Prognostic Meteorological Discussion
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FXUS02 KWBC 271552
PMDEPD

EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1151 AM EDT THU JUL 27 2017

VALID 12Z SUN JUL 30 2017 - 12Z THU AUG 03 2017

...PATTERN OVERVIEW...

FROM THE MULTI-DAY MEAN PERSPECTIVE GUIDANCE HAS BEEN CONSISTENT
IN SHOWING A BUILDING WRN U.S. RIDGE LATE WEEK INTO THE WEEKEND
WITH THIS RIDGE THEN PERSISTING THROUGH AT LEAST NEXT THU, PERHAPS
EVEN BECOMING A BIT STRONGER BY THAT TIME.  DOWNSTREAM TROUGHING
HAS ALSO BEEN A CONSISTENT FEATURE BUT THE CHARACTER OF THIS
TROUGH ON ANY PARTICULAR DAY HAS VARIED DEPENDING ON INDIVIDUAL
FEATURES THAT HAVE TENDED TO DISPLAY RELATIVELY LOW
PREDICTABILITY.  THESE FEATURES INCLUDE AN INITIAL SMALL SCALE
SHRTWV/UPR LOW SETTLING TOWARD THE EAST COAST DURING THE SHORT
RANGE PERIOD AND THEN VARIOUS PIECES OF NERN PAC/GULF OF ALASKA
ENERGY PROGRESSING ACROSS SRN CANADA.


...GUIDANCE EVALUATION AND PREFERENCES...

00Z/06Z GUIDANCE HAS MADE A PRONOUNCED ADJUSTMENT TOWARD A SLOWER
TROUGH/UPR LOW REACHING THE MID ATLC BY THE START OF THE PERIOD
SUN, ALONG WITH MUCH GREATER SEPARATION FROM A CLOSED LOW/TROUGH
OVER ERN CANADA.  AS A RESULT THE LATEST MAJORITY CLUSTER HOLDS
ONTO SFC LOW PRESSURE OFF THE MID ATLC COAST FOR A CONSIDERABLY
LONGER TIME THAN IN PRIOR RUNS.  THE ORIGINATING FEATURE NOW NEAR
THE U.S.-CANADIAN BORDER IS QUITE SMALL, WHICH MAKES IT DIFFICULT
FOR GUIDANCE TO RESOLVE ITS EVOLUTION PROPERLY VERY FAR IN
ADVANCE.  ONCE THIS TROUGH LIFTS AWAY THERE IS RELATIVE AGREEMENT
THAT TROUGHING SHOULD SETTLE INTO THE GREAT LAKES REGION BY NEXT
WED-THU.  DUE TO GUIDANCE CHANGING FOCUS ON WHICH BUNDLE OF SHRTWV
ENERGY WILL LEAD TO THIS TROUGHING, THE LATE PERIOD NRN STREAM
AMPLIFICATION IS ESSENTIALLY OCCURRING ABOUT TWO DAYS LATER THAN
WAS FCST BY CONSENSUS TWO DAYS AGO.  SEPARATE ENERGY ROUNDING THE
WRN RIDGE AND REACHING THE PLAINS/MS VALLEY IN THE LATTER HALF OF
THE PERIOD WILL RELOAD THE MORE DIFFUSE SRN PART OF THE OVERALL
ERN TROUGH.  HGTS OVER THE SERN U.S. SHOULD RISE WITH TIME AS A
STRONG RIDGE OVER THE ATLC GRADUALLY BUILDS WWD.

IN ORDER TO DEPICT THE LATEST CONSENSUS EVOLUTION TO A MORE
REFINED EXTENT THAN THE MEANS WHILE DOWNPLAYING SPECIFICS OF ANY
INDIVIDUAL MODEL RUN, THE SUN TO EARLY TUE PERIOD STARTED WITH AN
OPERATIONAL MODEL BLEND CONSISTING OF THE 06Z GFS/00Z ECMWF AND TO
A SLIGHTLY LESSER EXTENT 00Z UKMET/CMC.  AFTER EARLY SUN MODEL
DETAILS DIVERGED ENOUGH TO REQUIRE A FAIRLY RAPID TRANSITION
TOWARD MOSTLY THE 06Z GEFS/00Z ECMWF MEANS AND CONTINUITY.


...WEATHER HIGHLIGHTS...

ABUNDANT MONSOONAL MOISTURE ALONG WITH MULTIPLE IMPULSES ALOFT
TRACKING AROUND THE CORE OF THE STRONG WRN U.S. RIDGE WILL
MAINTAIN THE POTENTIAL FOR AREAS OF HEAVY CONVECTION THAT SHOULD
BE MOST LIKELY FROM THE SRN HALF OF THE ROCKIES EWD INTO THE
PLAINS.  ALBEIT WITH SOMEWHAT LOWER 5-DAY RAINFALL TOTALS EXPECT
SOME OF THIS ACTIVITY TO EXTEND INTO THE SOUTHWEST AS WELL.
CONFIDENCE IN SPECIFICS FOR TIMING/LOCATION OF HEAVIEST CONVECTION
WITHIN THE FAVORED AREA WILL LIKELY BE LOW UNTIL WELL INTO THE
SHORT RANGE TIME FRAME.  WAVY FRONT EXTENDING OFF THE SERN/GULF
COASTS SHOULD PROVIDE A FOCUS FOR PERIODS OF HEAVY RAIN ESPECIALLY
OVER NRN-CNTRL FLORIDA WITH SOME CONVECTION ALSO POSSIBLE AT TIMES
ALONG THE GULF/SERN COASTS AND SRN FL.  ONE OR MORE FRONTAL
BOUNDARIES AFFECTING THE NRN TIER MAY BRING SOME EPISODES OF
CONVECTION OF VARYING INTENSITY BUT SO FAR WITH LESS OF A SIGNAL
FOR HEAVY AMOUNTS COMPARED TO AREAS HIGHLIGHTED ABOVE.

THE WRN RIDGE ALOFT WILL SUPPORT WELL ABOVE NORMAL TEMPS FROM
INLAND PARTS OF NRN-CNTRL CA AND PAC NW INTO THE NRN ROCKIES, WITH
MULTIPLE DAYS OF PLUS 5-15F ANOMALIES.  ON THE OTHER HAND HIGHS
WILL BE BELOW NORMAL, LOCALLY BY AT LEAST 10F ON ONE OR MORE DAYS,
WHERE THERE IS SHWR/TSTM ACTIVITY OVER THE FOUR CORNERS STATES
INTO THE CNTRL-SRN PLAINS.  OVER THE EAST EXPECT MEAN TROUGHING
ALOFT TO MAINTAIN NEAR TO BELOW NORMAL TEMPS FOR A MAJORITY OF THE
PERIOD.

RAUSCH

$$





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