978
FXSA20 KWBC 011632
PMDSA
SOUTH AMERICA FORECAST DISCUSSION - INTERNATIONAL DESKS
NWS HYDROMETEOROLOGICAL PREDICTION CENTER CAMP SPRINGS MD
1232 PM EDT FRI AUG 01 2008
GFS DATA AT FTPPRD.NCEP.NOAA.GOV/PUB/DATA/NCCF/COM/GFS/PROD/
MODEL COMPARISON (VALID FROM 00Z AUG 01). MAIN DIFFERENCE AMONG
THE MODELS IS ON THE SOUTHERN STREAM FLOW...JUST WEST OF THE
DRAKE PASSAGE. IN THIS AREA BOTH EUROPEAN MODELS GRADUALLY
DEVELOP A CLOSED LOW/BROAD TROUGH PATTERN BY THE END OF THE
CYCLE...WHILE THE GFS IS FAVORING A HIGHER AMPLITUDE/OPEN TROUGH.
THE CONSENSUS OF THE GLOBAL ENSEMBLES FAVORS THE EUROPEAN
SOLUTION...AND THIS IS STARTING TO SHOW ON THE 06 RUN OF THE GFS
MODEL. SO EXPECT CORRECTIONS TO FUTURE RUNS.
ON THE NORTHERN STREAM...A MID/UPPER LEVEL TROUGH WILL MOVE
OVER CENTRAL SOUTH AMERICA EARLY THIS PERIOD...WHERE IT
WILL REMAIN THROUGH 54-60 HRS. IT IS TO THEN PULL EAST TO
THE WESTERN ATLANTIC BY MID CYCLE. AS IT ENTERS MID SECTIONS OF
SOUTH AMERICA...IT WILL MERGE WITH A HIGH AMPLITUDE TROUGH OVER
THE SOUTHERN CONE/WESTERN ATLANTIC BY 24-48 HRS. THE SHORT WAVE
TROUGH IS TO INITIALLY FOCUS ITS SHORT WAVE ENERGY ACROSS
PARAGUAY-SOUTHERN BRASIL...BUT THROUGH 36-48 HRS THIS IS TO
EXPAND TO CENTRAL BOLIVIA/CHACO PARAGUAYO-MATO GROSSO DO SUL
BRASIL. THIS TROUGH IS INTERACTING WITH A SURFACE FRONT THAT
STRETCHES ACROSS SOUTHERN BRASIL-PARAGUAY-BOLIVIA...AS IT
CONTINUES TO TRIGGER SCATTERED DEEP CONVECTION AND FORMATION OF
FRONTAL WAVES/LOWS. ACROSS PARAGUAY-SOUTHERN BRASIL THIS BOUNDARY
WILL REMAIN QUITE ACTIVE THROUGH 36 HRS...WHILE OVER CENTRAL/
NORTHERN BOLIVIA-RONDONIA BRASIL AND SOUTHERN/CENTRAL PERU IT
WILL BE ACTIVE BY 36-72 HRS. OVER SOUTHERN/SOUTHEAST BRASIL-
PARAGUAY IT WILL SUSTAIN MAXIMA OF 20-35MM THROUGH 36 HRS...AND
05-10MM/DAY THEREAFTER THROUGH AT LEAST 72 HRS.
ALSO AT MID LEVELS...A BROAD MID LEVEL TROUGH IS TO EXTEND
BETWEEN 70W/30W AND SOUTH OF 35S DURING THE NEXT 36-48 HRS. THIS
TROUGH IS TO SLOWLY AMPLIFY TO THE NORTH-NORTHWEST INTO CENTRAL
ARGENTINA...WHERE IT WILL INTERACT WITH THE AFOREMENTIONED MID
LEVEL TROUGH OVER NORTHERN ARGENTINA-PARAGUAY-BRASIL. BY 60-72
HRS...AS THE NORTHERN STREAM SHORT WAVE TROUGH MOVES TO THE
WESTERN ATLANTIC...THE LONG WAVE AXIS WILL START TO WEAKEN WHILE
ENERGY SHEARS EAST. BY 96-120 A BROAD/WANING TROUGH WILL THEN
REMAIN OVER THE SOUTH ATLANTIC. AS THE TROUGH PULLS AWAY...THE
SUBTROPICAL JET OVER CENTRAL SOUTH AMERICA IS EXPECTED TO WEAKEN
THROUGH 72-84 HRS...WITH MAIN AXIS MOVING TO THE SOUTH ATLANTIC.
FURTHERMORE...A BUILDING RIDGE TO THE WEST WILL MOVE ALONG
65W/70W TO THE ANTARCTIC PENINSULA BY 24 HRS. AT 60-72 HRS A HIGH
IS TO CLOSE NEAR 62S 50W...WHICH IS TO THEN ANCHOR A RIDGE SOUTH
OF 55S ACROSS THE WENDELL SEA TO JUST WEST OF THE ANTARCTIC
PENINSULA. THE EVOLVING RIDGE IS TO MEANWHILE FEED COLD/POLAR
ENERGY INTO THE BACKSIDE OF THE AMPLIFYING POLAR TROUGH...TO
RESULT IN THE AFOREMENTIONED HIGH AMPLITUDE LONG WAVE PATTERN. AT
LOW LEVELS...A PROGRESSIVE FRONT MOVED ACROSS RIO DE LA PLATA
BASIN...AND THROUGH 24 HRS IT WILL RACE ACROSS URUGUAY TO
SOUTHERN BRASIL. BY 36-48 HRS IT WILL MERGE WITH THE OLD FRONT
OVER BRASIL...REINFORCING THIS BOUNDARY. BY 48 HRS A 1023-1025
HPA POLAR HIGH IS TO BUILD ACROSS LA PAMPA/CENTRAL ARGENTINA. THE
HIGH MOVES FARTHER NORTH THROUGH 60 HRS...THEN STARTS TO MODIFY
OVER SOUTHERN BRASIL. IN THIS PROCESS IT WILL DISPLACE THE
SURFACE FRONT FARTHER NORTH ACROSS BRASIL. AT 72-84 HRS THE FRONT
WILL MOVE FARTHER NORTH ACROSS SOUTHEAST BRASIL-MATO GROSSO TO
RONDONIA-SOUTHERN/CENTRAL PERU. BY 96 HRS THE FRONT WILL START TO
WEAKEN AS IT RETROGRESSES TO SOUTHERN BRASIL-PARAGUAY. AS THE
FRONT MOVES ACROSS PARAGUAY TO NORTHERN BOLIVIA/SOUTHERN PERU IT
WILL SUPPORT SCATTERED CONVECTION...WITH MAXIMA OF 25-50MM.
CONVECTION WILL RAPIDLY BUILD WEST ACROSS SOUTHERN PERU...WITH
SIMILAR AMOUNTS. PREFRONTAL CONVECTION OVER THE PERUVIAN JUNGLE
WILL SUSTAIN DAILY MAXIMA OF 20-35MM THROUGH 48 HRS.
OTHER MID LEVEL VORTICES ARE TO STREAM TOWARDS THE SOUTHERN
CONE...WITH ONE TO ENTER AT 54-60 HRS...THEN PUSH EAST ACROSS
CENTRAL ARGENTINA BY 72 HRS. A BROAD TROUGH IS TO FOLLOW...TO
ENTER THE SOUTHERN CONE BY 96-108 HRS. MODEL UNCERTAINTY AS IT
PERTAINS TO THIS SYSTEM SUGGESTS FURTHER CORRECTIONS ARE EXPECTED
IN FUTURE RUNS OF THE MODEL. AT LOW LEVELS PROGRESSIVE FRONTS
WILL ENTER CHILE/PATAGONIA SOUTH OF 38S DURING THE NEXT FOUR TO
FIVE DAYS. THE AIR MASS WILL BE COLD ENOUGH TO SUSTAIN ORGANIZED
SNOWFALL ON THE SOUTHERN ANDES AND POSSIBLY AS FAR SOUTH AS
TIERRA DEL FUEGO. ALONG THE COAST...MIXED PRECIPITATION IS
EXPECTED...WITH MOSTLY LIQUID PRECIPITATION NORTH OF PUERTO
MONTT. DAILY MAXIMA WILL RANGE BETWEEN 10-15MM...WITH LOCALLY
HIGHER AMOUNTS ON DAY 04 AND 05.
AT 200 HPA A RIDGE DOMINATES CONTINENTAL AREA NORTH OF 20S. UNDER
THE INFLUENCE OF THE AFOREMENTIONED POLAR INCURSION IT IS
FORECAST TO FLATTEN/NEARLY COLLAPSE BY 72-84 HRS. LOW LEVEL TRADE
WIND EASTERLY CONVERGENCE WILL SUSTAIN COASTAL RAINFALL OVER
NORTHEAST BRASIL...WITH MOST INTENSE ACROSS NORTHERN ESPIRITO
SANTO AND BAHIA WITH MAXIMA OF 10-15MM/DAY THROUGH 24-30 HRS AND
AGAIN BY 96-120 HRS. OTHER CONVECTION WILL CONCENTRATE ACROSS THE
NORTHERN COAST OF BRASIL...WITH SIMILAR AMOUNTS. HIGHER AMOUNTS
ARE EXPECTED OVER AMAPA/AMAZON RIVER DELTA TO ASSOCIATE WITH
TROPICAL WAVES...WITH MAXIMA TO PEAK AT 20-35MM. OVER WESTERN
ECUADOR AND CAUCA VALLEY IN SOUTHWEST COLOMBIA THE DAILY MAXIMA
WILL PEAK AT 10-15MM. ACTIVITY IS TO ALSO DOT THE PERUVIAN JUNGLE
OVER THE NEXT TWO DAYS. A SURGE IN ACTIVITY IS EXPECTED LATER IN
THE CYCLE AS THE POLAR FRONT MOVES NORTH ACROSS MID SECTIONS OF
SOUTH AMERICA.
GUZMAN...SENAMHI (BOLIVIA)
DAVISON...HPC (USA)
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