492  
FXSA20 KWBC 261419  
PMDSA  
 
SOUTH AMERICA FORECAST DISCUSSION - INTERNATIONAL DESKS  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
1019 AM EDT FRI MAY 26 2017  
 
GFS DATA AT FTPPRD.NCEP.NOAA.GOV/PUB/DATA/NCCF/COM/GFS/PROD/  
 
LAST NO AMENDS...NEXT BULLETIN ON MAY 30.  
 
MODEL DISCUSSION (VALID FROM MAY 26 AT 0000 UTC): THE GLOBAL  
MODELS REMAIN IN GOOD AGREEMENT DURING THE FORECAST  
PERIOD...FORESEEING A SIMILAR EVOLUTION ACROSS THE SOUTH AMERICAN  
DOMAIN. THIS IS WELL SUPPORTED BY THE MEAN OF THE GLOBAL  
ENSEMBLES...LEADING TO A HIGH CONFIDENCE FORECAST THROUGH DAY 06.  
 
A DEEP/HIGH AMPLITUDE TROUGH IS TO AMPLIFY ACROSS THE WESTERN  
ATLANTIC EARLY IN THE CYCLE. THIS IS TO THEN PULL ACROSS 20W/30W  
LATER ON SATURDAY. A MEANDERING SHORT WAVE TROUGH OFF THE CENTRAL  
COAST OF CHILE TRAILS THIS SYSTEM...WHILE ANCHORING ON A CLOSED  
LOW NEAR THE ARCHIPELAGO DE JUAN FERNANDEZ. ON SATURDAY IT IS TO  
SPILL ACROSS THE ANDES INTO THE CENTRAL/NORTHERN PROVINCES IN  
ARGENTINA...AND EARLY ON SUNDAY IT IS TO STREAM ACROSS THE RIO DE  
LA PLATA BASIN TO THE WESTERN ATLANTIC. MEANWHILE...AS IT MEANDERS  
OFF THE COAST OF CHILE...THE MID LEVEL VORTEX IS TO SHEAR SHORT  
WAVE PERTURBATIONS ACROSS THE CENTRAL/NORTHERN ANDES INTO NORTHERN  
ARGENTINA/PARAGUAY-SOUTHERN STATES OF BRASIL/URUGUAY. THESE ARE TO  
PROVIDE DYNAMICAL SUPPORT TO ORGANIZED DEEP CONVECTION OVER THE  
NEXT TWO DAYS. AT 250 HPA...THE TROUGH ALOFT IS TO FOCUS A  
SUBTROPICAL JET ACROSS THE NORTHERN ANDES OF CHILE/ARGENTINA INTO  
MID SECTIONS OF SOUTH AMERICA. THE JET ALOFT WILL FAVOR GENERATION  
OF LEESIDE PERTURBATIONS ACROSS THE NORTHERN PROVINCES IN  
ARGENTINA WHILE ALSO FAVORING AN UPPER DIVERGENT PATTERN.  
 
AT LOW LEVELS...DEEPENING POLAR TROUGH OVER THE WESTERN ATLANTIC  
WILL SUSTAIN A POLAR FRONT ACROSS CENTRAL ARGENTINA EARLY IN THE  
CYCLE...THAT MIGRATES NORTH ACROSS RIO DE LA PLATA BASIN/NORTHERN  
ARGENTINA LATER TODAY. AS IT MEANDERS NORTH THIS WILL THEN MERGE  
WITH REMNANTS OF AN OLD FRONT OVER MIDSECTIONS OF SOUTH AMERICA.  
THE MEANDERING FRONT WILL REMAIN FOCUS OF LOW LEVEL MOISTURE  
CONVERGENCE ACROSS SOUTHERN BRASIL-PARAGUAY/MISIONES IN ARGENTINA  
AND SOUTHEAST PARAGUAY. IN THIS AREA EXPECTING ORGANIZED DEEP  
CONVECTION OVER THE NEXT TWO DAYS TO TRIGGER RAINFALL AMOUNTS OF  
35-70MM THROUGH SATURDAY MORNING...AND 30-60MM ON SATURDAY TO  
SUNDAY...WITH LESSER AMOUNTS EXPECTED ON SUNDAY AS MID LEVEL  
VORTEX SHEARS AWAY.  
 
CONSISTENT WITH PREVIOUS FORECASTS...AN AMPLIFYING MID LEVEL  
TROUGH WILL PULL ACROSS 95W LATER TODAY...NEARING THE COAST OF  
CHILE ON SATURDAY EVENING. ON SUNDAY...UNDER FRICTIONAL EFFECT OF  
THE ANDES...THE TROUGH IS TO THEN SPLIT IN TWO. ITS SOUTHERN HALF  
WILL THEN PULL ACROSS PATAGONIA IN ARGENTINA TO THE WESTERN  
ATLANTIC...WHILE THE NORTHERN HALF STALLS OFF THE CENTRAL COAST OF  
CHILE. ON MONDAY...THE REMNANTS WILL THEN SPILL ACROSS THE CENTRAL  
ANDES INTO CUYO IN ARGENTINA...AND LATER ON TUESDAY IT WILL MOVE  
ACROSS ENTRE RIOS IN ARGENTINA TO URUGUAY/SOUTHERN BRASIL. THE  
DEEP MID LEVEL VORTEX IS TO THEN FAVOR HEIGHT FALL OF 75-125GPM AS  
IT MOVES ACROSS PARAGUAY/SOUTHERN BRASIL ON TUESDAY TO WEDNESDAY.  
AT LOW LEVELS THIS WILL THEN INTERACT WITH MEANDERING FRONT OVER  
NORTHERN ARGENTINA...TO TRIGGER A FRONTAL WAVE/LOW OVER  
CORRIENTES/ENTRE RIOS. THIS WILL THEN DRIVE THE FRONT NORTH ACROSS  
PARAGUAY TO MATO GROSSO DO SUL IN BRASIL/SANTA CRUZ IN EASTERN  
BOLIVIA EARLY NEXT WEEK...WHILE ALSO TRIGGERING ORGANIZED DEEP  
CONVECTION. NOTE THAT THE EXPECTED MESO-SYNOPTIC FORCING IS LIKELY  
TO TRIGGER SEVERE CONVECTION IN THIS REGION.  
 
POLAR TROUGH STREAMING ACROSS NORTHERN ARGENTINA EARLY IN THE  
CYCLE WILL THEN PRESS AGAINST THE SUBTROPICAL RIDGE TO THE EAST  
AND NORTH. AT 200 HPA THE RIDGE IS EXPECTED TO GRADUALLY FLATTEN  
EARLY ON SATURDAY MORNING...WHEN IT IS TO THEN CONFINE TO  
CONTINENTAL AREA TO THE NORTH OF 20S. AS IT MEANDERS OVER THE  
CONTINENT THIS WILL VENT DEEP CONVECTION ON THE PERUVIAN  
JUNGLE-WESTERN AMAZONAS/ACRE IN BRASIL AND EASTERN PORTIONS OF  
ECUADOR. IN THIS AREA EXPECTING RAINFALL AMOUNTS OF 05-10MM/DAY  
AND MAXIMA OF 15-20MM IN ISOLATED TO SCATTERED CONVECTION. OTHER  
CONVECTION IS TO CLUSTER OVER NORTHEAST BRASIL...TO SUSTAIN  
RAINFALL AMOUNTS OF 20-30MM/DAY AND MAXIMA OF 20-45MM. ACTIVITY IS  
TO GRADUALLY SPREAD WEST ALONG THE NORTH COAST THROUGH SUNDAY  
EVENING...TO SUSTAIN RAINFALL AMOUNTS OF 10-15MM IN ISOLATED TO  
SCATTERED CONVECTION.  
 
ABDEMUR...FAA (ARGENTINA)  
ESPINOLA...DNM (PARAGUAY)  
DAVISON...WPC (USA)  

 
 
CLICK HERE TO GO TO PREVIOUS BULLETINS.

The Nexlab HPC Page Main Text Page