Area Forecast Discussion
Issued by NWS Sterling, VA

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000
FXUS61 KLWX 230819 AAA
AFDLWX

AREA FORECAST DISCUSSION...UPDATED
NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC
419 AM EDT WED JUL 23 2014

.SYNOPSIS...
A COLD FRONT FROM THE GREAT LAKES WILL SLOWLY APPROACH THE REGION
THROUGH TONIGHT. THE BOUNDARY WILL SLOWLY PASS THROUGH THE AREA
THURSDAY INTO THURSDAY NIGHT AND HIGH PRESSURE WILL RETURN FOR
FRIDAY. HIGH PRESSURE WILL MOVE OFF THE COAST DURING THE WEEKEND
AND A COLD FRONT WILL PASS THROUGH THE AREA EARLY NEXT WEEK.

&&

.NEAR TERM /THROUGH TONIGHT/...
A CUT-OFF UPPER LOW OVER THE GULF COAST AND A STALLED UPPER TROUGH
JUST OFF THE CAROLINA COAST...WHILE A LARGE UPPER TROUGH IS SLOWLY
DIGGING DOWN TOWARD THE AREA - READY FOR A PASSAGE IN THE NEXT DAY
OR SO. TODAY WILL BE THE WARMEST DAY OF THE STRETCH...NOT ONLY IN
AMBIENT TEMPS BUT CONSIDERING REL HUMIDITIES AS WELL. DEWPOINTS
WON`T STRAY FAR FROM THE L70S ALL-DAY AND EVEN INTO THE OVERNIGHT
HRS TONIGHT. THIS WILL BE AMPLE NEAR-SFC MOISTURE FOR THE QUICK
DEVELOPMENT OF UPDRAFTS GIVEN A PRE-EXISTING OR INCOMING SFC
BOUNDARY LATER TODAY. BY ITSELF...THE INSTABILITY FROM DAYTIME
HEATING MAY NOT BE ENOUGH FOR INITIATION...EVEN W/ TEMPS REACHING
THE L90S DURING THE MID-AFTN. DURING THE FIRST HALF OF THE DAY...A
WARM NOSE IN THE 10-15KFT REGION OVERHEAD MAY KEEP UNFAVORABLE LAPSE
RATES IN PLACE...EVEN AS THE LOW LEVEL CAPPING INVERSION IS BEING
BROKEN.

LACK OF SHEAR WILL BE THE OTHER ISSUE IN TERMS OF CONVECTIVE
INITIATION. A WEAK COLUMN EXISTS OVERHEAD...W/ OUR AREA STILL ON THE
WRN PERIPHERY OF THE BERMUDA HIGH AND LITTLE/NO DYNAMIC FEATURES
NEARBY. A SERIES OF WEAK PRE-FRONTAL TROUGHS ARE MAKING THEIR WAY
DOWN ACROSS THE UPPER MIDWEST ATTM...BUT WILL ONLY GRADUALLY WORK
THEIR WAY TOWARD THE CNTRL APLCNS AND EVENTUALLY OVER OUR AREA LATER
THIS EVE/TONIGHT. THE COLD FRONT ITSELF WILL ALSO BE SLOW-MOVING AND
WON`T ARRIVE UNTIL DURING THE OVERNIGHT HRS. BEFORE
THEN...INSTABILITY WILL GRADUALLY INCREASE DURING THE AFTN HRS W/
AMPLE SUNSHINE TO START THE DAY BUT A CUMULUS FIELD WILL QUICKLY
DEVELOP AND DAYTIME BOUNDARY LAYER MIXING WILL START TO CREATE THE
TYPICAL BAY BREEZE AND LAND BREEZE BOUNDARIES.

LOCAL HI-RES WRF GUIDANCE SUGGESTING THAT A MID-AFTN INITIATION OF
DISCRETE SHOWERS/TSTMS WILL DEVELOP ALONG OR W/IN A COUNTY OF THE
NRN VA BLUE RIDGE - LIKELY W/ A PRE-FRONTAL LEE TROUGH AXIS. THE
ACTIVITY WOULD THEN DRIFT SE OVER TIME AND POTENTIALLY DEVELOP NEW
OUTFLOW-DRIVEN CELLS FURTHER EAST/SE. CHANCES FOR PRECIP BEFORE 18Z
ARE SLIM BUT A BOUNDARY SUCH AS A LOW LEVEL TROUGH MAY HELP QUICKLY
ELEVATE THE RISK OF TSTMS. HOWEVER...STILL NOT A STRONG SIGNAL
TOWARD THIS...ESPEC W/ MINIMAL SHEAR - ONLY ABOUT 15KT BULK IN THE
MID LEVELS AND POSSIBLY 5KT IN THE LOW LEVELS...TOUGH TO SUSTAIN
UPDRAFTS IN THAT ENVIRONMENT.

HEADING INTO THE LATE AFTN/EVE HRS...AS SHEAR SLOWLY BUT SURELY
BEGINS TO ARRIVE FROM THE NW...THE POTENTIAL WILL INCREASE. HEATING
WILL CONTINUE THROUGHOUT THE EVE - STILL BEING LATE JULY W/ THE
LONGER DAYTIME PERIOD. DEWPOINTS WILL STAY HIGH...SO THE POTENTIAL
FOR STRONG AND EVEN A FEW SEVERE STORMS WILL BE POSSIBLE AS MORE
DYNAMIC SHEAR ARRIVES AND BEGINS TO SHAPE ONGOING ACTIVITY. DAMAGING
WINDS WOULD BE THE MAIN THREAT...W/ THE PROFILE NOT AS FAVORABLE FOR
HAIL W/ SUCH SHORT-LIVED AND WEAKLY FORCED UPDRAFTS.

TONIGHT...BEFORE THE COLD FRONT ARRIVES FROM THE NORTH...TEMPS WILL
STILL BE FAIRLY WARM. 80S WILL STILL DOT THE MAP WELL AFT SUNSET BUT
AS THE FRONT MOVES IN FROM THE NW...TEMPS WILL SLOWLY DROP OVER THE
NWRN PART OF THE AREA AS DRIER NW WINDS TAKE DOWN TEMPS AND
DEWPOINTS.

&&

.SHORT TERM /THURSDAY THROUGH FRIDAY/...
AN UPPER-LEVEL TROUGH WILL REMAIN OVER THE REGION THURSDAY THROUGH
FRIDAY. A COLD FRONT WILL SLOWLY PASS THROUGH THE AREA THURSDAY
INTO EVENING. MORE SHOWERS AND THUNDERSTORMS ARE POSSIBLE AHEAD OF THE
FRONT...ESPECIALLY ACROSS CENTRAL AND SOUTHERN PORTIONS OF THE
CWA WHERE MOISTURE WILL BE DEEPER. DRIER AIR WILL WORK ITS WAY
INTO MOST AREAS OVERNIGHT THURSDAY.

HIGH PRESSURE WILL BUILD OVER THE REGION FRIDAY. A SCT TO BKN CU
DECK SHOULD DEVELOP DURING THE AFTERNOON DUE TO THE UPPER-LEVEL
TROUGH OVERHEAD. TERRAIN CIRCULATION COULD LEAD TO AN ISOLATED
SHOWER WEST OF THE BLUE RIDGE MOUNTAINS...BUT THE FORECAST REMAINS
DRY FOR NOW THINKING THAT LOW-LEVEL DRY AIR SHOULD SUPPRESS
CONVECTION FOR MOST AREAS. MAX TEMPS WILL BE NEAR CLIMO...RANGING
FROM THE 70S IN THE MOUNTAINS TO THE MID AND UPPER 80S ACROSS MOST
OTHER LOCATIONS...AND IT WILL FEEL NOTICEABLY LESS HUMID COMPARED
TO RECENT DAYS.

&&

.LONG TERM /FRIDAY NIGHT THROUGH TUESDAY/...
HIGH PRESSURE WILL SLOWLY MOVE OFF THE COAST FRIDAY NIGHT INTO
SATURDAY AND IT WILL REMAIN OVER THE ATLANTIC OCEAN FOR SUNDAY. A
RETURN SOUTHERLY FLOW WILL ALLOW FOR THE HUMIDITY TO RETURN
DURING THE WEEKEND. A COUPLE SHOWERS AND THUNDERSTORMS ARE
POSSIBLE SATURDAY AFTERNOON AND EVENING...BUT CONVECTION SHOULD BE
LIMITED IN COVERAGE DUE TO THE LACK OF A STRONG LIFTING MECHANISM.

HOWEVER...A POTENT SHORTWAVE IS EXPECTED TO DIG THROUGH THE GREAT
LAKES AND INTO NEW ENGLAND SUNDAY. THIS WILL INCREASE SHEAR
PROFILES AND CARVE OUT A TROUGH OF LOW PRESSURE BOTH AT THE
UPPER LEVELS AND LOWER LEVELS OF THE ATMOSPHERE. SHOWERS AND
THUNDERSTORMS MAY INCREASE IN COVERAGE FOR THESE REASONS SUNDAY. A
POTENT COLD FRONT WILL LIKELY PASS THROUGH THE REGION
MONDAY...BRINGING THE CHANCE FOR MORE SHOWERS AND THUNDERSTORMS
BEFORE COOLER AND DRIER AIR MOVES INTO THE REGION DURING THE
MIDDLE PORTION OF NEXT WEEK.

&&

.AVIATION /08Z WEDNESDAY THROUGH SUNDAY/...
AN UPPER RIDGE KEEPING THE AIRMASS OVERHEAD WILL KEEP THE AREA UNDER
MOIST AND HUMID CONDITIONS THROUGHOUT THE DAY. THE TYPICAL TERRAIN
CIRCULATIONS OCCURRING OVER THE APLCNS TO THE WEST OF THE METRO
AREAS...WHEN THERE IS A LARGE OFFSHORE HIGH AS THERE IS CURRENTLY.
THE MTNS RECEIVE PERIODS OF LOW LEVEL CONVERGENCE W/
MOISTURE...HELPING TO MAKE SCATTERED BATCHES OF MID-LEVEL DECKS.
MOSTLY CLEAR FURTHER EAST...AS IT WILL REMAIN SO IN THE COMING HRS.

ONLY THE DAYTIME HEATING OF THE MID-LATE MRNG WILL BEGIN DEVELOPING
SCATTERED CUMULUS CLOUD DECKS ACROSS THE REGION AND EVENTUALLY HELP
W/ ISOLATED SHOWERS/TSTMS AS THE DAY PROGRESSES. THE CONVECTIVE
POTENTIAL INCREASES LATER TODAY...AS THE WINDS IN THE COLUMN
INCREASE - ALBEIT SLIGHTLY AND SLOWLY. INCOMING 20-30KT LOW LEVEL
SHEAR SHOULD BE ENOUGH TO CREATE INCREASED CONVECTIVE POTENTIAL OVER
MORE OF THE AREA LATER TONIGHT. A COLD FRONT WILL SLOWLY ARRIVE OUT
OF THE NW LATE TONIGHT AND INTO THE OVERNIGHT...TURNING SFC FLOW OUT
OF THE NW AND NORTH...THOUGH STILL FAIRLY LIGHT. THIS WILL ALSO
SLOWLY END THE CONVECTIVE POTENTIAL...MAKING ONGOING ACTIVITY TURN
INTO SHOWERS.

SUBVFR CIGS AND VSBYS ARE POSSIBLE FROM PATCHY LOW CLOUDS AND FOG
THURSDAY MORNING. A COLD FRONT WILL SLOWLY PASS THROUGH THE
TERMINALS THURSDAY INTO THURSDAY EVENING. SHOWERS AND
THUNDERSTORMS ARE POSSIBLE AHEAD OF THE FRONT...WITH THE MOST
WIDESPREAD COVERAGE BEING ACROSS THE CENTRAL AND SOUTHERN
TERMINALS. SUBVFR CONDITIONS ARE POSSIBLE IN ANY SHOWERS AND
THUNDERSTORMS.

DRIER AIR WILL MOVE IN BEHIND THE COLD FRONT THURSDAY NIGHT
THROUGH FRIDAY. PATCHY BR MAY CAUSE SUBVFR VSBYS EARLY FRIDAY
MORNING...ESPECIALLY ACROSS KCHO WHERE DRIER AIR WILL BE LOWER TO
MOVE IN. HIGH PRESSURE WILL BUILD OVERHEAD FRIDAY INTO FRIDAY
NIGHT BEFORE MOVING OFF THE COAST DURING THE WEEKEND. A SOUTHERLY
FLOW WILL CAUSE MORE MOISTURE TO RETURN ALONG WITH AN INCREASED
CHANCE FOR SHOWERS AND THUNDERSTORMS...ESPECIALLY SUNDAY AFTERNOON
AND EVENING.

&&

.MARINE...
LIGHT WINDS OVER THE WATERS ATTM...W/ ONLY SOME SLY CHANNELING
ACROSS THE MID-BAY REGION. THIS REGIME WILL STAY IN PLACE FOR MUCH
OF THE DAY...EVEN AS PRES GRADIENT INCREASES. A FEW NEAR-SCA GUSTS
MAY APPEAR LATER THIS AFTN. WINDS WILL SHIFT TO THE NORTHWEST
BEHIND A SURFACE TROUGH TONIGHT. WINDS WILL BE BELOW SCA
CRITERIA...10-15KT OR LESS. THUNDERSTORMS ARE POSSIBLE THIS
AFTERNOON AND EVENING ACROSS THE WATERS. THUNDERSTORMS WILL BE
CAPABLE OF PRODUCING GUSTY WINDS AND HAIL.

A COLD FRONT WILL SLOWLY PASS THROUGH THE WATERS THURSDAY INTO
THURSDAY EVENING. SHOWERS AND THUNDERSTORMS ARE POSSIBLE DURING
THIS TIME...ESPECIALLY ACROSS THE MIDDLE PORTION OF THE BAY AND
THE LOWER TIDAL POTOMAC RIVER. A PRESSURE SURGE BEHIND THE FRONT
MAY CAUSE NORTHERLY WINDS TO GUST NEAR SCA CRITERIA OVERNIGHT
THURSDAY INTO FRIDAY MORNING ACROSS THE MARYLAND PORTION OF THE
CHESAPEAKE BAY AND THE LOWER TIDAL POTOMAC RIVER.

HIGH PRESSURE WILL BUILD OVER THE WATERS FRIDAY AND WINDS WILL
WEAKEN AND PERHAPS EVEN TURN ONSHORE DURING THE AFTERNOON. HIGH
PRESSURE WILL MOVE OFF THE COAST SATURDAY AND SUNDAY AND A
SOUTHERLY FLOW WILL RETURN DURING THIS TIME. THE SOUTHERLY FLOW
WILL BRING MORE MOISTURE...INCREASING THE CHANCE FOR SHOWERS AND
THUNDERSTORMS...ESPECIALLY SUNDAY. A POTENT COLD FRONT WILL MOVE
TOWARD THE WATERS MONDAY...BRINGING THE CHANCE FOR MORE
THUNDERSTORMS.

&&

.TIDES/COASTAL FLOODING...
A SOUTHERLY FLOW HAS CAUSED TIDAL ANOMALIES TO BE AROUND ONE-HALF
TO THREE QUARTERS OF A FOOT ABOVE NORMAL. THE MAX HIGH TIDE WILL
BE EARLY THIS MORNING...BUT WATER LEVELS SHOULD REMAIN JUST BELOW
MINOR FLOODING THRESHOLDS. THE POSITIVE ANOMALIES WILL CONTINUE
THIS AFTERNOON AND EVENING...BUT THE HIGH TIDE WILL BE THE LOWER
OF THE TWO SO MINOR FLOODING IS NOT EXPECTED. THE FLOW WILL
TURN OFFSHORE BEHIND A SURFACE TROUGH LATE TONIGHT INTO
THURSDAY...SO ANOMALIES ARE EXPECTED TO DECREASE DURING THIS
TIME.

&&

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

&&

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







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