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South American Forecast Discussion
 
(Caution: Version displayed is not the latest version. - Issued 1731Z Jan 20, 2015)
 
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SOUTH AMERICA FORECAST DISCUSSION - INTERNATIONAL DESKS
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1231 PM EST TUE JAN 20 2015

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

MODEL DISCUSSION (VALID FROM JANUARY 20 AT 00UTC): GLOBAL MODELS
AND ENSEMBLE MEMBERS ARE IN GENERALLY GOOD AGREEMENT ON THE
EVOLUTION OF SYNOPTIC SCALE SYSTEMS. THE UKMET MODEL IS THE ONLY
ONE FROM THE GLOBAL MODELS THAT IS HAVING SOME TROUBLE SOUTH OF
25S STARTING AFTER 72-84 HRS. THERE ARE ALSO SOME DISCREPANCIES ON
PRECIPITATION FIELDS FROM THE ECMWF AND THE GFS...ESPECIALLY AFTER
84 HRS.

QUIET PATTERN IS ESTABLISHED IN THE SOUTHERN CONE UNDER THE
INFLUENCE OF A STRONG MID-LEVEL RIDGE. THIS WILL START CHANGING
LATE ON WEDNESDAY AS A SHORT WAVE TROUGH MOVES INTO
CENTRAL/SOUTHERN CHILE/NORTHERN PATAGONIA FROM THE NORTHWEST. NI
THE CHILEAN SIDE OF THE ANDES MOISTURE WILL BE LIMITED...BUT ONCE
THE SYSTEM ENTERS NORTHERN PATAGONIA IT WILL ENCOUNTER A MOISTER
AIRMASS AND LEAD TO SCATTERED THUNDERSTORM DEVELOPMENT WITH MAXIMA
OF 15-20MM/DAY BY WEDNESDAY INTO EARLY THURSDAY. THE TROUGH WILL
THEN MOVE INTO CENTRAL ARGENTINA WHERE EXPECTING STRONGEST STORMS
TO PRODUCE ISOLATED MAXIMA OF 30-60MM/DAY BY THURSDAY INTO EARLY
FRIDAY. MODELS START TO DIVERGE IN PRECIPITATION SOLUTIONS
AFTERWARDS. GIVEN THE TREND INTO A WETTER-THAN-AVERAGE PATTERN
ACROSS NORTHERN ARGENTINA AND PLENTIFUL SOIL MOISTURE...WE ARE
LEANING TOWARDS A WETTER SOLUTION DURING FRIDAY INTO SATURDAY WITH
SCATTERED MAXIMA OF 15-30MM/DAY ACROSS NORTHERN ARGENTINA AND
URUGUAY. AMOUNTS ARE LIKELY TO DECREASE AFTERWARDS.

ACROSS SOUTHERN CHILE...A SUBTROPICAL MOISTURE CONNECTION WILL
ESTABLISH BY THURSDAY INTO EARLY FRIDAY TO PRODUCE SCATTERED
MAXIMA OF 15-30MM/DAY SOUTH OF PUERTO MONTT.

OTHER REGION OF INTEREST WILL BE THE SERRA DO MAR OF SANTA
CATARINA/PARANA/SAO PAULO AND PART OF THE PLANALTO OF PARANA AND
SAO PAULO. AN UPPER TROUGH WILL PROVIDE SUFFICIENT VENTILATION AND
CYCLONIC VORTICITY ADVECTION FOR ANY CONVECTION THAT DEVELOPS.
FURTHERMORE...EXPECTING STRONG 20-25KT ONSHORE WINDS IN A MOISTURE
POOL WILL SIGNIFICANTLY ENHANCE OROGRAPHIC UPLIFT AGAINST THE
SERRA DO MAR. THIS WILL SUSTAIN MODERATE RAINFALL AMOUNTS WITH
MAXIMA OF 25-50MM/DAY BY WEDNESDAY INTO EARLY THURSDAY INCREASING
TO 30-60MM/DAY BY THURSDAY INTO EARLY FRIDAY. AMOUNTS ARE TO
DECREASE TO MAXIMA OF 20-35MM/DAY AFTERWARDS. NOTE THAT UNDER
STRONG OROGRAPHIC FORCING...EXPECTING VERY ISOLATED HIGHER AMOUNTS.

OTHER REGION OF ACTIVE CONVECTION WILL BE THE WESTERN AMAZON AND
THE CENTRAL ANDES FROM COLOMBIA/ECUADOR SOUTH INTO NORTHERN CHILE
AND SOUTHERN BOLIVIA. ALTHOUGH A VERY UNUSUAL UPPER CIRCULATION
PATTERN IS DOMINATING THE SOUTHAMERICAN TROPICS...VENTILATION AND
MOISTURE ADVECTION FROM THE EAST WILL BE APPROPRIATE TO SUSTAIN AN
ACTIVE PATTERN OF DIURNAL CONVECTION. THE SUBTROPICAL HIGH IS
REESTABLISHING ACROSS WESTERN BOLIVIA...AND ALL MODELS HAVE IT
MEANDERING INTO THE EASTERN PACIFIC OFF THE COAST OF NORTHERN
CHILE BY WEDNESDAY-THURSDAY. THIS WILL RESTORE EASTERLY FLOW
ACROSS MOST OF THE ALTIPLANO AND THE PERUVIAN/ANDES...BRINGING
CONVECTION BACK INTO THE WESTERN CORDILLERA. THIS WILL LEAD TO A
PARTICULARLY ACTIVE PATTERN OF CONVECTION ACROSS THE WESTERN
ALTIPLANO INCLUDING PARTS OF NORTHERN CHILE. EXPECTING
ACCUMULATIONS WITH MAXIMA IN THE ORDER OF 10-15MM/DAY...WITH VERY
ISOLATED HIGHER AMOUNTS. FURTHER NORTH ACROSS THE CENTRAL PERUVIAN
ANDES EXPECTING MAXIMA OSCILLATING BETWEEN 15-20MM/DAY AND
10-15MM/DAY THROUGH THE CYCLE. ACROSS ECUADOR...LARGEST AMOUNTS
ARE STILL EXPECTED ACROSS THE WESTERN SLOPES OF THE ANDES WITH
MAXIMA OF 20-45MM/DAY DECREASING AFTER THURSDAY. ACTIVE CONVECTION
WILL DOMINATE THE ECUADORIAN ANDES THROUGH THE CYCLE.

ACROSS THE AMAZON BASIN...MOST ACTIVE IS EXPECTED ACROSS EASTERN
PERU/NORTHERN BOLIVIA EARLY IN THE CYCLE WHERE STRONG
THUNDERSTORMS AND THE RISK OF MCS FORMATION WILL LEAD TO MAXIMA OF
40-80MM/DAY THROUGH EARLY WEDNESDAY. BY WEDNESDAY INTO THURSDAY
THE FOCUS WILL SHIFT NORTHWARD INTO EASTERN ECUADOR/NORTHERN
PERU/SOUTHERN COLOMBIA/WESTERN BRASIL WHERE EXPECTING SCATTERED TO
WIDESPREAD MAXIMA OF 25-50MM/DAY AND VERY ISOLATED HIGHER AMOUNTS.
LATER IN THE CYCLE...STRONGEST CONVECTION WILL CLUSTER FURTHER
EAST INTO THE CENTRAL AMAZON BASIN...WHERE EXPECTING MAXIMA
GENERALLY IN THE 20-45MM/DAY RANGE.

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