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Extended Forecast Discussion
 
(Latest Discussion - Issued 1554Z Jul 26, 2017)
 
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Abbreviations and acronyms used in this product
 
Geographic Boundaries -  Map 1: Color  Black/White       Map 2: Color  Black/White


EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1154 AM EDT WED JUL 26 2017

VALID 12Z SAT JUL 29 2017 - 12Z WED AUG 02 2017

...OVERVIEW...


RIDGING IS FORECAST TO BUILD INTO THE INTERIOR WEST NEXT WEEK AS
TROUGHING DIPS INTO THE EASTERN STATES. AFTER A ROBUST LOW
PRESSURE SYSTEM DEPARTS THE MID-ATLANTIC AND NEW ENGLAND WATERS ON
SATURDAY, A SURFACE FRONT WILL SETTLE ALONG THE GULF COAST AS A
NORTHERN STREAM SYSTEM THROUGH CANADA DRAGS ANOTHER COLD FRONT
THROUGH THE HIGH PLAINS AND UPPER MIDWEST INTO THE GREAT LAKES AND
NORTHEAST THROUGH THE PERIOD.


...GUIDANCE EVALUATION/PREFERENCES...

MODELS AND ENSEMBLES REMAIN IN GOOD OVERALL AGREEMENT OVER THE
CONUS WITH THE SYNOPTIC PATTERN AND A GENERAL MODEL BLEND OFFERED
A GOOD STARTING POINT. THIS INCLUDED THE GFS/ECMWF/UKMET/CANADIAN
TO START, WHICH SUPPORTS A RATHER DEEP (FOR JULY) NON-TROPICAL LOW
PRESSURE CENTER EAST OF ATLANTIC CITY (NEAR THE LOWEST PMSL VALUES
PER THE CFSR CLIMATOLOGY (1979-PRESENT) FOR THIS TIME OF YEAR).
AFTER SATURDAY, REMOVED THE UKMET FOLLOWED BY THE CANADIAN AS THEY
DIFFERED FROM THE ENSEMBLE CONSENSUS AROUND THE EDGES OF THE CONUS
AND THEN THE GFS RUNS BY NEXT MONDAY AS THE 00Z/06Z RUNS TOOK THE
REMNANTS OF CURRENT HURRICANE HILARY NORTHWARD TOWARD THE OFFSHORE
WATERS OF SOUTHERN CALIFORNIA. LATEST NHC TRACK MAINTAINS THE
CONSENSUS OF A WESTWARD TURN ALONG 20N. BY NEXT TUE/WED, A BLEND
OF THE ECMWF WITH THE GEFS/ECENS MEANS AND OVERNIGHT CONTINUITY
ROUNDED OUT THE FORECAST AS TROUGHING LINGERED IN THE EAST AS
SUBTROPICAL ATLANTIC UPPER RIDGING ATTEMPTS TO BUILD WESTWARD.


...WEATHER HIGHLIGHTS...

THE PRIMARY CONCERNS FOR HEAVY RAINFALL THIS WEEKEND AND INTO
EARLY NEXT WEEK WILL BE FROM THE SOUTHEAST AND NORTHERN FLORIDA TO
THE CENTRAL GULF COAST, WHERE THE TAIL END OF A FRONTAL BOUNDARY
PUSHING OFF THE EAST COAST ON SATURDAY WILL STALL AND SERVE AS A
FOCUS FOR CONVECTION. THE FOUR CORNERS STATES WILL ALSO SEE
PERSISTENT MONSOONAL MOISTURE WHICH SHOULD LEAD TO MULTIPLE DAYS
OF LOCALLY HEAVY SHOWERS AND THUNDERSTORMS (ESPECIALLY IF THERE IS
ANY CONNECTION WITH MOISTURE FROM EASTERN PACIFIC TROPICAL
SYSTEMS). HEAVY RAINFALL COULD ALSO BECOME A THREAT OVER THE
CENTRAL/SOUTHERN HIGH PLAINS BACK TO THE FOOTHILLS DURING THE
FIRST HALF OF NEXT WEEK AS ENERGY DROPPING SOUTHWARD AROUND THE
WESTERN U.S. RIDGE INTERACTS WITH ANOMALOUS MOISTURE ACROSS THE
REGION, BUT THE DETAILS OF THIS FEATURE REMAIN VERY UNCERTAIN.
LOWER LEVEL FLOW OUT OF THE GULF THROUGH THE TX/OK PANHANDLE COULD
SUSTAIN HIGHER MOISTURE LEVELS FOR SEVERAL DAYS. THE GEFS
M-CLIMATE QPF SHOWS THESE PREDICTED RAINFALL VALUES LIE ABOVE THE
99TH PERCENTILE OVER SE CO AND NE NM.

TEMPERATURES SHOULD GENERALLY BE BELOW NORMAL FROM THE MISSISSIPPI
TO THE EAST COAST BENEATH ANOTHER UPPER TROUGH SETTING UP OVER THE
EASTERN HALF OF THE NATION THIS WEEKEND AND EARLY NEXT WEEK.
MEANWHILE, RIDGING BUILDING BACK INTO THE WESTERN U.S. WILL BRING
ABOVE NORMAL TEMPERATURES TO MUCH OF THE WEST, WITH THE EXCEPTION
OF THE FOUR CORNERS REGION, WHERE MONSOONAL CONVECTION SHOULD KEEP
DAYTIME TEMPERATURES CLOSER TO SUMMERTIME AVERAGES.


FRACASSO/GERHARDT