Prognostic Meteorological Discussion
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000
FXSA20 KWBC 241624
PMDSA

SOUTH AMERICA FORECAST DISCUSSION - INTERNATIONAL DESKS
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1223 PM EDT WED MAY 24 2017

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

MODEL DISCUSSION (VALID FROM MAY 24 AT 0000 UTC): THE SYSTEM OF
CONCERN IS A MID LEVEL TROUGH ON THE NORTHERN STREAM THAT MEANDERS
OFF THE CENTRAL/NORTHERN COAST OF CHILE. SHORT WAVE TROUGH IS TO
REMAIN NEARLY STATIONARY THROUGH FRIDAY EVENING...THEN SPILL
ACROSS THE ANDES INTO NORTHWEST ARGENTINA EARLY ON SATURDAY. AS IT
MEANDERS TO THE WEST THE TROUGH IS TO FOCUS A SUBTROPICAL JET
ACROSS THE NORTHERN ANDES OF CHILE/ARGENTINA INTO MID SECTIONS OF
SOUTH AMERICA. THE JET...IN-TURN...WILL SUSTAIN AN UPPER DIVERGENT
PATTERN THAT IS TO VENT ORGANIZED DEEP CONVECTION. AS IT FOCUSES
SUBTROPICAL MOISTURE ACROSS CENTRAL REGIONS OF CHILE THIS IS TO
TRIGGER ORGANIZED CONVECTION ACROSS THE CENTRAL ANDES...WITH HEAVY
SNOWFALL AMOUNTS EXPECTED ON ELEVATIONS ABOVE 3000 METERS. DURING
THE NEXT 24 HRS EXPECTING MAXIMA OF 25-50CM...WITH LOCALLY HIGHER
AMOUNTS TO PEAK AT 75-100CM DUE TO POTENTIAL FOR THUNDER SNOW.

AT LOW LEVELS...BROAD RIDGE OVER THE CENTRAL/WESTERN ATLANTIC
FAVORS A NORTHERLY FLOW ACROSS BOLIVIA-PARAGUAY. THIS FLOW
CONVERGES ALONG A MEANDERING FRONT OVER SOUTHERN BRASIL/NORTHERN
ARGENTINA-PARAGUAY. ENVIRONMENTAL CONDITIONS IN THIS AREA ARE TO
REMAIN HIGHLY FAVORABLE AND CONDUCIVE TO GENERATION OF MESO SCALE
CONVECTIVE SYSTEMS DURING THE NEXT 48-60 HRS. FURTHERMORE
FORECASTED INSTABILITY INDICES SHOW RISK OF SEVERE CONVECTION
DURING THE SAME PERIOD...WITH LARGE HAIL EXPECTED ACROSS PORTIONS
OF THE CHACO PROVINCE IN ARGENTINA-CORRIENTES AND SOUTHEAST
PARAGUAY. THIS IS TO ALSO SUSTAIN HEAVY RAINFALL AMOUNTS...WITH
MAXIMA OF 35-70MM THROUGH THURSDAY MORNING AND 50-100MM ON
THURSDAY TO FRIDAY. ON FRIDAY TO SATURDAY FOCUS OF THE HEAVY
CONVECTION SHIFTS TO THE SOUTHERN STATES OF BRASIL... DECREASING
FROM 35-70MM ON FRIDAY TO 30-60MM ON SATURDAY. PREFRONTAL
CONVECTION ACROSS CENTRAL BOLIVIA ON FRIDAY IS TO THEN FAVOR
RAINFALL AMOUNTS OF 15-30MM IN SCATTERED CONVECTION.

UPSTREAM OVER THE SOUTH PACIFIC...A MID LEVEL RIDGE DOMINATES THE
FLOW BETWEEN 90W-110W. THE RIDGE IS STEERING PERTURBATIONS IN THE
SOUTHERN STREAM NORTH ACROSS THE BELLINGSHAUSEN SEA TO THE DRAKE
PASSAGE-SOUTHERN CHILE/TIERRA DEL FUEGO TO PATAGONIA IN ARGENTINA.
IN THIS PATTERN A STRONG VORTEX PULLS ACROSS THE SOUTHERN CONE
EARLY IN THE CYCLE. AS IT MIGRATES TO THE SOUTHWEST ATLANTIC ON
THURSDAY THIS IS TO THEN DEEPEN. THE DEEPENING TROUGH WILL SUSTAIN
A DEEP OCCLUDED LOW ACROSS THE DRAKE PASSAGE LATER TODAY THAT IS
TO INTENSIFY OVER THE WEDDELL SEA/SOUTHWEST ATLANTIC ON THURSDAY.
THE DEEPENING TROUGH WILL THEN DRIVE A SURFACE FRONT NORTH ACROSS
PATAGONIA IN ARGENTINA TO HELP SUSTAIN A WELL DEFINED BAROCLINIC
BOUNDARY FAR TO THE NORTH. AS IT ENTERS TIERRA DEL FUEGO THE DEEP
OCCLUDED LOW WILL TRIGGER SNOW SHOWERS ACROSS THE SOUTHERN ANDES
WITH ACCUMULATION OF 05-10CM.

LATER ON FRIDAY ANOTHER SHORT WAVE TROUGH IS TO APPROACH FROM THE
WEST...WITH MID LEVEL VORTEX TO ENTER SOUTHERN CHILE EARLY ON
SATURDAY MORNING. THIS MOVES TO PATAGONIA IN ARGENTINA-CENTRAL
CHILE ON SATURDAY-SUNDAY MONDAY. AXIS IS TO THEN SPLIT IN
TWO...WITH SHORT WAVE TROUGH ON THE NORTHERN STREAM TO THEN
MEANDER OFF THE CENTRAL COAST OF CHILE AS THE SOUTHERN HALF
PROPAGATES ACROSS PATAGONIA TO THE WESTERN ATLANTIC. THE NORTHERN
STREAM VORTEX IS TO LIKELY TRIGGER SNOW SHOWERS ON THE CENTRAL
ANDES EARLY NEXT WEEK...WHILE OVER CENTRAL SOUTH AMERICA IT IS TO
REINFORCE MEANDERING FRONT OVER SOUTHERN BRASIL-PARAGUAY/NORTHERN
ARGENTINA.

AT 200 HPA...A CELL OF THE SUBTROPICAL RIDGE ENVELOPS MOST OF
BRASIL-PERU-ECUADOR. THIS PATTERN WILL HOLD NEARLY UNCHANGED
DURING THE NEXT 36-48 HRS. IT IS THEN FORECAST TO WEAKEN LATER ON
FRIDAY/SATURDAY MORNING AS A HIGHER AMPLITUDE TROUGH STREAMS
ACROSS THE SOUTHERN CONE. MEANWHILE...THE RIDGE ALOFT WILL VENT
DIURNAL CONVECTION ACROSS CENTRAL-WESTERN BRASIL. ACROSS CENTRAL
BRASIL THE DAILY MAXIMA IS TO RANGE BETWEEN 10-15MM...WHILE OVER
NORTHWEST BRASIL/NORTHERN JUNGLE OF PERU-SOUTHERN COLOMBIA TO
EASTERN ECUADOR THE MAXIMA IS TO PEAK AT 15-30MM DURING THE NEXT
COUPLE OF DAY. THROUGH FRIDAY/SATURDAY MORNING...AS THE RIDGE
WEAKENS...THIS WILL DECREASES TO 10-15MM/DAY. ON THE PERUVIAN
JUNGLE TO THE SOUTH MAXIMA WILL INITIALLY PEAK AT 15-20MM. THROUGH
THURSDAY EVENING/FRIDAY MORNING IT WILL DECREASE TO AT
05-10MM/DAY. OVER NORTHEAST BRASIL...MEANWHILE...AN OLD FRONT OVER
THE SOUTH ATLANTIC SUSTAINS A PREFRONTAL SHEAR LINE ACROSS
PARAIBA-NORTHERN BAHIA. THIS IS ENHANCING LOW LEVEL CONVERGENCE
WHILE TRIGGERING SCATTERED CONVECTION. IN THIS AREA EXPECTING
RAINFALL AMOUNTS OF 15-30MM/DAY WITH LOCALIZED MAXIMA OF 20-45MM.
THIS IS TO PERSIST DURING THE NEXT 72-96 HRS.

ABDEMUR...FAA (ARGENTINA)
ESPINOLA...DNM (PARAGUAY)
DAVISON...WPC (USA)
$$




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