290
FXUS61 KPHI 120806
AFDPHI
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE MOUNT HOLLY NJ
306 AM EST FRI MAR 12 2010
.SYNOPSIS...
AN AREA OF LOW PRESSURE NEAR THE MID MISSISSIPPI VALLEY WILL MEANDER
AROUND THROUGH TONIGHT BEFORE GRADUALLY MOVING EAST. MEANWHILE, A
SECONDARY LOW PRESSURE SYSTEM IS DEVELOPING OVER THE SOUTH
CAROLINA COASTAL WATERS. THIS LOW PRESSURE SYSTEM WILL MOVE SLOWLY
NORTH AND REACH THE DELMARVA PENINSULA LATE ON SATURDAY BEFORE
HEADING OFFSHORE SUNDAY AND MONDAY. A WEAK COLD FRONT SHOULD SLIDE
THROUGH THE REGION LATE TUESDAY BEFORE A HIGH PRESSURE SYSTEM
STARTS BUILDING TOWARD THE EAST COAST ON WEDNESDAY AND THURSDAY.
&&
.NEAR TERM /UNTIL 6 PM THIS EVENING/...
HE WRF-NMM INITIALIZATION WAS SHARPER THAN THE GFS WITH THE 00Z
SOUNDINGS AND ITS OVERALL FORECAST EVOLUTION IS CLOSER TO THE ECMWF
AND UKMET AS WELL AS MODEL CONSENSUS/CONSISTENCY. THE GFS HAS BEEN
STRUGGLING WITH THIS SYSTEM SINCE DAY 1 AND ITS A RED FLAG WHEN ITS
ENSEMBLE MEAN SOLUTION IS FARTHER NORTH THAN THE OPERATIONAL RUN.
ALSO NO OTHER MODEL ADVECTS COLD AIR INTO THE NWRN PART OF OUR CWA
AS FAST, IF AT ALL, AS THE GFS DOES. NO CHANGES TO THE FLOOD WATCH
AND WE HAVE ISSUED A WIND ADVISORY FOR THE COASTAL AREAS FOR LATER
TONIGHT INTO SATURDAY.
TO ADD FTHR CONFIDENCE TO THIS WRF-NMM 00Z SOLUTION, THROUGH 06Z
THE MODEL WAS FORECASTING THE QPF EXTENT AND AMOUNTS BETTER THAN
THE GFS, CAN RGEM AND ECMWF. THERE ARE NOT TOO MANY MODEL
DIFFERENCES OVERALL FOR TODAY. THE FORECAST MODELS HAVE INCREASED
THIS FIRST SHOT OF PRECIPITATION OVER PREVIOUS MODEL RUNS.
ALTHOUGH THE FORECAST ISENTROPIC LIFT AND MID LEVEL WARM AIR
ADVECTION IS NOT THAT STRONG AND IS EXPECTED TO WEAKEN AS THIS
IMPULSE MOVES NORTH THROUGH OUR CWA TODAY. THE AROUND AN INCH PCPN
THE MODELS ARE FORECASTING FOR TODAY IN THE SOUTHERN HALF OF OUR
CWA CAN BE HANDLED WITHOUT ANY RUNOFF ISSUES OTHER THAN THE USUAL POOR
DRAINAGE AREAS THAT HAVE PROBLEMS ANYTIME THERE IS MODERATE OR
GREATER RAIN INTENSITY. THE PROBLEM IS THAT IT PRIMES THE REGION
FOR THE MORE SIGNIFICANT SHOT OF PRECIPITATION EXPECTED LATER
TONIGHT INTO SATURDAY EVENING.
THE OTHER SENSIBLE WEATHER WE WANT TO CONTINUE TO MENTION FOR TODAY
IS PATCHY/AREAS OF FOG OVER THE HIGHER TERRAIN LOCATIONS AS WELL
AS OVER DELMARVA. THERE IS SOME LOCALLY DENSE FOG, BUT NOT
WIDESPREAD ENOUGH TO ISSUE ADVISORIES. THERE IS MUCH MORE OF A
MARINE FEEL TO THE AIR TONIGHT THAN THERE WAS YESTERDAY AND LOWER
MOS GUIDANCE HAS BEEN ACCEPTED FOR THIS REASON.
&&
.SHORT TERM /6 PM THIS EVENING THROUGH SUNDAY/...
AN ACTIVE PERIOD IS EXPECTED DURING THE BULK OF THIS TIME FRAME AS A
HEAVY RAIN EVENT LOOKS LIKELY TO MOVE THROUGH. WE ARE OFF TO AN
OMINOUS START AS THERE IS NOT MUCH UPRIGHT CONVECTION OVER THE
DEVELOPING LOW OVER THE CAROLINA COASTAL WATERS. SOMETIMES THE
CONVECTION CAN STALL THE NORTHWARD PROGRESS OF HEAVIER PRECIPITATION,
BUT NOT THE CASE THIS TIME. THE HEAVIEST RAIN LOOKS TO FALL DURING
THE CALENDAR DAY ON SATURDAY. WE CONTINUE TO SEE THE FLOOD
POTENTIAL THIS WEEKEND, THEREFORE THE FLOOD WATCH WILL BE
CONTINUED.
AN ABUNDANCE OF MOISTURE WILL BE DRAWN NORTHWARD INTO OUR AREA FROM
THE EXPANSIVE CIRCULATION ASSOCIATED WITH THE MIDWESTERN CLOSED
LOW SYSTEM. WE ARE ALREADY SEEING PWAT VALUES EXCEEDING 200
PERCENT OF NORMAL STACKED FROM THE GREAT LAKES SOUTH THROUGH
FLORIDA.
THIS MOISTURE ADVECTION WILL BE ENHANCED BY A STRONG EAST TO
SOUTHEASTERLY LOW-LEVEL JET THAT WILL REACH FORECAST VALUES OF 70 TO
80 KNOTS ACROSS THE REGION ON SATURDAY. AS FOR FORCING, THAT RATHER
ROBUST LOW TO MID LEVEL WIND FIELD WITHIN A WAA/MOISTURE ADVECTION
REGIME WILL ALLOW FOR STRONG VERTICAL VELOCITIES TO OVERSPREAD THE
ENTIRE AREA LATER FRIDAY NIGHT AND ESPECIALLY SATURDAY. THIS WILL
WORK IN CONJUNCTION WITH THE SURFACE LOW DEVELOPING OFF THE SOUTH
CAROLINA COAST. AS HEIGHTS FALL AND THERE IS SOME DIFFLUENCE
ALOFT, THE VERTICAL VELOCITIES WILL RESPOND BY INCREASING. IN
ADDITION, A BELT OF STRONG FRONTOGENETIC FORCING IS FORECAST TO
MOVE AND INTENSIFY FROM SOUTH TO NORTH ACROSS OUR CWA DURING
SATURDAY AS STRONG PVA ARRIVES IN CONJUNCTION WITH THE STRONGEST
WIND FIELD, WAA, MID LEVEL TROWAL AND MID LEVEL QVEC CONVERGENCE.
THIS ALL POINTS TO MODERATE TO HEAVY RAIN MARCHING ACROSS THE CWA.
THE FRONTOGENESIS FROM 850 MB TO 700 MB SUGGESTS THAT THERE MAY BE
BANDS OF HEAVIER RAIN ELEMENTS WITHIN A LARGER RAIN SHIELD. THIS
IS WHERE THE HIGHEST RAINFALL RATES WILL OCCUR.
THE STRENGTHENING WIND FIELD WILL ALLOW FOR BREEZY TO WINDY
CONDITIONS TO DEVELOP LATER FRIDAY NIGHT AND SATURDAY. THIS IS NOT
THE MOST CONFIDENT OF ADVISORIES AS THERE WILL OBVIOUSLY BE A
STRONGER PRECIPITATION AND MARINE INVERSION THAN WE HAD WITH OUR
WIND ADVISORY/HIGH WIND EVENT ON JANUARY 25TH. ON THE OTHER HAND,
THERE WILL BE A SURFACE HIGH PRESSURE SYSTEM OVER NORTHEASTERN NEW
ENGLAND AND THE CANADIAN MARITIMES TO ENHANCE THE SURFACE PRESSURE
GRADIENT. THIS INGREDIENT WAS MISSING DURING OUR LAST TWO WINTER
STORMS WHEN THE GUIDANCE FORECAST WIND SPEEDS WERE OVERDONE. SO AS
A FIRST START WE WILL ISSUE A WIND ADVISORY FOR THE COASTAL STRIP
AND A FEW OTHER COUNTIES THAT HAVE NORTHEASTERN TO EASTERN
EXPOSURE ON THE BAYS. THE LLJ IS FORECAST TO INTENSIFY AS IT MOVES
NORTH, SO BEST CHANCES FOR THE STRONGEST WINDS WOULD BE IN OUR
NERN NJ CWA. THIS FCST 70 TO 80 KT LLJ WILL MOVE THROUGH OUR
ENTIRE CWA, BUT CONFIDENCE ABOUT PART OF THE WINDS MIXING DOWN
SUFFICIENTLY TO BREAK THROUGH THE INVERSION AND REACH ADVISORY
CRITERIA OVER HIGHER TERRAIN LOCATIONS IS NOT HIGH ENOUGH ATTM TO
ISSUE ONE.
AS FAR AS THUNDER GOES, THERE IS LESS FORECAST UPRIGHT
INSTABILITY THAN THERE WAS WITH LAST NIGHT'S MODEL RUNS. ONCE
AGAIN OUR DELMARVA COUNTIES COULD BE CLOSE SATURDAY. GIVEN THE
LOWER PROBABILITY/CONFIDENCE OF THUNDER ATTM, WE DECIDED TO NOT
INCLUDE IT FOR NOW. AS THE LARGE CLOSED LOW MOVES ACROSS OUR AREA
DURING THE WEEKEND, THE STRONGEST LIFT AND WIND FIELD IS PUSHED TO
THE NORTH. THIS WILL TAKE THE PLUME OF STRONG MOISTURE
ADVECTION/LIFT AND SHOVE IT NORTHWARD. HOWEVER, THERE MAY BE SOME
COMMA HEAD RAIN WRAPPING BACK AROUND OUR CWA SATURDAY NIGHT AND
EVEN THROUGH SUNDAY. OVERALL, THE TREND OF LIGHTER RAINFALL IS
ANTICIPATED THE SECOND HALF OF SATURDAY NIGHT AND ESPECIALLY
SUNDAY AS THE RAIN TRANSITIONS TO SHOWERS. THE GFS IS THE ONLY
MODEL THAT MAKES IT COLD ENOUGH FOR SOME SNOW SATURDAY NIGHT IN
OUR NWRN ZONES, MAINLY BECAUSE IT IS FASTER AND FARTHER SOUTH WITH
THE UPPER AND SURFACE LOWS. ATTM THIS IS AT ODDS WITH ALL OF THE
OTHER MODELS AND ITS OWN ENSEMBLE MEAN TEMPERATURES THAT ARE
WARMER, SO NO MENTION FOR NOW.
AS FOR TEMPERATURES, THERE COULD BE CHALLENGES WITH THIS GIVEN THE
STRONG WAA THAT WILL BE AIMED INTO OUR AREA FOR ESPECIALLY SATURDAY.
MEANWHILE, A SURFACE HIGH UP ACROSS NORTHERN NEW ENGLAND WILL TRY
AND PUSH SOME COOLER AIR INTO OUR REGION. THE MOS GUIDANCE HAS
TRENDED AND REMAINED COOLER ACROSS A GOOD PART OF OUR CWA. DID NOT
WANT TO GO FULLY TOWARD THIS ESPECIALLY ACROSS SOUTHERN AREAS. AS
A RESULT, WE GENERALLY TOOK A BLEND OF THE GFS/NAM MOS/CURRENT
TEMP FORECASTS AS A COMPROMISE FOR THE SOUTHERN AREAS. WE DID
GO WITH A COOLER SOLUTION NORTHERN HALF.
&&
.LONG TERM /SUNDAY NIGHT THROUGH THURSDAY/...
HPC HAS GONE WITH A FORECAST THAT DEPENDS HEAVILY ON THE ECMWF EARLY
AND THAT INCORPORATES THE ECMWF ENSEMBLES LATE. THIS HAS THE
STACKING LOW PRESSURE SYSTEM THAT LIKELY WILL CAUSE US SOME PROBLEMS
THROUGH THE SHORT TERM SLOWLY EXITING OUR AREA IN THE SUNDAY NIGHT
TO MONDAY TIME FRAME. THE PRECIPITATION TYPE IN THE NORTHWEST AS
THIS SYSTEM EXITS STILL DOES NOT LOOK AS IF IT WILL BE A SIGNIFICANT
ISSUE.
AFTER THAT, IT APPEARS THAT WE WILL HAVE WEAK HIGH PRESSURE AT THE
SURFACE PUNCTUATED BY SOME DRY TROUGHS OR COLD FRONTS THANKS TO AN
EASTERN CANADIAN VORTEX AT MID LEVELS. IF THIS COMES TO PASS /AND
MODEL CONSENSUS IS FAIRLY GOOD/, WE EVENTUALLY WILL SEE SOME WELCOME
DRYING WITH TOLERABLE WINDS. TEMPERATURES THROUGH THE PERIOD ARE
FORECAST TO REMAIN ABOVE NORMAL, ALTHOUGH NOT QUITE AS MILD AS THEY
HAVE BEEN RECENTLY.
&&
.AVIATION /08Z FRIDAY THROUGH TUESDAY/...
THE FOLLOWING DISCUSSION IS FOR KPHL, KPNE, KTTN, KABE, KRDG, KILG,
KMIV, KACY AND SURROUNDING AREAS.
WIDESPREAD IFR CONDITIONS HAVE ALREADY ARRIVED ACROSS THE AREA AHEAD
OF THE FIRST BATCH OF RAIN. THE RAINS WILL MOVE SW TO NE ACROSS THE
TAF SITES EARLY THIS MORNING. I AM NOT EXPECTING MUCH IMPROVEMENT IN
CIGS OR VSBYS TODAY AS THE E TO NE FLOW WILL CONTINUE. MODELS ARE
NOT REALLY SHOWING ANY SIGNAL ABOUT WHEN THE RAINS WILL END (UNTIL
SUNDAY NGT)...SO I WILL JUST CARRY RAIN ALL DAY. THE RAINS WILL
LIKELY PICK UP IN INTENSITY THIS AFTERNOON. WIND SPEEDS WILL
INCREASE LATER TODAY AND REMAIN UP OVERNIGHT FRI. LLWS MAY BECOME
AND ISSUE.
OUTLOOK...
WIDESPREAD IFR CONDITIONS UNTIL SUNDAY NIGHT WITH RAIN, LOW CLOUDS
AND FOG. VFR CONDITIONS BACK HOPEFULLY IN TIME FOR THE MON MORNING
RUSH.
&&
.MARINE...
LOW PRESSURE APPROACHING FROM THE SOUTH WILL MOVE ACROSS THE WATERS
LATE SAT NIGHT AND SUN MORNING. THERE WILL BE AN INCREASING GRADIENT
TODAY THROUGH SATURDAY WITH GALES LOOKING MORE LIKELY. WE WILL
PROBABLY SEE THE GALE GUSTS WITHIN 24 HRS OF THE 4AM CWF
ISSUANCE...SO TO SIMPLIFY...A GALE WARNING WILL BE ISSUED NOW AND IT
WILL CONTINUE THROUGH SAT NIGHT. SEAS INCREASE TO SCA CRITERIA THIS
AFTERNOON...THEN 7 TO 10 FT TONIGHT AND 10 TO 12 FT SAT.
&&
.HYDROLOGY...
PREDICTED RAINFALL, TODAY THROUGH EARLY SUNDAY, REMAINS PRETTY
MUCH THE SAME. A WIDESPREAD 2 TO 4 INCHES LOOKS LIKELY ACROSS THE
HSA. HIGHER AMOUNTS REMAIN POSSIBLE. A FLOOD WATCH HAS BEEN ISSUED.
WITH THESE NUMBERS, BOTH SMALLER STREAMS AND LARGER RIVERS WILL
EXPERIENCE FLOODING THIS WEEKEND INTO EARLY NEXT WEEK. STREAMFLOW IS
ALREADY RUNNING HIGH ACROSS SE PA, SO THEY DON'T NEED THE
SNOWMELT TO FLOOD. ON THE OTHER HAND, RIVERS LIKE THE DELAWARE
WILL NEED THE SNOWMELT TO FLOOD, AND IN THIS CASE, IT APPEARS A
PORTION OF THE HEAVY RAIN WILL FALL ACROSS THE HEADWATER SNOWPACK,
WHICH IS THREE TIMES NORMAL FOR THIS TIME OF YEAR.
SO IN VERY GENERAL TERMS, 1 TO 2 INCHES OF WIDESPREAD RAINFALL WILL
CAUSE MINOR FLOODING ACROSS THE SMALLER STREAMS, CREEKS AND RIVERS
ACROSS THE PASSAIC, RARITAN, AND DELAWARE BASINS, WITH LITTLE OR NO
FLOODING ALONG THE MAINSTEM RIVERS /LEHIGH, SCHUYLKILL, DELAWARE/.
2.0 TO 3.5 INCHES WOULD CAUSE MODERATE FLOODING ALONG THESE SAME
SMALLER CREEKS AND STREAMS, WITH SOME MINOR FLOODING POSSIBLE ALONG
THE MAINSTEM RIVERS, ESPECIALLY THE SCHUYLKILL.
3.5 TO 5.0 INCHES OF RAINFALL, BOTH LOCALLY AND OVER THE EXISTING
SNOWPACK IN THE NORTH, WOULD CAUSE WIDESPREAD MODERATE FLOODING,
WITH MINOR FLOODING ALONG THE MAINSTEM DELAWARE. A SMATTERING OF
MAJOR FLOODING CANNOT BE RULED OUT EITHER.
THE LEHIGH VALLEY HAS BEEN A BIT DRIER OVER THE LAST 30, 60, AND
90 DAYS, AND FOR THIS REASON CAN TOLERATE A LITTLE MORE WATER THAN
ADJACENT BASINS.
&&
.TIDES/COASTAL FLOODING...
THE LATEST ECS GUIDANCE IS SHOWING 3.0 TO 4.0 DEPARTURES ACROSS THE
COAST SAT-SUN. THE GFS MODEL (THE BASIS FOR THIS GUIDANCE) IS NOT
THE PREFERRED CHOICE (NOW) WITH THE UPCOMING SYSTEM. A LOCAL SCHEME
SHOWS DEPARTURES JUST UNDER 2.0 FT AT LEWES, DE ON SAT MORNING.
THIS WOULD PUT THE COASTAL AREAS IN THE LOW END OF MINOR TIDAL
FLOODING SAT-SUN. THERE APPEARS TO BE SOME TIME STILL, SINCE THE
PEAK DEPARTURES WILL BE LATER SAT (PERHAPS DURING THE LOW TIDE). WE
WILL BRIEF THE AM SHIFT REGARDING THE TIDAL ISSUES IN CASE ANY FLAGS
ARE NEEDED LATER. THE WORDING IN HWO WILL BE REFRESHED TOO.
&&
.PHI WATCHES/WARNINGS/ADVISORIES...
PA...FLOOD WATCH FROM THIS EVENING THROUGH SUNDAY MORNING FOR
PAZ054-055-060>062-067>071.
NJ...FLOOD WATCH FROM THIS EVENING THROUGH SUNDAY MORNING FOR
NJZ001-007>010-012>027.
WIND ADVISORY FROM 1 AM TO 1 PM EST SATURDAY FOR NJZ021>025.
WIND ADVISORY FROM 1 AM TO 7 PM EST SATURDAY FOR NJZ012>014-
020-026-027.
DE...FLOOD WATCH FROM THIS EVENING THROUGH SUNDAY MORNING FOR
DEZ001>004.
WIND ADVISORY FROM 1 AM TO 1 PM EST SATURDAY FOR DEZ002>004.
MD...FLOOD WATCH FROM THIS EVENING THROUGH SUNDAY MORNING FOR
MDZ008-012-015-019-020.
MARINE...GALE WARNING FROM NOON EST TODAY TO 6 AM EDT SUNDAY FOR ANZ430-
431-450>455.
&&
$$
SYNOPSIS...GIGI
NEAR TERM...GIGI
SHORT TERM...GIGI/GORSE
LONG TERM...DELISI
AVIATION...O'HARA
MARINE...O'HARA
HYDROLOGY...KRUZDLO
TIDES/COASTAL FLOODING...O'HARA
