Preliminary Forecasts
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FXUS02 KWNH 270626
PREEPD

PRELIMINARY EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
225 AM EDT WED JUL 27 2016

VALID 12Z SAT JUL 30 2016 - 12Z WED AUG 03 2016

...OVERVIEW AND GUIDANCE EVALUATION/UNCERTAINTY ASSESSMENT...

MULTI-DAY MEAN CHARTS OFFER SIMILAR IDEAS FOR THE LARGE SALE FLOW.
 EXPECT A MEAN TROUGH TO BECOME ESTABLISHED ALONG THE WEST COAST
WHILE A DOWNSTREAM MS VLY TROUGH GRADUALLY PROGRESSES TOWARD THE
EAST COAST/WRN ATLC.  SOME RIDGING IS FCST TO PERSIST OVER THE
SOUTHWEST/FOUR CORNERS REGION BUT HIGHEST HGTS BY A SMALL MARGIN
SHOULD TEND TO MOVE INTO THE CENTRAL U.S..  AT THE SAME TIME THE
WRN PERIPHERY OF A RETROGRADING ATLC RIDGE WILL LIKELY NUDGE ITS
WAY TOWARD THE SERN COAST AROUND SUN-MON.

WHILE NEARLY ALL SOLNS AGREE ON THE ESTABLISHMENT OF THE WEST
COAST MEAN TROUGH THE FCST FOR EXACT DETAILS APPEARS AT LEAST AS
UNCERTAIN AS IT DID 24 HRS AGO.  ALREADY AT THE START OF THE FCST
PERIOD THERE ARE DEVELOPING DETAIL DIFFS WITH WRN CANADA/NERN PAC
ENERGY THAT INITIALLY FORMS THE WEST COAST MEAN TROUGH.  THEN
ONGOING SPREAD THAT ARISES FROM THE BERING SEA/ALASKA REGION
FURTHER ENHANCES THE DETAIL UNCERTAINTIES FOR THE REST OF THE
PERIOD FROM THE NERN PAC ACROSS SRN CANADA AND NRN TIER CONUS.
THERE IS STILL REASONABLE CONTINUITY FROM ECMWF/ECMWF MEAN RUNS
TOWARD GREATER PROGRESSION OF THE UPSTREAM FLOW AND PARTIAL
SUPPORT FROM THE 12Z CMC MEAN.  GFS/GEFS RUNS CONTINUE TO HOLD THE
ENERGY WELL WWD AS DOES THE OPERATIONAL 12Z CMC.  NEW 00Z GFS/CMC
RUNS HAVE TRENDED SOMEWHAT FASTER WITH THE BERING SEA-NERN PAC
ENERGY THOUGH ARE STILL SLOWER THAN THE ECMWF/ECMWF MEAN.
OPERATIONAL MODEL RUNS INCREASINGLY DIVERGE ACROSS THE NRN
U.S./SRN CANADA MID-LATE PERIOD AND ENSEMBLE MEANS DIFFER WITH
SOME SHRTWV SPECIFICS... BUT BY DAY 7 WED THE 18Z GEFS AND 12Z
ECMWF/NAEFS MEANS ARE REMARKABLY SIMILAR WITH LEADING ENERGY THAT
SUPPORTS THE NRN TIER COLD FRONT.  ALSO IN SPITE OF DIFFERENT WAYS
OF HANDLING UPSTREAM FLOW... BY DAY 7 THE MEANS REFLECT THE
CONSENSUS WEST COAST TROUGH WITH ONLY MILD DIFFS IN
AMPLITUDE/LONGITUDE.  THESE POINTS OF AGREEMENT LEAD TO A STRONG
PREFERENCE TOWARD THE ENSEMBLE MEANS BY THE LATTER HALF OF THE
FCST PERIOD.

THE FCST FOR THE ERN TROUGH ALOFT AND CORRESPONDING SFC EVOLUTION
STILL INVOLVES SOME DEGREE OF SPREAD BUT TRENDS OVER THE PAST
12-24 HRS HAVE VASTLY IMPROVED GUIDANCE CLUSTERING.  THE MOST
PROMINENT TREND HAS BEEN IN THE ECMWF-BASED SOLNS WITH A WEAKER
MID LVL EVOLUTION AND MORE SUPPRESSED SFC PATTERN IN THE SAT-MON
TIME FRAME.  A GENERAL BLEND OF LATEST MODEL/ENSEMBLE GUIDANCE
PROVIDES A REASONABLE INTERMEDIATE SOLN WITHIN THE CURRENT
ENVELOPE.

A MODEL/ENSEMBLE MEAN BLEND INCORPORATING THE 18Z GFS/GEFS AND 12Z
ECMWF/ECMWF MEAN REFLECTS THE DESIRED INTERMEDIATE SOLNS FOR BOTH
TROUGHS OF INTEREST DAYS 3-4 SAT-SUN.  OPERATIONAL WEIGHTING
DECREASES ON DAY 5 MON ON THE WAY TO A 50/30/20 BLEND OF THE 12Z
ECMWF MEAN/12Z NAEFS MEAN/18Z GEFS MEAN FOR DAYS 6-7 TUE-WED.


...SENSIBLE WEATHER HIGHLIGHTS...

THE WAVY SFC FRONT EXTENDING FROM THE MID ATLC BACK INTO THE
PLAINS... WITH THE PLAINS PORTION OF THE BNDRY LIFTING NEWD AS A
WARM FRONT... WILL BE THE PRIMARY SYNOPTIC SCALE FOCUS FOR LOCALLY
HVY RNFL DURING THE PERIOD.  BEST POTENTIAL FOR HIGHEST TOTALS
DURING THE 5-DAY PERIOD CURRENTLY EXISTS NEAR THE SRN HALF OF THE
MID ATLC COAST.  ACTIVITY NEAR THE CNTRL GULF COAST MAY ALSO BE
LOCALLY HVY.  FRONTAL SYSTEM CROSSING THE NRN TIER SHOULD BE
ACCOMPANIED BY AREAS OF SHWRS/TSTMS.  EXPECT MONSOONAL CONVECTION
TO BE FAIRLY ACTIVE FROM THE SOUTHWEST INTO THE SRN HALF OF THE
ROCKIES.

LOCATIONS FROM CA INTO THE NRN ROCKIES WILL LIKELY SEE HIGHS 5-15F
ABOVE NORMAL ON SAT BEFORE TRENDING COOLER IF NOT QUITE DOWN TO
NORMAL.  THE SRN HIGH PLAINS AND CAROLINAS/GA SHOULD SEE ABOVE
NORMAL TEMPS MOST OF THE PERIOD.  FRONTAL PROGRESSION E OF THE
ROCKIES WILL SPREAD SOME OF THE INITIAL WRN U.S. WARMTH ACROSS THE
PLAINS AND MIDWEST THOUGH WITH MOST LOCATIONS SEEING ANOMALIES OF
LESS THAN PLUS 10F.  THIS WARMTH WILL DISPLACE AN AREA OF MODESTLY
BELOW NORMAL HIGHS CENTERED OVER THE E-CNTRL U.S. DURING THE
WEEKEND.

RAUSCH

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