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 261523
PMDSA

SOUTH AMERICA FORECAST DISCUSSION - INTERNATIONAL DESKS
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1123 AM EDT TUE AUG 26 2014

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

MODEL DISCUSSION (VALID FROM AUGUST 26 AT 00UTC): GLOBAL MODELS
AGREE ON GENERAL PATTERN EVOLUTION THROUGH 60-72 HRS...THEN START
TO DIVERGE ON THE TIMING AND AMPLITUDE OF SHORT WAVE PERTURBATIONS
ENTERING THE DOMAIN. THIS IS ALSO RESULTING IN CYCLE-TO-CYCLE
INCONSISTENCIES AS MODELS MAKE PATTERN CORRECTIONS. AS A
RESULT...CONFIDENCE IN THE FORECAST BEYOND 72/84 HRS IS LOW.

DEEP MID LEVEL TROUGH ON THE NORTHERN STREAM CONTINUES TO DOMINATE
THE WEATHER ACROSS MID SECTIONS OF SOUTH AMERICA. IN A WEAK
STEERING FLOW...THE TROUGH IS TO MEANDER EAST ACROSS 45W/50W TO
SOUTHERN BRASIL EARLY IN THE CYCLE...WITH AXIS TO ANCHOR ON A
CLOSED LOW NEAR 41S 45W. THROUGH 48 HRS THE TROUGH IS TO SLOWLY
PULL ACROSS 40W...WHILE THE CLOSED LOW GRADUALLY WEAKEN/FILLS. BY
72-96 HRS THE TROUGH IS TO THEN STRETCH TO THE NORTHWEST ALONG 35S
25W TO RIO DE JANEIRO/SOUTHEAST BRASIL. AT LOW LEVELS IT SUSTAINS
A DEEP OCCLUDED LOW EAST OF THE BUENOS AIRES PROVINCE. THROUGH 24
HRS THIS IS TO DEEPEN TO A 990 HPA LOW WHILE DRIFTING TO THE
EAST-SOUTHEAST...AND BY 36-60 HRS IT IS TO DEEPEN TO A 986 HPA
LOW. AS THE SURFACE LOW/TROUGH MEANDERS TO THE
EAST-SOUTHEAST...AND A POLAR RIDGE BUILDS ACROSS ARGENTINA TO
PARAGUAY...THE ASSOCIATED FRONT IS TO MEANDER NORTH ACROSS RIO DE
JANEIRO-SOUTHERN MINAS GERAIS-MATO GROSSO IN BRASIL TO NORTHERN
BOLIVIA EARLY IN THE CYCLE. BUT AS THE POLAR TROUGH MOVES FARTHER
EAST...AND POLAR RIDGE EVOLVES...TRAILING END OF THE FRONT IS TO
START RETROGRESSING ACROSS MATO GROSSO TO MATO GROSSO DO
SUL-PARAGUAY-SOUTHERN BOLIVIA BY 72-84 HRS...WHERE IT IS TO
MEANDER THROUGH 96-108 HRS. AS THE FRONT UNDULATES NORTH ACROSS
BOLIVIA TO SOUTHERN PERU EARLY IN THE CYCLE IT IS TO TRIGGER
MODERATE CONVECTION WITH ACCUMULATION OF 15-25MM. THROUGH 48 HRS
THIS DECREASES TO 10-15MM. OTHER ACTIVITY IS EXPECTED ACROSS RIO
DE JANEIRO/ESPIRITO SANTO IN BRASIL BY 48-84 HRS...WITH RAINFALL
AMOUNTS OF 05-10MM/DAY. BY 96-120 HRS FOCUS OF THE COASTAL
CONVECTION SHIFTS TO EASTERN BAHIA...WITH ACCUMULATION OF 05-10MM.
AS THE TRAILING END OF THE FRONT MEANDERS SOUTH ACROSS PARAGUAY
LATER IN THE CYCLE...IT IS TO THEN TRIGGER SCATTERED CONVECTION
WITH ACCUMULATION OF 15-25MM. MOST ACTIVE ON THE SOUTHERN STATES
OF BRASIL-MISIONES IN ARGENTINA AND SOUTHEAST PARAGUAY.

BLOCKING MID/UPPER LEVEL RIDGE PATTERN PERSISTS ACROSS THE FAR
EASTERN PACIFIC/SOUTHERN CONE OF SOUTH AMERICA. THROUGH 36-48 HRS
THE RIDGE RELOCATES ACROSS CHILE TO ARGENTINA...WHERE IT IS TO
REMAIN THROUGH 96-120 HRS. SHORT WAVE PERTURBATIONS ON THE
NORTHERN AND SOUTHERN STREAM FLOW ARE TO PRESS AGAINST THE LONG
WAVE RIDGE. THROUGH 48-72 HRS SHORT WAVE PERTURBATIONS ARE TO
COMBINE INTO A BROAD TROUGH OVER THE EASTERN PACIFIC BETWEEN
100W-75W AND TO THE SOUTH OF 15S. AS THE RIDGE RELOCATES AND
WEAKENS...THIS WILL ALLOW SHORT WAVE ENERGY TO FOCUS ACROSS
SOUTHERN CHILE TO PATAGONIA IN ARGENTINA BY 72-96 HRS...INTO
CENTRAL REGIONS OF CHILE BY 108-120 HRS. AT LOW LEVELS...THE RIDGE
ALOFT IS TO SUSTAIN A SURFACE RIDGE ACROSS CHILE-ARGENTINA OVER
THE NEXT FEW DAYS...WHILE THE TROUGH ALOFT SUSTAINS A BROAD AREA
OF LOW PRESSURE OVER THE EASTERN PACIFIC. POLAR FRONTS ARE TO
REVOLVE AROUND THE MEANDERING PRESSURE TROUGH. BUT AS THEY CLASH
WITH THE RIDGE TO THE EAST...THEY ARE TO SHEAR SOUTH ACROSS TIERRA
DEL FUEGO/DRAKE PASSAGE...WHERE IT IS TO FAVOR LIGHT CONVECTION.
LATER IN THE CYCLE...AS THE SURFACE RIDGE STARTS TO
WEAKEN...FRONTS WILL PUSH EAST INTO SOUTHERN-CENTRAL PORTIONS OF
CHILE WHERE THEY ARE TO ENHANCE MOISTURE CONVERGENCE WHILE
TRIGGERING MODERATE RAINFALL AMOUNTS. BY 72-84 HRS IT IS TO FAVOR
RAINFALL AMOUNTS OF 05-10MM...AND BY 96-120 HRS THIS INCREASES TO
15-25MM WHILE CONVECTION BUILDS NORTH ACROSS CENTRAL CHILE.

AT 200 HPA...A HIGH OVER CENTRAL PERU ANCHORS A RIDGE OVER
NORTHWEST SOUTH AMERICA/EASTERN TROPICAL PACIFIC. THROUGH 24 HRS
THE HIGH IS TO RELOCATE TO ACRE IN BRASIL/NORTHERN BOLIVIA...WHILE
SIMULTANEOUSLY THE SUBEQUATORIAL RIDGE BUILDS ACROSS NORTHERN
BRASIL TO THE GUIANAS. THROUGH 60-72 HRS THE ONE TO THE SOUTH
WEAKENS/ NEARLY COLLAPSES...WHILE THE ONE TO THE NORTH ESTABLISHES
ACROSS NORTHERN SOUTH AMERICA. THE RIDGE ALOFT IS TO VENT
CONVECTION ACROSS EQUATORIAL SOUTH AMERICA...WITH ACCUMULATION OF
10-15MM. HIGHER AMOUNTS...HOWEVER...ARE EXPECTED ON THE LEE OF THE
ANDES OVER PERU-ECUADOR...WHERE MAXIMA IS TO PEAK AT 15-25MM.

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




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