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492
FXUS02 KWBC 271600
PMDEPD

EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1059 AM EST TUE JAN 27 2015

VALID 12Z FRI JAN 30 2015 - 12Z TUE FEB 03 2015

...OVERVIEW...

MOST GUIDANCE EXPECTS LARGE SCALE FLOW TO EVOLVE TOWARD A BROAD
CONUS MEAN TROUGH DOWNSTREAM FROM A RIDGE NEAR OR JUST OFFSHORE
THE WEST COAST.  WITHIN THIS DEVELOPING MEAN PATTERN THE MOST
SIGNIFICANT FCST PROBLEM THIS PERIOD APPEARS TO BE THE
TIMING/DEPTH OF AMPLIFYING WRN CANADA FLOW AND DEGREE OF
INTERACTION WITH SRN STREAM FLOW INITIALLY CONTAINING AN UPR LOW
OVER THE EXTREME SOUTHWEST.  EXACT DETAILS OF THESE FEATURES AND
THEIR INTERACTION WILL AFFECT THE SFC EVOLUTION AND PCPN
TYPE/INTENSITY/COVERAGE FROM THE SWRN STATES THROUGH MUCH OF THE
CNTRL-ERN U.S. FROM LATE THIS WEEK INTO THE START OF NEXT WEEK.
THERE IS ALSO SOME LINGERING SPREAD WITH A VIGOROUS SYSTEM TO
AFFECT THE NORTHEAST EARLY IN THE FCST.  MEANWHILE SOME ERN PAC
ENERGY PUSHING THROUGH THE WEST COAST MEAN RIDGE WILL BRING SOME
MSTR INTO THE NORTHWEST DURING THE LATTER HALF OF THE PERIOD.


...GUIDANCE EVALUATION AND PREFERENCES...

FOR A DAYS 3-4 FCST THE FULL ENSEMBLE ENVELOPE IS A LITTLE BROADER
THAN DESIRED FOR THE SYSTEM EXPECTED TO AFFECT THE NORTHEAST
FRI-SAT.  THE 00Z ECMWF IS A TAD ON THE SRN SIDE OF THE SPREAD AT
SOME FCST HRS WHILE THE 06Z GFS REPRESENTS A MODEST SWD ADJUSTMENT
FROM THE 00Z RUN AND 00Z/06Z GEFS MEANS... AND THE 00Z UKMET/CMC
ARE CLOSER TO THE MIDDLE OF THE SPREAD.  THUS A COMPROMISE IS
REASONABLE AT THIS TIME.

00Z/06Z GUIDANCE HAS TRENDED NOTICEABLY SLOWER THAN PREVIOUS SOLNS
WITH WRN CANADA FLOW EXPECTED TO AMPLIFY INTO THE CONUS... PUSHING
A FRONT INTO THE NRN TIER BY SAT AND SUPPORTING THE DEVELOPMENT OF
LOW PRESSURE FROM THE ERN STATES INTO THE CANADIAN MARITIMES
SUN-MON.  THE SLOWER TIMING ON AVG IS ALLOWING FOR A LITTLE MORE
INTERACTION WITH THE INITIAL SWRN CONUS TROUGH/UPR LOW AND MORE
DOWNSTREAM RIDGING TOWARD THE EAST COAST AROUND SUN.  CONFIDENCE
IN THE CURRENT SCENARIO WOULD BE CONSIDERED AVG OR LOWER BASED ON
THE DIFFS FROM PREVIOUS FCST CYCLES AND HIGHER LATITUDE ENERGY
ORIGINATING FROM AN AREA OF COMPLEX FLOW OVER/NEAR ALASKA.
HOWEVER THE SHARPNESS OF THE WEST COAST RIDGE AROUND DAY 4 SAT AND
NUMBER OF DIFFERENT SOLNS MAKING THE SLOWER ADJUSTMENT APPEAR
SUFFICIENT TO SUGGEST A LITTLE MORE POTENTIAL FOR WHAT LATEST
GUIDANCE IS SHOWING VERSUS CONTINUITY.  OVERALL A BLEND AMONG THE
06Z GFS/00Z ECMWF/00Z ECMWF MEAN PROVIDES THE BEST COMPROMISE AT
THIS TIME.  THIS SOLN YIELDS A SFC LOW TRACK BETWEEN THE FARTHER
NWD 00Z UKMET AND MORE SUPPRESSED 00Z CMC.

ANOTHER NOTICEABLE TREND IN LATEST GUIDANCE IS THE IDEA TOWARD
MORE ERN PAC ENERGY CUTTING THROUGH THE WEST COAST MEAN RIDGE AND
AMPLIFYING TO SOME DEGREE OVER THE WRN HALF OF THE CONUS.
OPERATIONAL GFS/ECMWF RUNS AND THEIR ENSEMBLE MEANS ALL SHOW THIS
GENERAL TREND.  THIS TROUGH LEADS IN REASONABLY WELL TO
TELECONNECTION-FAVORED FLOW... BASED ON A CORE OF POSITIVE HGT
ANOMALIES NEAR KAMCHATKA... SHOWING A BROAD POSITIVELY TILTED
TROUGH THAT SHOULD ULTIMATELY REACH A GRTLKS TO SRN PLAINS
ORIENTATION.

BASED ON ABOVE PREFS AND REASONABLE MODEL DETAIL... DAYS 3-4
FRI-SAT PLACE PRIMARY EMPHASIS ON A 06Z GFS/00Z ECMWF COMPROMISE.
DAYS 5-6 SUN-MON RAISE ECMWF MEAN WEIGHTING TO 40-50 PCT TO TONE
DOWN THE OPERATIONAL SOLNS SOMEWHAT.  BY DAY 7 TUE A GENERAL BLEND
OF THE 06Z GEFS/00Z ECMWF MEANS WITH MINORITY INPUT FROM THE 06Z
GFS/00Z ECMWF REPRESENTS LATEST CONSENSUS WELL.


...SENSIBLE WEATHER HIGHLIGHTS...

VIGOROUS SYSTEM AFFECTING THE NORTHEAST LATE THIS WEEK WILL BRING
A PERIOD OF WINTRY WEATHER AND STRONG WINDS.  UPR LOW INITIALLY
OVER THE SOUTHWEST WILL SUPPORT VARIOUS PCPN TYPES FROM THE FOUR
CORNERS REGION INTO THE HIGH PLAINS.  THE PCPN SHIELD WILL THEN
CONTINUE ACROSS THE PLAINS INTO THE EAST AS NRN STREAM ENERGY
GAINS INFLUENCE.  AT THIS TIME GUIDANCE HAS NOT YET STABILIZED ON
A PARTICULAR SOLN SO CONFIDENCE IS LOWER THAN DESIRED WITH RESPECT
TO EXACT PLACEMENT OF PCPN TYPES FOR THIS SYSTEM.  BASED ON
CURRENT CONSENSUS THAT IS SOMEWHAT NWWD OF CONTINUITY... BEST
POTENTIAL FOR SOME SNOW WOULD EXTEND FROM THE CNTRL PLAINS ACROSS
THE NRN OH VLY/GRTLKS INTO NEW ENGLAND WITH A MIX OF PCPN TYPES OR
CHANGEOVER JUST TO THE S.  SOME LOCATIONS WITHIN THE BROAD PCPN
AREA MAY SEE LOCALLY HVY AMTS.  PASSAGE OF THIS SYSTEM SHOULD
SUPPORT A PERIOD OF LAKE EFFECT SNOW.  DRY CONDS IN THE NORTHWEST
WILL TREND WETTER SUN-MON AS ERN PAC ENERGY SLIPS THROUGH THE
LONGER TERM MEAN RIDGE ALOFT.  SOME ENHANCEMENT IS PSBL OVER
FAVORED TERRAIN.  GREATEST ANOMALIES FOR TEMPS SHOULD BE OF THE
NEGATIVE VARIETY OVER THE EAST WITH ONE OR MORE DAYS 10-20F BELOW
NORMAL AT SOME LOCATIONS.  ON A MORE LOCALIZED BASIS PCPN/UPSLOPE
FLOW MAY LEAD TO SIMILAR ANOMALIES OVER THE SRN HIGH PLAINS.  THE
NRN PLAINS WILL SEE THE MOST DRAMATIC CHANGE WITH TIME... FROM
WELL ABOVE NORMAL FRI TO WELL BELOW ON SUN BEFORE MODERATING
SOMEWHAT.  THE WEST SHOULD EXPERIENCE NEAR TO ABOVE NORMAL TEMPS
FOR MOST OF THE PERIOD.

RAUSCH

$$






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