Preliminary Forecasts
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FXUS02 KWNH 070646
PREEPD

PRELIMINARY EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
245 AM EDT TUE JUL 07 2015

VALID 12Z FRI JUL 10 2015 - 12Z TUE JUL 14 2015

...OVERVIEW...

FROM THE MULTI-DAY MEAN PERSPECTIVE GUIDANCE REMAINS CONSISTENT IN
ITS EXPECTATION THAT FLOW ALOFT WILL STEADILY EVOLVE TOWARD AN
AMPLIFIED TROUGH/RIDGE/TROUGH PATTERN.  THIS SHOULD OCCUR BY WAY
OF NRN PAC ENERGY FEEDING INTO A TROUGH JUST OFF THE WEST COAST...
A STRENGTHENING RIDGE THAT RETROGRADES FROM THE SOUTHEAST INTO THE
PLAINS/ROCKIES WITH A RIDGE ULTIMATELY EXTENDING THROUGH WRN
CANADA AS WELL... AND THEN TROUGHING DOWNSTREAM FROM THIS RIDGE.
QUESTION MARKS WILL PERSIST WITH SOME OF THE DETAILS INCLUDING
THOSE THAT DETERMINE TIMING/PATH OF CONVECTION AT SOME LOCATIONS
BUT THE LARGE SCALE OF MEAN FEATURES SHOULD GENERALLY SUPPORT
IMPROVED PREDICTABILITY.


...GUIDANCE EVALUATION/PREFERENCES...

EARLY IN THE PERIOD THERE IS FAIRLY GOOD CLUSTERING FOR THE FCST
AT THE SFC THOUGH NOT QUITE TO THE SAME EXTENT ALOFT ACROSS THE
NRN CONUS/SRN CANADA.  THUS FOR DAYS 3-4 FRI-SAT A CONSENSUS BLEND
AMONG THE 18Z GFS/12Z ECMWF WITH LESSER WEIGHTING OF THE 18Z
GEFS/12Z ECMWF MEANS IS REASONABLE.  GREATER SPREAD EMERGES FOR
SOME DETAILS AFTER SAT SO THE DAYS 5-6 SUN-MON FCST ADJUSTS TO
SOMEWHAT HIGHER WEIGHTING OF THE MEANS... WITH SUFFICIENTLY LOW
WEIGHTING OF EITHER OPERATIONAL RUN TO DOWNPLAY SMALLER SCALE
FEATURES THAT HAVE LOWER CONFIDENCE.  THEN THE CONSISTENT AND
AGREEABLE ENSEMBLE MEANS FORM THE BASIS FOR DAY 7 TUE.

LATE PERIOD PREFERENCE AWAY FROM OPERATIONAL SOLNS WAS BASED ON
12Z/18Z GFS RUNS BECOMING FASTER THAN THE MEANS AND 12Z ECMWF/CMC
WITH THE TROUGH NEAR THE WEST COAST AND DIFFS IN VARIOUS ASPECTS
OF ERN NOAM FLOW.  THE 18Z GFS STRAYS TOWARD MORE SEWD AMPLITUDE
WITH THE ERN TROUGH... THE 12Z GFS INTRODUCES AN UPR MS VLY TO
ONTARIO RIDGE ALOFT WHERE CONSENSUS HAS CYCLONIC FLOW... AND THE
12Z ECMWF UPR LOW NEAR JAMES BAY IS SW OF CONSENSUS.

WITHIN THE FCST EVOLUTION ONE OF THE PRIMARY SUBPLOTS WILL INVOLVE
WHAT HAPPENS TO ENERGY ASSOC WITH THE SHORT RANGE UPR LOW REACHING
CA.  THERE IS REASONABLE AGREEMENT IN PRINCIPLE THAT THIS ENERGY
SHOULD ROUND THE BUILDING ROCKIES/HIGH PLAINS RIDGE AND THEN HEAD
INTO THE DEVELOPING ERN TROUGH.  HOWEVER SOLNS HAVE NOT YET LOCKED
ONTO EXACTLY HOW SHEARED THE ENERGY WILL BECOME AS IT ROUNDS THE
RIDGE AND WHAT SHAPE IT WILL TAKE DOWNSTREAM.  HOW MODELS HANDLE
ASSOC CONVECTION FURTHER COMPLICATES THE FCST FOR THIS ENERGY.


...SENSIBLE WEATHER HIGHLIGHTS...

ENERGY ASSOC WITH THE UPR SYSTEM INITIALLY EJECTING THROUGH THE
WEST SHOULD SUPPORT AN AREA OF ENHANCED RNFL EARLY IN THE PERIOD
FROM JUST INLAND OF THE N-CNTRL WEST COAST INTO THE NRN ROCKIES.
DOWNSTREAM THIS ENERGY ALONG WITH THE OVERALL AMPLIFYING ERN NOAM
TROUGH ALOFT SHOULD GENERATE AREAS OF CONVECTION FROM THE NRN
PLAINS EWD/SEWD AS LOW PRESSURE AND A FRONTAL SYSTEM PROGRESS
ACROSS THE NERN QUADRANT OF THE LOWER 48.  AHEAD OF THIS ACTIVITY
EXPECT SOME RAIN/TSTMS ALONG A FRONT THAT SHOULD INITIALLY EXTEND
FROM THE CNTRL PLAINS THROUGH THE MID ATLC AND LIFT NEWD AS A WARM
FRONT.  CURRENTLY EXPECT CONVECTION OVER THE SRN HALF OF THE
ROCKIES TO HAVE GREATEST COVERAGE/INTENSITY EARLIER IN THE PERIOD.
 IMPULSES WITHIN THE TROUGH NEAR THE WEST COAST MAY ALLOW FOR SOME
PERSISTENCE OF UNSETTLED CONDS OVER THE NW AT TIMES BUT TO A
LESSER EXTENT THAN EARLY IN THE PERIOD.  DIURNALLY FAVORED SERN
CONVECTION MAY BE BETTER ORGANIZED AT TIMES OVER FL.

THE NORTHWEST SHOULD BE IN THE PROCESS OF COOLING DOWN EARLY IN
THE PERIOD WITH TEMPS STABILIZING WITHIN A FEW DEGS OF NORMAL
THEREAFTER.  THE REMAINDER OF THE WEST WILL LIKELY SEE BELOW
NORMAL HIGHS... WITH SOME ANOMALIES OF MINUS 10-15F OR SO... AND
GRADUAL TRENDING CLOSER TO NORMAL BY NEXT WEEK.  OVER THE
CNTRL-ERN STATES THE SOUTHEAST SHOULD BE MOST CONSISTENTLY ABOVE
NORMAL WITH PLUS 5-8F ANOMALIES AT SOME LOCATIONS.  SIMILAR
ANOMALIES EITHER PLUS OR MINUS ARE PSBL ELSEWHERE THOUGH THEY
SHOULD TYPICALLY BE MORE LOCALIZED OR BRIEF.

RAUSCH

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