Prognostic Meteorological Discussion
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000
FXSA20 KWBC 041412
PMDSA

SOUTH AMERICA FORECAST DISCUSSION - INTERNATIONAL DESKS
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1012 AM EDT FRI SEP 04 2015

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

LAST NO AMENDS...NEXT ON TUESDAY SEPTEMBER 8.

MODEL DISCUSSION (VALID FROM SEP 04 AT 0000 UTC): ONCE AGAIN THE
MODELS ONLY MADE MINOR CORRECTIONS TO PREVIOUS FORECAST. THE
CURRENT SOLUTION IS WELL SUPPORTED BY THE MEAN OF THE GLOBAL
ENSEMBLES... WITH LITTLE VARIABILITY NOTED AMONG THE MEMBERS
THROUGH 108-120 HRS. CONFIDENCE IN THE FORECAST REMAINS HIGH.

A STRONG MID LEVEL PERTURBATION ON THE SOUTHERN STREAM FLOW IS TO
ENTER THE SOUTHERN CONE EARLY IN THE CYCLE. THIS IS TO FOCUS SHORT
WAVE ENERGY ACROSS SOUTHERN PORTIONS OF CHILE TO PATAGONIA IN
ARGENTINA. AT LOW LEVELS THIS IS TO SUSTAIN AN ELONGATED FRONT
ACROSS SOUTHERN PATAGONIA-EXTREME SOUTHERN PORTIONS OF CHILE EARLY
IN THE PERIOD...WITH BOUNDARY TO SLOWLY UNDULATE NORTH ACROSS
PATAGONIA-SOUTHERN CHILE TO TEMUCO THROUGH 48 HRS. AS IT ENTERS
THE CONTINENT THIS WILL SUSTAIN A TIGHT PRESSURE GRADIENT...AND
LOW LEVEL WINDS THAT ARE TO PEAK AT 35-50KT OVER THE NEXT TWO
DAYS. THIS IS TO ENHANCE TOPOGRAPHICALLY INDUCED CONVECTION TO THE
SOUTH TO FAVOR RAINFALL MAXIMA OF 15-20MM THROUGH 36 HRS. BY 36-60
HRS THIS DECREASES TO 10-15MM...BUT AS A COOLER AIR MASS ADVECTS
ACROSS SOUTHERN CHILE EXPECTING MIXED PRECIPITATION TO DEVELOP
(RAIN AND SNOW SHOWERS).

THIS IS TO THEN SET THE STAGE FOR A DEEPER MID LEVEL PERTURBATION
TO SURGE ACROSS THE SOUTHEAST PACIFIC TO THE SOUTHERN PORTIONS OF
CHILE BY 72-84 HRS. THIS IS TO THEN MOVE EAST ACROSS PATAGONIA IN
ARGENTINA TO THE WESTERN ATLANTIC BY 108-120 HRS. A BUILDING RIDGE
TO THE WEST IS TO THEN SUSTAIN A COLD ADVECTIVE PATTERN THAT IS TO
RESULT IN FURTHER INTENSIFICATION OF THE MID/UPPER LEVEL TROUGH AS
IT MOVES ACROSS ARGENTINA. AT LOW LEVELS THIS IS TO SUSTAIN A DEEP
OCCLUDED TROUGH OVER THE SOUTHEAST PACIFIC BY 60-72 HRS...THAT IS
TO GRADUALLY PUSH EAST AND NORTH ACROSS THE DRAKE PASSAGE TO THE
SOUTHERN CONE. THIS WILL BE ACCOMPANIED BY A SHARP DROP IN
TEMPERATURE...WITH ENVIRONMENTAL CONDITIONS TO RAPIDLY BECOME
FAVORABLE AND HIGHLY CONDUCIVE TO ORGANIZED SNOWFALL AMOUNTS. AT
60-84 HRS EXPECTING SNOWFALL AMOUNTS OF 15-20CM...WITH AN
ADDITIONAL 10-15CM BY 84-108 HRS...WITH STORM TOTAL SNOWFALL
AMOUNTS TO PEAK AT 20-35CM.

AS THE POLAR TROUGH SURGES TO THE SOUTH...A SHORT WAVE TROUGH ON
THE NORTHERN STREAM IS FORECAST TO SLOWLY MIGRATE EAST TOWARDS THE
CONTINENT. THROUGH 24 HRS THE 500 HPA TROUGH IS TO MOVE ACROSS
87W/88W...AND BY 60-72 HRS IT REACHES CENTRAL CHILE. BY 84-96 HRS
THE TROUGH WILL SPILL ACROSS THE ANDES INTO CENTRAL/NORTHERN
PROVINCES IN ARGENTINA...MEANWHILE FAVORING HEIGHT FALLS OF
75-125GPM. AS IT ENTERS THE CONTINENT A SUBTROPICAL JET IS TO
BOUND THE NORTHERN FRINGES OF THIS TROUGH. THE JET MOVES INLAND
INTO NORTHERN ARGENTINA THROUGH 84-96 HRS. AS IT ENTERS CENTRAL
CHILE THIS WILL FAVOR AN UPPER DIVERGENT PATTERN...LEADING TO AN
INCREASE IN COASTAL CONVECTION BY 60-84 HRS...WITH ACCUMULATION OF
20-35MM WHILE OVER THE ANDES EXPECTING RAINFALL AMOUNTS OF
15-20MM. LIGHT SNOWFALL AMOUNTS ARE EXPECTED ON THE ANDES TO THE
NORTH OF 32S/33S...WITH ACCUMULATION OF 03-05CM.

AS IT ENTERS THE CONTINENT THE MID LEVEL TROUGH IS TO THEN
INTERACT WITH MEANDERING FRONT OVER CENTRAL SOUTH AMERICA. THROUGH
72 HRS THIS BOUNDARY IS TO MEANDER ACROSS SOUTHEAST
BRASIL-PARAGUAY...MEANWHILE FAVORING SCATTERED COASTAL CONVECTION.
ACROSS SAO PAULO-RIO DE JANEIRO THIS WILL RESULT IN RAINFALL
AMOUNTS OF 10-15MM...WHILE ON THE SOUTHERN STATES OF BRASIL MAXIMA
IS TO PEAK AT 20-35MM BY 48-84 HRS. LATER IN THE CYCLE...AS
MID/UPPER TROUGH PUSHES EAST ACROSS THE ANDES...THIS IS TO FAVOR
GENERATION OF A FRONTAL WAVE/LOW OVER PARAGUAY/MESOPOTAMIA IN
ARGENTINA. THIS DEEPENS/STRENGTHENS AS IT MOVES ACROSS SOUTHERN
BRASIL TO THE WESTERN ATLANTIC BY 96-108 HRS. UNDER FAVORABLE JET
DYNAMICS...WITH JETS TO COUPLE ON THEIR DIVERGENT SIDE...EXPECTING
PROBABILITY OF SEVERE CONVECTION ACROSS SOUTHEAST
PARAGUAY-NORTHERN MESOPOTAMIA VALLEY TO THE SOUTHERN STATES OF
BRASIL BY 84-120 HRS. OVER PARANA-SANTA CATARINA TO SOUTHEAST
PARAGUAY MAXIMA IS NOW FORECAST TO PEAK AT 30-60MM BY 96-120 HRS.

NORTH OVER THE CONTINENT...AT 200 HPA...THE SUBEQUATORIAL RIDGE IS
TO GRADUALLY STRENGTHEN ITS FOOTHOLD ACROSS EQUATORIAL SOUTH
AMERICA. THROUGH 48-72 HRS THE RIDGE BUILDS WESTWARD ACROSS BRASIL
TO ECUADOR/NORTHERN PERU...WHILE ANCHORING ON A CLOSED HIGH OVER
NORTHERN PARA/SOUTHERN GUIANAS. IN THIS PATTERN DIURNAL CONVECTION
IS TO CONFINE TO NORTHWEST SOUTH AMERICA...WITH ACTIVITY OVER
NORTHERN JUNGLE OF PERU-SOUTHERN COLOMBIA AND AMAZONAS IN BRASIL
TO FAVOR RAINFALL AMOUNTS OF 10-15MM/DAY IN ISOLATED TO SCATTERED
CONVECTION. ON THE SOUTHERN SIERRA OF PERU EXPECTING RAINFALL
AMOUNTS OF 05-10MM/DAY...WHILE ON THE SOUTHERN JUNGLE TO CENTRAL
BOLIVIA THE MAXIMA IS TO PEAK AT 15-30MM/DAY. MOST ACTIVE
CONVECTION IS EXPECTED THROUGH 72-84 HRS.

ROMERO...DMC (CHILE)
FARINA...DMH (PARAGUAY)
DAVISON...WPC (USA)
GALVEZ...WPC (USA)

$$





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