Prognostic Meteorological Discussion
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FXUS02 KWBC 080653
PMDEPD

EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
252 AM EDT WED JUL 08 2015

VALID 12Z SAT JUL 11 2015 - 12Z WED JUL 15 2015

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

THE LARGE SCALE FCST IS STILL ON TRACK WITH A MEAN TROUGH LIKELY
TO PERSIST NEAR THE WEST COAST... A RETROGRADING SRN TIER RIDGE
ULTIMATELY SETTLING OVER THE SRN HIGH PLAINS/ROCKIES WITH RIDGING
ALSO EXTENDING TO THE N... AND AN AMPLIFYING TROUGH DOWNSTREAM
FROM THIS RIDGE.  THIS PATTERN IS ALSO CONSISTENT WITH
TELECONNECTIONS RELATIVE TO A CORE OF NEGATIVE HGT ANOMALIES NEAR
THE ALEUTIANS/AK PENINSULA AND POSITIVE HGT ANOMALIES CLOSE TO THE
NORTH POLE.  HOWEVER EMBEDDED WITHIN THE AGREEABLE AND CONSISTENT
FCST PATTERN THERE ARE MEANINGFUL DETAIL DIFFS THAT MAY STILL TAKE
A WHILE TO BE RESOLVED.

OVER THE ERN HALF OF THE CONUS THE EVOLUTION OF ENERGY ASSOC WITH
THE UPR LOW NOW NEAR THE CA COAST... FCST TO REACH THE NRN
ROCKIES/PLAINS AS OF DAY 3 SAT... CONTINUES TO BE A SIGNIFICANT
SOURCE OF FCST UNCERTAINTY.  ONE OR MORE LEADING MID LVL IMPULSES
THAT MAY BE CONVECTIVELY RELATED WHETHER PROPERLY CAPTURED BY
GUIDANCE OR NOT ADD ANOTHER LAYER OF COMPLEXITY TO THE FCST.
SPREAD EXISTS WITH CANADIAN FLOW HEADING TOWARD THE NERN STATES AS
WELL.  RECENT GUIDANCE HAS BEEN SUGGESTING THAT MID LVL ENERGY
SHOULD BE ON THE SHEARED SIDE THUS LEADING TO A SOMEWHAT DIFFUSE
SFC PATTERN BEYOND THE NRN PLAINS WHERE LOW PRES IS BETTER DEFINED
AT THE START OF THE FCST.

COMPARING GUIDANCE THROUGH THE 18Z CYCLE... INDIVIDUAL MODEL RUNS
WERE FAIRLY QUICK TO SHOW SOME DIFFS AMONG EACH OTHER AND THE
ENSEMBLE MEANS FOR SFC DETAILS BOTH FROM THE NRN PLAINS EWD AND
OVER THE WRN ATLC.  THESE DIFFS WERE SUFFICIENT TO FAVOR PRIMARY
EMPHASIS ON THE 18Z GEFS/12Z ECMWF MEANS THROUGH THE PERIOD WITH
MINOR ADJUSTMENTS WHERE APPROPRIATE.  EVEN THOUGH THE ENSEMBLE
MEANS HAVE BEEN MORE AGREEABLE/CONSISTENT IN PRINCIPLE THE PAST
TWO ECMWF MEANS SHOW A BETTER DEFINED SFC WAVE HOLDING BACK OVER
THE MIDWEST/OH VLY MON-WED IN CONTRAST TO GEFS MEANS THAT HAVE
GENERALLY BEEN SHOWING THE MAJORITY OF MIDWEST/GRTLKS LOW PRES
TRACKING INTO THE NORTHEAST.  IT IS NOT NECESSARILY A STRONG
SIGNAL BUT THERE HAVE BEEN OCCASIONAL MODEL RUNS SUGGESTING SOME
SEPARATION OF FLOW WITHIN THE OVERALL ERN TROUGH ALOFT.  THUS THE
ECMWF MEAN IDEA DESERVES EVEN WEIGHTING WITH THE 18Z GEFS MEAN...
AND SOME HEDGING IN THAT DIRECTION BY THE NEW 00 GEFS MEAN
PROVIDES CONFIRMATION FOR THE TIME BEING.

REGARDING THE TROUGH ALOFT THE WEST COAST THERE IS REASONABLE
AGREEMENT THAT THE FEATURE SHOULD BE STRONGEST DURING THE FIRST
HALF OF THE PERIOD.  THERE HAS BEEN SOME SPREAD IN HOW ENERGY MAY
EJECT EWD LATE IN THE PERIOD WITH PRIMARILY ECMWF/ECMWF MEAN SOLNS
RECENTLY TRENDING TOWARD A WEAKER TROUGH AND THUS SOMEWHAT HIGHER
POTENTIAL FOR EJECTING OF ENERGY THAN 24 HRS AGO.  GFS RUNS STILL
APPEAR A LITTLE FAST TO EJECT ENERGY LATE IN THE PERIOD...
FAVORING THE ENSEMBLE MEAN FCST... THOUGH UPSTREAM NRN PAC FLOW
APPEARS QUITE PROGRESSIVE SO THE QUICKER EJECTION CANNOT BE
COMPLETELY RULED OUT.


...SENSIBLE WEATHER HIGHLIGHTS...

MULTIPLE EPISODES OF CONVECTION ARE PSBL FROM THE NRN PLAINS
EWD/SEWD... WITH THE FOCUS FIRST BEING PROVIDED BY A WARM FRONT
LIFTING THROUGH THE MIDWEST AND VICINITY FOLLOWED BY THE FRONTAL
SYSTEM/LOW PRES SAGGING SEWD ACROSS THE ERN HALF OF THE CONUS.
ONGOING UNCERTAINTY REGARDING IMPORTANT SHRTWV DETAILS MAKES IT
DIFFICULT TO DETERMINE PRECISE TIMING/TRACK OF HEAVIEST RNFL.
MEANWHILE THE NRN ROCKIES AND VICINITY SHOULD SEE SOME ACTIVITY
DOWNSTREAM FROM THE WEST COAST TROUGH ALOFT AND THE FOUR CORNERS
WILL LIKELY SEE PERIODS OF CONVECTION ASSOC WITH THE FLOW OF MSTR
AROUND THE WRN SIDE OF THE SRN PLAINS UPR HIGH.  AS FOR TEMPS...
THE NORTHWEST SHOULD BE MODESTLY ABOVE NORMAL WHILE THE REST OF
THE WEST SHOULD SEE A GRADUAL WARMING TREND AFTER BELOW NORMAL
READINGS EARLY IN THE PERIOD.  THE SOUTHEAST SHOULD BE ABOVE
NORMAL EARLY-MID PERIOD BEFORE MODERATING THEREAFTER WHILE THE
RIDGE BUILDING INTO THE PLAINS WILL LIKELY PROMOTE A WARMING TREND
AFTER SAT.  AREAS FARTHER NWD SHOULD SEE A MODERATE COOLING TREND
BEHIND THE SFC FRONT PUSHING SWD OVER THE CNTRL-ERN STATES.

RAUSCH

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