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-- Discussion containing changed information from previous version are highlighted. --
000
FXUS61 KLWX 131434
AFDLWX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC
1034 AM EDT MON MAY 13 2013

.SYNOPSIS...
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AN UPPER TROUGH WILL CROSS THE MID-ATLANTIC REGION THROUGH THIS
EVENING. HIGH PRESSURE WILL BUILD OVER THE REGION TUESDAY...AND
MOVE OFFSHORE EARLY WEDNESDAY AS A WARM FRONT ADVANCES
NORTHEASTWARD ACROSS THE MID ATLANTIC. A COLD FRONT WILL APPROACH
THE REGION LATE WEDNESDAY... BUT STALL OUT THROUGH THE END OF THE
WEEK.
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&&

.NEAR TERM /THROUGH TONIGHT/...
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AN EXPANSIVE SFC HIGH THAT IS CENTERED OVER THE GULF COAST AND
MIDWEST STATES THIS MRNG WILL CONTINUE TO BUILD TOWARD THE ERN
SEABOARD. THE OTHER PROMINENT FEATURE IS A NEARLY VERTICALLY-
STACKED LOW OVER QUEBEC. A SHORTWAVE DISTURBANCE AND UPPER JET
STREAK WILL DIG SEWD AROUND THE BACKSIDE OF LARGE-SCALE TROUGH.
THIS FEATURE WILL TRAVERSE THE CWA THIS AFTN AND EVE.

12Z IAD RAOB REVEALED AN ALREADY DEEP BOUNDARY LAYER TO ABOUT 7
KFT. EXPECT THE MIXED LAYER TO DEEPEN FURTHER THIS AFTN AS SFC
HEATING STEEPENS LLVL LAPSE RATES AND COLD POOL ASSOCIATED WITH
THE TROUGH STEEPENS MLVL LAPSE RATES. FCST MODEL SOUNDINGS FOR
THIS AFTN CONTINUE TO SHOW AN THERMODYNAMIC ENVIRONMENT THAT IS
FAVORABLE FOR MODEST CONVECTION WHILE QG FORCING FOR ASCENT
INCREASES WITH THE APPROACH OF THE MID-LVL TROUGH. COVERAGE AND
INTENSITY OF SHOWERS THIS AFTN SHOULD BE VERY LOW WITH SUCH A DRY
AIRMASS OVER THE REGION. BASED ON LOCATION OF BEST LIFT/MOISTURE
AND LATEST HIRES REFLECTIVITY FCST...LOW CHANCE POPS COVERS THE
MTS...CENTRAL VA AND LWR SRN MD. ONLY ISO SPRINKLES EXPECTED
ELSEWHERE. GIVEN INVERTED V SOUNDING...SHOWERS CAPABLE OF
TRANSPORTING 30-35 MPH GUSTS DOWN TO THE SFC.

WNDS WL DCPL TNGT AS HIPRES BLDS. WL TAKE WNDS DOWN SHARPLY BY
SUNSET...AND HV LGT WNDS AFTER MIDNGT. THERE IS STILL UNCERTAINTY
IF WINDS DECOUPLE FULLY ALONG AND EAST OF I-95 WITH THE HIGH STILL
BUILDING IN FROM THE WEST.

MET MOS PERFORMED BETTER YDA. WUD XPCT THE COOLER SOLN TO BE
PREFERRED DUE TO AMPLITUDE OF TROF...AND WENT THAT WAY FOR MAXT TDA.
WENT ON THE COOLER SIDE FOR MIN-T TNGT AS WELL...BUT DIDNT UNDERCUT
TOO MUCH YET. WUD RATHER WAIT FOR MDL PERFORMANCE FM THIS MRNG
FIRST. AREAS OF FROST COZY UP TO THE WRN BURBS OF DC-BALT. MIN-T
FCST JUSTIFY ADDING FDKMD/CARROLL CNTYS TO FRZ WATCH...OTRW AM
KEEPING FRZ WATCH AS IS FOR NOW. ANTICIPATE A TRANSITION TO FROST
ADVY/FRZ WRNG IN STEP W/ MIN-T ASSESSMENT THIS AFTN.
-- End Changed Discussion --

&&

.SHORT TERM /TUESDAY THROUGH TUESDAY NIGHT/...
ONE MORE ABNORMALLY COOL NWLY FLOW DAY ON TUE...AS THE UPPER TROUGH
TAKES A SHARP TURN OFF THE NEW ENGLAND COAST BUT NEEDS ANOTHER DAY
TO COMPLETELY LEAVE THE REGION. HIGHS WILL APPROACH THE M-U60S BY
MIDDAY. A LIGHT N-NWLY SFC FLOW WILL KEEP DRY/COOL AIR LOCKED-IN
FROM THE PREVIOUS COUPLE OF DAYS...AS SCATTERED MID-HIGH LEVEL
CLOUDS BEGIN TO STREAM IN FROM THE NW DURING THE SECOND HALF OF THE
DAY. ONE LAST COOL-ISH OVERNIGHT PERIOD ON TUE NIGHT...MORE OF A
TRANSITION - U40S - FROM THE NEAR-FREEZING TEMPS AND THE
CONSIDERABLY DIFFERENT AND WARMER OVERNIGHT LOWS STARTING WED
NIGHT.

&&

.LONG TERM /WEDNESDAY THROUGH SUNDAY/...
A FAST-MOVING AND LOCALIZED UPPER VORT WILL ACCELERATE OUT OF THE
UPPER MIDWEST LATE TUE INTO WED...WHILE THE LARGER UPPER TROUGH IS A
BLOCKADE IN ITS EWD PROGRESS. THE INCOMING VORT WILL BE DISPERSED
EARLY WED...HAVING LITTLE EFFECT ON THE MID ATLC REGION BUT HELPING
TO OPEN A CLEARER PATH FOR THE NEXT SYSTEM TO PROGRESS AS IT MOVES
TOWARD THE NORTHEAST. FAST OF THE HEELS OF THE EARLY WED UPPER LEVEL
FEATURE WILL BE A POTENT BUT RELATIVELY SMALL SYSTEM THAT WILL SLIDE
ACROSS THE US/CANADIAN BORDER TUE/WED. FAST UPPER FLOW WILL TAKE THE
SRN STREAM PORTION OF THE SYSTEM OVER THE GREAT LAKES DURING THE
DAYTIME HRS...W/ THE REMNANT CONVECTION SLIDING ACROSS NY/PA AND THE
NRN TIER OF OUR CWA LATE WED/EARLY THU. A NEAR 10 DEG INCREASE IN
TEMPS IS EXPECTED ON WED AFTN FROM THE PAST COUPLE OF DAYS. INSTEAD
OF BEING AROUND 10 DEG BELOW AVG FOR THIS TIME OF YEARS...WE`LL
REACH DAILY HIGHS AROUND 10 DEG ABOVE AVG FOR THE SECOND HALF OF THE
WEEK AND INTO EARLY NEXT WEEK.

THE LEFTOVER PORTION OF THE COLD FRONT FROM THE WED STORM SYSTEM
WILL BE FORCED TO STALL NEARLY RIGHT ALONG THE I-70 CORRIDOR OF THE
UPPER MIDWEST FROM WED-TO-FRI. THIS WILL SET-UP THIS REGION FOR
CONVECTION EACH AFTN...TAPERING OFF OVER THE CNTRL APLCNS. WE`LL
HAVE LOW CHANCES FOR SHOWERS/TSTMS THU AND FRI FROM THE PORTION OF
THE BOUNDARY HOVERING OVER THE AREA...BUT FAVORABLE SVR WX
PARAMETERS WILL BE MARGINAL - INCLUDING INSTABILITY...FORCING...LL
CONVERGENCE AND SHEAR.

MED RANGE GUIDANCE INCLUDING THE GFS/NAM/EURO ALL IN GOOD AGREEMENT
ON THE SYNOPTIC-SCALE DYNAMICS FOR OUR AREA THRU FRI. ON BOARD W/
THE NAM`S DEPICTION OF THE LATE WED FEATURE...THOUGH THE EURO/GFS DO
SHOW THE TAIL END OF THE COLD FRONT SLIDING ACROSS OUR NORTH BUT IN
LESS DETAIL. THE NEXT WX-MAKER ON THE SCOPE WILL LIKELY BE ANOTHER
POTENT STORM SYSTEM OVER THE NRN PLAINS SUN/MON THAT MODELS SHOW AS
BECOMING MORE COMPLEX AS IT MOVES TOWARD THE EAST EARLY NEXT WEEK.

&&

.AVIATION /14Z MONDAY THROUGH FRIDAY/...
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VFR TDA-TNGT. A TROF AXIS WL CROSS TERMINALS TAFTN...BRINGING A PD
OF HIGH-BASED STCU /060-070/ AND NW WNDS G20-25 KT. SKIES SHUD CLR
AND WNDS DIMINISH NEAR/SOON AFTER SUNSET. LGT SHRA OR SPRINKLES
DEVELOP DURING THE PEAK HEATING HRS BUT COVERAGE TOO LOW TO
INCLUDE IN TAFS.

TUE WILL START OFF CLEAR W/ MID-UPPER LEVEL CLOUD DECKS SPILLING
OVER THE MTNS FROM THE WEST LATER IN THE DAY. SFC WINDS WILL REMAIN
LIGHT INTO EARLY WED AS THE SWITCH TO SLY. AN APPROACHING COLD FRONT
ON WED AFTN WILL INCREASE THE SLY WINDS DURING THE DAYTIME HRS. THE
COLD FRONT WILL ARRIVE LATE WED NIGHT...STALLING ACROSS THE REGION
FOR THU AND EARLY FRI. THE STALLED BOUNDARY WILL POTENTIALLY
GENERATE SCATTERED SHOWERS/TSTMS DURING THE AFTN HRS ON THU AND FRI.
-- End Changed Discussion --

&&

.MARINE...
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HIPRES CONTINUES TO BUILD IN FROM THE MIDWEST. PRESSURE GRADIENT
STRONG ENOUGH TO PRODUCE NW WINDS 15-20 KT THIS MRNG. HAVE THUS
ISSUED A SCA FOR ALL OF THE WATERS FOR THE REMAINDER OF THE DAY.
WHEN MIXING IS DEEPEST THIS AFTN...WIND GUSTS AROUND 25 KT
POSSIBLE. THERE IS SOME CONCERN FOR HIGHER WIND GUSTS TO MIX DOWN
TO THE SFC IF SHOWERS DEVELOP OVER THE WATERS. MAX WIND SPEEDS IN
THE CLOUD LAYER AROUND 35 KT...SO COULD SEE GUSTS JUST APPROACHING
GALE THRESHOLD. COVERAGE OF SHOWERS WILL BE HIGHEST OVER THE SRN
MOST ZONES...BUT STILL BE WIDELY SCT OR ISO. THEREFORE OPTED NOT TO
ISSUE A GALE WRNG AT THIS TIME.

AS CHANNELING WORKS DOWN WATERS...EMPHASIS SHIFTS TO THE MID BAY/LWR
PTMC TNGT.

WINDS WILL DROP OFF ON TUE...EVEN DURING THE AFTN HRS AS HIGH
PRESSURE DRIFTS OVERHEAD AND MOVES OFFSHORE. WINDS WILL THEN SWITCH
TO SLY OVERNIGHT AND INTO EARLY WED. SLY CHANNELING WILL BEGIN W/
THE HIGH OFF THE COAST AND A COLD FRONT MOVING IN FROM THE WEST. SCA
CONDITIONS WILL LIKELY RETURN FOR THE DAYTIME HRS ON WED...SUBSIDING
AFTER THE FRONT ARRIVES AND STALLS OVER THE AREA FOR THE LATTER HALF
OF THE WEEK.
-- End Changed Discussion --

&&

.LWX WATCHES/WARNINGS/ADVISORIES...
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DC...NONE.
MD...FREEZE WATCH FROM LATE TONIGHT THROUGH TUESDAY MORNING FOR
     MDZ003>005-501-502.
VA...FREEZE WATCH FROM LATE TONIGHT THROUGH TUESDAY MORNING FOR
     VAZ025>031-503-504.
WV...FREEZE WATCH FROM LATE TONIGHT THROUGH TUESDAY MORNING FOR
     WVZ050>053-055-501>506.
MARINE...SMALL CRAFT ADVISORY UNTIL 6 AM EDT TUESDAY FOR ANZ532>534-537-
     540-541-543.
     SMALL CRAFT ADVISORY UNTIL 7 PM EDT THIS EVENING FOR ANZ535-
     536-538-542.
     SMALL CRAFT ADVISORY UNTIL 2 AM EDT TUESDAY FOR ANZ530-531-539.
-- End Changed Discussion --

&&

$$
UPDATE...KLEIN
PREV DISC...HTS/GMS