Area Forecast Discussion
Issued by NWS Sterling, VA

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944 FXUS61 KLWX 032034 AFDLWX AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC 334 PM EST WED FEB 3 2016 .SYNOPSIS...
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A COLD FRONT SLOWLY MOVES THROUGH THE REGION LATE TODAY BEFORE STALLING JUST OFFSHORE THROUGH FRIDAY. MULTIPLE LOW PRESSURES WILL RIDE THIS FRONT WITH HIGH PRESSURE BUILDING IN FOR THE WEEKEND. LOW PRESSURE IMPACTS THE REGION THE FIRST HALF OF NEXT WEEK.
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&& .NEAR TERM /THROUGH TONIGHT/...
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18Z SFC ANALYSIS SHOWING WARM FRONT ZIG ZAGGING ACROSS THE CWA...WITH THE COLD AIR WEDGE PERSISTING ACROSS CENTRAL MD. ASSOCIATED LOW PRESSURE BACK OVER THE GREAT LAKES WITH THE COLD FRONT EXTENDING SOUTH THROUGH THE OH RIVER VALLEY. GUIDANCE SHOWING LOW PROGRESSION OF THIS FRONT...EVENTUALLY MVG INTO THE CWA THIS EVENING AND SLOWLY SINKING SOUTH ACROSS THE CWA BY THURS MORNING BEFORE STALLING JUST TO THE SOUTH. PCPN OCCURRING NEARLY EVERYWHERE ACROSS THE CWA THIS AFTN...BEING DRIVEN BY STRONG LLJ ALIGNED PARALLEL TO APPALACHIANS AND STRONG SW FLOW ALOFT SURGING GOM MOISTURE ALL THE WAY UP THE EAST COAST. STRONG WINDS NOTED ALOFT...BUT OUTSIDE OF HEAVY SHOWERS...NOT SEEING NOR ANTICIPATING MUCH MIXING OF THE WINDS TO THE SFC. GUSTS TO 35 KTS PSBL WITH THE HEAVIEST SHOWERS. URBAN AND RIVER FLOODING REMAIN A THREAT...WITH THE FLOOD WATCH STILL IN EFFECT INTO TOMORROW. SEE HYDRO SECTION FOR MORE DETAILS. RAIN WILL END WEST OF THE BLUE RIDGE THIS EVENING...CONTINUING UP TO DC METRO THRU THE EARLY EVENING HOURS...AND LASTING OVER SOUTHERN MD THRU THE ENTIRE NIGHT. WITH LIGHT SOUTH WINDS...AND THE POOLING OF MOISTURE UNDER A LOW LVL INVERSION...EXPECTING FOG DEVELOPMENT FOR A GOOD PORTION OF THE NIGHT...UNTIL THE COLD FRONT MOVES THRU...SHIFTING AND INCRSG WINDS.
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&& .SHORT TERM /THURS THRU SAT/...
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12Z MODEL GUIDANCE HAS THE COLD FRONT JUST SOUTH OF THE AREA BY 12Z THURS. HOWEVER...WITH THE UPPER LVL TROUGH STILL WELL OFF TO THE WEST...THE LACK OF FORCING WILL NEARLY STALL THE BOUNDARY JUST OFFSHORE THURS INTO FRI. MEANWHILE...MULTIPLE SHORTWAVES RIDING THE FLOW WILL RESULT IN MULTIPLE LOWS RIDING THE STALLED FRONT...CONTINUING THE PCPN THREAT...ESP SOUTH AND EAST OF DC METRO DURING THIS TIME PERIOD. THE LATEST MODEL SUITE DOES DIVERGE ON THE SOLUTIONS ON THE NORTHERN EXTENT OF THE PCPN AND AS SUCH...WILL MAINTAIN LOWER POPS UNTIL CONFIDENCE OF COVERAGE FOR LATER THURS AND THURS NIGHT. NW WINDS COULD ALSO PRODUCE ISO-SCT UPSLOPE SNOW SHOWERS...BUT WITH LACK OF MOISTURE IN SNOW GROWTH ZONE...NOT ANTICIPATING MORE THAN A COUPLE TENTHS OF AN INCH FOR PORTIONS OF THE POTOMAC HIGHLAND FROM THURS MORNING THRU THURS NIGHT. LOSS OF MOISTURE OF DRIER AIR FINALLY MOVES IN SHOULD CUT OFF ANY SNOW SHOWERS BY FRI MORNING. THE UPPER LVL TROUGH FINALLY SWINGS THRU THURS NIGHT...WITH TEMPS RETURNING BACK TO NEAR NORMAL BY FRI. BEHIND THE TROUGH...RIDGING AND SFC HIGH PRESSURE BUILDING IN FROM THE WEST WILL PUSH THE LOW PRESSURE SYSTEM OUT OF THE AREA AND BRING IN A PERIOD OF DRY WX. THE RIDGE AXIS TRAVERSES THE REGION QUICKLY AND BY THE COMING WEEKEND WILL SEE RETURN FLOW SETTING UP.
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&& .LONG TERM /SAT NIGHT THRU WED/...
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HIGH PRESSURE OVER THE MID ATLANTIC WILL BECOME ELONGATED FROM THE TENNESSEE VALLEY TO THE OPEN WESTERN ATLANTIC OCEAN SATURDAY NIGHT. A COLD FRONT WILL SAG ACROSS THE EASTERN GREAT LAKES SATURDAY NIGHT BEFORE PUSHING TO THE EAST COAST. AT THE TAILEND OF THIS FRONT...THERE IS THE POTENTIAL FOR AN AREA OF LOW PRESSURE TO DEVELOP AND INTENSIFY NEAR THE CAROLINAS. THERE IS LOW CERTAINTY AS TO WHERE AND WHEN THIS LOW COULD DEVELOP. IT DOES APPEAR THAT THE LOW WILL DEVELOP TOO LATE TO HAVE A SIGNIFICANT IMPACT ON OUR WEATHER. ADDITIONAL SHORTWAVE ENERGY WILL BE DIVING INTO THE CENTRAL U.S. AND WESTERN GREAT LAKES...ALLOWING THIS SYSTEM TO PUSH FARTHER EAST THAN NORTH. THIS WOULD KEEP THE LOW TOO FAR TO OUR SOUTH BUT THIS WILL HAVE TO BE MONITORED SINCE IT IS STILL SEVERAL DAYS OUT. THE SYSTEM DIVING INTO THE CENTRAL U.S. SUNDAY MAY DEVELOP INTO A COASTAL LOW DURING THE EARLY PORTION OF NEXT WEEK. LATEST DETERMINISTIC GFS AND ECMWF SHOW THIS HAVING A BETTER CHANCE OF IMPACTING OUR AREA. THE GEFS MEAN SHOWS A STRONG UPPER-LEVEL TROUGH OVERHEAD WHICH WOULD ALSO SUPPORT THE POSSIBILITY OF A COASTAL LOW. CONFIDENCE IS HIGH FOR A HIGH AMPLITUDE PATTERN WITH A POTENT UPPER- LEVEL TROUGH OVERHEAD SATURDAY THROUGH TUESDAY...BUT THE DETAILS AND TIMING OF THE SHORTWAVE ENERGY ARE HIGHLY UNCERTAIN WHICH LEADS TO A LOW CONFIDENCE FORECAST. HOWEVER...AS OF NOW IT APPEARS THAT SATURDAY AND SUNDAY WILL TURN OUT DRY AND SEASONABLY CHILLY. A COASTAL STORM MAY BRING THE CHANCE FOR WINTRY PRECIPITATION TO THE AREA EARLY NEXT WEEK.
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&& .AVIATION /20Z WEDNESDAY THROUGH SUNDAY/...
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MOD CONFIDENCE FORECAST THRU TONIGHT...WITH HIGH CONFIDENCE OF RETURN TO VFR CONDITIONS FOR THURSDAY. VARYING CONDITIONS THIS AFTN...WITH CIG/VIS JUMPING BETWEEN IFR AND VFR. ANY VFR CONDITIONS LATE THIS AFTN WILL DROP AGAIN THIS EVENING...GENERALLY BETWEEN 22-02Z...WITH DEVELOPING FOG AND STRATUS PRIOR TO THE COLD FRONTS ARRIVAL. WINDS REMAIN LESS THAN 10 KTS FROM THE SOUTH. WINDS AT 2KFT BETWEEN 30-35 KTS. COLD FRONT MOVES THROUGH BETWEEN 06-09Z TONIGHT...BRINGING A SHIFT IN THE WINDS TO THE NW AND IMPROVING CONDITIONS. GUSTS 20-25 KTS WILL BE PSBL WITH THE WIND SHIFT AS WELL. NW FLOW AND VFR CONDITIONS LAST THRU FRI. VFR CONDITIONS SATURDAY NIGHT AND SUNDAY. WINDS SOUTHWEST WINDS AROUND 10 KNOTS. WINDS BECOMING NORTHWEST 10 TO 15 KNOTS GUSTS TO 20 KNOTS.
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&& .MARINE...
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SUB-SCA CONDITIONS ON MOST OF THE WATERS THIS AFTN WITH THE STABLE AIRMASS KEEPING ANY OF THE STRONGER WINDS FROM MIXING DOWN. GUSTS TO 35 KTS PSBL WITH ANY OF THE RAIN SHOWERS...WHICH WILL BE COVERED BY SMWS. ONLY PLACE SEEING SCA GUSTS ON THE MIDDLE CHESAPEAKE BAY AND HAVE UPDATED SCA TO ACCOUNT FOR THE LATEST CONDITIONS. PERIOD WITH ALL WATERS SUB-SCA TONIGHT WITH WINDS INCRSG FROM THE NW WITH THE COLD FROPA THE SECOND HALF OF THE NIGHT. SCA CONDITIONS WILL CONTINUE ON ALL WATERS TOMORROW MORNING... THE SECOND HALF OF THE DAY. WINDS WILL INCREASE THURS NIGHT WITH THE CAA PRESSURE SURGE...SO EXPECTING ANOTHER SCA WILL BE NEEDED THURS AND INTO FRIDAY AS HIGH PRESSURE BUILDS IN. NO MARINE HAZARDS SATURDAY NIGHT. SMALL CRAFT ADVISORIES POSSIBLE SUNDAY.
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&& .HYDROLOGY...
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AFTER A WET DAY...RAIN WILL CONTINUE TO SPREAD ACROSS THE LOWER POTOMAC AND RAPPAHANNOCK BASINS THIS AFTERNOON AND EVENING. RAINFALL AMOUNTS RANGE FROM A HALF INCH TO INCH ACROSS THE POTOMAC...SHENANDOAH AND RAPPAHANNOCK BASINS WITH ISOLATED AMOUNTS UP TO AN INCH AND A QUARTER. THIS COUPLED WITH TEMPERATURES AND DEWPOINTS IN THE 40S/50S ALLOWED MUCH OF THE REMAINING SNOW TO MELT AND FURTHER SATURATE THE SOIL. SMALL AND LARGE STREAMS ARE ON THE RISE THIS AFTERNOON DUE TO THE COMBINATION OF RAIN AND SNOWMELT. PARTIAL ICE BLOCKAGES MAY STILL BE A FACTOR...ESPECIALLY IN THE EASTERN WV PANHANDLE AND NORTHERN MARYLAND. ICE WAS ALSO REPORTED MOVING DOWN THE MIDDLE POTOMAC YESTERDAY BUT IT DOES NOT APPEAR IT IS CAUSING A SUBSTANTIAL BLOCKAGE AT THIS TIME. CONFIDENCE IS HIGH FOR SOME FLOOD POTENTIAL DUE TO THE COMBINATION OF SNOWMELT AND RAIN. THE HIGHEST RISK AREA IS IN THE FAR EASTERN WV PANHANDLE AND NORTHERN MD...BUT SOME URBAN FLOODING AND POTENTIALLY SIGNIFICANT PONDING OF WATER IS POSSIBLE IN THE URBAN CORRIDOR ESPECIALLY DUE TO PLOW-PILE-COVERED STORM DRAINS. ALTHOUGH THE RAIN MAY BE OVER IN SOME AREAS MAINLY ALONG AND WEST OF THE BLUE RIDGE...RUNOFF WILL CONTINUE TO LEAD TO STREAM RISES. RIVER FLOOD WARNINGS ARE CURRENTLY IN EFFECT FOR CACAPON...OPEQUON...MONACACY...POTOMAC FROM POINT OF ROCKS TO EDWARDS FERRY...SENECA CREEK AND SHENANDOAH AT MILLVILLE FOR FLOODING LATER TODAY AND TOMORROW. A RIVER FLOOD WATCH CONTINUES FOR POTOMAC RIVER INCLUDING HARPERS FERRY AND LITTLE FALLS. PLEASE SEE FLOOD WATCH AND FLOOD WARNING PRODUCTS FOR MORE INFORMATION.
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&& .TIDES/COASTAL FLOODING...
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LIGHT...BUT PERSISTENT SOUTHERLY FLOW INCRSG TIDAL ANOMALIES TODAY. GUIDANCE STILL SHOWING MINOR FLOODING THIS AFTERNOON AND EVENING ACROSS THE NORTHERN PORTION OF THE CHESAPEAKE BAY NEAR BOWLEYS QUARTERS AND HAVRE DE GRACE. A COASTAL FLOOD ADVISORY REMAINS IN EFFECT THRU THIS EVENINGS HIGH TIDE TO ACCOUNT FOR THIS. BALTIMORE AND ANNAPOLIS ARE CLOSE...BUT GUIDANCE CONTINUES TO SHOW WATER LEVELS JUST BELOW MINOR FLOODING THRESHOLDS. A NORTHWEST FLOW WILL DEVELOP LATE TONIGHT INTO THURSDAY ALLOWING FOR TIDAL ANOMALIES TO DROP.
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&& .LWX WATCHES/WARNINGS/ADVISORIES...
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DC...FLOOD WATCH THROUGH LATE TONIGHT FOR DCZ001. MD...FLOOD WATCH THROUGH LATE TONIGHT FOR MDZ013-014-503>506. FLOOD WATCH THROUGH THURSDAY AFTERNOON FOR MDZ003>006-011-507- 508. COASTAL FLOOD ADVISORY UNTIL 8 PM EST THIS EVENING FOR MDZ011- 508. VA...FLOOD WATCH THROUGH LATE TONIGHT FOR VAZ052>056-505-506. WV...FLOOD WATCH THROUGH THURSDAY AFTERNOON FOR WVZ051>053. MARINE...SMALL CRAFT ADVISORY UNTIL 1 AM EST THURSDAY FOR ANZ530>534- 537-543. SMALL CRAFT ADVISORY UNTIL 6 PM EST THIS EVENING FOR ANZ535- 536-538>542.
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&& $$ SYNOPSIS...SEARS NEAR TERM...SEARS SHORT TERM...SEARS LONG TERM...KLW AVIATION...SEARS/KLW MARINE...SEARS/KLW HYDROLOGY...HAS/JE TIDES/COASTAL FLOODING...SEARS

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