Prognostic Meteorological Discussion
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FXUS02 KWBC 010647
PMDEPD

EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
246 AM EDT MON MAY 01 2017

VALID 12Z THU MAY 04 2017 - 12Z MON MAY 08 2017

...PATTERN OVERVIEW AND GUIDANCE EVALUATION...

WITH INCOMING 00Z MODELS THUS FAR AND THE 00Z GEFS MEAN FOLLOWING
UP ON THE 12Z/18Z CYCLE, THERE IS FINALLY DECENT AGREEMENT AND
CONTINUITY FOR THE DETAILS WITHIN WHAT LOOKS TO BE A VERY
AMPLIFIED AND BLOCKY REGIME HIGHLIGHTED BY A DEEP TROUGH/UPR LOW
EVENTUALLY SETTLING OVER ERN CANADA/NERN U.S., STRONG RIDGE OVER
THE CENTRAL U.S., AND AN AMPLIFYING WEST COAST TROUGH THAT APPEARS
LIKELY TO DEPOSIT A FAIRLY DEEP UPR LOW OVER/NEAR CALIFORNIA.

BY FAR THE GREATEST SPREAD AND RUN TO RUN VARIABILITY HAD EXISTED
FOR THE EVOLUTION OF ERN U.S. UPR TROUGH/CLOSED LOW ENERGY AND
ASSOC SFC SYSTEM.  LATEST MODEL RUNS NOW AGREE FAIRLY WELL THAT AN
UPR LOW SHOULD CLOSE OFF AROUND THE START OF THE PERIOD NEAR THE
CONFLUENCE OF THE OH/MS RIVERS WITH THE UPR LOW MAKING STEADY NEWD
PROGRESS TO THE W OF APLCHNS, REACHING ERN CANADA/NEW ENGLAND BY
THE LATTER HALF OF THE PERIOD.  MAJORITY MODEL CLUSTER IS
SUGGESTING THE UPR LOW WILL BE SUFFICIENTLY DEEP TO SUPPORT A SFC
LOW TRACK W OF THE APLCHNS AS WELL.  WHILE THE 12Z/18Z CYCLE WAS
THE BEST CLUSTERED MODEL/ENSEMBLE MEAN PACKAGE UP TO THAT POINT,
SYSTEM HISTORY LED A SLIGHTLY CONSERVATIVE INITIAL PREFERENCE FOR
AN EVEN MODEL/ENSEMBLE MEAN BLEND AS A STARTING POINT EXCEPT FOR
HIGHER MODEL WEIGHT DAY 3 THU.  BASED ON THE 00Z GUIDANCE IN THUS
FAR, THE FARTHER SEWD SFC LOW TRACK IN THE 12Z ECMWF MEAN IS
LOOKING LESS PROBABLE.

ALONG THE WEST COAST THE GUIDANCE AS A WHOLE HAS BEEN SIGNALING A
MOST LIKELY SCENARIO OF UPR TROUGH ENERGY CONSOLIDATING INTO A
FAIRLY DEEP CLOSED LOW OVER/NEAR SRN CALIFORNIA.  INDIVIDUAL RUNS
HAVE VARIED ON DAY TO DAY DETAILS, WHETHER IN TERMS OF EMBEDDED
CLOSED LOW POSN OR EXACTLY WHEN THE CLOSED LOW WOULD REACH THE SRN
CA VICINITY.  LATEST GFS/ECMWF RUNS AGREE FAIRLY WELL WITH THE
WEAKER MEANS IN PRINCIPLE, AND ONCE THE UPR LOW SETTLES OVER SRN
CA THE OPERATIONAL RUNS DEPICT SOME HGT ANOMALIES EXCEEDING 3
STDEVS BELOW NORMAL.  AT LEAST THROUGH THE 12Z/18Z CYCLES THERE
WAS STILL ENOUGH UNCERTAINTY TO FAVOR A MODEL/ENSEMBLE MEAN BLEND.

RECENT TRENDS TOWARD A STRONGER CNTRL U.S. RIDGE ARE NOT AS
PRONOUNCED AS SEEN PREVIOUSLY BUT THERE IS STILL A TREND OVER THE
PAST DAY TOWARD SLOWER PROGRESSION OF LEADING HGT FALLS/SFC FRONT
INTO THE NWRN STATES.

THE 18Z GFS/GEFS MEAN AND 12Z ECMWF/ECMWF MEAN PROVIDED THE INPUT
FOR THE CURRENT FCST PACKAGE.  OPERATIONAL WEIGHT WAS 70 PCT DAY 3
THU AND 50/50 MODELS/MEANS THEREAFTER.


...WEATHER HIGHLIGHTS...

BASED ON LATEST CONSENSUS FOR THE STRONG STORM FCST TO AFFECT THE
ERN STATES, EXPECT THE BEST PROBABILITY FOR SIGNIFICANT RNFL FROM
PARTS OF THE OH VLY/ERN GRTLKS INTO THE NORTHEAST.  OVER NEW
ENGLAND A PERIOD OF STRONG ATLC INFLOW MAY ENHANCE ACTIVITY.
MONITOR SPC OUTLOOKS FOR LATEST INFO REGARDING POTENTIAL FOR
STRONG TO SEVERE CONVECTION IN THE WARM SECTOR.  MOST OF THE
HEAVIEST PRECIP IS LIKELY TO DEPART FROM THE NORTHEAST EARLY IN
THE WEEKEND BUT PERSISTENT UPR TROUGH/CLOSED LOW IN THE VICINITY
SHOULD MAINTAIN UNSETTLED WEATHER OVER THE NORTHEAST FOR MOST OF
THE PERIOD.  DEPENDING ON DEPTH OF THE UPR SYSTEM AND HOW MUCH
COLD AIR EVENTUALLY FEEDS IN FROM CANADA, THERE MAY BE POCKETS OF
HIGHER ELEV SNOW.  ALSO EXPECT SOME AREAS TO SEE WINDY CONDS FOR A
PERIOD OF TIME.

UPR TROUGH/LEADING FRONTAL SYSTEM INITIALLY HEADING TOWARD THE
WEST COAST WILL BRING AREAS OF MOSTLY LGT-MDT PRECIP TO THE NWRN
STATES.  AS THE UPR TROUGH AMPLIFIES AND LIKELY BRINGS A CLOSED
UPR LOW TO CA, THERE SHOULD BE INCREASING COVERAGE OF SCT PRECIP
OVER THE WEST ALONG WITH SOME DIURNALLY FAVORED ACTIVITY OVER THE
ROCKIES.

THROUGH LATE WEEK MUCH OF THE WEST WILL SEE VERY WARM TO HOT TEMPS
WITH WIDESPREAD PLUS 10-20F ANOMALIES.  SOME DAILY RECORD WARM
LOWS ARE PSBL WHILE RECORD HIGHS SHOULD BE LESS NUMEROUS BUT NOT
OUT OF THE QUESTION.  THE UPR TROUGH ARRIVING OVER THE WEST COAST
WILL BRING A PRONOUNCED COOLING TREND TO THE WEST COAST STATES AND
THEN THE INTERIOR WEST WHILE THE WARMTH EXTENDS INTO THE HIGH
PLAINS.  MEANWHILE THE EAST WILL SEE BELOW TO WELL BELOW NORMAL
TEMPS FOR MULTIPLE DAYS, THOUGH WITH MODERATION TOWARD NORMAL OVER
THE SOUTH BY SUN-MON.

RAUSCH

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