####018005720####
FXSA20 KWBC 131733
PMDSA 
 
SOUTH AMERICA FORECAST DISCUSSION - INTERNATIONAL DESKS
NWS HYDROMETEOROLOGICAL PREDICTION CENTER CAMP SPRINGS MD
1232 PM EST FRI FEB 13 2009
 
GFS DATA AT FTPPRD.NCEP.NOAA.GOV/PUB/DATA/NCCF/COM/GFS/PROD/
 
COR

NOTE: LAST NO AMENDS...NEXT BULLETIN TO BE ISSUED O/A FEB 17.

MODEL COMPARISON (VALID FROM 00Z FEBRUARY 13). THE GFS ONCE AGAIN
MAKES AMPLITUDE/TIMING CORRECTIONS TO SHORT WAVE PERTURBATIONS
STREAMING ACROSS THE EASTERN PACIFIC TO THE SOUTHERN CONE. LATEST
RUN(S) FAVORS SLIGHTLY SLOWER AND AMPLER PERTURBATIONS...WITH
MOST SIGNIFICANT CHANGE NOTED ON DAY 05 WHEN IT SHOWS A HIGH
AMPLITUDE TROUGH ACROSS ARGENTINA...WITH A LOW CUTTING OFF NEAR
CORDOBA. NON OF THE OTHER MODELS OFFER THIS SOLUTION...WITH BOTH
EUROPEAN MODELS AND LARGE MAJORITY OF THE GLOBAL ENSEMBLES
SUSTAINING THE PREVIOUS TREND.

THE SURFACE ANALYSIS SHOWS AN ELONGATED FRONT OVER THE SOUTH
ATLANTIC TO SAO PAULO IN SOUTHEAST BRASIL. THE FRONT WILL REMAIN
NEARLY STATIONARY THROUGH 72 HRS...THEN RAPIDLY WEAKENS. THIS
BOUNDARY LINKS WITH THE SOUTH ATLANTIC CONVERGENCE ZONE OVER
BRASIL AS IT EXTENDS ACROSS SAO PAULO-MATO GROSSO/RONDONIA TO
NORTHERN BOLIVIA. BUT THE BOUNDARY IS BECOMING ILL ORGANIZED...
AND THROUGH 36-48 HRS IT WILL WEAKEN TO A TROUGH...THAT GRADUALLY
WEAKENS THROUGH 72-84 HRS. ALTHOUGH INITIALLY MAXIMA ACROSS
SOUTHEAST BRASIL IS TO PEAK AT 25-50MM/DAY...AFTER 36 HRS IT WILL
DECREASE TO 15-30MM/DAY. OVER BOLIVIA TO SOUTHERN PERU...THE
MAXIMA WILL PEAK AT 10-20MM/DAY THROUGH 36 HRS...THEN SURGE TO
25-50MM/DAY ON DAY 02 AS A MID/UPPER LEVEL TROUGH INTERACTS WITH
THE REMNANTS OF THE SURFACE TROUGH.

OVER THE EASTERN PACIFIC...IN A TIGHT BELT OF MID LATITUDE
WESTERLIES...A PROGRESSIVE SHORT WAVE TROUGH ENTERED THE SOUTHERN
CONE. THE 500 HPA TROUGH MOVES TO THE WESTERN ATLANTIC ALONG
50W/55W BY 24 HRS...AND CONTINUES ACROSS 30W BY 48 HRS. THE
ASSOCIATED FRONT EXTENDS ACROSS PATAGONIA/SOUTHERN CHILE TO THE
EASTERN PACIFIC...AND THROUGH 24 HRS IT WILL MOVE TO THE BUENOS
AIRES PROVINCE/RIO DE LA PLATA...WHERE IT WILL WEAKEN/DISSIPATE
THROUGH 36-48 HRS. CONVECTION WITH THIS BOUNDARY WILL LIMIT TO
SOUTHERN CHILE...WHERE MAXIMA WILL PEAK AT 10-20MM/DAY IN DEEP
CONVECTION. STRONG BOUNDARY LAYER WINDS ARE TO PERSIST OVER
SOUTHERN CHILE THROUGH 48 HRS.

ANOTHER MID LEVEL PERTURBATION FOLLOWS...FORECAST ACROSS 90W/95W
BY 48 HRS. THIS TROUGH WILL CONTINUE ACROSS 75W BY 72 HRS...WITH
SHORT WAVE ENERGY FOCUSING OVER CONTINENTAL AREA SOUTH OF 30S. IT
THEN MOVES ACROSS 60W TO 30S BY 96 HRS...AND THEN QUICKLY PULLS
EASTWARD ACROSS 35W BY 120 HRS. MODELS CONTINUE TO MAKE
ADJUSTMENTS TO THE AMPLITUDE/SPEED OF THIS TROUGH...SO
UNCERTAINTY REMAINS HIGH. THE ASSOCIATED FRONT IS TO ENTER
SOUTHERN CHILE BY 24-36 HRS...THEN MOVE NORTH ACROSS PATAGONIA BY
48 HRS...INTO LA PAMPA/CENTRAL CHILE BY 72 HRS. AT A SLOWER PACE
THAN PREVIOUSLY INDICATED...IT IS TO NOW MOVE ACROSS THE BUENOS
AIRES PROVINCE-CENTRAL CUYO BY 96 HRS. AS IT ENTERS SOUTHERN
CHILE...THE GFS SHOWS HIGH MOISTURE CONTENT WITH THIS
BOUNDARY...WITH MIXING RATIO VALUES OF 12-13G/KG...WHICH IS QUITE
HIGH FOR THIS AREA. THIS WILL BE CONDUCIVE TO ORGANIZED
CONVECTION...HEAVY AT TIMES...WITH RAINFALL MAXIMA OF 15-
35MM/DAY. THE MOST INTENSE AT 48-72 HRS...WITH LOCALLY HIGHER
AMOUNTS IN EXCESS OF 50MM QUITE POSSIBLE. STRONG BOUNDARY LAYER
WINDS ARE ALSO EXPECTED OVER CHILE/PATAGONIA SOUTH OF 40S. OTHER
CONVECTION IS EXPECTED OVER CENTRAL ARGENTINA ON DAYS 03-04...
WITH MAXIMA OF 10-15MM/DAY. OTHER CONVECTION IS POSSIBLE ON THE
LEE OF THE ANDES ACROSS NORTHWEST ARGENTINA...WITH MAXIMA OF 10-
20MM/DAY EXPECTED ON DAYS 01 AND 03.

WATER VAPOR IMAGERY NOW SHOWS THE SUBTROPICAL HIGH CENTERING OVER
THE EASTERN PACIFIC NEAR 20S 80W. AT 200 HPA THE HIGH IS FORECAST
TO MEANDER WEST TO 20S 95W BY 72 HRS. SIMULTANEOUSLY...ANOTHER
HIGH WILL FORM OVER THE CONTINENT NEAR 15S 50W...WITH THE LATTER
TO SLOWLY BUILD A RIDGE TO THE NORTHWEST ACROSS BRASIL TO PERU.
THE INHERENT WEAKNESS BETWEEN THE TWO HIGHS/RIDGES... WILL ALLOW
FOR NORTHWARD AMPLIFICATION OF SHORT WAVE TROUGHS ACROSS
NORTHWEST ARGENTINA TO SOUTHERN BOLIVIA...WITH A STRONG
PERTURBATION TO MOVE ACROSS NORTHERN CHILE TO NORTHWEST
ARGENTINA/SOUTHERN BOLIVIA BY 36-42 HRS...WHERE IT WILL REMAIN
THROUGH 60-72 HRS. AS THE TROUGH ENTERS THE CONTINENT...IT WILL
FAVOR A SURGE IN CONVECTION ACROSS CENTRAL/NORTHERN BOLIVIA-
RONDONIA IN BRASIL...WHERE RAINFALL MAXIMA WILL PEAK AT 25-
50MM/DAY BY 36-60 HRS...WITH MODERATE CONVECTION TO THEN PERSIST
THROUGH 48-72 HRS. OTHER CONVECTION IS EXPECTED FARTHER NORTH
ACROSS NORTHWEST BRASIL TO SOUTHERN COLOMBIA-NORTHERN PERU TO
ECUADOR...WITH MAXIMA OF 20-40MM/DAY ON DAY 01...TO THEN SETTLE
AT 15-30MM/DAY ON DAYS 02-04. 

FURTHERMORE...AS THE SUBTROPICAL RIDGE ESTABLISHES OVER THE
CONTINENT...A TROUGH WILL AMPLIFY OVER THE ATLANTIC ALONG 30W. BY
72 HRS THE TROUGH MOVES ALONG 35W...WITH A CLOSED LOW FORMING
NEAR 05S 35W. THIS LOW MOVES INLAND ACROSS BAHIA BY 72 HRS...AND
CONTINUE WEST TO 10S 55W BY 120 HRS. THIS IS CONSISTENT WITH
PREVIOUS FORECASTS. AS THE PATTERN ESTABLISHES...IT WILL SUSTAIN
A SURGE IN CONVECTION ACROSS TOCANTINS/GOIAS-MINAS GERAIS/EASTERN
BAHIA...WITH MAXIMA OF 35-50MM/DAY EXPECTED BY 36-72 HRS. THROUGH
72-84 HRS THIS SPREADS WEST TO THE AMAZON RIVER DELTA...AND INTO
AMAPA/RORAIMA-GUIANAS BY THE END OF THE CYCLE. IN THIS AREA
STRONG TOPOGRAPHICAL FORCING WILL LIKELY FAVOR RAINFALL MAXIMA IN
EXCESS OF FORECAST GUIDANCE.

PEREZ...SENAMHI (BOLIVIA)
DAVISON...HPC (USA)$$