Area Forecast Discussion
Issued by NWS Sterling, VA

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000
FXUS61 KLWX 121430
AFDLWX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC
1030 AM EDT SAT JUL 12 2014

.SYNOPSIS...
OFFSHORE HIGH PRESSURE WILL DOMINATE THE MID-ATLANTIC INTO SUNDAY.
A COLD FRONT WILL APPROACH THE AREA SUNDAY NIGHT INTO
MONDAY...WITH A STRONGER COLD FRONT LIKELY CROSSING THE AREA LATE
TUESDAY. HIGH PRESSURE WILL BUILD ALONG THE EASTERN SEABOARD FOR
THE SECOND HALF OF THE WEEK.

&&

.NEAR TERM /THROUGH TONIGHT/...
AS OF 14Z...SFC HIGH PRESSURE AXIS IS ALONG THE MID-ATLANTIC AND
SRN NEW ENGLAND COAST. MID-LEVEL CLOUDS EAST OF THE I-95 CORRIDOR
WILL CONTINUE TO DRIFT EAST FROM THE AREA THROUGH MIDDAY.

UPDATED POP/WX FORECAST BASED ON 11Z HRRR WITH A FARTHER EAST
FOCUS OF AFTERNOON SHOWER AND THUNDERSTORM ACTIVITY. CONVECTIVE
STORMS SHOULD INITIATE NEAR THE BLUE RIDGE AND PROGRESS OVER AT
LEAST THE WESTERN BALT-WASH SUBURBS. THIS WILL CONTINUE TO
MONITORED.

CONVECTION SHOULD BE DIURNALLY-DRIVEN AND DISSIPATE WITH THE SETTING
OF THE SUN. PATCHY FOG MAY FORM AGAIN OVERNIGHT...PARTICULARLY IN
CLIMATOLOGICALLY FOG PRONE AREAS AND ALSO PLACES THAT RECEIVE
RAINFALL.

&&

.SHORT TERM /SUNDAY THROUGH SUNDAY NIGHT/...
MODELS HAVE BEEN CONSISTENT THAT MOISTURE AND INSTABILITY WILL
INCREASE FOR SUNDAY. GFS HAS PRECIPITABLE WATER VALUES INCREASING
CLOSE TO 2 INCHES BY DAY/S END...WITH DEWPOINTS NEAR 70 DEGREES.
MODELS ALSO SHOW A DECENT VORT MAX AFFECTING THE CWA...PROMOTING AT
LEAST SCATTERED SHOWERS AND THUNDERSTORMS. WHILE SHEAR STILL LOOKS
BEST NORTHWEST OF THE CWA...INSTABILITY AND STRENGTH OF VORT MAX MAY
PROMOTE A FEW STRONG OR SEVERE STORMS DURING THE AFTERNOON.

ACTIVITY FROM SUNDAY AFTERNOON SHOULD DIMINISH/MOVE AWAY SUNDAY
EVENING BUT WILL CONTINUE WITH LOW POPS ACROSS NORTHWEST PORTION OF
THE CWA AS FASTER ADVANCE OF A TROUGH/COLD FRONT MAY ALLOW FOR SOME
OVERNIGHT CONVECTION WITHIN THIS ZONE.

LEANED CLOSER TO MAV FOR MAXIMA SUNDAY GIVEN SOUTHWEST FLOW IN THE
LOW LEVELS...MAV/MET WERE SIMILAR FOR SUNDAY NIGHT.

&&

.LONG TERM /MONDAY THROUGH FRIDAY/...
FCST FOR THE BGNG OF THE WK WL BE DOMINATED BY AN INCRSGLY AMPLIFIED
H5 PTTN...WHERE S/WV ENERGY WL DIVE ACRS THE GRTLKS...PUSHING A WELL
DEFINED CDFNT TWD THE ERN SEABOARD. AS CAN BE XPCTD W/ ANY ANOMALOUS
SOLN...VARIANCES EXIST AMONGST GDNC MEMBERS. REGARDLESS OF SPECIFICS
THERE IS CONSENSUS THAT CWFA MON WL BE W/IN WM SECTOR... AFFECTED BY
A HOT/HUMID/UNSTBL AMS. A LEE TROF AXIS MAY PROVIDE A NCSRY FOCUSING
MECHANISM...ALTHO ANOTHER SOURCE OF UVV WUD RESIDE ACRS THE NWRN CWFA
DUE TO APPROACHING BULK SHEAR AND OROGRAPHIC LIFT. HV OPTED TO PLACE
FOCUS...BY WAY OF LIKELY POPS...THERE. XPCT UPDRAFTS TO BE VIGOROUS
ENUF TO SUSTAIN THEMSELVES...AND HV CARRIED LKLY POPS INTO THE I-95
CRRDR BY EVNG. ALL NCSRY INGREDIENTS AVBL FOR TSTMS TO NOT ONLY
BECOME SVR...BUT ALSO BE ORGANIZED. JUST NEED TO SEE HOW IT ALL
SHAKES OUT.

AM THINKING THAT THE GFS MAY BE A LTL TOO QUICK W/ PROGRESSION OF
CDFNT. ITS TIMING WL ULTIMATELY DETERMINE THE FATE FOR TUE. A FASTER
FNT WUD CURTAIN SVR TSTM CHCS. TOO MANY DEBRIS CLDS WUD YIELD THE
SAME OUTCOME. EITHER WAY...THE I-95 CRRDR STANDS THE BEST CHC AT
RECEIVING MEASUREABLE PCPN...WHICH WARRANTS LKLY POPS TUE. TO THE
W...POPS HELD BACK AT CHC LVLS. SVR TSTM RISK FOR BOTH MON AND TUE
WL BE CONT TO BE CARRIED IN THE HWO.

MAXT MON SIMLR TO PRVS FCST...GOING A PINCH ABV GDNC TO ACCT FOR
WARM H8 TEMPS AND AMPLE INSOLATION. TUE MAXT NEARER CLIMO DUE TO
XPCTD CLDS. IN FACT...W OF BLURDG A BIT BLO CLIMO. THIS FCST PD MAY
HV THE HIEST ERROR POTL IN THE XTNDD FCST. STAYED WARM FOR MIN-T MON
NGT...AS DEWPTS NEAR 70F WL INHIBIT SUBSTANTIVE COOLING.

BY TUE NGT-WED...CDFNT WL BE PUSHING AWAY FM CWFA...PERMITTING CNDN
HIPRES TO BLD. THIS HIGH WL BE THE CONTROLLING WX INFLUENCE FOR THE
REST OF THE WK. TEMPS/DEWPTS WL BE REFRESHING FOR JULY IN THE MID
ATLC.

&&

.AVIATION /14Z SATURDAY THROUGH WEDNESDAY/...
A FEW THUNDERSTORMS MAY FORM NEAR THE HIGHER TERRAIN THIS
AFTERNOON...MRB/CHO MOST VULNERABLE. SOME GUIDANCE SUGGESTS THERE
COULD BE CONVECTION MOVING EAST TO AFFECT IAD LATER IN THE
AFTERNOON. CONFIDENCE LOW...AND HAVE RESTRICTED CHANCES ALONG/WEST
OF THE BLUE RIDGE.

IF SKIES CLEAR OUT TONIGHT...SOME FOG IS POSSIBLE ESPECIALLY
CHO/MRB. HIGHER COVERAGE OF THUNDERSTORMS IS EXPECTED SUNDAY WITH
BETTER MOISTURE/INSTABILITY AND A SHORTWAVE. AFTERNOON THUNDERSTORMS
WILL BE POSSIBLE ALL TERMINALS.

FLGT RESTRICTIONS LKLY AT TIMES MON-TUE INVOF TSRA. VFR WL PREVAIL
FOR A MAJORITY OF THE TIME...BUT BRIEF PDS AOB IFR PSBL.

HIPRES BLDS WED. VFR.

&&

.MARINE...
SLY FLOW 5-10 KT THIS MORNING WILL INCREASE THROUGH THIS
AFTERNOON INTO TONIGHT AS HIGH PRESSURE PUSHES EAST FROM THE AREA.
SCA IS EFFECT FOR THE MAIN OF THE CHESAPEAKE BAY AND INTO THE
LOWER TIDAL POTOMAC LATE TODAY INTO TONIGHT. THERE MAY BE A LULL
DURING THE DAY SUNDAY...BUT IT/S POSSIBLE WINDS INCREASE INTO SCA
CRITERIA AGAIN SUNDAY EVENING OR SUNDAY NIGHT.

INTERVALS OF TSRA LKLY MON-TUE...EACH POSING A GUSTY WIND THREAT.
GRADIENT FLOW MAY BE ENUF TO PLACE WATERS ON THE CUSP OF SCA
ANYWAYS. ANY ADDTL WIND WUD NECESSITATE SMW/S. THE FINAL WAVE WUD BE
A CDFNT. ATTM GDNC NOT SUGGESTING GUSTY WNDS IN NW FLOW
POST-FROPA...BUT BASED ON TEMP CONTRAST...SUSPECT THAT WL CHG.
THERE/S A BIT OF UNCERTAINTY ON EXACTLY WHEN CFP WUD BE. SINCE THATS
AT THE END OF THE MARINE PD...WL OMIT ATTM. LATER FCSTS CAN ADDRESS
THESE DETAILS.

&&

.TIDES/COASTAL FLOODING...
WATER LEVELS ARE A COUPLE TENTHS FOOT ABOVE THE ASTRONOMICAL
PREDICTION THIS MORNING. THIS ANOMALY WILL INCREASE AS SOUTHERLY
FLOW STRENGTHENS INTO TONIGHT. THIS INCREASE AND A FULL MOON SOON
WILL ALLOW WATER LEVELS TO APPROACH MINOR FLOODING THRESHOLDS
AT SENSITIVE SITES LIKE ANNAPOLIS DURING THE PREFERRED SUNDAY
MORNING HIGH TIDE.

&&

.LWX WATCHES/WARNINGS/ADVISORIES...
DC...NONE.
MD...NONE.
VA...NONE.
WV...NONE.
MARINE...SMALL CRAFT ADVISORY FROM 6 PM THIS EVENING TO 6 AM EDT SUNDAY
     FOR ANZ531-539>541.
     SMALL CRAFT ADVISORY FROM 4 PM THIS AFTERNOON TO 6 AM EDT
     SUNDAY FOR ANZ532>534-537-543.

&&

$$
SYNOPSIS...BAJ/HTS
NEAR TERM...BAJ/BPP
SHORT TERM...BPP
LONG TERM...HTS
AVIATION...BAJ/BPP/HTS
MARINE...BAJ/BPP/HTS
TIDES/COASTAL FLOODING...BAJ








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