Preliminary Forecasts
Issued by NWS

Home | Current Version | Previous Version | Text Only | Print | Product List | Glossary On
Versions: 1 2 3 4 5 6 7 8 9 10 11 12 13 14
905
FXUS02 KWNH 260635
PREEPD

PRELIMINARY EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
235 AM EDT TUE JUL 26 2016

VALID 12Z FRI JUL 29 2016 - 12Z TUE AUG 02 2016

...OVERVIEW...

INITIAL NERN PAC TROUGH ENERGY WILL AMPLIFY AS IT HEADS TOWARD WRN
CANADA AND THE PAC NW DURING FRI-SUN.  THE CORE OF THIS TROUGH
SHOULD THEN CONTINUE ACROSS SRN CANADA THROUGH TUE...HELPING TO
PUSH A COLD FRONT INTO THE NRN PLAINS.  SOME DEGREE OF RESIDUAL
TROUGHING SHOULD PERSIST ALONG THE WEST COAST.  AHEAD OF THIS
TROUGH EXPECT THE RIDGE OVER THE GREAT BASIN/SOUTHWEST AS OF EARLY
FRI TO MOVE STEADILY EWD INTO THE PLAINS.  DOWNSTREAM A TROUGH
ALIGNED OVER THE MIDWEST WILL PROGRESS INTO THE NORTHEAST.


...GUIDANCE EVALUATION/UNCERTAINTY ASSESSMENT...

ACROSS THE ERN PAC AND WRN NOAM A MODEL/ENSEMBLE MEAN BLEND LOOKS
REASONABLE INTO DAY 5 SUN WITH SOME LINGERING DETAIL OR TIMING
DIFFS AS TROUGHING AMPLIFIES INTO THE WEST COAST.  IN SOME
RESPECTS GUIDANCE ACTUALLY LOOKS A LITTLE MORE SIMILAR BY EARLY
SUN THAN IN THE TWO DAYS LEADING UP TO THAT TIME.  AFTER EARLY SUN
GUIDANCE BEGINS DIVERGING IN RESPONSE TO ISSUES THAT DEVELOP WITH
UPSTREAM BERING SEA/ALASKA/NERN PAC FLOW.  TO VARYING DEGREES
THERE IS DECENT AGREEMENT THAT THIS UPSTREAM FLOW SHOULD BE MORE
PROGRESSIVE THAN DEPICTED IN 12Z/18Z GFS AND GEFS MEAN RUNS...
RESULTING IN MORE SRN CANADA PROGRESSION OF THE LEADING SYSTEM
THAN DEPICTED BY THE 18Z GFS/GEFS MEAN IN PARTICULAR.  THE
GFS/GEFS SCENARIO ACROSS SRN CANADA AND NRN TIER CONUS LATE IN THE
PERIOD REPRESENTS A SLOWER TREND FROM 24 HRS AGO WHEN THOSE SOLNS
WERE MORE SIMILAR TO OTHER GUIDANCE.  BASED ON MODEL/ENSEMBLE
SPREAD THROUGH THE 12Z/18Z CYCLE AND DIFFS IN NEW 00Z SOLNS THUS
FAR IT APPEARS THE BERING SEA/NERN PAC WILL BE A SIGNIFICANT
SOURCE OF UNCERTAINTY FOR THE WEST COAST FCST IN COMING DAYS.

ACROSS THE ERN HALF OF THE COUNTRY THE PERIOD STARTS WITH
UNUSUALLY LOW CONFIDENCE FOR A DAY 3 FCST AS SUBTLE DIFFS WITHIN
THE E-CNTRL U.S. TROUGH LEAD TO SIGNIFICANT SPREAD AT THE SFC.
THESE DIFFS ARISE IN THE LATTER HALF OF THE SHORT RANGE PERIOD.
IT APPEARS THERE IS SOME MID LVL SUPPORT FOR A LEADING WAVE NEAR
THE EAST COAST IN RESPONSE TO SHORT RANGE ENERGY LIFTING OUT OF
THE LWR MS VLY AND CAPTURED BY FLOW AHEAD OF THE MEAN TROUGH.
UPSTREAM ENERGY ORIGINATING FROM THE NORTHWEST MAY SUPPORT ANOTHER
WAVE FARTHER WWD.  AT THE VERY LEAST PREFER TO LEAN AWAY FROM
SPECIFICS OF RECENT ECMWF RUNS.  IN SPITE OF RELATIVE CONSISTENCY
OF THE PAST THREE RUNS THROUGH 12Z/25... DEVELOPMENT SFC/ALOFT
ACROSS THE GRTLKS LOOKS OVERDONE.  HOWEVER ECMWF MEAN RUNS HAVE
BEEN CONSISTENT IN DEPICTING A MORE MODEST WAVE CROSSING THE LWR
GRTLKS.  IN THE INTEREST OF MAINTAINING CONTINUITY WHILE WAITING
FOR STRONGER CONFIRMATION OF A CONFIDENT ALTERNATE SCENARIO...
PREFER TO MAINTAIN A FCST THAT LEANS CLOSEST TO THE ECMWF MEAN FOR
THE TRAILING WAVE.  A MORE GENERAL COMPROMISE AMONG GUIDANCE
APPEARS REASONABLE FOR THE LEADING EAST COAST WAVE DURING THE
FIRST HALF OF THE PERIOD.  CONSULT THE MODEL DIAGNOSTIC DISCUSSION
PMDHMD FOR INFO/PREFS REGARDING NEW 00Z GUIDANCE UP TO 12Z FRI.

IN ORDER TO MESH THE DIFFERING PREFS OVER EACH AREA OF INTEREST...
THE FCST BLEND INCLUDED HIGHEST WEIGHTING TOWARD THE 12Z ECMWF
MEAN WITH SMALLER 12Z ECMWF AND 18Z GFS/GEFS MEAN COMPONENTS
THROUGH DAY 5 SUN.  LATE PERIOD PREFS FAVORED ADJUSTING THE BLEND
TOWARD A 50/30/20 ECMWF MEAN/NAEFS MEAN/ECMWF SOLN.


...SENSIBLE WEATHER HIGHLIGHTS...

UNCERTAINTY IN SPECIFICS OVER THE EAST FROM THE START OF THE FCST
PERIOD ONWARD CONTINUES TO CAUSE DIFFICULTY IN DETERMINING
COVERAGE/INTENSITY OF RNFL OVER SOME AREAS... ESPECIALLY OVER THE
NRN THIRD OF THE EAST.  THERE APPEARS TO BE SOMEWHAT BETTER
CONSISTENCY IN SIGNALS FOR POTENTIAL OF LOCALLY HEAVIER ACTIVITY
FROM THE LWR MS VLY/CNTRL GULF COAST IN ASSOC WITH A MID LVL
WEAKNESS AND EXTENDING NEWD TOWARD THE WAVY FRONTAL BNDRY
AFFECTING AREAS FARTHER NWD.  IMPULSES CARRIED WITHIN NWLY FLOW
ALOFT MAY SUPPORT ONE OR MORE ORGANIZED AREAS OF CONVECTION OVER
THE PLAINS DURING THE FIRST HALF OF THE PERIOD.  COLD FRONT
REACHING THE NRN PLAINS EARLY NEXT WEEK COULD SUPPORT A PERIOD OF
SHWRS/TSTMS.  MEANWHILE EXPECT DIURNAL CONVECTION OVER THE
SOUTHWEST/FOUR CORNERS STATES TO INCREASE IN COVERAGE/INTENSITY AS
THE INITIAL WRN U.S. RIDGE WEAKENS/MOVES EWD.

THE WEST WILL BE ON THE HOT SIDE FRI WITH FAIRLY BROAD COVERAGE OF
HIGHS 10-15F ABOVE NORMAL.  A FEW DAILY RECORDS FOR HIGHS OR WARM
LOWS MAY BE PSBL.  ARRIVAL OF THE WEST COAST TROUGH ALOFT WILL
BRING A RAPID COOLING TREND WITH MOST HIGHS A FEW DEGS ON EITHER
SIDE OF NORMAL SUN-TUE.  SOME OF THE WRN HEAT WILL SPREAD INTO THE
NRN PLAINS AHEAD OF THE FRONT REACHING THE AREA BY MON-TUE.
EXPECT THE CAROLINAS AND GA/NRN FL TO BE PERSISTENTLY WARM DURING
THE PERIOD WITH TEMPS AVERAGING SEVERAL DEGS ABOVE NORMAL.  ISOLD
RECORD WARM LOWS ARE PSBL ON ONE OR MORE DAYS.

RAUSCH

$$





USA.gov is the U.S. government's official web portal to all federal, state and local government web resources and services.