Area Forecast Discussion
Issued by NWS Sterling, VA

Current Version | Previous Version | Text Only | Print | Product List | Glossary Off
Versions: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50

000
FXUS61 KLWX 160814 AAA
AFDLWX

AREA FORECAST DISCUSSION...UPDATED
NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC
414 AM EDT SAT AUG 16 2014

.SYNOPSIS...
HIGH PRESSURE WILL MOVE OFF THE COAST TODAY AND AN UPPER-LEVEL
DISTURBANCE WILL PASS THROUGH THE REGION SUNDAY. A STRONGER
DISTURBANCE AND ITS ASSOCIATED SURFACE LOW WILL PASS THROUGH THE
AREA LATER MONDAY INTO TUESDAY. THE COLD FRONT ASSOCIATED WITH
THIS LOW WILL STALL OUT NEAR THE AREA DURING THE MIDDLE PORTION OF
NEXT WEEK.

&&

.NEAR TERM /THROUGH TONIGHT/...
A COUPLE OF WEAK EMBEDDED SHORTWAVES HAVE BEEN SWINGING AROUND THE
BASE OF A LARGE UPPER TROUGH FROM THE GREAT LAKES TO THE MID-ALTC
COAST. THE CLOSEST SHORTWAVE HAS HELPED KICK-OFF A HANDFUL OF
SHOWERS ALONG THE SRN PERIPHERY OF THE CWA FROM N CNTRL VA ALONG THE
TIDAL PTMC AND LOWER SRN MD. THIS ACTIVITY IS MOVING OVER SRN
PORTIONS OF THE MD BAY...THE LAST EXPECTED PRECIP FOR THE REGION
UNTIL EARLY SUN W/ THE ARRIVAL OF A COLD FRONT.

UNTIL THE ARRIVAL OF THE FRONT...HIGH PRESSURE WILL ROLL ACROSS THE
AREA AND OFF THE COAST AHEAD OF THE COLD FRONT. THE SFC HIGH ITSELF
IS A FAIRLY WEAK AND ELONGATED FEATURE...STRETCHED ACROSS THE ERN
SEABOARD STATES AND THE CENTER HOVERING OVER THE SRN APLCNS. THE
POSITION OF THE HIGH WILL ALLOW FOR A WEAK SWLY SFC WIND LATER THIS
AFTN THAT WILL HELP ADVECT RELATIVELY WARMER AND MORE MOIST AIR BACK
INTO THE REGION THAN WE RECEIVED ON FRIDAY. AFTER ANOTHER COOL
OVERNIGHT PERIOD...TEMPS WILL RISE BACK INTO THE 70S AND L80S TOWARD
THE LATE MRNG HRS TODAY. HIGHS FOR MUCH OF THE AREA WILL REACH THE
L80S...W/ A FEW M80S ALONG AND NEAR THE I-95 CORRIDOR/DC-BALT METRO
AREA...UNDER MOSTLY CLEAR SKIES. BASE MAV VALUES SEEMED A BIT
HIGH...THOUGH THE BIAS-CORRECTED VALUES ARE MORE REASONABLE.
FORECAST HIGHS ARE A BLEND OF THE BC-MAV/ADJ-MET AND COUPLE OF WRF
DERIVATIVES.

A DEWPOINT GRADIENT WILL ALSO BE STATIONED ALONG AND E OF THE I-95
CORRIDOR...LEADING TO SOME WEAK CONVERGENCE AREAS LATER THIS AFTN.
S-SW FLOW INTO THE ZONE COULD LEAD TO SOME ISOLATED SHOWER ACTIVITY
DEVELOPING ACROSS AND/OR EAST OF THE CHES BAY THIS AFTN. RECENT
MESOANALYSIS INDICATES A WEAK SFC LOW OVER THE NRN NECK WHICH IS
EXPECTED TO DRIFT NE ACROSS THE DELMARVA PENINSULA OVER THE NEXT
SEVERAL HRS...POTENTIALLY PROVIDING THE LIFT/CONVERGENCE FOR SOME
ISOLATED SHOWERS AND PATCHY MID STRATUS DECKS.

A BRIEF PERIOD OF ZONAL UPPER FLOW TOWARD THE END OF TODAY WILL
QUIET DOWN WX ACROSS THE REGION EVEN FURTHER...CLEARING SKIES OUT
AND DROPPING WINDS BACK DOWN TO NEAR-CALM CONDITIONS. THE GRADUAL
INCREASE IN DEWPOINTS WILL TEMPER OVERNIGHT LOWS...KEEPING THEM
LOCKED IN THE L-M60S FOR MUCH OF THE AREA.

&&

.SHORT TERM /SUNDAY THROUGH SUNDAY NIGHT/...
BY SUNRISE...A COLD FRONT WILL ALREADY BE ON THE NRN DOORSTEP OF THE
CWA. THE FRONT WILL BE CONNECTED TO A LOW THAT WILL BE QUICKLY SWEPT
ACROSS THE NRN NEW ENGLAND STATES OVER THE COURSE OF THE DAY. THE
UPPER FLOW WILL CARRY THE SYSTEM AND MUCH OF THE DYNAMICS WELL OFF
TO OUR NORTH...W/ NOT MUCH LEFT TO PUSH THE COLD FRONT STEADILY
ACROSS OUR AREA. SOME LIGHT SHOWER ACTIVITY WILL PUSH INTO THE CNTRL
APLCNS DURING THE FIRST HALF OF THE DAY...W/ SOME FRACTIONS OF THE
ACTIVITY MOVING TOWARD THE BLUE RIDGE AND EAST...BUT MAINLY JUST
CLOUD DEBRIS WILL COVER THE METRO AREAS AND EAST W/ LITTLE MORE THAN
A BRIEF SHOWER.

THE INCREASING CLOUD COVER MAY TEMPER THE EXPECTED HIGHS FOR SUNDAY
WHICH ARE M-U80S. THE FRONT ITSELF IS NOT EXPECTED TO NECESSARY
CLEAR THE AREA BUT INSTEAD BECOME STATIONARY AS THE SFC LOW EXITS
OFF TO THE NE AND AN INCOMING LOW FROM THE WEST BEGINS TO STRENGTHEN
THE PRE-STORM WARM FRONTAL REGION ACROSS THE UPPER MIDWEST. THE LACK
OF AN ACTUAL PASSAGE AND THE MODIFYING OF THE AIRMASS WILL ALLOW
TEMPS TO CLIMB BACK INTO THE 80S AND AN LIKELY EVEN TOP-OUT A COUPLE
OF DEGREES HIGHER THAN ON SAT. AN INCREASE IN THE LOW LEVEL MOISTURE
PROFILE WILL ALSO INCREASE THE HUMIDITY AND THEREFORE THE HEAT
INDICES - WHICH MAY APPROACH OR BARELY EXCEED THE 90-DEG MARK SUN
AFTN.

A SHORTWAVE WILL MOVE OFF TO OUR EAST SUNDAY NIGHT AND A COLD
FRONT WILL REMAIN STALLED OUT OVER THE AREA. ANY EVENING
CONVECTION SHOULD DISSIPATE AND MOST AREAS ARE EXPECTED TO TURN
OUT DRY SUNDAY NIGHT DUE TO SUBSIDENCE BEHIND THE SHORTWAVE.
HOWEVER...THERE WILL BE SOME CLOUDS THAT REMAIN OVER THE CENTRAL
AND SOUTHWESTERN PORTIONS OF THE CWA AS ANOTHER DISTURBANCE
APPROACHES FROM THE WEST.

&&

.LONG TERM /MONDAY THROUGH FRIDAY/...
THE BOUNDARY OVERHEAD WILL SHIFT NORTH AND DISSIPATE
MONDAY...ALLOWING FOR SOUTHERLY WINDS TO BRING MORE WARM AND HUMID
CONDITIONS. AN UPPER-LEVEL DISTURBANCE AND ITS ASSOCIATED SURFACE
LOW WILL TRACK THROUGH THE OHIO VALLEY DURING THIS TIME. MOST OF
THE FORCING WILL REMAIN TO OUR WEST...BUT THE WARM AND HUMID
ATMOSPHERE SHOULD PROVIDE ENOUGH INSTABILITY TO TRIGGER SOME
SHOWERS AND THUNDERSTORMS...ESPECIALLY ACROSS THE POTOMAC
HIGHLANDS AND CENTRAL VIRGINIA...WHERE MOISTURE WILL BE DEEPEST.

THE UPPER-LEVEL DISTURBANCE AND ITS ASSOCIATED LOW WILL PASS
THROUGH THE AREA MONDAY NIGHT INTO TUESDAY...BRINGING A BETTER
CHANCE FOR SHOWERS AND POSSIBLE THUNDERSTORMS. GUIDANCE STILL
DIVERGES IN ITS FORECASTED INTENSITY OF THIS SYSTEM...AND THAT
WILL HAVE A SIGNIFICANT IMPACT ON THE FORECAST. IF THIS SYSTEM
IS STRONGER LIKE THE GFS AND NAM SUGGEST...THEN THE FORCING WILL
COMBINE WITH TROPICAL MOISTURE TO BRING HEAVY RAINFALL TO THE AREA
DURING THIS TIME. HOWEVER...IF THE DISTURBANCE IS WEAKER AND
FARTHER SOUTH LIKE THE EURO AND CMC SUGGEST...THEN SHOWERS ARE
LIKELY BUT THE HEAVY RAIN THREAT WOULD NOT BE AS SIGNIFICANT.
GIVEN THE DEEP MOISTURE THAT WILL BE IN PLACE DURING THIS
TIME...EVEN A LITTLE FORCING WOULD INDICATE A THREAT FOR HEAVY
RAIN AND THIS WILL BE COVERED IN THE HWO FOR NOW.
HOWEVER...CERTAINTY IN THE COVERAGE OF HEAVY RAINFALL AND EXACTLY
HOW HEAVY RAIN WILL BE REMAINS LOW AT THIS TIME.

THIS SYSTEM WILL MOVE AWAY FROM THE AREA LATER TUESDAY...BUT A
BOUNDARY WILL REMAIN STALLED OUT OVER THE AREA. A NORTHWEST FLOW
ALOFT WILL DEVELOP DURING THE MIDDLE AND LATTER PORTIONS OF THE
WEEK AS A RIDGE BUILDS OVER THE CENTRAL CONUS. SEVERAL UPPER-LEVEL
DISTURBANCES MOVING OVERHEAD ALONG WITH THE BOUNDARY NEARBY
SUGGESTS THAT UNSETTLED CONDITIONS WILL OCCUR.

&&

.AVIATION /08Z SATURDAY THROUGH WEDNESDAY/...
A WEAK SFC LOW NEAR THE MD CHES BAY HELPING TO DEVELOP SOME PATCHES
OF MID-LEVEL STRATUS ACROSS THE REGION WHICH WILL DISSIPATE AND MOVE
EAST TOWARD THE PREDAWN HRS. HIGH PRESSURE WILL MOVE OFF THE COAST
LATER TODAY...BUT STILL KEEPING MUCH OF THE AREA CLEAR AND BRINGING
IN A LIGHT SW FLOW BY MID AFTN. SOLID VFR CONDITIONS THRU THE
CURRENT TAF PERIOD...W/ MID CLOUD DECKS AND A FEW SHOWERS ACROSS THE
WEST ARRIVING TOWARD THE END OF THE PERIOD...A PREVIEW OF THE COMING
ROUTINE CYCLE.

VFR CONDITIONS ARE EXPECTED SUNDAY EVENING...BUT PATCHY FOG IS
POSSIBLE OVERNIGHT SUNDAY INTO EARLY MONDAY. LOW PRESSURE WILL
APPROACH THE TERMINALS MONDAY BEFORE PASSING THROUGH MONDAY NIGHT
INTO TUESDAY. THERE IS A BETTER CHANCE FOR SHOWERS AND
THUNDERSTORMS DURING THIS TIME. THERE IS A POTENTIAL FOR LOCALLY
HEAVY RAINFALL DURING THIS TIME...BUT CERTAINTY REMAINS LOW.
SUBVFR CIGS/VSBYS ARE POSSIBLE IN SHOWERS AND THUNDERSTORMS. THE
LOW WILL MOVE AWAY FROM THE AREA TUESDAY...BUT A STALLED BOUNDARY
WILL REMAIN OVERHEAD...BRINGING THE CHANCE FOR CONVECTION THROUGH
WEDNESDAY.

&&

.MARINE...
A FEW SHOWERS MOVING OVER THE BAY WILL EXIT SHORTLY. LIGHT WINDS
OVER MUCH OF THE BAY AND TP RVR OVERNIGHT...THOUGH A FEW 10-15KT
BREEZES ONGOING OVER THE SRN MD BAY. HIGH PRESSURE WILL KEEP THE
LIGHT WINDS OVER THE WATERS THRU MUCH OF THE DAY. A COLD FRONT WILL
ARRIVE ON SUN MRNG...BUT WINDS ARE EXPECTED TO REMAIN BELOW SCA
LEVELS THROUGHOUT THE DAYTIME HRS.

NO MARINE HEADLINES ARE EXPECTED SUNDAY NIGHT INTO MONDAY. LOW
PRESSURE WILL APPROACH THE WATERS LATER MONDAY BEFORE PASSING
THROUGH MONDAY NIGHT INTO TUESDAY. THERE IS A BETTER CHANCE FOR
SHOWERS AND THUNDERSTORMS DURING THIS TIME. THE LOW WILL MOVE AWAY
FROM THE WATERS LATER TUESDAY...BUT A BOUNDARY WILL REMAIN NEARBY
BRINGING UNSETTLED CONDITIONS.

&&

.TIDES/COASTAL FLOODING...
POSITIVE TIDAL ANOMALIES OVER THE LOWER MD BAY ARE STILL HOVERING
BETWEEN 1/2 AND 3/4 FT ABOVE NORMAL...WHILE THE MIDDLE AND NRN BAY
ARE A BIT LOWER - MAINLY BELOW A 1/2 FT. HOWEVER...STILL COMING OUT
OF THE LATEST FULL MOON CYCLE AND WINDS OVER THE BAY AT TIMES
SHOWING AN ELY COMPONENT...LEVELS CLOUD INCREASE FURTHER HEADING
INTO THE NEXT COUPLE OF H.T. CYCLES. THE ARRIVAL OF A COLD FRONT ON
SUN MRNG AND SUBSEQUENT WLY FLOW SHOULD BEGIN TO CHOP AWAY AT HIGHER
ANOMALIES DURING THE DAY.

&&

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

&&

$$
SYNOPSIS...BJL
NEAR TERM...GMS
SHORT TERM...BJL/GMS
LONG TERM...BJL
AVIATION...BJL/GMS
MARINE...BJL/GMS
TIDES/COASTAL FLOODING...GMS






USA.gov is the U.S. government's official web portal to all federal, state and local government web resources and services.