FXUS02 KWBC 151908
PMDEPD
 
EXTENDED FORECAST DISCUSSION
NWS HYDROMETEOROLOGICAL PREDICTION CENTER CAMP SPRINGS MD
207 PM EST WED FEB 15 2012
 
VALID 12Z SAT FEB 18 2012 - 12Z WED FEB 22 2012
 
MEDIUM RANGE GUIDANCE IN GENERAL SHOWS BETTER THAN AVERAGE
AGREEMENT AND CONTINUITY WITH RESPECT TO AN EVOLUTION TOWARD A
BROAD POSITIVELY TILTED MEAN TROF ORIENTED FROM NEAR THE UPR MS
VLY INTO NRN MEXICO BY THE MIDDLE OF NEXT WEEK.  DEVELOPMENT OF
THIS TROF WILL BE LED BY A SYSTEM FCST TO BE OVER THE PAC NW AS OF
EARLY DAY 3 SAT.  AT THAT TIME THE 06Z GFS HAS ADJUSTED SLOWER
THAN THE 00Z GFS AND OTHER GUIDANCE SO THE 00Z ECMWF OFFERS A FAIR
COMPROMISE VERSUS THE CURRENT MAJORITY THAT IS A LITTLE EWD OF THE
ECMWF.  AS THIS SYSTEM MOVES THRU THE WEST INTO THE PLAINS...
LATEST MODELS/ENSEMBLE MEANS SHOW TIGHTER CLUSTERING THAN SEEN
OVER THE PAST COUPLE DAYS... WITH ONLY MODERATE AMPLITUDE AS
SUPPORTED BY TELECONNECTIONS RELATIVE TO THE UPSTREAM RIDGE AND
GREATER FLOW SEPARATION THAN SEEN IN THE 12Z/14 ECMWF.  EVEN
THOUGH THE 06Z GFS DETAILS ARE SOMEWHAT OF A QUESTION MARK DAYS
3-4... IT ACTUALLY TRENDS INTO BETTER AGREEMENT WITH CONSENSUS
THAN THE 00Z GFS FROM THE PLAINS NEWD BY DAYS 5-7.  THE 00Z GFS
STRAYED FASTER THAN THE GREAT MAJORITY OF GUIDANCE IN THIS TIME
FRAME.  BY DAY 7 WED THE 00Z ECMWF DEVELOPS A FAIRLY ROBUST WAVE
ALONG THE TRAILING FRONT THAT NEARS THE EAST COAST.  SOME WAVINESS
IS PLAUSIBLE GIVEN THE LARGE SCALE PATTERN BUT PREDICTABILITY OF
THE 00Z ECMWF SPECIFICS BY DAY 7 IS TOO LOW TO GIVE IT MORE THAN
ABOUT 1/3 WEIGHTING.  BEHIND THIS LEADING SYSTEM... GUIDANCE
BRINGS MULTIPLE WEAKER PIECES OF ENERGY INTO WRN SIDE OF THE
EVOLVING MEAN TROF.  THERE IS DECENT AGREEMENT REGARDING A WARM
FRONT NEARING THE PAC NW COAST AROUND SUN-MON WITH LOW PRESSURE
AND TRAILING COLD FRONT REACHING SRN CANADA/NRN CONUS BY WED.  THE
00Z GFS IS ON THE FASTER SIDE OF THE ENVELOPE WITH ITS DAY 7 SFC
LOW WHILE THE 06Z GFS HAS SLOWED DOWN TO AGREE BETTER WITH MOST
OTHER SOLNS.
FARTHER EWD... THERE IS CONTINUED SPREAD WITH RESPECT TO THE
HANDLING OF EJECTING SRN PLAINS/NRN MEXICO ENERGY AND NRN STREAM
FLOW ACROSS THE NERN QUADRANT OF THE CONUS.  THUS IMPORTANT
DETAILS ARE YET TO BE RESOLVED FOR THE AREA OF LOW PRESSURE FCST
TO TRACK FROM NEAR THE GULF COAST INTO THE WRN ATLC.  AMONG LATEST
GUIDANCE THE 00Z GFS IS THE CLEAR EXTREME IN BEING FASTER WITH ITS
SRN STREAM SHRTWV AND DEEP/SWD/CLOSED WITH ITS NRN STREAM ENERGY
TO YIELD A VERY DEEP/NWD SFC SYSTEM.  MINUS THE 00Z GFS THE
REMAINING SFC LOW SPREAD IS STILL QUITE BROAD AS OF EARLY DAY 4
SUN WITH ONE OR MORE CENTERS POSSIBLE IN AN AREA FROM THE SERN
CONUS TO OFFSHORE THE CNTRL-SRN MID ATLC COAST.  THE 00Z ECMWF
WHICH SHOWS ITS BEST DEFINED SFC LOW NEAR THE SERN COAST EARLY SUN
IS CLOSER TO HPC CONTINUITY OVER THE PAST DAY.  THE 00Z CMC IS
SLOWEST WITH ITS SERN CONUS SFC LOW.  THE ECMWF MEAN IS MORE
BALANCED BETWEEN THE SWRN/NERN SIDE OF THE SPREAD WHILE THE GEFS
MEAN/06Z GFS AND TO SOME DEGREE 00Z UKMET EMPHASIZE A LEADING WAVE
AS OF EARLY SUN.  FOR NOW WILL LEAN CLOSER TO THE 00Z ECMWF TO
MAINTAIN SOME CONTINUITY WITH ANY 12Z GUIDANCE TRENDS BEING
INCORPORATED FOR THE FINAL FCST.
DAYS 3-4 SAT-SUN START WITH A 70/30 WEIGHTING OF THE 00Z ECMWF/00Z
ECMWF MEAN BASED ON ABOVE CONSIDERATIONS FOR THE INDIVIDUAL
SYSTEMS AFFECTING THE ERN CONUS AND WRN STATES.  GOOD LARGE SCALE
AGREEMENT FAVORS A CONSENSUS APPROACH BY DAYS 5-7 MON-WED... WITH
A NEARLY EVEN BLEND OF THE 00Z ECMWF/00Z GEFS MEAN/00Z ECMWF MEAN
USED TO REPRESENT THE CURRENT MAJORITY SOLN.
12Z UPDATE... WITH THE WEEKEND SYSTEM AFFECTING THE EAST THE
GFS/UKMET HAVE ADJUSTED TOWARD THE STG/NRN 00Z GFS SFC LOW ALBEIT
WITH A SOMEWHAT LESS EXTREME NRN STREAM SYSTEM ALOFT VERSUS THE
00Z GFS.  THE 12Z GEFS MEAN IS CLOSE TO THE 00Z ECMWF LATE SAT AND
THEN TRENDS TO A COMPROMISE TRACK BUT FASTER THEREAFTER.  THE
00Z/12Z GFS RUNS ARE ON THE NWRN SIDE OF THE GEFS SPREAD BUT NOT
QUITE TO THE POINT OF BEING OUTLIERS.  FROM THE SHORT RANGE THE
12Z CMC IS A SLOW OUTLIER WITH THE SRN STREAM SHRTWV RESULTING IN
A VERY SLOW/SUPPRESSED SFC WAVE.  THE 12Z ECMWF DIFFERS WITH NRN
STREAM DETAILS BUT STILL MINIMIZES PHASING SO THE END RESULT IS
SIMILAR TO THE 00Z ECMWF.  AS A RESULT THE FINAL FCST MAINTAINS
CONTINUITY WITH UPDATED PRELIM ISSUANCE.  FOR THE DEVELOPING
WRN/PLAINS TROF... 12Z SOLNS OFFER VARYING DETAIL CHANGES/DIFFS
THAT FALL WITHIN THE LARGE SCALE MEAN PATTERN BUT DIFFER FROM
ESTABLISHED CONSENSUS IN SOME WAYS.  THE MOST COMMON SUGGESTION
FROM 12Z SOLNS AS A WHOLE IS A SLIGHTLY NWD TREND WITH PLAINS/MS
VLY LOW PRESSURE EARLY NEXT WEEK.  THIS IS PARTIALLY ACCOUNTED FOR
IN THE FINAL FCST.  ELSEWHERE DETAIL CHANGES ARE MINOR.
IN ASSOC WITH THE SYSTEM TRACKING FROM NEAR THE GULF COAST INTO
THE WRN ATLC DURING THE WEEKEND... BEST POTENTIAL FOR LOCALLY HVY
RNFL SHOULD BE FROM THE CNTRL GULF COAST/FL PANHANDLE NEWD. 
FARTHER NWD THERE IS STILL SIGNIFICANT UNCERTAINTY WITH THE
COVERAGE/INTENSITY OF PCPN... AND ALSO PCPN TYPE FROM THE CNTRL
APLCHNS/NRN MID ATLC INTO SRN NEW ENGLAND.  EVEN WITH A SRN TRACK
OF THE PRIMARY SFC LOW THE GRTLKS/NORTHEAST MAY SEE SOME SNOW
SAT-SUN DUE TO NRN STREAM ENERGY WHILE A SFC LOW TRACK ON THE
STG/NRN SIDE OF THE SPREAD WOULD LEAD TO HIGHEST SNOWFALL OVER
THIS REGION.
FARTHER WWD THE PRIMARY FEATURE WILL BE A SYSTEM FCST TO TRACK
FROM THE PAC NW THRU THE WEST AND THEN THE PLAINS/GRTLKS FROM THE
WEEKEND INTO NEXT WEEK... SUPPORTING RAIN/HIER ELEV SNOW OVER
PORTIONS OF THE WEST AND SNOW N/RAIN S FROM THE N-CNTRL PLAINS
NEWD.  GULF INFLOW AHEAD OF THE TRAILING FRONT MAY ENHANCE RNFL
REACHING THE ERN STATES BY LATE IN THE FCST PERIOD.  ONCE THIS
SYSTEM EXITS THE WEST A RIDGE BUILDING INTO THE ERN PAC/SWRN CONUS
SHOULD CONFINE MOST PCPN TO AREAS FROM THE PAC NW TO NRN-CNTRL
ROCKIES.  CONTINUE TO EXPECT MOST PERSISTENT ABOVE NORMAL DAYTIME
HIGHS ACROSS THE NRN TIER... WHILE BELOW NORMAL READINGS OVER THE
WEST EARLY-MID PERIOD SHOULD MODERATE THEREAFTER.  ELSEWHERE TEMPS
SHOULD BE VARIABLE AND MOSTLY WITHIN 5-10 F OF NORMAL MOST DAYS. 
RAUSCH
$$