Prognostic Meteorological Discussion
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FXSA20 KWBC 241558
PMDSA

SOUTH AMERICA FORECAST DISCUSSION - INTERNATIONAL DESKS
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1158 AM EDT THU JUL 24 2014

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

MODEL DISCUSSION (VALID FROM 24 JULY 00UTC): OVER THE CONTINENT...
THERE IS GOOD AGREEMENT AMONG THE GLOBAL MODEL GUIDANCE THROUGH
DAY 07. OUR CONFIDENCE IN THE FORECAST IS HIGH.

AT 500 HPA...A NORTH TO SOUTH RIDGE EXTENDS ACROSS THE FAR EASTERN
PACIFIC TO THE BELLINGSHAUSEN SEA/POLAR ICE CAP. THIS RIDGE IS TO
HOLD NEARLY STATIONARY THROUGH 60-72 HRS...THEN STARTS TO RELOCATE
ACROSS THE SOUTHERN CONE WHILE YIELDING TO A HIGH AMPLITUDE
TROUGH. EAST OF THIS AXIS...A  TROUGH ON THE SOUTHERN STREAM
EXTENDS ACROSS THE SOUTHWEST ATLANTIC TO EASTERN PATAGONIA IN
ARGENTINA. UNDER INFLUENCE OF THE RIDGE TO THE WEST...PROGRESSIVE
SHORT WAVE PERTURBATIONS ARE LIFTING ACROSS THE DRAKE PASSAGE TO
THE SOUTHERN CONE...WITH ONE TO ENTER PATAGONIA IN ARGENTINA EARLY
THIS CYCLE. THROUGH 48 HRS IT WILL LIFT ALONG THE COAST OF
PATAGONIA TO THE BUENOS AIRES PROVINCE...THEN PULLS TO THE EAST
AROUND THE BROAD TROUGH. AT LOW LEVELS THIS WILL SUSTAIN AN
OCCLUDING LOW OFF THE COAST OF PATAGONIA EARLY IN THE CYCLE...WITH
ASSOCIATED FRONT TO RACE NORTH ACROSS THE BUENOS AIRES
PROVINCE/RIO DE LA PLATA BASIN THROUGH 54-60 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/EASTERN PATAGONIA IN ARGENTINA. THROUGH 30-36 HRS THIS IS TO
FAVOR SNOWFALL AMOUNTS OF 05-10CM ALONG THE EAST COAST...AND BY
48-60 HRS MOST ACTIVE EXPECTED ACROSS SOUTHERN BUENOS AIRES
PROVINCE/SIERRA DE LA VENTANA-TANDIL WITH ACCUMULATION OF 00-05CM.
LIGHT SNOW/SLEET IS POSSIBLE ACROSS PORTIONS OF BUENOS AIRES TO
SOUTHERN URUGUAY BY 54-60 HRS. AS THE POLAR RIDGE BUILDS INLAND
ACROSS THE CONTINENT...BELOW FREEZING TEMPERATURES ARE TO ENVELOP
SOUTHERN-CENTRAL PORTIONS OF ARGENTINA.

FURTHERMORE...THE TROUGH TO THE SOUTH...AS IT MEANDERS OVER THE
WESTERN ATLANTIC...IS TO INTERACT WITH A SHORT WAVE TROUGH ON THE
NORTHERN STREAM. THE TROUGH WILL MOVE ACROSS NORTHERN ARGENTINA/
SOUTHERN BRASIL EARLY THIS CYCLE...AND THROUGH 24-36 HRS THESE ARE
TO COMBINE INTO A LONG WAVE TROUGH OVER THE WESTERN ATLANTIC. AT
250 HPA...A SUBTROPICAL JET IS TO ROUND THE BASE OF THE LONG WAVE
TROUGH...WITH AXIS EAST ACROSS BOLIVIA-SOUTHEAST BRASIL TO THE
ATLANTIC. THIS JET IS FORECAST TO PERSIST DURING THE NEXT FEW
DAYS. THE JET ALOFT IS TO FAVOR A DIVERGENT PATTERN ACROSS MINAS
GERAIS-ESPIRITO SANTO TO MATO GROSSO IN BRASIL. THIS WILL VENT
CONVECTIVE DEVELOPMENT OVER THE NEXT FEW DAYS. AT LOW LEVELS...THE
ASSOCIATED SURFACE FRONT SURGES ACROSS SAO PAULO-MATO GROSSO IN
BRASIL TO NORTHERN BOLIVIA/SOUTHERN PERU AS A POLAR RIDGE BUILDS
ACROSS ARGENTINA TO PARAGUAY. THE BUILDING RIDGE WILL SUSTAIN A
SOUTHERLY LOW LEVEL JET ACROSS PARAGUAY/BOLIVIA TO SOUTHERN PERU
EARLY IN THE PERIOD. THROUGH 42-48 HRS THE FRONT MOVES NORTH
ACROSS RIO DE JANEIRO TO ESPIRITO SANTO/MINAS GERAIS...WHILE
TRAILING ACROSS MATO GROSSO/RONDONIA TO NORTHERN BOLIVIA. THE
FRONT IS TO THEN REMAIN NEARLY STATIONARY. AS THE FRONT MOVES
NORTH ACROSS SAO PAULO-MATO GROSSO IN BRASIL IT IS TO TRIGGER
SCATTERED CONVECTION WITH ACCUMULATION OF 20-40MM. SIMILAR AMOUNTS
ARE EXPECTED ACROSS ESPIRITO SANTO/RIO DE JANEIRO-MINAS BY 36-96
HRS...WHILE ACROSS MATO GROSSO THIS IS TO DECREASE TO 10-15MM/DAY.
ACROSS ACRE/NORTHERN BOLIVIA IT IS TO SUSTAIN ACCUMULATION OF
20-40MM THROUGH 36 HRS...WHILE ACROSS SOUTHERN/CENTRAL JUNGLE OF
PERU THE MAXIMA IS TO PEAK AT 35-70MM. THROUGH 72-84 HRS FOCUS OF
THE CONVECTION WILL SHIFT TO NORTHERN PERU/SOUTHERN
COLOMBIA...WITH ACCUMULATION OF 20-30MM.

THE INCREASE IN TROPICAL 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
03...WITH RAINFALL MAXIMA OF 20-30MM. CONVECTIVE ACTIVITY IS TO
THEN GRADUALLY WEAKEN LATER IN THE CYCLE. ACROSS NORTHEAST
BRASIL...TRADE WIND EASTERLIES ARE TO CONVERGE ALONG THE
COAST...TRIGGERING LIGHT COASTAL CONVECTION OVER THE NEXT FEW
DAYS.

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





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