Prognostic Meteorological Discussion
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FXUS02 KWBC 060642
PMDEPD

EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
241 AM EDT MON JUL 06 2015

VALID 12Z THU JUL 09 2015 - 12Z MON JUL 13 2015

...OVERVIEW...

RECENT GUIDANCE HAS BEEN PROVIDING A FAIRLY CONSISTENT SIGNAL
TOWARD MEAN TROUGHING JUST OFF THE WEST COAST AND A SRN TIER
RIDGE/UPR HIGH THAT SHOULD RETROGRADE INTO THE SRN PLAINS/ROCKIES
BY LATE IN THE PERIOD.  AS MIGHT BE EXPECT THERE HAS BEEN SOME
DEGREE OF SPREAD/TRENDING WITH THE DETAILS THOUGH... WITH THE MOST
PROMINENT EVOLUTION OF INTEREST BEING WITH AN UPR LOW EJECTING
FROM CA AND ITS ENERGY THAT MAY CONTRIBUTE TO A DEVELOPING ERN
TROUGH DOWNSTREAM FROM THE LATE PERIOD PLAINS/ROCKIES RIDGE.
AHEAD OF THIS EVOLUTION THERE ARE STILL MEANINGFUL SHRTWV DIFFS
WITHIN LOW AMPLITUDE MEAN FLOW ACROSS THE NRN CONUS/SRN CANADA.


...GUIDANCE EVALUATION/PREFERENCES...

WHILE SOME REGIONAL SCALE ASPECTS OF THE 18Z GFS AND 12Z ECMWF
DIFFER FROM EACH OTHER AND/OR LATEST ENSEMBLE MEANS... THOSE TWO
RUNS ARE CLOSE ENOUGH TO ALLOW FOR INCLUDING WITH THE 18Z GEFS/12Z
ECMWF MEANS THROUGH THE PERIOD TO YIELD A CONSENSUS BLEND THAT
IMPROVES UPON ENSEMBLE MEAN DETAIL SOMEWHAT.  THE BLEND LEANS A
LITTLE MORE TOWARD THE OPERATIONAL RUNS DURING THE FIRST HALF OF
THE PERIOD AND SLIGHTLY TO THE MEANS THEREAFTER.

FOR THE EJECTING CA UPR LOW RECENT TRENDS EARLY IN THE PERIOD...
SOMEWHAT FASTER IN THE ECMWF/ECMWF MEAN AND A LITTLE SLOWER THAN
18Z/4 AND 00Z/5 GFS RUNS... YIELD GOOD CLUSTERING NOW INTO DAY 4
FRI.  FOR WHAT ULTIMATELY HAPPENS TO THE UPR LOW ENERGY AFTER FRI
GUIDANCE HAS SPANNED THE FULL SPECTRUM FROM SHEARING IT OUT TO
MAINTAINING A CONCENTRATED BUNDLE OF ENERGY REACHING THE
MIDWEST/GRTLKS.  LATEST TRENDS SEEMED TO BE BEST CAPTURED BY THE
18Z GFS/12Z ECMWF THAT REFLECT THE LATTER IDEA AND THE NEW 00Z GFS
OFFERS REASONABLE CONTINUITY.  THE 12Z GFS WAS SLOWER AS WAS THE
PRIOR 00Z RUN.  HAVING THIS ENERGY CONTRIBUTE TO A DEVELOPING ERN
TROUGH SEEMS REASONABLE GIVEN THE RIDGE BUILDING INTO THE
PLAINS/ROCKIES LATER IN THE PERIOD.

REGARDING THIS RIDGE THE OVERALL GUIDANCE AVG OVER RECENT DAYS HAS
BEEN TRENDING SOMEWHAT STRONGER AS THE FEATURE MOVES ACROSS THE
SOUTHEAST ON THE WAY TO ITS EXPECTED DESTINATION OVER THE SRN
PLAINS/ROCKIES WHERE RIDGE STRENGTH HAS SHOWN BETTER CONTINUITY.
TO VARYING DEGREES GFS/CMC/UKMET RUNS STARTED THE TREND EARLIER
THAN ECMWF-BASED GUIDANCE.  PREFERRED TO LEAN AWAY FROM THE 12Z
GFS AS IT WAS SLOWER THAN MOST OTHER SOLNS AS THE RIDGE
RETROGRADES OVER THE SOUTHEAST.

CONTINUITY HAS BEEN GOOD WITH THE IDEA OF PERSISTENT TROUGHING OFF
THE WEST COAST IN THE WAKE OF THE CA UPR LOW.  HOWEVER
MODELS/ENSEMBLE MEANS HAVE BEEN SHOWING SOME DAY TO DAY
OSCILLATION IN DEPTH.  TRENDS OVER THE PAST 24 HRS HAVE BEEN
SOMEWHAT DEEPER IN CONTRAST TO THE OPPOSITE TREND SEEN OVER THE
DAY BEFORE.

LOW AMPLITUDE FLOW INITIALLY ACROSS THE NRN STATES SHOULD SUPPORT
A WAVY FRONT EXTENDING FROM THE PLAINS THROUGH MID ATLC WITH THE
WRN PART OF THE FRONT LIFTING NEWD AS A WARM FRONT.  ESPECIALLY
AFTER EARLY THU THE MID LVL/SFC DETAILS BECOME MURKY SO WOULD
EXPECT FURTHER CONTINUITY ADJUSTMENTS.  BEHIND THIS FRONT...
CURRENTLY EXPECT EJECTING CA ENERGY TO SUPPORT LOW PRES THAT
REACHES THE GRTLKS LATE IN THE PERIOD.  LACK OF PRIOR CONSENSUS
AND TYPICAL GUIDANCE ERROR 6-7 DAYS OUT IN TIME TEMPER CONFIDENCE
BUT AT LEAST THE LATEST GFS/ECMWF RUNS FIT WITHIN THE GENERAL
FRAMEWORK OF THE GEFS/ECMWF MEANS.


...SENSIBLE WEATHER HIGHLIGHTS...

POTENTIAL EXISTS FOR ONE OR MORE EPISODES OF HVY RNFL AT SOME
LOCATIONS WITHIN AN AREA FROM THE NRN PLAINS ACROSS THE MID-UPR MS
VLY... GRTLKS/OH VLY/TN VLY... AND PSBLY THE MID ATLC.  INITIAL
FOCUS SHOULD BE ALONG A WAVY FRONT FROM THE PLAINS THROUGH MID
ATLC WITH ENCOURAGEMENT FROM ONE OR MORE SHRTWVS ALOFT.  CA UPR
LOW ENERGY AND ASSOC SFC SYSTEM FCST TO EMERGE INTO THE
PLAINS/MIDWEST/GRTLKS WOULD LIKELY GENERATE ANOTHER AREA OF
ENHANCED ACTIVITY.  EARLIER IN THE PERIOD THE CA UPR LOW SHOULD
PRODUCE ENHANCED RNFL FROM JUST INLAND OF THE CNTRL WEST COAST
INTO THE NRN ROCKIES.  MEANWHILE THE SRN HALF OF THE ROCKIES AND
PORTIONS OF THE SOUTHEAST SHOULD SEE PERIODS OF CONVECTION AS
WELL.  CONSULT SPC OUTLOOKS FOR INFO REGARDING SEVERE POTENTIAL.

THE INTERIOR NORTHWEST SHOULD SEE A PRONOUNCED COOLING TREND AFTER
PLUS 10-20F MAX TEMP ANOMALIES ON THU... STABILIZING AT WITHIN A
FEW DEGS OF NORMAL.  OTHERWISE BELOW NORMAL HIGHS SHOULD PREVAIL
OVER THE WEST WITH SOME MODERATION LATE WEEKEND/EARLY NEXT WEEK.
FARTHER EWD TEMPS WILL DEPEND TO SOME EXTENT ON TIMING OF
CLOUDS/RNFL.  TENDENCY SHOULD BE TOWARD BELOW NORMAL READINGS
NRN-CNTRL AREAS THU AND THEN NEAR TO SLIGHTLY ABOVE NORMAL BEFORE
TRENDING DOWN AGAIN NEAR THE LATE PERIOD MIDWEST/GRTLKS SYSTEM.
RIDGING ALOFT SHOULD PROMOTE ABOVE NORMAL TEMPS ESPECIALLY OVER
THE SOUTHEAST BUT GRADUALLY SPREADING WWD WITH TIME CORRESPONDING
TO LIKELY MOVEMENT OF THE BEST DEFINED UPR HIGH.

RAUSCH

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