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South American Forecast Discussion
 
(Latest Discussion - Issued 1555Z Apr 22, 2014)
 
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SOUTH AMERICA FORECAST DISCUSSION - INTERNATIONAL DESKS
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1155 AM EDT TUE APR 22 2014

GFS DATA AT FTPPRD.NCEP.NOAA.GOV/PUB/DATA/NCCF/COM/GFS/PROD/

MODEL DISCUSSION (VALID FROM 22 APRIL 00UTC): GLOBAL MODELS AND
ENSEMBLE MEMBERS AGREE WELL IN THE EVOLUTION OF THE LARGE SCALE
PATTERNS.

A VERY LARGE MID-UPPER TROUGH IS MOVING SLOWLY ACROSS THE EASTERN
PACIFIC. THE TROUGH WILL MOVE VERY SLOWLY TOWARDS THE SOUTHERN
CONE AS THE CYCLE PROGRESSES. IT WILL START AFFECTING SOUTHERN
CHILE ON DAY 04 WHERE IT WILL PRODUCE ISOLATED MAXIMA OF
15-20MM/DAY. ON DAY 05 EXPECTING AMOUNTS TO DECREASE TO
10-15MM/DAY FROM CONCEPCION TO THE SOUTH. AS THE TROUGH STARTS
CROSSING INTO ARGENTINA...IT WILL PRODUCE CYCLOGENESIS. MOISTURE
WILL BE LIMITED...WHICH WILL RESULT IN ACCUMULATIONS OF
10-15MM/DAY ON DAY 05.

ANOTHER SYSTEM OF INTEREST IS A STRONG UPPER TROUGH MOVING
EASTWARD AT MID-SECTIONS OF THE CONTINENT. THE DIVERGENT TIER OF
THIS TROUGH...LOCATED TO THE EAST OF THE MAIN AXIS...IS
INTERACTING WITH THE LEFT ENTRANCE OF AN UPPER JET. THIS IS
PROVIDING STRONG VENTILATION AND ENHANCING CONVECTION ACROSS
BOLIVIA AND PARAGUAY. SOUTHEASTERLIES WILL BECOME ENHANCED ACROSS
THE CHACO-SOUTHERN BOLIVIA AIDED BY POLAR HIGH AND STRENGTHENING
SURFACE TROUGH TO THE EAST. THIS WILL ENHANCE LOW-LEVEL
CONVERGENCE ACROSS SOUTHERN PERU AND MOST OF LOWER BOLIVIA LEADING
TO EXPLOSIVE THUNDERSTORMS AND ACCUMULATIONS OF 30-60MM/DAY
THROUGH 36 HRS. OTHER REGION WITH ACTIVE WEATHER WILL BE SOUTHERN
BRASIL...WHERE SCATTERED CONVECTION WILL LEAD TO MAXIMA OF
20-35MM/DAY FROM SAO PAULO/PARANA/SANTA CATARINA. ON DAY
02...STRONGEST ACTIVITY WILL SPLIT IN TWO. A LEFTOVER CONVECTION
ASSOCIATED WITH WEAK SOUTHEASTERLY SURGE IN PERU WILL NOW
CONCENTRATE ACROSS ECUADOR/NORTHERN PERU TO PRODUCE MAXIMA OF
30-60MM/DAY. TO THE EAST...ACTIVITY IN SOUTHEASTERN BRASIL WILL
LEAVE SCATTERED MAXIMA OF 15-25MM/DAY ACROSS MINAS GERAIS/NORTHERN
SAO PAULO AND PARTS OF RIO DO JANEIRO. ON DAY 03...EXPECTING A
DECREASE TO MAXIMA OF 10-15MM/DAY. ISOLATED HIGHER AMOUNTS ARE
POSSIBLE ACROSS THE SERRA DO MAR OF RIO DO JANEIRO IN INTERACTION
WITH OROGRAPHY. THIS WILL LEAD TO ISOLATED MAXIMA OF 20-35MM/DAY.

FRONTAL SYSTEM ACROSS EASTERN BRASIL WILL REORGANIZE BY DAY 04 AND
05. THIS WILL ENHANCE MOISTURE CONVERGENCE ACROSS ESPIRITO SANTO
AND SOUTHERN BAHIA TO PRODUCE ISOLATED MAXIMA OF 20-40MM/DAY.
LIGHTER AMOUNTS ARE EXPECTED INLAND.

NORTH ACROSS THE CONTINENT...MOST ACTIVE CONVECTION CONCENTRATES
ACROSS NORTH-CENTRAL AND NORTHWESTERN AMAZONIA. THIS REGION LIES
UNDER THE INFLUENCE OF VENTILATION IN THE PERIPHERY OF
SUBEQUATORIAL UPPER RIDGE ACROSS THE TROPICAL ATLANTIC...AND
ANOTHER RIDGE ACROSS THE EQUATORIAL PACIFIC. THIS WILL LEAD TO
ACCUMULATIONS IN THE PEAKING AT 30-60MM/DAY THROUGH MID-CYCLE...TO
THEN START DECREASING. EXPECTING ALSO AN INCREASE IN ACTIVITY IN
THE CENTRAL AND NORTHERN COAST OF ECUADOR IN RESPONSE TO IMPROVING
DYNAMICS AND WARMING OF THE COASTAL WATERS OF ECUADOR AND NORTHERN
PERU.

ITA...SENAMHI (PERU)
FERNANDES...INMET (BRASIL)
GALVEZ...WPC (USA)