Prognostic Meteorological Discussion
Issued by NWS

Home | Current Version | Previous Version | Text Only | Print | Product List | Glossary On
Versions: 1 2 3 4 5 6 7 8
000
FXSA20 KWBC 231901
PMDSA

SOUTH AMERICA SYNOPTIC DISCUSSION - INTERNATIONAL DESKS
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
301 PM EDT TUE SEP 23 2014

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

MODEL DISCUSSION (VALID FROM SEPTEMBER 23 AT 00UTC): GLOBAL MODEL
AGREE ON PATTERN EVOLUTION THROUGH 72-84 HRS. THE GFS THEN STARTS
TO DIVERGE FROM THE EUROPEAN MODELS ON HOW THE SOUTHERN STREAM IS
TO EVOLVE...WITH GFS FAVORING A MORE AMPLIFIED PATTERN THAN WHAT
THE EUROPEAN MODELS SUGGEST. IN THIS AREA THERE IS HIGH
VARIABILITY AMONG THE GLOBAL ENSEMBLE MEMBERS. AS A
RESULT...EXPECTING FURTHER CORRECTIONS IN THE NEXT FEW RUNS.
ALTHOUGH THEY DIVERGE ON HOW THE SOUTHERN STREAM IS GOING TO
EVOLVE...ON THE NORTHERN STREAM MODELS ARE IN CLOSER
AGREEMENT...FORECASTING SUCCESSIVE PERTURBATIONS TO MIGRATE ACROSS
CHILE TO ARGENTINA/MID SECTIONS OF SOUTH AMERICA. THESE ARE TO
PROVIDE DYNAMICAL SUPPORT TO MESO SCALE CONVECTIVE SYSTEMS OVER
THE NEXT FEW DAYS.

DEEP MID LEVEL PERTURBATION IN THE SOUTHERN STREAM REACHED
SOUTHERN CHILE EARLY THIS MORNING...AND THROUGH 24 HRS IT IS TO
QUICKLY PULL ACROSS PATAGONIA TO THE WESTERN ATLANTIC. A STRONGER
PERTURBATION FOLLOWS...TO ENTER SOUTHERN CHILE/DRAKE PASSAGE BY
24-30 HRS. THROUGH 48 HRS THESE ARE TO THEN COMBINE INTO A BROAD
TROUGH THAT IS TO ENVELOP THE SOUTHERN CONE OF SOUTH
AMERICA/WESTERN ATLANTIC. THROUGH 84-96 HRS BROAD TROUGH IS TO
THEN ESTABLISH ACROSS THE SOUTH ATLANTIC...WITH AXIS TO ENVELOP
AREA BETWEEN 65W-00W AND TO THE SOUTH OF 30S. AT LOW LEVELS THESE
ARE TO SUSTAIN AN OCCLUDED LOW OVER EASTERN PATAGONIA EARLY IN THE
CYCLE...WITH SYSTEM TO RAPIDLY DEEPEN AS IT MOVES ACROSS THE
MALVINAS/FALKLAND ISLANDS BY 48 HRS. POLAR FRONTS ARE TO REVOLVE
AROUND THE DEEPENING LOW...WITH ONE TO MIGRATE ACROSS LA
PAMPA-CENTRAL CHILE EARLY IN THE CYCLE...WITH ANOTHER TO QUICKLY
PULL ACROSS SOUTHERN CHILE-PATAGONIA THROUGH 24-30 HRS. THE LATTER
IS TO ALSO MEANDER NORTH ACROSS LA PAMPA/CENTRAL CHILE BY 48 HRS.
OVER CHILE SOUTH OF TEMUCO THESE ARE TO SUSTAIN MODERATE
CONVECTION WITH ACCUMULATION OF 10-15MM. HIGHER AMOUNTS ARE
EXPECTED OVER CENTRAL CHILE...WHERE PROGRESSIVE BAROCLINIC
BOUNDARIES ARE TO TRIGGER MODERATE TO HEAVY CONVECTION WITH
ACCUMULATION OF 15-20MM BY 36 HRS AND 20-35MM AT 36-60 HRS. THE
BROAD TROUGH IS TO SUSTAIN A TIGHT PRESSURE GRADIENT ACROSS THE
SOUTHERN CONE DURING THE NEXT COUPLE OF DAYS...WITH BOUNDARY LAYER
WINDS OF 35-45KT EXPECTED THROUGHOUT THE SHORT RANGE PERIOD.

A TROUGH ON THE NORTHERN STREAM MOVES ACROSS CENTRAL ARGENTINA
EARLY IN THE CYCLE...AND ACROSS RIO DE LA PLATA BASIN/URUGUAY BY
24 HRS. A SUBTROPICAL JET MAXIMA IS TO ACCOMPANY THIS TROUGH AS IT
PULLS ACROSS THE CONTINENT...FAVORING AN UPPER DIVERGENT PATTERN.
AT LOW LEVELS THIS SUSTAINS A POLAR FRONT ACROSS RIO DE LA PLATA
BASIN-MENDOZA IN ARGENTINA. BUILDING POLAR RIDGE TO THE
SOUTH...AND ENSUING PAMPERO JET...WILL THEN FORCE THE FRONT NORTH
ACROSS URUGUAY TO THE NORTHERN PROVINCES IN ARGENTINA BY 24-30
HRS. AS THE FRONT ACCELERATES ACROSS ARGENTINA...IT IS TO TRIGGER
A PREFRONTAL SQUALL LINE. HEAVY CONVECTION IS TO AFFECT THE
PROVINCES OF CHACO-CORRIENTES-MISIONES IN ARGENTINA...RIO GRANDE
DO SUL IN BRASIL AND CENTRAL/SOUTHEAST PORTIONS OF PARAGUAY. IN
POTENTIALLY SEVERE CONVECTION... AND UNDER FAVORABLE JET
DYNAMICS...EXPECTING MAXIMA OF 35-70MM BY 24-48 HRS. THROUGH 60
HRS THIS DECREASES TO 25-50MM.

SUCCESSIVE SHORT WAVE PERTURBATIONS ON THE NORTHERN STREAM ARE TO
THEN INTERACT WITH THIS FRONT AS IT MEANDERS OVER SOUTHERN
BRASIL-PARAGUAY. IN A MOIST NORTHERLY FLOW...EXPECTING
PRECIPITABLE WATER CONTENT OF 50-60MM ALONG THIS BOUNDARY. THIS
WILL PROVIDE THE ENERGY AND MOISTURE TO SUSTAIN ORGANIZED DEEP
CONVECTION. CONDITIONS APPEAR FAVORABLE AND CONDUCIVE TO FORMATION
OF MESO SCALE SYSTEMS ALONG THE MEANDERING FRONT. AS A RESULT WE
NOW EXPECT RAINFALL MAXIMA OF 30-60MM BY 60-84 HRS...AND 40-80MM
BY 84-108 HRS. DURING THAT PERIOD THERE IS A SLIGHT RISK OF SEVERE
CONVECTION.

AT 200 HPA...THE SUBTROPICAL RIDGE IS FORECAST TO GRADUALLY
STRENGTHEN AS THE CYCLE PROGRESSES. EARLY IN THE CYCLE THE RIDGE
IS TO CONFINE TO CONTINENTAL AREA NORTH OF 25S AND WEST OF 50W.
THROUGH 60 HRS THE RIDGE IS TO BUILD EAST ACROSS BRASIL...AND BY
72 HRS IT IS FORECAST TO ENVELOP CONTINENTAL AREA TO THE NORTH OF
30S. AS THE RIDGE BUILDS...A MID/UPPER CONVERGENT PATTERN IS TO
ESTABLISH ACROSS CENTRAL-EASTERN PORTIONS OF BRASIL.
THIS...IN-TURN...WILL SUSTAIN EROSION OF AVAILABLE MOISTURE. MOST
ACTIVE CONVECTION IS EXPECTED ACROSS WESTERN BRASIL-NORTHERN
PERU/ECUADOR...WHERE MAXIMA IS TO PEAK AT 15-20 EARLY IN THE
CYCLE. THROUGH 48-72 HRS THIS IS FORECAST TO DECREASE TO 10-15MM.
OTHER ACTIVITY IS TO DOT THE SOUTHERN SIERRA OF PERU AND THE
ALTIPLANO OF BOLIVIA...WITH MAXIMA OF 05-10MM OVER THE NEXT COUPLE
OF DAY...INCREASING TO 15-20MM LATER ON DAY 03.

JALFIN...SMN (ARGENTINA)
CAROCA...DMC (CHILE)
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.