-- Discussion containing changed information from previous version are highlighted. --
000
FXUS61 KLWX 130810
AFDLWX

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

.SYNOPSIS...
AN UPPER LEVEL TROUGH WILL CROSS THE REGION TODAY. 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.

&&

.NEAR TERM /THROUGH TONIGHT/...
HIPRES IN THE CENTRL CONUS RDGG INTO THE WVA MTNS THIS MRNG. MOST
AREAS HV DCPLD. HV CLDS IN THE APLCHNS/PTMC HIGHLANDS/NRN VLY/ERN
PANHNDL. THUS...BEST COOLING OUTSIDE OF FROST ADVY/FRZ WRNG AREAS...
IN THE SHELTERED VLYS E OF BLURDG. RDGS JUST W/S OF WRNG AREA NOT
FAR FM FRZG THO...AND THERE/S STILL SVRL HRS TO GO. WL LEAVE
ADVY/WRNG ALONE.

MDL GDNC HAS REMAINED QUITE CONSISTENT PAST 24 HRS. AN AMPLIFIED H5
TROF AXIS PIVOTS ACRS CWFA TDA...SPCLY DURING THE AFTN HRS. H8-5
LAPSE RATES BTWN 6.5-7.5 C/KM...W/ THE STEEPEST RATES /AND A PINCH
OF INSTBY REPRESENTED BY A HND J/KG CAPE OR TWO/ AT THE BASE OF THE
TROF ACRS CENTRL VA. WL BE BRINGING SCT SPRINKLES ACRS CWFA INVOF
TROF...AND CANT RULE OUT A STRAY SHRA COINCIDENT W/ THE HIER LAPSE
RATES. POPS 20-30 PCT.

THE MIXED LYR WL BE DP...UP TO ABT 10K FT. THERE/S 30 KT OF WND AT
THE TOP OF THE LYR...W/ MEAN LYR MIXING SUGGESTING GUSTS AT LEAST 20
KT CAN MIX TO THE SFC...SPCLY ACRS NRN MD/ADJCNT ERN WVA. HWVR...
WNDS WL DCPL TNGT AS HIPRES BLDS. WL TAKE WNDS DOWN SHARPLY BY
SUNSET...AND HV LGT WNDS AFTER MIDNGT.

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 LATER TDA.

&&

.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 /08Z MONDAY THROUGH FRIDAY/...
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.

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.

&&

.MARINE...
NW FLOW ACRS WATERS ELY THIS RMNG...BUT AS RDGG BLDS WNDS ARE
DIMINISHING. SHUD BE ON TRACK TO DROP SCA AT 4AM. FLOW PICKS BACK UP
AGN LATER TDA ALONG/BHD A TROF AXIS. MOMENTUM TRANSFER EQUATIONS
SUGGEST 20-25 KT AVBL IN MIXED LYR. HV ALREADY ADDED TO SCA
PREVIOUSLY ISSUED...SO THAT ALL WATERS UNDER ADVY AT SOME POINT.
WNDS PICK UP FIRST FOR NRN BAY...AND GUSTS SHUD BE STRONGEST THERE.
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.

&&

.LWX WATCHES/WARNINGS/ADVISORIES...
-- Changed Discussion --
DC...NONE.
MD...FREEZE WATCH FROM LATE TONIGHT THROUGH TUESDAY MORNING FOR
     MDZ003>005-501-502.
     FREEZE WARNING UNTIL 8 AM EDT THIS MORNING FOR MDZ501.
     FROST ADVISORY UNTIL 8 AM EDT THIS MORNING FOR MDZ003-502.
VA...FREEZE WATCH FROM LATE TONIGHT THROUGH TUESDAY MORNING FOR
     VAZ025>031-503-504.
     FREEZE WARNING UNTIL 8 AM EDT THIS MORNING FOR VAZ503-504.
     FROST ADVISORY UNTIL 8 AM EDT THIS MORNING FOR VAZ025>031.
WV...FREEZE WATCH FROM LATE TONIGHT THROUGH TUESDAY MORNING FOR
     WVZ050>053-055-501>506.
     FREEZE WARNING UNTIL 8 AM EDT THIS MORNING FOR WVZ501-503-505-
     506.
     FROST ADVISORY UNTIL 8 AM EDT THIS MORNING FOR WVZ050>053-055-
     502-504.
MARINE...SMALL CRAFT ADVISORY FROM 11 AM THIS MORNING TO 6 AM EDT
     TUESDAY FOR ANZ532-540.
     SMALL CRAFT ADVISORY FROM 3 PM THIS AFTERNOON TO 6 AM EDT
     TUESDAY FOR ANZ533-534-537-541-543.
     SMALL CRAFT ADVISORY FROM 3 PM THIS AFTERNOON TO 7 PM EDT THIS
     EVENING FOR ANZ535-536-542.
     SMALL CRAFT ADVISORY FROM 11 AM THIS MORNING TO 2 AM EDT
     TUESDAY FOR ANZ530-531-539.
     SMALL CRAFT ADVISORY FROM 11 AM THIS MORNING TO 7 PM EDT THIS
     EVENING FOR ANZ538.
-- End Changed Discussion --

&&

$$
SYNOPSIS...HTS
NEAR TERM...HTS
SHORT TERM...GMS
LONG TERM...GMS
AVIATION...HTS/GMS
MARINE...HTS/GMS