Area Forecast Discussion
Issued by NWS Sterling, VA

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000 FXUS61 KLWX 120754 AFDLWX AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC 354 AM EDT SAT JUL 12 2014 .SYNOPSIS... HIGH PRESSURE WILL SHIFT OFFSHORE...ALLOWING SOUTHERLY RETURN FLOW TO BECOME ESTABLISHED IN THE MID ATLANTIC THROUGH MONDAY. A COLD FRONT WILL CROSS THE AREA TUESDAY. HIGH PRESSURE WILL BUILD ALONG THE EASTERN SEABOARD FOR THE SECOND HALF OF THE WEEK. && .NEAR TERM /THROUGH TONIGHT/... BAROCLINIC ZONE WAS LOCATED FROM THE OUTER BANKS OF NORTH CAROLINA WESTWARD THROUGH THE SOUTHEAST STATES...ALLOWING WEAK HIGH PRESSURE TO RESIDE ACROSS THE NORTHEAST AND MID-ATLANTIC STATES. AREA OF CLOUDS WAS NOTED OVER THE CENTRAL SHENANDOAH VALLEY AND FOOTHILLS AT 06Z...WITH MOSTLY CLEAR SKIES ELSEWHERE. PATCHY FOG WAS DEVELOPING IN THE NORTHERN VIRGINIA PIEDMONT WHERE SKIES WERE MOSTLY CLEAR. FOG HAS YET TO DEVELOP WITHIN THE CENTRAL SHENANDOAH VALLEY/FOOTHILLS WHERE IT WAS LOCALLY DENSE YESTERDAY MORNING BUT IF SKIES CAN CLEAR BY DAYBREAK...THEN THERE WILL BE PATCHY FOG HERE AS WELL. FOR THE REST OF THE DAY...BANDS OF MID/HIGH CLOUDS VISIBLE UPSTREAM OVER THE OHIO VALLEY WILL SPREAD EAST THROUGH THE DAY LIKELY TRANSITIONING THE SKY TO PARTLY SUNNY BY AFTERNOON. DURING PEAK HEATING...DESPITE THE CLOUD COVER SCATTERED THUNDERSTORMS ARE EXPECTED TO DEVELOP NEAR THE HIGHER TERRAIN/RIDGES. IT/S NOT OUT OF THE QUESTION THAT A FEW STORMS COULD PUSH EAST OF THE BLUE RIDGE LATER IN THE AFTERNOON/EARLY EVENING AS SUGGESTED BY THE OPERATIONAL NAM/LWX WRF-ARW...BUT PREFERRED MORE OF A SREFS SOLUTION WITH POPS RELEGATED TO ALONG AND WEST OF THE BLUE RIDGE. 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 ANOMOLOUS 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 ANOTHR 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 /08Z SATURDAY THROUGH WEDNESDAY/... ALREADY HAVE SOME CLOUDS OVER CHO...WITH MORE UPSTREAM ON THE WAY FOR CHO AND MRB THROUGH SUNRISE. CLOUDS SHOULD HELP VIS FROM TANKING...THUS HAVE ALLOWED FOR MVFR RESTRICTIONS /BUT NOT IFR/ EARLY THIS MORNING. A FEW THUNDERSTORMS MAY FORM NEAR THE HIGHER TERRAIN THIS AFTERNOON...MRB MOST VULNERABLE. SOME GUIDANCE SUGGESTS THERE COULD BE CONVECTION MOVING EAST TO AFFECT CHO/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... WINDS WERE MAINLY FROM SOUTHEAST TO SOUTH EARLY THIS MORNING... FAVORING NEARLY DUE SOUTH THIS AFTERNOON INTO TONIGHT IN TANDEM WITH AN INCREASE IN SPEEDS. SCA IS ALREADY IN EFFECT FOR MUCH 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 WERE RUNNING CLOSE TO NORMAL EARLY THIS MORNING...BUT AS SOUTHERLY FLOW INCREASES SO TOO WILL ANOMALIES LATER TODAY INTO TONIGHT. NEXT COUPLE OF HIGH TIDES SHOULD BE COMFORTABLY BELOW MINOR FLOOD CRITERIA...BUT BY THE EARLY SUNDAY MORNING HIGH TIDE SENSITIVE SITES SUCH AS ANNAPOLIS MAY APPROACH MINOR FLOODING THRESHOLDS. && .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...HTS NEAR TERM...BPP SHORT TERM...BPP LONG TERM...HTS AVIATION...BPP/HTS MARINE...BPP/HTS TIDES/COASTAL FLOODING...BPP

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