Prognostic Meteorological Discussion
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FXSA20 KWBC 261554
PMDSA

SOUTH AMERICA FORECAST DISCUSSION - INTERNATIONAL DESKS
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1153 AM EDT MON JUN 26 2017

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

MODEL DISCUSSION (VALID FROM JUNE 26 AT 0000 UTC): CONFIDENCE IN
THE FORECAST IS HIGH...WITH MODELS IN GOOD AGREEMENT THROUGH
144-168 HRS.

AT MID LEVELS...A SHORT WAVE TROUGH ON THE NORTHERN STREAM
MEANDERS OFF THE CENTRAL COAST OF CHILE WHILE CENTERING ON A
CLOSED LOW TO THE EAST-SOUTHEAST OF JUAN FERNANDEZ ISLAND. THROUGH
WEDNESDAY MORNING THE LOW IS TO WEAKEN TO AN OPEN TROUGH AS IT
SHEARS SHORT WAVE ENERGY ACROSS THE ANDES INTO THE
CENTRAL/NORTHERN PROVINCES IN ARGENTINA-RIO DE LA PLATA BASIN. AT
LOW LEVELS THE MID LEVEL VORTEX SUSTAIN A WARM CORE SURFACE TROUGH
OFF THE CENTRAL COAST OF CHILE...CENTERING ON A CLOSED LOW TO THE
EAST OF JUAN FERNANDEZ. THROUGH TUESDAY EVENING THIS IS TO WEAKEN
AS THE UPPER LEVEL PERTURBATION FILLS. MEANWHILE...THIS WILL
ENHANCE MOISTURE CONVERGENCE ALONG THE COAST OF CHILE BETWEEN LA
SERENA-SANTIAGO...TO RESULT IN MODERATE CONVECTION WITH
ACCUMULATION OF 20-30MM. ON THE CENTRAL ANDES THIS IS TO TRIGGER
SCATTERED SNOW SHOWERS WITH ACCUMULATION OF 05-10CM.

ALSO AT LOW LEVELS...A POLAR RIDGE EXTENDS OVER PATAGONIA IN
ARGENTINA...WHILE A SURFACE FRONT MEANDERS TO THE NORTH ACROSS THE
BUENOS AIRES PROVINCE-MENDOZA. AS SHORT WAVE VORTICES SPILL ACROSS
THE ANDES THIS IS TO THEN INDUCE A FRONTAL WAVE ALONG THE
MEANDERING FRONT. THE LOW IS TO THEN OCCLUDE AS IT MOVES OFF THE
COAST OF BUENOS AIRES LATER ON TUESDAY. MOST ACTIVE CONVECTION
ALONG THIS FEATURE IS EXPECTED DURING THE NEXT 12-18 HRS...WITH
RAINFALL MAXIMA OF 30-60MM TO AFFECT BUENOS AIRES PROVINCE/CENTRAL
ARGENTINA...WHILE OVER CORDOBA-MENDOZA THE MAXIMA WILL PEAK AT
20-30MM. ON TUESDAY THIS DECREASES TO 05-10MM. ON
WEDNESDAY-THURSDAY...AS THE REMNANTS OF THE MID LEVEL TROUGH
SPILLS ACROSS THE ANDES...ACTIVITY ACROSS URUGUAY-NORTHERN
ARGENTINA WILL INCREASE TO 15-25MM...WHILE ON THURSDAY THE MAXIMA
IS TO PEAK AT 20-30MM WHILE SPREADING NORTH ACROSS URUGUAY TO RIO
GRANDE DO SUL/MESOPOTAMIA VALLEY.

PROGRESSIVE MID LEVEL PERTURBATIONS ARE TO POPULATE THE SOUTHERN
STREAM FLOW...WITH ONE ENTERING THE DRAKE PASSAGE/TIERRA DEL FUEGO
BY MIDDAY ON TUESDAY. A SECONDARY VORTEX WILL FOLLOW...MAKING
LANDFALL IN THE SAME AREA EARLY ON THURSDAY MORNING. AT LOW LEVELS
THIS IS TO SUSTAIN A BROAD TROUGH ACROSS THE DRAKE PASSAGE TO
SOUTHERN CHILE/PATAGONIA IN ARGENTINA LATER ON TUESDAY...WHERE IT
IS TO HOLD THROUGH THURSDAY MORNING. SUCCESSIVE POLAR FRONTS ARE
TO THEN REVOLVE AROUND THIS AXIS...ENHANCING MOISTURE CONVERGENCE
ALONG THE COAST BETWEEN PUERTO MONTT-PUNTA ARENAS. ON TUESDAY THIS
IS TO SUSTAIN RAINFALL AMOUNTS OF 15-20MM...WHILE ON WEDNESDAY
THIS INCREASES TO 20-30MM.

AT 200 HPA...BROAD CELL OF THE SUBTROPICAL RIDGE DOMINATES THE
FLOW OVER THE CONTINENT TO THE NORTH OF 30S. THE UPPER LEVEL RIDGE
ANCHORS ON A CLOSED HIGH OVER RONDONIA/NORTHERN BOLIVIA. AS THE
MID LEVEL TROUGH MOVES ACROSS CENTRAL/NORTHERN CHILE THE RIDGE IS
TO GRADUALLY FLATTEN TO THE SOUTH OF 20S. LATER IN THE WEEK IT IS
TO THEN CONFINE TO NORTHERN PORTIONS OF SOUTH AMERICA. A TROUGH TO
THE EAST...MEANWHILE...WILL EXTEND ACROSS BAHIA TO
TOCANTINS/GOIAS. THE TROUGH IS TO GRADUALLY WEAKEN AS THE RIDGE TO
THE WEST FLATTEN. MEANWHILE...THIS IS TO ENHANCE CONVECTION ALONG
THE NORTHEAST COAST OF BRASIL. ACROSS ESPIRITO SANTO/SOUTHERN
BAHIA THIS WILL FAVOR RAINFALL AMOUNTS OF 10-15MM/DAY...WHILE OVER
PERNAMBUCO-RIO GRANDE DO NORTE EXPECTING ACCUMULATION OF 20-30MM.
ON TUESDAY THIS INCREASES TO 20-40MM. OVER NORTHERN
BRASIL-SOUTHERN COLOMBIA- EXPECTING ACCUMULATION OF
15-25MM/DAY...INCREASING TO 20-30MM ON WEDNESDAY TO THURSDAY. OVER
SOUTHERN COLOMBIA-NORTHERN PERU-EASTERN ECUADOR THE DAILY MAXIMA
IS TO INITIALLY PEAK AT 10-15MM. THROUGH WEDNESDAY EVENING THIS
INCREASES TO 20-30MM AS ENHANCED BY NORTHERN HEMISPHERE TROPICAL
WAVES PROPAGATING ALONG THE NEAR EQUATORIAL TROUGH TO THE NORTH.

ESPINOLA...DNM (PARAGUAY)
GONZALEZ...DMC (CHILE)
DAVISON...WPC (USA)
$$





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