319
FXUS61 KCTP 131148
AFDCTP
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE STATE COLLEGE PA
748 AM EDT TUE AUG 13 2013
.SYNOPSIS...
AREAS OF HEAVY RAIN ARE EXPECTED TODAY AS REPEATED SHOWERS AND
THUNDERSTORMS PRODUCE HEAVY RAIN...ESPECIALLY OVER SOUTHERN
PENNSYLVANIA. A COLD FRONT WILL MOVE THROUGH LATER TODAY...AND
USHER IN MANY DAYS OF PLEASANT WEATHER.
&&
.NEAR TERM /UNTIL 4 PM THIS AFTERNOON/...
IR SAT PICS DEPICT A NICE BAROCLINIC LEAF DEVELOPING AS THE
EARLIER CONVECTION OVER LAKE ERIE AND NORTHERN PA BEGINS TO WANE.
THE LEAF HAS A WIDE SHIELD OF MODERATE RAINFALL AND EMBEDDED
THUNDER UNDER IT. CONTINUED DEVELOPMENT TO THE SYSTEM IS EXPECTED
IN THE RIGHT ENT QUAD OF THE JET OVER THE REGION AND TO THE EAST.
VERY HEAVY RAIN IS A POSSIBILITY THIS MORNING OVER THE SE...SO A
WATCH HAS BEEN POSTED FOR FLASH FLOODING. SEE HYDRO SECTION FOR
MORE THOUGHTS ON RAIN/FLOODING.
TWO COLD FRONTS...ONE WITH THE WIND SHIFT AND ONE WITH THE DRIER
AIR WILL PUSH THROUGH TODAY AND THIS EVENING. THE REAL DRY AIR
APPEARS TO BE N OF DETROIT AT THIS TIME...BUT MOVING CLOSER WITH
EACH HOUR. THE RAINS SHOULD TAPER OFF IN THE WEST LATER THIS
MORNING AND OVER EAST AFTER NOON. SOME SCT SHRA WILL BE LEFT OVER
AS THE COLDER AIR ALOFT MOVES OVERHEAD AND THE DOUBLE FRONTS PUSH
ACROSS.
&&
.SHORT TERM /4 PM THIS AFTERNOON THROUGH 6 PM WEDNESDAY/...
DRY AIR SHOULD BE INTO THE NW BY THE START OF THE PERIOD...AND THE
UPPER TROUGH AXIS WILL SWING THROUGH TONIGHT. EXPECT A RAPID
DECREASE IN SHOWERS BEFORE THE EVENING. THUS...MOST OF THE AREA
WILL BE DRY TONIGHT. SOME CLOUD COVER WILL BE PESKY OVER AT LEAST
THE WRN HIGHLANDS...AND FOG IS POSSIBLE IF THE DRY AIR DELAYS ANY
LONGER. WILL NOT MENTION FOG JUST YET...AS THE WESTERLY BREEZE
SHOULD STAY UP THROUGH THE NIGHT. REAL CLEARING IS NOT EXPECTED
UNTIL THE DAYTIME ON WED. BUT EVEN THEN...THE COOL AIR ALOFT COULD
ALLOW FOR PLENTIFUL CU OVER THE MTNS.
&&
.LONG TERM /WEDNESDAY NIGHT THROUGH MONDAY/...
OVERVIEW...THE LATEST ARRAY OF GUIDANCE SHOWS THE LARGE SCALE MEAN
FLOW OVER THE CONUS TRENDING/TRANSITIONING TOWARD A MORE TYPICAL
MID-AUGUST PATTERN WITH THE UPPER-LEVEL WESTERLIES SHIFTING NWD TO
LATITUDES ALONG AND NORTH OF THE US-CANADIAN BORDER BY EARLY NEXT
WEEK. THE PRONOUNCED/DEEP UPPER TROUGH GRIPPING THE NORTHEAST AND
MID-ATLANTIC STATES EARLY IN THE PERIOD SHOULD WEAKEN WITH
TIME...AS THE REMAINING NEGATIVE HEIGHT ANOMALY DRIFTS SWWD INTO
THE LWR MS RVR VLY PER THE 12Z GEFS MEAN. AT THE SFC...A LARGE
DOME OF HIGH PRESSURE /WITH ORIGINS OVER CENTRAL CANADA/ WILL
SPREAD SEWD FROM THE UPPER PLAINS ACROSS THE GRT LKS/OH VLY AND
TAKE UP RESIDENCE IN THE NEW ENGLAND AREA OVER THE WEEKEND. A WAVY
SFC FRONT OVER THE SE STATES IS PROGGED TO LIFT BACK NWD TOWARD
THE CAROLINA COAST/SRN MID-ATLC REGION BY SAT-MON.
HIGHLIGHTS...DRY WX SHOULD PREVAIL THROUGH THE MAJORITY OF THE
MEDIUM RANGE COURTESY OF HIGH PRES MIGRATING SLOWLY EWD FROM THE
UPPER MIDWEST TO THE NEW ENGLAND STATES. PWATS STAY BELOW NORMAL
THROUGH FRIDAY...RESULTING IN COMFORTABLE HUMIDITY AND COOL
NIGHTTIME TEMPS WITH LOWS IN THE 40S/50S. SOME UPPER 30S REMAIN
POSSIBLE OVER THE NRN TIER. CLEAR/CALM/COOL NIGHTS SHOULD ALSO
LEAD TO PREDAWN AND EARLY MORNING FOG IN THE VALLEYS. DAYTIME
HIGHS WILL AVERAGE NEAR TO BELOW NORMAL. A GRADUALLY MOISTENING
EAST-SOUTHEAST LOW LEVEL FLOW FAVORS AN INCREASE IN SKY COVER AND
LOW CHC FOR SHOWERS LATE IN THE WEEKEND AND INTO EARLY NEXT WEEK.
THE 12Z GFS AND 00Z ECMWF HANDLE THE EAST COAST FRONTAL BOUNDARY
REASONABLY WELL...WITH A CONSENSUS MULTI-MODEL/MOS/HPC SUPERBLEND
SUPPORTING THE HIGHEST POPS AROUND 19 AUGUST.
&&
.AVIATION /12Z TUESDAY THROUGH SATURDAY/...
SHOWERS AND STORMS SHOULD MOVE OUT RATHER FAST.
EXPECT VFR CONDITIONS BY EARLY AFT.
COLD FRONT TO THE WEST...THUS STILL HAVE TO WATCH FOR
NEW STORMS...BUT FOR NOW...WILL GO WITH A DRY FCST BY
AFT.
SOME LOWER SC LATE TONIGHT...AS WINDS ALOFT BECOME NW...
MAINLY AT BFD...BUT ALSO AT JST. OTHERWISE VFR CONDITIONS
SHOULD PREVAIL.
THE REST OF THE WEEK SHOULD BE DRY...WITH MAINLY VFR
CONDITIONS.
OUTLOOK...
WED-SAT...VFR. NO SIG WX.
&&
.HYDROLOGY...
HAVE POSTED A FLASH FLOOD WATCH FOR THE SRN TIER...ESP THE LOWER
SUSQ AND INTO THE POCONOS. REALLY JUICY AIR OF >2 INCH PWATS AND
>70F SFC DEWPOINTS IS SITTING JUST TO THE SOUTH OF THE MASON/DIXON
LINE. BUT THE STRONG ISENTROPIC LIFT OVERHEAD IS TRANSPORTING THE
MOISTURE INTO THE AREA VERY NICELY. A SHIELD OF MODERATE RAIN HAS
DEVELOPED AND THUNDERSTORMS ARE EMBEDDED IN THIS VERY
MOIST/TROPICAL AIR. RECENT RAINFALL ESTIMATES FROM THE DUAL POL
RADAR ALGORITHMS HAS PEGGED THE RAINFALL IN A FEW SPOT CHECKS OF
REAL GAGES V. RADAR. SOME ESTIMATES IN THE SE ARE ALREADY TOPPING
2 INCHES. THIS WILL BE A RELATIVELY LONG PERIOD OF MODERATE TO
HEAVY RAIN FOR THE AREA THIS MORNING AND PERHAPS INTO THE AFTN FOR
THE EASTERN SECTIONS OF THE WATCH. THE WIND SHIFT LATER TODAY WILL
CUT OFF THE BEST MOISTURE ADVECTION AND BRING AN END TO THE HEAVY
RAIN. THERE ARE STILL SCT SHRA POPPING UP NEAR KHLG - SO WHILE THE
BACK EDGE OF THE BIG SHIELD OF RAIN APPEARS TO BE FAIRLY
CLOSE...ADDITIONAL CONVECTIVE DEVELOPMENT IS POSSIBLE.
&&
.CTP WATCHES/WARNINGS/ADVISORIES...
FLASH FLOOD WATCH UNTIL 1 PM EDT THIS AFTERNOON FOR PAZ033>036-
056>059-063>066.
&&
$$
SYNOPSIS...DANGELO/LAMBERT
NEAR TERM...DANGELO
SHORT TERM...DANGELO
LONG TERM...STEINBUGL
AVIATION...MARTIN
HYDROLOGY...DANGELO