Prognostic Meteorological Discussion
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FXSA20 KWBC 271701
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SOUTH AMERICA FORECAST DISCUSSION - INTERNATIONAL DESKS
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1201 PM EST MON FEB 27 2017

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

MODEL DISCUSSION (VALID FROM FEBRUARY 25 AT 0000 UTC): GLOBAL
MODELS FOLLOW SIMILAR EVOLUTION ACROSS THE SOUTH AMERICAN DOMAIN
THROUGH 96-108 HRS...WITH ENVIRONMENTAL CONDITIONS ACROSS MID
SECTIONS OF SOUTH AMERICA TO BECOME HIGHLY FAVORABLE FOR
GENERATION OF MESO SCALE CONVECTIVE SYSTEMS. THE GLOBAL MODELS
THEN DIVERGE ON HOW SOUTHERN STREAM PATTERN IS GOING TO EVOLVE
DURING THE LATTER PART OF THE FORECAST...RESULTING IN A LOWER
CONFIDENCE IN THE FORECAST BEYOND 108 HRS.

A DEEP/HIGHLY AMPLIFIED MID/UPPER LEVEL TROUGH CROSSES THE
SOUTHERN CONE LATER ON TUESDAY/EARLY ON WEDNESDAY MORNING...WITH
AXIS FOCUSING SHORT WAVE ENERGY ACROSS SOUTHERN PORTIONS OF CHILE.
AS IT MOVES ACROSS THE SOUTHERN CONE...THE TROUGH WILL SUSTAIN
HEIGHT FALLS IN EXCESS OF 200GPM ON TUESDAY TO WEDNESDAY. THE
DEEP/HIGH AMPLITUDE TROUGH WILL COMBINE WITH ABOVE NORMAL SEA
SURFACE TEMPERATURES OVER THE EASTERN PACIFIC TO SUSTAIN A PLUME
OF SUBTROPICAL MOISTURE. IN THIS PATTERN...THE PRECIPITABLE WATER
CONTENT OVER SOUTHERN CHILE IS EXPECTED TO PEAK AROUND 50MM EARLY
ON TUESDAY MORNING. AT LOW LEVELS THIS WILL SUSTAIN A BROAD TROUGH
OVER THE SOUTHEAST PACIFIC LATER TODAY...THAT RAPIDLY MOVES ACROSS
SOUTHERN CHILE-PATAGONIA IN ARGENTINA BY MIDDAY ON TUESDAY. AS IT
CROSSES THE CONTINENT THIS WILL SUSTAIN A TIGHT PRESSURE
GRADIENT...WITH BOUNDARY LAYER WINDS OF 30-35KT EXPECTED THROUGH
TUESDAY EVENING. THE STRONG LOW LEVEL WINDS WILL ENHANCE
TOPOGRAPHICALLY INDUCED CONVECTION OVER CHILE BETWEEN TEMUCO-ISLA
DE CHILOE...TO RESULT IN HEAVY RAINS WITH MAXIMA OF 30-60MM
THROUGH TUESDAY MORNING...AND 15-20MM ON TUESDAY TO WEDNESDAY.

A SHORT WAVE TROUGH ON THE NORTHERN STREAM FLOW WILL FOLLOW...WITH
MID LEVEL AXIS TO MOVE ACROSS 100W AND SOUTH OF 30S LATER ON
TUESDAY. ON WEDNESDAY-THURSDAY IT IS TO SPILL ACROSS THE CENTRAL
ANDES OF CHILE INTO THE CENTRAL PROVINCES IN ARGENTINA. THIS WILL
BE ACCOMPANIED BY A SUBTROPICAL JET MAXIMA...THAT IS TO FAVOR AN
UPPER DIVERGENT PATTERN AS IT STREAMS ACROSS THE SOUTHERN CONE ON
THURSDAY-FRIDAY. THE TROUGH ALOFT WILL INTERACT WITH A MEANDERING
FRONT OVER LA PAMPA/BUENOS AIRES-CENTRAL CHILE. THIS WILL INDUCE A
FRONTAL WAVE/LOW ON THURSDAY...FORECAST TO GRADUALLY STRENGTHEN ON
FRIDAY. BUILDING POLAR RIDGE OVER PATAGONIA-CENTRAL ARGENTINA WILL
THEN DISPLACE THE SURFACE FRONT NORTH ACROSS NORTHERN ARGENTINA TO
PARAGUAY LATER ON FRIDAY. ACROSS CENTRAL ARGENTINA THIS IS TO
TRIGGER SCATTERED CONVECTION ON WEDNESDAY WITH MAXIMA OF 15-25MM.
ON THURSDAY-FRIDAY ENVIRONMENTAL CONDITIONS BECOME FAVORABLE FOR
GENERATION OF MESO SCALE CONVECTIVE SYSTEMS...TO RESULT IN
RAINFALL MAXIMA OF 40-80MM IN POTENTIALLY SEVERE CONVECTION. MOST
ACTIVE IS EXPECTED DURING THE EARLY MORNING HOURS ON FRIDAY...TO
CLUSTER ON THE NORTHERN PROVINCES IN ARGENTINA-URUGUAY/MESOPOTAMIA
VALLEY. ON FRIDAY AFTERNOON THE CONVECTION WILL THEN BUILD NORTH
ACROSS THE SOUTHERN STATES OF BRASIL TO PARAGUAY.

NORTH OVER THE CONTINENT...AT 200 HPA...BROAD CELL OF THE
SUBTROPICAL RIDGE DOMINATES THE FLOW TO THE NORTH OF 30S AND WEST
OF 50W...WHILE ANCHORING ON A CLOSED HIGH OVER SOUTHERN BOLIVIA.
THE TROUGH ALOFT IS STEERING SHORT WAVE PERTURBATIONS ACROSS
CENTRAL CHILE INTO ARGENTINA. THESE...IN-TURN...ARE TO TRIGGER
SCATTERED CONVECTION. OVER THE BUENOS AIRES PROVINCE/RIO DE LA
PLATA BASIN THIS IS TO FAVOR MODERATE TO HEAVY CONVECTION THROUGH
TUESDAY MORNING...WITH MAXIMA OF 30-60MM. OTHER CONVECTION TO THE
NORTH IS TO CLUSTER ON THE ALTIPLANO OF BOLIVIA-NORTHWEST
PROVINCES IN ARGENTINA...TO TRIGER MAXIMA OF 20-40MM/DAY OVER THE
NEXT COUPLE OF DAYS. ON WEDNESDAY TO THURSDAY THE RIDGE IS
FORECAST TO FLATTEN...LIMITING TO NORTHERN SOUTH AMERICA DURING
THE SECOND HALF OF THE WEEK. THE CLOSED HIGH WILL THEN RELOCATE TO
MATO GROSSO IN BRASIL. AS THE RIDGE EVOLVES...A SHORT WAVE TROUGH
OVER NORTHEASTERN BRASIL IS TO GRADUALLY MOVE EAST...MOVING OFF
THE COAST ON WEDNESDAY. THE RIDGE/TROUGH ALOFT...ARE TO MEANWHILE
FAVOR SCATTERED CONVECTION ACROSS NORTHERN SOUTH AMERICA. ACROSS
PARA-AMAZONAS/AMAZON RIVER DELTA REGION...THE DAILY MAXIMA IS TO
PEAK AT 30-60MM EARLY IN THE CYCLE. THROUGH THURSDAY THIS WILL
DECREASE TO 20-35MM/DAY. OVER MATO GROSSO-SAO PAULO/RIO DE
JANEIRO...MAXIMA IS TO INITIALLY PEAK AT 30-60MM/DAY. THROUGH
WEDNESDAY/THURSDAY THIS DECREASES TO 15-25MM. OTHER CONVECTION IS
TO CLUSTER ALONG THE HIGH JUNGLE OF PERU...WHERE THE DAILY MAXIMA
IS PEAK AT 25-50MM...WHILE OVER THE SIERRA EXPECTING RAINFALL
AMOUNTS OF 05-10MM/DAY. ACROSS WESTERN ECUADOR/NORTH COAST OF
PERU...ENVIRONMENTAL CONDITIONS BECOME MORE FAVORABLE FOR
CONVECTION TO DEVELOP ON WEDNESDAY AND ONWARD...WHEN THE DAILY
MAXIMA IS TO INCREASE TO 30-60MM/DAY AS ENHANCED BY A WESTERLY
LOW/MID LEVEL FLOW.

ABDEMUR...FAA (ARGENTINA)
TEPES...DMC (CHILE)
GALVEZ...WPC (USA)
$$





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