National Weather Service National Headquarters

• Home
• Site Map
• News
• Organization
• Search for: NWS All NOAA 

-- Discussion containing changed information from previous version are highlighted. --
000
FXUS61 KCTP 152321
AFDCTP

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE STATE COLLEGE PA
721 PM EDT WED MAY 15 2013

.SYNOPSIS...
A COLD FRONT WILL MOVE SOUTHWARD FROM THE LOWER GREAT LAKES LATE
THIS AFTERNOON INTO EARLY TONIGHT. THE COLD FRONT WILL BECOME
QUASI- STATIONARY OVER THE CENTRAL APPALACHIANS AND SOUTHERN MID-
ATLANTIC STATES INTO THE WEEKEND BEFORE RETURNING BACK TO THE
NORTH AS A WARM FRONT EARLY NEXT WEEK. ANOTHER COLD FRONT SHOULD
CROSS THE REGION AROUND THE MIDDLE OF NEXT WEEK.

&&

.NEAR TERM /UNTIL 6 AM THURSDAY MORNING/...
AN UPPER- LEVEL TROUGH WILL MOVE EWD ACRS SERN CANADA WITH TRIPLE-
POINT SFC LOW TRACKING EWD ACRS SRN ONT THEN NEWD THRU THE ST.
LAWRENCE VLY. THE TRAILING COLD FRONT WILL BE THE TRIGGER OR
FOCUSING MECHANISM FOR TSTM DEVELOPMENT THIS AFTN AS IT PUSHES
SEWD ACRS THE LWR LKS INTO WRN NY/PA. SOME MODELS /I.E. THE NAM/
STILL APPEAR TO BE TOO BULLISH WITH LLVL MSTR INFLUX...SHOWING SFC
DEWPOINTS IN THE MID 60S OVER CNTRL PA AHEAD OF THE COLD FRONT.
UPSTREAM OBS INDICATE SFC DEWPOINTS ARE MORE LKLY BE IN THE UPPER
50S F RESULTING IN SB CAPE VALUES BTWN 500 TO 1000 J/KG...OR ABOUT
1/2 OF THE CAPE VALUES THE NAM IS GENERATING. STILL...THIS AMOUNT
OF INSTABILITY SHOULD BE SUFFICIENT FOR STORM INITIATION. THE
DEEP-LAYER SHEAR IS MORE ROBUST WITH MEAN 0-6KM VALUES AROUND
40KTS AND UNIDIRECTIONAL WIND PROFILES. THIS CAPE/SHEAR
ENVIRONMENT SHOULD BE MORE THAN ADEQUATE TO SUPPORT SOME ORGANIZED
STORM STRUCTURES WITH THE MAIN TSTM HAZARD BEING DAMAGING WINDS.

SO THE QUESTION REMAINS WHY ARE THE MODELS NOT CRANKING OUT A
GREATER CVRG OF PCPN/TSTMS THIS AFTN? EVEN THE HI-RES MDLS ARE
SHOWING LIMITED STORM CVRG DURING PEAK HEATING AHEAD OF THE COLD
FRONT. WELL...A FEW THINGS TO CONSIDER: 1) THE CWA WILL BE LOCATED
IN THE UNFAVORABLE RIGHT EXIT REGION OF 80-100KT MID-UPPER LVL
JET. 2) PERHAPS THE STG MID-LVL FLOW/UNIDIRECTIONAL SHEAR IS
SIMPLY OVERWHELMING THE CONVECTIVE ENVIRONMENT. SO AFTER CLOSER
INSPECTION OF FORCING FIELDS WHICH DO NOT SEEM TO LINE-UP...I
TEND TO AGREE WITH SPC FCST REASONING THAT THE SVR WX THREAT IS
MARGINAL.

THE FRONT WILL PUSH SWD ACRS S-CNTRL PA DURING LATE EVE AND SHOULD
REACH THE MASON-DIXON LINE BY 03Z. THE THREAT OF SHOWERS AND TSTMS
WILL DECREASE FROM NORTH-SOUTH FROM LATE AFTN INTO EARLY TONIGHT
WITH POPS TAPERING DOWN TO SCHC AFT 06Z IN THE FAR SRN TIER PER
CONS MDL BLEND.

&&

.SHORT TERM /6 AM THURSDAY MORNING THROUGH 6 PM THURSDAY/...
W-E ORIENTED Q-STNRY FRONTAL BOUNDARY SHOULD LINGER JUST SOUTH OF
THE PA/MD BORDER EARLY THURS AM BEFORE SLOWLY SINKING SWD INTO
WV/VA. KEPT SOME SCHC TO LOW CHC POPS ALONG/SOUTH OF THE PA
TURNPIKE FOR DAY 2 WITH ANY AFTN CONVECTION REMAINING ISOLD TO SCT
AT BEST. OR TO PUT IT ANOTHER WAY...MOST OF THE CWA SHOULD BE DRY.

A WEAK SECONDARY/BACKDOOR COLD FRONT SHOULD PUSH SWD ACRS CNTRL PA
LATER THURS...BEFORE SFC RIDGING TAKES HOLD OVER THE AREA TOMORROW
NGT INTO DAY 3. DAYTIME MAXES SHOULD RANGE BTWN 70-80F WITH SOME
LOCATIONS OVER THE ERN VALLEYS CLIMBING INTO THE LOW 80S. LOWS
WILL VARY FROM AROUND 40F IN THE NORTH TO THE LOW 50S ALONG THE
SRN TIER ZONES.

&&

.LONG TERM /THURSDAY NIGHT THROUGH WEDNESDAY/...
FORECAST CONTINUES TO LEAN TOWARD A DRIER SOLUTION THU NIGHT
THROUGH SAT AS DRIER AIR EDGES IN FROM THE N/NW...HELPING TO NUDGE
FRONTAL BOUNDARY SOUTH OF PA. LOWS WILL DIP BACK INTO THE 40S
NORTH/50S SOUTH WITH DAYTIME HIGHS IN THE UPPER 60S TO MID 70S.

RIDGE CONTINUES TO BUILD IN OVERHEAD THROUGH THE WEEKEND...BUT
RETURN FLOW BEGINS AROUND SURFACE HIGH BY LATE WEEKEND WHICH WILL
PUSH A WARM FRONT BACK IN OUR DIRECTION. COULD SEE A SCT
SHOWER/TSTM ON SUNDAY...WITH BEST CHANCE IN THE SW.

BY EARLY NEXT WEEK UPPER-LEVEL TROUGH OVER ERN CANADA SHIFTS EWD
INTO THE NRN ATLC AND TROUGHING DEVELOPS OVER THE INTER MTN
WEST/HIGH PLAINS STATES. THE MODELS IN GENERAL AGREE ON THIS
PATTERN EVOLUTION. AT THE SFC...RETURN FLOW/INC LLVL MSTR BRINGS
INCREASING CHANCES OF AFTN SHOWERS/TSTMS MON-TUE. THE GFS IS MORE
AGGRESSIVE THAN THE EC WITH THE CONVECTION. WHILE THE ECMWF-BASED
GUIDANCE IS DRIER OVERALL IT IS A FEW TO SEVERAL DEGREES LOWER
WITH MAXES THAN THE GFS-BASED GUIDANCE...PERHAPS OWING MORE TO
COOLER EASTERLY LLVL FLOW WITH SOME INTERACTION WITH RETURNING
Q-STNRY BOUNDARY FROM THE SOUTH. THE AREA SHOULD BREAK INTO THE
WARM SECTOR BY TUESDAY ALLOWING TEMPS TO SURGE ABOVE NORMAL.

THE MID-TO-HIGH LATITUDE FLOW BECOMES INCREASINGLY BLOCKY BY LATE
IN THE PERIOD...WITH BROAD OPERATIONAL AND ENSEMBLE AGREEMENT ON A
TROUGH/RIDGE/TROUGH CONFIGURATION FROM THE PAC NW/PLAINS/NORTHEAST.
WHILE THE DETAILS ARE UNCERTAIN...THE GENERAL TREND IS TOWARD
SLOWING EASTWARD PROGRESSION OF THE TROUGH...THUS INCREASING POPS
FOR MID/LATE WEEK WITH POTENTIAL FOR SLOWER EVOLUTION OF SYNOPTIC
SYSTEMS IN HIGHLY AMPLIFIED LG SCALE PATTERN.

&&

.AVIATION /23Z WEDNESDAY THROUGH MONDAY/...

-- Changed Discussion --
AT 23Z A COLD FRONT EXTENDS FROM NEAR BGM SOUTHWEST TO AROUND DJ
AND INTO OHIO. AIRMASS AHEAD OF THE FRONT IS STILL UNSTABLE...BUT
LIMITED MOISTURE HAS KEPT AN EFFECTIVE LID ON MOST ACTIVITY. A
SMALL CLUSTER OF STORMS IS DYING AS IT MOVES THRU SRN LANCASTER
COUNTY. ANOTHER ISOLATED STORM CANNOT BE RULED OUT UNTIL THE FRONT
HAS SETTLED SOUTH OF THE AREA...BUT MOST OF THE NIGHT WILL BE
TRANQUIL WITH VFR PREDOMINATING. COULD BE SOME LATE NIGHT FOG
WHERE IT RAINED EARLIER TODAY...BUT CONFIDENCE IS LOW ON THIS.

THE FRONT WILL STALL JUST SOUTH OF THE PA BORDER THURSDAY...SO THE
PA TERMINALS WILL BE VFR AFTER ANY FOG ISSUES BURN OFF EARLY IN
THE DAY.


.OUTLOOK...

FRI...NO SIG WX EXPECTED.

SAT-SUN...AREAS OF REDUCED CONDITIONS WITH SCATTERED SHOWERS AND
ISOLATED THUNDERSTORMS.

MON...REDUCED CONDITIONS WITH RAIN POSSIBLE.
-- End Changed Discussion --

&&

.CTP WATCHES/WARNINGS/ADVISORIES...
NONE.

&&

$$
SYNOPSIS...GARTNER
NEAR TERM...GARTNER
SHORT TERM...GARTNER/STEINBUGL
LONG TERM...RXR
AVIATION...LA CORTE