910
FXUS61 KPHI 100826
AFDPHI
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE MOUNT HOLLY NJ
326 AM EST MON DEC 10 2018
SYNOPSIS
HIGH PRESSURE WILL NOSE INTO THE REGION TODAY AS LOW PRESSURE
OFF THE CAROLINA COAST MOVES FARTHER OFFSHORE. A WEAK SURFACE
LOW WILL MOVE FROM THE GREAT LAKES TONIGHT TO NEW ENGLAND
TUESDAY NIGHT, BRINGING A COLD FRONT THROUGH THE AREA ON
WEDNESDAY. HIGH PRESSURE WILL BUILD INTO THE NORTHEAST ON
THURSDAY. A STRONG SURFACE LOW WILL DEVELOP IN THE SOUTHERN U.S.
LATE THIS WEEK AND MOVE RAPIDLY NORTHEAST NEAR OR THROUGH THE
AREA BY EARLY THIS WEEKEND.
NEAR TERM /THROUGH TONIGHT/
PRECIPITATION IS DIMINISHING AND SHIFTING SOUTH AND EAST OF
DELMARVA EARLY THIS MORNING AS THE STRONG LOW OFF THE CAROLINA
COAST BEGINS ITS PUSH OFFSHORE. NO POPS ARE INCLUDED IN THE
FORECAST FOR THE REST OF THE NIGHT.
AN UPSTREAM PERTURBATION IN THE TENNESSEE VALLEY WILL ALLOW FOR
THE ELONGATION OF THE SURFACE LOW IN THE WESTERN ATLANTIC TODAY,
FOLLOWED BY A SECONDARY SURFACE LOW DEVELOPING NEAR THE CAROLINA
COAST TONIGHT. HOWEVER, LARGE-SCALE LIFT WILL REMAIN SUPPRESSED
TO OUR SOUTH AS THIS PROCESS OCCURS, AS SUBTLE RIDGING
DOWNSTREAM OF A NORTHERN-STREAM SHORTWAVE TROUGH WILL PRECLUDE
SUFFICIENT ASCENT FOR PRECIPITATION IN OUR AREA TODAY AND
TONIGHT.
THIS FLOW EVOLUTION WILL LEAD TO YET ANOTHER COLD/DRY DAY AND
NIGHT ACROSS THE AREA, WITH FORECAST HIGHS/LOWS REMAINING
A FEW (3-8) DEGREES BELOW SEASONAL AVERAGES. MAV MOS HAS
TRENDED A LITTLE COOLER, AND MET MOS HAS TRENDED A LITTLE
WARMER; HOWEVER, BOTH HAVE VERIFIED TOO WARM THE PAST FEW DAYS.
GENERALLY WENT A COUPLE DEGREES BELOW GUIDANCE TODAY, ALTHOUGH
WITH PERHAPS MORE SUN THAN SUNDAY, THIS MAY BE A LITTLE ON THE
PESSIMISTIC SIDE.
WITH CLEAR SKIES AND LIGHT WINDS TONIGHT, EXCELLENT RADIATIONAL
COOLING CONDITIONS WILL EXIST. MAV GUIDANCE LOOKS TOO WARM, SO
WENT MUCH CLOSER TO MET AND IN-HOUSE BIAS-CORRECTED GUIDANCE FOR
OVERNIGHT LOWS.
SHORT TERM /TUESDAY THROUGH WEDNESDAY NIGHT/
THE COLD/DRY PATTERN LOOKS TO CONTINUE THROUGH MIDWEEK, WITH THE
MAIN FEATURE OF INTEREST A MIDLEVEL VORT MAX DIGGING
SOUTHEASTWARD INTO THE NORTHEAST TUESDAY NIGHT. A WEAK SURFACE
LOW AND ATTENDANT COLD FRONT WILL ACCOMPANY THE UPPER-LEVEL
TROUGH, BUT MOISTURE WILL BE SEVERELY LACKING THANKS TO THE
RESIDUAL EFFECTS OF A SURFACE HIGH AFFECTING THE REGION THE PAST
FEW DAYS. OPERATIONAL MODELS ARE DEPICTING SOME LIGHT SNOW
SHOWERS TO OUR NORTHWEST, BUT THERE IS LITTLE INDICATION
SUFFICIENT LIFT WILL OCCUR IN OUR CWA TO GENERATE MEASURABLE
PRECIPITATION. THE MAIN INFLUENCE, THEN, WILL BE INCREASED
CLOUDS IN THE NORTHERN CWA TUESDAY NIGHT AND WEDNESDAY MORNING
(WITH A CAVEAT HERE THAT THE FORECAST MAY NOT BE PESSIMISTIC
ENOUGH IN THIS REGARD; MODELS TEND TO UNDERFORECAST SKY COVER
WITH THESE SYSTEMS).
AS MENTIONED A COUPLE DAYS AGO, THERE IS A SURFACE TROUGH THAT
DEVELOPS UPSTREAM FROM THE SECONDARY LOW THAT DEVELOPS OFF THE
CAROLINA COAST MONDAY NIGHT. AS IT MOVES OFFSHORE TUESDAY AND
TUESDAY NIGHT, THIS TROUGH LIFTS NORTHWARD TOWARD THE SOUTHERN
NEW ENGLAND COAST. HOWEVER, INTERACTION WITH THE UPSTREAM VORT
MAX LOOKS LIMITED AT BEST, AND MODELS DO NOT INDICATE SUFFICIENT
LIFT WILL BE PRESENT TO GENERATE PRECIPITATION FAR NORTHWEST OF
THE OFFSHORE LOW. THE 00Z ECMWF SEEMS MOST AGGRESSIVE WITH THIS,
BUT KEEPS PRECIP WELL OFFSHORE. AS SUCH, NO POPS ARE IN THE
FORECAST THROUGH THE PERIOD.
TEMPERATURES WILL REMAIN ON THE CHILLY SIDE THROUGH THE PERIOD,
AND WITH (ALBEIT WEAK) COLD ADVECTION UPSTREAM OF A COLD FRONT
PASSING THROUGH THE AREA ON WEDNESDAY, IT MAY END UP BEING A
LITTLE BIT COOLER THAN ON TUESDAY.
LONG TERM /THURSDAY THROUGH SUNDAY/
THE MEDIUM-RANGE PERIOD LOOKS ACTIVE, WITH A STRONG SYSTEM
AFFECTING THE REGION FRIDAY AND SATURDAY AND A PREDECESSOR VORT
MAX POSSIBLY AFFECTING THE AREA ON THURSDAY.
THE 00Z OPERATIONAL MODELS ARE IN VERY POOR AGREEMENT WITH A
VORT MAX MOVING INTO THE NORTHEAST ON THURSDAY. THE GFS IS WELL
TO THE NORTHWEST OF THE CMC AND ECMWF, WITH THE ECMWF FARTHEST
SOUTH AND SPEEDIEST WITH THE PERTURBATION. THIS DISAGREEMENT
APPEARS TO BE TIED TO THE UPSTREAM/DIGGING SOUTHERN-STREAM VORT
MAX REACHING THE SOUTHERN PLAINS BY THURSDAY EVENING, WITH THE
ECMWF CONSIDERABLY SLOWER/FARTHER WEST THAN THE NORTHEAST-
DISPLACED GFS/CMC. NOTABLY, THE GFS HAS TRENDED MUCH FASTER WITH
THE PERTURBATION AFFECTING THE AREA ON THURSDAY, WHICH APPEARS
TIED TO A SOMEWHAT FASTER PROGRESSION OF THE VORT MAX MOVING
THROUGH THE NORTHEAST TUESDAY NIGHT/WEDNESDAY. THE GFS LIFTS THE
THURSDAY VORT MAX NORTHEAST AS A RESULT OF SOME PHASING WITH A
CANADA TROUGH. IN SHORT, THERE ARE SOME COMPLEX INTERACTIONS AND
SENSITIVITIES HERE THAT SUGGEST A LOW-PREDICTABILITY PERIOD OF
THE FORECAST. A BLENDED APPROACH APPEARS REASONABLE, AS THE
OUTLIER POSITIONING OF THE GFS/ECMWF WITH THE THURSDAY VORT MAX
AND THE SOUTHERN PLAINS SYSTEM AT THESE TIMES SUGGESTS NEITHER
SOLUTION IS PROBABLE.
WITH THE 00Z ECMWF INDICATING A MORE SOUTHERN TRACK WITH THE
THURSDAY SYSTEM (I.E., ONE WITH MORE DIRECT IMPACTS ON THE CWA),
I WAS INCLINED TO INTRODUCE SOME SLIGHT-CHANCE POPS DURING THE
DAY FOR THE AREA. TEMPERATURES WOULD LIKELY BE COLD ENOUGH FOR
SOME SNOW SHOWERS, ESPECIALLY IN THE MORNING. QPF/SNOW AMOUNTS
WOULD BE QUITE LIGHT WITH SUCH A SYSTEM (IF ANY IMPACTS OCCUR
IN OUR AREA AT ALL, AND THAT IS A BIG IF), BUT THIS DEFINITELY
NEEDS TO BE MONITORED GIVEN THE LARGE UNCERTAINTY IN THE TRACK
OF THE VORT MAX AND THE POTENTIAL FOR THERMAL PROFILES COLD
ENOUGH FOR SNOW. I ALSO LOWERED TEMPERATURES ON THURSDAY GIVEN
THE POTENTIAL FOR AT LEAST SOME INFLUENCE FROM THIS VORT MAX.
ALL OF THIS IS A PRECURSOR TO THE MAIN EVENT IN THE MEDIUM
RANGE. THE AFOREMENTIONED SOUTHERN-STREAM VORT MAX MAKES THE
MOVE INTO THE SOUTHEAST BY FRIDAY NIGHT, WITH AN UPPER-LEVEL
TROUGH ACQUIRING A SLIGHT NEGATIVE TILT UPSTREAM OF A STRONG
250-MB JET STREAK IN NEW ENGLAND. A SURFACE LOW SHOULD READILY
DEVELOP IN THIS REGIME, BUT WHERE IT DEVELOPS/TRACKS IS A BIG
QUESTION MARK. INCREASINGLY, SO IS THE LOW'S INTENSITY. THE
ECMWF HAS SHOWN LARGE VARIABILITY RUN-TO-RUN, WITH THE NEW 00Z
SIMULATION CONSIDERABLY SLOWER AND SOMEWHAT FARTHER SOUTH THAN
PRIOR RUNS. THE FARTHER SOUTH TRACK IS PLAUSIBLE GIVEN THIS PAST
WEEKEND'S SOUTHERN-TRACK SYSTEM, BUT THE SLOWER TREND LOOKS
SUSPICIOUS GIVEN THE PROGRESSIVE NATURE OF THE MID- AND UPPER-
LEVEL FLOW OF LATE. THE 00Z GFS LOOKS RATHER DISORGANIZED WITH
THE SURFACE PHENOMENA OVERALL, WHICH SEEMS UNLIKELY GIVEN THE
FAVORABLE UPPER-LEVEL PATTERN FOR STRONG CYCLOGENESIS. THE CMC
IS WAY (WAY) FARTHER NORTH/WEST WITH THE SURFACE LOW TRACK (BY
HUNDREDS OF MILES) AND APPEARS MOSTLY TO BE AN OUTLIER BY THIS
POINT IN THE FORECAST.
PRECIPITATION LOOKS LIKELY IN OUR AREA LATE FRIDAY THROUGH EARLY
SATURDAY NO MATTER WHAT THE SOLUTION (AND NONE OF THOSE
DESCRIBED ABOVE WILL LIKELY END UP CORRECT), AND TEMPERATURES
LOOK WARM ENOUGH FOR THIS TO BE A MOSTLY-RAIN EVENT.
NEVERTHELESS, FINE-TUNING THE DETAILS IS A FRUITLESS ENDEAVOR AT
THIS POINT OWING TO THE LARGE VARIABILITY IN MODEL OUTPUT. THE
MAIN QUESTION MARKS SENSIBLE-WEATHER-WISE WILL BE (1) HOW SOON
PRECIPITATION REACHES THE AREA, WITH A FASTER ARRIVAL IMPLYING
SOME PRECIPITATION TYPE CONCERNS EARLY ON (I.E., THURSDAY NIGHT/FRIDAY
MORNING), (2) HOW CLOSE THE SYSTEM WILL BE TO THE AREA, WITH A
CLOSER TRACK LIKELY GENERATING STRONGER WINDS AND HIGHER QPF,
AND (3) HOW SLOW THE SYSTEM WILL BE, WITH RESULTANT IMPACTS ON
POTENTIAL FOR HEAVY RAIN AND FLOODING AND A FINAL TURNOVER TO
SNOW IN THE NORTH/WEST SATURDAY NIGHT.
TEMPERATURES WILL BE WARM FRIDAY AND SATURDAY AS MIDLEVEL
RIDGING DOWNSTREAM OF THE SOUTHERN-STREAM SYSTEM SHOULD LEAD TO
SUBSTANTIAL WARM/MOIST ADVECTION DURING THIS PERIOD.
CONDITIONS SHOULD DRY OUT AS NORTHWEST FLOW COMMENCES ON SUNDAY,
BUT THIS MAY LEAD TO A FEW WEAK CLIPPER-TYPE SYSTEMS EARLY NEXT
WEEK.
AVIATION /08Z MONDAY THROUGH FRIDAY/
THE FOLLOWING DISCUSSION IS FOR KPHL, KPNE, KTTN, KABE, KRDG, KILG,
KMIV, KACY AND SURROUNDING AREAS.
TODAY...MAINLY VFR, THOUGH THERE IS A SLIGHT CHANCE FOR A BRIEF
PERIOD OF MVFR AT RDG/ABE THIS MORNING. AFTER LIGHT/VARIABLE
WINDS EARLY THIS MORNING, NORTHERLY FLOW AROUND 10 KTS SHOULD
DEVELOP BY LATE MORNING INTO THE AFTERNOON. MODERATE CONFIDENCE.
TONIGHT...VFR WITH LIGHT NORTH OR NORTHEAST WINDS. HIGH
CONFIDENCE.
OUTLOOK...
TUESDAY THROUGH WEDNESDAY: MAINLY VFR WITH LIGHT WEST WINDS
TUESDAY AND TUESDAY NIGHT, BECOMING NORTHWEST AND INCREASING TO
7 TO 15 KTS ON WEDNESDAY (WITH HIGHER GUSTS POSSIBLE). MODERATE
CONFIDENCE.
WEDNESDAY NIGHT AND THURSDAY: LOW-CONFIDENCE FORECAST AS A WEAK
SYSTEM MAY AFFECT THE REGION DURING THIS PERIOD (ESPECIALLY
THURSDAY). BEST CHANCES ARE FOR VFR, BUT CANNOT RULE OUT A
PERIOD OF SUB-VFR IF THE SYSTEM MORE DIRECTLY IMPACTS THE AREA.
WINDS BECOMING EAST GENERALLY NEAR OR BELOW 10 KTS.
THURSDAY NIGHT AND FRIDAY: DETERIORATING CONDITIONS EXPECTED
THROUGH THE PERIOD, WITH SUB-VFR CONDITIONS LIKELY BY FRIDAY
AFTERNOON. INCREASING CHANCES OF RAIN. SOUTHEAST WINDS
INCREASING TO 7 TO 15 KTS ON FRIDAY, WITH HIGHER GUSTS POSSIBLE,
ESPECIALLY NEAR THE COAST. MODERATE CONFIDENCE.
MARINE
WINDS HAVE BEEN SLOW TO REACH ADVISORY LEVELS ACROSS THE
ATLANTIC WATERS OF SOUTHERN NEW JERSEY AND DELAWARE AND ON LOWER
PORTIONS OF DELAWARE BAY OVERNIGHT. GUSTS OF 20-25 KTS HAVE
BEEN OBSERVED AT DEWEY BEACH AND LEWES, BUT THE TREND HAS BEEN
RATHER STAGNANT RECENTLY. HOWEVER, SEAS HAVE REACHED 5-6 FEET AT
BUOY 44009 AND SHOULD STAY THERE THROUGH THE DAY. WINDS,
THOUGH, WILL LIKELY REMAIN SUB-ADVISORY LEVEL AFTER DAYBREAK.
FOR NOW, KEPT THE ADVISORY AS IS, WITH LOWER DELAWARE BAY SET TO
EXPIRE AT 6 AM. I DID NOT EXTEND OR CONTRACT THE ADVISORY FOR
THE ATLANTIC WATERS, AS CONFIDENCE IS TOO LOW REGARDING WAVE
HEIGHTS THIS AFTERNOON TO MAKE ANY CHANGES.
SUB-ADVISORY WINDS/SEAS ARE EXPECTED ON UPPER PORTIONS OF
DELAWARE BAY AND OFF THE NORTHERN/CENTRAL NJ COAST THROUGH THE
PERIOD.
OUTLOOK...
TUESDAY: SUB-ADVISORY WINDS/SEAS AND FAIR WEATHER EXPECTED.
TUESDAY NIGHT: A BRIEF PERIOD OF ADVISORY-LEVEL WINDS IS
POSSIBLE AS A COLD FRONT APPROACHES AND NORTHWEST FLOW BECOMES
ESTABLISHED.
WEDNESDAY THROUGH THURSDAY NIGHT: SUB-ADVISORY WINDS/SEAS
EXPECTED.
FRIDAY: SOUTHEAST WINDS WILL INCREASE THROUGH THE DAY AND MAY
APPROACH ADVISORY LEVELS LATE. INCREASING CHANCES FOR RAIN.
PHI WATCHES/WARNINGS/ADVISORIES
PA...NONE.
NJ...NONE.
DE...NONE.
MD...NONE.
MARINE...SMALL CRAFT ADVISORY UNTIL 6 AM EST EARLY THIS MORNING FOR
ANZ431.
SMALL CRAFT ADVISORY UNTIL 6 PM EST THIS EVENING FOR
ANZ453>455.
SYNOPSIS...CMS
NEAR TERM...CMS
SHORT TERM...CMS
LONG TERM...CMS
AVIATION...CMS
MARINE...CMS
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