Models Uncertain on a Major East-Coast Snowstorm around Dec 20
Posted by JAC on 12/13/2010, 5:20 am
EXTENDED FORECAST DISCUSSION
NWS HYDROMETEOROLOGICAL PREDICTION CENTER CAMP SPRINGS MD
225 PM EST SUN DEC 12 2010

VALID 12Z WED DEC 15 2010 - 12Z SUN DEC 19 2010

THE BASIC SURFACE ISOBARIC PATTERNS AND METEOROLOGICAL REASONING
WERE LEFT UNCHANGED IN OUR FINAL EDITION.  

THE MODELS ARE SHOWING AN UNUSUALLY ANOMALOUS UPPER HIGH
RETROGRADING FROM GREENLAND TO CENTRAL CANADA DURING THE MEDIUM
RANGE PERIOD. FAIRLY DEEP MEAN TROFS OFF EACH COAST THIS PERIOD
WILL BE BOOKENDS TO A VERY FLAT MEAN RIDGE OVER THE ROCKIES. THE
NEW SET OF 00Z/12 ENSEMBLE SPAGHETTI PLOTS SUPPORTED THE REASONING
OF THE PRELIMS. AN UPPER CYCLONE OVER THE GULF OF ALASKA SLOWLY
PIVOTS TOWARD THE PACIFIC NORTHWEST WHILE ASSOCIATED SHORTWAVE
TROUGHS ON ITS S SIDE MOVE ACROSS CA/THE GRT BASIN/THE ROCKIES.
GUIDANCE SHOWS CONSIDERABLE SPREAD DEVELOPING WITH THESE SHORTWAVE
FEATURES THU AND BEYOND IN THEIR TREK ACROSS THE LOWER 48 STATES.
BELOW NORMAL TEMPS WILL PREVAIL MOST PLACES OVER THE ERN HALF OF
THE CONUS WHILE MILDER AIR OVER THE WRN STATES STRUGGLES TO
PENETRATE THE COLD PATTERN OVER THE EAST. THE MAIN THRUST OF
MILDER AIR MAY BRING PRECIP TO THE SERN CONUS THU OR FRI. THE
PACIFIC NW WILL SEE FREQUENT INTERVALS OF PCPN IN ONSHORE FLOW
WITH HEAVY PCPN EXPECTED AS FAR S AS THE NRN HALF OF CA BY FRI DAY
5. FARTHER E...LAKE EFFECT SN WILL BE THE MAIN WEATHER STORY UNTIL
THU...WHEN AN ILL-DEFINED YET SIGNIFICANT AREA OF PCPN DEVELOPS S
OF THE OH RIVER IN CONNECTION WITH WHATEVER WAVES MIGHT BE
CROSSING THAT REGION.

12Z MODELS: THE MAIN PROBLEM CONTINUES TO BE RESOLVING THE PACIFIC
SHORTWAVES CROSSING THE CONUS UNDERNEATH THE RETROGRADING CANADIAN
BLOCK  THU DAY 4 AND BEYOND. THE 12Z/12 GFS IS FAIRLY CONSISTENT
WITH ITS OWN 00Z/12 CONTINUITY IN MOVING A NRN STREAM UPPER
LOW/SHORTWAVE ACROSS THE NERN QUARTER OF THE NATION DAYS 3-5 AND
DOWNPLAYING THE SRN STREAM. ON THE OTHER HAND...THE NEW
CANADIAN/UKMET SUGGEST OTHERWISE...COMING UP WITH A FORECAST QUITE
AT ODDS WITH THAT OF THE GFS. THE UKMET AND CANADIAN BOTH ROUGHLY
FOLLOW OUR PRELIM ECMWF/ECENS MEAN CONTINUITY THU/FRI...YET STILL
DIFFER SIGNIFICANTLY FROM EACH OTHER THOSE DAYS. THE UKMET GIVE A
BETTER FIT TO OUR CONTINUITY DAY 4 WHILE THE CANADIAN GIVES A
BETTER FIT DAY 5. THE UKMET APPEARS TO TRACK A WAVE TOO FAR NE FRI
DAY 5 GIVEN THE MEAN DEEP TROF OFF THE E COAST. THE NEW 12Z ECMWF
SUPPORTS THE FLATTER CANADIAN SOLUTION. THESE MODEL DIFFERENCES
LEAD INTO THE UNCERTAIN TIME FRAME NEXT WEEKEND OFF THE SE COAST
OF THE CONUS. AM NOT TERRIBLY CONFIDENT OF ANY SOLUTION NOW. THE
NEW 12Z ECMWF HAS ITS MAIN ERN CONUS SHORTWAVE ENERGY SLOWER DAYS
5-6 THAN THE CANADIAN...SLOW ENOUGH TO LEAD INTO THE CHANCY
CYCLOGENESIS OFF THE SE COAST NEXT WEEKEND DESCRIBED BELOW.  

00Z/12 ENSEMBLE 500MB SPAGHETTI PLOTS HIGHLIGHTED AN AREA OF
POSSIBLE CYCLOGENESIS OFF THE SE COAST OF THE CONUS LATER SAT 6
AND BEYOND. IT WAS MOSTLY ECMWF ENSEMBLE MEMBERS THAT WERE
SUPPORTING CYCLOGENESIS OFF THE SE COAST NEXT SAT OR SUN. THE
06Z/12 GFS RUN SEEMED TO BE PICKING UP ON THIS POSSIBILITY FOR
NEXT SAT/SUN....BUT THE NEW GFS RUN HAS GONE BACK FLAT. RECENT
RUNS OF THE ECMWF HAD EARLIER SHOWN A CHANCE FOR CYCLOGENESIS NEXT
WEEKEND OF THE SE COAST BUT THE MOST RECENT RUN HAD BACKED OFF
FROM IT. NOW THE 12Z/12 RUN OF THE ECMWF IS BACK ON
BOARD...DEVELOPING A MAJOR SNOWSTORM NEXT WEEKEND FROM INTERIOR NC
TO NEW ENG. IF CORRECT...IT COULD LAY DOWN A HEAVY BLANKET OF SNOW
IN THE SAME AREAS AS THE BIG SYS LAST YEAR...ALMOST TO THE DATE! A
WHITE CHRISTMAS FOR THAT AREA 6 DAYS LATER WOULD BE HIGHLY FAVORED
IN THE PERSISTENT COLD PATTERN.

FLOOD


















159
In this thread:
Models Uncertain on a Major East-Coast Snowstorm around Dec 20 - JAC, 12/13/2010, 5:20 am
< Return to the front page of the: message board | monthly archive this page is in
Post A Reply
This thread has been archived and can no longer receive replies.