494  
FXSA20 KWBC 241815  
PMDSA  
 
SOUTH AMERICA FORECAST DISCUSSION - INTERNATIONAL DESKS  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
115 PM EST WED JAN 24 2018  
 
GFS DATA AT FTPPRD.NCEP.NOAA.GOV/PUB/DATA/NCCF/COM/GFS/PROD/  
 
MODEL DISCUSSION (VALID FROM JAN 24 AT 0000 UTC): DEEP MID LEVEL  
TROUGH IS TO MEANDER EAST ACROSS THE SOUTH ATLANTIC...WITH AXIS TO  
EXTEND NORTH BETWEEN 50W-30W LATER TODAY. ON THURSDAY IT IS TO  
MIGRATE EAST ACROSS 30W...NEARING 10W LATER ON FRIDAY. AT LOW  
LEVELS THIS SUSTAINS AN OCCLUDING LOW OVER THE WESTERN ATLANTIC  
THAT IS TO DEEPEN AS IT MEANDERS TO THE EAST-SOUTHEAST. THE  
SURFACE LOW EXTENDS A FRONT TO THE WEST-NORTHWEST ACROSS SOUTHERN  
BRASIL TO THE NORTHERN PROVINCES IN ARGENTINA. AT 250 HPA A  
SUBTROPICAL JET EXTENDS ACROSS CENTRAL CHILE INTO CENTRAL/NORTHERN  
ARGENTINA. THE PERSISTENT UPPER LEVEL JET WILL HELP SUSTAIN THE  
BAROCLINIC BOUNDARY DURING THE NEXT FEW DAYS...WHILE ALSO FAVORING  
AN UPPER DIVERGENT PATTERN THAT IS TO VENT CONVECTION ALONG THIS  
BOUNDARY. ALSO AT LOW LEVELS...A NORTHERLY JET ACROSS EASTERN  
BOLIVIA/PARAGUAY IS TO FAVOR A WARM/MOIST ADVECTIVE PATTERN THAT  
IS TO CONVERGE ALONG THE MEANDERING FRONT OVER NORTHERN ARGENTINA.  
IN THIS PATTERN THE ENVIRONMENTAL CONDITIONS REMAIN FAVORABLE FOR  
AN MCS TO FORM OVER MID SECTIONS OF SOUTH AMERICA...TO FAVOR HEAVY  
CONVECTION FROM SOUTHERN BOLIVIA-ACROSS NORTHERN ARGENTINA TO  
SOUTHERN STATES OF BRASIL AND SOUTHEAST PORTIONS OF PARAGUAY. IN  
THIS AREA EXPECTING MAXIMA OF 40-80MM WITH LOCALIZED MAXIMA OF  
100-125MM HIGHLY PROBABLE. ON THURSDAY-SUNDAY THE DAILY MAXIMA  
OVER SOUTHERN BRASIL-CORRIENTES/MISIONES IN ARGENTINA IS TO PEAK  
AT 20-30MM. SIMILAR AMOUNTS ARE EXPECTED OVER NORTHWEST  
ARGENTINA/SOUTHERN BOLIVIA...EXCEPT FOR FRIDAY WHEN THE MAXIMA IS  
TO PEAK AT 30-60MM.  
 
A PROGRESSIVE MID LEVEL TROUGH FOLLOWS...WITH AXIS TO RACE ACROSS  
110W LATER THIS EVENING. ON THURSDAY THE TROUGH IS TO PULL ACROSS  
85W/87W... REACHING SOUTHERN CHILE EARLY ON FRIDAY MORNING. NOTE  
THAT THIS IS MOVING AT A FASTER PACE THAN PREVIOUSLY ANTICIPATED.  
THIS IS TO THEN CONTINUE EAST ACROSS 50W ON SATURDAY AS A  
SECONDARY PERTURBATION ENTERS THE DRAKE PASSAGE/SOUTHERN CONE OF  
SOUTH AMERICA. AT LOW LEVELS IT IS TO SUSTAIN A PROGRESSIVE FRONT  
THAT REACHES SOUTHERN CHILE LATER ON THURSDAY. ON FRIDAY THE FRONT  
MOVES NORTH ACROSS PATAGONIA TO LA PAMPA IN ARGENTINA. AS IT  
APPROACHES THE SOUTHERN CONE...THE LOW/MID LEVEL TROUGH WILL  
SUSTAIN A SUBTROPICAL CONNECTION...FAVORING ADVECTION OF  
WARM/MOIST AIR ACROSS THE EASTERN PACIFIC TO THE SOUTHERN REGIONS  
OF CHILE. THIS WILL HELP SUSTAIN SCATTERED CONVECTION WITH MAXIMA  
OF 15-20MM ON THURSDAY TO FRIDAY...WHILE ON FRIDAY TO SATURDAY  
EXPECTING MAXIMA OF 10-15MM. SIMILAR AMOUNTS ARE EXPECTED OVER LA  
PAMPA-CENTRAL ARGENTINA ON FRIDAY. OVER CORRIENTES/ENTRE RIOS IN  
ARGENTINA AND URUGUAY THIS INCREASES TO 15-25MM LATER ON SATURDAY  
TO SUNDAY.  
 
NORTH OVER THE CONTINENT...AT 200 HPA...A HIGH IS TO MEANDER  
BETWEEN SOUTHEAST BOLIVIA AND THE CHACO PARAGUAYO. THE HIGH ALOFT  
ANCHORS A BROAD CELL OF THE SUBTROPICAL RIDGE ACROSS MID SECTIONS  
OF SOUTH AMERICA. THIS IS A FAIRLY PERSISTENT PATTERN THAT IS  
FORECAST TO HOLD DURING THE NEXT FOUR TO FIVE DAYS. THE UPPER  
LEVEL RIDGE WILL VENT DEEP CONVECTION ACROSS SAO PAULO-MINAS  
GERAIS IN BRASIL...WITH MAXIMA OF 20-35MM EARLY IN THE CYCLE. ON  
THURSDAY-TO-FRIDAY THIS BECOMES BETTER ORGANIZED...WITH DAILY  
MAXIMA IN THIS AREA INCREASING TO 30-60MM/DAY.  
 
ALSO AT 200 HPA...TWO TROUGHS BOUND THE NORTHERN FRINGES OF THIS  
RIDGE...WITH A NEGATIVELY TILTED TROUGH EXTENDING TO NORTHERN  
PERU/ECUADOR WHILE A POSITIVELY TILTED TROUGH EXTENDS OVER THE  
NORTHEAST STATES OF BRASIL. THE ONE OVER THE EASTERN  
PACIFIC/NORTHERN PERU TENDS TO WEAKEN ON FRIDAY AS UPPER LEVEL  
RIDGE PATTERN OVER THE CONTINENT INTENSIFIES. THIS DISPLACES THE  
REMNANTS OF THIS TROUGH FARTHER OFFSHORE. OVER THE NEXT COUPLE OF  
DAYS...MEANWHILE...THE MEANDERING TROUGH WILL ENHANCE CONVECTION  
ALONG THE SIERRA OF PERU...WITH MAXIMA OF 10-15MM/DAY. THE ONE  
OVER NORTHEAST BRASIL WILL PERSIST OVER THE NEXT FEW DAYS. THIS IS  
TO INTERACT WITH THE NEAR EQUATORIAL TROUGH OVER NORTHERN BRASIL  
TO FAVOR SCATTERED DEEP CONVECTION WITH MAXIMA OF 20-45MM/DAY.  
 
OVIEDO...SHN (ARGENTINA)  
POMIER...SENAMHI (BOLIVIA)  
DAVISON...WPC (USA)  

 
 
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