Prognostic Meteorological Discussion
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000
FXSA20 KWBC 301431
PMDSA

SOUTH AMERICA FORECAST DISCUSSION - INTERNATIONAL DESKS
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1030 AM EDT THU MAR 30 2017

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

MODEL DISCUSSION (VALID FROM MARCH 30 AT 0000 UTC): OVERALL
CONFIDENCE IN THE FORECAST IS HIGH THROUGH 96 HRS...WITH GLOBAL
MODEL GUIDANCE THEN DIVERGING ON HOW SHORT WAVE TROUGH ENTERING
THE SOUTHERN CONE IS GOING TO EVOLVE. IN THIS AREA CYCLE-TO-CYCLE
INCONSISTENCIES ABOUND...WITH ENSEMBLE MEMBERS FAILING TO REACH A
CONSENSUS.

THE SYSTEM OF CONCERN IS A MEANDERING MID/UPPER LEVEL LOW THAT
LIES OFF THE SOUTHERN COAST OF CHILE....WHILE ANCHORING A TROUGH
OVER THE EASTERN PACIFIC-SOUTHERN CONE OF SOUTH AMERICA. AS IT
PRESSES AGAINST A RIDGE TO THE EAST...THE TROUGH IS TO SHEAR SHORT
WAVE ENERGY ACROSS THE CENTRAL/SOUTHERN ANDES...WHILE ALSO
FOCUSING A POLAR AND A SUBTROPICAL JET ACROSS CHILE TO ARGENTINA.
THE JET ALOFT WILL FAVOR AN UPPER DIVERGENT PATTERN THAT IS TO
VENT CONVECTION. AT LOW LEVELS...THE TROUGH ALOFT SUSTAINS AN
OCCLUDING LOW OVER PATAGONIA IN ARGENTINA AND A FRONT THAT
STRETCHES ACROSS THE CENTRAL PROVINCES TO MENDOZA. THROUGH FRIDAY
EVENING THE OCCLUDED LOW IS FORECAST TO WEAKEN. MEANWHILE...THIS
IS TO FAVOR A MOIST EASTERLY FLOW ACROSS PATAGONIA THAT IS TO FEED
CONVECTIVE DEVELOPMENT. THROUGH FRIDAY MORNING EXPECTING RAINFALL
AMOUNTS OF 30-60MM...DECREASING TO 05-10MM ON FRIDAY TO SATURDAY.
OVER CENTRAL ARGENTINA THE DAILY MAXIMA IS TO PEAK AT 25-50MM OVER
THE NEXT COUPLE OF DAYS...WITH RISK OF SEVERE CONVECTION AS
ENHANCED BY UPPER LEVEL JET MAXIMA. THIS IS TO BECOME BETTER
ORGANIZED/MORE ACTIVE ON SATURDAY...WHEN THE MID LEVEL TROUGH
SPILLS ACROSS THE CENTRAL ANDES INTO ARGENTINA WHILE FAVORING
HEIGHT FALLS OF 50-75GPM. THE INFLOW OF SHORT WAVE ENERGY IS TO
POTENTIALLY FAVOR SEVERE CONVECTION...WITH MAXIMA TO INCREASE TO
30-60MM. ON SUNDAY THIS IS TO RAPIDLY WEAKEN. OTHER CONVECTION IS
TO CLUSTER ON THE NORTHWEST PROVINCES IN ARGENTINA WITH MAXIMA OF
35-70MM THROUGH FRIDAY MORNING. ON FRIDAY TO SUNDAY MORNING IT IS
TO THEN FAVOR RAINFALL AMOUNTS OF 25-50MM/DAY.

PROGRESSIVE MID LEVEL PERTURBATION IS TO THEN ENTER THE SOUTH
AMERICAN DOMAIN LATER ON SATURDAY/EARLY SUNDAY MORNING. AS IT
NEARS SOUTHERN CHILE THIS WILL INTERACT WITH THE TROUGH TO THE
NORTH...AND THROUGH MONDAY MORNING THESE ARE TO COMBINE INTO A
BROAD TROUGH ACROSS THE SOUTHERN CONE. AT LOW LEVELS THIS WILL
SUSTAIN A BROAD TROUGH ACROSS SOUTHERN CHILE AND SOUTHERN/CENTRAL
PROVINCES IN ARGENTINA...WITH POLAR FRONTS TO REVOLVE AROUND THIS
AXIS WHILE FOCUSING MOISTURE ACROSS CHILE SOUTH OF CONCEPCION.
THIS IS TO GENERALLY FAVOR LIGHT CONVECTION WITH ACCUMULATION OF
05-10MM/DAY.

AT 200 HPA...A HIGH OVER BOLIVIA ANCHORS A BROAD CELL OF THE
SUBTROPICAL RIDGE OVER SOUTH AMERICA. RIDGE ALOFT IS TO GENERALLY
HOLD NEARLY UNCHANGED DURING THE NEXT FEW DAYS. LATER DURING THE
WEEKEND...AS THE AFOREMENTIONED TROUGH MOVES EAST ACROSS CHILE TO
ARGENTINA...THE RIDGE IS FORECAST TO FLATTEN TO THE SOUTH OF 35S.
MEANWHILE...THE LONG WAVE RIDGE AXIS OVER THE CONTINENT IS TO
SUSTAIN THE NORTHWARD AMPLIFICATION OF A TROUGH OVER THE WESTERN
ATLANTIC TO THE NORTHEAST STATES OF BRASIL. THE TROUGH SUSTAINS A
MEANDERING FRONT OVER BRASIL...THAT IS TO LIE ACROSS ESPIRITO
SANTO-MINAS GERAIS TO MATO GROSSO/SANTA CRUZ IN EASTERN BOLIVIA.
MOISTURE IS TO CONVERGE ALONG THIS BOUNDARY...TO SUSTAIN SCATTERED
DEEP CONVECTION. EARLY IN THE CYCLE MAXIMA ALONG THIS BOUNDARY IS
TO PEAK AT 20-35MM. BUT...UNDER FAVORABLE JET DYNAMICS ON SATURDAY
AND SUNDAY...EXPECTING CONVECTION TO BECOME BETTER ORGANIZED WITH
MODELS SHOWING RISK OF AN MCS FORMING OVER BAHIA-TOCANTINS/GOIAS.
DURING THAT PERIOD THE DAILY MAXIMA IS TO PEAK AT 40-80MM. OTHER
CONVECTION IS TO CLUSTER ALONG THE NEAR EQUATORIAL TROUGH OVER
NORTHERN SOUTH AMERICA. OVER PARA-AMAPA AND NORTH COAST OF BRASIL
THE DAILY MAXIMA IS TO PEAK AT 15-30MM...WHILE OVER
RORAIMA-AMAZONAS TO NORTHERN JUNGLE OF PERU THE DAILY MAXIMA IS TO
PEAK AT 25-50MM. OTHER CONVECTION IS TO CLUSTER OVER WESTERN
ECUADOR/NORTHERN PERU...WITH MAXIMA OF 75-125MM EXPECTED THROUGH
FRIDAY MORNING. ON FRIDAY TO SATURDAY THIS WILL DECREASE TO
20-45MM...WITH LESSER AMOUNTS ON SATURDAY TO SUNDAY.

ABDEMUR...FAA (ARGENTINA)
TEPES...DMC (CHILE)
DAVISON...WPC (USA)
$$




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