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FXUS02 KWNH 250643
PREEPD

PRELIMINARY EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
242 AM EDT MON JUL 25 2016

VALID 12Z THU JUL 28 2016 - 12Z MON AUG 01 2016

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

GUIDANCE REMAINS IN DECENT AGREEMENT FOR THE GENERAL FLOW
EVOLUTION OUT TO DAY 7 MON BUT WITH EMBEDDED DETAIL UNCERTAINTIES
THAT WILL TAKE MORE TIME TO BE RESOLVED.  NERN PAC TROUGH ENERGY
IS SCHEDULED TO REACH WRN CANADA AND THE NRN HALF OF THE WEST
COAST BY DAY 5 SAT.  THE CANADIAN PART OF THE TROUGH SHOULD
CONTINUE EWD AND PUSH A LEADING FRONT INTO THE NRN PLAINS BY EARLY
NEXT WEEK WHILE TRAILING ENERGY HOLDS A MEAN TROUGH AXIS NEAR THE
WEST COAST.  WITH THE ARRIVAL OF THE NERN PAC TROUGH EXPECT THE
LATE WEEK GREAT BASIN/SOUTHWEST RIDGE TO WEAKEN SOMEWHAT AND DRIFT
EWD.  THE DOWNSTREAM MEAN TROUGH ADVERTISED FOR THE MS VLY FROM
THU INTO SAT SHOULD HEAD INTO THE NORTHEAST/MID ATLC BY LATE IN
THE PERIOD.

DIFFS SEEN IN RECENT OPERATIONAL MODEL RUNS HINT AT THE WIDER
SPECTRUM OF ENSEMBLE MEMBERS FOR SHRTWV DETAILS WITHIN BOTH
TROUGHS OF INTEREST.  AT LEAST NEAR THE CONSENSUS TROUGH AXIS
THERE SEEMS TO BE GREATER AMPLITUDE SPREAD FOR THE MS VLY
TROUGH... WHICH LEADS TO A WIDE VARIETY OF POSSIBILITIES FOR ONE
OR MORE SFC WAVES FROM THE PLAINS INTO THE NORTHEAST/WRN ATLC.
THE 12Z ECMWF AND NEW 00Z UKMET ARE BOTH ON THE DEEPER SIDE OF THE
ENVELOPE WITH THE CORE OF THE UPR TROUGH AND ARE RELATIVELY
DEEP/NWD WITH A SFC LOW TRACKING INTO THE GRTLKS.  THERE IS SOME
ENSEMBLE SUPPORT FOR WEAKER LOW PRES REACHING THE ERN GRTLKS
THOUGH.  CLUSTERING IS FAIRLY ROBUST FOR THE ARRIVING NERN PAC
TROUGH INTO DAY 5 SAT BEFORE SOLNS DIVERGE FOR SOME OF THE
DETAILS.  IN PRINCIPLE THE 12Z/18Z GFS RUNS WERE SOMEWHAT CLOSER
TO THE ENSMEANS FOR TROUGH EVOLUTION VERSUS THE 12Z ECMWF THAT HAD
A MORE CLOSED SYSTEM.

THIS PATTERN CONTINUES TO SUPPORT A MODEL/ENSEMBLE BLEND APPROACH
TO REFLECT THE MOST SIMILAR ASPECTS OF GUIDANCE AND AS MUCH
CONTINUITY AS PSBL WHILE DOWNPLAYING LESS CONFIDENT SMALLER SCALE
DETAILS.  WEIGHTING FOR THE UPDATED FCST IS ABOUT 2/3 TOWARD THE
12Z-18Z GFS/12Z ECMWF RELATIVE TO THE 18Z GEFS/12Z ECMWF MEANS DAY
3 FRI AND ABOUT 2/3 TOWARD THE MEANS LATE.


...WEATHER HIGHLIGHTS/THREATS...

A COUPLE WAVY FRONTAL BOUNDARIES FROM THE PLAINS INTO THE EAST
ALONG WITH SHRTWVS CARRIED ALONG BY FLOW ALOFT WILL CONTRIBUTE TO
AREAS OF ORGANIZED CONVECTION... SOME OF WHICH MAY BE HEAVY AND
STRONG TO SEVERE.  UNCERTAINTY IN DETAILS ALOFT AND YET TO BE
DETERMINED MESOSCALE INFLUENCES CONTINUE TO MAKE IT DIFFICULT TO
PINPOINT MOST FAVORED AREAS FOR HVY AND STRONG CONVECTION.
CURRENTLY THE MOST OVERLAP IN GUIDANCE FOR HVY RNFL POTENTIAL
APPEARS TO BE FROM THE MID-LWR MS VLY INTO THE MID ATLC/NORTHEAST.
 CONSULT SPC OUTLOOKS FOR MORE INFO ON SEVERE THREATS AS DETAILS
BECOME CLEARER IN COMING DAYS.  MONSOONAL CONVECTION INITIALLY
FOCUSED OVER THE SRN ROCKIES IS LIKELY TO EXPAND IN COVERAGE
DURING THE PERIOD.

THE UPR TROUGH SETTLING NEAR THE WEST COAST BY SAT-MON WILL BRING
WRN U.S. TEMPS TO WITHIN A FEW DEGS OF NORMAL AFTER FAIRLY BROAD
COVERAGE OF PLUS 10-15F ANOMALIES FOR HIGHS THU-FRI WHEN ISOLD
DAILY RECORDS MAY BE PSBL.  WITH SOMEWHAT LESSER ANOMALIES SOME OF
THE WRN WARMTH WILL REACH THE NRN-CNTRL PLAINS SAT-MON...
REPLACING HIGHS OF 5-10F BELOW NORMAL THU-FRI.  TEMPS WILL
STEADILY MODERATE OVER NRN-CNTRL PARTS OF THE EAST BUT LOCATIONS
FROM THE CAROLINAS INTO GEORGIA SHOULD SEE HIGHS CONSISTENTLY
5-10F ABOVE NORMAL.

RAUSCH

$$





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