Prognostic Meteorological Discussion
Issued by NWS

Home | Current Version | Previous Version | Text Only | Print | Product List | Glossary On
Versions: 1 2 3 4
000
FXSA20 KWBC 201601
PMDSA

SOUTH AMERICA FORECAST DISCUSSION - INTERNATIONAL DESKS
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1201 PM EDT MON OCT 20 2014

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

MODEL DISCUSSION (VALID FROM OCTOBER 20 AT 00UTC): CONFIDENCE IN
THE FORECAST IS HIGH AS THE MODELS FOLLOW A SIMILAR PATTERN
EVOLUTION THROUGH DAY 06. THIS IS WELL SUPPORTED BY THE
DETERMINISTIC AND THE GLOBAL ENSEMBLE MEMBERS.

SOUTH OVER THE DOMAIN...A MID LEVEL SHORT WAVE TROUGH IS TO MOVE
ACROSS THE BELLINGSHAUSEN SEA/ANTARCTIC PENINSULA TO SOUTHERN
CHILE TROUGH 36-42 HRS. A RIDGE TO THE EAST IS TO EXTEND NORTH TO
SOUTH ALONG 50W. AS THE TROUGH PRESSES AGAINST THE RIDGE...SHORT
WAVE ENERGY IS TO GRADUALLY SHEAR TO THE SOUTH. THIS WILL LEAD TO
A SLOW EASTWARD PROGRESSION...WITH THE TROUGH TO MOVE ALONG 50W TO
40S BY 72 HRS...NEARING 30W BY 96 HRS. A SECONDARY VORTEX IS TO
CLOSELY FOLLOW...STREAMING ACROSS THE DRAKE PASSAGE/ANTARCTIC
PENINSULA BY 84 HRS. THIS IS TO FOCUS SUCCESSIVE POLAR FRONTS
ACROSS EXTREME SOUTHERN PORTIONS OF CHILE/TIERRA DEL FUEGO. THESE
ARE TO TRIGGER SCATTERED CONVECTION WITH MOST INTENSE EXPECTED
EARLY IN THE CYCLE...WITH MAXIMA OF 10-15MM. OTHERWISE...EXPECTING
RAINFALL AMOUNTS OF 05-10MM IN SCATTERED CONVECTION.

A SHORT WAVE TROUGH ON THE NORTHERN STREAM IS TO MOVE ACROSS 100W
EARLY IN THE CYCLE. THROUGH 48 HRS THIS IS TO EVOLVE INTO A
CLOSED/ CUT OFF LOW THAT IS TO CENTER NEAR 39S 91W. A RIDGE TO THE
EAST IS TO THEN EXTEND ACROSS CHILE AND ARGENTINA...BLOCKING THE
TROUGH FROM PUSHING FARTHER EAST. AT LOW LEVELS THIS IS TO SUSTAIN
A FRONTAL WAVE TO THE WEST OF JUAN FERNANDEZ ISLAND...WHERE IT IS
TO GENERALLY REMAIN THROUGH THE EXTENDED RANGE FORECAST PERIOD.

AT 200 HPA...SHORT WAVE RIDGE EXTENDS FROM WESTERN BRASIL...ACROSS
MATO GROSSO TO SOUTHEAST BRASIL. A TROUGH TO THE
EAST...MEANWHILE... IS TO EXTEND TO THE NORTHWEST ACROSS
BAHIA/NORTHEAST STATES OF BRASIL. BEST INSTABILITY ALOFT IS
EXPECTED BETWEEN THE TROUGH AND THE RIDGE...TO ENHANCE CONVECTIVE
DEVELOPMENT FROM TOCANTINS/GOIAS TO PARA/NORTHERN AMAZONAS TO THE
WEST. IN THIS AREA...CONVECTION IS TO GRADUALLY INTENSIFY/BECOME
BETTER ORGANIZED AS THE CYCLE PROGRESSES. THROUGH 72-96 HRS MODELS
SHOW MAXIMA OF 20-40MM IN DEEP CONVECTION. OTHER CONVECTION TO THE
WEST IS TO BUILD ACROSS ACRE IN BRASIL TO CENTRAL/NORTHERN
PERU...WITH MAXIMA IN THIS AREA TO PEAK AT 05-10MM. OVER
ECUADOR...MOST INTENSE IS TO CLUSTER ALONG THE ANDES/WEST
COAST...WHERE ONSHORE FLOW IS TO GENERALLY FAVOR RAINFALL AMOUNTS
OF 15-20MM/DAY.

ALSO AT UPPER LEVELS...A SHORT WAVE TROUGH IS TO ENTER NORTHERN
CHILE BY 36-48 HRS...TO THEN STREAM ACROSS THE NORTHERN PROVINCES
IN ARGENTINA/PARAGUAY. A HIGHER AMPLITUDE TROUGH IS TO FOLLOW...TO
REACH NORTHERN CHILE/SOUTHERN PERU BY 72 HRS. THIS IS TO CONTINUE
EAST ACROSS THE ANDES INTO NORTHWEST ARGENTINA/CENTRAL BOLIVIA BY
96-108 HRS. AS THEY SPILL ACROSS THE ANDES...THESE ARE TO INTERACT
WITH THERMAL LOW OVER NORTHWEST ARGENTINA...SUSTAINING AN INCREASE
IN DIURNAL CONVECTION. THROUGH 48-72 HRS THIS INCREASES TO
20-30MM/DAY. THESE ARE TO ALSO ENHANCE CONVECTION ACROSS SOUTHERN
SIERRA OF PERU/ALTIPLANO OF BOLIVIA...WITH MAXIMA OF 05-10MM IN
ISOLATED TO SCATTERED CONVECTION. HIGHER AMOUNTS...HOWEVER...ARE
FORECAST ACROSS THE SOUTHERN JUNGLE OF PERU/NORTHERN
BOLIVIA...WHERE THE TROUGH ALOFT IS TO FAVOR RAINFALL AMOUNTS OF
20-30MM.

CAROCA...DMC (CHILE)
DURAN...SENAHMI (PERU)
DAVISON...WPC (USA)
$$





USA.gov is the U.S. government's official web portal to all federal, state and local government web resources and services.