Preliminary Forecasts
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FXUS02 KWNH 030628
PREEPD

PRELIMINARY EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
227 AM EDT FRI JUL 03 2015

VALID 12Z MON JUL 06 2015 - 12Z FRI JUL 10 2015

...OVERVIEW...

DURING THE FCST PERIOD FLOW ALOFT WILL BE SETTLING INTO A PATTERN
MORE TYPICAL OF SUMMER WITH RIDGING TENDING TO PREVAIL OVER THE
SRN TIER... A TROUGH WITH EMBEDDED UPR LOW NEAR THE CA COAST...
AND PROGRESSIVE FLOW WITH MULTIPLE EMBEDDED SHRTWVS ACROSS THE NRN
STATES.  SIMILARITY OF MODEL/ENSEMBLE MEAN SOLNS IN DEPICTING THIS
GENERAL PATTERN AT THE MOMENT LEADS TO ABOVE AVG CONFIDENCE IN THE
MEAN FLOW.  HOWEVER THE SHRTWV DETAILS WILL LIKELY TAKE A WHILE TO
BE RESOLVED GIVEN THEIR TYPICALLY LOW PREDICTABILITY.


...GUIDANCE EVALUATION/PREFERENCES...

GIVEN THE INCREASING DIFFICULTY IN RESOLVING SMALLER SCALE DETAILS
WITH TIME... THE FCST TRENDS FROM A MAJORITY OPERATIONAL BLEND AT
THE START OF THE PERIOD TO MORE OF THE ENSEMBLE MEANS THEREAFTER
WITH THE MEANS USED EXCLUSIVELY BY DAYS 6-7 THU-FRI.  THE DAY 3
FRI BLEND WAS 2/3 TOTAL OF THE PAST TWO ECMWF RUNS AND 18Z GFS
WITH THE 18Z GEFS/12Z ECMWF MEANS FILLING IN THE REST.  BEST
CLUSTERING OF GUIDANCE SUGGESTS REMOVING THE ECMWF COMPONENT AFTER
DAY 3 AND THE 18Z GFS AFTER DAY 5 WED... LEADING TO INCREASED
WEIGHTING OF THE ENSEMBLE MEANS MID-PERIOD AND A HALF 12Z ECMWF
MEAN/REMAINDER 18Z GEFS/12Z NAEFS MEAN WEIGHTING BY DAYS 6-7
THU-FRI.

THE ENSEMBLE MEANS HAVE BEEN REASONABLY CONSISTENT OVER THE PAST
FEW 12-HRLY RUNS.  HOWEVER THERE ARE A COUPLE NOTICEABLE TRENDS...
ONE BEING GRADUALLY HIGHER HGTS FCST OVER THE NERN QUADRANT OF THE
LOWER 48 BY NEXT WED-FRI AND THE OTHER A SLIGHTLY GREATER EWD
PROGRESSION OF THE ERN PAC TROUGH TOWARD THE CA COAST.  INDIVIDUAL
GFS/ECMWF RUNS HAVE BEEN MUCH MORE ERRATIC WITH THE TIMING/PATH OF
THE ERN PAC TROUGH AND NOT SURPRISINGLY WITH SHRTWV DETAILS ACROSS
THE NRN HALF OF THE CONUS.

AS FOR INDIVIDUAL FEATURES EXPECT ONE FRONT FROM THE UPR MS VLY
SWWD INTO THE PLAINS TO PROGRESS E/NE WITH TIME.  BY MIDWEEK THERE
IS INCREASING UNCERTAINTY OVER EWD EXTENT OF THIS FRONT
CORRESPONDING TO HOW AMPLIFIED SUPPORTING SHRTWV ENERGY WILL BE BY
THAT TIME.  THE 12Z/2 ECMWF BECAME FAIRLY AMPLIFIED WITH ITS
SHRTWV AND THUS MORE PROGRESSIVE WITH THE FRONT.  NEW 00Z SOLNS
THUS FAR DO NOT CLARIFY THINGS AS THE GFS TRENDS TOWARD SOME 12Z
ECMWF IDEAS BUT THE GEFS MEAN ACTUALLY HAS SOME OF THE WEAKEST HGT
FALLS ALOFT OVER THE NORTHEAST BY TUE-WED... WITH THE UKMET/CMC
DETAILS DIFFERENT AS WELL.  THERE IS DECENT AGREEMENT REGARDING
ANOTHER FRONT REACHING THE NRN TIER BY DAY 5 WED WITH A LEADING
WAVE EMERGING FROM THE NRN HIGH PLAINS.  THE PRIMARY FEATURE ALONG
THE EAST COAST WILL BE A NWD MOVING WAVE/FRONT WHOSE TIMING MAY BE
INFLUENCED BY SOME DEGREE TO THE FLOW IMMEDIATELY TO THE NW.
GREATER PROGRESSION UPSTREAM AS IN THE 00Z GFS/12Z ECMWF WOULD
LEAD TO FASTER NWD MOVEMENT OF THE EAST COAST FEATURE VERSUS THE
CURRENTLY PREFERRED ENSEMBLE MEANS.


...SENSIBLE WEATHER HIGHLIGHTS...

A DECENT PERCENTAGE OF THE CONUS SHOULD SEE ONE OR MORE EPISODES
OF CONVECTION NEXT WEEK.  BEST POTENTIAL FOR HIGHEST RNFL TOTALS
SHOULD BE FROM THE S-CNTRL PLAINS INTO THE MID MS VLY AND PSBLY
CONTINUING INTO THE GRTLKS/OH VLY/TN VLY... ALONG AND S OF A
DECELERATING SFC FRONT.  PROXIMITY OF THE ERN PAC-CA COAST UPR
TROUGH/CLOSED LOW SHOULD SUPPORT SOME ACTIVITY JUST INLAND FROM
THE CNTRL WEST COAST WITH MULTIPLE IMPULSES EJECTING FROM THIS
TROUGH ALSO ENCOURAGING CONVECTIVE DEVELOPMENT DOWNSTREAM OVER THE
WEST.  MEANWHILE THE SOUTHEAST SHOULD SEE DIURNALLY FAVORED
SHWRS/TSTMS AND SOME AREAS FARTHER NWD NEAR THE EAST COAST MAY SEE
SOME ENHANCEMENT IN RNFL FROM THE NWD MOVING WAVE/FRONT.  DRIEST
AREAS SHOULD BE ALONG/INLAND FROM THE WRN HALF OF THE GULF
COAST... PARTS OF CA AND THE SOUTHWEST... AND PORTIONS OF THE
NORTHWEST.  FOR TEMPS THE ONLY PRONOUNCED ABOVE NORMAL READINGS
SHOULD BE OVER THE NORTHWEST WITH ANOMALIES OF PLUS 10-20F FOR
HIGHS GRADUALLY DECLINING INTO THE SINGLE DIGITS BY LATE WEEK.
SOME DAILY RECORDS FOR HIGHS/WARM LOWS MAY BE PSBL EARLY IN THE
WEEK.  COOLEST TEMPS VERSUS NORMAL SHOULD BE OVER PARTS OF THE
PLAINS/MS VLY MON-TUE.

RAUSCH

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