update (1/11 1630EST):
BOX AFD: Hopping on the band wagon:
.LONG TERM /SATURDAY THROUGH WEDNESDAY/...
SYNOPSIS: GRADUAL PATTERN CHANGE EVOLUTION APPEARS IN PROGRESS AS PNA
CONTINUES TO SLOWLY EVOLVE A BIT MORE POSITIVE...AND EVEN NOW THERE
IS SOME SENSE OF WEAKENING THE WLY FLOW OUT OF NE CANADA ACROSS
GREENLAND. GGEM 10 DAY NORMALIZED MEAN CONFIRMS AND SO WITH CROSS
POLAR FLOW INTO CANADA IT IS BECOMING SEASONABLY COLD THERE WITH TIME
AND THE EXCESSIVE HEAT THAT HAS DOMINATED HERE FOR SO LONG IS GOING
TO EBB. TODAY IS DAY 1...NEXT WEEK IS MUCH MORE SEASONABLE AND EPO
SUGGESTS EVEN SEVERAL DAYS BLO NORMAL. AO SHOWING SIGNS OF FINALLY
WEAKENING WHICH TIES TO EVENTUAL RELAXING OF THE STRONG N ATLC WLY
FLOW.
PRECIPITATION: MATTER OF TIMING BUT A MORE NORMAL WINTER PATTERN IS
ON THE WAY WHICH INCLUDES A GREATER LIKELIHOOD OF MIXED FROZEN
PRECIPITATION.
06Z ENSEMBLES FAVOR 2 WAVES SAT-MON OF NEXT WEEK AND COULD BE COMPLEX
ICY SITUATION INTERIOR NW PTN OF THE FA. HWO AND ALL PRODUCTS HAVE
IT. DETAILS AND TIMING TO BE DETERMINED.
THIS AFTN PKG IS A BLEND OF 14Z HPC GRIDS...12Z OP GFS/GGEM SOUTH
DISPLACEMENT OF THE WX SYSTEMS MODIFIED BY THE MORE NORTHERLY 12Z
UK/EC.
WITH SST SO ABNORMALLY WARM ITS DIFFICULT FOR ME TO SEE TOO MUCH
SNOW WITH THIS PATTERN AND FORESEE MORE OF AN ICY MIX IN THE
INTERIOR.
SUGGEST CKING BACK FRIDAY FOR A PROBABLE MORE CONFIDENT ASSESSMENT
OF THE DETERMINISTIC SOLNS IN WHAT PROMISES TO BE A COMPLEX HOLIDAY
WEEKEND FCST.
THE DAILIES...
SATUR"DAY"...CFP WITH A BAND OF SHOWERS...MOST PROBABLE AREA FOR
MEASURING SHOULD BE ALONG AND S OF THE MASS PIKE. UK/EC ENHANCED
THE GFS POPS. LESS THAN .10 EXPECTED.
SATURDAY NIGHT...A BREAK IN THE ACTION BUT FOR SOME REASON THE UK
KEEPS SPITTING A FEW HUNDREDTHS. OUT OF RESPECT FOR THIS OPTION
HAVE ABOUT A 20 POP.
SUNDAY...WAA ON ITS WAY BACK AND PROBABLY ARRIVES IN THE AFTN.
MARGINAL COLD FOR SLEET/SNOW/R MIX LATE IN THE DAY. GUIDANCE POPS
RAISED WITH RESPECT FOR THE EC/GGEM.
SUNDAY NIGHT...HARD TO BLV WE WONT RCV SOME MEASURABLE AND POPS
RAISED AGAIN. COMPLEX TEMP PROFILE BUT SOME ICE ANTICIPATED....AND
MAYBE SOME SNOW ACC IN S NH BY MORNING?
MONDAY...SHOULD BE MEASURING EVERYWHERE IN THE MORNING AND A DECENT
PCPN EVENT. COULD BE A DECENT ICE EVENT DISTANT INTERIOR BUT LESS
THAN ICE STORM PROPORTIONS. IF BL WINDS TURN E AT GREATER THAN 20
KTS...COASTAL TEMPS WILL WARM FASTER AND MORE THAN INDICATED DUE TO
WARM SST.
TUESDAY...THE COMPLEX MESS PROBABLY IS DONE AND DID NOT RELY ON
THE LAGGING GGEM. NW FLOW OF WHAT EVENTUALLY WILL BE SIG BELOW
NORMAL TEMPS.
TUE NIGHT-WEDNESDAY...BELOW NORMAL COLD ON THE WAY.
THURSDAY...HAD NO TIME TO MODIFY THE HPC GRIDS. EC SUGGESTS
ANOTHER APPROACHING CF W A PRD OF CLOUD CVR AND MAYBE A FEW SNOW
SHOWERS?
update (1/10 1000EST):
GYX AFD: Support of significant pattern change:
.LONG TERM /THURSDAY THROUGH TUESDAY/...
HIGH PRES MOVES OFF THE COAST THURSDAY WITH A RETURN WARM AIR
ADVECTION PATTERN THAT DEVELOPS SO INCREASING CLOUDS AND THE
CHANCE OF SNOW SHOWERS IN THE MOUNTAINS LATE THURSDAY AND THURSDAY
NIGHT. BY FRIDAY MOISTURE WHICH SPREADS EAST FROM THE OHIO VALLEY
OVERRUNS A BOUNDARY WHICH BECOMES STATIONARY ACROSS CENTRAL NEW
ENGLAND SO SNOW SHOWERS OR MIXED PRECIPITATION MAY DEVELOP OVER
SOUTHERN AREAS DURING THE DAY AND INTO THE NIGHT WITH SNOW OVER
THE MOUNTAINS. ON SATURDAY THE GFS MODEL HAS A COLD FRONT SAGGING
FURTHER SOUTH SO SOME CLEARING FROM NORTH TO SOUTH EXPECTED. BY
SUNDAY THOUGH A VERY COMPLEX SETUP DEVELOPS WITH A STRONG
BAROCLINIC ZONE IN PLACE OVER NORTHERN NEW ENGLAND WITH COLD AIR
DAMMING IN THE LOW LEVELS WHILE ALOFT WARM AIR TRIES TO SNEEK
IN...THIS BATTLE OF COLD/WARM AIR CONTINUES THROUGH MONDAY AND
MONDAY NIGHT. SOME ICING OR MIXED PRECIPITATION EXPECTED OVER
SOUTHERN AREAS LATE SUNDAY AND MONDAY WHILE THE MOUNTAINS SEE SNOW
AS AN ORGANIZED LOW PRES SYSTEM SYSTEM MOVES EAST FROM THE OHIO
VALLEY WITH A FAIR AMOUNT OF QPF. IMPORTANT TO NOTE EACH RUN HAS
BEEN COLDER WITH THIS SYSTEM. BY LATE MONDAY NIGHT GFS REDEVELOPS
LOW PRES OFF OF CAPE COD WHICH CHANGES ALL PRECIP BACK TO SNOW AND
MAY BECOME SIGNIFICANT FOR A TIME. CONSIDERING THIS TIME FRAME IS
NOW 150 HRS OUT THOUGH PLENTY CAN CHANGE AND PROBABLY WILL DUE TO
THE COMPLEXITY OF THE SITUATION. ONCE THIS SYSTEM EXITS TUESDAY
THE COLDEST AIR OF THE SEASON WILL BE FELT AND WILL LIKELY STICK
AROUND FOR QUITE A WHILE AS THE WEST COAST RIDGE BUILDS AND
BECOMES WELL ESTABLISHED WHILE THE LONG WAVE TROF IN THE EASTERN
HALF OF THE U.S. BECOMES PROMINENT...ALL LONG RANGE MODELS AGREE
THAT THIS WILL COMPLETE A MAJOR PATTERN CHANGE.
update (1/9 2000EST):
Everything is still lined up for a significant blast of cold next week plus the possibility of at least two significant snow events between January 15 and February 5th. The GFS has jumped onto the idea of two coastal events (one on the 19th and one on the 23rd). Personally, I have more confidence on the 23rd event, as there has been some continuity on this potential for the past few runs. Also, the current track of the AO and NAO indicates the pattern should give the green light for sure by the 20th. Obviously, this is a good deal into the future, so don't count on anything yet.
This post will just include long term thoughts. I will jump into the short term tomorrow. I talked yesterday about the current state of the teleconnections. As it is right now, the NAO is steady around +1, the AO has yet to drop from +4 and the PNA is right around neutral. Behind the front that passed through New England this afternoon, colder air (average highs through Thursday) will be reinforced by a developing +PNA ridge in the west. The trough in the east will present a slight decline in the NAO for midweek. On Friday, another storm system will move northward to the west of the region, allowing a resurging +NAO, and warmer air to start the weekend. Behind the storm, colder air will flow in for the start of next week. What will decide the intensity and longevity of the cold is whether or not the PNA ridge sticks around during the Friday-Saturday eastern ridge. If the +PNA can last into next week, a significant drop in the AO may finally allow some cold air to leak down from Canada. The ensemble forecast for AO is straight forward for the next 3 or 4 days, however after that, there is considerable disagreement between the ensembles after day 4. In fact, by day 14, the spread is over 5 points. If indeed, the PNA stays positive (in which the AO would bottom out), we could see a nice pattern change to normal winter weather (even below average temperatures) by the 15th. The GFS then shows a nice low off the coast on the 20th. Stay tuned, because we may have our first solid snowfall coming up during the end of January.
|posted by Sam Lillo @ 1/08/2007 09:55:00 PM
