Area Forecast Discussion
Issued by NWS Sterling, VA

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000 FXUS61 KLWX 221939 AFDLWX AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC 239 PM EST SAT NOV 22 2014 .SYNOPSIS... HIGH PRESSURE OVER EASTERN NORTH CAROLINA IS SHIFTING OFFSHORE. A DEEPENING LOW PRESSURE SYSTEM OVER THE GREAT LAKES WILL LIFT A WARM FRONT THROUGH THE AREA SUNDAY NIGHT. AN ASSOCIATED COLD FRONT IS EXPECTED TO MOVE THROUGH MONDAY NIGHT. THE FRONT STALLS JUST OFFSHORE AS HIGH PRESSURE BUILDS ACROSS THE AREA TUESDAY. LOW PRESSURE IS EXPECTED TO DEVELOP EAST OF GEORGIA WEDNESDAY MORNING... TRACKING NORTH ALONG THE COAST DURING THE DAY. && .NEAR TERM /TONIGHT/... HIGH PRES HAS MIGRATED OVR ERN N CAROLINA...BUT AS MDLS HAD BEEN PREDICTING IT IS DOING A GOOD JOB OF KEEP THE CLDS TO THE N AT BAY. MID LVL CLDS CAN BE SEEN ALONG THE MASON-DISON LN...AND THIS WL LKLY BE A WORST-CASE SCENARIO THIS EVE OVR MD. VA SHOULD CONT TO HV PRIMARILY CLR SKIES. IT WL NOT BE AS COLD AS LAST NGT..LOWS A30 MOST OF THE FCST AREA. && .SHORT TERM /SUNDAY/... SUNDAY WL BE THE LAST PD W/O MUCH WX TO TALK ABT. HIGH PRES CONTS TO DRIFT AWAY. RGN WL BE UNDER SRLY FLOW. HIGH TEMPS A FEW DEGS WARMER THAN TDA - M50S MOST OF THE AREA. && .LONG TERM /SUNDAY NIGHT THROUGH FRIDAY/... DEEP SOUTHERLY FLOW WILL BE IN PLACE SUNDAY NIGHT AHEAD OF AN UPPER LEVEL TROUGH OVER THE PLAINS. SHORT WAVE ENERGY AND AN ATTENDANT DEEPENING SURFACE LOW WILL BE PIVOTING NORTHWARD INTO THE OHIO VALLEY...WHILE A WARM FRONT PUSHES INTO THE MID ATLANTIC. A STRONG LLJ WILL TRANSPORT MOISTURE INTO THE REGION...WITH A SOLID SHIELD OF MODERATE RAIN EXPECTED TO OVERSPREAD THE AREA AFTER 00Z. RAISED POPS TO 100 ACROSS THE ENTIRE AREA EXCEPT THE FAR WESTERN RIDGES...AS THIS LOOKS LIKE A WELL FORCED SYNOPTIC EVENT WITH SIMILAR TIMING IN THE MODEL GUIDANCE. THE ONLY QUESTION IS HOW QUICKLY IS THE COOL NEAR-SURFACE AIR SCOURED OUT WITH A NIGHTTIME WARM FRONT AND POSSIBLE IN-SITU CAD. REGARDLESS OF THE TIMING...TEMPERATURES AND DEW POINTS WILL CLIMB STEADILY THROUGH THE NIGHT...ESPECIALLY EAST OF THE MOUNTAINS. 50 KT OF 0-1 KM SHEAR ALONG THE WARM FRONT...BUT INSTABILITY IS EXPECTED TO BE NEAR ZERO...ALTHOUGH THE NAM AND A FEW SREF MEMBERS BRING A LITTLE ELEVATED CAPE EAST OF I-95. LEFT MENTION OF THUNDER OUT...BUT LATER SHIFTS WILL NEED TO MONITOR THE POTENTIAL FOR EMBEDDED RUMBLES. LOW LEVEL WINDS ALSO FAVOR A SOUTHEAST UPSLOPE FLOW...SO THE HIGHEST QPF IS DEPICTED ALONG AND JUST EAST OF THE BLUE RIDGE. PWATS WILL APPROACH 1.5 INCHES...SO EXPECT SOME SPOTS COULD EASILY NEAR AN INCH OF RAIN. RIDGE TOPS COULD BE RATHER BREEZY DUE TO THE LLJ. MAIN SHIELD OF PRECIP WILL PULL NORTHEAST AFTER 09Z AS MID LEVEL DRYING BEGINS TO WORK IN. CWA WILL BE WARM SECTORED ON MONDAY. THIS WILL RESULT IN HIGHS IN THE LOWER TO MID 60S WEST OF THE BLUE RIDGE AND SOME LOWER 70S TO THE EAST...GETTING CLOSE TO RECORD HIGHS (SEE CLIMATE SECTION). IT WILL ALSO BE BREEZY WITH SOME GUSTS TOPPING 25 MPH. BIGGEST QUESTION OF THE DAY IS PRECIP POTENTIAL. THE 12Z NAM IS STILL AN OUTLIER WITH MORE MOISTURE AND A NARROW CAPE PROFILE...WITH SHOWERS DEVELOPING. THE 12Z RUNS OF THE GFS AND ECMWF SHOW MID LEVEL DRYING AND SOME CAPPING...AND THUS DRY. WILL LEAN THIS WAY...KEEPING VERY LOW POPS. HOWEVER THIS WILL NEED TO BE MONITORED AS WELL BECAUSE IF SHOWERS/STORMS DO DEVELOP...THEY WILL HAVE STRONG SHEAR TO TAP INTO. BY MONDAY EVENING...THE SURFACE LOW WILL MOVE INTO QUEBEC...WITH THE TRAILING COLD FRONT CROSSING THE MID ATLANTIC. MOISTURE WILL BE LIMITED...WITH THE NAM AND SREF THE MOST ROBUST WITH SHOWER DEVELOPMENT. WILL CONTINUE TO CARRY SMALL POPS. TEMPERATURES WILL FALL INTO THE 40S...WITH 30S WEST OF THE BLUE RIDGE WHERE THE COLDER AIR WILL ARRIVE EARLIER. GUIDANCE STILL DIFFERS SUBSTANTIALLY ON THE AMPLITUDE OF A RIDGE OVER THE WESTERN UNITED STATES...A SHORTWAVE TROUGH COMING ONSHORE OF WESTERN NORTH AMERICA AND THE INTERACTION OF TWO SHORTWAVE TROUGHS MOVING ACROSS THE CENTRAL AND EASTERN PART OF THE COUNTRY DURING THE MIDDLE PART OF NEXT WEEK. 00Z OPERATIONAL ECMWF IS MORE PRONOUNCED WITH THE RIDGE OUT WEST BECAUSE IT IS WEAKER WITH THE INCOMING PACIFIC SHORTWAVE...AND AS A RESULT ALLOWS MORE AMPLIFICATION/PHASING OF TWO SHORTWAVES OVER THE EASTERN UNITED STATES LEADING TO STRONGER CYCLOGENESIS MUCH CLOSER TO THE COAST. THE LATEST OPERATIONAL 12Z GFS HAS TRENDED IN THIS DIRECTION AS WELL...SO HAVE STARTED WITH WPC AS A BASELINE THEN TWEAKED POPS UPWARD A FEW PERCENT AND NUDGED TEMPERATURES DOWN ABOUT A DEGREE OR TWO /MORE AMPLIFIED NORTHERN STREAM WAVE AND STREAM INTERACTION BRINGS IN COLDER AIR/. OVER THE PAST 24 HOURS EACH MODEL CYCLE HAS A FEW MORE ENSEMBLE MEMBERS BRINGING LOW PRESSURE CLOSER TO THE COAST...BUT THE OVERALL PATTERN IS NOT A CLASSIC SETUP FOR HEAVY WINTRY PRECIPITATION IN THE METRO AREAS DUE IN LARGE PART TO THE RIDGE OUT WEST BEING UNDERCUT/WEAKENED BY A SHORTWAVE TROUGH. THIS WOULD ACT TO KEEP THE PATTERN LESS AMPLIFIED AND THE EAST COAST SYSTEM MORE PROGRESSIVE/TRANSIENT...WITH LESS COLD AIR REACHING THE CWA IN CONCERT WITH LOW PRESSURE DEVELOPING ALONG THE COAST. BOTTOM LINE...PRECIPITATION CHANCES HAVE INCREASED DURING THE MID-WEEK PERIOD WHICH COINCIDES WITH THE BUSIEST TRAVEL TIME OF THE YEAR SO IT DEFINITELY BEARS WATCHING. WINTRY PRECIPITATION CANNOT BE RULED OUT BUT AT THE MOMENT THIS SETUP DOES NOT APPEAR TO FAVOR A CLASSIC MID-ATLANTIC SNOWSTORM. BEHIND THIS SYSTEM...MORE UNSEASONABLY COLD AIR FOLLOWS LATER IN THE WEEK...GRADUALLY MODERATING INTO THE WEEKEND AS HIGH PRESSURE MOVES OVERHEAD THEN OFFSHORE. && .AVIATION /18Z SATURDAY THROUGH THURSDAY/... VFR CONDS TNGT AND SUN. MVFR/IFR CONDITIONS ARE EXPECTED SUNDAY NIGHT WITH RAIN. A PERIOD OF HEAVY RAIN IS POSSIBLE. SOUTHERLY WINDS WILL INCREASE WITH GUSTS UP TO 25 KT LATE SUNDAY NIGHT THROUGH MONDAY...DIMINISHING AND TURNING WESTERLY MONDAY NIGHT. VFR CONDTIONS EXPECTED MONDAY AND MONDAY NIGHT. W FLOW AOB 10 KTS TUE W/ VFR...BECOMING N OR NE TUE NIGHT-WED...UNCERTAIN IN EXACT MAGNITUDE/DIRECTION DUE TO MODEL DISAGREEMENT IN PLACEMENT OF LOW PRES ALONG COAST. LOW PRES ALSO MAY BE ACCOMPANIED BY LWR CIGS/VSBYS LATE TUE NIGHT-WED EVE. WINDS BECOME W AGAIN AROUND 10 KTS THU W/ RETURN TO VFR LIKELY. && .MARINE... WINDS ON THE WATERS ARE GUSTING TO NEAR 20 KT. SCA IS IN EFFECT UNTIL EARLY EVE. NO PROBS ARE FORESEEN OVRNGT OR SUNDAY. SMALL CRAFT CONDITIONS ARE EXPECTED SUNDAY NIGHT THROUGH MONDAY AS WINDS INCREASE BEHIND A WARM FRONT. A COLD FRONT WILL TURN WINDS TO THE WEST MONDAY EVENING...WITH GUSTS GRADUALLY WEAKENING. UNLESS LOW PRES WINDS UP MUCH MORE THAN CURRENTLY PROJECTED BY EVEN THE STRONGER MODEL SOLUTIONS TUE NIGHT-WED NIGHT...IT LOOKS LIKE WINDS/SEAS SHOULD REMAIN BELOW SCA CRITERIA THROUGH THE MIDDLE PORTION OF THE WEEK. && CLIMATE... ABNORMAL EARLY SEASON COLD CONTINUES...BUT WILL GIVE WAY TO NEAR RECORD WARMTH MONDAY. IAD TIED A RECORD LOW OF 14 DEGREES THIS MORNING...PREVIOUSLY SET BACK IN 1964. PERHAPS MORE TELLING IS THE FACT THAT BWI AND IAD HAVE NOT EXCEEDED 50 DEGREES IN A WEEK. TODAY`S HIGHS ARE FORECAST TO REMAIN IN THE 40S...WHICH WOULD BE THE 8TH CONSECUTIVE DAY WITH TEMPERATURES BELOW 50 AT BOTH SITES...SECOND MOST ON RECORD AT IAD IN THE MONTH OF NOVEMBER...AND THE LONGEST NOVEMBER STRETCH AT BWI SINCE 1944. STRONG SOUTHERLY FLOW AHEAD OF A COLD FRONT ON MONDAY WILL USHER IN UNSEASONABLY WARM TEMPERATURES...AND HIGHS MONDAY COULD APPROACH RECORD MAXIMUM VALUES. BELOW IS A LIST OF RECORD DAILY HIGH TEMPERATURES FOR 11/24. SITE RECORD (YEAR) DCA 74 (1958) BWI 73 (1979) IAD 74 (1979) && .LWX WATCHES/WARNINGS/ADVISORIES... DC...NONE. MD...NONE. VA...NONE. WV...NONE. MARINE...SMALL CRAFT ADVISORY UNTIL 7 PM EST THIS EVENING FOR ANZ530>543. $$ PRODUCTS...WOODY!/ADS/DFH

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