265
FXSA20 KWBC 291733
PMDSA
SOUTH AMERICA FORECAST DISCUSSION - INTERNATIONAL DESKS
NWS HYDROMETEOROLOGICAL PREDICTION CENTER CAMP SPRINGS MD
132 PM EDT FRI AUG 29 2008
GFS DATA AT FTPPRD.NCEP.NOAA.GOV/PUB/DATA/NCCF/COM/GFS/PROD/
MODEL COMPARISON (VALID FROM 00Z AUG 29)... A STRONG AMPLITUDE
PATTERN IS FORECAST TO CONTINUE THROUGH THE NEXT 5 DAYS ACROSS
THE HIGH/MIDDLE LATITUDES. ALL OF THE GLOBAL MODEL SOLUTIONS AT
0000 UTC SUGGEST ANOMALOUSLY DEEP TROUGHS OVER THE ATLANTIC AND
PACIFIC DAYS 1-3. THE DEEP TROUGH ALONG THE EAST COAST OF THE
CONTINENT IS FORECAST TO SLOWLY MOVE EASTWARD AWAY FROM THE
CONTINENT BY DAY 3. OVER THE PACIFIC.. THE GFS SHOWS THE MOST
AMPLIFICATION OF THE GLOBAL MODELS WITH THE NEGATIVELY TILTED
TROUGH. STANDARDIZED ANOMALIES OF THE ECMWF/CMC 500 HPA HEIGHT
FIELD SUGGEST A -3.0 HEIGHT ANOMALY WHILE THE GFS REACHES -4.0 TO
-5.0 THIS DISPARITY LEADS TO MAJOR DIFFERENCES IN THE MODELS FOR
DAYS 4-5 AS THE GFS DEVELOPS THE DEEP TROUGH INTO A FULL LATITUDE
TROUGH ALONG 80W AND RE-AMPLIFIES THE RIDGE OVER THE EASTERN
CONTINENT. MEANWHILE THE ECMWF/CMC ON DAYS 4-5 REDEVELOP THE
POLAR LOW MUCH FURTHER EAST NEAR DRAKE PASSAGE AND DO NOT PHASE
THE SOUTHERN AND NORTHERN STREAM. WITH THE LOWER HEIGHT REGIME..
A FRONT IS FORECAST TO BE DRAPED ACROSS URUGUAY AND NORTHERN
ARGENTINA WHICH BECOMES THE FOCUS FOR DAY 5 PRECIPITATION. THE
GFS ENSEMBLE MEAN MAINTAINS A SIMILAR PATTERN TO THE CONTROL GFS
WHILE THE ECMWF ENSEMBLE SHOWS A BIT MORE EASTERN CONTINENT RIDGE
BUT STILL A SPLIT FLOW IN HIGHER LATITUDES. RIGHT NOW WILL NOT
PLACE A FRONT ACROSS EASTERN ARGENTINA AND FOLLOW MORE CLOSELY
THE GFS SOLUTION AS THE GEFS PACKAGE IS CLOSE IN LINE WITH GFS.
BUT CONFIDENCE IS LOW AND THE GFS MAY VERY WELL TREND CLOSER TO
THE ECWMF/CMC WITH TIME.
A STRONG ONSHORE JET FROM THE EXIT REGION OF THE NEGATIVELY
TILTED TROUGH IS FORECAST TO PERSIST OVER SOUTHERN CHILE THROUGH
AT LEAST DAY 3 AND POSSIBLE BEYOND DEPENDING UP THE EVOLUTION THE
SOUTHERN/NORTHERN STREAMS LATE IN THE FORECAST CYCLE. ALL OF THE
MODELS SUGGEST COPIOUS RAINFALL AMOUNTS ON DAYS 1-3 AND THE
POSITIVE STANDARDIZED ANOMALIES OF PRECIPITABLE WATER AND
MOISTURE FLUX AT 850 HPA SUPPORT THE HIGHER AMOUNTS. THE MOISTURE
FLUX FIELDS SUGGEST AN ATMOSPHERIC RIVER OR PLUME PERSISTING
ACROSS THE EASTERN PACIFIC INTO THE CONTINENT WITH NORMALIZED
ANOMALIES OF +3.0 ADVECTING INTO SOUTHERN CHILE. ON DAY 1..
RAINFALL MAXIMA OF 25-50MM ARE POSSIBLE WHILE ON DAYS 2-3 40-80MM
MAXIMA AMOUNTS ARE NOT OUT OF THE QUESTION. BY DAY 4.. THE FLOW
IS EXPECTED TO BECOME ALIGNED MORE PARALLEL TO THE CONTINENT SO
THE THREAT FOR SIGNIFICANT HEAVY RAINFALL MAY SUBSIDE.
AREAS OF LIGHT PRECIPITATION OR SHALLOW CONVECTION ARE POSSIBLE
DAYS 1-2 OVER SAO PAULO.. RIO GRANDE DU SOL AND PARANA BRASIL. AS
A LINGER FRONTAL BOUNDARY ASSOCIATED WITH THE EXITING EAST COAST
TROUGH PERSISTS. 05-15MM OF RAINFALL PER DAY IS POSSIBLE IN LOCAL
PRECIPITATION BANDS. BY DAY 3 THE BOUNDARY IS FORECAST TO
DISSIPATE THEREFORE THE THREAT OF MEASURABLE RAINFALL SHOULD
SUBSIDE.
OVER THE NORTHERN CONTINENT.. A 200 HPA ANTICYCLONE IS FORECAST
TO PERSIST OVER PERU THROUGH THE FORECAST PERIOD. WIDESPREAD DEEP
CONVECTION IS EXPECTED TO OCCUR EACH DAY OVER THE PERUVIAN
JUNGLES AS WELL AS THE JUNGLES OF COLOMBIA AND WESTERN AMAZONIA.
THE WESTERN EDGE OF AN ATLANTIC ANTICYCLONE IS FORECAST TO EXTEND
INTO EXTREME NORTHEAST BRASIL AND CONVECTION VENT ALONG THE
COASTAL AREAS. RAINFALL AMOUNTS OF 05-15MM/DAY ARE POSSIBLE ON
DAYS 1-3.
GUZMAN...SENAMHI (BOLIVIA)
URRA.....DMC (CHILE)
BODNER...HPC (USA)
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