THE WEATHER PREDICTION CENTER

COLLEGE PARK, MD


EXTENDED FORECAST DISCUSSION




EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
103 AM EDT MON MAY 04 2015

VALID 12Z THU MAY 07 2015 - 12Z MON MAY 11 2015

...OVERVIEW AND GUIDANCE PREFERENCES...

MODELS AND ENSEMBLES CONTINUE TO FORECAST RIDGING IN THE NORTHEAST
CONUS AS WELL AS NW CANADA... WHICH FAVORS TROUGHING IN THE
SOUTHWESTERN STATES THAT WILL SLOWLY LIFT OUT ONTO THE PLAINS IN
ABOUT A WEEK. OFF THE SOUTHEAST/FLORIDA COAST... A 'LOST'
UPPER/SURFACE LOW -- PERHAPS SUBTROPICAL... BUT PROBABLY MINOR --
WILL MEANDER JUST OFF THE COAST UNDERNEATH THE RIDGE.

THE DETERMINISTIC MODELS HAVE MOSTLY FALLEN WITHIN THE ENSEMBLE
SPREAD OVER THE PAST SEVERAL DAYS AND THAT CONTINUES WITH THEIR 12
OR 18Z/03 RUNS... ON WHICH THIS FORECAST WAS BASED. THE ECMWF HAS
BEEN CURIOUSLY QUICKER THAN THE CONSENSUS AND THE BLOCKY NATURE OF
THE FLOW SEEMS TO ARGUE FOR A BIT SLOWER RATHER THAN QUICKER PACE.
18Z GFS SEEMED LIKE A REASONABLE SOLUTION AND USED IT FOR SOME
DETAILS ALONG WITH THE 18Z GEFS MEAN AND 12Z ECENS MEAN. PESKY
DETAILS YET TO BE WORKED OUT INCLUDE THE FRONTAL
PLACEMENT/STRENGTH IN THE NORTHEAST.... WHICH WILL AFFECT SURFACE
TEMPERATURES... AND TIMING OF THE NEXT TROUGH INTO THE PAC NW NEXT
SUN/MON.

OFF THE SE COAST... RECENT GFS RUNS AND ENSEMBLE MEANS --
GEFS/ECENS/CANADIAN -- FAVOR A BIT WESTWARD POSITION OF THE SFC
LOW WHILE THE 12Z/03 ECMWF/CANADIAN GLOBAL/UKMET LIE FARTHER EAST.
WEAK STEERING FLOW MEANS NOTHING IS REALLY FAVORED AT THIS
POINT... BUT STAYING WITH THE ENSEMBLES SEEMS PRUDENT FOR NOW.


...SENSIBLE WEATHER HIGHLIGHTS...

PRECIP FOCUS WILL LIE NEAR AND JUST DOWNSTREAM OF THE UPPER LOW IN
THE WEST... FROM THE GREAT BASIN THROUGH MY/CO AND OVER MUCH OF
THE PLAINS FROM TEXAS NORTHWARD. ECMWF ENSEMBLES WERE GENERALLY A
BIT WETTER THAN THE GFS AND GEFS MEMBERS OVER TX/OK/KS... BUT ALL
STILL INDICATE WIDESPREAD MODEST RAINS. LESSER PRECIP IS LIKELY IN
THE NORTHEAST/MID-ATLANTIC AS WELL AS SOUTHERN CALIFORNIA... WHILE
ZERO PRECIP LOOKS PROBABLE OVER SE CA INTO S AZ/NM. ULTIMATE TRACK
OF THE ATLANTIC LOW WILL DETERMINE HOW MUCH... IF ANY... PRECIP
WILL FALL OVER LAND. AT THE LEAST... ENOUGH INSTABILITY SHOULD
EXIST AROUND ITS CIRCULATION TO HELP INITIATE SOME ISOLATED OR
EVEN SCATTERED SHOWERS/CONVECTION.

TEMPERATURES WILL BE MILD/WARM IN THE EAST THANKS TO RIDGING...
WITH MANY PLACES REACHING THEIR HIGHEST TEMPS YEAR-TO-DATE. THE
WEST WILL BE RATHER COOL... ESPECIALLY DAYTIME MAXES... OWING TO
ABUNDANT CLOUDS AND SHOWERS.


FRACASSO





Last Updated: 103 AM EDT MON MAY 04 2015