Skip Navigation Links weather.gov 
NOAA logo - Click to go to the NOAA homepage National Weather Service   NWS logo - Click to go to the NWS homepage
The Weather Prediction Center
 
South American Forecast Discussion
 
(Caution: Version displayed is not the latest version. - Issued 1548Z Sep 08, 2014)
 
Version Selection
Versions back from latest:  0   1   2   3   4   5   6   7   8   9   10   
 
Abbreviations and acronyms used in this product


SOUTH AMERICA FORECAST DISCUSSION - INTERNATIONAL DESKS
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1148 AM EDT MON SEP 08 2014

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

MODEL DISCUSSION (VALID FROM SEPTEMBER 08 AT 00UTC): GLOBAL MODELS
FOLLOW SIMILAR EVOLUTION THROUGH 96-108 HRS...THEN DIVERGE ON HOW
SHORT WAVE TROUGH ON THE NORTHERN STREAM EVOLVES AS IT MOVES
TOWARDS NORTHERN CHILE LATER IN THE CYCLE. BOTH EUROPEAN MODELS
FAVOR A FASTER PROGRESSION THAT WHAT THE GFS SUGGESTS. CONSIDERING
FRICTIONAL EFFECTS OF THE ANDES AND PERSISTENT RIDGE TO THE
WEST...THE SLOWER GFS SOLUTION IS FAVORED.

OVER THE WESTERN ATLANTIC AT 500 HPA...A SHORT WAVE TROUGH
DOMINATES FLOW TO THE NORTH-NORTHEAST OF THE MALVINAS/FALKLAND
ISLANDS. THROUGH 24 HRS IT IS TO MEANDER EAST ACROSS 30W/35W WHILE
REMAINING SOUTH OF 30S. THROUGH 72 HRS IT IS TO ACCELERATE ACROSS
00W. AT LOW LEVELS THIS SUSTAINS A BROAD OCCLUDED TROUGH OVER THE
SOUTHWEST ATLANTIC...WITH A POLAR FRONT RAILING ACROSS SOUTHERN
BRASIL TO NORTHERN ARGENTINA. IN A NORTHERLY FLOW...THE FRONT
MIGRATES SOUTH ACROSS URUGUAY-ENTRE RIOS IN ARGENTINA EARLY IN THE
CYCLE...THEN DISSIPATES AS MID/UPPER LEVEL TROUGH PULLS AWAY.
MEANWHILE...THIS IS TO SUSTAIN MOISTURE CONVERGENCE ACROSS
URUGUAY-ENTRE RIOS IN ARGENTINA...TO RESULT IN RAINFALL AMOUNTS OF
20-35MM.

ANOTHER TROUGH IS TO CLOSELY FOLLOW...WITH MID LEVEL AXIS TO ENTER
THE SOUTHERN CONE BY 24 HRS...AND QUICKLY PULL ACROSS ARGENTINA TO
THE WESTERN ATLANTIC BY 48 HRS. MEANWHILE...THIS IS TO SUSTAIN
HEIGHTS FALLS OF 75-125GPM ACROSS CENTRAL ARGENTINA/RIO DE LA
PLATA BASIN. AS IT EMERGES TO THE EAST...A DEEP CLOSED LOW IS TO
FORM TO THE EAST-NORTHEAST OF THE MALVINAS/FALKLAND ISLANDS. THIS
IS TO THEN EVOLVE INTO A BROAD TROUGH OVER THE WESTERN
ATLANTIC...TO DOMINATE AREA BETWEEN 65W-25W AND TO THE SOUTH OF
25S BY 72-84 HRS. THIS IS TO SLOWLY PULL TO THE EAST-SOUTHEAST
LATER IN THE CYCLE. AT LOW LEVELS...TROUGH ALOFT IS TO SUSTAIN A
PROGRESSIVE FRONT ACROSS NORTHERN PATAGONIA-SOUTHERN CUYO IN
ARGENTINA/CENTRAL CHILE EARLY IN THE CYCLE. BUILDING POLAR RIDGE
IS TO THEN SUSTAIN A PAMPERO JET THAT DISPLACES THE FRONT NORTH
ACROSS URUGUAY-NORTHERN ARGENTINA BY 48 HRS. FRONT IS TO THEN
STALL OVER RIO GRANDE DO SUL IN BRASIL-NORTHERN PROVINCES IN
ARGENTINA. AS THE FRONT ENTERS SOUTHERN CHILE EARLY THIS
CYCLE...IT IS TO SUSTAIN SCATTERED CONVECTION WITH ACCUMULATION OF
15-30MM THROUGH 36 HRS. HIGHER AMOUNTS ARE EXPECTED AS THE FRONT
SURGES ACROSS ARGENTINA...WITH MODELS AGREEING ON HIGH RISK OF
HEAVY RAINS AND POTENTIALLY SEVERE CONVECTION OVER URUGUAY-ENTRE
RIOS/CORRIENTES IN ARGENTINA. UNDER FAVORABLE JET DYNAMICS
EXPECTING RAINFALL MAXIMA TO PEAK AT 75-125MM BY 36-60 HRS...WITH
FORECASTED HELICITY VALUES OF 350-400 INDICATIVE OF POSSIBLE
SUPERCELL DEVELOPMENT. BUT BY 60-84 HRS MAXIMA DECREASES TO
20-35MM.

A SHORT WAVE TROUGH ON THE NORTHERN STREAM IS TO THEN PULL ACROSS
45S 90W BY 48 HRS. BUILDING RIDGE TO THE WEST IS TO DISPLACE THIS
CENTER NORTH TO 34S 93W BY 72 HRS...NEARING 30S 82W BY 120 HRS. AS
PREVIOUSLY INDICATED...THE EUROPEAN MODELS THEN TAKE THIS VORTEX
EAST ACROSS NORTHERN CHILE...WHILE THE GFS MAINTAINS THE
ASSOCIATED LOW/TROUGH FARTHER TO THE WEST. INDEPENDENT ON WHEN IT
MAKES LANDFALL...THIS SYSTEM WILL BE DEEP ENOUGH TO FAVOR
CONVECTIVE DEVELOPMENT ACROSS THE NORTHERN ANDES OF CHILE...WITH
MOST ACTIVE CONVECTION AS IT INTERACTS WITH MEANDERING FRONT OVER
SOUTHERN BRASIL-PARAGUAY.

AT 200 HPA...A BROAD CELL OF THE SUBTROPICAL RIDGE DOMINATES AREA
TO THE NORTH OF 23S AND WEST OF 40W...WHILE ANCHORING ON A CLOSED
HIGH OVER RONDONIA IN BRASIL. THIS IS A MIGRATORY PATTERN...WITH
HIGH FORECAST TO RELOCATE OVER THE GALAPAGOS ISLANDS LATER ON DAY
02...WHERE IT IS TO REMAIN THROUGH DAY 04. AS THE RIDGE PULLS
AWAY...A TROUGH IS TO THEN MOVE TO THE NORTHEAST STATES OF BRASIL.
THROUGH 72-96 HRS THIS EVOLVES INTO AN EAST-TO-WEST TROUGH WITH
AXIS ALONG 13S/14S TO 60W. RIDGE ALOFT IS TO VENT SCATTERED
CONVECTION ACROSS WESTERN BRASIL...WHERE DIURNAL CONVECTION IS TO
SUSTAIN RAINFALL MAXIMA OF 15-25MM. THROUGH 96-108 HRS CONVECTION
ACROSS COLOMBIA-ECUADOR-NORTHERN PERU IS TO BECOME BETTER
ORGANIZED...WITH MAXIMA OF 20-40MM. THIS IS TO ALSO FAVOR
CONVECTION ACROSS THE CENTRAL-SOUTHERN JUNGLE OF PERU WITH
ACCUMULATION OF 10-15MM...MOST INTENSE EXPECTED BY 96-108 HRS.
OVER NORTHERN BRASIL...RETROGRESSING TROUGH IS TO ENHANCE SEA
BREEZE CONVERGENCE...TO FAVOR MAXIMA OF 05-10MM ACROSS ILHA DE
MARAJO AND AMAPA IN BRASIL. ACROSS PERNAMBUCO AND RIO GRANDE DO
NORTE...MAXIMA IS TO INITIALLY PEAK AT 15-25MM...AS ENHANCED BY
EASTERLY TRADE WIND CONVERGENCE. THIS DECREASES TO 10-15MM LATER
IN THE CYCLE.

JALFIN...SMN (ARGENTINA)
CAROCA...DMC (CHILE)
DAVISON...WPC (USA)