Prognostic Meteorological Discussion
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959
FXSA20 KWBC 211557
PMDSA

SOUTH AMERICA FORECAST DISCUSSION - INTERNATIONAL DESKS
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1157 AM EDT FRI JUL 21 2017

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

MODEL DISCUSSION (VALID FROM JUL 21 AT 0000 UTC): GLOBAL MODEL
GUIDANCE REMAIN IN EXCELLENT AGREEMENT ON PATTERN EVOLUTION OVER
THE CONTINENT DURING THE NEXT SEVEN DAYS. THE DETERMINISTIC
SOLUTION IS WELL SUPPORTED BY THE MEAN OF THE GLOBAL
ENSEMBLES...LEADING TO A HIGH CONFIDENCE IN THE FORECAST THROUGH
THE MEDIUM RANGE PERIOD.

A MID LEVEL SHORT WAVE TROUGH ON THE NORTHERN STREAM IS TO EXTEND
TO THE NORTH-NORTHWEST ACROSS SOUTHEAST BRASIL TO TOCANTINS/GOIAS
EARLY IN THE PERIOD. ON SATURDAY THE TROUGH MEANDERS EAST ACROSS
MINAS GERAIS-ESPIRITO SANTO IN BRASIL...MOVING OFF THE COAST TO
THE WESTERN ATLANTIC EARLY ON SUNDAY. AT LOW LEVELS...THE
ASSOCIATED FRONT EXTENDS TO THE NORTHWEST ACROSS BRASIL. THROUGH
SATURDAY EVENING...AS THE FRONT LOSES ITS UPPER LEVEL SUPPORT...IT
IS FORECAST TO FRONTOLIZE. MEANWHILE...THIS IS TO FAVOR LIGHT
COASTAL CONVECTION ACROSS RIO DE JANEIRO-ESPIRITO SANTO IN BRASIL.

UPSTREAM OVER THE SOUTH PACIFIC...PROGRESSIVE MID LEVEL TROUGH IS
TO PULL ACROSS 90W LATER TODAY. ON SATURDAY EVENING IT IS TO NEAR
THE SOUTH-CENTRAL COAST OF CHILE...AND ON SUNDAY MORNING IT WILL
MOVE ACROSS PATAGONIA IN ARGENTINA TO THE WESTERN ATLANTIC. AS IT
STREAMS ACROSS THE SOUTHERN CONE THE DEEP MID LEVEL TROUGH IS TO
INDUCE HEIGHT FALLS OF 150-200 GPM. THIS IS TO ALSO SUSTAIN A DEEP
TONGUE OF SUBTROPICAL MOISTURE THAT IS TO POOL ALONG THE SOUTH
COAST OF CHILE EARLY IN THE PERIOD. AT LOW LEVELS...THE ASSOCIATED
POLAR TROUGH/FRONT MOVE ACROSS SOUTHERN CHILE TO PATAGONIA IN
ARGENTINA LATER TODAY. ON SATURDAY THE FRONT IS TO THEN MEANDER
ACROSS NORTHERN PATAGONIA-TEMUCO CHILE TO THE EASTERN PACIFIC.
BOUNDARY IS TO THEN MIGRATE NORTH ACROSS RIO DE LA PLATA
BASIN-MENDOZA IN ARGENTINA-LA SERENA CHILE TO THE EASTERN PACIFIC
ON SUNDAY...WHERE IT IS TO REMAIN THROUGH TUESDAY EVENING. ALSO AT
LOW LEVELS...A MOIST NORTHERLY FLOW IS TO ESTABLISH ACROSS
PARAGUAY TO CENTRAL PROVINCES IN ARGENTINA ON SATURDAY...TO
PERSIST THROUGH MONDAY. THIS IS TO ENHANCE MOISTURE CONVERGENCE
ALONG THE SURFACE FRONT OVER RIO DE LA PLATA BASIN ON
SUNDAY-MONDAY. ON THE SOUTHERN REGIONS OF CHILE THIS WILL SUSTAIN
MODERATE CONVECTION WITH ACCUMULATION OF 20-30MM THROUGH SATURDAY
MORNING...AND 15-20MM ON SATURDAY TO SUNDAY. ACROSS
TEMUCO-CONCEPCION AND TIERRA DEL FUEGO THIS IS TO TRIGGER RAINFALL
AMOUNTS OF 05-10MM/DAY ON SATURDAY-SUNDAY. AS THE MID/UPPER LEVEL
TROUGH PULLS ACROSS CENTRAL CHILE ON SATURDAY-SUNDAY IT IS TO THEN
SUSTAIN SCATTERED CONVECTION ACROSS THE CENTRAL ANDES...WITH
CONDITIONS FAVORABLE FOR LIGHT TO MODERATE SNOWFALL AMOUNTS TO
SUSTAIN ACCUMULATION OF 05-10CM. OVER RIO DE LA PLATA BASIN THIS
IS TO FAVOR SCATTERED CONVECTION WITH ACCUMULATION OF 05-10MM.

SUCCESSIVE MID LEVEL SHORT WAVE PERTURBATIONS ON THE SOUTHERN
STREAM ARE TO THEN COMBINE IN SUPPORT OF A BROAD TROUGH OVER THE
EASTERN SOUTH PACIFIC ON SUNDAY-MONDAY...WHEN IT IS TO CENTER ON A
DEEP LOW NEAR 57S 90W. AT LOW LEVELS THIS WILL SUSTAIN A DEEP
POLAR TROUGH OVER THE SOUTHEAST PACIFIC EARLY ON SUNDAY
MORNING...WHERE IT IS TO GENERALLY PERSIST THROUGH TUESDAY NEXT
WEEK. AS IT MEANDERS OVER THE SOUTHEAST PACIFIC POLAR FRONTS ARE
TO REVOLVE AROUND THIS AXIS...WITH ONE TO ENTER SOUTHERN CHILE
LATER ON SUNDAY AND THE NEXT LATER ON MONDAY/EARLY TUESDAY
MORNING. IN A COLD ADVECTIVE PATTERN THE 1000-500 HPA THICKNESS
OVER SOUTHERN CHILE AND PORTIONS OF PATAGONIA IN ARGENTINA WILL
RANGE BETWEEN 522-528DM...COLD ENOUGH TO FAVOR SOLID/FROZEN
PRECIPITATION ACROSS THE SOUTHERN ANDES ON ELEVATIONS ABOVE 1000
METERS...TO RESULT ON SNOWFALL AMOUNTS OF 15-20CM ON
SUNDAY-MONDAY. ALONG THE COAST TO THE SOUTH OF TEMUCO EXPECTING
MODERATE RAINFALL AMOUNTS OF 10-15MM IN MIXED PRECIPITATION. OVER
TIERRA DEL FUEGO LIQUID PRECIPITATION WILL RESULT IN RAINFALL
AMOUNTS OF 05-10MM.

THE MID/UPPER LEVEL TROUGH OVER BRASIL SPLITS THE SUBTROPICAL
RIDGE IN TWO CELLS...WITH ONE OVER THE EASTERN PACIFIC AND THE
OTHER OVER THE TROPICAL ATLANTIC. BUT AS THE TROUGH PULLS ACROSS
BRASIL TO THE WESTERN ATLANTIC LATER ON SUNDAY THIS WILL THEN
ALLOW THE CELL OVER THE ATLANTIC TO BUILD WEST ACROSS EQUATORIAL
SOUTH AMERICA TO NORTHWEST BRASIL LATER ON SUNDAY/EARLY ON MONDAY.
IN RESPONSE...CONVECTION ACROSS EQUATORIAL SOUTH AMERICA IS TO
INTENSIFY WHILE BUILDING TO THE WEST-SOUTHWEST ACROSS THE
GUIANAS-SOUTHERN VENEZUELA TO NORTHERN PARA/RORAIMA IN
BRASIL-NORTHERN AMAZONAS/NORTHERN JUNGLE OF PERU. IN THIS AREA
INITIALLY EXPECTING RAINFALL AMOUNTS OF 10-15MM/DAY...INCREASING
TO 15-20MM/DAY ON MONDAY-TUESDAY. ON THE NORTH COAST OF BRASIL
INITIALLY EXPECTING RAINFALL AMOUNTS OF 15-20MM/DAY. BUT AS THE
UPPER PATTERN EVOLVES THIS DECREASES TO 05-10MM/DAY ON
SUNDAY-MONDAY. ON THE NORTHEAST COAST...BETWEEN ESPIRITO SANTO AND
EASTERN BAHIA TRADE WIND CONVERGENCE IS TO INITIALLY FAVOR LIGHT
RAINFALL AMOUNTS. ON SATURDAY-SUNDAY THIS INCREASES TO 10-15MM/DAY.

ESPINOLA...DNM (PARAGUAY)
GONZALEZ...DMC (CHILE)
DAVISON...WPC (USA)
$$





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