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South American Forecast Discussion
 
(Caution: Version displayed is not the latest version. - Issued 1549Z Jul 22, 2021)
 
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SOUTH AMERICA FORECAST DISCUSSION - INTERNATIONAL DESKS
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1149 AM EDT THU JUL 22 2021

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

FORECAST DISCUSSION FROM JUL 22/16UTC: AT MID/UPPER LEVELS...A
LONG WAVE TROUGH OVER THE EASTERN PACIFIC NOW EXTENDS NORTH ALONG
93W TO 15S...WITH AXIS PRESSING AGAINST A RIDGE TO THE EAST. THE
LATTER EXTENDS SOUTH FROM A CLOSED HIGH OVER NORTHERN CHILE TO THE
DRAKE PASSAGE. OVER THE NEXT COUPLE OF DAYS THE TROUGH IS TO
GRADUALLY WEAKEN WHILE SHEARING SHORT WAVE ENERGY UNDER THE RIDGE
TO THE EAST...AND EARLY ON SATURDAY IT IS TO WEAKEN TO A SHORT
WAVE TROUGH OFF THE CENTRAL COAST OF CHILE. AT LOW LEVELS...THE
TROUGH ALOFT SUSTAINS A FRONT THAT SURGES ACROSS PATAGONIA TO
CENTRAL ARGENTINA EARLY ON FRIDAY MORNING...WITH BOUNDARY STALLING
OVER URUGUAY/RIO DE LA PLATA BASIN LATER IN THE DAY. UNDER THE
INFLUENCE OF COUPLED JETS ALOFT...A FRONTAL LOW FORMS ALONG THIS
BOUNDARY ON SATURDAY. THIS WILL ENHANCE LOW LEVEL MOISTURE
CONVERGENCE ACROSS ENTRE RIOS IN ARGENTINA/URUGUAY...TO SUSTAIN
MODERATE TO HEAVY RAINFALL AMOUNTS WITH ACCUMULATION OF 20-45MM IN
POTENTIALLY SEVERE CONVECTION.

SIMULTANEOUSLY...A SHORT WAVE TROUGH IN THE SOUTHERN STREAM FLOW
IS TO CLOSELY FOLLOW...WITH THE MID LEVEL VORTEX RACING ACROSS 90W
LATER ON FRIDAY EVENING. BUT AS IT ENTERS THE SOUTHERN CONE ON
SATURDAY...A BUILDING RIDGE TO THE WEST INDUCES THE NORTHWARD
AMPLIFICATION OF THE TROUGH ACROSS THE SOUTHERN CONE OF SOUTH
AMERICA...WITH AXIS TO STRENGTHEN ON SUNDAY AS IT PHASES WITH THE
REMNANTS OF THE AFOREMENTIONED TROUGH. AT IT MOVES TO THE WESTERN
ATLANTIC ON SUNDAY TO MONDAY...THIS THEN EVOLVES INTO A BROAD
TROUGH THAT IS TO ENVELOP AREA BETWEEN 70W-40W AND TO TE SOUTH OF
28S. AT LOW LEVELS...THIS SUSTAINS A PROGRESSIVE FRONTAL TROUGH
THAT LIFTS ACROSS THE SOUTHEAST PACIFIC TO THE SOUTHERN CONE LATER
ON SATURDAY...WITH AXIS TO TRIGGER MODERATE RAINFALL AMOUNTS
ACROSS CHILE TO THE SOUTH OF 40S...WITH MAXIMA OF 15-25MM. THROUGH
SUNDAY THE FRONTAL TROUGH IS TO THEN AMPLIFY OVER THE WESTERN
ATLANTIC WHILE SIMULTANEOUSLY A POLAR RIDGE BUILDS NORTH ACROSS
ARGENTINA. THIS WILL SUSTAIN A COLD ADVECTIVE PATTERN WHILE
SIMULTANEOUSLY DISPLACING THE ASSOCIATED FRONT NORTH ACROSS
ARGENTINA TO MID SECTIONS OF SOUTH AMERICA EARLY NEXT WEEK. OVER
SOUTHERN CHILE THIS WILL FAVOR MODERATE CONVECTION...WITH
ACCUMULATION OF 15-25MM ON FRIDAY. ON SATURDAY TO SUNDAY...IN A
COLD ADVECTIVE PATTERN...THE CLOUDS TEMPERATURE WILL BE COLD
ENOUGH TO SUSTAIN SOLID PRECIPITATION (SNOW). ON SUNDAY EXPECTING
LIGHT SNOWFALL AMOUNTS ACROSS TIERRA DEL FUEGO/EXTREME SOUTHERN
CHILE...WHILE TO THE NORTH ACROSS CENTRAL CHILE IT WILL SUSTAIN
SNOWFALL AMOUNTS OF 10-15CM. OTHER SNOWFALL IS EXPECTED ACROSS THE
SIERRA DE LA VENTANA AND TANDIL...TO RESULT IN TRACE SNOWFALL
AMOUNTS. HIGHER AMOUNTS ARE EXPECTED ACROSS MATO GROSSO DO
SUL-CORRIENTES IN ARGENTINA TO SOUTHEAST PARAGUAY ON MONDAY...TO
SUSTAIN RAINFALL AMOUNTS OF 20-40MM.

NORTH OVER THE CONTINENT...AT 250 HPA...A LOW AMPLITUDE RIDGE
CONFINES TO EQUATORIAL SOUTH AMERICA. THROUGH THE END OF THE CYCLE
THIS IS EXPECTED TO AMPLIFY ACROSS BRASIL TO NORTHERN
BOLIVIA/PARAGUAY. MEANWHILE...THIS WILL VENT DEEP CONVECTION
ACROSS EASTERN ECUADOR TO SOUTHWEST COLOMBIA...WITH ACCUMULATION
OF 20-35MM. THROUGH THE WEEKEND THIS WEAKENS TO MAXIMA OF
05-10MM/DAY. OTHER CONVECTION IS EXPECTED BETWEEN AMAZONAS AND
AMAPA IN BRASIL...TO SUSTAIN MODERATE RAINFALL AMOUNTS WITH MAXIMA
OF 15-20MM IN SCATTERED DEEP CONVECTION.
DAVISON...WPC (USA)