Prognostic Meteorological Discussion
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FXSA20 KWBC 231538
PMDSA

SOUTH AMERICA FORECAST DISCUSSION - INTERNATIONAL DESKS
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1138 AM EDT FRI JUN 23 2017

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

MODEL DISCUSSION (VALID FROM JUNE 23 AT 0000 UTC): ENVIRONMENTAL
CONDITIONS REMAIN FAVORABLE FOR POSSIBLE FORMATION OF A
SUBTROPICAL CYCLONE NEAR THE ARCHIPELAGO DE JUAN FERNANDEZ DURING
THE EARLY MORNING HOURS ON SATURDAY. THE GLOBAL MODELS HAVE BEEN
FAIRLY CONSISTENT WITH THIS EVOLUTION...AND OVERALL CONFIDENCE IN
THE FORECAST IS HIGH. MODERATE HELICITY VALUES ALONG THE CENTRAL
COAST OF CHILE COULD LEAD TO POSSIBLE WATER SPOUTS LATER ON
SATURDAY AND DURING THE DAY ON SUNDAY.

A MID/UPPER LEVEL TROUGH ON THE SOUTHERN STREAM EXTENDS ACROSS THE
DRAKE PASSAGE TO SOUTHERN CHILE/PATAGONIA IN ARGENTINA. THIS IS TO
PULL TO THE SOUTHWEST ATLANTIC LATER TODAY. ON SATURDAY TO SUNDAY
IT IS TO EVOLVE INTO A BROAD TROUGH BETWEEN 60W-10E WHILE
BOTTOMING OUT TO THE SOUTH OF 30S. AT LOW LEVELS THIS SUSTAINS A
BROAD TROUGH OVER THE WEDDELL SEA/SOUTHWEST ATLANTIC...WITH
ASSOCIATED FRONT TRAILING TO THE BUENOS AIRES PROVINCE/CENTRAL
PROVINCES IN ARGENTINA. FURTHERMORE...A NORTHERLY LOW LEVEL JET
ACROSS PARAGUAY-NORTHERN ARGENTINA FAVORS A WARM/MOIST ADVECTIVE
PATTERN. MOISTURE IS TO CONVERGE ALONG THE FRONT TO THE
SOUTH...FEEDING CONVECTIVE DEVELOPMENT DURING THE DAY TODAY WHILE
TRIGGERING RAINFALL MAXIMA OF 20-30MM. ON SATURDAY THIS DECREASES
TO 10-15MM WITH MOST INTENSE OVER LA PAMPA/SOUTHERN BUENOS AIRES
PROVINCE.

TRAILING THIS SYSTEM...AT 500 HPA...A SHORT WAVE TROUGH ON THE
NORTHERN STREAM FLOW IS TO RAPIDLY INTENSIFY AS IT MEANDERS WEST
OF JUAN FERNANDEZ ISLAND LATER TODAY. ON SATURDAY TO SUNDAY
MORNING THE DEEP LOW/TROUGH IS TO MEANDER ACROSS THE
ARCHIPELAGO...NEARING THE CENTRAL COAST OF CHILE ON SUNDAY-MONDAY.
ON SATURDAY TO SUNDAY THIS IS FOCUS A JET MAXIMA ACROSS CENTRAL
CHILE THAT IS TO FAVOR AN UPPER DIVERGENT PATTERN.
FURTHERMORE...THE DEEP TROUGH IS TO SUSTAIN A SUBTROPICAL
CONNECTION AS IT PROPAGATES ACROSS THE EASTERN PACIFIC...WITH DEEP
MOISTURE TO POOL ALONG THE CENTRAL COAST OF CHILE. AT LOW LEVELS
THE SURFACE LOW IS TO RAPIDLY DEEPEN FROM A 1004 HPA LOW EARLY IN
THE CYCLE TO A 978 HPA LOW DURING EARLY MORNING HOURS ON
SATURDAY...WITH MODELS SHOWING MAXIMUM INTENSITY BETWEEN 06-09 UTC
ON SATURDAY. 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. NEAR THE ARCHIPELAGO DE JUAN FERNANDEZ THE WINDS ARE TO
PEAK AT 40-50KT. AS IT NEARS THE COAST OF CHILE ON SUNDAY THE
SYSTEM IS TO GRADUALLY WEAKEN...WITH TROPICAL DEPRESSION INTENSITY
WINDS OF 25-34KT EXPECTED ALONG THE COAST. 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. ON SUNDAY THIS DECREASES TO 20-40MM WITH MOST
INTENSE BETWEEN CONCEPCION-PUERTO MONTT...WHILE TO THE NORTH THE
MAXIMA IS TO PEAK AT 15-30MM. OVER THE CENTRAL ANDES THIS IS TO
TRIGGER SCATTERED SNOW SHOWERS...WITH STORM TOTAL AMOUNTS OF
15-25CM.

AS SHORT WAVE ENERGY SPILLS ACROSS THE ANDES OF CHILE INTO
ARGENTINA THIS IS TO THEN TRIGGER CYCLOGENESIS ON THE LEE OF THE
ANDES EARLY ON SUNDAY MORNING. THE LOW IS TO GRADUALLY DEEPEN AS
IT MEANDERS EAST ACROSS THE WESTERN SOUTH ATLANTIC. THIS IS TO
THEN DRIVE A FRONT NORTH ACROSS LA PAMPA LATER ON SUNDAY...TO THE
BUENOS AIRES PROVINCE/RIO DE LA PLATA BASIN ON MONDAY. ON TUESDAY
THIS MOVES NORTH ACROSS URUGUAY TO NORTHERN PROVINCES IN
ARGENTINA. AS A MOIST NORTHERLY FLOW PERSISTS...THIS IS TO
INITIALLY TRIGGER MODERATE RAINFALL AMOUNTS ACROSS
CENTRAL/NORTHERN PATAGONIA IN ARGENTINA EARLY ON SUNDAY
MORNING...WITH ACCUMULATION OF 20-40MM. ON SUNDAY THIS SPREADS TO
LA PAMPA TO FAVOR RAINFALL AMOUNTS OF 15-25MM. ON MONDAY THIS
INCREASES TO 30-60MM WHILE SPREADING NORTH ACROSS THE BUENOS AIRES
PROVINCE-CENTRAL ARGENTINA. AS THE CONVECTION INTENSIFIES THERE IS
A SLIGHT RISK OF SEVERE WEATHER DURING THE DAY ON MONDAY.

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 EXPECTED THROUGH SUNDAY
EVENING. 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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