Prognostic Meteorological Discussion
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FXSA20 KWBC 191642
PMDSA

SOUTH AMERICA FORECAST DISCUSSION - INTERNATIONAL DESKS
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1241 PM EDT FRI SEP 19 2014

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

MODEL DISCUSSION (VALID FROM SEPTEMBER 19 AT 00UTC): CONFIDENCE IN
THE FORECAST IS HIGHER DURING THE SHORT RANGE PERIOD...WHERE THE
DETERMINISTIC AND ENSEMBLE MODEL MEMBERS CONVERGE ON A SIMILAR
EVOLUTION. DURING MEDIUM RANGE PERIOD...HOWEVER...THEY CONTINUE TO
DIVERGE ON HOW TROUGH ENTERING THE SOUTHERN CONE IS TO EVOLVE.
DURING THAT PERIOD CYCLE-TO-CYCLE INCONSISTENCIES ABOUND...WITH
HIGH VARIABILITY AMONG THE GLOBAL ENSEMBLES LEADING TO A LOW
CONFIDENCE FORECAST.

OVER THE CONTINENT...A MID LEVEL TROUGH IS TO PULL ACROSS NORTHERN
ARGENTINA/MID SECTIONS OF SOUTH AMERICA EARLY IN THE CYCLE. A
SECONDARY VORTEX IS TO CLOSELY FOLLOW...TO THEN TRACK ACROSS
SOUTHERN BRASIL/URUGUAY BY 42/48 HRS. THESE ARE TO THEN COMBINE
WITH AN AMPLIFYING TROUGH OVER THE SOUTH ATLANTIC...WITH MODELS
THEN SHOWING A HIGH AMPLITUDE LONG WAVE TROUGH. A SUBTROPICAL JET
MAXIMA IS TO ACCOMPANY THESE PERTURBATIONS...TO FAVOR A DIVERGENT
PATTERN ALOFT ACROSS SOUTHERN BRASIL-MATO GROSSO DO SUL EARLY IN
THE CYCLE. THE FOCUS OF UPPER DIVERGENCE THEN SHIFTS ACROSS
BOLIVIA TO PERU/WESTERN BRASIL THROUGH 48-72 HRS. THE JET STREAM
IS TO THEN REMAIN OVER THE CONTINENT THROUGH 72-84 HRS. AT LOW
LEVELS THE TROUGH ALOFT SUSTAINS A SURFACE LOW THAT IS TO OCCLUDE
AS IT MOVES OFF THE COAST OF URUGUAY/RIO GRANDE DO SUL EARLY IN
THE CYCLE. BY 48-72 HRS...AS REINFORCE BY DEEPENING MID LEVEL
TROUGH...THE SURFACE LOW IS TO DEEPEN FROM 1000 HPA TO 986 HPA.
THE DEEPENING LOW WILL REINFORCE THE BAROCLINIC BOUNDARY AS IT
MEANDERS NORTH INTO SAO PAULO-SANTA CRUZ IN EASTERN BOLIVIA BY 24
HRS...WITH FRONT TO MOVE NORTH ACROSS RIO DE JANEIRO/MATO GROSSO
IN BRASIL TO NORTHERN BOLIVIA BY 36-48 HRS. IT IS TO CONTINUE
NORTH ACROSS ESPIRITO SANTO/MINAS GERAIS BY 96 HRS...WHILE THE
TRAILING END OVER MATO GROSSO/BOLIVIA STARTS TO FRONTOLIZE. AS THE
FRONT MOVES NORTH ACROSS  SAO PAULO-MATO GROSSO IT IS TO SUSTAIN
RAINFALL MAXIMA OF 20-45MM THROUGH 36 HRS... WHILE OVER RIO DE
JANEIRO/ESPIRITO SANTO THE MAXIMA IS TO PEAK AT 15-25MM BY 36-60
HRS. SIMILAR AMOUNTS ARE EXPECTED AS THE FRONT MOVES NORTH ACROSS
ESPIRITO SANTO TO EASTERN BAHIA LATER IN THE CYCLE. ACROSS BOLIVIA
EXPECTING MAXIMA OF 15-30MM BY 24-36 HRS. THROUGH 48-60 HRS THIS
INCREASES TO 20-40MM WHILE BUILDING NORTH AND WEST ACROSS ACRE IN
BRASIL TO SOUTHERN/CENTRAL JUNGLE IN PERU.

THE MODELS THEN FORECAST A DEEP TROUGH ON THE NORTHERN STREAM TO
PULL ACROSS 95W/100W TO 35S BY 24 HRS. THROUGH 48-60 HRS THE
TROUGH IS FORECAST TO DEEPEN AS IT INTERACTS WITH A SHORT WAVE
TROUGH TO THE SOUTH. AS IT ENTERS THE CONTINENT THIS IS TO THEN
FAVOR HEIGHT FALLS OF 200-250GPM WHILE FOCUSING SHORT WAVE ENERGY
ACROSS SOUTHERN CHILE TO PATAGONIA IN ARGENTINA. AS THE TROUGH
DEEPENS TO THE WEST...A RIDGE WILL THEN BUILD ACROSS EASTERN
ARGENTINA/WESTERN ATLANTIC TO THE WEDDELL SEA/ANTARCTIC PENINSULA.
THIS IS TO THEN SLOWDOWN THE MID/UPPER TROUGH. TROUGH IS TO SLOWLY
PUSH EAST ACROSS CHILE TO ARGENTINA THROUGH 84-96 HRS WHILE
BLOCKING RIDGE TO THE EAST RELOCATES TO 35W/40W. AT LOW LEVELS
THIS IS TO SUSTAIN A BROAD TROUGH OFF THE COAST OF CHILE BY 36-48
HRS...TO MOVE EAST ACROSS SOUTHERN CHILE TO PATAGONIA BY 72 HRS.
THE ASSOCIATED FRONT ENTERS SOUTHERN CHILE BY 48 HRS...WHERE IT IS
TO TRIGGER MODERATE TO HEAVY RAINS WITH ACCUMULATION OF 20-30MM.
POST FRONTAL CONVECTION ON DAY 03 IS TO THEN FAVOR ACCUMULATION OF
10-15MM. AS THE FRONT MOVES ACROSS LA PAMPA TO THE BUENOS AIRES
PROVINCE IT IS TO THEN FAVOR RAINFALL AMOUNTS OF 05-10MM IN
ISOLATED TO SCATTERED CONVECTION. MOST INTENSE IS EXPECTED BY
96-120 HRS...WHEN FRONT SURGES ACROSS RIO DE LA PLATA/URUGUAY TO
NORTHERN ARGENTINA/PARAGUAY. IN THIS AREA THE MODELS ARE IN
SURPRISINGLY CLOSE AGREEMENT...PROJECTING RAINFALL MAXIMA OF
20-40MM. UNDER FAVORABLE JET DYNAMICS...LOCALLY HIGHER AMOUNTS ARE
HIGHLY LIKELY.

AT 200 HPA...A WEAK CELL OF THE SUBTROPICAL RIDGE IS TO CONFINE TO
PARA/AMAZONAS IN BRASIL AND PERU THROUGH 60-72 HRS. LATER IN THE
CYCLE THE RIDGE WILL BEGIN TO BUILD...AMPLIFYING ACROSS PERU TO
THE EASTERN TROPICAL PACIFIC AND SOUTH ACROSS BOLIVIA TO MID
SECTIONS OF SOUTH AMERICA. A SHORT WAVE TROUGH TO THE EAST IS TO
REMAIN ACROSS THE NORTHEAST STATES OF BRASIL. AS THE UPPER LEVEL
PATTERN EVOLVES...DIURNAL CONVECTION ACROSS NORTHWEST SOUTH
AMERICA IS TO BECOME MORE ACTIVE/BETTER ORGANIZED. THROUGH 72-84
HRS THIS IS TO INCREASE TO 20-35MM IN SCATTERED DEEP CONVECTION.
LATER IN THE CYCLE IS TO ONCE AGAIN WANE...DECREASING TO
10-15MM/DAY.

JALFIN...SMN (ARGENTINA)
CAROCA...DMC (CHILE)
DAVISON...WPC (USA)
$$





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