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 1416Z Aug 25, 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
1016 AM EDT TUE AUG 25 2020

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

FORECAST DISCUSSION FROM AUGUST 25/14UTC: CONSISTENT WITH PREVIOUS
FORECASTS...MODELS CONTINUE TO PREDICT THE SOUTHWARD AMPLIFICATION
OF A LONG WAVE RIDGE OVER THE EASTERN SOUTH PACIFIC...WITH AXIS TO
EXTEND SOUTH 90W-120W TO THE POLAR ICECAP. UNDER INFLUENCE OF THE
BUILDING RIDGE TO THE WEST...SUCCESSIVE SHORT WAVE TROUGHS ARE TO
LIFT TO THE NORTHEAST ACROSS THE BELLINGSHAUSEN SEA/SOUTHEAST
PACIFIC TO THE SOUTHERN CONE...WITH A FAIRLY DEEP PERTURBATION
ENTERING THE SOUTHERN CONE EARLY ON THURSDAY MORNING. THE INFLOW
OF SHORT WAVE ENERGY WILL THEN HELP SUSTAIN A BROAD TROUGH OVER
THE WESTERN ATLANTIC TO MID SECTIONS OF SOUTH AMERICA LATER IN THE
CYCLE. AT LOW LEVELS...BROAD RIDGE WILL ALSO BUILD TO THE
WEST...TO CENTER ON A 1043-1045 HPA LATER ON THURSDAY-FRIDAY.
POLAR FRONTS ARE TO THEN REVOLVE AROUND THIS AXIS AS THEY STREAM
ACROSS SOUTHERN CHILE TO PATAGONIA IN ARGENTINA...SUSTAINING A
COLD ADVECTIVE PATTERN WITH BELOW FREEZING TEMPERATURES TO ENVELOP
THE SOUTHERN CONE. THIS WILL ALLOW FOR A PRECIPITATION PHASE
CHANGE ON WEDNESDAY...WHEN AIR MASS BECOMES COLD ENOUGH TO SUSTAIN
HEAVY SNOWFALL AMOUNTS ACROSS TIERRA DEL FUEGO AND THE SOUTHERN
ANDES OF CHILE...WITH ACCUMULATION OF 15-20CM/DAY EXPECTED BETWEEN
WEDNESDAY AND FRIDAY EVENING. FURTHERMORE...THE DEEPENING TROUGH
WILL BE ACCOMPANIED BY STRONG BOUNDARY LAYER WINDS OF 35-50KT.

A DEEP MID LEVEL TROUGH ON THE NORTHERN STREAM IS THE OTHER SYSTEM
OF CONCERN...WITH AXIS EXTENDING OFF THE CENTRAL/NORTHERN COAST OF
CHILE WHILE ANCHORING ON A CLOSED LOW NEAR ARCHIPELAGO DE JUAN
FERNANDEZ. 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. THE
SHORT WAVE TROUGH IS TO THEN FOCUS ITS SHORT WAVE ENERGY ACROSS
RIO DE LA PLATA BASIN-CENTRAL ARGENTINA WHILE SIMULTANEOUSLY
FAVORING HEIGHT FALLS OF 50-75GPM. AT 250 HPA...A
SUBTROPICAL-NORTHERN POLAR JET PAIR ARE TO ACCOMPANY THIS TROUGH
AS IT MOVES ACROSS THE SOUTHERN CONE...FAVORING AN UPPER DIVERGENT
PATTERN THAT IS TO VENT ORGANIZED DEEP CONVECTION DURING THE NEXT
FEW DAYS. AS THEY STREAM ACROSS ARGENTINA THESE JETS ARE LIKELY TO
COUPLE ON THEIR DIVERGENT EXIT/ENTRANCE REGIONS LATER TODAY AND ON
THURSDAY...TO PROVIDE FURTHER ENHANCEMENT TO DEVELOPMENT. AT LOW
LEVELS...THIS SUSTAINS A BROAD TROUGH OVER THE CENTRAL COAST OF
CHILE...WHERE IT IS TO MEANDER WHILE GRADUALLY FILLING EARLY ON
WEDNESDAY. MEANWHILE...THIS WILL ENHANCE LOW LEVEL MOISTURE
CONVERGENCE TO SUSTAIN MODERATE RAINFALL AMOUNTS WITH MAXIMA OF
15-30MM. ALONG THE CENTRAL ANDES EXPECTING SOLID
PRECIPITATION...WITH SNOWFALL AMOUNTS OF 10-15CM EARLY IN THE
CYCLE. SIMILAR AMOUNTS ARE ALSO EXPECTED ON THE NORTHERN ANDES
JUST EAST OF THE ATACAMA DESERT.

OVER CENTRAL ARGENTINA...AS THE MID LEVEL TROUGH STREAMS ACROSS
THE SOUTHERN CONE...IT IS TO SUSTAIN CYCLOGENESIS ALONG A
MEANDERING FRONT. THIS WILL INTENSIFY THE BAROCLINIC BOUNDARY
WHILE SUSTAINING HEAVY SEVERE CONVECTION. IN THIS AREA THERE IS A
MODERATE TO HIGH RISK OF LARGE HAIL PRODUCING THUNDERSTORMS...WITH
RAINFALL MAXIMA OF 40-80MM OVER THE BUENOS AIRES PROVINCE-CENTRAL
ARGENTINA-URUGUAY EARLY IN THE CYCLE. ON WEDNESDAY TO THURSDAY THE
FOCUS OF THE HEAVY CONVECTION AND SEVERE THUNDERSTORMS SHIFTS
NORTH TO URUGUAY-ENTRE RIOS/CORRIENTES IN ARGENTINA TO RIO GRANDE
DO SUL IN BRASIL...WITH MAXIMA INCREASING FROM 25-50MM ON
WEDNESDAY TO 35-70MM ON THURSDAY. DURING THE LATTER PERIOD...THE
CONDITIONS ALSO APPEAR FAVORABLE FOR AN MCS TO DEVELOP...SO
RAINFALL AMOUNTS ARE LIKELY TO EXCEED MODEL FORECAST GUIDANCE.


NORTH OVER THE CONTINENT...AT 200 HPA...AN UNSEASONALLY STRONG
CELL OF THE SUBTROPICAL RIDGE DOMINATES NORTHERN SOUTH
AMERICA...WHILE ANCHORING ON A CLOSED HIGH OVER TOCANTINS/GOIAS IN
BRASIL. ALTHOUGH THE CLOSED HIGH IS FORECAST TO WEAKEN OVER THE
NEXT COUPLE OF DAYS...THE RIDGE IS EXPECTED TO HOLD THROUGH THE
END OF THE CYCLE. MEANWHILE...THE RIDGE ALOFT IS TO CONTINUE
VENTING DEEP CONVECTION ACROSS EQUATORIAL SOUTH AMERICA. MOST
ACTIVE OVER NORTHERN PARA/RORAIMA IN BRASIL EARLY IN THE CYCLE
WILL RESULT IN ACCUMULATION OF 20-45MM. THROUGH THURSDAY ACTIVITY
SPREADS WEST ACROSS AMAZONIA IN BRASIL TO SOUTHERN
COLOMBIA/EASTERN ECUADOR...WHERE IT IS TO SUSTAIN MAXIMA OF
15-30MM. BROAD AREA OF CONVECTION IS TO THEN PERSIST THROUGH THE
END OF THE WEEK...WITH MAXIMA OF 15-20MM/DAY IN SCATTERED DEEP
CONVECTION.

DAVISON/GALVEZ...WPC (USA)