THE WEATHER PREDICTION CENTER

COLLEGE PARK, MD


EXTENDED FORECAST DISCUSSION




EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1100 AM EST SAT JAN 31 2015

VALID 12Z TUE FEB 03 2015 - 12Z SAT FEB 07 2015

...OVERVIEW AND PREFERENCES...

MODEL AND ENSEMBLE GUIDANCE MAINTAINS UNUSUALLY GOOD AGREEMENT AND
CONTINUITY FOR THE EXPECTED LARGE SCALE FLOW INTO NEXT WEEKEND. 
CONUS TROUGHING WILL AMPLIFY DURING THE FIRST HALF OF THE PERIOD
AS A BUILDING/SHARPENING RIDGE APPROACHES AND CROSSES THE WEST
COAST.  THE ERN PAC TROUGH/WRN RIDGE/ERN TROUGH PATTERN SHOULD
BROADEN SOMEWHAT BY LATE NEXT WEEK BUT REMAIN FAIRLY AMPLIFIED. 
TO RESOLVE LINGERING DETAIL QUESTIONS WITHIN THE AGREED UPON MEAN
FLOW PREFER TO START WITH A GENERAL MODEL/ENSEMBLE MEAN BLEND
AMONG 00Z/06Z SOLNS... A TAD MORE TOWARD THE 00Z ECMWF/ECMWF MEAN
RELATIVE TO THE 00Z-06Z GFS/06Z GEFS MEAN.


...GUIDANCE EVALUATION...

MULTIPLE UNCERTAINTIES PERSIST WITHIN AND ON THE SRN PERIPHERY OF
THE MEAN TROUGH ALOFT FCST TO EVOLVE OVER THE ERN HALF OF THE
CONUS.  THERE ARE SOME TIMING DIFFS WITH THE ENERGETIC SHRTWV
PROGRESSING FROM THE NRN PLAINS THROUGH THE NORTHEAST WED-THU. 
MODELS SUGGEST THAT SFC LOW PRES NORTHEAST OF MAINE  LIKELY MORE
SIGNIFICANT FROM THE PERSPECTIVE OF PCPN COVERAGE/TYPE WOULD BE
THE COMBINED ISSUES INVOLVING WEAK ERN PAC ENERGY FCST TO AMPLIFY
TOWARD THE SERN STATES... AND A LEADING UPR LOW EJECTING FROM
MEXICO.  THERE IS STILL SIGNIFICANT MODEL/ENSEMBLE SPREAD WITH THE
TRACK/TIMING OF ONE OR MORE ASSOC SFC WAVES FROM THE GULF OF
MEXICO NEWD INTO THE WRN ATLC.  THE 00Z UKMET IS CURRENTLY THE
MOST NWWD EXTREME FOR THE SFC SYSTEM AND NEAR THE NWRN FRINGE OF
THE ENSEMBLE ENVELOPE.  THE 00Z-06Z GFS/00Z CMC ARE ALSO A BIT
NWD/NWWD OF THE GUIDANCE AVG BUT AT LEAST THE LATEST GFS RUNS HAVE
TRENDED SUFFICIENTLY SLOWER TO ACHIEVE TIMING SIMILAR THE PAST
COUPLE ECMWF RUNS.  GIVEN THE POSN OF THE EJECTING UPR LOW AS OF
EARLY DAY 4 WED THERE SEEMS TO BE REASONABLE SUPPORT A SFC WAVE
FORMING OVER THE WRN GULF ON WED... WITH NRN STREAM FLOW DETAILS
BECOMING IMPORTANT THEREAFTER.  NOTE THAT THE 06Z GFS/00Z CMC MAY
BE OVERDONE WITH AMPLITUDE OF THE APPROACHING NRN STREAM SHRTWV.

BY LATE IN THE PERIOD DIFFS IN THE DETAILS OF FLOW ACROSS SRN
CANADA AND THE NRN TIER CONUS IMPACT THE POSN OF A PSBL FRONTAL
BOUNDARY AFFECTING PARTS OF THE NRN CONUS.  INSTABILITY OF
OPERATIONAL MODEL RUNS ARGUES FOR LEANING A LITTLE CLOSER TO THE
ENSEMBLE MEANS FOR THIS PART OF THE FCST BUT 06Z GEFS MEAN TRENDS
OFFER MODEST SUPPORT INCLUDING SOME OF LATEST OPERATIONAL RUNS
THAT PUSH THE FRONT/TRAILING SFC RIDGE SOMEWHAT FARTHER S INTO THE
UPR MIDWEST/UPR GRTLKS BY NEXT SAT.

ALONG AND JUST INLAND FROM THE WEST COAST... ONE OR MORE SHRTWVS
HEADING INTO/AROUND/THROUGH THE MEAN RIDGE ARE OF SUFFICIENTLY
SMALL SCALE TO HAVE LOW CONFIDENCE IN THEIR SPECIFICS.  THE ONE
NOTABLE ATTRIBUTE OF THE PREFERRED BLEND IS TO DOWNPLAY RECENT GFS
RUNS... ESP THE 00Z VERSION... WHICH ARE SOMEWHAT STRONGER WITH
ENERGY CROSSING THE WEST.


...SENSIBLE WEATHER HIGHLIGHTS...

AREAS FROM THE CNTRL-NRN WEST COAST INTO THE ROCKIES SHOULD SEE
TWO FAVORED PERIODS OF PCPN... ONE TUE-WED WITH PRIMARILY LGT-MDT
AMTS AND A SECOND LIKELY HEAVIER EVENT CONFINED TO AREAS FROM NRN
CA/PAC NW INTO THE NRN ROCKIES.  THE LATTER EVENT SHOULD HAVE SOME
MSTR SOURCE FROM LOW LATITUDES OF THE PAC HELPING TO ENHANCE PCPN
POTENTIAL THOUGH THE AXIS OF BEST DEEP MSTR MAY BE FAIRLY NARROW
WITH SHRTWV DETAILS HAVING SIGNIFICANT IMPACT ON TIMING/DURATION
OF ENHANCED ACTIVITY.  FARTHER EWD THE COMBINATION OF THE UPR LOW
EJECTING FROM MEXICO AND NRN STREAM ENERGY EVENTUALLY REACHING THE
SERN STATES SHOULD SUPPORT POTENTIAL FOR ENHANCED RNFL ALONG MOST
OF THE GULF COAST.  PSBL COVERAGE FARTHER NWD... AND POTENTIAL
PTYPE ISSUES... IS MUCH MORE UNCERTAIN AND WILL TAKE FURTHER TIME
TO RESOLVE.  NRN LOCATIONS SHOULD SEE ONE OR TWO AREAS OF SNOW
PASS THROUGH DURING THE PERIOD WHILE SOME LAKE EFFECT ACTIVITY IS
ALSO PSBL.

FOR TEMPS... PARTS OF THE NRN-CNTRL PLAINS SHOULD BE SOMEWHAT
BELOW NORMAL FOR A DAY OR TWO EARLY IN THE PERIOD BUT OTHERWISE
THE WRN-CNTRL STATES SHOULD BE QUITE WARM WITH SOME PLUS 20-30F
ANOMALIES OVER PARTS OF THE PLAINS BY FRI-SAT.  PLUS 10-20F
ANOMALIES SHOULD PREVAIL OVER THE INTERIOR WEST.  ONE CHILLY
AIRMASS WITH MINUS 10-20F ANOMALIES WILL DEPART FROM THE NORTHEAST
TUE AND THEN ANOTHER COOL SPELL OF SIMILAR DEGREE SHOULD CROSS THE
EAST LATER IN THE WEEK. 

RAUSCH





Last Updated: 1100 AM EST SAT JAN 31 2015