Area Forecast Discussion
Issued by NWS Sterling, VA

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000
FXUS61 KLWX 230224
AFDLWX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC
924 PM EST SAT NOV 22 2014

.SYNOPSIS...
HIGH PRESSURE OFF CAPE HATTERAS WILL CONTINUE TO DRIFT OFFSHORE
OVERNIGHT. A DEEPENING LOW PRESSURE SYSTEM OVER THE GREAT LAKES
WILL BRING A WARM FRONT THROUGH THE AREA SUNDAY NIGHT. AN
ASSOCIATED COLD FRONT IS EXPECTED TO MOVE THROUGH MONDAY NIGHT.
LOW PRESSURE IS EXPECTED TO TRACK NORTHEAST ALONG THE COAST
WEDNESDAY. HIGH PRESSURE THEN BUILDS INTO FRIDAY.

&&

.NEAR TERM /THROUGH TONIGHT/...
SFC HIGH PRES IS OFF CAPE HATTERAS...BUT ENOUGH GRADIENT EXISTS TO
MAINTAIN 10 MPH SLY FLOW. THEREFORE...DESPITE DEWPOINTS IN THE
TEENS...TEMPERATURES HAVE NOT DROPPED MUCH YET THIS EVENING. WITH
CLEAR SKIES THOUGH...ANY AREAS THAT SEE DECOUPLING WILL DROP
QUICKLY. FOR INSTANCE...IT IS ALREADY MID 30S AT KMRB WHERE IT WAS
CALM AT 02Z. MIN TEMPS GENERALLY LOW 30S...THOUGH PATCHY UPR 20S
WILL OCCUR. INVERSION WITH HIGHER TEMPS AT HIGHER ELEVATIONS AND
NEARSHORE AS WELL.

&&

.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.

POPS INCREASE FROM FROM THE SOUTH SUNDAY AFTERNOON. WARM AIR
ADVECTION TYPICALLY STARTS RAINING SOONER THAN MODELS DEPICT.


&&

.LONG TERM /SUNDAY NIGHT THROUGH SATURDAY/...
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 /02Z SUNDAY THROUGH THURSDAY/...
VFR CONDS TNGT AND INTO SUN AFTERNOON.

MVFR/IFR CONDITIONS ARE EXPECTED SUNDAY NIGHT WITH RAIN (MVFR
POSSIBLE SUNDAY LATE AFTERNOON NEAR KCHO). 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 CONDITIONS EXPECTED MONDAY AND MONDAY
NIGHT.

W FLOW AOB 10 KT 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/VSBY LATE TUE NIGHT-WED EVE. WINDS
BECOME W AGAIN AROUND 10 KT THU W/ RETURN TO VFR LIKELY.

&&

.MARINE...
SLY/SWLY FLOW AROUND 15 KT INTO THE OVERNIGHT. STRAY 18 KT GUST
POSSIBLE...BUT NOT ENOUGH FOR AN SCA.

SMALL CRAFT ADVISORY SUNDAY NIGHT...LIKELY CONTINUING INTO MONDAY
NIGHT 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...
IAD TIED A RECORD LOW OF 14 DEGREES THIS MORNING...PREVIOUSLY SET
BACK IN 1964.

8TH CONSECUTIVE DAY WITH TEMPERATURES BELOW 50 AT IAD AND BWI WAS
RECORDED TODAY...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 FROM MIDNIGHT SUNDAY NIGHT TO 6 AM EST
     MONDAY FOR ANZ530>532-535-538>540.
     SMALL CRAFT ADVISORY FROM 9 PM SUNDAY TO 6 AM EST MONDAY FOR
     ANZ533-534-536-537-541>543.

&&

$$
UPDATE...JACKSON
PREVIOUS...WOODY!/ADS/DFH






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