597
FXSA20 KWBC 301620
PMDSA
SOUTH AMERICA FORECAST DISCUSSION - INTERNATIONAL DESKS
NWS HYDROMETEOROLOGICAL PREDICTION CENTER CAMP SPRINGS MD
1219 PM EDT TUE SEP 30 2008
GFS DATA AT FTPPRD.NCEP.NOAA.GOV/PUB/DATA/NCCF/COM/GFS/PROD/
MODEL COMPARISON (VALID FROM 00Z SEP 30). GLOBAL MODELS ARE IN
BETTER AGREEMENT TODAY THAN YESTERDAY... BUT THERE ARE STILL
DIFFERENCES... ESPECIALLY WITH THE SOUTHERN STREAM AFTER 84 HRS.
THE GFS HAS SHOWN POOR CONTINUITY FROM YESTERDAY AND HAS TRENDED
TOWARD THE ECMWF AND UKMET SOLUTIONS. WHILE ALL MODELS AGREE ON
THE GENERAL EVOLUTION OVER THE NEXT 5 DAYS... THERE ARE STILL
SIGNIFICANT DIFFERENCES IN THE HANDLING OF SOUTHERN STREAM
IMPULSES LATER IN THE PERIOD.
AT 500 HPA... A NORTHERN STREAM SHORTWAVE TROUGH ALONG 75W SOUTH
OF 25S AT 36 HRS IS FORECAST BY THE GLOBAL MODELS TO MOVE EAST
ACROSS CENTRAL PORTIONS OF CHILE AND ARGENTINA AND INTO THE SOUTH
ATLANTIC BY 72 HRS. THE GFS IS A LITTLE WEAKER AND FASTER WITH
THIS SYSTEM THAN YESTERDAY BUT IS IN REASONABLE AGREEMENT WITH
THE ECMWF AND UKMET. THIS SYSTEM WILL SUPPORT RAINFALL OF 15-25MM
OVER CHILE/ARGENTINA IN SOUTHERN PATAGONIA ON DAY 1 AND OVER
BUENOS AIRES PROVINCE ON DAY 2.
A STRONGER SOUTHERN STREAM SHORTWAVE TROUGH WILL FOLLOW CLOSELY
BEHIND THIS TROUGH REACHING 80W-90W BY 60 HRS. AS A SERIES OF
IMPULSES ROTATE AROUND THE BASE OF THE TROUGH IT WILL SLOWLY
PROGRESS EASTWARD ACROSS SOUTHERN CHILE AND ARGENTINA REACHING
60W-70W BY 108 HRS. MODELS DIFFER SOMEWHAT ON THE FURTHER
EVOLUTION OF THE SYSTEM BUT IN GENERAL ALL DEPICT A DEEP LOW
SOUTHEAST OF TIERRA DEL FUEGO BY 132 HRS WITH A STRONG MID LEVEL
GRADIENT OVER THE SOUTHERN PORTIONS OF THE SOUTHERN CONE. OVER
EXTREME SOUTHERN CHILE EXPECT O5-10MM OF PRECIPITATION EACH DAY
EXCEPT 15-25MM ON DAYS 2 AND 5. FARTHER NORTH OVER CENTRAL
ARGENTINA THIS SYSTEM WILL SUPPORT RAINFALL OF 10-20MM ON DAY 3
OVER CORDOBA AND SAN LUIS PROVINCES. ON DAY 4 RAINFALL WILL
INCREASE TO 25-50MM OVER CORDOBA AND BUENOS AIRES PROVINCES.
A NEARLY STATIONARY SURFACE FRONT MEANDERING ACROSS SOUTHERN
BRASIL AND PARAGUAY WILL SERVE AS A FOCUS FOR CONVECTION FOR MUCH
OF THE CYCLE. WITH GOOD NORTHERLY INFLOW OF LOW LEVEL MOISTURE
NORTH OF THE FRONT PWS WILL INCREASE TO GREATER THAN 50MM EARLY
IN THE CYCLE PERSISTING THROUGH THE PERIOD. A SERIES OF WEEK MID
LEVEL IMPULSES EMBEDDED IN THE WESTERLY FLOW WILL INTERACT WITH
THE FRONT SUPPORTING RAINFALL OF 40-60MM/DAY ACROSS PARAGUAY AND
SOUTHERN BRASIL DAYS 2 -5.
NORTH OVER THE CONTINENT...AT 200 HPA....THE SUBTROPICAL RIDGE
WILL CONTINUE TO DOMINATE THE FLOW OVER NORTHERN SOUTH AMERICA
EARLY IN THE PERIOD. THE HIGH CENTER WILL LINGER OVER CENTRAL
PERU THROUGH 72 HRS THEN SHIFT WEST INTO THE EASTERN PACIFIC.
THE ASSOCIATED EAST TO WEST RIDGE ACROSS BRASIL ALONG 10S-12S
EARLY IN THE PERIOD WILL GRADUALLY SHIFT SOUTH TO 12S-15S BY DAY
5. THE RIDGE WILL SUPPORT SCATTERED CONVECTION ACROSS BRASIL TO
PERU-ECUADOR/SOUTHERN COLOMBIA... WITH MAXIMA OF 20-40MM/DAY.
GUZMAN...SENAMHI (BOLIVIA)
URRA...DMC (CHILE)
MOREYRA...SENAMHI PERU
DANAHER...HPC (USA)
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