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 1453Z May 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
1053 AM EDT TUE MAY 26 2020

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

FORECAST DISCUSSION FROM MAY 21/16UTC: A MID/UPPER LEVEL RIDGE
OVER THE EASTERN PACIFIC IS STEERING A SHORT WAVE TROUGH ACROSS
THE CENTRAL ANDES OF CHILE INTO CENTRAL ARGENTINA EARLY IN THE
CYCLE...WITH THE MID LEVEL TROUGH DEEPENING/BECOMING BETTER
ORGANIZED AS IT LIFTS ACROSS THE MESOPOTAMIA VALLEY IN
ARGENTINA/URUGUAY TO SOUTHERN BRASIL EARLY ON SATURDAY MORNING.
THIS IS TO THEN MEANDER OFF THE SOUTHEAST COAST OF BRASIL THROUGH
SUNDAY AFTERNOON WHILE CENTERING ON A CLOSED LOW...THEN ACCELERATE
TO THE SOUTHEAST AS ANOTHER MID LEVEL TROUGH LIFTS ALONG THE COAST
OF ARGENTINA EARLY NEXT WEEK. AT 250 HPA A SUBTROPICAL-POLAR JETS
ARE TO ACCOMPANY THIS FEATURE AS IT ENTERS MID SECTIONS OF SOUTH
AMERICA...WITH THE JETS COUPLING ON THEIR DIVERGENT EXIT/ENTRANCE
REGIONS OVER NORTHERN ARGENTINA-PARAGUAY.

AT LOW LEVELS...THE MID LEVEL TROUGH SUSTAINS CYCLOGENESIS ALONG A
MEANDERING FRONT OVER NORTHERN ARGENTINA. THE LOW IS FORECAST TO
INTENSIFY/RAPIDLY OCCLUDE AS IT LIFTS ACROSS RIO GRANDE DO SUL IN
BRASIL TO THE WESTERN ATLANTIC ON FRIDAY-SATURDAY. THE DEEPENING
FRONTAL LOW AND A BUILDING POLAR RIDGE TO THE SOUTH WILL THEN
FAVOR A PAMPERO (SOUTHERLY) LOW LEVEL JET ACROSS ARGENTINA TO
PARAGUAY. THE JET WILL RAPIDLY DISPLACE THE FRONT ACROSS NORTHERN
ARGENTINA TO SOUTHERN BRASIL-PARAGUAY/SOUTHERN BOLIVIA LATER
TODAY. IN A HIGH SHEAR ENVIRONMENT...THIS IS LIKELY TO TRIGGER
SEVERE THUNDERSTORMS ACROSS PARAGUAY-CORRIENTES/MISIONES IN
NORTHERN ARGENTINA AND RIO GRANDE DO SUL IN SOUTHERN
BRASIL...WHILE ALSO FAVORING HEAVY RAINFALL AMOUNTS WITH MAXIMA OF
50-100MM. ON FRIDAY THE FRONT SURGES TO SOUTHEAST BRASIL-MATO
GROSSO-NORTHERN BOLIVIA WHILE A DEEP OCCLUDED LOW CLOSES OVER RIO
GRANDE DO SUL. THIS DRIVES THE LOW LEVEL JET FARTHER NORTH AND
WEST ACROSS PARAGUAY...ENHANCING LOW LEVEL CONVERGENCE ACROSS
CENTRAL/NORTHERN BOLIVIA. ACROSS MATO GROSSO-SOUTHEAST BRASIL THIS
WILL THEN SUSTAIN MAXIMA OF 30-60MM...WHILE OVER URUGUAY/RIO
GRANDE DO SUL EXPECTING MAXIMA OF 40-80MM IN POTENTIALLY SEVERE
CONVECTION. LIKEWISE...OVER CENTRAL BOLIVIA...IT IS TO ALSO
TRIGGER HEAVY RAINFALL AMOUNTS WITH MAXIMA OF 40-80MM...WHILE TO
THE NORTH AND ACROSS ACRE TO RONDONIA/SOUTHERN JUNGLE OF PERU THE
MAXIMA WILL PEAK AT 20-35MM. ON SATURDAY THE SOUTHERLY JET DRIVES
THE FRONT FARTHER NORTH INTO TROPICAL SOUTH AMERICA...TRIGGERING A
PREFRONTAL SHEAR LINE ACROSS AMAZONAS IN BRASIL. UNDER INFLUENCE
OF THE FRONT AND THE PREFRONTAL SHEAR LINE HEAVY CONVECTION IS
EXPECTED ACROSS AMAZONAS-NORTHERN PERU TO SOUTHERN
COLOMBIA-EASTERN ECUADOR ON SATURDAY-SUNDAY...WITH MAXIMA OF
25-50MM/DAY. LOCALLY HIGHER AMOUNTS ARE POSSIBLE OVER NORTHERN
PERU-EASTERN ECUADOR DUE TO STRONG TOPOGRAPHICAL FORCING...WITH
SOME OF THE MODELS SHOWING LOCALIZED MAXIMA OF 40-80MM.

AS THE MID/UPPER LEVEL RIDGE HOLDS OVER THE EASTERN PACIFIC...IT
IS TO STEER SUCCESSIVE SHORT WAVE PERTURBATIONS ACROSS THE
SOUTHEAST PACIFIC TO THE SOUTHERN REGIONS OF CHILE/PATAGONIA IN
ARGENTINA. THE MODELS ARE MAKING CYCLE-TO-CYCLE CORRECTIONS TO THE
TIMING OF THESE PERTURBATIONS...WITH THE GFS CORRECTING IN FAVOR
OF A SLOWER PROGRESSION THAN WHAT IT PREVIOUSLY SUGGESTED A COUPLE
OF DAYS AGO. AT LOW LEVELS THESE WILL SUSTAIN AN ELONGATED FRONT
THAT IS TO STRETCH TO THE NORTHWEST ACROSS PATAGONIA-SOUTHERN
CHILE TO THE EASTERN PACIFIC. FRONTAL LOWS ARE TO PROPAGATE ALONG
THE MEANDERING SURFACE BOUNDARY...ENTERING SOUTHERN CHILE ON
FRIDAY AND SUNDAY MORNING. THESE WILL BE ACCOMPANIED BY STRONG
BOUNDARY LAYER WINDS...SUSTAINING A WARM/MOIST ADVECTIVE PATTERN.
THIS WILL FEED CONVECTIVE DEVELOPMENT ACROSS THE SOUTHERN REGIONS
OF CHILE...WITH PEAK IN CONVECTION ON FRIDAY-SATURDAY WHEN IT IS
TO SUSTAIN MAXIMA OF 20-35MM. OTHERWISE...THE DAILY MAXIMA IN THIS
AREA WILL PEAK AT 10-15MM.

NORTH OVER THE CONTINENT...AT 200 HPA...THE SUBTROPICAL RIDGE OVER
BRASIL BECOMES BETTER ORGANIZED EARLY IN THE CYCLE...WHEN IT IS TO
BECOME THE DOMINANT FEATURE TO THE NORTH OF 20S. THE RIDGE ALOFT
WILL THEN VENT THE AFOREMENTIONED CONVECTION ACROSS NORTHWEST
SOUTH AMERICA AHEAD OF THE SURGING SURFACE FRONT. IT IS TO ALSO
VENT DIURNAL CONVECTION ALONG THE NORTH COAST OF BRASIL...WITH
MAXIMA IN THIS AREA PEAKING AT 10-15MM...WHILE OVER PARA AND
AMAZONAS TO THE WEST INITIALLY EXPECTING MAXIMA OF 25-50MM.
THROUGH FRIDAY THE FOCUS OF THE CONVECTION SHIFTS TO SOUTHERN
COLOMBIA-NORTHERN PERU/EASTERN ECUADOR...WITH MAXIMA OF
20-40MM...THEN SURGES AGAIN AS ENHANCED BY THE PREFRONTAL SHEAR
LINE.

DAVISON...WPC (USA)
GALVEZ...WPC (USA)