FXUS61 KCTP 122025
AFDCTP
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE STATE COLLEGE PA
325 PM EST FRI MAR 12 2010
.SYNOPSIS...
SEVERAL AREAS OF SURFACE LOW PRESSURE...LOCATED OVER THE LOWER OHIO
AND TENNESSEE RIVERS AND ALONG THE CAROLINA COAST THIS
AFTERNOON...WILL CONSOLIDATE INTO A DEEP SURFACE LOW NEAR THE
DELMARVA COAST SUNDAY MORNING. A DEEP...EAST TO SOUTHEAST FLOW OF
ATLANTIC MOISTURE WILL LIFTED INTO THE MOUNTAINS OF SOUTHERN AND
CENTRAL PENNSYLVANIA...AND CONTRIBUTE TO WIDESPREAD HEAVY RAINFALL
OF 2 TO 3 INCHES ACROSS MUCH OF THE REGION TODAY THROUGH SATURDAY.
LOCALLY HEAVIER RAINFALL IS POSSIBLE ACROSS PORTIONS OF
SOUTHEASTERN PENNSYLVANIA. THE HEAVY RAINFALL COMBINED WITH
LOCATIONS EXPECTING PRECIPITOUS SNOW MELT WILL RESULT IN THE
POTENTIAL FOR SIGNIFICANT FLOODING. AS COLDER AIR FILTERS INTO THE
STORM SATURDAY NIGHT AND SUNDAY...AREAS OF WET SNOW ARE POSSIBLE
ACROSS THE NORTHERN AND WESTERN MOUNTAINS OF THE STATE. DRIER
WEATHER WITH TEMPERATURES REBOUNDING TO SLIGHTLY ABOVE NORMAL
VALUES WILL OCCUR NEXT WEEK.
&&
.NEAR TERM /THROUGH SATURDAY/...
UPPER DIFLUENCE AND LLVL CONVERGENCE/PRECIPITABLE WATER WILL RAMP
UP STEADILY OVERNIGHT AND SATURDAY...BRINGING DRENCHING RAINFALL AND
AN INCREASING THREAT FOR FLOODING TO MUCH OF THE CWA. LOWEST
PROBABILITY FOR FLOODING OF STREAMS AND RIVERS IS ACROSS THE NW
MTS...WHERE STORM TOTAL QPF SHOULD BE AOB 2 INCHES. COORDINATED WITH
BUF TO EXPAND OUR FLOOD WATCH NW TO COVER THE REMAINING...NW MTNS OF
PENN. HOWEVER...THE MAIN PROBLEM THERE MAY OCCUR WITH LONGER LAG
RUNOFF INTO THE LARGER STREAMS AND RIVERS.
THE INITIAL 35 TO 40 KT SOUTHEASTERLY WIND MAX AT 850 MB THIS
AFTERNOON WILL STRENGTHEN TO AN IMPRESSIVE -5 STANDARD
DEVIATION...ESE WIND AS ITS AXIS SHIFTS SLOWLY NORTH ACROSS PENN
SATURDAY AND SAT EVENING. THIS RATHER UNPRECEDENTED LLVL ESE WIND
MAX...AND EXTENDED PERIOD OF STRONG 925-850 MB THETA-E ADVECTION
WILL LIKELY RESULT IN WIDESPREAD 2-3 INCH RAINFALL AMOUNTS OVER THE
NEXT 36 HOURS. THERE ARE STILL A FEW AREAS WHERE WATER EQUIV IN THE
DWINDLING SNOWPACK (OF 1-1.5 INCHES) WILL HELP TO ACCENTUATE THE
RUNOFF. THIS WILL EQUAL (OR IN SOME CASES EXCEED) THE 1.5-2 INCH/12
HOUR FLASH FLOOD GUIDANCE VALUES...LEADING TO AT LEAST FLOODING
OF STREAMS AND CREEKS ACROSS APPROX THE SE HALF OF OUR CWA.
TEMPS LATE TODAY AND EARLY TONIGHT WILL STAY GENERALLY BETWEEN 45
AND 50F...BEFORE DIPPING BY SEVERAL DEG LATE TONIGHT. MAXS ON
SATURDAY WILL BE VERY SIMILAR TO TODAY...IF NOT A DEG OR SO COOLER
CONSIDERING THE WIDESPREAD MODERATE (TO AT TIMES HEAVY) RAINFALL.
ALSO DISCUSSED THE POTENTIAL ISSUANCE OF A WIND ADVISORY FOR THE
EASTERN MTNS AS THE LLVL EASTERLY WIND MAX OF 60-75 KTS LIFTS NWD
VERY LATE TONIGHT THROUGH SAT EVENING. THE COMBINED EFFECT OF THE
ANOMALOUSLY STRONG/ATYPICAL EASTERLY FLOW WITH THE WET GROUND COULD
LEAD TO SOME DOWNED TREES - ESPECIALLY ACROSS THE HIGHER TERRAIN.
FOR NOW...WILL LIMIT THE EASTERLY GUSTS TO THE 40-45 MPH RANGE AND
ALLOW THE EVENING CREW TO BETTER ASSESS THE STRONG WIND POTENTIAL.
&&
.SHORT TERM /SATURDAY NIGHT/...
EC/GFS AND GEFS MSLP CENTER OF 990-995 MB CONSOLIDATES OVER THE
DELMARVA REGION SAT NIGHT INTO SUNDAY. ALTHOUGH SIGNIF COLD AIR TO
SUPPORT SNOW IS INITIALLY ABSENT FROM THIS SYSTEM...DYNAMIC COOLING
ALOFT AND A FAVORABLE TRACK TO THE SFC/UPPER LOW CENTER TO OUR SOUTH
AND SE WILL USHER IN THE POSSIBILITY OF ACCUMULATING/WET SNOW ACROSS
THE NRN AND WRN MTNS LATE SAT NIGHT AND SUNDAY MORNING. FOR
NOW...I'LL PLAY THIS CARD RATHER CONSERVATIVELY WITH JUST A COATING
TO 2 INCHES PAINTED IN THE SNOW GRIDS AOA 1800 FT MSL.
TEMPS AND WET BULBS WILL FALL INTO THE LOWER TO MID 30S LATE SAT
NIGHT ACROSS THE NORTH AND WEST...BUT SHOULD HOLD IN THE U30S TO MID
40S FOR THE SE VALLEYS. PERIODS OF LIGHTER RAINFALL AND AREAS OF FOG
WILL OCCUR SAT NIGHT WITH DECREASING EASTERLY WINDS...BACKING TO THE
NE.
&&
.LONG TERM /SUNDAY THROUGH FRIDAY/...
DEEP SYSTEM ON THE E COAST SUNDAY WILL OPEN UP SUN NITE AND MOVE
WELL TO THE E OF THE REGION MONDAY. CYCLONIC FLOW ON THE WRN
SIDE OF THE LOW WILL KEEP SHRA GOING THRU MON AM. THE COLUMN COOLS
OFF ENUF TO MAKE WET SNOW OR AT LEAST A RA/SN MIX OVER THE HIGHER
ELEVS SUN AM AND LATER SUN NITE. THERE COULD BE A SLUSHY COATING
IN THE N/W SUN AM...BUT THE COVG OF SHRA/SN WILL DECREASE DURING
THE DAYTIME AND TEMPS RISE...SO IT SHOULD CHANGE TO RAIN. CHC POPS
FOR SUN NITE...AND WITH SPARSE COVG...WILL NOT MENTION ADDTNL
ACCUMS THEN.
BIG RIDGE ALOFT BUILDS OVER THE HIGH PLAINS. THIS LOOKS VERY
SIMILAR TO WHAT HAPPENED MOST OF THE PAST WEEK...VERY DRY AND
SUNNY UNDER THE NW FLOW. SFC RIDGE WILL BE A BIT CLOSER TO THE
REGION THAN THE LAST ONE...SO A MODERATION IN TEMPS WILL ENSUE
AFTER SUNDAY. LITTLE/NO CHC OF RA FOR 4-5 DAYS.
&&
.AVIATION /20Z FRIDAY THROUGH WEDNESDAY/...
EXPECT WIDESPREAD IFR/MVFR CIGS...AND OCCASIONAL LIGHT TO MODERATE
RAIN...TO CONTINUE FOR THE REST OF THE DAY INTO THIS EVENING. A
STRONG LOW PRESSURE SYSTEM WILL CONSOLIDATE OVER THE MID ATLANTIC
REGION THIS WEEKEND...CONTINUING WIDESPREAD IFR WITH PERIODS OF
MODERATE TO HEAVY RAIN. THE STRONG EAST- SOUTHEAST FLOW WILL ALSO
SUPPORT AREAS OF LLWS ~50KTS...LIKELY FOR ALL AIRFIELDS AFTER 3Z
SATURDAY.
OUTLOOK...
SAT-SUN...GENERALLY IFR CIGS/VSBY OCNL RA.
MON...DRYING/IMPROVEMENT TO VFR PSBL.
TUE-WED...NO SIG WX EXPECTED.
&&
.HYDROLOGY...
WIDESPREAD RAINFALL AMOUNTS OF 2 TO 3 INCHES ARE ANTICIPATED
ACROSS SOUTHERN AND EASTERN PA FROM LATE TONIGHT THROUGH SATURDAY
AS A 850 MB EASTELRY WIND MAX OF 60 TO 75 KTS LIFTS NWD ALONG THE
MID ATLANTIC PIEDMONT. LOCAL STORM TOTAL AMOUNTS UP TO 4 INCHES
ARE POSSIBLE OVER THE LOWER SUSQ VLY/EAST CENTRAL MTNS. THE HEAVY
RAINFALL COMBINED WITH RESIDUAL SNOW MELT IN SOME LOCATIONS WILL
RESULT IN THE POTENTIAL FOR SIGNIFICANT FLOODING. A FLOOD WATCH
HAS BEEN EXPANDED NWD TO COVER MUCH OF CENTRAL PENN AND PARTS OF
THE NCENT MTNS THROUGH SATURDAY NIGHT. THE HEAVY RAINFALL...MAINLY
FROM SATURDAY INTO SUNDAY...COULD CAUSE MANY OF THE HEADWATER
CREEKS TO APPROACH FLOOD LEVELS. CONSIDERABLE RISES ON MOST
STREAMS AND CREEKS ARE ALSO EXPECTED THIS WEEKEND IN THE WATCH
AREA.
&&
.CTP WATCHES/WARNINGS/ADVISORIES...
FLOOD WATCH FROM 7 PM EST THIS EVENING THROUGH LATE SATURDAY
NIGHT FOR PAZ004>006-010>012-017>019-025>028-034>037-041-042-
045-046-049>053-056>059-063>066.
FLOOD WATCH THROUGH LATE SATURDAY NIGHT FOR PAZ024-033.
&&
$$
SYNOPSIS...LAMBERT
NEAR TERM...LAMBERT
SHORT TERM...LAMBERT/STEINBUGL
LONG TERM...DANGELO
AVIATION...LAMBERT/DICKEY
HYDROLOGY...
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