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South American Forecast Discussion
 
(Caution: Version displayed is not the latest version. - Issued 1700Z Apr 22, 2015)
 
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SOUTH AMERICA FORECAST DISCUSSION - INTERNATIONAL DESKS
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
100 PM EDT WED APR 22 2015

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

MODEL DISCUSSION (VALID FROM APRIL 22 AT 0000 UTC): GLOBAL MODELS
AND ENSEMBLE MEMBERS AGREE ON FORECAST EVOLUTION THROUGH THE
CYCLE. DIFFERENCES APPEAR ONLY ON THE POSITION OF SHORT WAVES
AFTER 96-108 HRS. CONFIDENCE IS HIGH THROUGH THE
CYCLE...ESPECIALLY ON THE LARGE SCALE.

BROAD MID-LEVEL RIDGE HAS BUILT OVER THE SOUTHERN CONE AND WILL
SLOWLY PROPAGATE INTO THE SOUTH ATLANTIC AS THE CYCLE PROGRESSES.
THE RIDGE HAS PRESSED AGAINST A TROUGH IN THE BELLINGSHAUSEN SEA
AND IS LEADING TO A TIGHT BELT OF WESTERLIES AFFECTING EXTREME
SOUTHERN CHILE. ALTHOUGH AVAILABLE MOISTURE IS CURRENTLY LIMITED
EXPECTING STRONG WINDS TO CONTINUE ENHANCING OROGRAPHIC UPLIFT IN
COASTAL LOCATIONS WITH ISOLATED MAXIMA OF 15-20MM/DAY THROUGH
EARLY FRIDAY. INLAND OVER PUNTA ARENAS AND PUERTO NATALES
EXPECTING MAXIMA OF 05-10MM/DAY. BY FRIDAY INTO EARLY SATURDAY
EXPECTING LARGEST AMOUNTS TO CONCENTRATE BETWEEN CHILOE AND PUERTO
AYSEN WITH MAXIMA OF 15-20MM/DAY. DURING SATURDAY INTO SUNDAY A
SHORT WAVE UPPER TROUGH WILL ARRIVE IN THE REGION FROM THE
NORTHWEST. THIS WILL STIMULATE ONCE AGAIN PRECIPITATION  LEADING
TO ANOTHER ROUND OF ACCUMULATIONS OF 15-20MM/DAY BETWEEN ISLA
CHILOE AND THE AYSEN REGION. AMOUNTS ARE TO RAPIDLY DECREASE
AFTERWARDS A SURFACE HIGH BUILDS OVER SOUTHERN CHILE.

TO THE EAST OF THE ANDES...MOISTURE WILL BE MOSTLY LIMITED TO
AREAS NEAR AND NORTH OF A STATIONARY FRONT IN MID-SECTIONS OF THE
CONTINENT. A REGION OF INTEREST IS THE SERRA DO MAR/PLANALTO OF
SANTA CATARINA/PARANA/SAO PAULO/RIO DE JANEIRO. THE PRESENCE OF A
SURFACE HIGH OFFSHORE WILL LEAD TO ONSHORE WINDS AND ENHANCED
MOISTURE CONVERGENCE...AIDED FURTHERMORE BU A LEADING SURFACE COLD
FRONT. THIS WILL PRODUCE SCATTERED MAXIMA OF 15-20MM/DAY THROUGH
EARLY SUNDAY DECREASING AFTERWARDS. FOCUS OF ACTIVITY WILL THEN
CENTER OVER ESPIRITO SANTO AND SOUTHERN BAHIA. HERE...ENHANCED
LOW-LEVEL MOISTURE CONVERGENCE AND ENHANCEMENT IN THE DIVERGENT
ENTRANCE OF AN UPPER JET WILL LEAD TO A PEAK IN AMOUNTS DURING
SUNDAY INTO MONDAY. THEN...EXPECTING ACCUMULATIONS PEAKING AT
25-50MM/DAY. FOCUS FOR LARGEST AMOUNTS WILL CONTINUE MIGRATING
NORTHWARD WITH A DECREASING TREND AFTERWARDS.

NORTH OVER THE CONTINENT...SUBTROPICAL RIDGE AT 200 HPA CONTINUES
WELL ORGANIZED. THE RIDGE WILL CENTER OVER MATO GROSSO THROUGH
EARLY SATURDAY TO THEN MIGRATE NORTHWESTWARD AND END UP OVER
ACRE/RONDONIA BY EARLY NEXT WEEK. THE BEST VENTILATION LIES ALONG
THE NORTHERN PERIPHERY OF THE RIDGE IN INTERACTION WITH
SUBEQUATORIAL RIDGE TO THE NORTH. EXPECTING AREA WITH HEAVIEST
DIURNAL AMOUNTS TO OCCUR IN THESE REGION...WHERE THE ATLANTIC ITCZ
AND NEAR EQUATORIAL TROUGH INTERACT WITH THE UPPER DIVERGENT
PATTERN. EXPECTING LARGEST AMOUNTS TO CLUSTER CLOSE TO THE AMAZON
DELTA/AMAPA/SOUTHERN GUIANAS...AND TO WEST ACROSS NORTHWESTERN
AMAZONAS IN BRASIL-SOUTHERN COLOMBIA EXTREME NORTHEASTERN PERU AND
ECUADOR. AMOUNTS WILL PEAK AT MAXIMA OF 20-45MM/DAY EARLY IN THE
CYCLE DECREASING TO 20-35MM/DAY AFTERWARDS.

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