EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
126 AM EDT TUE MAY 21 2013

VALID 12Z FRI MAY 24 2013 - 12Z TUE MAY 28 2013



THE MODELS CONTINUE TO FCST 500 MB TROUGHS ALONG BOTH WEST/EAST
COASTS AND A RIDGE OVER THE CENTRAL STATES AND A CLOSED
ANTICYCLONE OVER NORTHERN MEXICO THROUGH THE WEEKEND INTO EARLY
NEXT WEEK...WHEN IT BUILDS INTO TEXAS. THIS FEATURE IN THE 12Z
ECMWF ENSEMBLE MEAN AND 18Z GEFS MEAN BUILDS SO 700 MB TEMP
ANOMALIES AND 500 MB HEIGHT ANOMALIES RUN 1-2 STD DEVIATIONS ABOVE
NORMAL.  THE STABILITY OF THE ANTICYCLONE ALLOWS A WARM AIR MASS
TO GRADUALLY BUILD AND SPREAD OUT OF THE SOUTHERN PLAINS INTO THE
CENTRAL PLAINS NEXT WEEK.

SOUTHERLY FLOW AHEAD OF THE TROUGH AND SFC LOW/WARM FRONT
DEVELOPMENT SHOULD FOCUS PRECIP OVER THE CENTRAL
PLAINS LATE IN THE WEEKEND AND INTO THE NORTHERN PLAINS/MID-UPPER
MS VALLEY/GREAT LAKES EARLY NEXT WEEK WHERE CONVECTION IS LIKELY
AS INDICATED IN THE GEFS/ECMWF ENSEMBLE MEMBERS AND GFS RUNS
WITHIN A LOW-MID LEVEL WARM ADVECTION PATTERN UNDERNEATH UPPER
DIVERGENCE MAXIMA/LOW LEVEL CONVERGENCE MAXIMA.  THE 12Z ECMWF
PRECIP AREAS WERE SOUTH OF THE MAJORITY OF THE ECMWF/GEFS ENSEMBLE
MEMBERS SUN 26 MAY-TUE 28 MAY.

THE CLOSED LOW OVER THE PAC NW WED-FRI IS FCST BY THE
MODEL/ENSEMBLE MEAN MAJORITY TO EJECT NORTH INTO CANADA OVER THE
WEEKEND. ADDITIONAL SHORTWAVE ENERGY DOWNSTREAM FROM THE EAST
PACIFIC RIDGE REINFORCES
THE WEST COAST TROUGH AFTERWARD.  TELECONNECTIONS FROM THE CLOSED
500 MB HIGH NORTH OF HAWAII NEAR 30N AND THE CLOSED 500 MB LOW
OVER THE ALEUTIANS POINT TOWARDS A PERSISTENT WEST COAST TROUGH.

IN THE EAST... THE MODELS/ENSEMBLES SHOW AN UPPER TROUGH MOVING
FROM THE GREAT LAKES AND ACROSS THE NORTHEAST OVER THE
WEEKEND....THEN DEPARTING EARLY NEXT WEEK AS UPSTREAM RIDGING IN
THE NORTHERN PLAINS BUILDS INTO THE UPPER MS VALLEY MON AND THEN
THE UPPER GREAT LAKES ON TUE.  THIS SETS THE STAGE FOR AN
EARLY-MID WEEK WARMING TREND FOR THE OH VALLEY/TN VALLEY/UPPER
LAKES.   

MANUAL PROGS USED A BLEND OF THE 18Z GEFS MEAN/12Z ECMWF ENSEMBLE
MEAN WITH LESS WEIGHTING ON THE
12Z ECMWF AND 18Z GFS HEIGHTS/SEA LEVEL PRESSURES...AS WELL AS THE
TEMPERATURES/PROBABILITY OF PRECIP FCSTS.  THE 18Z GFS CONTINUES
TO SHOW A FASTER INLAND DEPARTURE OF THE WEST TROUGH INTO THE
GREAT BASIN...WITH THE 18Z GEFS MEAN/12Z ECMWF MEAN SHOWING BETTER
AGREEMENT ON A SLOWER MOTION.


PETERSEN