Area Forecast Discussion
Issued by NWS Sterling, VA

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000 FXUS61 KLWX 170214 AFDLWX AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC 914 PM EST TUE DEC 16 2014 .SYNOPSIS...
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A WEAK COLD FRONT WILL CONTINUE TO PUSH THROUGH THE AREA TONIGHT. A REINFORCING COLD FRONT WILL CROSS THE AREA WEDNESDAY MORNING. HIGH PRESSURE THEN BUILDS IN THROUGH THURSDAY AND REMAINS THROUGH FRIDAY. A WEAK WAVE OF LOW PRESSURE WILL CROSS THE AREA SATURDAY NIGHT...BRINGING LIGHT RAIN AND A LIGHT WINTRY MIX TO THE AREA SATURDAY INTO SUNDAY.
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&& .NEAR TERM /THROUGH WEDNESDAY/...
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AS OF 02Z...SFC TROUGH FROM LEADING OCCLUDED/COLD FRONT IS OVER THE CHESAPEAKE BAY. HOWEVER...MOISTURE IS TRAPPED UNDER A SHALLOW INVERSION SO LIGHT DRIZZLE AND LOW CLOUDS LOOK TO LINGER WELL INTO TONIGHT IN SPITE OF A WEST WIND DEVELOPING. TOOK A BALANCE WITH THE FOG FORECAST...CLEARING MOST BEFORE SUNRISE AS THE PRESSURE GRADIENT INCREASES AND 18Z NAM FCST SNDGS MIX OUT SFC AFTER 06Z...WHILE THE 18Z GFS KEEPS SFC INVERSION THROUGH 12Z. MIN TEMPS MILD WITH WEAK COLD AIR ADVECTION OVERNIGHT AND EITHER MIXING OR CLOUDS KEEPING TEMPS UP...MINS UPR 30S TO LOW 40S FOR LOWER ELEVATIONS. MEASURABLE PRECIP LIMITED TO UPSLOPE WEST FROM THE ALLEGHENY FRONT TONIGHT WHERE SNOW IS EXPECTED TO BE ONGOING ABOVE 4KFT (32F OVER AT SNOWSHOE...38F AT KHSP). THAT SNOW ELEVATION WILL LOWER THROUGH THE NIGHT. HOWEVER...PRECIP WILL BE LIGHT WITH ONLY A SHALLOW INVERSION...1 TO 2 INCHES OF SNOW...ALL ABOVE ABOUT 2KFT. SECONDARY COLD FRONT IS OVER OHIO WILL FULLY MIX OUT THE FOG/MIST AS IT CROSSES TONIGHT THROUGH WEDNESDAY MORNING. BREEZY WLY FLOW BEHIND THIS FRONT...PEAK GUSTS 25 TO POSSIBLY 30 MPH DURING DAYLIGHT WEDNESDAY. DOWNSLOPING FLOW AND CLEARING SKIES WILL OFFSET THE COLD AIR ADVECTION AND ALLOW MAX TEMPS IN THE LOW 50S FOR MOST LOWER ELEVATIONS.
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&& .LONG TERM /WEDNESDAY NIGHT THROUGH TUESDAY/... LOW PRESSURE AT THE SURFACE AND ALOFT WILL CONTINUE TO SLOWLY SPIN INTO THE CANADIAN MARITIMES WEDNESDAY NIGHT AND THURSDAY...WHILE HIGH PRESSURE BUILDS SOUTHEAST FROM THE UPPER MIDWEST. A FAST ZONAL UPPER LEVEL JET WILL STRETCH FROM TEXAS ACROSS THE MID SOUTH. THEREFORE NO SIGNIFICANT WEATHER MAKERS OR WEATHER CHANGES. FORECAST SOUNDINGS STILL SHOW A SHALLOW SATURATED LAYER WITHIN THE UPSLOPE FLOW OVER THE MOUNTAINS THROUGH WEDNESDAY NIGHT. USED SNOW SHOWER/FLURRIES WORDING IN THE GRIDS...BUT COULD ALSO BE DZ/FZDZ. LOWS NEAR OR BELOW FREEZING ACROSS THE AREA. A WEAK MID LEVEL SHORTWAVE WILL APPROACH FROM THE WEST LATE THURSDAY AFTERNOON AND INTO THE OVERNIGHT HOURS. THIS WILL LIKELY INCREASE MID AND HIGH LEVEL CLOUDS...WHICH MAY HELP MUTE HIGH TEMPERATURES IN THE 40S. HOWEVER SOME MIXING WILL OCCUR AND ENOUGH GRADIENT STILL IN PLACE TO HAVE SOME GUSTS ABOVE 20 KT. HOWEVER OVERALL TRANQUIL WEATHER WHICH WILL CONTINUE INTO THURSDAY NIGHT...WITH LOWS FALLING BACK DOWN TO NEAR 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 06Z 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 /02Z WEDNESDAY THROUGH SUNDAY/...
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LIFR CONDS SLOW TO IMPROVE THROUGH MIDNIGHT AND POSSIBLY THROUGH SUNRISE DUE TO WEAK SURFACE FLOW. SECONDARY CD FNT WL CROSS THE RGN LATE TONIGHT. BRZY W WINDS XPCTD WED (GUSTS TO 22 KT) WITH VFR CONDS BY MID MORNING. VFR CONDITIONS WEDNESDAY NIGHT-THURSDAY NIGHT. WNW WIND GUSTS ABOVE 20 KT POSSIBLE DURING THE DAYLIGHT HOURS OF THURSDAY. MVFR AND IFR CONDITIONS ARE POSSIBLE IN SHOWERS AND LOW CEILINGS A LOW PRESSURE PASSES NEAR THE AREA SATURDAY.
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&& .MARINE...
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FLOW BECOMES WLY 10 KT OVERNIGHT...INCREASING BEHIND A SECONDARY COLD FRONT WEDNESDAY MORNING. SCA FOR ALL WATERS BEGINNING AT 9 AM AND CONTINUING THROUGH WEDNESDAY NIGHT. A SCA IS LIKELY DURING DIURNAL MIXING OF GUSTY WNW FLOW ON THURSDAY OVER PORTIONS IF NOT ALL OF THE WATERS. WINDS DIMINISH AGAIN THURSDAY EVENING. 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.
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&& .LWX WATCHES/WARNINGS/ADVISORIES...
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DC...NONE. MD...NONE. VA...NONE. WV...NONE. MARINE...SMALL CRAFT ADVISORY FROM 9 AM WEDNESDAY TO 6 AM EST THURSDAY FOR ANZ530>543.
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&& $$ UPDATE...JACKSON PREVIOUS...WOODY!/ADS/CEB

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