655  
FXSA20 KWBC 251553  
PMDSA  
 
SOUTH AMERICA FORECAST DISCUSSION - INTERNATIONAL DESKS  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
1052 AM EST MON JAN 25 2021  
 
GFS DATA AT FTPPRD.NCEP.NOAA.GOV/PUB/DATA/NCCF/COM/GFS/PROD/  
 
FORECAST DISCUSSION FROM JAN 25/16UTC: GLOBAL MODELS GENERALLY  
AGREE ON MID/UPPER LEVEL RIDGE ON THE SOUTHERN STREAM TO DOMINATE  
THE FLOW OVER THE SOUTHEAST PACIFIC DURING THE NEXT SEVERAL  
DAYS...WITH AXIS SETTLING BETWEEN 130W-90W AND TO THE SOUTH OF 45S  
EARLY IN THE CYCLE. DOWNSTREAM FROM THIS AXIS...A BROAD/LOW  
AMPLITUDE TROUGH IS INITIALIZED OVER THE SOUTHERN CONE TO THE  
WESTERN ATLANTIC...WHERE IT IS TO REMAIN DURING THE NEXT THREE  
DAYS WHILE SLOWLY SHEARING SHORT WAVE ENERGY. AT LOW LEVELS...THIS  
WILL SUSTAIN A BROAD TROUGH OVER THE DRAKE PASSAGE/SOUTHERN  
CONE...WHERE IT IS TO FAVOR STRONG LOW LEVEL WINDS THAT ARE TO  
PEAK AT 35-50KT DURING THE NEXT FEW DAYS. THIS WILL ENHANCE  
TOPOGRAPHICALLY INDUCED CONVECTION ACROSS SOUTHERN CHILE INITIALLY  
FAVOR RAINFALL AMOUNTS OF 10-15MM/DAY. ON TUESDAY-WEDNESDAY THIS  
INCREASES TO MAXIMA OF 15-25MM/DAY...WITH MOST INTENSE EXPECTED  
BETWEEN TEMUCO AND ISLA DE CHILOE.  
 
LATER IN THE WEEK THE TROUGH IS TO DAMPEN WHILE SHEARING EASTWARD.  
BUT AS THE MID/UPPER LEVEL RIDGE TO THE WEST HOLDS...THIS IS TO  
THEN STEER A SHORT WAVE TROUGH NORTHWARD ACROSS THE EASTERN  
PACIFIC TO THE CENTRAL REGIONS OF CHILE LATER ON FRIDAY. DEEP  
PLUME OF SUBTROPICAL MOISTURE IS TO ACCOMPANY THIS FEATURE AS IT  
LIFTS ACROSS THE EASTERN PACIFIC...TO FEED A SURGE IN ORGANIZED  
DEEP CONVECTION ON THURSDAY-SATURDAY. AT LOW LEVELS THIS WILL  
SUSTAIN A FRONTAL WAVE THAT ENTERS TEMUCO/CONCEPCION CHILE LATER  
ON WEDNESDAY...WITH LOW LEVEL TROUGH EXPECTED TO DEEPEN AS IT  
MEANDERS NORTH ALONG THE CENTRAL COAST OF CHILE ON  
FRIDAY-SATURDAY. UNDER FAVORABLE JET DYNAMICS PATTERN WILL BE  
HIGHLY FAVORABLE AND CONDUCIVE TO MODERATE TO HEAVY RAINFALL  
AMOUNTS...CLUSTERING BETWEEN TEMUCO-CONCEPCION ON THURSDAY TO  
FRIDAY WHILE SUSTAINING RAINFALL AMOUNTS OF 25-50MM/DAY. ON  
SATURDAY THIS INCREASES TO 25-50MM WHILE BUILDING NORTH BETWEEN  
CONCEPCION AND SANTIAGO IN CENTRAL CHILE. ON THE CENTRAL PROVINCES  
OF ARGENTINA THIS WILL SUSTAIN MODERATE RAINFALL AMOUNTS WITH  
ACCUMULATION OF 20-45MM ON THURSDAY...WHILE ON FRIDAY THIS  
INCREASES TO 30-60MM IN POTENTIALLY SEVERE CONVECTION.  
 
ALTHOUGH PATTERN TO THE SOUTH IS TO REMAIN FAVORABLE FOR  
DEVELOPMENT...THE SYSTEM OF CONCERN IS A MID/UPPER LEVEL SHORT  
WAVE TROUGH THAT MEANDERS TO THE NORTH...WITH THE LATTER TO MOVE  
INLAND ACROSS NORTHERN CHILE TO NORTHERN ARGENTINA-SOUTHERN  
BOLIVIA/PARAGUAY EARLY ON TUESDAY MORNING. THIS IS TO THEN MEANDER  
OVER MID SECTIONS OF SOUTH AMERICA THROUGH THE MIDDLE RANGE  
PERIOD. UNDER INFLUENCE OF THIS FEATURE CONDITIONS REMAIN HIGHLY  
FAVORABLE FOR AN MCS TO DEVELOP OVER NORTHERN ARGENTINA ON  
TUESDAY-WEDNESDAY...TO SUSTAIN RAINFALL AMOUNTS OF 75-150MM...WITH  
LOCALLY HIGHER AMOUNTS HIGHLY PROBABLE AS SUGGESTED BY SOME OF THE  
MODELS. ON WEDNESDAY-THURSDAY THIS THEN BUILDS EAST AND NORTH  
ACROSS BOLIVIA-PARAGUAY...TO SUSTAIN MAXIMA OF 35-70MM. ON  
THURSDAY THIS INCREASES TO 40-80MM WHILE BUILDING NORTH TO THE  
SOUTHERN JUNGLE OF PERU. HEAVY CONVECTION IS TO THEN PREVAIL IN  
THIS AREA THROUGH THE END OF THE CYCLE. ANOTHER HEAVY RAINFALL  
EVENT IS TO AFFECT THIS AREA DURING THE WEEKEND...WITH MAXIMA OF  
75-125MM EXPECTED ACROSS NORTHERN ARGENTINA/SOUTHERN PARAGUAY TO  
SOUTHERN BRASIL-URUGUAY.  
 
AT 250 HPA...A WANING CELL OF THE SUBTROPICAL RIDGE EXTENDS FROM  
PERU TO THE SOUTH-SOUTHWEST INTO THE EASTERN PACIFIC LATER TODAY.  
SHORT WAVE TROUGH TO THE EAST...HOWEVER...IS TO REMAIN ON THE  
NORTHEAST STATES OF BRASIL DURING THE NEXT FIVE DAYS. THIS IS  
LASTING LONGER THAN WHAT THE MODELS PREVIOUSLY SUGGESTED. ACROSS  
PARA-AMAPA-ILHA DE MARAJO...THE TROUGH ALOFT IS TO INTERACT WITH  
THE ATLANTIC ITCZ. IN THIS AREA CONVECTION TENDS TO INTENSIFY  
THROUGH WEDNESDAY...WHEN IT INCREASES FROM 20-35MM EARLY IN THE  
CYCLE TO 20-45MM ON WEDNESDAY-THURSDAY. BUT LOSING UPPER LEVEL  
SUPPORT...THIS DECREASES TO MAXIMA OF 20-35MM DURING THE WEEKEND.  
 
DAVISON...WPC (USA)  

 
 
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