SOUTH AMERICA FORECAST DISCUSSION - INTERNATIONAL DESKS
NWS HYDROMETEOROLOGICAL PREDICTION CENTER CAMP SPRINGS MD
1040 AM EST TUE FEB 09 2010
 
GFS DATA AT FTPPRD.NCEP.NOAA.GOV/PUB/DATA/NCCF/COM/GFS/PROD/
 
MODEL COMPARISON (VALID FROM 00Z FEB 09). MODEL DIFFERENCES
CONFINE TO THE WESTERN ATLANTIC ON DAYS 04-06...AS THE MODELS
DIVERGE ON INTENSITY OF A TROUGH ON THE SOUTHERN STREAM FLOW. THE
ECMWF...IN CONTRAST TO THE GFS-UKMET...FAVORS A DEEPER/MORE
AMPLIFIED PATTERN TO ESTABLISH FROM THE DRAKE PASSAGE NORTHWARD
INTO THE SOUTHERN CONE. THE GLOBAL ENSEMBLES SIDE WITH THE WEAKER
GFS/UKMET SOLUTION. BUT...HIGH VARIANCE AMONG THE ENSEMBLE
MEMBERS LEADS TO A LOW CONFIDENCE FORECAST. EXPECT CORRECTIONS TO
THIS FORECAST IN THE NEXT FEW RUNS OF THE MODELS.

AT 200 HPA...OVER NORTHERN SOUTH AMERICA...THE BOLIVIAN HIGH WILL
MEANDER BETWEEN SOUTHERN PERU AND WESTERN BOLIVIA DURING THE NEXT
FIVE DAYS. THE ASSOCIATED RIDGE WILL EXPAND ACROSS SOUTHERN PERU-
BOLIVIA-PARAGUAY/NORTHWEST ARGENTINA TO MATO GROSSO DO SUL IN
BRASIL. TOWARDS THE END OF THE CYCLE...HOWEVER...THE RIDGE IS
FORECAST TO INTENSIFY/BUILD ACROSS PARA/AMAZONAS IN WESTERN
BRASIL TO ENVELOP AREA TO THE NORTH OF 30S AND WEST OF 60W. A
TROUGH...MEANWHILE...WILL DOMINATE THE EASTERN HALF OF BRASIL. AN
ILL ORGANIZED LOW OVER NORTHERN BAHIA WILL ANCHOR THIS TROUGH
EARLY IN THE PERIOD. BUT BY MID CYCLE...A LOW OFF THE COAST OF
BRASIL NEAR 18S 32W WILL BECOME THE DOMINANT CIRCULATION. MOST
ACTIVE CONVECTION IS EXPECTED ACROSS NORTHEAST BRASIL THROUGH 36-
48 HRS...WITH MAXIMA OF 25-50MM/DAY...THEN DECREASE TO 15-
30MM/DAY WHILE CONCENTRATING AROUND THE AMAZON RIVER DELTA. BY
THE END OF THE CYCLE THE MAXIMA WILL PEAK AT 10-15MM/DAY. AN AREA
OF ORGANIZED CONVECTION IS ALSO EXPECTED FROM SOUTHERN
PERU/CENTRAL BOLIVIA TO SOUTHERN BRASIL...WITH MAXIMA OF 20-
45MM/DAY THROUGH 60-72 HRS. BY 96-120 HRS THE FOCUS OF THE
CONVECTION WILL SHIFT WEST TO CONCENTRATE OVER NORTHERN BOLIVIA-
PARA/AMAZONAS IN WESTERN BRASIL...WITH MAXIMA TO CONTINUE PEAKING
A 20-45MM/DAY. 

FARTHER SOUTH...A BROAD TROUGH IS INITIALIZED OVER THE SOUTHERN
CONE/WESTERN ATLANTIC...WITH AXIS TO SLOWLY MOVE BETWEEN 30W-60W
AND TO THE SOUTH OF 35S THROUGH 48 HRS. THIS TROUGH WILL PUSH
AGAINST A BLOCKING RIDGE TO THE EAST...WITH RIDGE AXIS SOUTH
ALONG 20W/30W. AS THEY COLLIDE...THE TROUGH IS TO GRADUALLY WANE
THROUGH 84 HRS. THE RIDGE...MEANWHILE...WILL COLLAPSE TO THE
NORTH OF 60S...WHILE TO THE SOUTH IT IS TO EVOLVE INTO A CLOSED
HIGH/RIDGE OVER THE WEDDELL SEA. AT LOW LEVELS IT WILL SUSTAIN A
BROAD TROUGH BETWEEN THE COAST OF PATAGONIA AND NORTHERN TIP OF
THE ANTARCTIC PENINSULA. THIS TROUGH IS TO SLOWLY WEAKEN AS IT
PULLS TO THE EAST-SOUTHEAST ACROSS THE SOUTH ATLANTIC. THE
ASSOCIATED SURFACE FRONT WILL EXTEND ACROSS LA PAMPA-CENTRAL CUYO
BY 24 HRS...WHERE IT IS FORECAST TO STALL/MEANDER THROUGH 72-96
HRS. THIS WILL FAVOR SCATTERED CONVECTION ACROSS THE BUENOS AIRES
PROVINCE TO CENTRAL/NORTHERN CUYO. MOST INTENSE CONVECTION IS
EXPECTED THROUGH 48-60 HRS...WITH DAILY MAXIMA OF 15-25MM.
LOCALIZED MAXIMA...IN THE ORDER OF 25-50MM ARE QUITE POSSIBLE DUE
TO FAVORABLE JET DYNAMICS ALOFT. AFTER 60 HRS THE DAILY MAXIMA
WILL DECREASE TO 10-20MM.

IN A TIGHT BELT OF MID LEVEL WESTERLIES...A PROGRESSIVE TROUGH
WILL EJECT ACROSS THE SOUTH PACIFIC...TO MOVE ALONG 105W/110W BY
48 HRS...AND ACROSS 90W BY 72 HRS. THE TROUGH WILL ENTER THE
SOUTHERN CONE BY 84-96 HRS. LATER IN THE CYCLE...AS IT MOVES
ACROSS PATAGONIA THROUGH 108 HRS...THE MODELS FORECAST THIS
SYSTEM TO DEEPEN/INTENSIFY AS A RIDGE BUILDS/ESTABLISHES TO THE
WEST ALONG 90W TO THE BELLINGSHAUSEN SEA. AS PREVIOUSLY
MENTIONED...THE MODELS DIVERGE ON INTENSITY/AMPLITUDE OF THIS
SYSTEM...AND FURTHER CORRECTIONS TO THIS PATTERN ARE EXPECTED ON
THE NEXT FEW RUNS. AT LOW LEVELS...AN OCCLUDING LOW WILL REACH
THE SOUTHERN CONE THROUGH 72-84 HRS...TO PULL ACROSS TIERRA DEL
FUEGO/SOUTHERN PATAGONIA BY 96 HRS. THIS SYSTEM IS TO THEN
RAPIDLY WEAKEN AS IT MOVES BETWEEN THE FALKLAND AND THE SOUTH
GEORGIA ISLANDS. THE ASSOCIATED FRONT WILL PULL ACROSS PATAGONIA
THROUGH 84-96 HRS...TO MOVE NORTH ACROSS THE BUENOS AIRES
PROVINCE TO CENTRAL CUYO IN ARGENTINA BY 120 HRS. A SOUTHERLY JET
OF 20-35KT WILL SUSTAIN THE NORTHWARD PROGRESSION OF THIS FRONT
ACROSS LA PAMPA/BUENOS AIRES PROVINCE. AS IT ENTERS SOUTHERN
CHILE IT WILL FAVOR SCATTERED CONVECTION WITH MAXIMA OF 05-
10MM/DAY. OVER ARGENTINA...MOST INTENSE CONVECTION IS EXPECTED ON
DAY 05...AS IT IS TO TRIGGER MAXIMA OF 15-35MM/DAY. DURING THAT
PERIOD...MID LEVEL COLD AIR INTRUSION WILL RESULT IN HEIGHT FALLS
OF 50-75GPM ON THE CENTRAL PROVINCES IN ARGENTINA. AS A
RESULT...A PREFRONTAL SQUALL LINE IS POSSIBLE...WITH SEVERE
CONVECTION LIKELY TO DEVELOP. DURING THAT PERIOD...LOCALIZED
MAXIMA OF 50-75MM ARE POSSIBLE.

LLANQUE...SENAMHI (BOLIVIA)
DAVISON...HPC (USA)Ñ%