Prognostic Meteorological Discussion
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FXSA20 KWBC 091739
PMDSA

SOUTH AMERICA FORECAST DISCUSSION - INTERNATIONAL DESKS
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1238 PM EST FRI DEC 09 2016

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

MODEL DISCUSSION (VALID FROM DECEMBER 09 AT 0000 UTC): OVER THE
CONTINENT AND WESTERN ATLANTIC THE GLOBAL MODELS CONTINUE TO AGREE
ON PATTERN EVOLUTION THROUGH DAY 06...FOLLOWING A SOLUTION THAT IS
WELL SUPPORTED BY THE GLOBAL ENSEMBLE MEMBERS. ACROSS THE EASTERN
PACIFIC...THEY AGREE THROUGH 108-120 HRS...THEN DISAGREE ON HOW A
DEEP TROUGH APPROACHING THE SOUTHERN CONE/BELLINGSHAUSEN SEA IS
GOING TO EVOLVE. IN THIS AREA THEA VARIABILITY AMONG THE ENSEMBLE
MEMBERS IS VERY HIGH...AND AS A RESULT OUR CONFIDENCE IN THE
FORECAST IS LOW.

ON THE NORTHERN STREAM...A 500 HPA LOW TO THE WEST-NORTHWEST OF LA
SERENA CHILE ANCHORS A SHORT WAVE TROUGH OVER THE FAR EASTERN
PACIFIC. THE SHORT WAVE TROUGH IS TO SLOWLY SHEAR SHORT WAVE
ENERGY ACROSS THE ANDES INTO THE NORTHERN PROVINCES IN
ARGENTINA-PARAGUAY/SOUTHERN STATES OF BRASIL. BUT AS THE ENERGY
SHEARS AWAY...THE SHORT WAVE TROUGH IS TO GRADUALLY WEAKEN THROUGH
SUNDAY AFTERNOON. MEANWHILE...THE MEANDERING TROUGH WILL FOCUS A
JET MAXIMA ACROSS MID SECTIONS OF SOUTH AMERICA...WHERE IT IS TO
FAVOR AN UPPER DIVERGENT PATTERN. ACROSS CENTRAL CHILE THIS IS TO
SUSTAIN MIXED CONVECTION WITH ACCUMULATION OF 00-05MM THROUGH
SATURDAY MORNING... WHILE OVER NORTHWEST ARGENTINA EXPECTING
MAXIMA OF 05-10MM. AS IT SPREADS ACROSS THE ANDES INTO MID
SECTIONS OF SOUTH AMERICA...THE MID/UPPER LEVEL PERTURBATION IS TO
INTERACT WITH A SURFACE FRONT MEANDERING ACROSS SOUTHERN
BRASIL-NORTHERN ARGENTINA/PARAGUAY. FURTHERMORE...A NORTHERLY JET
ACROSS BOLIVIA-PARAGUAY WILL ENHANCE MOISTURE
ADVECTION/CONVERGENCE ALONG THE LOW LEVEL BOUNDARY. IN THIS
PATTERN...THE ENVIRONMENTAL CONDITIONS ARE FAVORABLE AND HIGHLY
IDEAL FOR A MESO SCALE CONVECTIVE SYSTEM TO DEVELOP DURING THE
EVENING HOURS TODAY/EARLY MORNING ON SATURDAY. FOCUS OF THE HEAVY
CONVECTION WILL BE OVER PARAGUAY-SOUTHERN BRASIL WITH MAXIMA OF
40-80MM THROUGH SATURDAY MORNING AND 20-40MM ON SATURDAY TO SUNDAY
MORNING. ON SUNDAY-MONDAY FOCUS OF THE CONVECTION WILL SHIFT TO
THE SOUTHEAST STATES OF BRASIL WHERE THE DAILY MAXIMA IS TO PEAK
AT 20-45MM. OTHER CONVECTION IS EXPECTED BETWEEN CENTRAL BOLIVIA
AND SANTA CRUZ...WHERE UNDER INFLUENCE OF THE UPPER LEVEL TROUGH
EXPECTING ENHANCEMENT TO DIURNAL CONVECTION TO RESULT IN RAINFALL
AMOUNTS OF 20-35MM/DAY. THIS IS TO PERSIST DURING THE NEXT THREE
DAYS.

PROGRESSIVE SHORT WAVE PERTURBATIONS WILL POPULATE THE SOUTHERN
STREAM FLOW...WITH ONE TO PULL ACROSS THE DRAKE PASSAGE/SOUTHERN
CONE OF SOUTH AMERICA LATER TODAY. ANOTHER IS TO MAKE LANDFALL
OVER SOUTHERN CHILE EARLY ON SUNDAY...AND LATER IN THE DAY IT WILL
MOVE ACROSS SOUTHERN CHILE/PATAGONIA IN ARGENTINA. UNDER INFLUENCE
OF A RIDGE TO THE WEST THE LATTER IS TO THEN DEEPEN/AMPLIFY ALONG
THE COAST OF ARGENTINA...WITH AXIS TO EXTEND NORTH BETWEEN 60W-30W
TO 30S ON MONDAY AFTERNOON. AT LOW LEVELS THESE WILL SUSTAIN AN
ELONGATED FRONT ACROSS PATAGONIA IN ARGENTINA-SOUTHERN CHILE TO
THE EASTERN PACIFIC LATER THIS AFTERNOON. AS IT MEANDERS ACROSS
THE SOUTHERN CONE...THE MODELS AGREE ON A DEEP FRONTAL WAVE TO
PROPAGATE ACROSS SOUTHERN CHILE EARLY ON SUNDAY MORNING...AND
ACROSS PATAGONIA IN ARGENTINA LATER IN THE DAY. THROUGH MONDAY
EVENING THIS IS TO GRADUALLY DEEPEN AS A RIDGE BUILDS TO THE WEST.
THE DEEPENING LOW/TROUGH WILL THEN DRIVE THE FRONT NORTH ACROSS LA
PAMPA IN ARGENTINA TO CENTRAL CHILE LATER ON SUNDAY/EARLY MONDAY
MORNING. A PAMPERO LOW LEVEL JET WILL THEN DRIVE THIS BOUNDARY
FARTHER TO THE NORTH ACROSS RIO DE LA PLATA BASIN-MENDOZA IN
ARGENTINA LATER ON MONDAY. AS IT ENTERS SOUTHERN CHILE THIS IS TO
FAVOR SCATTERED CONVECTION WITH ACCUMULATION OF 10-15MM/DAY
EXPECTED OVER THE NEXT TWO DAYS...AND 05-10MM ON SUNDAY. LESSER
AMOUNTS ARE EXPECTED ACROSS TIERRA DEL FUEGO WHERE THE DAILY
MAXIMA IS TO RANGE BETWEEN TRACE AND 05MM/DAY. AS THE FRONT SURGES
ACROSS URUGUAY-CENTRAL ARGENTINA ON MONDAY MAXIMA IS TO PEAK AT
10-15MM.

NORTH OVER THE CONTINENT...AT 200 HPA...BROAD CELL OF THE
SUBTROPICAL RIDGE WILL DOMINATE AREA TO THE NORTH OF 30S WHILE
ANCHORING ON A CLOSED HIGH OVER THE SOUTHEAST STATES OF BRASIL.
THIS PATTERN WILL HOLD OVER THE NEXT FEW DAYS. MEANWHILE...IT IS
TO CONTINUE VENTING DIURNAL CONVECTION ACROSS CENTRAL-WESTERN
BRASIL WHERE THE DAILY MAXIMA IS TO PEAK AT 15-20MM. ACROSS
ECUADOR-PERUVIAN JUNGLE...MEANWHILE...THE DAILY MAXIMA IS TO PEAK
AT 05-10MM DURING THE NEXT THREE DAYS...INCREASING TO 15-25MM
LATER ON MONDAY. OVER EASTERN BRASIL...TO AFFECT
TOCANTINS-GOIAS-MINAS GERAIS AND BAHIA...THE DAILY MAXIMA IS TO
INITIALLY PEAK AT 20-35MM IN SCATTERED CONVECTION. THROUGH SUNDAY
THIS WILL INCREASE TO 20-45MM AS ENHANCED BY MID/UPPER LEVEL SHORT
WAVE TROUGH STREAMING ALONG THE SOUTHERN FRINGES OF THE
SUBTROPICAL RIDGE.

ALVA...SENAMHI (PERU)
DURAN...SMN (ARGENTINA)
DAVISON/GALVEZ...WPC (USA)
$$





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