EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
143 AM EDT WED MAY 22 2013

VALID 12Z SAT MAY 25 2013 - 12Z WED MAY 29 2013



THE MODELS CONTINUE TO FCST 500 MB TROUGHS ALONG BOTH WEST/EAST
COASTS TO DRIFT SLOWLY EAST IN A STABLE PATTERN OVER THE WEEKEND
AND EARLY NEXT WEEK.  A DEEP LAYER RIDGE RIDGE DRIFTS EAST OVER
THE CENTRAL STATES AND A CLOSED ANTICYCLONE PERSISTS OVER NORTHERN
MEXICO AND BUILDS EAST ACROSS INTO TEXAS INTO THE LOWER MS VALLEY
BY WED 29 MAY.  700 MB TEMP ANOMALIES AND 500 MB HEIGHT ANOMALIES
RUN 1-2 STD DEVIATIONS ABOVE NORMAL FROM THE ECMWF ENSEMBLE MEAN
AND GEFS MEAN.  THE STABILITY OF THE ANTICYCLONE ALLOWS A WARM AIR
MASS TO GRADUALLY BUILD AND SPREAD OUT OF THE SOUTHERN PLAINS INTO
THE CENTRAL PLAINS...WITH THE WARM FRONT CONTINUING NORTH ACROSS
THE UPPER MS VALLEY AND LAKES 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 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.  THE
TROUGH MOVES SLOWLY INLAND IN THE MIDDLE OF THE WEEK, FORCED BY A
STRONG WEST-EAST IN CONFLUENT FLOW MOVING EAST AS THE
ANTICYCLONE/CYCLONE COUPLET OVER THE CENTRAL PACIFIC MOVE SLOWLY
EAST IN TANDEM.

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 00Z GFS SHOWS A
FASTER INLAND DEPARTURE OF THE WEST TROUGH INTO THE
GREAT BASIN/ROCKIES...WITH THE 18Z GEFS MEAN/12Z ECMWF MEAN
SHOWING BETTER AGREEMENT ON A SLOWER MOTION.
A BLEND OF THE MEANS WAS USED TO MITIGATE DIFFERENCES IN AMPLITUDE
AMONG THE MEAN SOLUTIONS.

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 A COLD
WEEKEND OVER THE NORTHEAST AND THEN A EARLY-MID WEEK WARMING TREND
FOR THE OH VALLEY/TN VALLEY/UPPER LAKES.  


PETERSEN