Prognostic Meteorological Discussion
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000
FXSA20 KWBC 231808
PMDSA

SOUTH AMERICA FORECAST DISCUSSION - INTERNATIONAL DESKS
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
107 PM EST MON JAN 23 2017

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

MODEL DISCUSSION (VALID FROM JANUARY 23 AT 0000 UTC): ALTHOUGH THE
MODELS GENERALLY AGREE ON PATTERN EVOLUTION THROUGH DAY 06...THEY
TEND TO DIVERGE ON HOW A TROUGH AMPLIFYING ACROSS MID SECTIONS OF
SOUTH AMERICA IS GOING TO EVOLVE. BOTH EUROPEAN MODELS...AS WELL
AS A LARGE MAJORITY OF THE GLOBAL ENSEMBLES...TEND TO FAVOR A
WEAKER TROUGH THAN WHAT THE GFS SUGGESTS. THIS IS ADDING TO THE
UNCERTAINTY/LACK OF CONFIDENCE IN THE FORECAST BEYOND 84-96 HRS.

AT 200 HPA...UNDER THE INFLUENCE OF WARM SEA SURFACE
ANOMALIES...THE SUBTROPICAL HIGH MEANDERS OFFSHORE NEAR 22S 90W
WHILE ANCHORING A RIDGE OVER THE EASTERN PACIFIC. THIS
RIDGE...UNDER PRESSURE FROM POLAR PERTURBATIONS STREAMING TO THE
SOUTH...IS FORECAST TO MEANDER EAST AND NORTH TOWARDS THE
CONTINENT. AS A RESULT...LATER ON FRIDAY...IT IS TO ANCHOR ON A
CLOSED HIGH OVER NORTHERN CHILE/ SOUTHERN PERU...WHILE EXTENDING
FROM PERU/WESTERN BRASIL TO CENTRAL PROVINCES IN ARGENTINA. THE
RIDGE ALOFT WILL VENT CONVECTION ACROSS BOLIVIA TO FAVOR RAINFALL
AMOUNTS OF 15-20MM/DAY...INCREASING TO 20-40MM ON TUESDAY. ON THE
SOUTHERN SIERRA OF PERU-ALTIPLANO CHILENO THE MAXIMA IS TO
INITIALLY PEAK AT 05-10MM/DAY. THROUGH FRIDAY THIS INCREASES TO
10-15MM AS UPPER LEVEL RIDGE INTENSIFIES. THIS IS TO ALSO VENT
NEAR EQUATORIAL TROUGH RELATED CONVECTION ACROSS NORTHERN
BRASIL...WITH MAXIMA OF 30-60MM EXPECTED ON MONDAY-TUESDAY...AND
20-45MM/DAY THEREAFTER.

A TROUGH LIES TO THE EAST...AND AS THE RIDGE BUILDS INLAND IT IS
TO DISPLACE THE LATTER. ON TUESDAY TO WEDNESDAY THE TROUGH IS TO
THEN EXTEND ACROSS THE SOUTHERN STATES OF BRASIL TO MATO GROSSO IN
CENTRAL BRASIL. THE DEEPENING TROUGH WILL THEN DOMINATE THE FLOW
ACROSS CENTRAL-NORTHERN SOUTH AMERICA THROUGH THE END OF THE WEEK.
AT LOW LEVELS...A SURFACE TROUGH WILL EXTEND FROM SAO PAULO TO
RONDONIA IN BRASIL/NORTHERN JUNGLE OF BOLIVIA. THIS IS TO FOCUS
DEEP MOISTURE THAT IS TO THEN FEED ORGANIZED DEEP CONVECTION. OVER
SAO PAULO THIS IS TO INITIALLY FAVOR RAINFALL MAXIMA OF 20-40MM.
INFLOW OF SHORT WAVE ENERGY WILL SUSTAIN A GRADUAL SURGE...WITH
MAXIMA TO INCREASE TO 30-60MM/DAY. AS THE TROUGH
BUILDS...CONVECTION WIL THEN BUILD TO THE NORTH-NORTHWEST ACROSS
MATO GROSSO-TOCANTINS/GOIAS TO RONDONIA/NORTHERN BOLIVIA LATER ON
THURSDAY...WITH MAXIMA OF 25-50MM.

THE SUBTROPICAL RIDGE IS TO ALSO FOCUS SHORT WAVE PERTURBATIONS
ACROSS THE SOUTHERN CONE OF SOUTH AMERICA...WITH MID LEVEL TROUGH
TO MOVE ACROSS SOUTHERN CHILE TO PATAGONIA IN ARGENTINA LATER
TODAY...AND OFF THE COAST INTO THE WESTERN ATLANTIC LATER ON
TUESDAY. A SECONDARY VORTEX IS TO CLOSELY FOLLOW...TO LIFT ACROSS
EASTERN PATAGONIA ON WEDNESDAY...AND THEN NORTH ALONG THE COAST
INTO THE SOUTHERN STATES OF BRASIL LATER IN THE WEEK. THIS WILL
HELP SUSTAIN THE GRADUAL INTENSIFICATION OF MID LEVEL TROUGH AXIS.
AT LOW LEVELS...THE PROGRESSIVE TROUGH WILL SUSTAIN A SURFACE
FRONT THAT SURGES ACROSS PATAGONIA IN ARGENTINA TO LA PAMPA EARLY
ON TUESDAY...AND THEN NORTH ACROSS RIO DE LA PLATA ON TUESDAY
EVENING. BOUNDARY PULLS NORTH ACROSS SOUTHERN BRASIL TO PARAGUAY
LATER ON WEDNESDAY...WHERE IT IS EXPECTED TO STALL. AS THE FRONT
SURGES ACROSS BUENOS AIRES-URUGUAY...IT IS TO TRIGGER SCATTERED
CONVECTION WITH ACCUMULATION OF 15-25MM.

A HIGHER AMPLITUDE TROUGH WILL FOLLOW...WITH MID LEVEL TROUGH TO
EXTEND BETWEEN 120W-80W AND SOUTH OF 30S LATE RON ON WEDNESDAY. AS
IT PRESSES AGAINST THE SUBTROPICAL RIDGE TO THE NORTH...THIS IS TO
THEN SHEAR SHORT WAVE ENERGY ACROSS CENTRAL-SOUTHERN CHILE INTO
THE CENTRAL PROVINCES IN ARGENTINA. AT LOW LEVELS THIS WILL
SUSTAIN A BROAD TROUGH ACROSS THE BELLINGSHAUSEN SEA-SOUTHERN CONE
OF SOUTH AMERICA ON WEDNESDAY TO FRIDAY. POLAR FRONTS WILL REVOLVE
AROUND THIS AXIS...WITH ONE TO MOVE ACROSS PATAGONIA-SOUTHERN
CHILE LATER ON WEDNESDAY. BOUNDARY IS TO THEN REMAIN NEARLY
STATIONARY WHILE FOCUSING MOISTURE ON THE SOUTHERN REGIONS OF
CHILE. THIS WILL COMBINE WITH STRONG BOUNDARY LAYER WINDS TO
TRIGGER SCATTERED CONVECTION WITH ACCUMULATION OF 15-20MM/DAY.

DURAN...SMN (ARGENTINA)
TEPES...DMC (CHILE)
DAVISON/GALVEZ...WPC (USA)
$$




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