Prognostic Meteorological Discussion
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SOUTH AMERICA FORECAST DISCUSSION - INTERNATIONAL DESKS
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1049 AM EDT THU MAY 26 2016

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

MODEL DISCUSSION (VALID FROM MAY 26 AT 0000 UTC): OUR CONFIDENCE
IN THE FORECAST IS HIGH THROUGH 108 HRS...WITH MODELS MAKING SHORT
WAVE CORRECTIONS DURING THE MEDIUM RANGE PERIOD RESULTING IN AN
INCREASE IN THE UNCERTAINTY. THIS BECOMES MORE PRONOUNCED BY
144-168 HRS AS SHORT WAVE PERTURBATIONS IN THE SOUTHERN STREAM
PROPAGATE ACROSS THE DOMAIN.

A MID LEVEL RIDGE IN THE SOUTHERN STREAM REMAINS WELL ENTRENCHED
OVER PATAGONIA IN ARGENTINA/DRAKE PASSAGE-ANTARCTIC
PENINSULA...WITH AXIS ANCHORING ON A 500 HPA HIGH WEST 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 48-54 HRS...WHERE IT IS TO THEN REMAIN THROUGH 108-120 HRS.
LATER IN THE CYCLE IT TENDS TO FLATTEN AS SUCCESSIVE SHORT WAVE
TROUGHS PROPAGATE UNDER THIS AXIS.

EAST OF THIS RIDGE...A BROAD MID LEVEL TROUGH EXTENDS ACROSS THE
SOUTH ATLANTIC TO 30S. OVER THE NEXT FEW DAYS THE TROUGH IS
FORECAST TO BOUND BETWEEN 30W-10E. AT LOW LEVELS IT IS TO SUSTAIN
A SURFACE FRONT THAT EXTENDS ACROSS THE RIO DE LA PLATA BASIN TO
LA PAMPA IN ARGENTINA. BROAD RIDGE TO THE SOUTH...MEANWHILE...IS
TO ANCHOR ON A 1037 HPA HIGH OFF THE COAST OF PATAGONIA. UNDER
INFLUENCE OF THE RIDGE TO THE SOUTH A MOIST EASTERLY FLOW
ESTABLISHED ACROSS NORTHERN PATAGONIA/LA PAMPA IN
ARGENTINA...FAVORING CONVECTION ALONG THE LEE OF THE ANDES BETWEEN
CENTRAL CUYO AND NORTHWEST PATAGONIA. THROUGH 36-48 HRS THIS IS TO
FAVOR SCATTERED RAINS WITH ACCUMULATION OF 00-05MM/DAY.

ANOTHER TROUGH LIES TO THE NORTH OF THE MID LEVEL RIDGE...WITH
AXIS ACROSS CENTRAL/NORTHERN CHILE INTO WESTERN ARGENTINA. THROUGH
42-48 HRS THE TROUGH WILL MOVE INTO CENTRAL ARGENTINA WHILE
TRAILING TO THE NORTHWEST ACROSS BOLIVIA TO SOUTHERN PERU. THIS IS
A SLOW TO EVOLVE SYSTEM...AND THROUGH 96 HRS IT IS TO MEANDER EAST
INTO SOUTHERN BRASIL-MATO GROSSO DO SUL/MATO GROSSO. AT LOW LEVELS
THIS WILL SUSTAIN FRONTOGENESIS OVER PARAGUAY. THROUGH 84-96 HRS
BOUNDARY IS TO INTENSIFY WHILE A LOW OCCLUDES OFF THE SOUTH COAST
OF BRASIL. MODELS DIVERGE ON THE INTENSITY OF THIS FEATURE...WITH
THE GFS FAVORING A DEEPER/STRONGER PERTURBATION THAN WHAT THE GFS
SUGGESTS. ACROSS PARAGUAY THIS IS TO TRIGGER SCATTERED DEEP
CONVECTION...WITH MAXIMA OF 20-45MM EXPECTED THROUGH 36-48 HRS. BY
72-84 HRS MOST INTENSE SHIFTS INTO SOUTHERN BRASIL-MATO GROSSO DO
SUL WHERE THE MAXIMA IS TO PEAK AT 25-50MM. BY 96-108 HRS THIS
DECREASES TO 05-10MM AS THE LOW MEANDERS EAST. HOWEVER...AS THE
CYCLONE DEEPENS OFF THE COAST OF URUGUAY/RIO GRANDE DO SUL...IT IS
TO FAVOR A STRONG ONSHORE FLOW AND MODERATE CONVECTION WITH MAXIMA
OF 20-35MM.

BROAD TROUGH IS TO THEN PULL ACROSS THE EASTERN PACIFIC INTO
SOUTHERN-CENTRAL PORTIONS OF CHILE BY 84-96 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 72-96 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.

AT 200 HPA...A RIDGE IS TO BUILD OFF THE NORTH COAST OF PERU...TO
REMAIN OVER THE EASTERN PACIFIC THROUGH AT LEAST 60-72 HRS. THE
RIDGE ALOFT WILL INDUCE THE NORTHWARD AMPLIFICATION OF A SHORT
WAVE TROUGH ACROSS PERU TO ACRE/AMAZONAS IN BRASIL BY 36-48 HRS.
THE AMPLIFYING TROUGH WILL TRIGGER SCATTERED CONVECTION ACROSS
NORTHERN PERU/SOUTHERN COLOMBIA WITH MAXIMA OF 15-30MM. OTHER
CONVECTION IS TO BUILD ACROSS EQUATORIAL SOUTH AMERICA WITH DAILY
MAXIMA TO PEAK AT 10-15MM/DAY.

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

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