Prognostic Meteorological Discussion
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000
FXSA20 KWBC 201834
PMDSA

SOUTH AMERICA FORECAST DISCUSSION - INTERNATIONAL DESKS
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
234 PM EDT FRI OCT 20 2017

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

MODEL DISCUSSION (VALID FROM OCT 20 AT 0000 UTC): CONFIDENCE IN
THE FORECAST IS HIGH THROUGH 96 HRS TO THE SOUTH OF 45S...AND
THROUGH 120 HRS IN REGIONS TO THE NORTH. THE ECMWF MODEL IS
STRUGGLING ON CROSSING A TROUGH ACROSS THE SOUTHERN CONE BY 96
HRS. THE GFS AND UKMET ARE IN BETTER AGREEMENT ON THIS SYSTEM.

THE CLIMATE FORECAST SYSTEM MODEL...GFS AND EMPIRICAL WAVE
PROPAGATION MODEL OF CPC ARE ALL INDICATING THAT THE UPPER
DIVERGENT PHASE OF THE MADDEN-JULIAN OSCILLATION WILL ESTABLISH
OVER THE AMERICA DURING THE WEEKEND INTO EARLY NEXT WEEK...AND
PERSIST THROUGH THE END OF OCTOBER. UNDER THIS FAVORABLE LARGE
SCALE UPPER DIVERGENT PATTERN...EXPECTING ENHANCEMENT IN
PRECIPITATION ASSOCIATED WITH THE WEATHER SYSTEMS IN PLACE DURING
THE REST OF THE MONTH OF OCTOBER.

A ROBUST SHORT WAVE TROUGH IS CROSSING THE ANDES OF NORTHERN
ARGENTINA ON FRIDAY...AND IS INTERACTING WITH A CONVECTIVELY
UNSTABLE AIR MASS SITTING IN CENTRAL PARAGUAY...AS WELL AS WITH A
LOW-LEVEL JET FROM THE NORTH CONVERGING IN THE AREA. THIS WILL
SUSTAIN STRONG CONVECTION AND LOCALLY HEAVY RAINFALL ON
FRIDAY-SATURDAY WITH ACCUMULATIONS OF 75-125MM AND THE RISK FOR
MCS FORMATION. THE CONVECTIVE EVENT IS TO PROLONG INTO LATE
SATURDAY...WHEN EXPECTING ACCUMULATIONS OF 50-100MM IN EASTERN
PARAGUAY/SOUTHERN MATO GROSSO DO SUL AND PARANA IN BRASIL. ALSO ON
SATURDAY...UNDER THE INFLUENCE OF A DEVELOPING SOUTHERLY LOW-LEVEL
JET ACROSS NORTHERN ARGENTINA/SOUTHERN BOLIVIA...ENHANCED MOISTURE
CONVERGENCE WILL FAVOR ACCUMULATIONS OF 30-60MM/DAY IN CENTRAL AND
SOUTHERN BOLIVIA...WHILE A COLD FRONT STARTS PROPAGATING NORTHWARD
RAPIDLY. BY SUNDAY-MONDAY...THE LOW-LEVEL JET WILL REACH
CENTRAL/NORTHERN BOLIVIA...WHILE NORTHEASTERLY TRADES ENHANCE
MOISTURE CONVERGENCE IN AREAS TO THE NORTH. THIS WILL CONTINUE
SUSTAINING HEAVY RAINFALL...WITH ACCUMULATIONS OF 30-60MM/DAY IN
SOUTHERN PERU/NORTHERN BOLIVIA/ACRE AND RONDONIA. TO THE
NORTH...ACROSS THE PERUVIAN AMAZON AND THE ECUADORIAN
ORIENTE...EXPECTING ACCUMULATIONS OF 20-35MM. ALSO DURING THIS
PERIOD...ENHANCED FRONTAL CONVERGENCE AND INTERACTIONS WITH THE
SERRA DO MAR IN SAO PAULO/RIO WILL SUSTAIN ACCUMULATIONS OF
30-60MM/DAY. INLAND ACROSS MATO GROSSO DO SUL/MATO GROSSO EXPECTED
MAXIMA OF 15-25MM. BY MONDAY-TUESDAY...THE WANING SOUTHEASTERLY
SURGE ACROSS NORTHERN PERU/ECUADOR WILL STILL FAVOR MAXIMA OF
25-50MM/DAY IN THESE REGIONS. ELSEWHERE IN THE WESTERN AMAZON
EXPECTING MAXIMA OF 20-35MM. IN BRASIL...AS THE FRONT CONTINUES
INTERACTING WITH THE SERRA DO MAR OF RIO DE JANEIRO...EXPECTING
ACCUMULATIONS OF 20-40MM.

IN CHILE...A SUBTROPICAL MOISTURE CONNECTION WILL ARRIVE INTO THE
SOUTHERN CONE ON SATURDAY. THIS WILL SUSTAIN RAINFALL
ACCUMULATIONS OF 15-20MM/DAY ON SATURDAY THROUGH MONDAY. AFTER
THIS PERIOD...FRONTAL CONVERGENCE WITH THE SOUTHERN ANDES WILL
FAVOR ISOLATED AMOUNTS OF 10-15MM/DAY.

VANNUCCI...SMN (ARGENTINA)
RIVAS...SENAMHI (PERU)
GALVEZ...WPC (USA)
$$





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