817  
FXSA20 KWBC 291347  
PMDSA  
 
SOUTH AMERICA SYNOPTIC DISCUSSION - INTERNATIONAL DESKS  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
847 AM EST FRI DEC 29 2017  
 
GFS DATA AT FTPPRD.NCEP.NOAA.GOV/PUB/DATA/NCCF/COM/GFS/PROD/  
 
SYNOPSIS (VALID FROM DEC 30 AT 0000 UTC): AT 200 HPA...A RIDGE  
DOMINATES CONTINENTAL AREA TO THE NORTH OF 30S WHILE CENTERING ON  
CLOSED HIGHS OVER SOUTHERN BOLIVIA AND MATO GROSSO DO SUL IN  
BRASIL. THE RIDGE ALOFT IS VENTING DEEP CONVECTION FROM SOUTHEAST  
BRASIL...ACROSS BOLIVIA TO PERU. IT IS ALSO VENTING SCATTERED  
CONVECTION ACROSS PARA-AMAZONAS-ACRE AND RONDONIA TO THE NORTH  
OVER BRASIL. EAST OF THE RIDGE...OVER THE TROPICAL ATLANTIC...A  
TUTT EXTENDS ALONG 20S 28W...10S 35W...TO 00N 40W.  
 
THE 250 HPA JET ANALYSIS SHOWS THE SOUTHERN POLAR WITH ENTRANCE AT  
48S 108W...THEN ALONG 45S 97W...49S 82W...A 130KT MAXIMUM AT 53S  
65W...56S 60W...EXITING AT 50S 35W. THE NORTHERN POLAR HAS ITS  
ENTRANCE AT 43S 117W...THEN ALONG 40S 102W...A 143KT MAXIMUM AT  
41S 93W...A 138KT MAXIMUM AT 46S 81W...49S 67W...EXITING AT 50S  
51W. THE SUBTROPICAL JET HAS ITS ENTRANCE AT 36S 102W...THEN ALONG  
40S 86W...41S 70W...EXITING AT 42S 57W. A FINGER TO THE EAST  
EXTENDS BETWEEN 42S 54W AND 36S 32W. ANOTHER FINGER TO THE NORTH  
EXTENDS BETWEEN 29S 45W AND 25S 35W. OVER THE TROPICAL  
PACIFIC...AT 150 HPA...A BRANCH OF THE SUBEQUATORIAL JET EXTENDS  
ALONG 09S 115W...08S 107W...EXITING AT 10S 100W. A FINGER TO THE  
NORTH EXTENDS ALONG 03S 110W...EXITING AT 03S 99W.  
 
AT 500 HPA...BROAD TROUGH OVER THE SOUTHWEST PACIFIC DOMINATES  
AREA BETWEEN 105W-65W AND TO THE SOUTH OF 30S. THE TROUGH IS  
FOCUSING SHORT WAVE ENERGY ACROSS SOUTHERN REGIONS OF CHILE INTO  
PATAGONIA IN ARGENTINA. LOW AMPLITUDE RIDGE BETWEEN 55W-40W  
SEPARATES THIS RIDGE FROM BROAD TROUGH TO THE EAST OVER THE SOUTH  
ATLANTIC. ON THE NORTHERN STREAM...SHORT WAVE RIDGE MEANDERS  
ACROSS NORTHERN CHILE TO NORTHWEST ARGENTINA...WHILE EAST OF THIS  
AXIS A SHORT WAVE TROUGH IS STREAMING ACROSS URUGUAY TO CORRIENTES  
IN ARGENTINA. THIS IS PROVIDING DYNAMICAL SUPPORT TO CONVECTION  
OVER SOUTHEAST BRASIL.  
 
AT LOW LEVELS...RIDGE ON THE NORTHERN STREAM ENVELOPS THE EASTERN  
PACIFIC WHILE CENTERING ON TWO 1021 HPA HIGHS...WITH ONE AT 26S  
96W AND THE OTHER AT 29S 86W. SOUTH OF THIS RIDGE...BROAD TROUGH  
DOMINATES THE SOUTHEAST PACIFIC WHILE CENTERING ON AN OCCLUDED 962  
HPA LOW AT 58S 86W. POLAR FRONTS REVOLVE AROUND THIS AXIS...WITH  
ONE EXTENDING ALONG A 970 HPA LOW AT 60S 66W...55S 63W...50S  
71W...A 986 HPA LOW AT 50S 81W...45S 82W...TO 44S 89W. ANOTHER  
FRONT TO THE NORTH EXTENDS ALONG A 990 HPA LOW AT 52S 55W...48S  
57W...48S 61W...A 986 HPA LOW AT 50S 67W...44S 67W...41S 75W...A  
1006 HPA LOW AT 43S 83W...37S 89W...AND 35S 97W. AN ELONGATED  
FRONT ON THE NORTHERN STREAM LIES ALONG A 1010 HPA LOW AT 39S  
24W...37S 29W...35S 36W...37S 43W...A 1006 HPA LOW AT 44S 48W...TO  
SOUTHERN BUENOS AIRES/LA PAMPA...WHERE IT FAVORS ISOLATED DEEP  
CONVECTION. A RIDGE TO THE NORTH CENTERS ON A 1019 HPA HIGH AT 31S  
37W. AN OLD FRONT THEN MEANDERS ALONG A 1014 HPA LOW AT 30S  
20W...27S 23W...25S 27W...A 1014 HPA LOW AT 26S 31W...22S  
35W...24S 43W...RIO GRANDE DO SUL/NORTHERN URUGUAY TO CORDOBA IN  
ARGENTINA WHERE IT IS DISSIPATING.  
 
OVIEDO...SHN (ARGENTINA)  
POMIER...SENAMHI (BOLIVIA)  
RIVAS...SENAMHI (PERU)  
DAVISON...WPC (USA)  

 
 
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