Area Forecast Discussion
Issued by NWS Sterling, VA

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FXUS61 KLWX 240145
AFDLWX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC
845 PM EST TUE DEC 23 2014

.SYNOPSIS...

LOW PRESSURE OVER THE GULF STATES AND AN ASSOCIATED WARM FRONT
WILL TRACK NORTH OVERNIGHT. A COLD FRONT OVER THE CENTRAL PART OF
THE U.S. WILL TRACK EAST AND REACH THE MID ATLANTIC WEDNESDAY
NIGHT. BREEZY CONDITIONS WILL FOLLOW THE FRONT THURSDAY. HIGH
PRESSURE WILL BUILD INTO THE REGION TO CLOSE OUT THE WEEK.

&&

.NEAR TERM /THROUGH WEDNESDAY/...
DENSE FOG ADVSRY RMNS IN EFFECT ACROSS CENTRAL AND LWR SRN MD...AS
WELL AS WRN LOUDOUN UNTIL 1 AM.

QUITE AN INTERESTING WX PATTERN FOR 12/23. PCPN IS MARCHING INTO
THE MID ATLC...AND IT`S NOT OF THE WINTRY VARIETY. MDT RAFL CAN BE
SEEN ON RGNL RDR OVR NC MOVG N. HRRR HAS IT MOVG INTO THE CENTRAL
SHEN VLLY ARND 04Z...DC ARND 06Z...MASON-DIXON LN BY 09Z. THIS
SHOULD CAUSE LO LVL MIXING...AND THE VSBY TO SHOW SOME IMPVRMNT.

ALL RAIN AND NO CONVECTIVE EXPECTED OVERNIGHT...AS THE RAIN
BATCHES MAKE THEIR WAY NORTH AND ENCOUNTER THE EDGE OF THE CAD
WEDGE. LOCALLY HEAVY EMBEDDED SHOWERS POSSIBLE AT TIMES...ESPEC
ACROSS THE I-95 CORRIDOR AND EAST W/ SOME OF THE ACTIVITY
ORIGINATING AS DEEP CONVECTION WELL TO THE SOUTH.

WEDNESDAY...

BATCHES OF LIGHT/MODERATE RAIN WILL CONTINUE TO SPREAD FROM SW-TO-NE
ACROSS THE AREA...AIDED BY A STRENGTHENING AND POTENT LOW LEVEL JET
MAX. GLOBAL MODELS AND EVEN NEAR-TERM DERIVATIVES ARE IN GOOD
AGREEMENT ON THE INITIAL PHASES OF THE INCOMING STORM SYSTEM. A
COUPLE OF KEY FEATURES THAT HAVE HAD MANY DIFFERENT LOOKS AND
EFFECTS IN THESE RECENT RUNS ARE GRADUALLY BEING RESOLVED. AN
INTENSE SFC LOW WILL BE THE MAIN FEATURE OUT OF ALL THIS ENERGY
INTERACTION IN THE UPPER LEVELS OVER THE ERN HALF OF THE CONUS. THE
LOW WILL ORIGINATE DOWN OVER THE LA GULF COAST AND MAKE A PATH
STRAIGHT TOWARD THE UPPER MIDWEST/GREAT LAKES FROM LATE TODAY INTO
LATE WED EVE.

THE WARM FRONT OUT AHEAD OF THE SFC LOW WILL HAVE PASSED OVER THE
AREA BY EARLY WED MRNG...ALLOWING WARMER THAN AVG TEMPS TO FOLLOW UP
THE ERN SEABOARD. WHILE RAINING FOR A BETTER PART OF THE DAY...WE
WILL STILL SEE TEMPS CLIMB WELL INTO THE 50S...W/ SOME L60S
APPEARING OVER THE SERN SECTIONS OF THE CWA WED AFTN. TOTAL QPF
RANGES FOR THE 24-30 HR RAIN EVENT ARE EXPECTED TO BE IN THE 1-1.5"
RANGE ALONG AND E OF I-95...TAPERING OFF TO ABOUT 0.5-1.0 FROM THE
PIEDMONT WEST TO THE MTNS. ANOMALOUSLY HIGH PWATS WILL BE ASSOCIATED
W/ THIS SYSTEM CLOSE TO THE COAST...AS THE CONVECTIVE AND MODIFIED
TROPICAL CHARACTERISTICS CARRY AMPLE MOISTURE UP THE COAST.

&&

.SHORT TERM /WEDNESDAY NIGHT THROUGH FRIDAY NIGHT/...

CDFNT WL BE ON THE WRN EDGE OF CWFA AT START OF PD...AND SHUD BE
MARCHING ACRS AREA THRU THE EVNG INTO THE ELY OVNGT HRS. THIS TIMING
HASNT CHGD MUCH PAST CPL CYCLES...PERHAPS A PINCH FASTER THAN YDA.
FNT WL BE MARKED BY STRONG THERMAL GRADIENT AND BE W/IN ZONE OF DP
SLY FLOW AHD OF AMPLIFIED H5 TROF AXIS. THEREFORE...THERE WL BE
PLENTY OF WARM MOIST AIR TO BE TRANSPORTED NWD...W/ UPGLIDE STILL
PRESENT FOR ADDED LIFT.

AHD OF FNT...AMS UNCHARACTERISTICALLY WARM AND UNSTBL FOR LT DEC...
W/ DEWPTS IN THE 50S/PWAT 1.50-1.75 INCH/SVRL INSTBY PARAMETERS
STARTING TO REGISTER-- SUCH AS NONZERO MUCAPE...LIS NEAR 0...TQ
15-20...K APPCHG 30. WHILE AM DOUBTING HOW MUCH ACTUAL LTNG THERE WL
BE...SCOPE OF DYNAMICS/WIND FIELD SUGGESTS THAT FNT MAY BE MARKED BY
BKN LINE OF LOW TOPPED CNVCTN ALONG OR JUST AHD OF IT. THIS CUD
BRING DOWN SOME OF THE 40-50 KT KT WINDS PRESENT H9-7. THEREFORE...
HV EXPANDED AREA OF SCHC THUNDER TO JUST ABT ENTIRE CWFA IN THE
EVNG...AND WLL TRIM AS FROPA APPROACHES. PWAT WELL ABV 2SD NOW...
AND INCRSG...SO WL BE ADDING LCL FLOODING TO HWO.

THINK THERE WL BE RAPID DRYING BHD FNT WED NGT AS FLOW VEERS WLY. AM
STILL A LTL HESITANT TO BE TOO SHARP ON BACK SIDE OF POP FIELD IN
CASE LATER GDNC TIMING CHGS AGN...BUT FOR NOW HV MOST OF THE PCPN
ENDING BEFORE 12Z THU.

MIXING POTL WL BE MUCH BETTER THU...STILL W/ A GOOD WIND FIELD.
MEAN LYR MIXING WL YIELD 20-30 KT...W/ SOME GUSTS UP TO 40 KT PSBL
ACRS THE HIER TRRN. THIS WL BE A TIME PD TO MONITOR...AS GRAIDENT
MAY JUSTIFY WND ADVY FOR SOME WRN/NWRN CNTYS W/ AN UPCOMING FCST
CYCLE. WL HOLD THAT IN THE HWO FOR NOW.

EVEN W/ RELATIVELY STRONG CAA...TEMPS IN THE APLCNS WL ONLY
MARGINALLY SUPPORT SHSN...AND THE WLY TRAJ DOESNT HELP MUCH. WL BE
KEEPING CHC POPS FOR WRN UPSLP AREAS THRU THU...BUT WX TYPE SHRASN.
DRY ELSW. MAXT BASED ON MOS MEAN. WL BE ABT 10 DEGF COOLER THAN
WED...WHICH IS STILL ABV CLIMO.

AFTR AN ACTV PD...WX THU NGT THRU FRI NGT WL BE BENIGN AS HIPRES
BLDS. WL EVEN GET TO SEE THE SUN. TEMPS STILL AOA CLIMO.

&&

.LONG TERM /SATURDAY THROUGH TUESDAY/...
A COLD FRONT WILL MOVE ACROSS THE REGION SATURDAY BEFORE SLIDING OFF
TO THE SOUTH AND ACROSS NORTH CAROLINA SATURDAY NIGHT. MUCH OF THE
DAY SATURDAY SHOULD BE DRY. THERE IS A SLIGHT CHANCE OF A FEW RAIN
OR SNOW SHOWERS DEVELOPING POST-FRONTAL LATE SATURDAY AND SATURDAY
NIGHT. MOST OF ANY ENERGY APPEARS TO TAFFY-OUT WELL TO OUR NORTH.

THE SLIGHT CHANCE OF LIGHT STRATIFORM RAIN LINGERS ON SUNDAY AS
ADDITIONAL UPPER LEVEL ENERGY TRIES TO SCOOT SOUTHWARD FROM THE
LOWER GREAT LAKES TO BEHIND THE FRONT WHICH MAY STALL ACROSS THE
CAROLINAS. AS TEMPERATURES DECREASE INTO SUNDAY NIGHT...THERE EXISTS
A SLIGHT CHANCE OF LIGHT SNOW.

MODERATE LEVELS OF UNCERTAINTY LATE SUNDAY THROUGH MONDAY LIES WITH
THE EUROPEAN AND GFS MODELS TRYING TO DEVELOP A LOW ALONG THE
STALLED FRONT OVER THE CAROLINAS AND SPREADING SNOW NORTH INTO OUR
REGION. COLDER AIR FUNNELING IN BEHIND THE COLD FRONT ON A NORTHERLY
WIND AND SEVERAL WAVES OF UPPER ENERGY FROM THE OHIO VALLEY WOULD
PROBABLY SUPPORT THIS. HOWEVER...THE POSITION OF THE POSSIBLE
DEVELOPING LOW ALONG THE FRONT APPEARS TO BE TOO FAR SOUTH TO
PRODUCE A NOTICABLE THREAT OF SNOW. FOR NOW...WENT WITH SLIGHT
CHANCE OF SNOW SUNDAY NIGHT AND A SLIGHT CHANCE TO CHANCE OF LIGHT
RAIN OR LIGHT SNOW MONDAY NIGHT.

AS FOR TUESDAY...WE HAVE A SLIGHT CHANCE OF LIGHT RAIN OR LIGHT SNOW
SHOULD A LOW DEVELOP ALONG THE FRONT. IT ISN`T UNTIL THE MAIN TROUGH
OF LOW PRESSURE PIVOTS ACROSS THE REGION LATE TUESDAY WILL
CONDITIONS IMPROVE.

&&

.AVIATION /01Z WEDNESDAY THROUGH SUNDAY/...

LOW CLOUDS AND FOG CONTINUE ACROSS MUCH OF THE REGION. NOT UNTIL
AFTR MIDNIGHT W/ THE ONSET OF STEADY PRECIP WILL WE LOSE THE SUB-IFR
CONDITIONS. CIGS WILL REMAIN LOW THROUGH THE NEXT 24 HRS UNTIL A
COLD FRONT MOVES THRU WED NIGHT. RAIN WILL BE FAIRLY STEADY FROM
LATE TONIGHT AND THRU MUCH OF THE DAYTIME HRS ON WED. ONLY BRIEF
AND INTERMITTENT BREAKS EXPECTED...W/ IFR CIGS OR LOWER.

AOB IFR WL BE PREVALENT WED NGT. LLWS CONCERNS FM THE AFTN WL CARRY
INTO THE EVNG HRS. CFP EITHER LT EVNG OR JUST AFTR MIDNGT. ENUF
UNSEASONABLE WARMTH AND INSTBY FOR LOW TOPPED CNVCTN...MEANING BRIEF
HIER WND GUSTS EMBEDDED W/IN AREAS OF RA. G30-35 KT W/IN REASON.
WORST CASE SCENARIO WUD BE HIER THAN THAT. SLY WNDS WL BECOME WLY
BHD FNT.

MIXING BETTER THU...W/ A WIND FIELD THAT WUD SUPPORT W15G30KT. CIGS
WL LIFT. WL EITHER HV VFR OR MVFR THRU THE DAY.

VFR THU NGT-SAT UNDER HIPRES.

&&

.MARINE...
LIGHT WINDS OVER THE WATERS...THOUGH VSBYS ARE LOW - ESPEC OVER THE
MIDDLE/LOWER MD BAY. WINDS WL RMN LIGHT UNTIL WAVES OF
LIGHT/MODERATE RAIN MOVE IN OVERNIGHT AND INTO EARLY WED. BY
MIDDAY WED...SCA CONDITIONS WILL BECOME APPARENT FROM SOUTH TO
NORTH.

SLY SFC FLOW WL INCR WED NGT...TO ARND 15 KT. MOMENTUM TRANSFER
CHALLENGED...BUT 20-25 KT JUST OFF THE DECK...SO CANT RULE OUT THAT
IT WUD COME DOWN IN SHRA. HIER GUSTS THAT THAT NOT TTLY OUT OF THE
QSTN EITHER...BUT THINK THE ENVIRONMENT WUD MORE LKLY JUSTIFY SMW VS
GLW.

CDFNT WL CROSS WATERS ELY THU MRNG. NW FLOW BHD FRNT WL MIX MORE
EFFECTIVELY. SCA LKLY AND GLW PSBL. SINCE ITS BYD 36 HRS...WL KEEP
IN SYNOPSIS. WL CAP AT SCA LVL FOR THE FCST. WNDS WL SUBSIDE THU NGT
AS HIPRES BLDS.

&&

.TIDES/COASTAL FLOODING...
ANNAP REACHED 2.0 FT AT THE HIGH TIDE WHICH JUST PASSED - BARELY
REACHING ACTION STAGE. ASTRONOMICALLY THIS WAS THE HIGHER OF THE
TWO...SO NO PROBS XPCTD W/ THE MRNG HIGH TIDE. AFTER THAT...XPCT
ANOMALIES TO INCREASE...DRIVEN BY AN UPTICK IN SLY WINDS. THAT MAY
PUT A FEW SITES ALONG THE WESTERN SHORE OF THE BAY ON THE CUSP OF
MINOR FLOODING.

A COLD FRONT WILL PASS EAST OF WATERS BEFORE THE THU MRNG TIDE.
DEPARTURES SHOULD DECREASE A LTL AS A CONSEQUENCE...BUT AM NOT SURE
HOW QUICKLY BLOWOUT CONDS WILL ENSUE.

&&

.LWX WATCHES/WARNINGS/ADVISORIES...
DC...NONE.
MD...DENSE FOG ADVISORY UNTIL 1 AM EST WEDNESDAY FOR MDZ003>006-013-
     014-016>018-503>507.
VA...DENSE FOG ADVISORY UNTIL 1 AM EST WEDNESDAY FOR VAZ505.
WV...NONE.
MARINE...SMALL CRAFT ADVISORY FROM 9 PM WEDNESDAY TO 5 AM EST THURSDAY
     FOR ANZ535-536.
     SMALL CRAFT ADVISORY FROM 1 PM WEDNESDAY TO 5 AM EST THURSDAY
     FOR ANZ530>534-537>543.

&&

$$


UPDATE...WOODY!
PRVS...GMS/HTS/KLW





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