Prognostic Meteorological Discussion
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FXUS02 KWBC 301600
PMDEPD

EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1200 PM EDT SAT APR 30 2016

VALID 12Z TUE MAY 03 2016 - 12Z SAT MAY 07 2016

...OVERVIEW AND GUIDANCE EVALUATION/PREFERENCES...

MODEL/ENSEMBLE SOLNS CONTINUE TO DEPICT AN INCREASINGLY
AMPLIFIED/BLOCKY PATTERN NEXT WEEK.  OVERALL GUIDANCE HAS BEEN
BETTER BEHAVED WITH THE UPR LOW FCST TO CLOSE OFF NEAR THE WEST
COAST AROUND THU AND PUSH INLAND THEREAFTER VERSUS THE DETAILS OF
THE DEEPENING ERN NOAM TROUGH ALOFT AND CORRESPONDING SFC
EVOLUTION.

FROM THE ERN PAC INTO WRN U.S. THE PRIMARY ISSUE OVER RECENT DAYS
HAS BEEN WITH TIMING OF THE UPR TROUGH NEARING THE WEST COAST AND
LOW THAT CLOSES OFF WITHIN THIS TROUGH.  THE 00Z/06Z CYCLE HAS
ADJUSTED SOMEWHAT FASTER IN WHAT APPEARS TO HAVE BECOME AN ONGOING
DAILY OSCILLATION FOR TIMING.  AT THE VERY LEAST... GENERALLY SLOW
EVOLUTION OF THE PATTERN SHOULD FAVOR LEANING AWAY FROM THE 06Z
GFS/00Z CMC THAT BECOME SOMEWHAT FASTER THAN REMAINING SOLNS BY
THE LATTER HALF OF THE PERIOD.

FARTHER EWD... A SIGNIFICANT KEY TO THE FCST WILL BE WHAT HAPPENS
TO SHRTWV ENERGY TO THE W OF HUDSON BAY AS OF EARLY SUN.  AFTER
THAT TIME AND INTO THE MEDIUM RANGE PERIOD INDIVIDUAL MODEL RUNS
DIVERGE GREATLY AMONG EACH OTHER AND FROM PREVIOUS RUNS WITH THE
HANDLING OF THIS ENERGY AND TO A MEANINGFUL DEGREE WITH UPSTREAM
AMPLIFYING ENERGY THAT MAY FORM A CLOSED LOW... ULTIMATELY LEADING
TO SIGNIFICANT DIFFS IN STRENGTH/TRACK OF SFC LOW PRES ALONG THE
EAST COAST AFTER 12Z WED.  IN PRINCIPLE GUIDANCE CONSENSUS WOULD
SUGGEST THAT BY TUE THERE SHOULD BE MORE PLAINS/MS VLY ENERGY
PRESENT THAN DEPICTED IN 00Z/06Z GFS AND PARALLEL GFS RUNS.
HOWEVER WOULD BE HESITANT TO GIVE ANY MORE THAN PERHAPS 20 PCT
CONFIDENCE IN ANY SPECIFIC SCENARIO AT THIS TIME.  THUS PREFER TO
STAY CLOSER TO A SLIGHTLY DEEPER VERSION OF THE ENSEMBLE MEANS
WHICH HAVE PROVIDED BETTER RUN TO RUN STABILITY IN KEEPING LOW
PRES JUST OFF THE EAST COAST.

ANOTHER SOURCE OF UNCERTAINTY FOR FEATURES ALONG BOTH COASTS WILL
BE HOW NERN PAC ENERGY HEADING TOWARD ALASKA PANHANDLE ULTIMATELY
CONTINUES INLAND.  THE PAST COUPLE ECMWF RUNS HAVE BEEN ON THE
QUICK SIDE OF GUIDANCE WITH BRINGING THIS ENERGY INLAND AND THE
00Z ECMWF BECOMES INCREASINGLY OUT OF SYNC WITH CONSENSUS ACROSS
THE NERN PAC/NWRN NOAM BY DAY 7 SAT.

ABOVE CONSIDERATIONS LEAD TO FAVORING THE 00Z GEFS/ECMWF MEANS AS
THE MAJORITY BASIS FOR THE DAYS 3-7 TUE-SAT FCST.  THE BLEND
INCLUDES A MINORITY WEIGHT OF 00Z GFS/ECMWF FOR A PORTION OF THE
PERIOD ESPECIALLY CONSIDERING THE RELATIVE CLUSTERING WITH THE
WEST COAST TROUGH/UPR LOW... BUT NOT ENOUGH TO HAVE UNDUE
INFLUENCE ON THE EAST COAST EVOLUTION.


...WEATHER HIGHLIGHTS/THREATS...

UPR TROUGH/CLOSED LOW HEADING INTO THE WEST WILL SPREAD A BROAD
AREA OF PCPN... MOSTLY RAIN... FROM THE WEST COAST INTO THE
ROCKIES AND PSBLY AS FAR EAST AS THE PLAINS BY NEXT WEEKEND.  BEST
POTENTIAL FOR HIGHEST TOTALS OVER THE FCST PERIOD SHOULD EXTEND
OVER FAVORED TERRAIN INLAND FROM THE CNTRL WEST COAST AND EWD INTO
THE N-CNTRL/CNTRL ROCKIES.  NRN AREAS SHOULD SEE TEMPS REMAIN
5-15F ABOVE NORMAL MOST OF NEXT WEEK WITH THIS WARMTH EXTENDING
INTO THE NRN PLAINS.  CNTRL-SRN LOCATIONS OVER THE WEST WILL TREND
STEADILY COOLER WITH SOME HIGHS MORE THAN 10F BELOW NORMAL BY NEXT
SAT.

THE MOST CONFIDENT ASPECT OF THE FCST OVER THE EAST WILL BE THE
TREND TOWARD A COOL AND UNSETTLED PATTERN WITH BEST RNFL POTENTIAL
FROM THE ERN GRTLKS/OH VLY/APLCHNS TO EAST COAST.  AREAS OF
RELATIVELY HEAVIER RNFL ARE PSBL IN ASSOC WITH FRONTAL WAVINESS
OVER THE SOUTHEAST/SRN MID ATLC DURING THE FIRST HALF OF THE
PERIOD.  AFTER MIDWEEK POTENTIAL IMPACTS VARY CONSIDERABLY... WITH
VARIOUS SCENARIOS INCLUDING A MULTI-DAY WRN ATLC SYSTEM THAT WOULD
KEEP THE MOST SIGNIFICANT WINDS/RNFL ALONG OR OFF THE COAST OR A
DEEPER/MORE PROGRESSIVE SYSTEM TRACKING INTO THE NORTHEAST WHICH
WOULD SEE GREATER WIND/RNFL EFFECTS.  UPR LOW MAY ALSO PROVIDE
ANOTHER FOCUS FOR RNFL AT SOME LOCATIONS.

RAUSCH

$$





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