Prognostic Meteorological Discussion
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636
FXSA20 KWBC 241744
PMDSA

SOUTH AMERICA FORECAST DISCUSSION - INTERNATIONAL DESKS
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1244 PM EST TUE JAN 24 2017

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

MODEL DISCUSSION (VALID FROM JANUARY 24 AT 0000 UTC): THE GLOBAL
MODEL GUIDANCE NOW FOLLOW A SIMILAR EVOLUTION THROUGH DAY
06...WITH THE GFS MAKING CORRECTIONS TO SHORT WAVE TROUGH ON THE
NORTHERN STREAM OVER MID SECTIONS OF SOUTH AMERICA. THE MODEL NOW
FAVORS A WEAKER TROUGH AS THE OTHER MODELS PREVIOUSLY SUGGESTED.
IN A HIGHLY AMPLIFIED SINUSOIDAL WAVE PATTERN...CONFIDENCE IN THE
FORECAST IS HIGH THROUGH 96-108 HRS.

UNDER WARM SEA SURFACE TEMPERATURE ANOMALIES OFF THE COAST OF
PERU/NORTHERN CHILE...THE SUBTROPICAL RIDGE REMAINS MAROONED WEST
OF ITS CLIMATOLOGICAL POSITION WITH AXIS MEANDERING OVER THE
EASTERN PACIFIC BETWEEN 100W-70W. AT 200 HPA...IN RESPONSE TO
SURGING TROPICAL CONVECTION OVER BOLIVIA-PERU-ACRE/RONDONIA IN
BRASIL...A SECONDARY HIGH/RIDGE IS FORMING OVER THE CONTINENT. A
SHORT WAVE TROUGH OFF THE NORTH COAST OF CHILE/SOUTH OF PERU
SEPARATES THESE RIDGES. UNDER PRESSURE FROM AMPLIFYING POLAR
TROUGHS...THE CELL OVER THE EASTERN PACIFIC IS FORECAST TO
GRADUALLY WEAKEN THROUGH FRIDAY EVENING...WHILE THE RIDGE OVER THE
CONTINENT TENDS TO GRADUALLY BUILD/ BECOME BETTER ORGANIZED. THE
BUILDING RIDGE IS TO CONTINUE VENTING DEEP CONVECTION ACROSS
BOLIVIA-PERU AND CENTRAL/WESTERN PORTIONS OF PERU. ON THE SIERRA
OF PERU-ALTIPLANO OF BOLIVIA AND NORTHERN ANDES OF CHILE INITIALLY
EXPECTING MAXIMA OF 15-25MM/DAY. THROUGH FRIDAY...AS UPPER RIDGE
PATTERN INTENSIFIES... ACROSS BOLIVIA-MATO GROSSO-RONDONIA IN
BRASIL THE MAXIMA IS TO PEAK AT 35-70MM OVER THE NEXT COUPLE OF
DAYS...THEN BUILD WEST ACROSS ACRE/AMAZONAS TO CENTRAL PERU LATER
IN THE WEEK WHILE INCREASING TO 40-80MM. OTHER CONVECTION IS TO
CLUSTER ACROSS CENTRAL/NORTHERN JUNGLE OF PERU TO EASTERN
ECUADOR...WHERE THE MAXIMA PEAK AT 30-60MM OVER THE NEXT FEW DAYS.

EAST OF THE UPPER LEVEL RIDGE...A 200 HPA LOW IS TO MEANDER
BETWEEN NATAL-RECIFE WHILE ANCHORING A SHORT WAVE TROUGH ACROSS
THE NORTHEAST STATES OF BRASIL. THE TROUGH IS ENHANCING CONVECTIVE
DEVELOPMENT ACROSS NORTHEAST BRASIL...WHERE MAXIMA IS TO PEAK AT
40-80MM OVER THE NEXT COUPLE OF DAYS. THROUGH THURSDAY THIS
DECREASES TO 20-45MM/DAY WHILE BUILDING WEST ACROSS EQUATORIAL
SOUTH AMERICA. LATER IN THE WEEK THE MAXIMA IS TO PEAK AT 15-25MM
AS BUILDING RIDGE OVER THE CONTINENT DISPLACES THE TROUGH TO THE
NORTH AND EAST.

AS THE SUBTROPICAL RIDGE MEANDERS OVER THE EASTERN PACIFIC...IT IS
TO FOCUS SHORT WAVE PERTURBATIONS ACROSS THE SOUTHERN CONE OF
SOUTH AMERICA. IN THIS FLOW...PROGRESSIVE PERTURBATION WILL MOVE
ACROSS SOUTHERN CHILE TO PATAGONIA IN ARGENTINA LATER TODAY...TO
THEN LIFT TO THE NORTH-NORTHEAST ACROSS ARGENTINA WHILE FEEDING
INTO A TROUGH TO THE EAST. INFLOW OF SHORT WAVE ENERGY WILL FAVOR
FORMATION OF A CLOSED LOW ALONG THIS AXIS AND OFF THE COAST OF
URUGUAY LATER ON WEDNESDAY. IT IS TO ALSO SUSTAIN THE NORTHWARD
AMPLIFICATION OF THE TROUGH ACROSS SOUTHERN BRASIL-PARAGUAY. AT
LOW LEVELS...THE PROGRESSIVE TROUGH WILL SUSTAIN A SURFACE FRONT
THAT SURGES ACROSS PATAGONIA IN ARGENTINA TO LA PAMPA EARLY ON
TUESDAY...AND THEN NORTH ACROSS RIO DE LA PLATA ON TUESDAY
EVENING. BOUNDARY PULLS NORTH ACROSS SOUTHERN BRASIL TO PARAGUAY
LATER ON WEDNESDAY...WHERE IT IS EXPECTED TO STALL. AS THE FRONT
SURGES ACROSS URUGUAY...IT IS TO TRIGGER SCATTERED CONVECTION WITH
ACCUMULATION OF 15-25MM. IN INTERACTION WITH A SURFACE TROUGH OVER
SOUTHEAST BRASIL THIS IS TO THEN FAVOR A SURGE IN CONVECTION
ACROSS SAO PAULO-MATO GROSSO IN BRASIL ON
WEDNESDAY-THURSDAY...WITH RAINFALL MAXIMA OF 30-60MM. LATER ON
FRIDAY IT DECREASES TO 20-40MM WHILE BUILDING NORTH AND WEST
ACROSS MATO GROSSO TO RONDONIA/NORTHERN BOLIVIA.

A HIGH AMPLITUDE LONG WAVE TROUGH WILL FOLLOW...WITH MID LEVEL
TROUGH TO EXTEND BETWEEN 120W-80W AND SOUTH OF 30S LATER ON
WEDNESDAY. AS IT PRESSES AGAINST THE SUBTROPICAL RIDGE TO THE
NORTH...THIS IS TO THEN SHEAR SHORT WAVE ENERGY ACROSS
CENTRAL-SOUTHERN CHILE INTO THE CENTRAL PROVINCES IN ARGENTINA.
THE LONG WAVE AXIS IS TO ALSO ESTABLISH A SUBTROPICAL
CONNECTION...WITH DEEP MOISTURE TO FOCUS OVER CHILE BETWEEN TEMUCO
AND PUERTO MONTT. AT LOW LEVELS THIS WILL SUSTAIN A BROAD TROUGH
ACROSS THE BELLINGSHAUSEN SEA-SOUTHERN CONE OF SOUTH AMERICA ON
WEDNESDAY TO FRIDAY. POLAR FRONTS WILL REVOLVE AROUND THIS
AXIS...WITH ONE TO MOVE ACROSS PATAGONIA-SOUTHERN CHILE LATER ON
WEDNESDAY. THE FRONTAL BOUNDARY IS TO THEN REMAIN NEARLY
STATIONARY WHILE FOCUSING MOISTURE ON THE SOUTHERN REGIONS OF
CHILE. THIS WILL COMBINE WITH STRONG BOUNDARY LAYER WINDS TO
TRIGGER SCATTERED CONVECTION WITH ACCUMULATION OF 15-30MM/DAY ON
WEDNESDAY...AND 20-40MM ON THURSDAY.

DURAN...SMN (ARGENTINA)
TEPES...DMC (CHILE)
DAVISON...WPC (USA)
$$





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