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Extended Forecast Discussion
 
(Caution: Version displayed is not the latest version. - Issued 1557Z Jan 29, 2015)
 
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Abbreviations and acronyms used in this product
 
Geographic Boundaries -  Map 1: Color  Black/White       Map 2: Color  Black/White


EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1057 AM EST THU JAN 29 2015

VALID 12Z SUN FEB 01 2015 - 12Z THU FEB 05 2015

...OVERVIEW...

RECENT MULTI-DAY MEANS FROM THE MODELS/ENSEMBLE MEANS HAVE BEEN
MORE AGREEABLE AND CONSISTENT THAN AVERAGE... SHOWING THAT THE
PATTERN SHOULD SETTLE INTO A WEST COAST RIDGE/CNTRL-ERN CONUS
TROUGH CONFIGURATION.  THIS PATTERN ALSO HAS GOOD TELECONNECTION
SUPPORT RELATIVE TO UPSTREAM FEATURES... A CORE OF NEG HGT
ANOMALIES NEAR 160W AND A CORE OF POS HGT ANOMALIES NEAR
KAMCHATKA.  FCSTS OF THESE ANOMALY CENTERS ARE ALSO REMARKABLY
SIMILAR IN THE D+8 MEANS.  WHILE CONFIDENCE IS ABOVE AVG IN THE
EVOLVING LARGE SCALE FLOW BY THE LATTER HALF OF THE PERIOD THERE
ARE STILL PERSISTENT UNCERTAINTIES WITH SIGNIFICANT FEATURES...
INCL THE SYSTEM AFFECTING THE ERN HALF OF THE CONUS SUN-MON AS
WELL AS TIMING OF A FRONT DROPPING SEWD FROM CANADA AND AN UPR LOW
FCST TO EJECT FROM NRN MEXICO.


...GUIDANCE/UNCERTAINTY EVALUATION AND PREFERENCES...

FOR DAYS 3-6 SUN-WED THE UPDATED WPC FCST INCORPORATES A BLEND OF
00Z ECMWF/00Z-06Z GFS RUNS AND 06Z GEFS/00Z ECMWF MEANS... A
LITTLE MORE TOWARD THE OPERATIONAL RUNS DAYS 3-5 AND ENSMEANS DAY
6.  THIS SOLN REFLECTS THE MOST COMMON ASPECTS OF LATEST GUIDANCE
WHILE DOWNPLAYING LOWER CONFIDENCE DETAILS OF ONE OR MORE
INDIVIDUAL SOLNS.  DAY 7 THU USES A BLEND OF HALF 00Z ECMWF MEAN
AND THE REMAINDER 06Z GEFS/00Z NAEFS MEAN AS CONFIDENCE IN MODEL
SPECIFICS FURTHER DECLINES.

CONFIDENCE REMAINS LOWER THAN DESIRED FOR THE ERN SYSTEM SUN-MON. 
WOULD NOT BE SURPRISED TO SEE CONTINUED VARIABILITY IN THE
GUIDANCE AT LEAST UNTIL THE UPR SUPPORT... WEAK NERN PAC ENERGY
AND SHEARED ENERGY OVER ALASKA... FINALLY REACH WRN CANADA BY SAT.
 THE SMALL SCALE NATURE OF BOTH PIECES OF ENERGY IS LIKELY
CONTRIBUTING TO FCST DIFFICULTY.  OVER MULTIPLE DAYS
MODEL/ENSEMBLE GUIDANCE HAS WAFFLED CONSIDERABLY BTWN
WEAK/PROGRESSIVE AND STRONGER/SLOWER SFC SOLNS.  YDAYS 12Z MDLS
GENERALLY ADJUSTED MUCH WEAKER/FASTER THAN WHAT CONSTITUTED A
MAJORITY CLUSTER FROM THE PAST 1-2 DAYS... BUT 00Z/06Z SOLNS HAVE
BACKED UP A BIT TO WHAT SEEMS A REASONABLE INTERMEDIATE FCST
ESPECIALLY IN LIGHT OF 00Z CMC/UKMET RUNS HOLDING ONTO A
SLOWER/WWD SFC SYSTEM MORE SIMILAR TO SOME EARLIER GFS/ECMWF RUNS.
 THE FULL ENSEMBLE SPREAD FOR SFC LOWS IS STILL UNUSUALLY BROAD
GIVEN THE FCST TIME FRAME WITH THE ONLY IMPROVEMENT TODAY BEING A
TRIMMING OF THE NRN SIDE OF THE ENVELOPE.

UPSTREAM FROM THIS SYSTEM... RECENT TRENDS HAVE BEEN TOWARD A
WEAKER DEPICTION OF ERN PAC ENERGY FLOWING THROUGH WEST COAST MEAN
RIDGE AROUND SUN-MON.  THESE TRENDS AND RELATIVE WEAKNESS OF THE
ENERGY IN GENERAL SEEM TO FAVOR DOWNPLAYING THE 00Z CMC AND
ESPECIALLY 00Z ECMWF THAT BRING A WELL DEFINED SFC WAVE INTO THE
NRN PAC NW.  THE FAVORED STARTING BLEND HAS SUFFICIENTLY LOW 00Z
ECMWF WEIGHTING TO MINIMIZE THE DEFINITION OF SUCH A FEATURE. 
MEANWHILE SOMEWHAT BETTER MAINTENANCE OF THE RIDGE IS CONSISTENT
WITH SLIGHTLY FASTER TRENDS FOR THE COLD FRONT DENOTING THE
LEADING EDGE OF COLDER AIR DROPPING INTO THE NRN PLAINS BY EARLY
TUE AND CONTINUING SEWD THEREAFTER.

THE FCST ALONG THE SRN TIER AND EAST COAST DURING THE LATTER HALF
OF THE PERIOD IS STILL UNCERTAIN WITH SIGNIFICANT DIFFS PERSISTING
FOR THE UPR LOW EJECTING FROM MEXICO.  THERE IS A STRONG ENOUGH
SIGNAL TO INDICATE SOME WAVINESS FROM THE GULF COAST INTO THE WRN
ATLC BUT WITH SOMEWHAT LESS IMPACT THAN RECENT ECMWF RUNS.  ON THE
OTHER HAND GFS/GEFS MEAN RUNS MAY BECOME A LITTLE FAST WITH THE
CONUS TROUGH LATE IN THE PERIOD AND PUSH THE PCPN THREAT TOO FAR
OFFSHORE.  THE PREFERRED BLEND OFFERS A BALANCE BTWN THESE TWO
EXTREMES.

ONE LAST NOTE IS THAT THE 00Z GFS ON DAY 6 WED AND 00Z ECMWF ON
DAY 7 THU MAY BE OVERDONE WITH THE AMOUNT OF ERN PAC ENERGY THAT
PUSHES INTO THE WEST COAST RIDGE... FAVORING EXCLUSION OF THOSE
SOLNS AT THE TIMES INDICATED.


...SENSIBLE WEATHER HIGHLIGHTS...

FOR THE SUN-MON SYSTEM OVER THE EAST... BASED ON MAJORITY GUIDANCE
SOLNS OF THE PAST 12-24 HRS EXPECT BEST POTENTIAL FOR SIGNIFICANT
WINTER WEATHER FROM THE MID MS VLY/OH VLY THROUGH THE NRN HALF OF
THE MID ATLC/EXTREME SRN NEW ENGLAND.  CURRENT FLATTER DEPICTION
OF THIS SYSTEM RELATIVE TO SOME EARLIER SOLNS SUGGESTS PCPN WOULD
BE MOSTLY RAIN S/SNOW N WITH THE TRANSITION BEING A BAND OF SNOW
WITH ABOVE FREEZING SFC TEMPS.  CONFIDENCE FOR THIS SYSTEM IS
BELOW AVG SO FURTHER CHANGES FROM THIS MOST LIKELY SCENARIO ARE
QUITE PSBL.  BEHIND THIS SYSTEM EXPECT A PERIOD OF SNOW TO THE LEE
OF GREAT LAKES WITHOUT ICE COVER.  WRN CONUS PCPN WILL BE CONFINED
TO NRN AREAS WITH GENERALLY BRIEF/LOCALIZED ENHANCED TOTALS OVER
FAVORED TERRAIN.  FROM MON ONWARD SOME OF THIS MSTR MAY BE CARRIED
ACROSS THE PLAINS/NORTHEAST BY A WAVE/FRONT AT THE LEADING EDGE OF
COLD AIR PUSHING SEWD FROM CANADA.  MEANWHILE SOME RNFL IS PSBL
FROM MON NIGHT ONWARD ACROSS THE SOUTH/SOUTHEAST IN ASSOC WITH THE
UPR LOW EJECTING FROM MEXICO BUT WITH LOW CONFIDENCE FOR
TIMING/COVERAGE/INTENSITY OF RNFL.  TIMING OF COLDER AIR ARRIVING
FROM THE NW WILL HAVE TO BE WATCHED FOR WINTER WEATHER POTENTIAL
IN THE NWRN PERIPHERY OF THIS PCPN SHIELD BUT CURRENT
PROBABILITIES ARE FAIRLY LOW.  THE MEAN PATTERN WILL FAVOR ABOVE
NORMAL TEMPS OVER THE WEST... VARIABLE READINGS OVER THE PLAINS...
AND BELOW NORMAL TEMPS OVER THE EAST.  GREATEST WARM ANOMALIES
SHOULD BE IN THE PLUS 10-15F RANGE OVER/NEAR THE GRTBASIN WHILE
MINUS 15-25F OR SO ANOMALIES MAY EXTEND FROM FROM THE GRTLKS/OH
VLY/TN VLY NEWD INTO NEW ENGLAND MON-TUE. 

RAUSCH