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
 
(Latest Discussion - Issued 1544Z Oct 22, 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
1144 AM EDT WED OCT 22 2014

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

MODEL DISCUSSION (VALID FROM OCTOBER 22 AT 00UTC): ON THE NORTHERN
STREAM THE GLOBAL MODELS CONTINUE TO CONVERGE ON A SIMILAR
SOLUTION THROUGH THE MEDIUM RANGE PERIOD. AS A RESULT...CONFIDENCE
IN THE FORECAST TO THE NORTH OF 50S IS HIGH. ON THE SOUTHERN
STREAM...THEY ONLY AGREE THROUGH 60-72 HRS...THEN RAPIDLY DIVERGE
ON HOW THE PATTERN IS GOING TO EVOLVE...DISAGREEING ON THE SPEED
AND AMPLITUDE OF SHORT WAVE PERTURBATIONS STREAMING ACROSS THE
BELLINGSHAUSEN SEA/ANTARCTIC PENINSULA. IN THIS AREA...THE
VARIABILITY AMONG THE ENSEMBLE MEMBERS REMAINS TO LARGE TO
ESTABLISH ANY CONFIDENCE IN THE MEDIUM RANGE FORECAST.

A MID LEVEL TROUGH ON THE SOUTHERN STREAM MOVES ACROSS THE DRAKE
PASSAGE TO THE WEDDELL SEA/SOUTHWEST ATLANTIC EARLY IN THE CYCLE
AS ANOTHER PERTURBATION APPROACHES FROM THE WEST. THROUGH 48-72
HRS THESE ARE TO COMBINE INTO A BROAD TROUGH OVER THE SOUTH
ATLANTIC...TO ENVELOP AREA BETWEEN 50W-00W AND TO THE SOUTH OF
30S. BROAD TROUGH PATTERN IS TO PERSIST THROUGH 84-96 HRS...THEN
GRADUALLY WEAKEN LATER IN THE CYCLE AS SHORT WAVE ENERGY SHEARS
EASTWARD ACROSS THE SOUTH ATLANTIC. AT LOW LEVELS THIS IS TO
SUSTAIN A BROAD TROUGH ACROSS THE SOUTHERN CONE TO SOUTHWEST
ATLANTIC EARLY IN THE CYCLE...THAT SLOWLY EXPANDS ACROSS THE SOUTH
ATLANTIC TO THE SOUTH OF 40S/45S THROUGH 72-96 HRS. POLAR FRONTS
REVOLVING AROUND THIS FEATURE ARE TO CONFINE TO EXTREME SOUTHERN
CHILE/TIERRA DEL FUEGO...WHERE THEY ARE TO GENERALLY FAVOR LIGHT
CONVECTION. A MEANDERING FRONT TO THE NORTH...MEANWHILE...IS TO
EXTEND WEST ACROSS THE SOUTH ATLANTIC TO LA PAMPA IN
ARGENTINA-CENTRAL CHILE...WHERE IT IS TO REMAIN THROUGH 84-96 HRS.
ALONG THIS BOUNDARY EXPECTING ISOLATED TO SCATTERED CONVECTION TO
TRIGGER MAXIMA OF 05-10MM.

A SHORT WAVE TROUGH ON THE NORTHERN STREAM...MEANWHILE...IS TO
MEANDER OVER THE EASTERN PACIFIC AND OFF THE COAST OF CHILE
THROUGH 96-108 HRS...WITH AXIS TO BOUND BETWEEN 110W-80W AND TO
THE SOUTH OF 18S. AS THE TROUGH HOLDS TO THE WEST...AN INDUCED
RIDGE IS TO EXTEND SOUTH ACROSS ARGENTINA TO THE SOUTHERN CONE OF
SOUTH AMERICA. THROUGH 120 HRS THE TROUGH WILL PRESS AGAINST THE
RIDGE TO THE EAST...LEADING TO GRADUAL EROSION OF THE RIDGE AND
WEAKENING OF THE TROUGH AS SHORT WAVE ENERGY SHEARS ACROSS CENTRAL
CHILE TO ARGENTINA. BY 120-132 HRS THE INFLOW OF SHORT WAVE ENERGY
WILL RESULT IN HEIGHT FALLS OF 100-125GPM ACROSS CENTRAL CHILE. AT
LOW LEVELS...THIS WILL THEN INTERACT WITH SURFACE FRONT MEANDERING
OVER LA PAMPA...INDUCING A FRONTAL WAVE OVER NORTHERN PATAGONIA/LA
PAMPA IN ARGENTINA. THE LOW IS TO THEN MIGRATE TO THE
EAST-SOUTHEAST WHILE THE FRONT MEANDERS NORTH ACROSS CENTRAL
ARGENTINA. ALSO AT LOW LEVELS...A NORTHERLY JET ACROSS WESTERN
ARGENTINA IS TO SUSTAIN A WARM/MOIST ADVECTIVE PATTERN...WITH
PRECIPITABLE WATER CONTENT ALONG THE FRONT TO INCREASE TO 35-40MM
LATER IN THE CYCLE. THIS WILL HELP SUSTAIN ORGANIZED/POTENTIALLY
SEVERE CONVECTION ON THE CENTRAL PROVINCES OF ARGENTINA...WITH
MAXIMA OF 25-50MM EXPECTED BY 120-132 HRS.

AT 200 HPA...A SHORT WAVE TROUGH MOVES ACROSS NORTHERN
CHILE-SOUTHERN PERU THROUGH 42-48 HRS...WITH AXIS TO SETTLE ACROSS
SOUTHERN BRASIL-PARAGUAY-BOLIVIA LATER IN THE CYCLE. AS THE TROUGH
MOVES EAST...IT IS TO FAVOR AN UPPER DIVERGENT PATTERN FROM
SOUTHERN PERU/NORTHERN BOLIVIA-ACRE IN BRASIL TO SOUTHEAST BRASIL.
THIS IS TO THEN VENT DEEP CONVECTION ACROSS TROPICAL-SUBTROPICAL
PORTIONS OF SOUTH AMERICA. AT LOW LEVELS THIS IS TO THEN FAVOR
GENERATION OF A TROUGH/CONVERGENCE ZONE THAT IS TO EXTEND FROM
NORTHERN BOLIVIA TO SAO PAULO IN BRASIL LATER IN THE CYCLE. DEEP
MOISTURE IS TO CONVERGE ALONG AND NORTH OF THIS TROUGH. EARLY IN
THE CYCLE ACTIVITY IS TO CLUSTER FROM NORTHERN AMAZONAS/RORAIMA IN
BRASIL TO BAHIA. THROUGH 48-72 HRS CONVECTION IS TO BUILD WEST AND
SOUTH ACROSS MATO GROSSO/ MATO GROSSO DO SUL TO RONDONIA IN
BRASIL-NORTHERN PERU...AND LATER IN THE CYCLE AMPLIFIES FARTHER
WEST TO INCLUDE THE PERUVIAN JUNGLE/NORTHERN BOLIVIA. IN THIS AREA
EXPECTING RAINFALL MAXIMA OF 20-45MM/DAY...WITH LOCALLY HIGHER
AMOUNTS HIGHLY LIKELY.

CAROCA...DMC (CHILE)
DURAN...SENAHMI (PERU)
DAVISON...WPC (USA)