Mt. Holly Updated AFD discounts the EURO solution late week:
SO WHAT COULD HAPPEN THAT ULTIMATELY INFLUENCES SENSIBLE WEATHER
IN THE NORTHERN MID-ATLANTIC THIS WEEK? WELL, IT SEEMS LIKELY
THAT COLD FRONTAL PASSAGE WITH THE FIRST EJECTING SHORTWAVE
TROUGH SUNDAY NIGHT THROUGH MONDAY NIGHT WILL PROVIDE A PERIOD
OF RAIN (AND PROBABLY SOME SNOW IN THE POCONOS AND NORTHWEST NEW
JERSEY ON SUNDAY NIGHT). FAIRLY STRONG WARM ADVECTION IN ADVANCE
OF THE EJECTING TROUGH SHOULD TREND SURFACE TEMPERATURES UPWARD
LATE SUNDAY NIGHT ONWARD, SO EXPECTING SNOW AMOUNTS TO BE FAIRLY
TAME, EVEN IN THE FAR NORTHWEST CWA. PRECIPITATION SHOULD BE
VIRTUALLY ALL RAIN BY MONDAY MORNING AS THE FRONT CONTINUES ITS
SLOW TREK THROUGH THE AREA. BY MONDAY EVENING, THE GREATEST
POPS ARE SOUTHEAST OF THE I-95 CORRIDOR. MAY SEE AN INCREASE IN
QPF DURING THIS TIME FRAME, AS A WAVE OF LOW PRESSURE MAY
DEVELOP ALONG THE FRONT, AIDED BY ANOTHER WEAK PERTURBATION IN
THE SOUTHWEST MIDLEVEL FLOW. THOUGH CHANCES ARE LOWER,
PRECIPITATION MAY NOCTURNALLY MIX WITH SNOW IN THE FAR NORTHWEST
ONCE AGAIN.
AS THE SECONDARY PERTURBATION MOVES EAST OF THE AREA BY TUESDAY
EVENING, PRECIPITATION CHANCES SHOULD DROP TUESDAY NIGHT AND
WEDNESDAY AS A TRANSIENT SURFACE HIGH MOVES THROUGH THE REGION.
THIS IS GENERALLY WHEN THE AFOREMENTIONED LARGE-SCALE
DISCREPANCIES BEGIN TO IMPACT THE CONFIDENCE IN THE FORECAST.
HOW FAST THE SURFACE HIGH MOVES OFFSHORE AND HOW THE UPSTREAM
SYSTEM AFFECTS THE REGION APPEAR QUITE DIFFERENT AMONG
OPERATIONAL MODELS. THE ECMWF IS MUCH LESS AMPLIFIED WITH THE
NORTHERN-STREAM SYSTEM IN EASTERN CANADA AND MUCH MORE AMPLIFIED
WITH THE UPSTREAM KICKER, AND THIS LEADS TO A LIFTING SURFACE
LOW WELL NORTHWEST OF THE AREA. THIS RESULTS IN A WARM/WET
SYSTEM THURSDAY/THURSDAY NIGHT FOR THE AREA. MEANWHILE, THE
GFS/CMC HAVE THE REVERSE APPEARANCE IN THE LARGE SCALE, LEADING
TO A MUCH FARTHER SOUTH TRACK OF THE EJECTING SURFACE LOW FROM
THE WESTERN U.S. TROUGH. THE RESULT IS A COLDER SYSTEM FOR OUR
AREA, WITH RAIN ON THURSDAY MIXING WITH/CHANGING TO SNOW FOR THE
NORTHERN PORTIONS OF THE CWA THURSDAY NIGHT INTO FRIDAY
MORNING.
THE RESULTING FORECAST IS COLDER (GIVEN A FAIRLY DECENT MODEL
TREND IN THAT DIRECTION) BUT FAIRLY CONSERVATIVE WITH POPS GIVEN
THE LARGE UNCERTAINTIES WITH TEMPERATURES, TIMING, AND ULTIMATE
PRECIPITATION TYPE. I ALSO BROADENED THE PERIOD OF POPS INTO
FRIDAY FOR A COUPLE OF REASONS. FIRST, THE LARGE TIMING
UNCERTAINTIES ALREADY EXISTING AMONG THE MODELS SUGGEST
COLLECTIVE PHASE ERRORS ARE POSSIBLE. SECOND, THE KICKER SYSTEM
MAY GENERATE A SLUGGISH SHIELD OF PRECIPITATION AS IT DIGS
SOUTHEAST INTO THE EASTERN U.S. ON FRIDAY. THUS, I DISCOUNT THE
ECMWF'S RATHER DRY LOOK OF THURSDAY NIGHT AND FRIDAY ACROSS THE
AREA. WILL NEED TO WATCH HOW THE LARGE-SCALE PHENOMENA TREND IN
SUBSEQUENT MODEL RUNS, AS A LARGE NUMBER OF OUTCOMES APPEAR
POSSIBLE IN OUR AREA LATE NEXT WEEK. NOT OVERLY CONCERNED ABOUT
A SIGNIFICANT WINTER EVENT (ESPECIALLY GIVEN THE NON-WINTER WE
HAVE HAD SO FAR), BUT THERE ARE SUGGESTIONS THAT COLDER
SOLUTIONS ARE POSSIBLE WITH THE LATE-WEEK SYSTEM.
NEXT WEEKEND LOOKS FAIRLY QUIET BUT COLDER AS HIGH PRESSURE
BUILDS INTO THE NORTHEAST.
