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 1419Z Aug 26, 2020)
 
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
1019 AM EDT WED AUG 26 2020

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

FORECAST DISCUSSION FROM AUGUST 26/14UTC: BUILDING MID/UPPER LEVEL
RIDGE IS QUICKLY BECOMING THE DOMINANT SYNOPTIC FEATURE OVER THE
EASTERN SOUTH PACIFIC...WITH AXIS REACHING MAXIMUM AMPLITUDE EARLY
ON THURSDAY MORNING...WHEN IT WILL EXTEND SOUTH BETWEEN 90W-120W
TO THE POLAR ICECAP. IN RESPONSE TO THE BUILDING RIDGE TO THE
WEST...A SHORT WAVE TROUGH LIFTS ACROSS THE SOUTHEAST PACIFIC
EARLY IN THE CYCLE...WITH PERTURBATION FORECAST TO INTENSIFY AS IT
ENTERS THE SOUTHERN CONE/DRAKE PASSAGE ON THURSDAY AFTERNOON. AS
THE MID LEVEL RIDGE HOLDS TO THE WEST...SECONDARY VORTICES ARE TO
LIFT ACROSS THE DRAKE PASSAGE TO TIERRA DEL FUEGO/PATAGONIA DURING
THE WEEKEND. THIS WILL HELP SUSTAIN THE NORTHWARD AMPLIFICATION OF
THE TROUGH ACROSS LA PAMPA TO CENTRAL ARGENTINA WHILE ALSO
EXPANDING EAST ACROSS THE SOUTHWEST ATLANTIC-THE SOUTH GEORGIA
ISLANDS. BROAD TROUGH IS TO THEN ENVELOP THE WESTERN-CENTRAL
ATLANTIC BY THE END OF THE CYCLE.

AT LOW LEVELS...IN RESPONSE TO EVOLVING UPPER LEVEL PATTERN...A
BROAD RIDGE IS TO ALSO BUILD TO THE WEST. THIS IS TO CENTER ON
MASSIVE A 1043-1045 HPA HIGH LATER ON THURSDAY-FRIDAY....WHILE TO
THE EAST A BROAD POLAR TROUGH IS TO ENVELOP THE SOUTHERN
CONE/WESTERN ATLANTIC. THE DEEPENING LOW LEVEL TROUGH WILL SUSTAIN
A TIGHT GRADIENT AND STRONG BOUNDARY LAYER WINDS OF 35-50KTS
ACROSS THE SOUTHERN CONE. THIS WILL HELP SUSTAIN A COLD ADVECTIVE
PATTERN WHILE DRIVING SUCCESSIVE FRONTS NORTH ACROSS SOUTHERN
CHILE TO PATAGONIA IN ARGENTINA. BELOW FREEZING TEMPERATURES ARE
TO THEN ENVELOP THE SOUTHERN PROVINCES OF ARGENTINA AND SOUTHERN
REGION OF CHILE...WITH CONDITIONS QUICKLY BECOMING FAVORABLE FOR
HEAVY SNOWFALL TO AFFECT TIERRA DEL FUEGO AND THE SOUTHERN ANDES.
OVER THE NEXT COUPLE OF DAYS EXPECTING SNOWFALL AMOUNTS OF
15-25CM/DAY...WHILE ON SATURDAY TO SUNDAY EXPECTING ACCUMULATION
OF 10-15CM. ON SUNDAY-MONDAY THE POLAR TROUGH MEANDERS FARTHER
EAST INTO THE SOUTH ATLANTIC WHILE YIELDING TO A BUILDING RIDGE
OVER SOUTHERN-CENTRAL ARGENTINA. THIS WILL DRIVE THE SURFACE FRONT
NORTH ACROSS THE BUENOS AIRES PROVINCE/RIO DE LA PLATA BASIN TO
THE SOUTHERN STATES OF BRASIL WHERE IT WILL REINFORCE/MERGE WITH A
MEANDERING FRONT TO THE NORTH.

ANOTHER FEATURE OF INTEREST IS A MID LEVEL SHORT WAVE TROUGH ON
THE NORTHERN STREAM OFF THE CENTRAL/NORTHERN COAST OF CHILE. AS
THE AFOREMENTIONED TROUGH AMPLIFIES ACROSS THE SOUTHERN CONE...IT
IS TO DRAW THE NORTHERN STREAM VORTEX EASTWARD ACROSS THE CENTRAL
REGIONS OF CHILE TO CENTRAL ARGENTINA...WHERE IT IS TO RAPIDLY
WEAKEN WHILE SHEARING SHORT WAVE ENERGY EASTWARD UNDER THE
SUBTROPICAL RIDGE TO THE NORTH.  AT 250 HPA...A SUBTROPICAL AND A
NORTHERN POLAR JETS ARE ROUNDING THE BASE OF THE TROUGH...WITH
JETS TO SUSTAIN AN UPPER DIVERGENT PATTERN AS THEY COUPLE OVER THE
BUENOS AIRES PROVINCE/ENTRE RIOS IN ARGENTINA EARLY IN THE CYCLE.
AT LOW LEVELS THIS SUSTAINS A DEEPENING LOW TO THE SOUTH-SOUTHEAST
OF THE BUENOS AIRES PROVINCE LATER TODAY...WITH SURFACE LOW TO
RAPIDLY INTENSIFY AS IT MOVES TOWARDS THE SOUTH GEORGIA ISLANDS ON
THURSDAY. THIS WILL THEN DRIVE A SURFACE FRONT NORTH ACROSS
URUGUAY TO NORTHERN ARGENTINA ON THURSDAY...WITH BOUNDARY BRIEFLY
STALLING OVER SOUTHERN BRASIL-PARAGUAY/NORTHERN ARGENTINA DURING
THE WEEKEND. UNDER FAVORABLE JET DYNAMICS...THE RISK OF SEVERE
CONVECTION WITH THIS FEATURE IS HIGH DURING THE NEXT TWO
DAYS...WITH MAXIMA OVER ENTRE RIOS-URUGUAY PEAKING AT 25-50MM
EARLY IN THE CYCLE. ON THURSDAY THIS INCREASES TO 35-70MM AS IT
BUILDS NORTH ACROSS RIO GRANDE DO SUL IN BRASIL TO CORRIENTES IN
ARGENTINA. ACTIVITY IS TO THEN GRADUALLY WANE DURING THE WEEKEND.

BROAD CELL OF THE SUBTROPICAL RIDGE WILL REMAIN THE DOMINANT
FEATURE OVER NORTHERN SOUTH AMERICA DURING THE NEXT FEW DAYS.
EARLY IN THE CYCLE THIS CENTERS ON A CLOSED HIGH OVER MATO GROSSO
IN BRASIL...WITH THE CLOSED CIRCULATION SHIFTING EAST TO WESTERN
MINAS GERAIS LATER ON FRIDAY. MEANWHILE...AS THE UPPER LEVEL RIDGE
HOLDS OVER NORTHERN SOUTH AMERICA IT IS VENT DIURNAL CONVECTION
ACROSS THE NORTHERN STATES OF BRASIL-SOUTHERN COLOMBIA/NORTHERN
PERU-EASTERN ECUADOR. IN THIS AREA EXPECTING RAINFALL AMOUNTS OF
15-20MM/DAY IN SCATTERED DEEP CONVECTION...WITH LOCALLY HIGHER
OVER SOUTHERN COLOMBIA-NORTHERN PERU-EASTERN ECUADOR EARLY IN THE
CYCLE...WHEN THE MAXIMA PEAKS AT 15-30MM/DAY.

DAVISON/GALVEZ...WPC (USA)