785  
FXSA20 KWBC 121702  
PMDSA  
 
SOUTH AMERICA FORECAST DISCUSSION - INTERNATIONAL DESKS  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
1202 PM EST FRI JAN 12 2018  
 
GFS DATA AT FTPPRD.NCEP.NOAA.GOV/PUB/DATA/NCCF/COM/GFS/PROD/  
 
MODEL DISCUSSION (VALID FROM JAN 12 AT 0000 UTC): PATTERN  
CORRECTIONS AMONG THE GLOBAL MODEL GUIDANCE LIMITS TO SOUTHERN  
STREAM FLOW OVER THE EASTERN PACIFIC...WHERE IN TIGHT BELT OF  
UPPER LATITUDE WESTERLIES THE GLOBAL MODELS DISAGREE ON THE  
SPEED/AMPLITUDE OF SHORT WAVE PERTURBATIONS ENTERING THE SOUTH  
AMERICAN DOMAIN. ON THE NORTHERN STREAM FLOW THEY ARE IN BETTER  
AGREEMENT...WITH MODELS FOLLOWING SIMILAR EVOLUTION THROUGH DAY 05.  
 
A HIGH AMPLITUDE MID LEVEL TROUGH ENTERED SOUTHERN CHILE EARLY  
THIS MORNING...AND LATER TODAY IT IS TO PULL ACROSS PATAGONIA TO  
THE WESTERN ATLANTIC...WHERE IT ALIGNS ALONG 60W TO CENTRAL  
PROVINCES IN ARGENTINA. AS IT STREAMS ACROSS THE SOUTHERN CONE  
THIS IS TO SUSTAIN HEIGHT FALLS OF 50-75GPM ACROSS  
CENTRAL/NORTHERN ARGENTINA-RIO DE LA PLATA BASIN. LATER ON  
SATURDAY THE TROUGH WILL ACCELERATE ACROSS 40W...DAMPENING AS IT  
NEARS 00W LATER ON SUNDAY. AT LOW LEVELS...BUILDING RIDGE OVER  
PATAGONIA IN ARGENTINA SUSTAINS A PAMPERO LOW LEVEL JET. THIS  
DISPLACES THE ASSOCIATED FRONT NORTH ACROSS LA PAMPA-CENTRAL CHILE  
LATER THIS AFTERNOON...WHILE ON SATURDAY IT WILL RACE ACROSS RIO  
DE LA PLATA BASIN TO CORDOBA/MENDOZA IN ARGENTINA. ON  
SUNDAY-MONDAY THE FRONT IS TO THEN MEANDER OVER URUGUAY/ RIO  
GRANDE DO SUL TO NORTHERN ARGENTINA. AS IT SURGES ACROSS CENTRAL  
ARGENTINA THIS IS TO SUSTAIN A SQUALL LINE AND POTENTIALLY SEVERE  
CONVECTION. OVER THE BUENOS AIRES PROVINCE-MENDOZA EXPECTING  
MAXIMA OF 30-60MM THROUGH SATURDAY MORNING. ON SATURDAY TO SUNDAY  
THIS INCREASES TO 40-80MM WHILE BUILDING NORTH ACROSS  
URUGUAY-MESOPOTAMIA VALLEY IN ARGENTINA...AND ON SUNDAY TO MONDAY  
IT DECREASES TO MAXIMA OF 20-40MM. ACROSS SOUTHERN BOLIVIA THE  
PAMPERO JET WILL THEN TRIGGER MAXIMA OF 25-50MM ON  
SATURDAY...INCREASING TO 40-80MM ON SUNDAY WHILE ENVELOPING  
NORTHERN BOLIVIA-SOUTHERN JUNGLE OF PERU AND ACRE/RONDONIA IN  
BRASIL.  
 
A NEAR ZONAL WESTERLY FLOW IS TO THEN ESTABLISH ACROSS THE  
SOUTHEAST PACIFIC. IN A TIGHT BELT OF MID LATITUDE  
WESTERLIES...PROGRESSIVE MID LEVEL PERTURBATIONS ARE TO THEN  
STREAM ACROSS THE SOUTHEAST PACIFIC TO EXTREME SOUTHERN PORTIONS  
OF CHILE/DRAKE PASSAGE DURING THE WEEKEND/EARLY NEXT WEEK. AT LOW  
LEVELS THIS IS TO SUSTAIN AN ELONGATED FRONT ACROSS SOUTHERN  
CHILE-PATAGONIA IN ARGENTINA ON SATURDAY AND ONWARD. IN A TIGHT  
PRESSURE GRADIENT EXPECTING BOUNDARY LAYER WINDS OF 30-40KT TO  
GENERALLY PERSIST OVER THE NEXT FEW DAYS. ACROSS SOUTHERN CHILE  
THIS IS TO FAVOR SCATTERED CONVECTION WITH ACCUMULATION OF  
05-10MM/DAY...WITH LOCALLY HIGHER AMOUNTS POSSIBLE ON MONDAY.  
 
NORTH OVER THE CONTINENT...AT 200 HPA...BROAD CELL OF THE  
SUBTROPICAL RIDGE DOMINATES AREA TO THE NORTH OF 35S/40S...WITH  
RIDGE TO ANCHOR ON A CLOSED HIGH THAT MEANDERS BETWEEN BOLIVIA AND  
PARAGUAY DURING THE NEXT FEW DAYS. THE RIDGE ALOFT IS STEERING  
SHORT WAVE PERTURBATIONS ACROSS CENTRAL/NORTHERN ARGENTINA THEN  
NORTHWARD ACROSS THE SOUTHERN STATES OF BRASIL. INFLOW OF SHORT  
WAVE ENERGY WILL ENHANCE AFOREMENTIONED CONVECTION ACROSS  
CENTRAL-NORTHERN ARGENTINA DURING THE NEXT COUPLE OF DAYS...WHILE  
OVER SOUTHEAST BRASIL THE MAXIMA PEAKS AT 25-50MM EARLY IN THE  
CYCLE. THROUGH SUNDAY THIS DECREASES TO 15-20MM. THE RIDGE ALOFT  
IS TO ALSO VENT DIURNAL CONVECTION ALONG THE NEAR EQUATORIAL  
TROUGH OVER NORTHERN BRASIL. OVER AMAZONAS TO SOUTHERN COLOMBIA  
THIS IS TO FAVOR RAINFALL MAXIMA OF 25-50MM EARLY IN THE  
CYCLE...DECREASING TO 20-35MM ON SUNDAY. A SECONDARY MAXIMA ON  
MONDAY IS TO PEAK AROUND 25-50MM. ACROSS ECUADOR EXPECTING  
SCATTERED DEEP CONVECTION TO CLUSTER ALONG THE SIERRA AND  
JUNGLE...WITH RAINFALL MAXIMA OF 15-25MM. DUE TO STRONG  
TOPOGRAPHICAL FORCING LOCALLY HIGHER AMOUNTS ARE HIGHLY PROBABLE.  
 
A TUTT TO THE EAST-NORTHEAST OF THE SUBTROPICAL RIDGE EXTENDS OVER  
NORTHEAST BRASIL WHILE CENTERING ON A CLOSED LOW NEAR 05S 40W. AS  
IT MEANDERS ACROSS NORTHEAST BRASIL THE TROUGH ALOFT WILL ENHANCE  
CONVECTION ALONG THE ITCZ OVER AMAPA-FRENCH GUIANA...WITH MAXIMA  
INCREASING FROM 15-25MM EARLY IN THE CYCLE TO 20-35MM/DAY ON  
SATURDAY AND ONWARD. OTHER CONVECTION ALONG THE NEAR EQUATORIAL  
TROUGH TO THE SOUTH IS TO FAVOR MAXIMA OF 15-25MM/DAY.  
 
OVIEDO...SHN (ARGENTINA)  
POMIER...SENAMHI (BOLIVIA)  
DAVISON...WPC (USA)  

 
 
CLICK HERE TO GO TO PREVIOUS BULLETINS.

The Nexlab HPC Page Main Text Page