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South American Forecast Discussion
 
(Caution: Version displayed is not the latest version. - Issued 1715Z Jan 16, 2015)
 
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SOUTH AMERICA FORECAST DISCUSSION - INTERNATIONAL DESKS
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1215 PM EST FRI JAN 16 2015

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

MODEL DISCUSSION (VALID FROM JANUARY 16 AT 00UTC): MODELS CONTINUE
AGREEING ON FORECAST EVOLUTION WITH SOME DIFFERENCES ON THE SHORT
WAVE PERTURBATIONS EMBEDDED IN EXPECTED LONG WAVE PATTERN.

MID-UPPER RIDGE IS EXPECTED TO DOMINATE ACROSS THE EXTREME
SOUTHEASTERN PACIFIC DURING THE NEXT SEVERAL DAYS...WHILE A LONG
WAVE TROUGH DOMINATES THE SOUTHERN ATLANTIC AS BOTH SYSTEMS SLOWLY
MOVE TO THE EAST. IN THE MEAN TIME...A COUPLE OF SHORT WAVE
PERTURBATIONS WILL IN THE TIGHT BELT OF SOUTHWESTERLIES ACROSS THE
SOUTHERN CONE. ONE IS TO CROSS THE ANDES DURING SUNDAY TO
REINFORCE UPPER TROUGH PATTERN INTO THE BUENOS AIRES PROVINCE
DURING MONDAY. INITIALLY...ACCUMULATIONS WILL CONFINE TO SOUTHERN
CHILE...WHERE ISOLATED TO SCATTERED MAXIMA OF 05-10MM/DAY IS
EXPECTED THROUGH EARLY SUNDAY. PASSING TROUGH WILL UNDULATE A
SURFACE FRONT THAT WILL CROSS CENTRAL ARGENTINA/RIO DE LA PLATA
REGION INTO NORTHERN URUGUAY BY MONDAY. INITIALLY AS SHORT WAVE
TROUGH CROSSES THE ANDES...EXPECTING AN ENHANCEMENT OF ACTIVITY TO
PRODUCE SCATTERED MAXIMA OF 20-35MM/DAY DURING SUNDAY INTO EARLY
MONDAY. A SHORT-LIVED SOUTHEASTERLY PAMPERO JET WILL DEVELOP
ACROSS THE BUENOS AIRES PROVINCE INTO SAN LUIS/SOUTHERN CORDOBA ON
MONDAY. THIS WILL ENHANCE FRONTAL AND PRE-FRONTAL ACTIVITY ACROSS
NORTH-CENTRAL ARGENTINA TO PRODUCE MAXIMA OF 25-50MM/DAY AND THE
RISK FOR SEVERE CONVECTION. THE FRONT IS THEN TO RAPIDLY
STALL...SO EXPECTING LESS ORGANIZED CONVECTION TO PREVAIL ACROSS
NORTHERN ARGENTINA/SOUTHERN BRASIL ON TUESDAY.

NORTH ACROSS THE CONTINENT...UNUSUAL PATTERN CHARACTERIZED BY A
WEAK SUBTROPICAL HIGH SOUTH/SOUTHEAST OF ITS CLIMATOLOGICAL
POSITION AND A DOMINANT TROUGH/CAVADO ACROSS CENTRAL BRASIL IS TO
SLOWLY START ITS EVOLUTION TOWARDS A MORE CLIMATOLOGICAL ONE.
INTENSE CONVECTION ACROSS SOUTHERN PERU/BOLIVIA/RONDONIA IS
STARTING TO REBUILD THE RIDGE OVER PARAGUAY/BOLIVIA...AND MODELS
HAVE IT MIGRATING INTO CENTRAL BOLIVIA BY EARLY NEXT WEEK. THE
CAVADO WILL HOWEVER REMAIN IN ITS PLACE...WHILE A MID-LEVEL RIDGE
CONTINUES DOMINATING MOST OF EASTERN AND SOUTHEASTERN BRASIL. THIS
WILL CONTINUE SUSTAINING UNUSUALLY DRY PATTERN OVER THE REGION
WELL INTO NEXT WEEK. ACROSS NORTHERN/WESTERN BRASIL AND THE REST
OF TROPICAL SOUTHAMERICA...HOWEVER...CONVECTION HAS BECOME MORE
WIDESPREAD AND ENHANCED WITH RESPECT TO LAST WEEK PARTLY IN
ASSOCIATION WITH THE ARRIVAL OF THE DIVERGENT PHASE OF THE
MADDEN-JULIAN OSCILLATION. THIS WILL CONTINUE SUSTAINING ACTIVE
CONVECTION IN THE REGION...WITH THE STRONGEST CLUSTERING IN THE
WESTERN AND CENTRAL PARTS OF THE AMAZON BASIN. EXPECTING MAXIMA IN
THE ORDER OF 25-50MM/DAY MIGRATING FROM CENTRAL/SOUTHERN
PERU/NORTHERN BOLIVIA ON FRIDAY INTO ECUADOR/SOUTHERN
COLOMBIA/CENTRAL-NORTHERN PERU/WESTERN AMAZONAS DURING THE
WEEKEND. AMOUNTS ARE TO GRADUALLY DECREASE TO MAXIMA OF
20-40MM/DAY...YET ISOLATED HIGHER AMOUNTS ARE ALWAYS POSSIBLE IN
STRONGEST THUNDERSTORMS. ACROSS THE CENTRAL/SOUTHEASTERN
AMAZON...EXPECTING ACTIVE DIURNAL CONVECTION TO PRODUCE SCATTERED
MAXIMA OF 15-25MM/DAY EXTENDING EAST INTO MOST OF PARA/MARANHAO IN
BRASIL. MODELS ARE ALSO SHOWING AN ACTIVATION OF THE SOUTHERN ITCZ
IN BRASIL. THIS SHOULD LEAD TO AN INCREASE IN ACTIVITY ACROSS THE
INTERIOR NORDESTE.

ACROSS ECUADOR...WET PATTERN IS RAPIDLY ESTABLISHING. MID-LEVEL
SOUTHEASTERLIES ARE HELPING MOISTURE TRANSPORT INTO THE ANDEAN
REGION. UPPER VENTILATION IS ALSO IMPROVING. FURTHERMORE...A SURGE
IN PRECIPITABLE WATER AND ONSHORE WINDS ALONG THE PACIFIC COAST
WILL LEAD TO A VERY RAINY PERIOD ALONG THE WESTERN SLOPES/COASTAL
AREAS OF ECUADOR. EXPECTING SCATTERED AFTERNOON/NOCTURNAL STORMS
INCREASING ON FRIDAY AND PEAKING ON SATURDAY TO PRODUCE SCATTERED
MAXIMA OF 30-60MM/DAY. AMOUNTS ARE TO START DECREASING AFTERWARDS
TO MAXIMA OF 20-45MM/DAY ON SUNDAY. NOTE THAT INTERACTIONS WITH
OROGRAPHY ARE LIKELY TO LEAD TO ISOLATED HIGHER
AMOUNTS...ESPECIALLY ALONG THE WESTERN SLOPES. NOTICE THAT SEA
SURFACE TEMPERATURES HAVE BEEN SLIGHTLY WARMER THAN THE
USUAL...WHICH IS ENHANCING FORECAST CONFIDENCE ON HIGH RAINFALL
AMOUNTS. ACROSS THE CENTRAL ANDES...CONVECTION IS TO GRADUALLY
RETURN INTO THE CENTRAL RANGES/WESTERN CORDILLERA DURING SUNDAY
INTO MONDAY AS MID-LEVEL EASTERLIES/SOUTHEASTERLIES RETURN. THIS
WILL LEAD TO A ONCE AGAIN ACTIVE PATTERN OF CONVECTION
ESTABLISHING NEXT WEEK...THIS TIME WITH ADDITIONAL SUPPORT OF A
STRONGER SUBTROPICAL HIGH.

ARREAGA...INAMHI (ECUADOR)
DURAN...SENAHMI (PERU)
GALVEZ...WPC (USA)