Prognostic Meteorological Discussion
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091
FXSA20 KWBC 271502
PMDSA

SOUTH AMERICA FORECAST DISCUSSION - INTERNATIONAL DESKS
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1102 AM EDT FRI MAY 27 2016

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

MODEL DISCUSSION (VALID FROM MAY 27 AT 0000 UTC): CONFIDENCE IN
THE FORECAST REMAINS HIGH THROUGH DAY 04...WITH GLOBAL MODEL
GUIDANCE FOLLOWING A SIMILAR EVOLUTION. LATER IN THE CYCLE
UNCERTAINTY INCREASES AS A SERIES OF SHORT WAVE PERTURBATIONS
START TO POPULATE THE SOUTHERN STREAM FLOW...LEADING TO DIVERGENCE
AMONG THE MODELS ON HOW FAST/STRONG THE WAVES ARE GOING TO BE.

SOUTH OVER THE CONTINENT...A MID LEVEL RIDGE EXTENDS OVER
ARGENTINA/SOUTHWEST ATLANTIC TO THE WEDDELL SEA...WITH AXIS
ANCHORING ON A 500 HPA HIGH EAST OF THE FALKLAND ISLANDS/MALVINAS.
UNDER PRESSURE FROM A BROAD TROUGH TO THE WEST...THE RIDGE IS TO
RELOCATE ALONG 50W TO THE WEDDELL SEA BY 24-30 HRS...WHERE IT IS
TO THEN REMAIN THROUGH 108 HRS. LATER IN THE CYCLE IT TENDS TO
FLATTEN AS SUCCESSIVE SHORT WAVE TROUGHS PROPAGATE UNDER THIS AXIS.

DOWNSTREAM FROM THIS RIDGE...A BROAD MID LEVEL TROUGH EXTENDS
ACROSS THE SOUTH ATLANTIC TO 30S. OVER THE NEXT FOUR DAYS THE
TROUGH WILL BOUND BETWEEN 30W-10E. AT LOW LEVELS IT IS TO SUSTAIN
A SURFACE FRONT THAT EXTENDS ACROSS THE RIO DE LA PLATA BASIN TO
CENTRAL ARGENTINA. A BROAD RIDGE TO THE SOUTH...MEANWHILE...IS TO
ANCHOR ON A 1035 HPA HIGH OFF THE COAST OF PATAGONIA. UNDER
INFLUENCE OF THE RIDGE TO THE SOUTH A MOIST EASTERLY FLOW
ESTABLISHED ACROSS CENTRAL ARGENTINA...FAVORING STRATIFIED CLOUD
COVER AND LIGHT RAIN.

NORTH OF THE MID LEVEL RIDGE...IN A SPLIT FLOW PATTERN...A SHORT
WAVE TROUGH IS PULLING ACROSS NORTHERN ARGENTINA/PARAGUAY TO
SOUTHERN BRASIL. THIS IS A SLOW TO EVOLVE SYSTEM...FORECAST TO
GRADUALLY DEEPEN/STRENGTHEN AS IT MEANDERS ACROSS SOUTHERN BRASIL
BY 48-60 HRS. AT LOW LEVELS THE MID LEVEL TROUGH SUSTAINS AN
OCCLUDING LOW OVER SOUTHERN BRASIL. THIS IS TO DEEPEN THROUGH
60-66 HRS...ENHANCING ONSHORE FLOW AS IT INTENSIFIES OFF THE SOUTH
COAST OF BRASIL. ACROSS EASTERN PARAGUAY-SOUTHERN BRASIL THIS WILL
SUSTAIN HEAVY RAINS WITH ACCUMULATION OF 30-60MM BY 24-48
HRS...THEN DECREASING TO 15-20MM BY 48-72 HRS. AS THE LOW DEEPENS
OFF THE COAST...IT IS TO THEN FAVOR MODERATE TO HEAVY CONVECTION
ACROSS URUGUAY/RIO DE LA PLATA BASIN WITH MAXIMA OF 25-50MM BY
60-84 HRS.

DURING THE MEDIUM RANGE PERIOD...A BROAD MID LEVEL TROUGH PULLS
ACROSS THE EASTERN PACIFIC INTO SOUTHERN-CENTRAL PORTIONS OF CHILE
BY 60-72 HRS. AS IT PRESSES AGAINST THE MID LEVEL RIDGE TO THE
EAST...THE TROUGH IS TO GRADUALLY SHEAR SHORT WAVE ENERGY ACROSS
THE SOUTHERN-CENTRAL ANDES INTO ARGENTINA. AT LOW LEVELS THIS WILL
SUSTAIN A SURFACE FRONT THAT PULLS ACROSS SOUTHERN CHILE INTO
PATAGONIA IN ARGENTINA BY 48-72 HRS. THIS BOUNDARY IS TO TRIGGER
LIGHT TO MODERATE CONVECTION BETWEEN CONCEPCION-PUERTO
MONTT...WITH MAXIMA OF 10-15MM. SOUTH OF PUERTO MONT THE MAXIMA
PEAKS AT 05-10MM. ON THE CENTRAL ANDES OF CHILE IT IS TO THEN
FAVOR ORGANIZED SNOWFALL AMOUNTS WITH MAXIMA TO PEAK AT 20-40CM BY
72-96 HRS.

AT 200 HPA...A BUILDING RIDGE OVER THE EASTERN PACIFIC IS TO
INDUCE THE NORTHWARD AMPLIFICATION OF A TROUGH ACROSS PERU TO
AMAZONAS IN BRASIL. THE TROUGH IS TO THEN PULL TO THE
EAST-SOUTHEAST THROUGH 60-72 HRS. MEANWHILE...THIS WILL ENHANCE
DIURNAL CONVECTION ACROSS AMAZONAS AND PARA IN BRASIL...WITH
RAINFALL AMOUNTS OF 15-25MM/DAY EXPECTED OVER THE NEXT COUPLE OF
DAYS. AS THE TROUGH DAMPENS THIS WILL DECREASE TO 05-10MM/DAY.

ENRIQUEZ...DGAC (ECUADOR)
AYALA...DINAC (PARAGUAY)
DAVISON...WPC (USA)

$$





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