Preliminary Forecasts
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000
FXUS02 KWNH 040637
PREEPD

PRELIMINARY EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
236 AM EDT SAT JUL 04 2015

VALID 12Z TUE JUL 07 2015 - 12Z SAT JUL 11 2015

...PATTERN OVERVIEW...

THUS FAR THERE IS REASONABLE CONTINUITY WITH THE EXPECTED LARGE
SCALE EVOLUTION AND THE MOST PROMINENT UNCERTAINTIES RELATING TO
FCST DETAILS.  A MEAN TROUGH NEAR THE WEST COAST WILL FIRST
CONSIST OF AN UPR LOW FAIRLY DEEP FOR THE SEASON... NEARING THE CA
COAST EARLY IN THE PERIOD.  UPSTREAM NRN PAC HGT FALLS APPROACHING
MID-LATE PERIOD SHOULD ENCOURAGE THE UPR LOW TO EJECT INLAND LATE
IN THE WEEK.  TROUGHING SHOULD LINGER AFTER THIS EJECTION BUT WITH
CORE OF LOWEST HGTS ADJUSTING MORE TO THE BC COAST.  TIMING THE
UPR LOW EJECTION IS ONE NOTABLE UNCERTAINTY... AND ANOTHER
UNCERTAINTY AFFECTING A GREATER PORTION OF THE LOWER 48 WILL BE
THE DIFFICULT TO RESOLVE SHRTWV DETAILS BTWN A SRN TIER CONUS
RIDGE AND CNTRL CANADA MEAN LOW.  SOME OF THIS ENERGY MAY FILTER
INTO WEAK ERN TROUGHING AS THE SRN TIER RIDGE MAY
CONSOLIDATE/STRENGTHEN SOMEWHAT OVER THE SRN PLAINS.


...GUIDANCE EVALUATION/PREFERENCES...

FROM EARLY IN THE PERIOD SOME DETAILS IN THE OPERATIONAL MODELS
ARE AT ODDS WITH EACH OTHER AND THE ENSEMBLE MEANS... ULTIMATELY
FAVORING A 50/30/20 BLEND OF THE 12Z ECMWF MEAN/18Z GEFS MEAN/12Z
NAEFS MEAN TO PROVIDE BETTER CONTINUITY WHILE AWAITING BETTER
GUIDANCE CLUSTERING.

ALONG THE WEST COAST... THE ENSEMBLE MEANS OFFER GOOD SUPPORT FOR
GFS-ECMWF TRACK/TIMING OF THE UPR LOW THROUGH AT LEAST THU.  THE
NEW 00Z UKMET/CMC STRAY TO THE SE OF CONSENSUS BY WED.  ONE
QUESTION MARK IN THE 00Z GFS IS HOW IT DEEPENS THE UPR LOW BEYOND
OTHER SOLNS AROUND WED NIGHT-THU.  THERE IS DECENT AGREEMENT THAT
THE UPR LOW SHOULD START EJECTING INLAND AROUND FRI BUT CURRENT
SPREAD FOR UPSTREAM NRN PAC HGT FALLS LEADS TO CORRESPONDING
SPREAD FOR TIMING/TRACK OF EJECTING ENERGY ACROSS THE WEST.
TAKING MODEL/ENSEMBLE GUIDANCE AS A WHOLE THERE HAS BEEN SOME
TRENDING OVER THE PAST 24-36 HRS TOWARD A STRONGER TROUGH NEAR THE
PAC NW/BC COAST LATE IN THE PERIOD.

FARTHER EWD GUIDANCE IS STILL AT ODDS AS TO THE
AMPLITUDE/PROGRESSION OF AN INITIAL ONTARIO INTO UPR MS VLY
SHRTWV... LEADING TO ONGOING SPREAD FOR EWD EXTENT OF THE SFC
FRONT APCHG THE NORTHEAST AROUND WED.  THE 00Z GFS SEEMS TO BE ON
THE FAST EDGE OF GUIDANCE WHILE OTHER SOLNS VARY.  THERE IS THE
POTENTIAL FOR THE FAVORED ENSMEANS TO BE A TAD SLOW WITH THE FRONT
BUT AT THE VERY LEAST OTHER GUIDANCE INDICATES THAT LATEST ECMWF
RUNS THROUGH 12Z/3 COULD BE TOO AGGRESSIVE WITH HGT FALLS ALOFT SO
SLOWER TIMING THAN THE ECMWF SEEMS REASONABLE.  TIMING OF THIS
FRONT SHOULD HAVE SOME INFLUENCE ON A WEAK WAVE/FRONT LIFTING UP
THE EAST COAST.  THE WAVE APPEARS SLIGHTLY WEAKER VERSUS FCSTS
FROM 24 HRS AGO.  BEHIND THESE TWO ERN FEATURES SFC DETAILS WILL
BECOME INCREASINGLY DEPENDENT ON UNCERTAIN SHRTWVS ORIGINATING
FROM MULTIPLE STREAMS AND PSBLY THE EJECTING WEST COAST UPR LOW AS
WELL.  AMID THE SPREAD AMONG INDIVIDUAL SOLNS THERE HAS BEEN A
NOTICEABLE TREND TOWARD LOWER SFC PRESSURES OVER THE NRN PLAINS BY
THE LATTER HALF OF THE PERIOD.


...SENSIBLE WEATHER HIGHLIGHTS...

EXPECT BEST POTENTIAL FOR HIGHEST RNFL TOTALS DURING THE PERIOD TO
BE FROM THE S-CNTRL PLAINS E/NE TO BTWN THE TN VLY AND LOWER
GRTLKS... AHEAD OF A FRONT SETTLING OVER THE CNTRL PLAINS-GRTLKS.
THE NRN PART OF THE FRONT SHOULD BE ACCOMPANIED BY SOME RNFL AS
WELL WHILE UPSTREAM SHRTWV IMPULSES/SFC REFLECTIONS MAY ENCOURAGE
OTHER AREAS OF CONVECTION ACROSS THE NRN STATES.  EXPECT DIURNALLY
FAVORED CONVECTION OF VARYING INTENSITY OVER THE SOUTHEAST.  WHILE
THE WEAK WAVE LIFTING NWD ALONG THE NRN HALF OF THE EAST COAST MAY
LOCALLY ENHANCE RNFL... GUIDANCE SIGNALS ARE NOT PARTICULARLY
STRONG FOR THAT AT THE MOMENT.  THE UPR LOW NEAR THE CA COAST
SHOULD SUPPORT ONE OR MORE CONVECTIVE EPISODES OVER NRN CA-NV/SRN
OR AND THEN AREAS FARTHER E/NE AS THE FEATURE EJECTS INLAND.
SHRTWV IMPULSES AHEAD OF THIS SYSTEM SHOULD ALSO ENHANCE DIURNAL
CONVECTION OVER/NEAR THE ROCKIES.  HEAT OVER THE INTERIOR
NORTHWEST SHOULD BE STUBBORN AS SOME MAX TEMP ANOMALIES REMAIN
ABOVE PLUS 10F INTO THU... FINALLY COOLING CLOSER TO NORMAL
FRI-SAT AS HGTS ALOFT DECLINE.  COOLEST READINGS RELATIVE TO
NORMAL FOR THE TUE-SAT PERIOD SHOULD BE FROM THE SRN HALF OF THE
WEST THROUGH THE PLAINS AND INTO THE OH VLY/GRTLKS.  GREATEST
NEGATIVE ANOMALIES FOR MAX TEMPS SHOULD BE OVER THE PLAINS AND
VICINITY ON TUE.

RAUSCH

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