162  
FXSA20 KWBC 181433  
PMDSA  
 
SOUTH AMERICA SYNOPTIC DISCUSSION - INTERNATIONAL DESKS  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
932 AM EST MON DEC 18 2017  
 
GFS DATA AT FTPPRD.NCEP.NOAA.GOV/PUB/DATA/NCCF/COM/GFS/PROD/  
 
SYNOPSIS (VALID FROM DEC 18 AT 0000 UTC): AT 200 HPA...RIDGE  
EXTENDS OVER NORTHWEST SOUTH AMERICA WHILE ANCHORING ON A CLOSED  
HIGH OVER NORTHERN BOLIVIA. A TROUGH TO THE EAST EXTENDS FROM A  
CLOSED LOW AT 35S 32W...ACROSS RIO DE JANEIRO TO MINAS GERAIS.  
THESE COMBINE IN SUPPORT OF SCATTERED DEEP CONVECTION ACROSS  
NORTHERN SOUTH AMERICA...WITH THE MOST ACTIVE CLUSTERING OVER  
BOLIVIA-PARAGUAY-MATO GROSSO DO SUL IN BRASIL.  
 
AT 250 HPA...THE SOUTHERN POLAR HAS ITS ENTRANCE AT 56S  
118W...THEN ALONG 55S 94W...54S 74W...EXITING AT 56S 66W. IT  
REFORMS AT 55S 41W...ALONG 59S 26W...AND 59S 11W. THE NORTHERN  
POLAR LIES ALONG 50S 120W...50S 99W...A 126KT MAXIMUM AT 49S  
74W...49S 57W...EXITING AT 44S 49W. IT REFORMS AT 45S 45W...THEN  
ALONG 54S 31W...AND A 181KT MAXIMUM AT 56S 10W. A FINGER OF THE  
SUBTROPICAL JET LIES BETWEEN 30S 114W AND 38S 99W. IT REFORMS AT  
23S 77W...THEN ALONG 33S 70W...34S 55W...38S 45W...48S 31W...51S  
19W...46S 08W...EXITING AT 39S 06W. AT 150 HPA...THE SUBEQUATORIAL  
JET LIES ALONG 06S 110W...05S 100W...EXITING AT 02S 91W.  
 
AT 500 HPA...A BROAD/LOW AMPLITUDE TROUGH EXTENDS OVER THE  
SOUTHEAST PACIFIC TO THE SOUTH OF 40S...WITH AXIS CENTERING ON A  
CLOSED LOW AT 63S 89W. NORTH OF THIS AXIS...A SHORT WAVE TROUGH ON  
THE NORTHERN STREAM IS MOVING TOWARDS CENTRAL CHILE. A NORTH TO  
SOUTH RIDGE EXTENDS FROM THE BUENOS AIRES PROVINCE TO THE  
ANTARCTIC PENINSULA. DOWNSTREAM FROM THIS RIDGE A TROUGH MEANDERS  
OVER THE ATLANTIC TO THE SOUTH OF 57S. A SHORT WAVE TROUGH TO THE  
NORTH EXTENDS FROM THE SOUTH GEORGIA ISLANDS....ALONG 50S 45W...TO  
URUGUAY/RIO GRANDE DO SUL.  
 
AT LOW LEVELS...BROAD/LOW AMPLITUDE TROUGH ON THE SOUTHERN STREAM  
EXTENDS ACROSS THE SOUTHEAST PACIFIC WHILE CENTERING ON A 958 HPA  
LOW AT 63S 88W. POLAR FRONTS REVOLVE AROUND THIS TROUGH...WITH ONE  
EXTENDING FROM AN OCCLUDED 964 HPA LOW AT 64S 76W...A 976 HPA LOW  
AT 60S 64W...55S 62W...A 994 HPA LOW AT 53S 69W...48S 69W...47S  
74W...A 1010 HPA LOW AT 49S 79W...45S 82W...43S 87W...WEAKENING  
ALONG 40S 113W. A DUAL BARRELED RIDGE TO THE NORTH CENTERS ON A  
1025 HPA HIGH AT 38S 82W AND A 1023 HPA HIGH AT 38S 58W. A POLAR  
FRONT TO THE EAST EXTENDS ALONG A 986 HPA LOW AT 49S 36W...40S  
40W...33S 44W...A 1010 HPA LOW AT 32S 47W...28S 48W...MISIONES  
ARGENTINA-SOUTHEAST PARAGUAY TO CHACO ARGENTINO. THIS TRIGGERED A  
PREFRONTAL SQUALL LINE ACROSS PARAGUAY-BOLIVIA-MATO GROSSO DO SUL  
IN BRASIL.  
 
OVIEDO...SHN (ARGENTINA)  
POMIER...SENAMHI (BOLIVIA)  
RIVAS...SENAMHI (PERU)  
GALVEZ...WPC (USA)  

 
 
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