Prognostic Meteorological Discussion
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FXSA20 KWBC 221618
PMDSA

SOUTH AMERICA FORECAST DISCUSSION - INTERNATIONAL DESKS
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1218 PM EDT TUE JUL 22 2014

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

MODEL DISCUSSION (VALID FROM 22 JULY 00UTC): EXCELLENT AGREEMENT
AMONG THE GLOBAL MODELS THROUGH DAY 06...WITH ENSEMBLE MEMBERS
SHOWING LITTLE VARIABILITY WELL BEYOND THE MEDIUM RANGE PERIOD.
OUR CONFIDENCE IN THE FORECAST IS HIGH. DURING SHORT RANGE
PERIOD...UNDER FAVORABLE JET DYNAMICS...EXPECTING SEVERE
CONVECTION TO AFFECT THE SOUTHERN STATES OF BRASIL-MESOPOTAMIA
VALLEY IN ARGENTINA-PARAGUAY. THIS IS TO ALSO FAVOR HEAVY RAINFALL
AMOUNTS.

A 500 HPA TROUGH LIFTS ACROSS THE BELLINGSHAUSEN SEA TO THE DRAKE
PASSAGE/SOUTHERN CONE OF SOUTH AMERICA EARLY IN THE CYCLE. UNDER
INFLUENCE OF A BUILDING RIDGE TO THE WEST...ADDITIONAL SHORT WAVE
PERTURBATIONS ARE TO THEN LIFT ACROSS THE BELLINGSHAUSEN
SEA/ANTARCTIC PENINSULA. THESE ARE TO THEN REVOLVE AROUND THE
TROUGH AS IT MEANDERS OVER THE SOUTHERN CONE. THE INFLOW OF COLD
AIR...AND A CONTINENTAL POLAR AIR MASS...IS TO THEN INDUCE THE
GRADUAL AMPLIFICATION/INTENSIFICATION OF THIS TROUGH AS THE CYCLE
PROGRESSES. AT LOW LEVELS A BROAD TROUGH IS TO ENVELOP THE
ANTARCTIC PENINSULA/WEDDELL SEA-SOUTHWEST ATLANTIC EARLY IN THE
CYCLE...WHILE A RIDGE TO THE WEST IS TO EXTEND ACROSS THE
BELLINGSHAUSEN SEA TO SOUTHERN CHILE. THIS RIDGE IS TO FUNNEL COLD
ANTARCTIC AIR NORTHWARD ACROSS THE DRAKE PASSAGE TO THE SOUTHERN
CONE. THIS IS TO THEN TRIGGER SCATTERED SNOW SHOWERS ACROSS
SOUTHERN PORTIONS OF CHILE...WITH ACCUMULATION OF 10-15CM OVER THE
NEXT COUPLE OF DAYS. IT IS TO ALSO FAVOR SNOW FALL ALONG THE COAST
OF PATAGONIA TO THE SOUTHERN PORTIONS OF THE BUENOS AIRES PROVINCE
ON DAYS 03-04...WITH ACCUMULATION OF 05-10CM ACROSS SIERRA DE LA
VENTANA/TANDIL. AS COLD/MOIST AIR ADVECTS ACROSS THE BUENOS AIRES
PROVINCE/RIO DE LA PLATA BASIN THERE IS A POTENTIAL FOR LIGHT
SNOWFALL...TO WITH MIXED PRECIPITATION TO AFFECT SOUTHERN URUGUAY
ON DAY 04. AS THE POLAR RIDGE BUILDS INLAND ACROSS
PATAGONIA...BELOW FREEZING TEMPERATURES ARE TO ENVELOP
SOUTHERN-CENTRAL PORTIONS OF ARGENTINA.

ON THE NORTHERN STREAM...ALSO AT 500 HPA...A TROUGH IS TO EXTEND
ALONG THE CENTRAL/NORTH COAST OF CHILE TO SOUTHERN PERU EARLY IN
THE CYCLE. THROUGH 36-48 HRS IT IS TO SPILL ACROSS THE ANDES INTO
THE NORTHWEST PROVINCES IN ARGENTINA...MEANWHILE TRIGGERING HEIGHT
FALLS OF 100-125GPM OVER MID SECTIONS OF SOUTH AMERICA. AS IT
PULLS ACROSS THE CONTINENT...A SUBTROPICAL/POLAR JET PAIR IS TO
ACCOMPANY THIS TROUGH...WITH JETS TO COUPLE ON THEIR CORRESPONDING
DIVERGENT REGIONS OVER MID SECTIONS OF SOUTH AMERICA. THIS IS TO
RESULT IN A LARGE AREA OF DIVERGENCE THAT IS TO EXPAND FROM
SOUTHERN BRASIL TO PARAGUAY. AT LOW LEVELS...THE TROUGH ALOFT
SUSTAINS A POLAR FRONT ACROSS THE BUENOS AIRES PROVINCE-MENDOZA IN
ARGENTINA. BUILDING POLAR RIDGE AND A PAMPERO LOW LEVEL JET WILL
DISPLACE THIS BOUNDARY NORTH ACROSS URUGUAY/NORTHERN PROVINCES IN
ARGENTINA BY 24 HRS. THROUGH 48-72 HRS...AS THE POLAR HIGH
STRENGTHENS TO A 1027 HPA CIRCULATION...THE FRONT WILL SURGE
ACROSS SOUTHERN BRASIL-PARAGUAY TO BOLIVIA. BY 72-96 HRS THE FRONT
IS TO MOVE ACROSS RIO DE JANEIRO/SOUTHERN MINAS GERAIS IN BRASIL
TO NORTHERN BOLIVIA/SOUTHERN JUNGLE OF PERU. THE SURGING POLAR
BOUNDARY WILL TRIGGER ORGANIZED CONVECTION ACROSS URUGUAY-SOUTHERN
BRASIL-MESOPOTAMIA VALLEY IN ARGENTINA AND PARAGUAY. THROUGH 36
HRS THIS IS TO PEAK AT 35-70MM. UNDER FAVORABLE JET DYNAMICS THIS
INCREASES TO 100-150MM BY 36-60 HRS IN POTENTIALLY SEVERE
CONVECTION. MODERATE HELICITY DURING THIS PERIOD WILL FAVOR LONG
LASTING CONVECTIVE CELLS. THIS WILL COMBINE WITH STRONG UPWARD
VERTICAL VELOCITIES TO TRIGGER LARGE HAIL STONES. AS THE FRONT
SURGES ACROSS BOLIVIA TO SOUTHERN PERU IT WILL SUSTAIN MAXIMA OF
50-100MM BY 60 HRS. BY 60-84 HRS EXPECTING MAXIMA OF 35-70MM
ACROSS ACRE IN BRASIL TO SOUTHERN PERU/NORTHERN BOLIVIA. BY 84-108
HRS THE FOCUS OF THE ORGANIZED CONVECTION SHIFTS TO CENTRAL/
NORTHERN PERU...WITH MAXIMA OF 20-35MM. SIMILAR AMOUNTS ARE THEN
EXPECTED ALONG THE MEANDERING FRONT ACROSS RIO DE JANEIRO-SOUTHERN
MINAS GERAIS TO MATO GROSSO IN BRASIL.

AT 200 HPA...OVER NORTHERN SOUTH AMERICA...A NEAR ZONAL WESTERLY
FLOW IS EXPECTED TO DOMINATE CONTINENTAL AREA TO THE NORTH OF 20S.
THIS IS TO GENERALLY FAVOR LIGHT CONVECTION ALONG THE LEE OF THE
ANDES OVER NORTHERN JUNGLE OF PERU/EASTERN ECUADOR-NORTHERN
AMAZONAS IN BRASIL...WITH RAINFALL AMOUNTS IN THIS AREA TO PEAK AT
05-10MM. A GRADUAL INCREASE...HOWEVER...IS POSSIBLE BY 72-108 HRS
AS AFOREMENTIONED POLAR TROUGH PATTERN OVER ARGENTINA-PARAGUAY
STRENGTHENS. ACROSS NORTHEAST BRASIL...MEANWHILE...A SURFACE FRONT
IS TO MEANDER ACROSS THE SOUTH ATLANTIC TO NORTHERN ESPIRITO
SANTO/SOUTHERN BAHIA. THIS IS TO ENHANCE LOW LEVEL MOISTURE
CONVERGENCE WHILE FAVOR SCATTERED CONVECTION. EARLY IN THE CYCLE
THIS IS TO RESULT IN RAINFALL AMOUNTS OF 20-35MM. THROUGH 48-72
HRS THIS IS TO DECREASE TO 15-20MM/DAY.

FERNANDES...INMET (BRASIL)
JALFIN...SMN (ARGENTINA)
DAVISON...WPC (USA)
$$




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