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 1635Z Sep 07, 2021)
 
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
1235 PM EDT TUE SEP 07 2021

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

FORECAST DISCUSSION FROM SEP 07/17UTC: A MID/UPPER LEVEL CLOSED
LOW NEAR CONCEPCION CHILE ANCHORS A SHORT WAVE TROUGH ALONG THE
CENTRAL ANDES. EARLY IN THE CYCLE THIS WEAKENS TO AN OPEN TROUGH
WHILE SHEARING SHORT WAVE ENERGY ACROSS THE CENTRAL PROVINCES IN
ARGENTINA. ON WEDNESDAY...UNDER FAVORABLE JET DYNAMICS...IT IS TO
ONCE AGAIN ORGANIZED INTO A CLOSED LOW AS IT MEANDERS EAST ACROSS
CENTRAL ARGENTINA. THE CLOSED LOW IS TO THEN MEANDER EAST ACROSS
THE RIO DE LA PLATA BASIN/URUGUAY EARLY ON THURSDAY MORNING...TO
THEN MEANDER OFFSHORE INTO THE WESTERN ATLANTIC LATER IN THE DAY.
AT LOW LEVELS...THE DEEP MID LEVEL VORTEX WILL INTERACT WITH A
SURFACE FRONT MEANDERING OVER PARAGUAY/BOLIVIA. THIS WILL
STRENGTHEN THE SURFACE BOUNDARY WHILE SUSTAINING CYCLOGENESIS OVER
CENTRAL ARGENTINA. THIS LOW IS TO RAPIDLY OCCLUDE OVER THE BUENOS
AIRES PROVINCE ON WEDNESDAY...FAVORING TIGHTENING OF THE PRESSURE
GRADIENT WHILE INDUCING A SOUTHERLY LOW LEVEL JET ACROSS NORTHERN
ARGENTINA/PARAGUAY TO CENTRAL BRASIL. THIS...IN-TURN...DRIVES THE
ASSOCIATED FRONT NORTH ACROSS PARAGUAY TO SOUTHERN BRASIL-MATO
GROSSO DO SUL TO NORTHERN BOLIVIA ON WEDNESDAY. ON THURSDAY THE
FRONT MOVES NORTH ACROSS SAO PAULO TO MATO GROSSO/RONDONIA...WHERE
IT IS EXPECTED TO STALL/FRONTOLIZE. ACROSS URUGUAY/RIO GRANDE DO
SUL THIS WILL TRIGGER HEAVY RAINFALL AMOUNTS WITH MAXIMA OF
75-150MM EARLY IN THE CYCLE. ON WEDNESDAY...AS THE FRONT SURGES
ACROSS PARAGUAY TO NORTHERN BOLIVIA THIS WILL TRIGGER SCATTERED
CONVECTION ACROSS PARAGUAY AND SOUTHERN/SOUTHEAST STATES OF
BRASIL...WITH MOST INTENSE BETWEEN CENTRAL BOLIVIA AND SOUTHERN
JUNGLE OF PERU. IN THIS AREA EXPECTING ACCUMULATION OF 40-80MM
THROUGH TODAY...INCREASING TO 50-100MM AS IT BUILDS NORTH AND WEST
ACROSS ACRE TO THE SOUTHERN JUNGLE OF PERU. OVER RONDONIA/SOUTHERN
AMAZONAS THE MAXIMA ON THURSDAY-FRIDAY WILL PEAK AT 25-50MM. ON
FRIDAY THE FOCUS OF THE CONVECTION SHIFTS TO CENTRAL/NORTHERN PERU
WHERE IT IS TO SUSTAIN RAINFALL AMOUNTS OF 25-50MM. OTHER
CONVECTION TO THE SOUTH IS EXPECTED IN ASSOCIATION WITH THE
OCCLUDING SURFACE LOW. EARLY IN THE CYCLE MOST ACTIVE IS EXPECTED
BETWEEN THE BUENOS AIRES PROVINCE AND LA PAMPA...WITH MAXIMA OF
40-80MM. ON WEDNESDAY THIS INCREASES TO 50-100MM WHILE BUILDING
NORTH ACROSS THE BUENOS AIRES PROVINCE TO URUGUAY.

BROAD TROUGH TO THE SOUTHEAST DOMINATES THE SOUTH PACIFIC. THROUGH
WEDNESDAY EVENING THE TROUGH IS TO PULL UNDER A RIDGE TO THE
EAST...WITH A HIGH AMPLITUDE TROUGH TO THEN TAKE ITS PLACE EARLY
ON THURSDAY MORNING. THE LATTER IS TO THEN AMPLIFY OVER THE
EASTERN PACIFIC...WITH AXIS REACHING MAXIMUM AMPLITUDE EARLY ON
FRIDAY MORNING. LATER ON SATURDAY IT WILL PRESS EAST ACROSS THE
SOUTHERN/CENTRAL REGIONS OF CHILE TO WESTERN ARGENTINA. AT LOW
LEVELS...BROAD SURFACE TROUGH DOMINATES THE FLOW OVER THE
SOUTHEAST PACIFIC...WITH AXIS FAVORING A TIGHT GRADIENT AND STRONG
BOUNDARY LAYER WINDS ACROSS SOUTHERN REGIONS OF CHILE. THIS
RAPIDLY WEAKENS ON WEDNESDAY AS A DEEPER PERTURBATION APPROACHES
FROM THE WEST. THIS IS TO THEN PRESS EAST ACROSS SOUTHERN CHILE TO
PATAGONIA IN ARGENTINA...WITH THE FRONTAL BOUNDARY AMPLIFYING
ACROSS THE SOUTHERN CONE ON FRIDAY TO SATURDAY. EARLY NEXT
WEEK...DRIVEN BY A SOUTHERLY LOW LEVEL JET...THE FRONT WILL THEN
SURGE ACROSS ARGENTINA TO MID SECTIONS OF SOUTH AMERICA. OVER
SOUTHERN CHILE THESE WILL COMBINE IN SUPPORT OF ORGANIZED
CONVECTION...WITH DAILY MAXIMA OF 20-35MM/DAY EXPECTED DURING THE
NEXT THREE DAYS. ON FRIDAY...CONVECTION INTENSIFIES AS IT BUILDS
ACROSS PUERTO MONTT/TEMUCO TO CONCEPCION IN CENTRAL CHILE...WITH
MAXIMA INCREASING TO 20-45MM. ON FRIDAY...THE FOCUS OF THE
CONVECTION SHIFTS TO CENTRAL CHILE. ALONG THE COAST EXPECTING
MODERATE SNOWFALL AMOUNTS...WITH MAXIMA OF 15-20MM. HEAVY SNOWFALL
AMOUNTS ARE EXPECTED ACROSS THE CENTRAL ANDES ON SATURDAY...WITH
MAXIMA OF 15-25CM. ON SUNDAY EXPECTING ADDITIONAL SNOWFALL AMOUNGS
OF 15-20CM...WITH MOST ACTIVE CLUSTERING ALONG THE CENTRAL ANDS
OUTHERN ANDES.

NORTH OVER THE CONTINENT...AT 200 HPA...AN ILL ORGANIZED CELL OF
THE SUBTROPICAL RIDGE CONFINES TO NORTHWEST SOUTH AMERICA. BUT AS
THE AFOREMENTINED CONVECION BUILDS ACROSS PERU AND NORTHWEST
BRASIL ON THURSDAY-FRIDAY...THE RELEASE OF LATENT HEAT BY THIS
RIDGE WILL INDUCE ITS GRADUAL INTENSIFICATION THROUGH FRIDAY. AS
PREVIOUSLY INDICATED...MOST INTENSE CONVECTION IS EXPECTED ACROSS
CENTRAL-SOUTHERN PERU ON WEDNESDAY AND THURSDAY...WHILE ACROSS
EQUATORIAL SOUTH AMERICA THE ACTIVITY BARELY SURGES DURING THE
WEEKEND.



DAVISON...WPC (USA)