Prognostic Meteorological Discussion
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FXSA20 KWBC 021804
PMDSA

SOUTH AMERICA FORECAST DISCUSSION - INTERNATIONAL DESKS
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
103 PM EST MON MAR 02 2015

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

MODEL DISCUSSION (VALID FROM MARCH 02 AT 00UTC): DETERMINISTIC
GLOBAL MODELS AND THE ENSEMBLE MEMBERS FOLLOW A SIMILAR EVOLUTION
THROUGH DAY 6. AS A RESULT...OUR CONFIDENCE IN THE FORECAST IS
HIGH.

PROGRESSIVE SHORT WAVE PERTURBATIONS ARE TO POPULATE THE SOUTHERN
STREAM FLOW...WITH A 500 HPA TROUGH TO ENTER THE SOUTHERN CONE
EARLY THIS CYCLE. ANOTHER IS TO FOLLOW...WITH THE LATTER FORECAST
TO REACH THE CONTINENT BY 72-84 HRS. THIS IS TO QUICKLY PULL
ACROSS PATAGONIA IN ARGENTINA TO THE SOUTHWEST ATLANTIC. AT LOW
LEVELS...THESE ARE TO SUSTAIN PROGRESSIVE FRONTS THAT ARE TO
STREAM ACROSS SOUTHERN CHILE-PATAGONIA-LA PAMPA WHILE SUSTAINING
STRONG BOUNDARY LAYER WINDS OF 30-40KT. THIS IS TO ENHANCE
MOISTURE CONVERGENCE OVER SOUTHERN PORTIONS OF CHILE WHERE WE
EXPECT DAILY MAXIMA OF 10-15MM THROUGH 60 HRS. BY 72-84 HRS THIS
INCREASES TO 15-25MM AS THE APPROACHING MID/UPPER LEVEL TROUGH IS
TO ESTABLISH A SUBTROPICAL CONNECTION.

A DEEPER MID LEVEL TROUGH IS TO MIGRATE ACROSS THE EASTERN PACIFIC
TO THE SOUTHERN CONE OF SOUTH AMERICA...REACHING SOUTHERN CHILE BY
120-132 HRS...AND EAST INTO PATAGONIA BY 144 HRS. AT LOW LEVELS
THIS SI TO SUSTAIN A BROAD/DEEP OCCLUDED LOW OFF THE SOUTH COAST
OF CHILE LATER ON DAY 05...WITH ASSOCIATED FRONT TO QUICKLY MOVE
ACROSS SOUTHERN CHILE TO PATAGONIA IN ARGENTINA. THE DEEP TROUGH
IS TO MAINTAIN ITS SUBTROPICAL CONNECTION...ENHANCING MOISTURE
TRANSPORT WHILE FAVORING RAINFALL MAXIMA OF 15-20MM.

NORTH OVER THE CONTINENT...BROAD CELL OF THE SUBTROPICAL RIDGE IS
TO DOMINATE THE UPPER LEVELS...AS IT IS TO CENTER ON A CLOSED HIGH
OVER WESTERN BOLIVIA/SOUTHERN PERU. AN ANTICYCLONICALLY CURVED
SUBTROPICAL JET MAXIMA IS TO BOUND THE SOUTHERN FRINGES OF THIS
RIDGE...WITH AXIS ACROSS NORTHERN CHILE-ARGENTINA-RIO DE LA PLATA
BASIN. THE JET ALOFT IS TO FAVOR A DIVERGENT PATTERN ACROSS
NORTHERN PROVINCES IN ARGENTINA...WHILE ALSO FAVORING GENERATION
OF LEESIDE PERTURBATIONS. AT LOW LEVELS...UNDER INFLUENCE OF EL
CHACO LOW OVER NORTHWEST ARGENTINA...A MOIST NORTHERLY FLOW IS TO
PERSIST ACROSS PARAGUAY TO NORTHERN ARGENTINA/RIO DE LA PLATA
BASIN. MOISTURE IS TO THEN CONVERGE ACROSS URUGUAY/MESOPOTAMIA IN
ARGENTINA TO JUJUY/SALTA TO THE NORTHWEST...WITH PRECIPITABLE
WATER CONTENT TO PEAK AT 50MM OVER THE NEXT FEW DAYS. MOST ACTIVE
CONVECTION IS EXPECTED OVER THE NEXT TWO DAYS...WHEN DAILY MAXIMA
IS TO PEAK AT 25-50MM IN POTENTIALLY SEVERE CONVECTION.
THEREAFTER...DAILY MAXIMA IS TO PEAK AT 20-40MM IN SCATTERED DEEP
CONVECTION.

ALSO AT 200 HPA...AN UPPER LEVEL LOW BOUNDS THE EASTERN FRINGES OF
THE SUBTROPICAL RIDGE...WITH AXIS NORTH ACROSS NORTHEAST BRASIL.
UNDER INFLUENCE OF THE RIDGE TO THE WEST AND SOUTH...THE TROUGH IS
FORECAST TO GRADUALLY AMPLIFY ACROSS THE NORTHEAST TO CENTRAL
STATES OF BRASIL...WITH BROAD AREA OF DIFFLUENCE TO ESTABLISH
ACROSS PARA-AMAZONAS-RORAIMA TO COLOMBIA-ECUADOR/NORTHERN PERU
LATER ON DAY 02/03. DEEP MOISTURE IS TO THEN CLUSTER ALONG THE
EQUATORIAL TROUGH TO THE NORTH. ACROSS NORTHERN AND NORTHEAST
BRASIL THE DAILY MAXIMA PEAKS AT 25-50MM EARLY IN THE CYCLE...BUT
THROUGH 72-96 HRS IT DECREASES TO 20-35MM/DAY. OVER AMAZONAS TO
THE WEST-SOUTHERN COLOMBIA/PERUVIAN JUNGLE THE DAILY MAXIMA IS TO
PEAK AT 20-45MM THROUGH 60 HRS. BY 60-96 HRS THIS INCREASES TO
30-60MM. OVER WESTERN ECUADOR MODERATE TO HEAVY CONVECTION IS
EXPECTED THROUGH 48-60 HRS...WHEN THE DAILY MAXIMA IS TO PEAK AT
20-45MM. BUT THIS THEN DECREASES TO 10-15MM/DAY.

ARREAGA...INAMHI (ECUADOR)
SCHNEIDER...INMET (BRASIL)
DAVISON...WPC (USA)

$$





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