Area Forecast Discussion
Issued by NWS Sterling, VA

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000 FXUS61 KLWX 080220 AAA AFDLWX AREA FORECAST DISCUSSION...UPDATED NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC 920 PM EST SUN FEB 7 2016 .SYNOPSIS...
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LOW PRESSURE WILL PASS WELL TO OUR SOUTH AND EAST OVERNIGHT. ANOTHER LOW PRESSURE SYSTEM WILL DIVE SOUTH INTO THE OHIO VALLEY MONDAY BEFORE PASSING THROUGH OUR AREA MONDAY NIGHT INTO TUESDAY. HIGH PRESSURE WILL SLOWLY BUILD TOWARD OUR AREA DURING THE MIDDLE PORTION OF NEXT WEEK.
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&& .NEAR TERM /THROUGH MONDAY/...
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HIGH CLOUDS ASSOCIATED WITH STORM SYSTEM OFF THE NC COAST SHOULD THIN OUT OVERNIGHT LEADING TO CLEAR SKIES BY DAYBREAK. HEIGHT FALLS ASSOCIATED WITH AMPLIFLYING UPPER LEVEL TROUGH OVER THE GREAT LKS WILL INDUCE SFC LOW DEVELOPMENT OVER SRN VA MON NIGHT. PRECIP WILL DEVELOP EAST OF UPPER TROF AXIS MON AND SPREAD QUICKLY ACROSS THE ENTIRE AREA MON AFTERNOON. GUIDANCE IS STILL IN DISAGREEMENT WITH RESPECT TO ONSET/TIMING OF PRECIP WITH 18Z GFS/GEFS FASTER THAN 12Z ECMWF. GIVEN THAT THERE IS A CHANCE THAT PRECIP COULD START BEFORE 18Z MON DECIDED TO ISSUE A WINTER WX ADVISORY FOR THE FIVE WESTERN MOST COUNTIES. THIS WAS ALL COORDINATED/COLLABORATED WITH RLX AND PBZ.
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&& .SHORT TERM /MONDAY NIGHT THROUGH WEDNESDAY/...
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UPDATE...PRECIP TYPE ISSUES AND POTENTIAL FOR DRY SLOT TO WORK NWD INTO OUR SRN COUNTIES MAKE FOR UNCERTAIN FCST DETAILS BUT CONFIDENCE IS HIGH THAT EVENING RUSH HOUR COMMUTE MON WILL BE FINE AS SFC TEMPS ARE EXPECTED TO BE ABOVE FREEZING. SINCE ANY IMPACTS ARE NOT LIKELY TO OCCUR UNTIL MON NIGHT...WE`LL NOT ISSUE ANY ADVISORIES ANY FURTHER EAST. PREVIOUS DISCUSSION... AS THE SUNSETS MONDAY NIGHT AND LOW PRESSURE FORMS OFF THE MID- ATLANTIC COAST RAIN WILL TRANSITION TO SNOW OVERNIGHT AND INTO TUESDAY MORNING. THERMAL PROFILES ACROSS THE REGION WITH THE EXCEPTION OF HIGHER ELEVATIONS WILL LIMIT SNOWFALL ACCUMULATION WHEN SNOW BEGINS MONDAY NIGHT INTO TUESDAY MORNING. AS TEMPS BEGIN TO RISE TUESDAY IN THE LOW LANDS AND EAST OF THE BLUE RIDGE SNOWFALL WILL BE DIFFICULT TO ACCUMULATE UNLESS BANDING OCCURS ACROSS THE REGION. AS STATED MANY TIMES WITH THIS SYSTEM...MOISTURE AND QPF FIELDS DIFFER IN MODEL GUIDANCE AS MOST OF THE BANDING ACTIVITY WILL BE CONVECTIVE IN NATURE. THE STRONG 925- 850MB EASTERLY JET ONCE THE SFC LOW FORMS ALONG THE COAST WILL ALLOW INSTABILITY TO INCREASE AND SNOWFALL RATES TO INCREASE. AT THIS TIME LOCATION AND EXACT TIMING OF THESE INSTABILITY BANDS ARE UNCERTAIN BUT THE BEST TIMING WILL BE TUESDAY MORNING INTO TUESDAY EVENING. THE SNOWFALL ACCUMULATION FORECAST IS THERMALLY BASED WITH SNOWFALL TOTALS HIGHER WHERE BOUNDARY LAYER CONDITIONS ARE COLDER FOR SNOW SUCH AS NEAR THE MD/PA BORDER...HIGHER ELEVATIONS AND THE WESTERN SLOPES OF THE ALLEGHENY FRONT. FURTHER SOUTH AND EAST...TEMPS WILL REACH THE MID TO UPPER 30S TUESDAY AND SNOWFALL WILL LIKELY ACCUMULATE AND MELT AND DRIER AIR WILL LIKELY MOVE INTO CENTRAL VA TUESDAY. ACCUMULATIONS OF 3-6 INCHES EXPECTED ACROSS THE NRN HALF OF THE MID-ATLANTIC AND 1-3 IN THE SOUTHERN HALF WITH HIGHER AMTS ALONG THE RIDGES. THE BROAD UPPER LEVEL TROUGH WILL STAY ACROSS THE AREA INTO WEDNESDAY AND SCATTERED SNOW SHOWERS WILL BE POSSIBLE. LIGHT ACCUMULATION IS POSSIBLE ACROSS THE REGION. SNOW SHOWERS ARE EXPECTED ACROSS THE WESTERN SLOPES OF THE ALLEGHENY FRONT AS NW WINDS CONTINUE TO DRAW DOWN MOISTURE FROM THE GREAT LAKES. ACCUMULATING SNOWFALL IS EXPECTED THROUGH THURSDAY FOR THIS AREA WITH TOTAL SNOWFALL ACCUMULATION OF 6-8 INCHES.
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&& .LONG TERM /WEDNESDAY NIGHT THROUGH SUNDAY/... THE MAIN UPPER LEVEL TROUGH OF LOW PRESSURE WILL PIVOT ACROSS THE REGION LATER IN THE DAY WEDNESDAY INTO WEDNESDAY NIGHT. ADDITIONAL UPSLOPE SNOW EXPECTED IN THE POTOMAC HIGHLANDS...WHILE AN OCCASIONAL SNOW SHOWER OR TWO CANNOT BE RULED OUT ACROSS THE I-81 AND I-95 CORRIDORS. MUCH COLDER AIR WILL BE ON THE HEELS OF THIS UPPER TROUGH WEDNESDAY NIGHT AS A COLD DOME OF HIGH PRESSURE BUILDS IN FROM THE WEST. HIGH PRESSURE WILL DOMINATE THURSDAY AND THURSDAY NIGHT WITH VERY COLD AND DRY AIR ACROSS THE REGION. TEMPERATURES WILL BE 10 TO 15 DEGREES BELOW NORMAL. AS THE HIGH FLATTENS OUT LATE THURSDAY NIGHT INTO FRIDAY...AN AREA OF LOW PRESSURE SHOULD SCOOT ACROSS THE TENNESSEE VALLEY. THIS LOW SHOULD JUST SPREAD ADDITIONAL CLOUD COVER ACROSS THE SOUTHERN HALF OF OUR REGION. A BRIEF PERIOD OF LIGHT SNOW CANNOT BE RULED OUT ACROSS THE VIRGINIA PIEDMONT TO THE MOUTH OF THE CHESAPEAKE BAY. VERY COLD TEMPERATURES WILL CONTINUE FRIDAY INTO FRIDAY NIGHT WITH TEMPERATURES ABOUT 10 TO 15 DEGREES BELOW NORMAL. BEHIND THE AREA OF LOW PRESSURE...THE MAIN UPPER LEVEL TROUGH OF SUPPORT WILL PIVOT EAST WITH A FIRM RIDGE OF HIGH PRESSURE QUICKLY TO FOLLOW IT. ASIDE FROM DIURNAL CLOUD COVER SATURDAY...THIS TROUGH WILL MAINLY SUPPORT ARCTIC AIR SURGING INTO THE MID ATLANTIC SATURDAY AND SATURDAY NIGHT. THE SAME RIDGE OF HIGH PRESSURE BUILDING INTO THE REGION WILL BECOME REENFORCED SUNDAY INTO SUNDAY NIGHT. THUS...HIGH AND LOW TEMPERATURES WILL REMAIN WELL BELOW NORMAL WITH THE POTENTIAL OF EXPERIENCING LOWS IN THE SINGLE DIGITS BELOW ZERO TO HIGHS IN THE TEENS ACROSS A LARGE PORTION OF THE REGION. && .AVIATION /02Z MONDAY THROUGH FRIDAY/...
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CIGS EXPECTED TO DROP QUICKLY MON AFTERNOON WITH A RAIN/SNOW MIX MOST TAF SITES EXCEPT ALL SNOW AT KMRB. TIMING OF CHANGEOVER TO SNOW AND PRECIP RATES MON NIGHT REMAIN IN QUESTION ATTM. -SNSH POSSIBLE WEDNESDAY AS UPPER LEVEL TROUGH CONTINUES TO MOVE OVERHEAD. PREVAILING VFR CONDITIONS EXPECTED WEDNESDAY. MVFR CONDITIONS WEDNESDAY WITH A CHANCE OF SNOW SHOWERS AT ANY TERMINALS. WINDS WEST TO WEST-NORTHWEST 5 TO 10 KNOTS GUSTS 15 KNOTS WEDNESDAY. VFR CONDITIONS WEDNESDAY NIGHT. WINDS WEST-NORTHWEST 5 TO 10 KNOTS GUSTS 15 KNOTS.
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&& .MARINE...
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SMALL CRAFT ADVISORY CONDITIONS CURRENTLY BEING OBSERVED OVER THE LOWER BAY AND POTOMAC BUT MODEL TREND IS FOR WINDS TO STRENGTHEN THROUGH 06Z MON THEN DIMINISH AS DEEP COASTAL LOW MOVES FURTHER AWAY. NORTHWEST WINDS WILL INCREASE TUESDAY AFTERNOON AND CONTINUE THROUGH THE END OF THE WEEK. SMALL CRAFT ADVISORY CONDITIONS LIKELY TUE THROUGH MUCH OF NEXT WEEK.
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&& .COASTAL FLOODING...
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WATER LEVELS ARE UP TO HALF A FOOT ABOVE NORMAL ON THE WATERS THIS EVENING. NORTH FLOW BECOMES SELY MONDAY AFTERNOON WITH WATER LEVELS INCREASING THROUGH MONDAY NIGHT AS LOW PRESSURE CROSSES THE AREA. MINOR COASTAL FLOODING AT SENSITIVE SITES IS LIKELY AROUND HIGH TIDE MONDAY NIGHT INTO TUESDAY.
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&& .LWX WATCHES/WARNINGS/ADVISORIES...
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DC...NONE. MD...WINTER WEATHER ADVISORY FROM NOON MONDAY TO 1 AM EST TUESDAY FOR MDZ501-502. VA...WINTER WEATHER ADVISORY FROM NOON MONDAY TO 1 AM EST TUESDAY FOR VAZ503-504. WV...WINTER WEATHER ADVISORY FROM NOON MONDAY TO 1 AM EST TUESDAY FOR WVZ501>506. MARINE...SMALL CRAFT ADVISORY UNTIL 9 AM EST MONDAY FOR ANZ532>534-537- 540-541-543.
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&& $$ SYNOPSIS...LFR NEAR TERM...LFR SHORT TERM...HAS/LFR LONG TERM...KLW AVIATION...LFR/KLW MARINE...LFR/KLW

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