREAT OF SEVERE
THUNDERSTORMS. LOCALLY DAMAGING WIND GUSTS AND LARGE HAIL WOULD BE
THE PRIMARY THREATS. DO FEEL THAT THE SEVERE THREAT WILL BE
LOCALIZED SIMILAR TO WEDNESDAY AND NOT AS WIDESPREAD AS TUESDAY OF
THIS WEEK.

ANOTHER CONCERN IS FOR HEAVY RAINFALL. THE SHEAR VECTORS INDICATE
THAT STORMS WILL TRAIN OVER THE SAME AREAS...AND WITH THE RETURN
OF MOISTURE PWATS WILL RETURN TO AROUND 1.75 TO 2.00 INCHES. THE
SURFACE TROUGH WILL ALSO BE SLOWLY MOVING AND THE SHEAR VECTORS
ARE NEARLY PARALLEL TO THAT. THEREFORE...FLASH FLOODING IS A
CONCERN...ESPECIALLY FROM THE SHENANDOAH VALLEY/NORTH-CENTRAL
MARYLAND EASTWARD LATE THIS AFTERNOON INTO TONIGHT. DID NOT ISSUE
A FLASH FLOOD WATCH AT THIS TIME DUE TO LOW CONFIDENCE...BUT WILL
COVER THE THREAT IN THE HAZARDOUS WEATHER OUTLOOK FOR NOW.

THE UPPER LEVEL TROUGH WILL SHIFT TOWARD THE MID-ATLANTIC COAST
LATE TONIGHT AND SHOWERS AND THUNDERSTORMS WILL MOVE OFF TO THE
EAST BY FRIDAY MORNING. THE TROUGH AXIS WILL REMAIN NEAR THE MID-
ATLANTIC COAST FRIDAY. AN ISOLATED SHOWER OR THUNDERSTORM CANNOT
BE RULED OUT...BUT MOST AREAS WILL END UP DRY SINCE WE WILL BE ON
THE SUBSIDENCE SIDE OF THE TROUGH.

&&

.SHORT TERM /FRIDAY NIGHT THROUGH SATURDAY/...
ANY CONVECTION FROM FRIDAY AFTERNOON SHOULD DISSIPATE DURING THE
EVENING...WITH CLEARING SKIES PROMOTING PATCHY FOG DEVELOPMENT
OVERNIGHT. FRONTAL BOUNDARY REMAINS SOUTH OF THE CWA ON
SATURDAY...AND IN CONJUNCTION WITH FLAT RIDGING ALOFT MAY HELP TO
INHIBIT THUNDERSTORM DEVELOPMENT HOWEVER CAN/T RULE OUT A FEW
TERRAIN-INDUCED DIURNAL STORMS AND THIS IS WHERE LOW CHANCE POPS
RESIDE.

&&

.LONG TERM /SATURDAY NIGHT THROUGH WEDNESDAY/...
FRONTAL BOUNDARY /OR WHAT IS LEFT OF IT/ LOOKS TO LIFT BACK TO THE
NORTH AS A WARM FRONT ON SUNDAY. MOISTURE WILL BE BETTER AND WITH
SOME AFTERNOON INSTABILITY THERE WILL BE A CHANCE OF THUNDERSTORMS
BACK FOR THE ENTIRE CWA.

CONVECTIVE CHANCES LIKELY INCREASE FURTHER EARLY NEXT WEEK WITH
DEEPER MOISTURE AND DECENT INSTABILITY ALONG WITH LOWER HEIGHTS
FROM AN UPPER TROUGH AND ALSO A SURFACE TROUGH ON MONDAY FOLLOWED
BY A COLD FRONT ON TUESDAY. THIS COLD FRONT IS EXPECTED TO MOVE
THROUGH BY TUESDAY NIGHT...ALLOWING FOR DRIER AIR TO MOVE IN FOR
WEDNESDAY.

&&

.AVIATION /14Z THURSDAY THROUGH MONDAY/...
VFR CONDITIONS ARE EXPECTED MOST OF THE TIME THROUGH THIS EVENING.
SHOWERS AND THUNDERSTORMS WILL INCREASE IN COVERAGE LATER THIS
AFTERNOON AND EVENING. A FEW THUNDERSTORMS WILL BE CAPABLE OF
PRODUCING GUSTY WINDS AND HAIL ALONG WITH LOCALLY HEAVY RAINFALL
THAT CAN REDUCE CIGS/VSBYS TO IFR LEVELS. FOG/BR IS EXPECTED LATE
TONIGHT.

A FRONTAL BOUNDARY REMAINS TO THE SOUTH INTO SATURDAY THEN LIFTS
BACK NORTH SUNDAY. COLD FRONT THEN WILL AFFECT THE AREA EARLY NEXT
WEEK WITH A CHANCE OF THUNDERSTORMS.

&&

.MARINE...
WINDS WILL TURN TO THE SOUTHEAST THIS AFTERNOON THROUGH
TONIGHT...BUT SPEEDS WILL REMAIN BELOW SCA CRITERIA. SHOWERS AND
THUNDERSTORMS ARE POSSIBLE LATE THIS AFTERNOON WELL INTO TONIGHT.
SOME THUNDERSTORMS WILL BE CAPABLE OF PRODUCING GUSTY WINDS AND
HAIL ALONG WITH LOCALLY HEAVY RAINFALL THAT MAY REDUCE VSBYS BELOW
ONE MILE AT TIMES.

RELATIVELY WEAK GRADIENT SHOULD PRECLUDE SCA CONDITIONS INTO THE
FIRST PART OF THE WEEKEND. WILL HAVE TO WATCH SOUTHERLY FLOW BY
SUNDAY AS MARGINAL SCA CONDITIONS MAY BE POSSIBLE UP THE BAY BY
EVENING AND POSSIBLY CONTINUING INTO EARLY NEXT WEEK AHEAD OF A COLD
FRONT.

&&

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

&&

$$
SYNOPSIS...BPP/HAS
NEAR TERM...BJL/HAS
SHORT TERM...BPP
LONG TERM...BPP
AVIATION...BJL/BPP/HAS
MARINE...BJL/BPP/HAS







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