Prognostic Meteorological Discussion
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FXSA20 KWBC 221657
PMDSA

SOUTH AMERICA FORECAST DISCUSSION - INTERNATIONAL DESKS
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1257 PM EDT THU JUN 22 2017

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

MODEL DISCUSSION (VALID FROM JUNE 22 AT 0000 UTC): GLOBAL MODEL
GUIDANCE REMAINS IN GENERAL AGREEMENT ON PATTERN EVOLUTION ACROSS
THE SOUTH AMERICAN DOMAIN THROUGH DAY 06. THIS IS WELL SUPPORTED
BY THE GLOBAL ENSEMBLE MODELS...LEADING TO A HIGH CONFIDENCE IN
THE FORECAST. NOTE THAT THE ENVIRONMENTAL CONDITIONS REMAIN
FAVORABLE FOR POSSIBLE SUBTROPICAL STORM FORMING NEAR ARCHIPELAGO
DE JUAN FERNANDEZ LATER ON FRIDAY/SATURDAY MORNING. THIS WILL
SUSTAIN HEAVY RAINS WITH TROPICAL STORM INTENSITY WINDS TO AFFECT
JUAN FERNANDEZ-CENTRAL CHILE.

DEEP MID LEVEL TROUGH ON THE SOUTHERN STREAM DOMINATES THE FLOW
ACROSS THE DRAKE PASSAGE-SOUTHERN CONE. UNDER INFLUENCE OF A HIGH
AMPLITUDE RIDGE TO THE WEST...COLD ANTARCTIC AIR IS MOVING NORTH
ACROSS THE DRAKE PASSAGE TO SOUTHERN CHILE/PATAGONIA IN ARGENTINA.
AT LOW LEVELS THIS WILL SUSTAIN A DEEP OCCLUDED LOW JUST NORTH OF
THE ANTARCTIC PENINSULA...WITH ASSOCIATED FRONT STREAMING ACROSS
THE MALVINAS/FALKLAND ISLANDS TO PATAGONIA IN ARGENTINA LATER THIS
EVENING. UNDER INFLUENCE OF THIS FEATURE EXPECTING SCATTERED SNOW
SHOWERS TO AFFECT TIERRA DEL FUEGO/EXTREME SOUTHERN CHILE AND
CENTRAL PORTIONS OF PATAGONIA IN ARGENTINA. IN THIS AREA EXPECTING
SNOWFALL AMOUNTS OF 04-08CM...WHILE ALONG THE CENTRAL COAST OF
PATAGONIA EXPECTING RAINFALL AMOUNTS OF 05-10MM THROUGH FRIDAY
MORNING.

BROAD TROUGH LIES TO THE NORTH...DOMINATING MID LEVEL FLOW BETWEEN
100W-70W AND TO THE SOUTH OF 20S. THIS SUSTAINS A SURFACE FRONT
ACROSS RIO DE LA PLATA BASIN-MENDOZA IN ARGENTINA-LA SERENA CHILE
TO THE EASTERN PACIFIC WHERE IT IS TO FRONTOLIZE.
MEANWHILE...ACROSS THE BUENOS AIRES PROVINCE THIS IS TO TRIGGER
SCATTERED CONVECTION WITH ACCUMULATION OF 05-10MM...INCREASING TO
20-30MM ON FRIDAY. POST FRONTAL CONVECTION ACROSS CENTRAL CHILE
WILL RESULT IN RAINFALL AMOUNTS OF 10-15MM...WHILE ACROSS THE
CENTRAL ANDES IT IS TO TRIGGER SNOWFALL AMOUNTS OF 20-30CM.

THROUGH FRIDAY EVENING THE MID LEVEL TROUGH IS TO EVOLVE INTO A
DEEP CLOSED LOW TO THE WEST-NORTHWEST OF ARCHIPELAGO DE JUAN
FERNANDEZ. ON SATURDAY TO SUNDAY IT IS TO MEANDER ACROSS THE
ISLANDS...NEARING THE CENTRAL COAST OF CHILE ON SUNDAY-MONDAY. AS
IT NEARS THE COAST...THE TROUGH ALOFT IS TO FAVOR AN UPPER
DIVERGENT PATTERN THAT IS TO VENT DEEP CONVECTION ON CENTRAL
REGIONS OF CHILE. FURTHERMORE...THIS IS TO SUSTAIN A MOIST
ADVECTIVE PATTERN...WITH SUBTROPICAL MOISTURE TO POOL ALONG THE
COAST. AT LOW LEVELS THE DEEPENING MID LEVEL VORTEX IS TO INTERACT
WITH MEANDERING FRONT TO THE NORTH...TO SUSTAIN CYCLOGENESIS NEAR
30S 95W EARLY IN THE CYCLE. THIS IS TO RAPIDLY DEEPEN FROM A 1006
HPA LOW TO AN INTENSE 986 HPA CYCLONE ON FRIDAY AS IT MEANDERS TO
THE EAST-SOUTHEAST TOWARDS JUAN FERNANDEZ. AS THE LOW
DEEPENS...WARM SUBTROPICAL AIR IS TO WRAP AROUND THE LOW LEVEL
CIRCULATION. THIS IS TO THEN FAVOR A CONVECTIVELY UNSTABLE AIR
MASS AROUND THE SURFACE CYCLONE. LATENT HEAT RELEASE COULD THEN
SUSTAIN GRADUAL TRANSITION TO A WARM CORE CYCLONE EARLY ON
SATURDAY MORNING. OFFICIAL DETERMINATION/ CLASSIFICATION WILL BE
MADE BY THE METEOROLOGICAL SERVICE OF CHILE. AS IT NEARS JUAN
FERNANDEZ THIS IS TO TRIGGER HEAVY CONVECTION AND STRONG BOUNDARY
LAYER WINDS THAT ARE TO PEAK BETWEEN 40-50KT. ON THE CENTRAL
REGIONS OF CHILE THE WINDS ON SATURDAY-SUNDAY ARE TO PEAK AT
30-50KT. EARLY ON SATURDAY MORNING THIS IS TO SUSTAIN LIGHT
COASTAL CONVECTION OVER CENTRAL CHILE...WITH ACCUMULATION OF
00-05MM/DAY. DURING THE DAY ON SATURDAY THIS IS TO BECOME MORE
ACTIVE AND BETTER ORGANIZED...TRIGGERING RAINFALL AMOUNTS OF
35-70MM IN POTENTIALLY SEVERE CONVECTION. OVER ARGENTINA THIS IS
TO THEN FAVOR A MOIST ONSHORE FLOW ACROSS THE BUENOS AIRES
PROVINCE TO PATAGONIA...WITH ACCUMULATION OF 10-15MM OVER BUENOS
AIRES-LA PAMPA AND 20-40MM OVER CENTRAL/NORTHERN PATAGONIA. ON
SUNDAY CONVECTION SPREADS NORTH ALONG THE COAST OF CHILE TO LA
SERENA...FAVORING RAINFALL AMOUNTS OF 15-20MM...WHILE ON THE
CENTRAL ANDES EXPECTING SNOWFALL AMOUNTS OF 10-15CM.

NORTH OVER THE CONTINENT...AT 200 HPA...DOMINANT FEATURE IS A
DISORGANIZED CELL OF THE SUBTROPICAL RIDGE ENVELOPING AREA TO THE
NORTH OF 15S. THROUGH SUNDAY EVENING THE RIDGE BECOMES BETTER
ORGANIZED AS IT AMPLIFIES ACROSS MATO GROSSO-MATO GROSSO DO SUL IN
BRASIL. THE RIDGE ALOFT IS TO VENT DEEP CONVECTION ACROSS
EQUATORIAL SOUTH AMERICA...WITH ACCUMULATION OF 10-15MM/DAY AND
MAXIMA OF 20-30MM...WITH MOST ACTIVE TODAY AND ON SATURDAY AS
ENHANCED BY NORTHERN HEMISPHERE TROPICAL WAVES STREAMING ACROSS
NORTHERN SOUTH AMERICA. ON THE NORTHEAST COAST OF BRASIL EXPECTING
RAINFALL AMOUNTS OF 15-20MM/DAY IN SCATTERED DEEP
CONVECTION...WITH LOCALIZED MAXIMA OF 30MM...WHILE OVER RIO DE
JANEIRO/ESPIRITO SANTO EXPECTING ACCUMULATION OF 05-10MM/DAY AND
MAXIMA OF 15-20MM/DAY.

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





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