NWS Philadelphia/Mount Holly wrote its last area forecast discussion before the first event at Jun 23, 9:34 AM EST, 3 hours 46 minutes earlier.
Area forecast discussion, Jun 23, 9:34 AM EST, 3 hours 46 minutes before
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE MOUNT HOLLY NJ
1034 AM EDT TUE JUN 23 2015
.SYNOPSIS...
A COLD FRONT WILL MOVE THROUGH THE REGION LATE TODAY. WEAK HIGH
PRESSURE WILL BUILD IN BEHIND THE FRONT FOR TONIGHT AND WEDNESDAY.
LOW PRESSURE IN THE MIDWEST ON THURSDAY WILL BE MOVE EAST AND
CROSS THE AREA ON FRIDAY. ADDITIONAL LOW PRESSURE FROM THE OHIO
VALLEY WILL MOVE EASTWARD THROUGH OR SOUTH OF THE AREA OVER THE
WEEKEND.
&&
.NEAR TERM /UNTIL 6 PM THIS EVENING/...
1030AM UPDATE...SEVERE THUNDERSTORM WATCH ISSUED FOR THE NORTHERN
2/3RDS OF THE CWA...#342...IN AFFECT 700PM. AN ADDITIONAL WATCH
IS POSSIBLE FURTHER SOUTH LATER THIS AFTERNOON.
900AM UPDATE...THE WEAKENING MCS IS ENTERING THE POCONOS AT THIS
TIME. LIGHTNING IS ON THE DECREASE AS IS THE SEVER THREAT.
COVERING WITH AN SPS FOR SOME GUSTY WINDS AND BRIEF HEAVY
RAINFALL.
WITH THIS FEATURE HOLDING TOGETHER, MID-MORNING POPS HAVE BEEN
BUMPED UP ACROSS THE SOUTHERN POCONOS AND NORTHWEST NJ. ALSO
TWEAKED THE SKY COVER TO ACCOUNT FOR MORE CLOUDS UP NORTH.
THE HEADLINES FOR THIS AFTERNOON HAVEN'T CHANGED....HEAT AND
THREAT OF SEVERE. THE COASTAL PLAIN, SOUTH OF THE MCS-INDUCED
CLOUDS, IS ALREADY RIPE WITH SBCAPES IN EXCESS OF 2K J/KG AND SB
LI IN THE -4 TO -6 RANGE.
A QUESTION WE HAVE IS, WILL THESE INCOMING CLOUDS (OVERCAST) HAVE
AN AFFECT ON AFTERNOON CONVECTIVE INITIATION? CURRENT THINKING IS
THAT THE MAJORITY MOVES THROUGH. SO THE SEVERE THREAT REMAINS
WITH GREATEST THREAT THIS AFTERNOON...STRAIGHT LINE WINDS.
WITH THE EXPECTATION OF SOME SUN THIS AFTERNOON ACROSS THE NORTH,
MORE SO ACROSS THE SOUTH, WE LEFT TEMPS AS IS. HEAT INDICES LOOK
TO BE IN THE UPPER 90S ACROSS THE I95 CORRIDOR TO AROUND 105
ACROSS THE DELMARVA.
630AM UPDATE...AN MCS ACROSS WESTERN PA CONTINUES TO MAKE FAST
PROGRESS SOUTHEAST. THE HRRR IS NOW SHOWING THIS ARRIVING IN OUR
CWA AS EARLY AS 15Z (BY CURRENT RADAR TRENDS IT WOULD ARRIVE
EARLIER, BUT EXPECT FORWARD SPEED TO SLOW AS DIURNAL MIXING AND
ENHANCED SOUTHWESTERLY FLOW AHEAD OF THE SYSTEM DEVELOP). THIS MCS
IS NOT ON THE FRONT, RATHER CONSIDERABLY AHEAD OF IT, BUT IF IT
CONTINUES ITS PROGRESS AND ARRIVES IN OUR CWA BY MID DAY, THIS
WOULD LIMIT CONVECTIVE INITIATION LATER ALONG THE FRONT. FOR NOW,
HAVE POPS BROAD ENOUGH TO COVER EITHER SCENARIO, BUT WILL CONTINUE
TO WATCH THIS CLOSELY.
PREVIOUS NEAR TERM DISCUSSION...STILL SOME UNCERTAINTY IN THE
TIMING OF THE FRONT (AND THUS THUNDERSTORMS) TODAY. IN FACT THE
00Z RUN OF THE NAM WAS ALMOST 6 HOURS SLOWER THAN THE GFS WHICH
HAS BEEN PRETTY CONSISTENT RUN TO RUN AT CLEARING THE FRONT OFF
THE SHORE BY 00Z. BY SATELLITE IMAGERY, IT LOOKS LIKE THE UPPER
LEVEL SHORT WAVE TROUGH (NOW OVER THE NORTHERN GREAT LAKES REGION)
HAS BEEN RATHER PROGRESSIVE OVER THE LAST SEVERAL HOURS, AND THE
00Z RAOBS INDICATE MODEST HEIGHT FALLS AHEAD OF THE TROUGH, SO SEE
LITTLE REASON TO GO WITH THE SLOWER SOLUTION.
THE FIRST THREAT OF THE DAY WILL BE THE HEAT, PRIMARILY IN THE URBAN
CORRIDOR FROM WILMINGTON TO TRENTON. FOR THE DELMARVA PENINSULA,
CONDITIONS WILL BE CLOSE, BUT HAVE HEAT INDEX VALUES FALLING JUST
SHORT OF CRITERIA AS IT APPEARS THE MODELS MAY BE UNDERESTIMATING
THE MIXING EARLY IN THE DAY.
AS FOR THE SEVERE THREAT, STILL LOOKING AT CONSIDERABLE INSTABILITY
BY MID AFTERNOON (CAPE VALUES ON THE ORDER OF 2000 J/KG). MODEL
SHEAR VALUES HAVE DECREASED SLIGHTLY FROM PREVIOUS RUNS (AROUND 30
KT VS THE 40 KT WE SAW WITH YESTERDAYS MODEL SOUNDINGS), BUT IS
STILL SUFFICIENT TO SUPPORT SUSTAINED UPDRAFTS. SOUTHWESTERLY WINDS
IN THE BOUNDARY LAYER WILL LEAD TO INCREASING LAPSE RATES. THERE
DOES APPEAR THAT A MODEST MID LEVEL CAP WILL BE IN PLACE, AT LEAST
THROUGH EARLY AFTERNOON, IF NOT LATER, BUT STILL EXPECT CONVECTIVE
TEMPERATURE TO BE REACHED. THE VERY HIGH MELTING LAYER WILL LIKELY
SOMEWHAT LIMIT THE LARGE HAIL THREAT, BUT GIVEN HOW HIGH THE
EQUILIBRIUM LEVEL WILL BE, CAN'T RULE OUT SOME HAIL BEING POSSIBLE.
THE MAIN HAZARD THOUGH LOOKS TO BE STRONG WINDS. GIVEN A WIND
PROFILE THAT IS ALMOST UNIDIRECTIONAL A MID LEVEL JET, STRONG WINDS
COULD EASILY MIX DOWN WITH STRONGER STORMS.
AS MENTIONED BY THE PREVIOUS SHIFT, GIVEN THE FAST STORM MOTIONS,
FLASH FLOOD THREAT APPEARS TO BE QUITE LOW AT THIS TIME.
&&
.SHORT TERM /6 PM THIS EVENING THROUGH 6 AM WEDNESDAY/...
GENERALLY WENT BELOW THE MOS POP VALUES OVER NIGHT AS I THINK THE
FRONT WILL BE MOSTLY IF NOT ENTIRELY THROUGH THE REGION BY 00Z.
OTHERWISE, BEHIND THE FRONT, THE MAIN STORY WILL BE DRY AND COLD AIR
ADVECTION. DEPENDING ON HOW QUICKLY THE FRONT WILL SWEEP THROUGH,
COULD SEE WIDESPREAD DEW POINTS IN THE 50S AND LOWER 60S, AND LOWS
GENERALLY IN THE 60S.
&&
.LONG TERM /WEDNESDAY THROUGH MONDAY/...
THE EXTENDD FCST STARTS OFF DRY AND PLEASANT AND THEN HAS QUITE A
BIT OF UNCERTAINTY IN IT AFTER THAT.
HIGH PRES WILL BE OVER THE REGION ON WED AND EXPECT A SUNNY DAY
WITH PLEASANT TEMPS AND NWLY FLOW AFTER THE PASSAGE OF THE CDFNT
LATE TUE.
THIS HIGH WILL GRADUALLY MOVE EWD WED NIGHT BUT STILL EXPECT DRY
WX, BUT WITH INCREASING CLOUDS.
ON THU, AN AREA OF LOW PRES OVER THE MIDWEST WILL MOVE EWD AND BY
LATER THU WILL BRING SOME PRECIP CHCS TO THE AREA. AS IS OFTEN THE
CASE, THE GFS IS A BIT FASTER THAN THE ECMWF. THE NAM IS EVEN A
BIT SLOWER, WITH NOTHING BEFORE 26/00Z. THE GUID IS SUGGESTING
ATTM THAT THE BEST PRECIP CHCS WOULD BE S.
THEN, AFTER THIS LOW MOVES BY, WE SHUD GET AT LEAST A PARTIAL
BREAK ON FRI, ESPECIALLY FOR NRN AREAS.
AFTER FRI, CONFIDENCE DROPS TREMENDOUSLY.
A MAJOR PATN SHIFT IS ALSO IN THE WORKS WHICH ALSO HELPS EXPLAIN
THE DROP IN FCST CONFIDENCE. WE WILL GO FROM ZONAL FLOW WHICH WE
HAVE BEEN IN FOR WEEKS TO A MAJOR RIDGE IN THE W AND ALMOST
UNSEASONABLE TROF IN THE E BY THE WEEKEND.
THE GUID AGREES THAT LOW PRES WILL MOVE FROM THE OHIO VLY EWD.
HOWEVER, THE GFS AND MOST OF THE MDLS ARE FURTHER N WITH THE
PRECIP SHIELD AND KEEP FRI NIGHT THRU ERLY SUN IN DECENT CHCS FOR
SHOWERS. ON THE OTHER HAND, THE ECMWF IS FURTHER S WITH THE LOW
AND WITH THE EXCEPTION OF SRN AREAS, MUCH OF THIS PD WOULD BE DRY.
THE CMC HAS DIFFERENT TIMING. SLOWER TO MOVE THE PRECIP IN ON SAT.
LINGERS IT LONGER ON SUN.... SO FOR NOW, WILL JUST KEEP CHC POPS.
IT STILL SEEMS THAT PRECIP CHCS ARE BETTER SAT THAN SUN AS BOTH
THE GFS AND ECMWF HAVE LOW PRES DEPARTING THE AREA ON SUN.
SMALL PRECIP CHCS REMAIN ON MON, BUT IT CUD END UP BEING DRY.
TEMPS WILL START OUT NR NRML AND END UP MUCH BELOW NRML OVER THE
WEEKEND AS E TO NE ONSHORE FLOW PREVAILS.
&&
.AVIATION /15Z TUESDAY THROUGH SATURDAY/...
THE FOLLOWING DISCUSSION IS FOR KPHL, KPNE, KTTN, KABE, KRDG, KILG,
KMIV, KACY AND SURROUNDING AREAS.
FOR THE 12Z TAFS...MOSTLY VFR CONDITIONS ARE EXPECTED. THE
EXCEPTION WILL BE WITH ANY THUNDERSTORMS THAT DEVELOP WHICH ARE
LIKELY TO AFFECT ALL OF TAF SITES LATER TODAY. THERE ARE TWO
WINDOWS OF POTENTIAL TSRA. FIRST, A MESOSCALE CONVECTIVE COMPLEX
SLIDING OUT OF WESTERN PA, COULD ARRIVE IN OUR AREA BY MID DAY.
SECOND, STORMS COULD DEVELOP ALONG THE COLD FRONT THIS AFTERNOON.
HOWEVER, IT SHOULD BE NOTED THAT TIMING OF THE FRONT IS STILL
UNCERTAIN (ONE MODEL, THE NAM, IS AS MUCH AS 6 HOURS SLOWER THAN
THE REST OF THE MODEL CONSENSUS). HAVE CHOSEN TO GO WITH TIMING
SHOWN FOR THE GFS GUIDANCE, WHICH HAS BEEN THE MOST CONSISTENT RUN
TO RUN. WITH ANY STORMS THAT DEVELOP, COULD SEE BRIEF IFR
CONDITIONS AND VARIABLE AND GUSTY WINDS. FOR NOW WIND GUSTS TO
35KT WERE INCLUDED IN THE TAFS, BUT WIND GUSTS NEAR OR ABOVE 50 KT
WILL BE POSSIBLE WITH THE STRONGEST STORMS.
ONCE THE FRONT ARRIVES, SHOULD SEE CONDITIONS QUICKLY RETURN TO VFR,
AND WILL ALSO SEE A WIND SHIFT TO NORTHWESTERLY.
OUTLOOK...
WED ...VFR. HIGH PRES. W TO NW WIND 10 TO 15 KT IN THE AFTN. HIGH
CONFIDENCE.
THU AND FRI...VFR CONDS ERLY THU THEN LOWERING CIGS BY LATER THU
AND INTO THU NIGHT INTO FRI. MVFR AND IFR PSBL IF NOT LIKELY IN
SHRA AND FG. GRADUALLY LOWERING TO MVFR WITH POSSIBLE IFR CONDS
THURSDAY NIGHT IN SHOWERS/ST/FOG. SLY WIND SHIFT TO NE. LOW
CONFIDENCE.
SAT...E-NE GUSTS 20 KT. A SERIES OF LOW PRES SYS CUD IMPACT THE
REGION OR REMAIN S. CONFIDENCE IS VERY LOW, BUT THERE COULD BE
MVFR/IFR CONDS AND SHRA/FG FOR AT LEAST A PORTION OF SAT.
&&
.MARINE...
SOUTHWESTERLY WINDS NEAR 25KT WILL BUILD BY MID DAY, WITH SEAS
BUILDING NEAR 5 FT IN RESPONSE. THUS SCA CONDITIONS ARE LIKELY FROM
MID DAY INTO LATE AFTERNOON ON THE BAY, AND EARLY EVENING ON THE
ATLANTIC WATERS (WHERE SEAS MAY BE A BIT SLOWER TO DECREASE.
OUTLOOK...
WED THRU FRI...LTST FCST HAS WIND AND SEAS REMAINING BELOW SCA
CRITERIA.
FRI NIGHT THRU SAT...SCA LIKELY. SEAS SHOULD BUILD TO 7 TO 8 FEET
ON E TO NE FETCH. GUSTS AROUND 25 TO 30 KT AND PSBLY HIGHER.
&&
.RIP CURRENTS...
THERE IS A MODERATE RISK FOR RIP CURRENTS ALONG THE NEW JERSEY
COAST AND LOW RISK FOR DELAWARE. IN HOUSE PROCEDURE WAS A MODERATE,
WHILE GRIDDED CALCULATION WAS LOW. GIVEN THE WIND SCENARIO, THE
MORNING MAY START WITH LOW RISKS EVERYWHERE AND THEN INCREASE TO
MODERATE AS THE DAY PROGRESSES.
&&
.CLIMATE...
PHILADELPHIA HEAT WAVE CULMINATES WITH POSSIBLE NEAR RECORD
WARMTH THIS AFTERNOON.
TUESDAY JUNE 23 RECORDS: IN ALL PROBABILITY WILL REMAIN BELOW ALL
VALUES LISTED BELOW, BUT COULD BE ESPECIALLY CLOSE AT KGED AND
POSSIBLY OTHERS.
KACY 98-1988
KILG 100-1894
KPHL 97-1888
KABE 95-1965
KTTN 97-1894
KRDG 96-1908
KMPO 90-1908
KGED 100-1988
&&
.PHI WATCHES/WARNINGS/ADVISORIES...
PA...HEAT ADVISORY UNTIL 6 PM EDT THIS EVENING FOR PAZ070-071-102-
104-106.
NJ...HEAT ADVISORY UNTIL 6 PM EDT THIS EVENING FOR NJZ015-017>019.
DE...HEAT ADVISORY UNTIL 6 PM EDT THIS EVENING FOR DEZ001.
MD...HEAT ADVISORY UNTIL 6 PM EDT THIS EVENING FOR MDZ008.
MARINE...SMALL CRAFT ADVISORY UNTIL 11 PM EDT THIS EVENING FOR
ANZ450>455.
SMALL CRAFT ADVISORY UNTIL 6 PM EDT THIS EVENING FOR ANZ430-
431.
&&
SYNOPSIS...NIERENBERG
NEAR TERM...JOHNSON/KRUZDLO
SHORT TERM...JOHNSON
LONG TERM...NIERENBERG
AVIATION...JOHNSON/NIERENBERG
MARINE...JOHNSON/NIERENBERG
RIP CURRENTS...
CLIMATE...