205  
FXSA20 KWBC 261557  
PMDSA  
 
SOUTH AMERICA FORECAST DISCUSSION - INTERNATIONAL DESKS  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
1156 AM EDT THU OCT 26 2017  
 
GFS DATA AT FTPPRD.NCEP.NOAA.GOV/PUB/DATA/NCCF/COM/GFS/PROD/  
 
MODEL DISCUSSION (VALID FROM OCT 26 AT 0000 UTC): GLOBAL MODELS  
REMAIN IN EXCELLENT AGREEMENT THROUGH 96-108 HRS...THEN DISAGREE  
ON HOW A SHORT WAVE TROUGH LIFTING ACROSS THE EASTERN PACIFIC IS  
GOING TO EVOLVE. IN THIS AREA...VARIABILITY AMONG THE ENSEMBLE  
MEMBERS IS TOO HIGH TO ESTABLISH CONFIDENCE IN THE FORECAST.  
 
MID LEVEL SHORT WAVE PERTURBATIONS ON THE NORTHERN STREAM CONTINUE  
TO CROSS THE CENTRAL ANDES OF CHILE-CENTRAL PROVINCES IN  
ARGENTINA. IN THIS PATTERN A SHORT WAVE TROUGH CROSSES THE ANDES  
EARLY IN THE CYCLE AS ANOTHER MIGRATES ACROSS RIO DE LA PLATA  
BASIN/SOUTHERN STATES OF BRASIL. THROUGH FRIDAY THESE ARE TO  
COMBINE INTO A BROAD TROUGH OFF THE SOUTH COAST OF BRASIL/URUGUAY.  
AT 250 HPA A SUBTROPICAL-POLAR JET PAIR ACCOMPANY THESE  
PERTURBATIONS. THE JETS ARE FORECAST TO COUPLE ON THEIR RESPECTIVE  
ENTRANCE/EXIT REGIONS TO FAVOR A BROAD AREA OF DIVERGENCE ALOFT  
ACROSS CENTRAL PROVINCES IN ARGENTINA AND ACROSS SOUTHERN BRASIL  
TO PARAGUAY. THE INFLOW OF MID LEVEL ENERGY AND FAVORABLE JET  
DYNAMICS WILL HELP SUSTAIN ORGANIZED DEEP CONVECTION. OVER BUENOS  
AIRES PROVINCE/CENTRAL ARGENTINA THIS IS TO FAVOR MODERATE  
RAINFALL AMOUNTS WITH ACCUMULATION OF 20-35MM IN SEVERE  
CONVECTION. ACROSS SOUTHERN BRASIL-PARAGUAY CONVECTION IS TO  
CLUSTER ALONG A MEANDERING FRONT TO RESULT IN RAINFALL AMOUNTS OF  
40-80MM IN SEVERE CONVECTION. ON FRIDAY-SATURDAY THIS DECREASES TO  
20-40MM/DAY. LATER ON SUNDAY EVENING/EARLY MONDAY MORNING  
ENVIRONMENTAL CONDITIONS ARE TO ONCE AGAIN BECOME FAVORABLE FOR  
ORGANIZED DEEP CONVECTION TO BUILD ALONG THE MEANDERING  
FRONT...WITH AN MCS OVER PARAGUAY-SOUTHERN BRASIL TO TRIGGER  
MAXIMA OF 75-125MM.  
 
A DEEPENING SHORT WAVE TROUGH ON THE SOUTHERN STREAM FLOW  
FOLLOWS... WITH MID LEVEL AXIS TO MOVE ACROSS 95W TO 35S LATER  
TODAY. ON FRIDAY...AS IT NEARS THE SOUTH COAST OF CHILE...THE MID  
LEVEL PERTURBATION IS FORECAST TO DEEPEN...CENTERING ON A CLOSED  
LOW JUST WEST OF ISLA DE CHILOE. THROUGH SATURDAY THIS EVOLVES  
INTO A BROAD TROUGH ACROSS THE SOUTHERN CONE...FOCUSING ITS SHORT  
WAVE ENERGY ACROSS PATAGONIA IN ARGENTINA-LA PAMPA TO CUYO. IN  
THIS AREA EXPECTING HEIGHT FALLS OF 150-200 GPM. THIS IS STRONG  
ENOUGH TO LIKELY FAVOR SEVERE CONVECTION ACROSS LA PAMPA IN  
CENTRAL ARGENTINA BY MIDDAY ON SATURDAY. AT LOW LEVELS THIS WILL  
SUSTAIN A DEEP OCCLUDED LOW OFF THE SOUTH COAST OF CHILE LATER ON  
FRIDAY...WHILE THE ASSOCIATED FRONT MOVES EAST ACROSS PATAGONIA IN  
ARGENTINA. ON SATURDAY THE FRONT MEANDERS EAST ACROSS LA  
PAMPA-SOUTHERN CUYO IN ARGENTINA-CENTRAL CHILE TO THE EASTERN  
PACIFIC. ON SUNDAY...AS A POLAR RIDGE BUILDS TO THE SOUTH...THE  
FRONT IS TO MOVE NORTH ACROSS RIO DE LA PLATA/CORDOBA-MENDOZA IN  
ARGENTINA. OVER SOUTHERN CHILE THE DEEP LOW IS TO SUSTAIN MODERATE  
CONVECTION WITH MAXIMA OF 20-30MM ON FRIDAY. OVER PATAGONIA IN  
ARGENTINA...THE DEEP OCCLUDED LOW WILL SUSTAIN A MOIST  
NORTHEASTERLY FLOW THAT IS TO CONVERGE/LIFT ON THE ARGENTINEAN  
SIDE OF THE ANDES. ON FRIDAY THIS IS TO RESULT IN RAINFALL AMOUNTS  
OF 15-20MM...WHILE ON SATURDAY THE MAXIMA INCREASES TO 20-35MM. AS  
THE FRONT SURGES ACROSS LA PAMPA-CENTRAL ARGENTINA ON  
SATURDAY...UNDER FAVORABLE JET DYNAMICS...IT WILL SUPPORT MODERATE  
TO HEAVY CONVECTION WITH ACCUMULATION OF 30-60MM IN POTENTIALLY  
SEVERE CONVECTION. ON SUNDAY IT DECREASES TO 15-20MM.  
 
NORTH OVER THE CONTINENT...A 200 HPA...AN UPPER LEVEL RIDGE  
EXTENDS OVER THE CONTINENT TO THE NORTH OF 20S. AS DEEP TROPICAL  
MOISTURE CONVERGES ACROSS NORTHWEST SOUTH AMERICA AND RELEASES  
LATENT HEAT...THIS WILL SUSTAIN THE RAPID INTENSIFICATION OF THE  
RIDGE ALOFT. AXIS REACHES MAXIMUM AMPLITUDE LATER TODAY/EARLY  
FRIDAY MORNING...CENTERING ON A CLOSED HIGH OVER AMAZONAS IN  
BRASIL. AS THE RIDGE BUILDS/IT IS TO THEN INDUCE THE NORTHWARD  
AMPLIFICATION OF A TROUGH ACROSS THE NORTHEAST STATES OF BRASIL.  
BEST INSTABILITY ALOFT IS EXPECTED BETWEEN THE RIDGE TO THE WEST  
AND THE TROUGH TO THE EAST. OVER NORTHWEST SOUTH AMERICA EXPECTING  
SCATTERED CONVECTION TO FAVOR RAINFALL AMOUNTS OF 20-30MM/DAY.  
THROUGH SATURDAY THIS INCREASES TO 20-45MM/DAY...WITH MODERATE TO  
HEAVY CONVECTION TO PERSIST THROUGHOUT THE WEEKEND. ON THE  
SOUTHERN/CENTRAL JUNGLE OF PERU THE DAILY MAXIMA IS TO PEAK AT  
15-20MM/DAY...WITH SIMILAR AMOUNTS ACROSS THE SOUTHERN SIERRA. ON  
THE CENTRAL/NORTHERN SIERRA THE MAXIMA WILL PEAK AT 10-15MM.  
 
OVIEDO...SHIN (ARGENTINA)  
VANNUCCI...SMN (ARGENTINA)  
RIVAS...SENAMHI (PERU)  
DAVISON...WPC (USA)  

 
 
CLICK HERE TO GO TO PREVIOUS BULLETINS.

The Nexlab HPC Page Main Text Page