Area Forecast Discussion
Issued by NWS Sterling, VA

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000 FXUS61 KLWX 280213 AFDLWX AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC 913 PM EST SAT DEC 27 2014 .SYNOPSIS... HIGH PRESSURE OVER THE WESTERN ATLANTIC WILL PROVIDE DRY CONDITIONS INTO MUCH OF THE OVERNIGHT. A COLD FRONT WILL MOVE INTO THE REGION SUNDAY. LOW PRESSURE WILL MOVE ALONG THE STALLED FRONT SUNDAY AFTERNOON AND EVENING...PUSHING THE FRONT SOUTH OF THE AREA. ANOTHER LOW PRESSURE SYSTEM WILL MOVE ACROSS THE CAROLINAS MONDAY AND MONDAY NIGHT. STRONG HIGH PRESSURE WILL BUILD OVER MUCH OF THE COUNTRY BY TUESDAY...AND GRADUALLY PUSH EASTWARD DURING THE REST OF THE WORK WEEK. && .NEAR TERM /THROUGH SUNDAY NIGHT/... STRANDS OF MID LEVEL CLOUDS ARE STREAMING IN ACROSS PORTIONS OF THE CENTRAL SHENANDOAH VALLEY AND VIRGINIA PIEDMONT. ALTHOUGH THE RADAR WILL APPEAR TO BE QUIET THROUGH THE REMAINDER OF THE EVENING AND INTO THE FIRST PORTION OF THE OVERNIGHT...WE CAN`T RULE OUT A FEW SPRINKLES MAINLY IN THE SOUTHERN ZONES UNTIL MIDNIGHT WHILE A HIT AND MISS RAIN SHOWER MAY OCCUR SHORTLY BEFORE THE PERSISTENT RAIN MOVES IN FROM THE WEST. THERE IS STILL DRY AIR IN PLACE IN THE LOW LEVELS OF THE ATMOSPHERE WITH TEMPERATURES READING IN THE UPPER 40S AND DEWPOINT TEMPERATURES IN THE LOWER 30S. HOWEVER THIS GAP BETWEEN THE TWO WILL LESSEN AS MORE MID LEVEL CLOUDS MOVE IN FROM THE WEST AND LIGHT RAIN DEVELOPS OVERNIGHT. OUR LOW TEMPERATURES MAY NEED TO BE ADJUSTED DOWN A FEW MORE DEGREES OVERNIGHT AS 9PM TEMPERATURES ARE JUST A FEW DEGREES HIGHER THAN OUR FORECASTED LOW TEMPERATURES. THE THICKENING MID-LEVEL CLOUDS AND PRECIPITATION HAS SLOWED IN FORWARD PROGRESS...THUS ALLOWING FOR MAINLY CLEAR SKIES TO DOMINATE OUR DOWNWARD TEMPERATURE TREND. NOT QUITE THE STANDARD MID-LATITUDE CYCLONE EXPECTED FOR THE NEXT COUPLE OF DAYS TO AFFECT THE EAST COAST. CURRENTLY...TWO SEPARATE SYSTEMS AND LINKED TOGETHER BY THEIR PLACEMENT ALONG THE UPGLIDE REGION OF AN ELONGATED UPPER TROUGH. THE NORTHERN-STREAM SYSTEM WILL CONTINUE TO SPEED OFF TO THE NE ACROSS THE GREAT LAKES...DRAGGING A COLD FRONT AND LIGHT PRECIP ACROSS THE UPPER MIDWEST. THE FRONT IS CONNECTED TO A DEVELOPING SYSTEM OVER THE DEEP SOUTH...W/ MUCH MORE MOISTURE ASSOCIATED W/ IT. THIS FEATURE WILL EVENTUALLY MAKE ITS WAY OVER THE REMAINDER OF THE SOUTHEAST AND JUST INTO OUR AREA BY EARLY SUN. THE DEEP NATURE OF THE UPPER TROUGH WILL WANE SOMEWHAT AS WE HEAD INTO THE DAYTIME HRS SUNDAY...WHICH WILL HAVE AN EFFECT OF HOW MUCH PRECIP WE GET. ALL GUIDANCE MEMBERS HAVE BEGUN TO BACK OFF A BIT ON EXPECTED QPFS AND OVERALL INTENSITY. LOOKING LIKE A DAY-LONG PERIOD OF GENERALLY LIGHT RAIN W/ ONLY ABOUT A QUARTER-INCH OR LESS TOTAL RAINFALL ANTICIPATED THRU LATE SUN. BY SUNSET SUN EVE...ONLY SOME LIGHT RESIDUAL ACTIVITY HANGING AROUND INTO THE LATE NIGHT HRS W/ THE POTENTIAL FOR SOME LIGHT RAIN/SNOW MIX ON THE BACK SIDE OF THIS ACTIVITY...ESPEC THE HIGHER TERRAIN FOR A BRIEF PERIOD. && .SHORT TERM /MONDAY THROUGH MONDAY NIGHT/... AS THE FIRST UPPER WAVE PULLS AWAY EARLY MONDAY...PRECIPITATION WILL LIKELY BE ONGOING IN THE VICINITY OF THE 850 MB FRONT...WHICH SHOULD BE SOUTH OF THE METRO AREA. SOUNDINGS BY 15Z AT DCA SHOW A LOT OF DRYING...ESPECIALLY ABOVE 700 MB AND AROUND 850 MB. BUT THE 15Z SOUNDING AT NHK IS SATURATED BETWEEN 700-900 MB. KNOWING THAT EXACT PLACEMENT ON DAY 3 IS UNLIKELY...HAVE CARRIED BETTER THAN 50/50 POPS MONDAY MORNING IN THE SOUTHERN HALF OF THE FORECAST AREA...TAPERING TO CHANCE OR EVEN SLIGHT CHANCE IN THE AFTERNOON. THERE COULD BE A BRIEF WINDOW OF SNOW POTENTIAL IN THE MORNING ALONG THE ALLEGHENY FRONT BUT THAT WOULD NOT AMOUNT TO MUCH. MONDAY NIGHT...ALL THE MODELS BRING BACK IN SOME MID-LEVEL MOISTURE...WITH N/NE FLOW IN THE LOW LEVELS OVERLAIN BY DEEP AND STRONG WESTERLY FLOW ALOFT. PREVIOUS FORECASTER MENTIONED THE MODEL DIFFERENCES...MAINLY IN QPF...AND THOSE DIFFERENCES STILL PERSIST WITH THE 12Z MODEL RUNS. GIVEN THIS...I LOWERED POPS SLIGHTLY...BUT DID NOT REMOVE THEM AS THERE IS AN UPPER SHORTWAVE APPROACHING OVERNIGHT. MORE THAN LIKELY...ANY PRECIP THAT DOES OCCUR WOULD BE LIGHT. LOWS ARE NEAR FREEZING WEST OF I-95...SO THERE IS A MENTION OF RAIN/SNOW ALONG AND WEST OF THE BLUE RIDGE...AND ALL SNOW ON THE ALLEGHENY FRONT. KEPT THE LESS THAN ONE INCH ACCUMULATION OUT THERE FROM THE PREVIOUS FORECAST. && .LONG TERM /TUESDAY THROUGH SATURDAY/... NAM/SREF AND NOW 12Z GFS ARE TRYING TO HINT AT A THIRD WAVE OF LOW PRESSURE DEVELOPING ALONG A STALLED FRONT OFF THE CAROLINA COAST LATE MONDAY NIGHT INTO TUESDAY. THE SURFACE LOW TRACK IS WELL SOUTH OF WHAT WOULD BE IDEAL FOR PRECIP IN OUR AREA /BETWEEN NORFOLK AND CAPE HATTERAS IS THE TYPICAL LOCATION/ BUT THE BEST PVA AT 500 MB IS FURTHER NORTH ACROSS OUR AREA. IT IS AN OPEN WAVE SO ANY LOW PRESSURE AREA THAT DEVELOPS SHOULD MOVE QUICKLY OFFSHORE BEFORE ANY SIGNIFICANT PRECIPITATION OCCURS. FOR NOW HAVE LOW END POPS TO ACCOUNT FOR THE CHANCE OF SOME LIGHT PRECIP. WILL HAVE TO BE WATCHED IN FUTURE UPDATES...ESPECIALLY IF MID-UPPER DISTURBANCE IS ABLE TO UNDULATE THE FLOW IN THE LOW-LEVELS AND RESULT IN FAVORABLE UPSLOPE TRAJECTORIES. TEMPERATURES WILL TAKE A NOSEDIVE TUESDAY NIGHT AS HIGH PRESSURE WITH ARCTIC ORIGINS TAKES HOLD TO THE WEST OF THE LOCAL AREA. WITH 850 MB TEMPS BETWEEN -8 AND -11 C...HIGH TEMPERATURES SHOULD ONLY TOP OUT IN THE 30S...5 TO 10 DEGREES BELOW NORMAL FOR THIS TIME OF YEAR. THE COLD AIRMASS WILL LINGER OVER THE AREA TUESDAY NIGHT THROUGH WEDNESDAY NIGHT. THERE MAY BE A FEW FLURRIES WEDNESDAY AS A SHORTWAVE TROUGH PASSES BUT THERE IS NOT NEARLY ENOUGH CONFIDENCE TO INCLUDE THAT IN THE FORECAST AT THIS TIME. OVERNIGHT LOWS WILL DEPEND ON HOW STRONG THE WINDS ARE AND IF THERE ARE ANY CLOUDS...THOUGH AT THIS POINT NEITHER NIGHT LOOKS TO BE A CLASSIC WIDESPREAD RADIATIONAL COOLING NIGHT. EVEN SO...DEW POINTS IN THE SINGLE DIGITS MEAN THAT ANYWHERE WINDS DO GO CALM AND CLEAR WILL LIKELY FREEFALL INTO THE TEENS. TEMPERATURES WILL MODERATE SOME THURSDAY INTO FRIDAY AHEAD OF ANOTHER COLD FRONT. AT THIS POINT IT LOOKS LIKE TEMPERATURES SHOULD WARM ENOUGH FOR A MOSTLY RAIN EVENT EXCEPT PERHAPS IN THE HIGHER ELEVATIONS WITH THIS NEXT SYSTEM...WITH ONLY THE 00Z ECMWF SHOWING TEMPERATURES COLD ENOUGH FOR SNOW AT ANY TIME LATE IN THE FORECAST PERIOD /AND THAT IS DUE TO A SUSPICIOUSLY STRONG SURFACE LOW AMIDST A RELATIVELY WEAK 500 MB PERTURBATION LATE IN THE WEEK/. && .AVIATION /02Z SUNDAY THROUGH THURSDAY/... SOLID VFR CONDITIONS THRU THE 06-12Z TIME FRAME. GENERALLY DENSE MID-LEVEL DECKS MOVING IN TOWARD DAWN SUN...THEN SCATTERED SHOWERS MOVING ACROSS THE REGION THROUGHOUT THE DAYTIME HRS SUN W/ LOW-END VFR CIGS AND SOME MVFR INTO THE LATE NIGHT HRS. DESPITE THE PRECIP CHANCES MONDAY AND MONDAY NIGHT...CEILINGS LOOK MOSTLY HIGH ENOUGH TO BE VFR. THERE IS HOWEVER SOME THREAT OF LOWER CIGS EAST DEPENDING ON VERY LOW-LEVEL MOISTURE INFLOW. PRECIP COULD RESTRICT VSBY AT TIMES...MAINLY AT CHO. WINDS LOOK GENERALLY LIGHT. MAINLY VFR EXPECTED TUE-WED...WIND N 10-15 KTS TUE PM...BECOMING LIGHTER 5-10 KTS WED. && .MARINE... LIGHT AND VARIABLE WINDS CONTINUE THE REMAINDER OF THIS EVENING AS HIGH PRESSURE LINGERS OVER THE WESTERN ATLANTIC OCEAN. A COLD FRONT WILL MOVE THRU EARLY SUN W/ SCATTERED SHOWERS SLIDING OVER THE REGION FROM SUN MRNG INTO THE LATE EVE HRS. WINDS WILL GENERALLY STAY AOB 10KT. MARINE WINDS SHOULD BE GENERALLY LIGHT MONDAY AND MONDAY NIGHT...BUT COULD EXCEED 10 KNOTS IN THE BAY NEAR THE MD/VA BORDER MONDAY NIGHT WITH A DECENT NORTHERLY FETCH. CHANCE OF RAIN ON THE WATERS BOTH MONDAY AND MONDAY NIGHT. NORTHERLY CHANNELING BEHIND A COLD FRONT AND AHEAD OF AN APPROACHING AREA OF HIGH PRESSURE COULD RESULT IN SMALL CRAFT ADVISORY LEVEL WINDS TUESDAY NIGHT. WINDS SLACKEN WEDNESDAY INTO THURSDAY AS THE GRADIENT RELAXES WITH HIGH PRESSURE NEARBY...THEN COULD COME CLOSE TO SMALL CRAFT ADVISORY LEVELS AGAIN LATE IN THE WEEK DUE TO SOUTHERLY CHANNELING AHEAD OF A COLD FRONT. && .LWX WATCHES/WARNINGS/ADVISORIES... DC...NONE. MD...NONE. VA...NONE. WV...NONE. MARINE...NONE. && $$ SYNOPSIS...JCE/KLW NEAR TERM...GMS/KLW SHORT TERM...JCE LONG TERM...DFH AVIATION...JCE/KLW/DFH MARINE...JCE/KLW/DFH

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