Prognostic Meteorological Discussion
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FXSA20 KWBC 041617
PMDSA

SOUTH AMERICA FORECAST DISCUSSION - INTERNATIONAL DESKS
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1217 PM EDT WED MAY 04 2016

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

MODEL DISCUSSION (VALID FROM MAY 04 AT 0000 UTC): MODELS GRADUALLY
REACHING A CONSENSUS ON HOW PATTERN ACROSS THE EASTERN PACIFIC IS
GOING TO EVOLVE...WITH ENSEMBLE MODEL GUIDANCE GIVING STRONG
SUPPORT TO THE DETERMINISTIC SOLUTION. OVER THE NEXT FEW DAYS THE
BLOCKING RIDGE PATTERN IS FORECAST TO DEVELOP OVER THE
BELLINGSHAUSEN SEA/SOUTHEAST PACIFIC. IN AN OMEGA BLOCK
FASHION...THE RIDGE WILL BE BOOKENDED BY TWO TROUGHS...A PATTERN
THAT IS THEN FORECAST TO HOLD FOR SEVERAL DAYS.

THE RIDGE EXTENDS NORTH-TO-SOUTH ALONG THE COAST OF CHILE TO THE
BELLINGSHAUSEN SEA. SUCCESSIVE SHORT WAVE PERTURBATIONS ARE TO
PRESS AGAINST THIS AXIS....LEADING TO ITS GRADUAL EROSION TO THE
NORTH OF 40S WHILE TO THE SOUTH THE RIDGE IS EXPECTED TO HOLD.
THROUGH 84-96 HRS THIS WILL EVOLVE INTO A CLOSED MID LEVEL HIGH
THAT IS TO CENTER NEAR 52S 90W. PERTURBATIONS STREAMING ACROSS THE
EASTERN PACIFIC ARE TO THEN SPLIT AS THEY CLASH WITH THE RIDGE.
THE BULK OF THE SHORT WAVE ENERGY IS TO SHEAR SOUTH AROUND THE
RIDGE WHILE WEAKER VORTICES STREAM TO THE NORTH INTO CENTRAL
PORTIONS OF CHILE.

IN THIS PATTERN A MID LEVEL SHORT WAVE TROUGH IS FORECAST TO ENTER
CENTRAL CHILE BY 30-36 HRS...TO SPILL ACROSS THE CENTRAL ANDES
INTO CUYO/CENTRAL ARGENTINA BY 54-60 HRS. ANOTHER WILL
FOLLOW...REACHING CENTRAL CHILE BY 72-84 HRS. THIS ONE IS TO ALSO
SPILL ACROSS THE ANDES INTO CENTRAL ARGENTINA BY 96-108 HRS. AT
LOW LEVELS...A WANING FRONT IS TO REACH CENTRAL CHILE BY 42-48
HRS...AND THE NEXT BY 96-108 HRS. LACKING MOISTURE...THESE ARE TO
ONLY TRIGGER LIGHT RAINFALL AMOUNTS AS THEY ENTER CENTRAL
CHILE...WITH ACCUMULATION OF 00-05MM IN ISOLATED TO SCATTERED
CONVECTION.

UNDER INFLUENCE OF THE MID/UPPER LEVEL RIDGE TO THE SOUTH...A
TROUGH IS AMPLIFYING ALONG 45W/50W TO 30S. THIS IS TO SLOWLY PULL
ACROSS 30W BY 78-84 HRS...NEARING 10W LATER IN THE CYCLE. AT LOW
LEVELS THE RIDGE ALOFT WILL SUSTAIN A RIDGE FROM LA PAMPA IN
ARGENTINA TO THE SOUTHEAST PACIFIC...TO ANCHOR ON CLOSED HIGHS
OVER PATAGONIA AND SOUTH OF TIERRA DEL FUEGO CHILE. A BROAD TROUGH
WILL LIE TO THE EAST. POLAR FRONTS WILL REVOLVE AROUND THIS
AXIS...WITH ONE TO LIFT ACROSS PATAGONIA TO LA PAMPA/BUENOS AIRES
PROVINCE EARLY IN THE CYCLE. AS IT MEANDERS ACROSS CENTRAL
ARGENTINA THIS WILL PHASE WITH INFLOW OF MID LEVEL VORTICES
STREAMING ACROSS CENTRAL CHILE. THIS...IN-TURN...WILL TRIGGER
SCATTERED CONVECTION ACROSS CENTRAL ARGENTINA/RIO DE LA PLATA
BASIN BY 36-60 HRS...WITH RAINFALL AMOUNTS OF 15-20MM. THROUGH 72
HRS THIS WILL THEN DECREASE TO 00-05MM.

ANOTHER FRONT TO THE NORTH EXTENDS ACROSS SOUTHERN BRASIL-PARAGUAY
TO CORRIENTES/CHACO IN ARGENTINA. IN A NORTHERLY LOW LEVEL
FLOW...MOISTURE CONTENT ALONG THE MEANDERING FRONT IS FORECAST TO
GRADUALLY INCREASE THROUGH 60-72 HRS. THIS...IN-TURN...WILL FEED
CONVECTIVE DEVELOPMENT TO RESULT IN RAINFALL AMOUNTS OF 10-15MM BY
48-60 HRS...INCREASING TO 15-30MM BY 60-84 HRS. UNDER FAVORABLE
JET DYNAMICS LOCALLY HIGHER AMOUNTS ARE HIGHLY LIKELY.

NORTH OVER THE CONTINENT...AT 200 HPA...A NEAR ZONAL WESTERLY FLOW
IS TO PREVAIL ACROSS THE CONTINENT TO THE NORTH OF 20S. SHORT WAVE
PERTURBATIONS TO THE SOUTH ARE TO STREAM ACROSS NORTHERN
CHILE/SOUTHERN PERU INTO BOLIVIA/NORTHWEST ARGENTINA...WITH ONE TO
CROSS THE ANDES BY 36-48 HRS...AND ANOTHER BY 108 HRS. AS LOW
LEVEL MOISTURE POOLS ALONG THE JUNGLE OF PERU TO BOLIVIA THIS WILL
THEN FEED CONVECTIVE DEVELOPMENT. THROUGH 96-108 HRS THIS WILL
BECOME MORE INTENSE/BETTER ORGANIZED...TO RESULT IN MAXIMA OF
20-45MM/DAY. OTHER CONVECTION IS TO CLUSTER ACROSS EQUATORIAL
SOUTH AMERICA...WITH ACTIVITY ACROSS PARA-AMAZONAS-RORAIMA IN
BRASIL TO NORTHERN JUNGLE OF PERU TO RESULT IN DAILY RAINFALL
AMOUNTS OF 20-30MM. ALONG THE NORTH COAST OF BRASIL SCATTERED
CONVECTION WILL SUSTAIN RAINFALL AMOUNTS OF 15-20MM...WITH MOST
INTENSE ACROSS AMAPA/AMAZON RIVER DELTA REGION. OVER
ECUADOR...DIURNAL CONVECTION IS TO CLUSTER ALONG THE ANDES...WITH
RAINFALL AMOUNTS OF 10-15MM/DAY. SLIGHTLY HIGHER AMOUNTS ARE
POSSIBLE LATER IN THE CYCLE.

ENRIQUEZ...DGAC (ECUADOR)
AYALA...DINAC (PARAGUAY)
GALVEZ/DAVISON...WPC (USA)

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