Prognostic Meteorological Discussion
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FXSA20 KWBC 231658
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SOUTH AMERICA FORECAST DISCUSSION - INTERNATIONAL DESKS
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1258 PM EDT WED JUL 23 2014

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

MODEL DISCUSSION (VALID FROM 23 JULY 00UTC): THE GLOBAL MODELS ARE
IN EXCELLENT AGREEMENT THROUGH THE MEDIUM RANGE PERIOD...WITH
GLOBAL ENSEMBLE MEMBERS PROVIDING SUPPORT TO THE DETERMINISTIC
SOLUTION. CONFIDENCE IN THE FORECAST IS HIGH. SYSTEM OF CONCERN IS
A MID LATITUDE TROUGH THAT ENTERS THE CONTINENT EARLY IN THE
CYCLE. UNDER FAVORABLE JET DYNAMICS THIS WILL SUSTAIN
ORGANIZED/POTENTIALLY SEVERE CONVECTION AND HEAVY RAINFALL
AMOUNTS.

AT 500 HPA...A TROUGH ON THE SOUTHERN STREAM ENVELOPS THE DRAKE
PASSAGE/SOUTHERN CONE OF SOUTH AMERICA. UPSTREAM FROM THIS
AXIS...A NORTH-TO-SOUTH RIDGE IS TO EXTEND ALONG 90W TO 70S. UNDER
INFLUENCE OF THE RIDGE TO THE WEST SHORT WAVE VORTICES ARE TO LIFT
ACROSS THE BELLINGSHAUSEN SEA ALONG THE BACKSIDE OF THE
TROUGH...STREAMING ACROSS PATAGONIA TO LA PAMPA/BUENOS AIRES
PROVINCE IN ARGENTINA. IN THIS PATTERN A STRONG VORTEX MOVES OFF
THE COAST OF ARGENTINA EARLY IN THE CYCLE. ANOTHER IS TO THEN
ENTER TIERRA DEL FUEGO BY 30-36 HRS...THEN NORTH ALONG THE COAST
OF PATAGONIA THROUGH 48-54 HRS...DEEPENING OVER THE BUENOS AIRES
PROVINCE/RIO DE LA PLATA BASIN BY 60-72 HRS. IN A DEEP LAYER COLD
ADVECTIVE PATTERN...INFLOW OF SHORT WAVE ENERGY FROM THE SOUTH
WILL HELP SUSTAIN SCATTERED SNOWFALL ACROSS TIERRA DEL
FUEGO/SOUTHERN PATAGONIA IN ARGENTINA...WITH ACCUMULATION OF
10-15CMM EXPECTED THROUGH 36 HRS. THIS IS TO THEN FAVOR SCATTERED
SNOWFALL ACROSS SOUTHERN BUENOS AIRES PROVINCE/SIERRA DE LA
VENTANA-TANDIL BY 48-72 HRS. LIGHT SNOW/SLEET IS POSSIBLE ACROSS
PORTIONS OF BUENOS AIRES TO SOUTHERN URUGUAY BY 66-84 HRS. AS THE
POLAR RIDGE BUILDS INLAND ACROSS PATAGONIA...BELOW FREEZING
TEMPERATURES ARE TO ENVELOP SOUTHERN-CENTRAL PORTIONS OF ARGENTINA.

A MID LATITUDE TROUGH ON THE NORTHERN STREAM IS FORECAST TO SPILL
ACROSS THE CENTRAL/NORTHERN ANDES OF CHILE EARLY IN THE CYCLE...
MEANWHILE FOCUSING SHORT WAVE ENERGY ACROSS PARAGUAY-MESOPOTAMIA
VALLEY IN ARGENTINA TO THE SOUTHERN STATES OF BRASIL. THE INFLOW
OF MID LEVEL COLD AIR WILL SUSTAIN HEIGHT FALLS OF 100-125GPM
ACROSS MID SECTIONS OF SOUTH AMERICA. AS THE TROUGH 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. THROUGH 48-60 HRS THE TROUGH MOVES ACROSS
URUGUAY/SOUTHERN BRASIL. AS IT CLEARS THE COAST OF ARGENTINA IT IS
TO THEN MERGE WITH AFOREMENTIONED TROUGH TO THE SOUTH. THESE ARE
TO THEN COMBINE INTO A LONG WAVE TROUGH OVER THE WESTERN ATLANTIC
THAT IS TO EXTEND BETWEEN 60W-30W AND TO THE SOUTH OF 20S. AT LOW
LEVELS...THE TROUGH ALOFT SUSTAINS A POLAR FRONT ACROSS URUGUAY TO
THE NORTHWEST PROVINCES IN ARGENTINA. BUILDING POLAR RIDGE TO THE
SOUTH IS TO SUSTAIN A PAMPERO LOW LEVEL JET ACROSS ARGENTINA. THIS
WILL SUSTAIN A COLD ADVECTIVE PATTERN ACROSS MID SECTIONS OF SOUTH
AMERICA. IT IS TO ALSO  DISPLACE THE POLAR BOUNDARY NORTH ACROSS
SOUTHERN BRASIL-PARAGUAY TO MATO GROSSO IN BRASIL-CENTRAL BOLIVIA
EARLY IN THE CYCLE. THROUGH 48 HRS IT WILL MOVE NORTH ACROSS SAO
PAULO/MATO GROSSO/RONDONIA IN BRASIL TO NORTHERN BOLIVIA. IT IS TO
THEN STALL AS MID/UPPER LEVEL TROUGH PULLS AWAY. THE SURGING POLAR
BOUNDARY WILL TRIGGER ORGANIZED CONVECTION ACROSS SOUTHERN
BRASIL-MESOPOTAMIA VALLEY IN ARGENTINA AND SOUTHEAST
PARAGUAY...WITH MAXIMA OF 100-150MM THROUGH 36 HRS. UNDER
FAVORABLE JET DYNAMICS AND WEAK HELICITY EXPECTING LONG
LASTING/POTENTIALLY SEVERE CONVECTION TO DEVELOP...WITH RISK OF
LARGE HAIL STONES. AS THE FRONT MOVES ACROSS SOUTHERN TO SOUTHEAST
BRASIL THIS DECREASES TO 20-40MM...AND BY 60-96 HRS EXPECTING
ACCUMULATION OF 20-35MM...WITH MOST ACTIVE EXPECTED ACROSS
ESPIRITO SANTO/RIO DE JANEIRO-MINAS GERAIS TO MATO GROSSO. STRONG
SOUTHERLY JET ACROSS PARAGUAY WILL SUSTAIN AN AREA OF HEAVY
CONVECTION ALONG THE TAIL END OF THE FRONT OVER BOLIVIA/SOUTHERN
PERU EARLY IN THE CYCLE...WITH RAINFALL MAXIMA OF 75-100MM
EXPECTED BY 36 HRS. AT 36-72 HRS FOCUS OF THE HEAVY CONVECTION
SHIFTS TO ACRE IN BRASIL-CENTRAL/SOUTHERN PERU WITH MAXIMA OF
35-70MM. BY 84-96 HRS THIS WILL DECREASE TO 20-35MM WHILE BUILDING
NORTH INTO CENTRAL/NORTHERN PERU AND EASTERN ECUADOR.

SURGE IN CONVECTION ACROSS PERU/WESTERN BRASIL IS TO THEN INDUCE
THE BRIEF INTENSIFICATION OF THE SUBTROPICAL RIDGE OVER NORTHWEST
SOUTH AMERICA. AT 200 HPA THE RIDGE IS TO ANCHOR ON A CLOSED HIGH
OVER NORTHERN AMAZONAS IN BRASIL-NORTHERN JUNGLE OF PERU. THIS
WILL VENT DEEP CONVECTION IN THIS AREA THROUGH DAY 04. ACTIVITY IS
TO THEN GRADUALLY WEAKEN LATER IN THE CYCLE. ACROSS NORTHEAST
BRASIL...MEANWHILE...A PREFRONTAL SHEAR LINE IS TO EXTEND ACROSS
THE SOUTH ATLANTIC TO PERNAMBUCO/RIO GRANDE DO NORTE. THIS WILL
COMBINE WITH BRISK TRADE WIND EASTERLIES IN SUPPORT OF SCATTERED
COASTAL CONVECTION OVER THE NEXT 24-36 HRS...WITH ACCUMULATION OF
10-15MM IN SCATTERED CONVECTION.

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





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