653
FXSA20 KWBC 211723
PMDSA
SOUTH AMERICA FORECAST DISCUSSION - INTERNATIONAL DESKS
NWS HYDROMETEOROLOGICAL PREDICTION CENTER CAMP SPRINGS MD
1222 PM EST FRI NOV 21 2008
GFS DATA AT FTPPRD.NCEP.NOAA.GOV/PUB/DATA/NCCF/COM/GFS/PROD/
MODEL COMPARISON (VALID FROM 00Z NOVEMBER 21) THE GLOBAL MODELS
REMAIN IN EXCELLENT AGREEMENT THROUGH THE NEXT 5 DAYS. A STRONG
EASTERN PACIFIC TROUGH WILL PUSH ACROSS THE SOUTHERN CONE DURING
THE NEXT COUPLE OF DAYS TEMPORARILY WEAKENING THE STRONG WESTERN
ATLANTIC RIDGE THAT EXTENDS ACROSS CENTRAL AND NORTHERN
ARGENTINA. HOWEVER BY DAYS 4-5 THE MODELS SHOW THIS RIDGE
RE-BUILDING AS ANOTHER POWERFUL TROUGH AMPLIFIES IN THE EASTERN
PACIFIC. BASED ON THE MODEL CONSENSUS AND RELATIVELY LOW SPREAD
AMONG THE ENSEMBLES CONFIDENCE IN THE DAILY FORECASTS REMAINS
HIGH.
OVER THE SOUTHERN CONE THE STRONG EASTERN PACIFIC TROUGH WILL
PUSH A COLD FRONT ACROSS SOUTHERN CHILE TIERRA DEL FUEGO AND
SOUTHERN PATAGONIA DURING THE NEXT 24-36 HOURS. THE MODELS SHOW
THIS TROUGH AMPLIFYING RIGHT BEFORE MOVING ONSHORE AND COMBINED
WITH A VERY STRONG ONSHORE FLOW EXPECT WIDESPREAD HEAVY RAINFALL
ACROSS SOUTHERN CHILE FROM ISLA DE CHILOE SOUTHWARD WITH AMOUNTS
UP TO 20-40MM. THE FRONT WILL PUSH NORTHWARD INTO CENTRAL
ARGENTINA DAY 2 AND INTO BUENOS AIRES PROVINCE DAY 3 TRIGGERING
SCATTERED CONVECTION. MEANWHILE OVERRUNNING AHEAD OF AN UPSTREAM
SHORT WAVE WILL SPREAD MOSTLY LIGHT PRECIPITATION INTO SOUTHERN
CHILE BY 60 HOURS WITH HEAVIER RAINS OF UP TO 15-25MM POSSIBLE AS
THIS FEATURE AND ITS ASSOCIATED FRONT CROSS THE REGION BETWEEN
72-84 HOURS. THIS SHORT WAVE WILL ACT TO INCREASE ACTIVITY ALONG
THE FRONT DRAPED THROUGH CENTRAL ARGENTINA ON DAY 4. INCREASING
LOW-LEVEL CONVERGENCE AND LEFT ENTRANCE REGION JET DYNAMICS WILL
PROVIDE LIFT FOR AN AREA OF ORGANIZED CONVECTION FROM CENTRAL
ARGENTINA ACROSS BUENOS AIRES PROVINCE WITH MAXIMUM AMOUNTS OF UP
TO 15-30MM POSSIBLE.
FARTHER NORTH THE STRONG SURFACE HIGH IN THE WESTERN ATLANTIC
WILL SUSTAIN A PERSISTENT MOIST EAST TO NORTHEAST FLOW INTO
SOUTHERN BRASIL FOR MUCH OF THE PERIOD. THIS WILL SUPPORT
COASTAL RAINFALL FROM RIO DE JANEIRO SOUTHWARD THROUGH SAO
PAULO PARANA AND SANTA CATARINA. MAXIMUM DAILY RAINFALL THROUGH
DAY 3 WILL RANGE FROM 15-35MM. WITH THE ASSOCIATED UPPER RIDGE
TEMPORARILY BREAKING DOWN THERE MAY BE SOME WEAKENING TO THIS
ONSHORE FLOW LATER IN THE PERIOD. WHILE DAILY CONVECTION WILL
CONTINUE RAINFALL AMOUNTS SHOULD BE SLIGHTLY LIGHTER DAYS 4-5.
OVER NORTHWESTERN AND WESTERN ARGENTINA MODELS ARE INDICATING
THAT THE AIR MASS WILL BECOME INCREASINGLY MOIST AND UNSTABLE BY
DAY 3 LIKELY A RESULT OF SOME SUBTROPICAL STREAM ENERGY EJECTING
OUT OF THE EASTERN PACIFIC. THIS WILL SUPPORT AN INCREASING
THREAT FOR ORGANIZED CONVECTION OVER THE HIGHER TERRAIN ALONG
WITH ISOLATED SEVERE WEATHER. MAXIMUM AMOUNTS OF 10-15MM ARE
POSSIBLE DAY 3 INCREASING TO UP TO 30-35MM DAYS 4-5.
OVER THE ATLANTIC A MID-UPPER LEVEL TROUGH WILL EXTEND INTO
SOUTHERN/SOUTHEAST BRASIL AND PERSIST THROUGH THE FORECAST
PERIOD. AT THE SAME TIME THE SACZ STRETCHES THROUGH THIS REGION
WEST-NORTHWEST ACROSS SOUTHERN AMAZONIA AND THIS FEATURE IS ALSO
LIKELY TO PERSIST THROUGH THE NEXT 5 DAYS. A SUBTROPICAL JET
ROUNDING THE WESTERN AND NORTHERN ENDS OF THE ATLANTIC TROUGH
WILL RESULT IN AN UPPER DIVERGENT PATTERN THROUGH ESPIRITO SANTO
AND MINAS GERAIS TO GOIAS. COMBINED WITH A MOIST EASTERLY
ONSHORE FLOW AND CONVERGENCE ALONG THE SACZ THERE IS A GOOD
CHANCE FOR ORGANIZED DAILY CONVECTION FROM ESPIRITO SANTO
WESTWARD THROUGH MINAS GERAIS AT LEAST THROUGH DAY 3. AMOUNTS
COULD REACH 35-70MM DAY 1 WITH SOMEWHAT LESSER TOTALS DAYS 2-3.
BY DAY 4-5 MODELS ARE INDICATING THAT THE ONSHORE FLOW WILL
WEAKEN SO PRECIPITATION WILL LIKELY FOCUS MORE ALONG THE COAST.
AT 200 HPA THE SUBTROPICAL RIDGE WILL ENCOMPASS MUCH OF THE
CONTINENT NORTH OF 20S THIS PERIOD WITH A PERSISTENT TROUGH
EXTENDING ALONG THE PERUVIAN COAST AT LEAST THROUGH DAY 4. THE
RIDGE ALOFT WILL CONTINUE VENTING DEEP CONVECTION ALONG THE SACZ
ACROSS BRASIL. MAXIMUM DAILY AMOUNTS WILL RANGE FROM 25-50MM.
ACTIVITY IS EXPECTED TO INCREASE FARTHER WEST THROUGH THE JUNGLES
OF SOUTHERN/CENTRAL PERU BY DAY 3 AS LOW LEVEL EAST-NORTHEAST
FLOW OVER BOLIVIA AND SOUTHERN PERU WEAKENS AND ALLOWS THE AREA
OF DEEPEST TROPICAL MOISTURE TO BUILD SOUTHWARD. DAILY MAXIMUM
RAINFALL TOTALS UP TO 20-35MM ARE POSSIBLE.
URRA...DMC (CHILE)
MOREYRA...SENAMHI PERU
KLEIN...HPC (USA)
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