THE WEATHER PREDICTION CENTER

COLLEGE PARK, MD


SOUTH AMERICAN MODEL DISCUSSION




SOUTH AMERICA FORECAST DISCUSSION - INTERNATIONAL DESKS
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1139 AM EDT FRI APR 24 2015

GFS DATA AT FTPPRD.NCEP.NOAA.GOV/PUB/DATA/NCCF/COM/GFS/PROD/

MODEL DISCUSSION (VALID FROM APRIL 24 AT 0000 UTC): GLOBAL MODELS
AND ENSEMBLE MEMBERS ARE IN GOOD AGREEMENT ON FORECAST EVOLUTION
OVER THE CONTINENT. SOME DISCREPANCIES ARISE OVER THE OCEANS AFTER
96 HRS. FORECAST CONFIDENCE IS HIGH OVER THE CONTINENT.

THE SUBTROPICAL RIDGE CONTINUES STRONG FOR THE TIME OF THE YEAR.
THE HIGH IS FORECAST TO CENTER IN CENTRAL SOUTH AMERICA ABOUT
10S-15S SLOWLY MEANDERING FROM SOUTHERN PARA EARLY IN THE CYCLE
WEST INTO RONDONIA BY LATE CYCLE. INITIALLY...ENHANCED VENTILATION
WILL INTERACT WITH ATLANTIC ITCZ TO ENHANCE ACTIVITY ALONG THE
NORTH COAST OF BRASIL. EXPECTING MAXIMA OF 20-45MM/DAY THROUGH
EARLY SATURDAY DECREASING AFTERWARDS. MOST OF THE STRONGEST
CONVECTION WILL EXTEND ACROSS CENTRAL TROPICAL SOUTH AMERICA AND
GRADUALLY BECOME ENHANCED ACROSS WESTERN EQUATORIAL SOUTH AMERICA.
MAXIMA WILL BE IN THE ORDER OF 20-35MM/DAY...WITH ISOLATED LARGER
AMOUNTS WEST 65W. ISOLATED DIURNAL CONVECTION IS ALSO EXPECTED IN
COASTAL ECUADOR WITH MAXIMA IN THE ORDER OF 15-25MM/DAY EARLY IN
THE CYCLE...DECREASING TO 05-10MM/DAY INTO SATURDAY/SUNDAY. AS THE
UPPER HIGH RELOCATES TO THE WEST AND INSTABILITY INCREASES
SIMULTANEOUSLY...EXPECTING AN ACTIVATION OF ANDEAN CONVECTION INTO
EARLY NEXT WEEK. THIS WILL LEAD DIURNAL MAXIMA OF 10-15MM/DAY IN
THE CENTRAL/NORTHERN PERUVIAN ANDES.

BROAD UPPER TROUGH PATTERN CONTINUES OVER THE SOUTHEASTERN PACIFIC
WHILE A RIDGE IS FORECAST TO DOMINATE THE SOUTHERN CONE. THE RIDGE
WILL MEANDER EASTWARD VERY SLOWLY. UNDER THIS PATTERN EXPECTING
TRAINS OF FRONTS TO CONSTRAIN TO EXTREME SOUTHERN CHILE WHILE
MOVING EAST-SOUTHEASTWARD. HIGHEST RAINFALL AMOUNTS ARE EXPECTED
THROUGH EARLY SATURDAY TO REACH MAXIMA OF 15-20MM/DAY ACROSS THE
AYSEN REGION IN CHILE. AMOUNTS ARE TO DECREASE AFTER. EXPECTING AN
INCREASE IN ACTIVITY ACROSS NORTHERN PATAGONIA DURING SUNDAY INTO
EARLY NEXT WEEK. HOWEVER...LIMITED MOISTURE WILL LIMIT RAINFALL
AMOUNTS. EXPECTING ALSO AN ACTIVATION OF CONVECTION IN WESTERN
PARAGUAY/NORTHWESTERN ARGENTINA AS EAST-NORTHEASTERLIES DEVELOP.
EXPECTING ISOLATED MAXIMA TO INCREASE TO 15-25MM/DAY BY SUNDAY
INTO MONDAY.

COLD FRONT OFF THE COAST OF BRASIL IS FORECAST TO MEANDER
NORTHWARD TO EXTEND INTO SOUTHERN ESPIRITO SANTO BY SATURDAY
EVENING...AND THEN STALL OVER NORTHERN ESPIRITO SANTO AFTERWARDS.
THIS FRONT IS SUSTAINING AN ILL-DEFINED SHEAR LINE INTO CENTRAL
BAHIA THROUGH EARLY SATURDAY. ALTHOUGH THE SHEAR LINE IS FORECAST
TO WEAKEN...INTERACTION OF TRADES WITH COASTAL REGIONS WILL
ENHANCE ACCUMULATIONS. EXPECTING MAXIMA OF 10-15MM/DAY THROUGH
EARLY SATURDAY INCREASING GRADUALLY TO MAXIMA OF 25-50MM/DAY
DURING SUNDAY INTO MONDAY...AIDED BY UPPER TROUGH APPROACHING FROM
THE SOUTHWEST. AMOUNTS WILL START DECREASING AFTER MONDAY.

SCHNEIDER...INMET (BRASIL)
CALLE...UNALM (PERU)
CHARPENTIER...DMC (CHILE)
DAVISON/GALVEZ...WPC (USA)




Last Updated: 1139 AM EDT FRI APR 24 2015