910
FXSA20 KWBC 211632
PMDSA
SOUTH AMERICA FORECAST DISCUSSION - INTERNATIONAL DESKS
NWS HYDROMETEOROLOGICAL PREDICTION CENTER CAMP SPRINGS MD
1232 PM EDT MON SEP 21 2009
GFS DATA AT FTPPRD.NCEP.NOAA.GOV/PUB/DATA/NCCF/COM/GFS/PROD/
MODEL COMPARISON (VALID FROM 00Z SEP 21). ON THE NORTHERN STREAM
THE MODELS AGREE THROUGH DAY 05...WHILE ON THE SOUTHERN STREAM
THEY START TO DIVERGE ON DAY 04. IN THIS REGION THE GFS SHOWS A
STRONGER/DEEPER TROUGH TO ENTER THE DRAKE PASSAGE/SOUTHERN CONE.
BOTH EUROPEAN MODELS FAVOR A WEAKER/LOWER AMPLITUDE TROUGH TO
ENTER THE CONTINENT. THE MEAN OF THE GLOBAL ENSEMBLES TEND TO
FAVOR THE GFS SOLUTION...BUT THE SPREAD ON BOTH SIDES OF THE AXIS
IS TO HIGH TO ESTABLISH CONFIDENCE IN THE FORECAST. FURTHERMORE
THE 06 UTC GFS CORRECTED IN FAVOR OF A WEAKER AXIS...AND WE
EXPECT FUTURE RUNS OF THE MODEL TO CONTINUE WITH THIS TREND.
AT 200 HPA...A HIGH SOUTH OF THE GALAPAGOS ISLANDS EXTENDS A
RIDGE EAST ACROSS PERU AND BRASIL. ALTHOUGH THIS RIDGE PERSISTS
OVER THE EASTERN TROPICAL PACIFIC...THE CONTINENTAL PORTION
COLLAPSES EARLY IN THE CYCLE AS A SHORT WAVE TROUGH MOVES INLAND.
THE TROUGH IS TO EXTEND FROM NORTHERN CHILE TO AMAZONAS BRASIL BY
24 HRS...AND THROUGH 48 HRS IT WILL MOVE ALONG 60W WHILE
EXTENDING ACROSS PARAGUAY/EASTERN BOLIVIA TO PARA IN BRASIL. THE
TROUGH IS TO WEAKEN/DAMPEN AS IT EJECTS ACROSS SOUTHERN BRASIL BY
72 HRS. THIS TROUGH IS TO INTERACT WITH A MEANDERING SURFACE
FRONT OVER BRASIL...WITH BOUNDARY TO EXTEND ACROSS SOUTHEAST
BRASIL-MATO GROSSO/RONDONIA TO NORTHERN BOLIVIA. AS THEY
INTERACT...EXPECT ORGANIZED DEEP CONVECTION ACROSS PORTIONS OF
PARAGUAY-MATO GROSSO DO SUL AND SAO PAULO IN BRASIL...WHERE WE
EXPECT RAINFALL MAXIMA OF 35-70MM/DAY THROUGH AT LEAST 60 HRS.
ALONG THE TAIL END OF THE FRONT...EXPECT RAINFALL AMOUNTS OF
20-35MM/DAY FROM NORTHERN BOLIVIA TO THE PERUVIAN JUNGLE/SOUTHERN
COLOMBIA AND AMAZONAS IN BRASIL. THIS WILL PERSIST THROUGH DAY
03...WHEN MAXIMA IN THIS AREA IS TO INCREASE TO 25-50MM/DAY. AS
CONVECTION OVER BOLIVIA-PERU BECOMES BETTER ORGANIZED... AND
LATENT HEAT IS RELEASED INTO THE ATMOSPHERE...THE SUBTROPICAL
RIDGE ALOFT IS FORECAST TO BUILD. BY THE END OF THE CYCLE A HIGH
OVER NORTHERN BOLIVIA WILL ANCHOR THIS RIDGE AS IT EXTENDS
BETWEEN 50W-85W AND TO THE NORTH OF 30S.
ON THE SOUTHERN STREAM FLOW...A BROAD/LOW AMPLITUDE TROUGH IS
INITIALIZED OVER THE SOUTHEAST PACIFIC...ENVELOPING AREA BETWEEN
140-70W AND TO THE SOUTH OF 40S. THE BROAD LOW AMPLITUDE TROUGH
PATTERN WILL PERSIST THROUGH DAY 03. ON DAY 04-05...AS A MID
LEVEL RIDGE BUILDS SOUTH ALONG 90W/100W...THE MODELS FORECAST
THIS TROUGH TO AMPLIFY NORTH INTO THE SOUTHERN CONE. ALTHOUGH
THEY AGREE ON THE NORTHWARD AMPLIFICATION OF THIS AXIS...THEY
DISAGREE ON THE INTENSITY OF THE POLAR SURGE. AT LOW LEVELS A
BROAD/DEEP TROUGH WILL DOMINATE THE SOUTHERN STREAM FLOW OVER THE
SOUTHEAST PACIFIC. PROGRESSIVE POLAR FRONTS WILL REVOLVE AROUND
THIS AXIS...AND THEY ARE TO QUICKLY MOVE ACROSS SOUTHERN PORTIONS
OF CHILE AND PATAGONIA. IN A TIGHT PRESSURE GRADIENT EXPECT
STRONG BOUNDARY LAYER WINDS OF 20-35KT TO ENVELOP AREA TO THE
SOUTH OF 43S. TOPOGRAPHICALLY AS WELL AS FRONTALLY INDUCED
PRECIPITATION IS EXPECTED ACROSS SOUTHERN CHILE AND TIERRA DEL
FUEGO. THE DAILY MAXIMA WILL PEAK AT 05-10MM THROUGH DAY
02...INCREASING TO 15-20MM ON DAYS 03-04. ON DAY 05 WE EXPECT
ACTIVITY TO WANE. ORGANIZED SNOWFALL IS EXPECTED ON THE SOUTHERN
ANDES.
GARCIA...SENAMHI (PERU)
MAZA...SMN (ARGENTINA)
DAVISON...HPC (USA)
CLICK HERE TO GO TO PREVIOUS BULLETINS.
Main Text Page