Area Forecast Discussion
Issued by NWS Sterling, VA

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000 FXUS61 KLWX 160357 AAA AFDLWX AREA FORECAST DISCUSSION...UPDATED NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC 1057 PM EST MON DEC 15 2014 .SYNOPSIS... HIGH PRESSURE BUILDS ACROSS THE REGION OVERNIGHT. LOW PRESSURE IS CENTERED OVER THE MIDDLE OF THE COUNTRY. A COLD FRONT ASSOCIATED WITH THAT LOW WILL PASS THROUGH THE AREA TUESDAY AFTERNOON. HIGH PRESSURE IS EXPECTED TO RETURN FOR THE LATTER PART OF THE WEEK. && .UPDATE...
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SURFACE HIGH PRESSURE HAS MOVED OFF THE MIDDLE ATLANTIC COAST AND LOW LEVEL WINDS HAVE TURNED TO A LIGHT E-ESE OVER EASTERN SECTIONS. HAVE INTRODUCED PATCHY FOG TO THE WEATHER GRIDS FOR THE OVERNIGHT PERIOD. PATCHY FOG MOST LIKELY EAST OF THE BLUE RIDGE. PREVIOUS DISCUSSION AS FOLLOWS... .NEAR TERM /THROUGH TUESDAY/... FORECAST ON TRACK. MID AND HIGH LEVEL CLOUDS WILL CONTINUE STREAMING IN OVERNIGHT WHICH WILL SLOW THE TEMPERATURE DROP. OVERNIGHT LOWS EXPECTED TO RANGE FROM THE 30S TO 40 DEGREES. LOW PRESSURE WILL TRACK EAST ACROSS THE MIDWEST OVERNIGHT AND THROUGH THE GREAT LAKES ON TUESDAY. FORCING AHEAD OF AN ADVANCING COLD FRONT WILL INCREASE FROM WEST TO EAST OVERNIGHT INTO TUESDAY. SHOWERS WILL DEVELOP FROM WEST TO EAST ACROSS THE FORECAST AREA BEGINNING IN THE MORNING AND TRANSITIONING EAST DURING THE DAY. HAVE UPPED POPS TO CATEGORICAL DURING THIS TIME FRAME. AFTERNOON RAINFALL AMOUNTS IN THE 0.10 TO 0.25 INCH RANGE CAN BE EXPECTED WITH LOCALLY HIGHER AMOUNTS POSSIBLE. BY LATE AFTERNOON...THE MAIN AREA OF LIFT WILL MOVE EAST WITH SHOWERS ENDING FOR MOST AREAS. UPSLOPE FLOW WILL KEEP RAIN SHOWER CHANCES GOING OVER THE WESTERN SLOPES OF THE POTOMAC HIGHLANDS INTO THE EVENING.
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&& .SHORT TERM /TUESDAY NIGHT/... AS THE FLOW TURNS WESTERLY...COLDER/DRIER AIR WILL ONLY SLOWLY FILTER IN TUESDAY NIGHT. LOWS GENERALLY IN THE 30S TO AROUND 40 EXCEPT THE HIGHEST ELEVATIONS. THIS MEANS ANY UPSLOPE PRECIPITATION WILL BE SLOW TO CHANGE OVER TO SNOW. NOT A TERRIBLY IMPRESSIVE SETUP WITH THE DUE WESTERLY FLOW AND A VERY SHALLOW MOISTURE LAYER THAT WILL LIMIT ICE NUCLEATION. MAY BE MORE DRIZZLE/FLURRIES WITH LOW CLOUDS. && .LONG TERM /WEDNESDAY THROUGH MONDAY/... WITH ELONGATED LOW PRESSURE OVER THE EASTERN GREAT LAKES/NEW ENGLAND AND STRONG HIGH PRESSURE BUILDING INTO THE UPPER MIDWEST...WEDNESDAY WILL FEATURE GUSTY WEST WINDS. A MIX OF CLOUDS AND SUN IS EXPECTED WITH MORE CLOUDS TOWARD THE MOUNTAINS...WITH THE LOW TO THE NORTH AND A STRONG ZONAL JET OVERHEAD. SIDED WITH WARMER GUIDANCE WITH GOOD MIXING AND DOWNSLOPE FLOW. HIGH IN THE MID 40S TO MID 50S. IF ANY UPSLOPE PCPN LINGERS IN THE MOUNTAINS...IT WILL BE LIGHT AND WANING AS MOISTURE THINS THROUGH THE DAY. THE UPPER LEVEL LOW WILL BE PULLING EAST WEDNESDAY NIGHT. ONE FINAL SHORTWAVE TROUGH MAY PIVOT THROUGH THE MID ATLANTIC BUT WILL HAVE MINIMAL IMPACT ON THE SENSIBLE WEATHER. WINDS WILL DIMINISH BUT NOT BECOME COMPLETELY CALM...ALLOWING LOW TEMPERATURES TO SETTLE NEAR OR JUST BELOW FREEZING. THE LONG TERM PERIOD WILL START OUT WITH A FAIRLY SEASONABLE DAY ON THURSDAY. TEMPS MAY BE JUST A COUPLE OF DEGREES BELOW NORMAL THANKS TO CANADIAN HIGH PRESSURE RIDGING INTO THE MID-ATLANTIC...BUT WITH WEAK RIDGING/ZONAL FLOW ALOFT THERE SHOULD BE ENOUGH SUNSHINE TO KNOCK OFF SOME OF THE CHILL DURING THE DAY. HIGH PRESSURE WILL BEGIN TO RETREAT TO THE NORTH ON FRIDAY AS A STRONG SHORTWAVE MOVING ACROSS THE MIDDLE OF THE COUNTRY DEVELOPS SURFACE LOW PRESSURE NEAR THE TEXAS GULF COAST. MODELS REALLY BEGIN TO DIVERGE IN SOLUTIONS AT THIS POINT. THE PRIMARY VARIANCE INVOLVES THE STRENGTH OF THE SHORTWAVE TROUGH AS IT CONTINUES ITS MARCH ACROSS THE EASTERN CONUS. DETERMINISTICALLY...THE EURO HAS A MUCH MORE AMPLIFIED SHORTWAVE...WHILE THE GFS NEARLY ELIMINATES THE SHORTWAVE ALTOGETHER...AND THE STRENGTH OF THE SURFACE LOW REFLECTS THIS WITH THE EUROS SURFACE LOW BEING NEARLY 20 MB DEEPER AT 6Z SUNDAY OVER SOUTHEAST VIRGINIA. WITHIN THE ENSEMBLE MEMBERS OF BOTH MODELS THERE ARE RUNS THAT RESEMBLE THE DETERMINISTIC RUNS OF THE OPPOSITE MODEL...SO BOTH SOLUTIONS REMAIN POSSIBLE...WITH SOME SOLUTION IN BETWEEN BEING MOST LIKELY. DESPITE THE LARGE SPREAD AMONGST GLOBAL MODELS...THERE ARE SOME ASPECTS THAT WE CAN BE PRETTY CONFIDENT ABOUT. CLOUD COVER WILL BEGIN TO INCREASE FRIDAY NIGHT AS MOISTURE ADVECTS IN AHEAD OF THE APPROACHING LOW FRIDAY NIGHT. MOST OF THE AREA WILL LIKELY SEE SOME FORM OF PRECIP SATURDAY AND SATURDAY NIGHT AS THE LOW CENTER PASSES NEAR THE AREA. AS EXPECTED...THERE IS UNCERTAINTY IN P-TYPE AT THIS POINT...BUT HIGHER ELEVATIONS WILL HAVE A BETTER CHANCE AT SNOW THAN LOW ELEVATIONS...SO GENERALLY STUCK WITH MOSTLY SNOW ACROSS THE WESTERN PORTION OF THE CWA WITH MORE OF A MIX BAG OF WINTRY PRECIP FOR THE EASTERN PORTION. HIGH PRESSURE WILL BUILD BACK INTO THE AREA SUNDAY AND TEMPS WILL BE SLIGHTLY BELOW NORMAL WITH DRY CONDITIONS TO BEGIN NEXT WEEK. && .AVIATION /04Z TUESDAY THROUGH SATURDAY/...
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PATCHY FOG WILL BE POSSIBLE OVERNIGHT...ESPECIALLY AT KBWI.OTHERWISE...VFR CONDITIONS WILL PREVAIL FOR MUCH OF THE REGION. MVFR CIGS AND VSBYS IN RAIN SHOWERS WILL BE COMMON FROM WEST TO EAST ACROSS THE REGION DURING TUESDAY. HIGHEST IMPACT FOR THE TERMINALS WILL LIKELY BEGIN BY 16Z AT KMRB AND BY 18Z FOR THE REMAINDER OF THE TERMINALS. MVFR CIGS MAY LINGER THROUGH PART OF TUESDAY EVENING/NIGHT. VFR WEDNESDAY/WEDNESDAY NIGHT. WESTERLY WINDS MAY GUST ABOVE 20KT ON WEDNESDAY. MVFR AND IFR CONDITIONS ARE POSSIBLE IN SHOWERS AND LOW CEILINGS A LOW PRESSURE PASSES NEAR THE AREA SATURDAY.
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&& .MARINE... WINDS XPCTD TO RMN BLO SCA LVLS TNGT AND TUE. A FEW GUSTS COULD COME DOWN IN RW TUE AFTN. A LOW LEVEL INVERSION WILL LIKELY KEEP WINDS BELOW SCA CRITERIA TUESDAY NIGHT. SCA CONDITIONS ARE LIKELY ON WEDNESDAY WITH STRONG WESTERLY WINDS...AND COULD LINGER INTO WEDNESDAY NIGHT FOR PORTIONS OF THE WATERS. A SMALL CRAFT MAY BE NEEDED INTO THE DAY THURSDAY IN BREEZY NORTHWEST WINDS. A SMALL CRAFT ADVISORY WILL LIKELY BE NEEDED SATURDAY AS LOW PRESSURE PASSES NEAR THE AREA. && .TIDES/COASTAL FLOODING... WATER LEVELS RUNNING ABOUT A HALF TO 3/4 FT ABV ASTRO NORMALS. WHILE ELEVATED...NO ISSUES EXPECTED TONIGHT. THE SAME CAN`T BE SAID WITH CERTAINTY FOR TUE-TUE NIGHT AS WINDS TURN SOUTHERLY. THE RISK IS NOT SIGNIFICANT...BUT LEVELS MAY REACH THE MINOR THRESHOLDS. && .LWX WATCHES/WARNINGS/ADVISORIES... DC...NONE. MD...NONE. VA...NONE. WV...NONE. MARINE...NONE. && $$ SYNOPSIS...KRW NEAR TERM...KRW SHORT TERM...ABW LONG TERM...ADS AVIATION...ADS/KRW MARINE...ADS/KRW TIDES/COASTAL FLOODING...ADS/WOODY!

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