316  
FXSA20 KWBC 271438  
PMDSA  
 
SOUTH AMERICA SYNOPTIC DISCUSSION - INTERNATIONAL DESKS  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
938 AM EST WED DEC 27 2017  
 
GFS DATA AT FTPPRD.NCEP.NOAA.GOV/PUB/DATA/NCCF/COM/GFS/PROD/  
 
SYNOPSIS (VALID FROM DEC 27 AT 0000 UTC): AT 200 HPA...THE FLOW  
OVER NORTHERN SOUTH AMERICA DIVERGES BETWEEN A CELL OF THE  
SUBTROPICAL RIDGE AND A SHORT WAVE TROUGH TO THE NORTH. THE RIDGE  
EXTENDS FROM PERU/BOLIVIA TO SOUTHEAST BRASIL...WHILE CENTERING ON  
A CLOSED HIGH AT 17S 63W. THE TROUGH TO THE NORTH EXTENDS ALONG  
16S 40W...10S 50W...TO A CLOSED LOW OVER THE AMAZON RIVER DELTA.  
THESE ARE VENTING ORGANIZED DEEP CONVECTION ACROSS PARA IN  
BRASIL...WHILE ALSO VENTING CONVECTION OVER SOUTH AMERICA TO THE  
NORTH OF 20S AND WEST OF 50W.  
 
AT 250 HPA...THE SOUTHERN POLAR LIES ALONG 52S 120W...48S  
106W...55S 76W...EXITING AT 50S 51W. IT REFORMS AT 52S 44W...THEN  
ALONG A 141KT MAXIMUM AT 54S 34W...EXITING AT 57S 10W. THE  
NORTHERN POLAR LIES ALONG 44S 120W...44S 100W...A 144KT MAXIMUM AT  
48S 88W...49S 76W...EXITING AT 45S 64W. IT REFORMS AT 42S  
54W...THEN ALONG 48S 39W...53S 19W...AND 49S 06W. THE SUBTROPICAL  
JET HAS A FINGER THAT EXTENDS BETWEEN 32S 75W AND 34S 54W. A  
BRANCH TO THE NORTH HAS ITS ENTRANCE AT 28S 62W...ALONG 30S  
41W...32S 22W...EXITING AT 34S 05W. AT 150 HPA THE SUBEQUATORIAL  
JET HAS A FINGER OVER THE EASTERN PACIFIC WITH AXIS ALONG 09S  
115W...09S 106W...EXITING AT 10S 98W. ANOTHER FINGER TO THE NORTH  
EXTENDS ALONG 04S 110W...04S 100W...EXITING AT 04S 91W. FARTHER  
EAST...ANOTHER FINGER OF THE SUBEQUATORIAL JET HAS ITS ENTRANCE AT  
10S 51W AND EXITS AT 01N 56W. IT REFORMS BETWEEN 02N 43W AND 05S  
37W.  
 
AT 500 HPA...A BROAD/LOW AMPLITUDE TROUGH ON THE SOUTHERN STREAM  
EXTENDS BETWEEN 130W-20W AND TO THE SOUTH OF 35S. THIS ANCHORS ON  
CLOSED LOW AT 59S 95W...67S 80W...AND 65S 35W. SHORT WAVE TROUGHS  
REVOLVE AROUND THIS AXIS...WITH ONE EXTENDING FROM 54S 93W...ALONG  
45S 95W...TO 38S 110W. A LOW AMPLITUDE RIDGE OVER SOUTHERN  
CHILE-DRAKE PASSAGE SEPARATES THE LATTER FROM ANOTHER TROUGH TO  
THE EAST...WITH THE LATER EXTENDING TO THE NORTHWEST FROM THE  
SOUTH GEORGIA ISLANDS...ALONG 47S 45W...TO THE BUENOS AIRES  
PROVINCE.  
 
AT LOW LEVELS...A RIDGE ON THE NORTHERN STREAM CENTERS ON A 1021  
HPA HIGH AT 28S 103W AND A 1021 HPA HIGH AT 29S 87W. BROAD TROUGH  
TO THE SOUTH CENTERS ON AN OCCLUDED 966 HPA LOW AT 59S 107W. POLAR  
FRONT REVOLVING AROUND THIS AXIS EXTENDS FROM AN OCCLUDED 972 HPA  
LOW AT 63S 90W...A 974 HPA LOW AT 62S 79W...58S 68W...55S 71W...A  
982 HPA LOW AT 55S 80W...50S 80W...46S 88W...45S 93WL...A 1002 HPA  
LOW AT 44S 103W...AND 39S 110W. OVER THE SOUTH ATLANTIC...BROAD  
TROUGH TO THE SOUTH CENTERS ON A 966 HPA LOW AT 65S 31W...WITH A  
POLAR FRONT EXTENDING FROM A 994 HPA LOW AT 48S 43W...ALONG A 994  
HPA LOW AT 49S 39W...44S 41W...39S 49W...BUENOS AIRES  
PROVINCE-CENTRAL CUYO...A 1016 HPA LOW AT 36S 74W...JUAN FERNANDEZ  
ISLANDS...36S 84W...40S 88W...TO A 1002 HPA LOW AT 43S 93W. A 1013  
HPA POLAR HIGH AT 42S 60W ANCHORS A RIDGE OFF THE COAST OF  
PATAGONIA. ANOTHER FRONT TO THE EAST AND NORTH EXTENDS ALONG A  
1002 HPA LOW AT 34S 19W...29S 23W...25S 29W...24S 37W...29S  
44W...TO RIO GRANDE DO SUL. THIS FRONT SEPARATES TWO RIDGES...WITH  
ONE CENTERING ON A 1019 HPA HIGH AT 35S 36W AND THE OTHER ON A  
1017 HPA HIGH AT 22S 16W.  
 
OVIEDO...SHN (ARGENTINA)  
POMIER...SENAMHI (BOLIVIA)  
RIVAS...SENAMHI (PERU)  
DAVISON...WPC (USA)  

 
 
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