Prognostic Meteorological Discussion
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FXSA20 KWBC 231453
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SOUTH AMERICA SYNOPTIC DISCUSSION - INTERNATIONAL DESKS
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
953 AM EST THU FEB 23 2017

GFS DATA AT FTPPRD.NCEP.NOAA.GOV/PUB/DATA/NCCF/COM/GFS/PROD/

SYNOPSIS (VALID FROM FEBRUARY 23 AT 0000 UTC): AT 200 HPA...THE
BOLIVIAN HIGH./SUBTROPICAL UPPER RIDGE CONTINUES CENTERING OFF THE
COAST OF NORTHERN CHILE AT 20S 76W. THIS SYSTEM IS TO THE
SOUTHWEST OF ITS CLIMATOLOGICAL POSITION. THE HIGH EXTENDS AN AXIS
TO THE EAST-SOUTHEAST INTO THE PILCOMAYO RIVER/PARAGUAY-ARGENTINA
BORDER...AND INTO SOUTHEASTERN PARAGUAY. TO THE NORTHEAST OF THIS
RIDGE...A BROAD TROUGH CENTERS OVER ACRE/SOUTHEASTERN AMAZONAS IN
BRASIL. INTERACTION BETWEEN THE RIDGE AND THE TROUGH ARE LEADING
TO A PERSISTENT UPPER DIVERGENT PATTERN IN THE WESTERN AMAZON
BASIN...PERU...ECUADOR AND SOUTHERN COLOMBIA. A REGION OF CONCERN
IS NORTHERN PERU...WHERE SEA SURFACE TEMPERATURES EXCEEDING 28C
ARE ALLOWING THE SOUTHERN BAND OF THE ITCZ TO EXTEND INTO COASTAL
AREAS. THIS IS STIMULATING DEEP CONVECTION IN PIURA/TUMBES AND
PARTS OF SOUTHERN ECUADOR. THE NORTHWESTERN AMAZON BASIN IS ALSO
UNSEASONABLE ACTIVE DUE TO THE UPPER DIVERGENT PATTERN...ENHANCED
LOW-LEVEL CONVERGENCE FROM A SOUTHERLY WIND SURGE...AND THE
WEAKENING OF THE LLANO-JET IN VENEZUELA/EASTERN COLOMBIA. TO THE
EAST IN TROPICAL SOUTH AMERICA...THE CAVADO DO NORDESTE CENTERS ON
A LOW OVER BAHIA AND ESPIRITO SANTO. THIS IS LIMITING ACTIVITY IN
THESE REGIONS BUT SUSTAINING A SEASONALLY ACTIVE PATTERN OF
CONVECTION IN THE AMAZON DELTA/MARANHAO/TOCANTINS REGION....WHERE
ORGANIZED DEEP CONVECTION IS OCCURRING. FINALLY...ANOTHER REGION
WITH DEEP CONVECTION IS RORAIMA/GUYANA...AS DEEP-LAYER INSTABILITY
INTERACTS WITH THE DIVERGENT TIER OF A NORTH HEMISPHERE TROUGH
LOCATED OVER THE EXTREME EASTERN CARIBBEAN.

THE UPPER JET ANALYSIS SHOWS THE SOUTHERN POLAR JET EXTENDING
ALONG 51S 120W ALONG 52S 112W...53S 104W...55S 98W...64S
90W...EXITING AT 64S 71W. THE NORTHERN POLAR JET FORMS AT 47S 11W
ALONG 50S 97W...59S 88W...61S 79W...A 130KT MAXIMA AT 53S
63W...48S 48W...A 122KT AT 46S 35W...A 120KT MAXIMA AT 43S 16W. A
SECOND BRANCH OF THE NORTHERN POLAR FORMS AT 43S 110W ALONG A
139KT MAXIMA AT 48S 95W...EXITINGA T 50S 79W. THE SUBTROPICAL JET
EXTENDS ALONG A 122KT MAXIMA AT 36S 122W...37S 110W...49S
102W...44S 96W...EXITING AT 47S 81W. IT REFORMS AT 46S 80W ALONG
44S 68W...EXITING AT 40S 55W.

AT 500 HPA...AN UPPER RIDGE IS FORMING OFF THE COAST OF CHILE.
THIS RIDGE CENTERS ON A HIGH AT 31S 83W...AND EXTENDS A BROAD AXIS
JUST OFF THE COAST OF CHILE SOUTH INTO THE DRAKE PASSAGE. THE
BUILDING OF THIS RIDGE WILL LIMIT THE INCURSION OF FRONTAL SYSTEMS
INTO SOUTHERN CHILE. THIS RIDGE ALSO EXTENDS AN AXIS INTO THE
CONTINENT TO THE NORTHWEST...INTO A HIGH THAT CENTERS OVER THE
ARGENTINEAN CHACO...PARAGUAY AND MATO GROSSO DO SUL. TO THE EAST
OF THIS RIDGE...A BROAD TROUGH DOMINATES THE SOUTHERN ATLANTIC.
THIS TROUGH EXTENDS AS FAR NORTH AS 40S AND ALONG 60W-40W. TO THE
NORTH OF THIS TROUGH...A SHORT WAVE TROUGH EXTENDS OVER URUGUAY
AND EXTREME SOUTHERN BRASIL-MISIONES IN ARGENTINA.

THE SURFACE ANALYSIS SHOWS A 998 HPA OCCLUDED LOW AT 49S 84W
EXTENDING A FRONT INTO A 1006 HPA AT 46S 78W...43S 76W...39S 82W.
A 994 HPA OCCLUDED LOW CENTERS AT 58S 58W. A 1013 HPA HIGH CENTERS
AT 44S 62W. A 1010 HPA LOW CENTERS AT 42S 37W AND EXTENDS A FRONT
ALONG 40S 43W...40S 50W...38S 55W...39S 65W. ISOLATED
THUNDERSTORMS WERE OCCURRING IN THE BUENOS AIRES PROVINCE ALONG
THIS BOUNDARY.

ABDEMUR...FAA (ARGENTINA)
TEPES...DMC (CHILE)
GALVEZ...WPC (USA)
$$





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