Area Forecast Discussion
Issued by NWS Sterling, VA

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000
FXUS61 KLWX 210112
AFDLWX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC
912 PM EDT SUN APR 20 2014

.SYNOPSIS...
HIGH PRESSURE OVER EASTERN NEW ENGLAND WILL BUILD INTO THE AREA
THROUGH MONDAY. A COLD FRONT WILL MOVE THROUGH THE AREA TUESDAY
AND TUESDAY EVENING. HIGH PRESSURE BUILDS BACK IN FOR THE SECOND
HALF OF THE WORK WEEK.

&&

.NEAR TERM /THROUGH MONDAY NIGHT/...
AXIS OF SURFACE HIGH HAS MOVED LTL SINCE TAFTN. IT REMAINS ALONG
THE SRN SHORE OF LONG ISLAND EWD ACRS ACK. ITS ALREADY EXPANDING
WWD INTO THE MID ATLC...AND IT/LL CONT TO DO SO OVNGT. ALOFT...A
RDG AXIS IS ALSO SETTING UP...WHICH WL AIDE IN COOLER/DRIER AIR
DRAINING SWWD. WHILE DEWPTS STILL IN THE LWR-MID 30S LCLLY...
WIDESPREAD MID-UPR 20S DEWPTS PRESENT ACRS NJ/ERN PA. THUS...PTTN
IN PLACE FOR WINDS TO DECOUPLE OVERNIGHT RESULTING IN GOOD
RADIATIONAL COOLING.

HV MADE A FEW MORE TWEAKS TO TEMPS/DEWPTS BASED ON LTST DATA. THE
PART OF THE CWFA WHICH SHUD SEE THE BEST RADL COOLING /BALT-WASH
CRRDR/ ALSO HAS THE HIEST DEWPTS AND BEST WIND GRADIENT CURRENTLY.
AM STILL A LTL WORRIED ABT LOUDOUN-MONTCO-HOWARD CNTYS...BUT TEMPS
HV FAR TO DROP AND DEWPTS NEED TO EDGE DOWN A LTL AS WELL. SUSPECT
INVOF HEF WL SEE SOME FROST...BUT DOUBT IT/LL BE A MAJORITY OF PW
CNTY. THEREFORE...DONT HV ENUF CONFIDENCE TO ADD ANYONE TO A
FROST ADVY ATTM. IF LWR DEWPTS DO INDEED DRAIN SWD AND TEMPS START
PLUMMETING...THEN THE ADVY MAY NEED TO BE XPNDD. OTRW...FCST LOOKS
REASONABLE.

BY MONDAY AFTERNOON AND NIGHT SURFACE LOW PRESSURE MOVES INTO THE
GREAT LAKE STATES AND A COLD FRONT BEGINS TO APPROACH THE AREA.
MODELS KEEP SUNSHINE IN PLACE FOR MOST OF TOMORROW BEFORE HI
CLOUDS INCREASE LATE IN THE DAY AND NIGHT. LIGHT SOUTHERLY WINDS
DEVELOP BUT DRY AIR REMAINS IN PLACE FOR MUCH OF THE DAY. WOULD
EXPECT TEMPERATURES TO BE A BIT WARMER WITH HIGHS IN THE UPPER
50/S TO UPPER 60/S...AND IT WILL FEEL MILDER WITH LESS WIND. MIN
TEMPS MON NGT IN THE MID 40S TO LOWER 50S.

&&

.SHORT TERM /TUESDAY THROUGH WEDNESDAY/...
SUB-1000 MB SFC LOW TRACKS EWD ACROSS UPSTATE NY AND NRN NEW ENGLAND
ON TUE. ATTENDANT COLD FRONT OVER THE OH VLY IS EXPECTED TO CROSS
THE APPALACHIANS BY ABOUT 18Z TUE BEFORE MOVING EWD THRU THE CWA
BETWEEN APPROX 18Z TUE AND 00Z WED. THE BEST FORCING LOOKS TO STAY
NORTH OF CWA AND CLOSER TO TO SFC LOW AND UPPER SHORTWAVE TROUGH.
PREVIOUS FCST HAD LIKELY POPS WITH FROPA. DID NOT WANT TO INCREASE
POPS FURTHER DUE TO THE LIMITED FORCING AND PROGRESSIVE NATURE WITH
THIS SYSTEM. THUNDER A POSSIBILITY WITH TIMING OF FROPA COINCIDENT
WITH PEAK HEATING. WEAK MID-LVL LAPSE RATES AND INCREASING CLOUD
COVER AHEAD OF THE FRONT DURING THE MRNG SHOULD LIMIT DEGREE OF
DESTABILIZATION. FCST MEAN MLCAPE VALUES FROM THE 09Z SREF ARE UNDER
500 J/KG FOR THE ENTIRE CWA AND MLCAPE PROBABILITIES AOA 500 J/KG
ARE LOW...JUST TWO INDICATIONS OF A VERY LIMITED TSTM POTENTIAL.
EVEN WITH CLOUD COVER...MAX TEMPS IN THE 70S AHEAD OF THE FRONT.

THE COLD FRONT MOVES OFF THE DELMARVA COAST TUE NGT WHILE HIPRES
BUILDS IN FROM CENTRAL CANADA. A STRONG PRESSURE GRADIENT BETWEEN
THESE TWO SYSTEMS WILL PRODUCE BREEZY NW WINDS TUE NGT AND
CONTINUING INTO WED. 12Z NAM/GFS BUFKIT PROFILES SHOW A POTENTIAL
FOR WIND GUSTS OF 30-35 MPH TO MIX DOWN THE SFC ON WED. MAX TEMPS A
FEW DEGREES BELOW NORMAL ON WED OWING TO THE CAA IN WAKE OF FROPA.

&&

.LONG TERM /WEDNESDAY NIGHT THROUGH SUNDAY/...
SURFACE HIGH BUILDING ACROSS AREA WEDNESDAY NIGHT. TEMPERATURES MAY
DROP 5 DEGREES BELOW NORMAL BEFORE REBOUNDING THROUGH THURSDAY
NIGHT.

HIGH PRESSURE MOVING OFFSHORE FRIDAY EVENING AND NIGHT AS COLD
FRONT FROM CENTRAL PLAINS TRACK EAST ACROSS GREAT LAKES/OHIO
VALLEY. MARGINALLY SUPPORT FOR PRECIPITATION WITH THE FRONT AS
MAIN AREA PVA IS NORTH OF AREA. INCREASED CHANCES OF PRECIPITATION
SATURDAY MORNING WHEN A SECOND FRONT SUPPORTED BY STRONG PVA
ENTERS THE AREA FROM THE NORTH.

&&

.AVIATION /01Z MONDAY THROUGH FRIDAY/...
VFR SKC-SCT250 THRU MONDAY AFTERNOON AT THE TERMINALS. E/SE WNDS
AOB 10 KT WL CONT TO DIMINISH OVNGT...AND WL REMAIN LGT MON AS
HIPRES OHD. IF THERE/S ANY WIND TMRW...ITLL HV AN ELY COMPONENT...
GRDLY BCMG SLY BY THE PM PUSH.

A COLD FRONT IS ANTICIPATED TO MOVE THRU THE TERMINALS FROM WEST TO
EAST BETWEEN 18Z TUE AND 00Z WED. SHRA LIKELY AND ISO TSRA DURING
THE AFTN WITH FROPA. BRIEF/LOCAL RESTRICTIONS POSSIBLE WITH HEAVIER
SHRA OR TSRA. SLY WINDS AROUND 10 KT AHEAD OF THE FRONT WILL BECOME
NWLY 10-15 KT FOLLOWING FROPA. WIND GUSTS UP TO 30 KT POSSIBLE ON
WED AS HIPRES BUILDS IN FROM THE NW.

VFR WITH HIPRES OVERHEAD WED NGT THRU FRI.

&&

.MARINE...
WATERS SANDWICHED BTWN HIPRES OVER FAR ERN NEW ENGLAND AND LOPRES
OFF THE CAROLINAS. STILL HV A FAIR AMT OF GRADIENT WND ACRS THE
MARINE AREA...BUT GNLY IN THE 10-15 KT RANGE. THE GRADIENT WL BE
TIGHTEST FOR THE LWR PTMC AND SRNMOST TWO BAY ZONES. HV THRESHOLD
SCA CONDS THERE ATTM...AND THE P-GRAD SHUD BE THERE MOST OF TNGT.
PRIND SUGGEST SCA APPROPRIATE WHERE CURRENTLY PLACED...THO MESO
MDL GDNC HINTING ITLL BE A CLOSE CALL ON THE MAIN CHANNEL OF THE
BAY FOR ANTHR CPL HRS. FCST RELYING UPON GRADIENT SEPARATING FM
BNDRY LYR. IF THAT DOESNT HPPN...THEN END TIME MAY NEED TO BE
PUSHED BACK-- AGAIN.

WINDS WILL BE LIGHT/VRBL MON-MON NGT IN RESPONSE TO RDG AXIS.

SLY FLOW AHEAD OF A COLD FRONT GENERALLY 10 KT ON TUE. THERE IS A
LIMITED POTENTIAL HOWEVER FOR WINDS TO REACH SCA CRITERIA IN THE
MAIN STEM OF THE CHSPK BAY DUE TO SLY CHANNELING. CAPPED WINDS AT 15
KT IN THESE ZONES FOR NOW WITH SUCH A MARGINAL WIND FIELD. SHRA AND
POSSIBLY AN ISO TSTMS WITH THE FROPA LATE TUE AFTN AND EVE. NW WINDS
BEHIND THE FRONT WILL BECOME GUSTY AS HIPRES BUILDS IN FROM THE NW.
SCA LIKELY TUE NGT AND WED.

WINDS BELOW SCA LVLS BY WED NGT AS HIPRES BUILDS OVERHEAD.

&&

.LWX WATCHES/WARNINGS/ADVISORIES...
DC...NONE.
MD...FROST ADVISORY FROM 2 AM TO 8 AM EDT MONDAY FOR MDZ004>007.
VA...NONE.
WV...NONE.
MARINE...SMALL CRAFT ADVISORY UNTIL 1 AM EDT MONDAY FOR ANZ534-537-543.

&&

$$
SYNOPSIS...HTS/JRK
NEAR TERM...HTS/SDG
SHORT TERM...JRK
LONG TERM...CEM
AVIATION...HTS/JRK/CEM
MARINE...HTS/JRK/CEM







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