Preliminary Forecasts
Issued by NWS

Home | Current Version | Previous Version | Text Only | Print | Product List | Glossary On
Versions: 1 2 3 4 5 6 7 8 9 10 11
000
FXUS02 KWNH 260615
PREEPD

PRELIMINARY EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
114 AM EST THU FEB 26 2015

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

...OVERVIEW...

A POSITIVELY TILTED MEAN TROUGH EXTENDING FROM NERN CANADA THROUGH
THE SWRN CONUS WILL BE REINFORCED BY UPSTREAM ENERGY MON-TUE
BEFORE STARTING TO PROGRESS EWD IN RESPONSE TO FLATTENING OF THE
UPSTREAM RIDGE.  WITHIN THIS MEAN PATTERN THERE HAS BEEN SOME
ATTEMPT AT GUIDANCE CONVERGENCE FOR THE UPSTREAM ENERGY... LEAVING
THE EJECTION OF AN INITIAL TROUGH OVER CA/GRTBASIN AND ASSOC SFC
EVOLUTION OVER THE CNTRL-ERN STATES TUE ONWARD AS PROBABLY THE
MOST SIGNIFICANT UNCERTAINTY AT THIS TIME.  THERE HAS BEEN BETTER
AGREEMENT/CONTINUITY WITH A STRONG COLD FRONT DROPPING INTO THE
NRN TIER BY MON NIGHT.


...GUIDANCE EVALUATION AND PREFERENCES...

WITH THE ENERGY DROPPING SWD-SEWD FROM THE NERN PAC/NWRN NOAM...
LATEST TRENDS HAVE BEEN TOWARD SOMEWHAT FASTER SWD PROGRESSION BY
MON-TUE.  OVER THE PAST 1-2 DAYS GFS/GEFS GUIDANCE HAS GENERALLY
TRENDED TOWARD PULLING THIS ENERGY A LITTLE FARTHER WWD WHILE THE
OPPOSITE TREND IS NOTED IN ECMWF/ECMWF MEAN SOLNS.  OVERALL THESE
TRENDS RECOMMEND A COMPROMISE BETWEEN THE TWO SOLN CLUSTERS.

DOWNSTREAM THERE IS REASONABLE AGREEMENT WITH THE INITIAL
CA/GRTBASIN SHRTWV AND ASSOC SFC EVOLUTION THROUGH ABOUT DAY 4
MON.  AFTER THIS TIME MODELS DIVERGE IN THE DEPICTION OF REMAINING
ENERGY ALOFT AS IT BECOMES EMBEDDED WITHIN THE FAST SWLY MEAN
FLOW... WITH INDIVIDUAL MODEL RUNS AND ENSEMBLE MEMBERS OFFERING
QUITE VARIED SOLNS FOR HOW THE CORRESPONDING SFC PATTERN WILL
EVOLVE FROM THE PLAINS EWD/NEWD.  THUS FAR ENSEMBLE SFC LOW PLOTS
SHOW LITTLE IN THE WAY OF TRUE CLUSTERING.  RECENT GFS RUNS HAVE
HAD MEANINGFUL FLUCTUATIONS IN STRENGTH OF THE PRIMARY SFC SYSTEM
BUT OVERALL HAVE BEEN FAIRLY STABLE WITH THE GENERAL IDEA OF A
TRACK INTO THE NERN CONUS/SERN CANADA AS PER THE LATEST ENSEMBLE
MEANS.  ECMWF RUNS HAVE BEEN MORE ERRATIC.  THE 12Z RUN THAT
BECOMES QUITE SUPPRESSED AT THE SFC OVER THE E BY WED IS
PARTICULARLY QUESTIONABLE AS IT HOLDS MUCH MORE ERN CANADA
TROUGHING ALOFT OVER NEW ENGLAND VERSUS MOST OTHER SOLNS BY
TUE-WED.  AS A SIDE EFFECT OF THIS... THE 12Z ECMWF ALSO APPEARS
TO BE ON THE SLOW SIDE WITH THE UPSTREAM SHRTWV PUSHING
INTO/ACROSS THE NRN TIER TUE ONWARD.

BASED ON RELATIVE CONSENSUS OF GUIDANCE AND DESIRE TO INCLUDE SOME
OPERATIONAL DETAIL EARLY IN THE PERIOD... DAYS 3-4 SUN-MON START
WITH A BLEND OF THE 18Z GFS/GEFS MEAN AND 12Z ECMWF/ECMWF MEAN.
SUFFICIENT TRENDS OF THE 18Z GEFS MEAN TOWARD THOUGH NOT YET
COMPLETELY TO THE 12Z ECMWF MEAN OVER THE WEST AND SIMILARLY
FAVORABLE SLOWER/WWD TREND WITH LOW PRES REACHING NEW ENGLAND BY
WED ALLOW FOR A BLEND OF THE 18Z GEFS/12Z ECMWF MEANS TO SERVE AS
THE STARTING POINT FOR DAYS 5-7 TUE-THU.


...SENSIBLE WEATHER HIGHLIGHTS...

A PROLONGED PERIOD OF SWLY FLOW ALOFT... FIRST FROM INITIAL TROUGH
ENERGY OVER CA/GRTBASIN AND THEN UPSTREAM REINFORCING FLOW... MAY
SUPPORT A SIGNIFICANT EVENT OF SNOW AND LOWER ELEV RAIN FOCUSED
OVER WINDWARD TERRAIN FROM AZ NEWD INTO CO/NM PRIMARILY DURING
SUN-TUE WITH PCPN TRENDING LIGHTER AND MORE SCT BY WED-THU.  THE
COMBINATION OF THE TWO UPR FEATURES SHOULD GENERATE A BROAD AREA
OF LGT-MDT PCPN AWAY FROM THE AFOREMENTIONED HEAVIEST ACTIVITY.
MOST OF THE WEST SHOULD BE DRY BY THE END OF THE PERIOD THU.
FARTHER EWD THE DETAILS HAVE VARIED A LITTLE FROM DAY TO DAY BUT
IN GENERAL CONTINUE TO EXPECT THE NEWD PROGRESSION OF EJECTING WRN
ENERGY/MEAN SWLY FLOW ALOFT ALONG WITH LOW LVL GULF INFLOW
INTERACTING WITH A WAVY FRONTAL BNDRY TO PROVIDE THE FAVORABLE
INGREDIENTS FOR A THREAT OF HVY PCPN WITHIN AN AREA FROM THE SERN
PLAINS/LWR MS VLY INTO THE CNTRL-SRN APLCHNS.  THE MAJORITY OF
PCPN IN THIS AREA SHOULD BE IN THE FORM OF RAIN WHILE A TRANSITION
ZONE OF WINTRY MIX SHOULD EXIST BETWEEN THE RAIN AREA AND SNOW TO
THE N FROM THE CNTRL PLAINS NEWD.  HVY RNFL AT SOME LOCATIONS MAY
BE PROBLEMATIC DUE TO PRIOR HVY PCPN IN THE PAST 1-2 WEEKS AND/OR
SNOW MELT.

A MAJORITY OF THE LOWER 48 SHOULD SEE BELOW TO WELL BELOW NORMAL
TEMPS DURING THE PERIOD.  THE ONE EXCEPTION WILL LIKELY BE OVER
THE GULF COAST/SOUTHEAST WHERE THERE MAY BE MULTIPLE DAYS WITH
HIGHS 5-15F ABOVE NORMAL FOR HIGHS AND 10-20F ABOVE NORMAL FOR
LOWS.  ELSEWHERE EXPECT THE MOST EXTREME ANOMALIES TO BE OVER THE
CNTRL HIGH PLAINS ON SUN WITH HIGHS AT LEAST 20-25F BELOW
NORMAL... AND THEN FROM THE NRN HIGH PLAINS SEWD TUE ONWARD WITH
GREATEST ANOMALIES ALSO MINUS 20-25F OVER THE NRN-CNTRL PLAINS
TUE-WED.  ANOMALIES SHOULD BE LESS EXTREME OVER THE WEST BUT STILL
WITH SOME POCKETS OF TEMPS 10-15F BELOW NORMAL.

RAUSCH

$$





USA.gov is the U.S. government's official web portal to all federal, state and local government web resources and services.