126  
FXSA20 KWBC 141633  
PMDSA  
 
SOUTH AMERICA FORECAST DISCUSSION - INTERNATIONAL DESKS  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
1133 AM EST TUE NOV 14 2017  
 
GFS DATA AT FTPPRD.NCEP.NOAA.GOV/PUB/DATA/NCCF/COM/GFS/PROD/  
 
MODEL DISCUSSION (VALID FROM NOV 14 AT 0000 UTC): GLOBAL MODELS  
CONTINUE TO FOLLOW SIMILAR PATTERN EVOLUTION THROUGH THE MEDIUM  
RANGE PERIOD...A SOLUTION WELL SUPPORTED BY THE MEAN OF THE GLOBAL  
ENSEMBLES. CONFIDENCE IN THE FORECAST IS HIGH...WITH MODELS  
SHOWING ENVIRONMENTAL CONDITIONS BECOMING HIGHLY FAVORABLE AND  
CONDUCIVE FOR ORGANIZED DEEP CONVECTION TO DEVELOP ACROSS MID  
SECTIONS OF SOUTH AMERICA ON FRIDAY-SATURDAY.  
 
A MID/UPPER LEVEL RIDGE OVER ARGENTINA IS TO STEER A SHORT WAVE  
TROUGH ACROSS PATAGONIA IN ARGENTINA TO THE WESTERN ATLANTIC EARLY  
IN THE CYCLE. A SECONDARY MID LEVEL TROUGH FOLLOWS...CROSSING  
CENTRAL CHILE LATER THIS EVENING AND THEN ACROSS CENTRAL ARGENTINA  
ON WEDNESDAY. AT LOW LEVELS THE ASSOCIATED FRONT SURGES ACROSS LA  
PAMPA TO THE BUENOS AIRES PROVINCE-CENTRAL CUYO IN  
ARGENTINA/CENTRAL CHILE LATER THIS AFTERNOON...THEN NORTH ACROSS  
URUGUAY-ENTRE RIOS/ CORDOBA-MENDOZA LATER ON WEDNESDAY. ON THE  
CENTRAL ANDES OF CHILE THIS IS TO SUSTAIN RAINFALL MAXIMA OF  
05-10MM THROUGH WEDNESDAY MORNING...WHILE OVER THE BUENOS AIRES  
PROVINCE-RIO DE LA PLATA BASIN THE MAXIMA IS TO PEAK AT 15-30MM ON  
TUESDAY TO WEDNESDAY...WHILE ACROSS URUGUAY-ENTRE RIOS THE MAXIMA  
ON WEDNESDAY PEAKS AT 15-25MM.  
 
A PROGRESSIVE 500 HPA SHORT WAVE TROUGH ON THE SOUTHERN STREAM IS  
TO FOLLOW...WITH MID LEVEL VORTEX REACHING SOUTHERN CHILE LATER ON  
WEDNESDAY EVENING/EARLY MORNING HOURS ON THURSDAY. A BUILDING LONG  
WAVE RIDGE OVER THE EASTERN PACIFIC IS TO THEN SUSTAIN THE  
NORTHWARD AMPLIFICATION OF THIS TROUGH ACROSS PATAGONIA TO CENTRAL  
ARGENTINA ON THURSDAY...MEANWHILE FAVORING HEIGHT FALLS OF  
150-200GPM. ON FRIDAY THE TROUGH IS TO ENVELOP CONTINENTAL AREA TO  
THE SOUTH OF 20S...FOCUSING ITS SHORT WAVE ENERGY ACROSS THE  
MESOPOTAMIA VALLEY IN ARGENTINA/URUGUAY-RIO GRANDE DO SUL IN  
BRASIL. AT LOW LEVELS THE ASSOCIATED FRONT SURGES ACROSS SOUTHERN  
CHILE TO PATAGONIA IN ARGENTINA ON THURSDAY MORNING...AND THROUGH  
FRIDAY EVENING IT RACES ACROSS URUGUAY TO NORTHERN ARGENTINA. THIS  
IS TO THEN MERGE WITH/REINFORCE THE OLD BOUNDARY TO THE NORTH. AS  
IT ENTERS SOUTHERN CHILE THIS WILL TRIGGER SCATTERED CONVECTION TO  
THE SOUTH OF ISLA DE CHILOE...WITH MAXIMA OF 10-15MM. ON THURSDAY  
THIS BUILDS NORTH ACROSS TEMUCO TO CONCEPCION WHERE IT IS TO FAVOR  
SIMILAR RAINFALL AMOUNTS. AS THE FRONTS COMBINE TO THE NORTH THESE  
ARE TO TRIGGER HEAVY CONVECTION OVER SOUTHERN BRASIL-MISIONES IN  
ARGENTINA TO SOUTHEAST PARAGUAY...TO TRIGGER MAXIMA OF 35-70MM ON  
THURSDAY TO FRIDAY. ON FRIDAY TO SATURDAY THE ENVIRONMENTAL  
CONDITIONS BECOME FAVORABLE FOR AN MCS TO DEVELOP ACROSS  
PARAGUAY-MATO GROSSO DO SUL IN BRASIL. IN THIS AREA NOW EXPECTING  
MAXIMA OF 75-150MM IN POTENTIALLY SEVERE CONVECTION. ON SATURDAY  
THE CONVECTION IS TO SPREAD ACROSS SOUTHERN TO SOUTHEAST BRASIL  
WHERE IT IS TO TRIGGER RAINFALL AMOUNTS OF 25-50MM. ACROSS  
BOLIVIA...AS A 30-35KT SOUTHERLY JET SPREADS ACROSS  
ARGENTINA-PARAGUAY...THIS IS TO FAVOR MAXIMA OF 75-125MM. ON THE  
SOUTHERN JUNGLE OF PERU THE MAXIMA WILL THEN PEAK AT 30-60MM.  
 
FARTHER EAST...OVER THE WESTERN SOUTH ATLANTIC...A BROAD MID/UPPER  
LEVEL TROUGH EXTENDS OFF THE COAST OF ARGENTINA-BRASIL...WITH AXIS  
NORTH BETWEEN 40W-10W TO 20S. THE TROUGH IS TO SLOWLY MOVE EAST  
ACROSS 10W LATER ON WEDNESDAY. AT LOW LEVELS THIS SUSTAINS AN  
ELONGATED FRONT THAT EXTENDS TO THE NORTHWEST ACROSS THE SOUTH  
ATLANTIC TO SOUTHEAST BRASIL. THE BOUNDARY OVER THE CONTINENT IS  
TO FRONTOLIZE LATER ON WEDNESDAY...WHILE REMNANTS OVER THE  
ATLANTIC WEAKEN LATER ON WEDNESDAY/THURSDAY MORNING. MOST ACTIVE  
CONVECTION WITH THIS FEATURE IS EXPECTED TO THE NORTH...TO FAVOR  
MAXIMA OF 20-40MM ACROSS EASTERN BAHIA EARLY IN THE CYCLE. HIGHER  
AMOUNTS ARE EXPECTED OVER WESTERN BAHIA-TOCANTINS/GOIAS...WHERE  
THIS IS TO FAVOR MAXIMA OF 35-70MM. ON WEDNESDAY THIS DECREASES TO  
20-45MM.  
 
NORTH OVER THE CONTINENT...AT 200 HPA...THE SUBTROPICAL RIDGE  
GRADUALLY BECOMES BETTER ORGANIZED EARLY ON WEDNESDAY WHILE  
CENTERING ON A CLOSED HIGH OVER NORTHERN BOLIVIA/SOUTHERN AMAZONAS  
IN BRASIL. THE CLOSED CIRCULATION IS TO PERSIST THROUGH THE END OF  
THE WEEK. UNDER INFLUENCE OF THIS FEATURE A SHORT WAVE TROUGH IS  
TO AMPLIFY ACROSS THE NORTHEAST STATES OF BRASIL ON WEDNESDAY. AS  
THE RIDGE TO THE WEST HOLDS...THE TROUGH IS TO THEN MEANDER ACROSS  
NORTHEAST BRASIL THROUGH THE END OF THE WEEK/WEEKEND. THE RIDGE  
ALOFT IS TO VENT DEEP CONVECTION ACROSS NORTHWEST SOUTH  
AMERICA...WITH MAXIMA OF 20-35MM TO AFFECT SOUTHERN  
COLOMBIA-CENTRAL/NORTHERN JUNGLE OF PERU AND AMAZONAS IN BRASIL  
DURING THE NEXT FEW DAYS. ON THE ALTIPLANO OF BOLIVIA INITIALLY  
EXPECTING RAINFALL AMOUNTS OF 10-15MM. PEAK IN ACTIVITY IS  
EXPECTED ON WEDNESDAY...WHEN GDI SHOWS POTENTIAL FOR MODERATE TO  
HEAVY RAINFALL AMOUNTS. DURING THAT PERIOD THE MAXIMA WILL PEAK AT  
15-30MM. THROUGH THURSDAY-FRIDAY IT DECREASES TO 15-20MM.  
 
OVIEDO...SHN (ARGENTINA)  
VANNUCCI...SMN (ARGENTINA)  
RIVAS...SENAMHI (PERU)  
DAVISON...WPC (USA)  

 
 
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