609  
FXSA20 KWBC 211657  
PMDSA  
 
SOUTH AMERICA SYNOPTIC DISCUSSION - INTERNATIONAL DESKS  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
1157 AM EST THU DEC 21 2017  
 
GFS DATA AT FTPPRD.NCEP.NOAA.GOV/PUB/DATA/NCCF/COM/GFS/PROD/  
 
SYNOPSIS (VALID FROM DEC 21 AT 0000 UTC): THE 200 HPA ANALYSIS  
SHOWS BROAD CELL OF THE SUBTROPICAL RIDGE OVER THE CONTINENT  
ENVELOPING AREA NORTH OF 30S AND WEST OF 45W...WHILE CENTERING ON  
A CLOSED HIGH OVER THE ALTIPLANO DE BOLIVIA. AN UPPER TROUGH  
FLANKS THE EASTERN FRINGES OF THIS RIDGE...WITH AXIS TO THE  
NORTHWEST ALONG 30S 25W...15S 35W...A CLOSED LOW AT 10S 38W...TO  
THE AMAZON RIVER DELTA REGION. THE TROUGH ALOFT IS ENHANCING SEA  
BREEZE RELATED CONVECTION ALONG THE NORTH COAST OF BRASIL...WHILE  
THE RIDGE ALOFT VENTS DEEP CONVECTION ACROSS SAO PAULO-MATO GROSSO  
DO SUL TO BOLIVIA...AND ACROSS AMAZONAS IN WESTERN BRASIL.  
 
THE JET ANALYSIS SHOWS THE SOUTHERN POLAR WITH AXIS AT 250 HPA  
EXTENDING ALONG 63S 119W...52S 102W...48S 93W...A 136KT MAXIMUM AT  
46S 73W...49S 65W...52S 62W...A 135KT MAXIMUM AT 59S 61W...65S  
53W...A 123KT MAXIMUM AT 60S 35W...EXITING AT 49S 19W. THE  
NORTHERN POLAR HAS ITS ENTRANCE AT 53S 120W...THEN ALONG 48S  
108W...44S 100W...43S 83W...44S 65W...EXITING AT 53S 54W. THE  
SUBTROPICAL JET HAS A FINGER THAT EXTENDS BETWEEN 36S 77W AND 38S  
55W. IT REFORMS AT 31S 50W...ALONG 32S 38W...EXITING AT 24S 33W.  
AT 175 HPA...THE SUBEQUATORIAL JET HAS A FINER THAT EXTENDS  
BETWEEN 29S 71W AND 27S 54W. IT REFORMS BETWEEN 20S 40W AND 06S  
46W. ANOTHER FINGER OF THE SUBEQUATORIAL JET TO THE NORTH EXTENDS  
AT 150 HPA BETWEEN 01S 43W AND 04S 33W.  
 
AT 500 HPA...BROAD TROUGH OVER THE SOUTHEAST PACIFIC EXTENDS  
BETWEEN 110W-60W AND TO THE SOUTH OF 34S...WHILE CENTERING ON A  
CLOSED LOW AT 63S 80W. THIS IS FOCUSING SHORT WAVE ENERGY ACROSS  
SOUTHERN CHILE TO PATAGONIA IN ARGENTINA. A RIDGE TO THE EAST  
EXTENDS FROM 45S 45W TO THE WEDDELL SEA/POLAR ICECAP. THE RIDGE  
SEPARATES THE TROUGH TO THE WEST FROM ANOTHER TO THE EAST...WITH  
THE LATTER EXTENDING BETWEEN 30W-10E AND TO THE SOUTH OF 38S.  
SHORT WAVE TROUGH ON THE NORTHERN STREAM MEANDERS OFF THE SOUTH  
COAST OF BRASIL...WITH AXIS NORTHWEST FROM A LOW AT 38S 46W TO RIO  
GRANDE DO SUL.  
 
AT LOW LEVELS...BROAD RIDGE ON THE NORTHERN STREAM EXTENDS OVER  
THE PACIFIC WHIEL CENTERING ON A 1025 HPA HIGH AT 36S 102W. BROAD  
TROUGH TO THE SOUTH EXTENDS FROM THE BELLINGSHAUSEN SEA TO THE  
SOUTHEAST PACIFIC/SOUTHERN CONE...WHILE CENTERING ON AN OCCLUDED  
958 HPA LOW AT 61S 81W. POLAR FRONTS REVOLVE AROUND THIS  
AXIS...WITH ONE EXTENDS FROM AN OCCLUDED 958 HPA LOW AT 62S  
66W...ALONG A 962 HPA LOW AT 64S 67W...56S 55W...53S 58W...A 996  
HPA LOW AT 52S 64W...48S 60W...TO NORTHERN PATAGONIA. ANOTHER  
FRONT TO THE EAST EXTENDS ALONG A 986 HPA LOW AT 59S 51W...53S  
47W...50S 51W...A 994 HPA LOW AT 50S 56W...43S 56W...38S 60W...A  
1000 HPA LOW AT 37S 66W...31S 72W...30S 80W...AND 30S 88W. THIS  
SUSTAINS SCATTERED DEEP CONVECTION ACROSS CENTRAL ARGENTINA. OVER  
THE ATLANTIC...A 1025 HPA HIGH AT 40S 35W ANCHORS A RIDGE ON THE  
NORTHERN STREAM FLOW. AN ELONGATED FRONT TO THE NORTH EXTENDS  
ALONG 34S 16W...33S 26W...A 1020 HPA LOW AT 32S 30W...30S 34W...A  
1016 HPA LOW AT 30S 41W...TO SOUTHERN BRASIL.  
 
OVIEDO...SHN (ARGENTINA)  
POMIER...SENAMHI (BOLIVIA)  
RIVAS...SENAMHI (PERU)  
GALVEZ...WPC (USA)  

 
 
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