Prognostic Meteorological Discussion
Issued by NWS

Home | Current Version | Previous Version | Text Only | Print | Product List | Glossary On
Versions: 1 2 3 4 5 6 7 8 9
000
FXSA20 KWBC 301101
PMDSA

SOUTH AMERICA FORECAST DISCUSSION - INTERNATIONAL DESKS
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
701 AM EDT THU JUL 30 2015

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

MODEL DISCUSSION (VALID FROM JUL 29 AT 0000 UTC): CORRECTIONS TO
FORECAST PATTERN LIMIT TO MEDIUM RANGE PERIOD...WITH GLOBAL MODELS
MAKING ADJUSTMENTS TO MID LEVEL TROUGH ENTERING THE SOUTHERN CONE.
IN COMPARISON WITH PREVIOUS RUNS...MODELS HAVE BEEN TRENDING IN
FAVOR OF A FASTER EVOLUTION. DURING THIS PERIOD THE VARIABILITY
AMONG THE GLOBAL ENSEMBLE MEMBERS IS HIGH...AND FORECAST
CONFIDENCE IS LOW.

SOUTH OVER THE DOMAIN...BROAD MID/UPPER LEVEL TROUGH EXTENDS
ACROSS THE FAR EASTERN PACIFIC. THIS TROUGH IS TO GRADUALLY SHIFT
ACROSS CHILE TO ARGENTINA THROUGH 36-48 HRS. AS IT MIGRATES INTO
THE SOUTHERN CONE THIS IS TO INITIALLY FOCUS SHORT WAVE ENERGY AND
SUBTROPICAL MOISTURE INTO CENTRAL PORTIONS OF CHILE...WHERE IN
INTERACTION WITH A SURFACE FRONT EXPECTING SCATTERED CONVECTION TO
SUSTAIN MAXIMA OF 15-20MM.

THROUGH 54-60 HRS THE FOCUS OF THE SHORT WAVE ENERGY SHIFTS TO
CENTRAL PROVINCES IN ARGENTINA-RIO DE LA PLATA BASIN...WHERE THE
MID LEVEL TROUGH IS TO SUSTAIN HEIGHT FALLS OF 100-150 GPM. THIS
IS TO THEN RAPIDLY PULL ACROSS THE COAST TO THE WESTERN ATLANTIC
THROUGH 66-72 HRS. AT LOW LEVELS AN OLD/ELONGATED FRONT MEANDERS
WEST ACROSS THE SOUTH ATLANTIC TO RIO DE LA PLATA BASIN-CENTRAL
REGIONS IN ARGENTINA. IN A NORTHERLY LOW LEVEL JET THIS FRONT IS
TO RETROGRESS AS A WARM FRONT ACROSS URUGUAY. PRECIPITABLE WATER
CONTENT VALUE IS TO THEN INCREASE TO 40-50MM BY 42-48 HRS...THIS
IS TO THEN FEED CONVECTIVE DEVELOPMENT LATER ON THURSDAY THROUGH
FRIDAY MORNING. ANOTHER FRONT IS TO SIMULTANEOUSLY APPROACH FROM
THE WEST...TO MOVE TO PATAGONIA-CUYO IN ARGENTINA BY 42-48
HRS...TO SURGE ACROSS URUGUAY TO SOUTHERN BRASIL-NORTHERN
ARGENTINA BY 66-72 HRS. THE LATTER IS TO TRIGGER MODERATE TO HEAVY
CONVECTION ACROSS THE BUENOS AIRES PROVINCE-ENTRE RIOS IN
ARGENTINA/SOUTHERN URUGUAY...WITH BULK OF THE RAINFALL EXPECTED
OVER ARGENTINA WITH MAXIMA OF 30-60MM IN POTENTIALLY SEVERE
CONVECTION. ACROSS SOUTHERN URUGUAY THE MAXIMA IS LIKELY TO PEAK
AT 20-40MM. THROUGH 84 HRS THIS DECREASES TO 05-10MM WHILE
FOCUSING OVER URUGUAY-RIO GRANDE DO SUL. BY 96-108 HRS CONVECTION
IS TO INCREASE AGAIN AS THE FRONT MEANDERS OVER URUGUAY/ENTRE RIOS
IN ARGENTINA...WITH MAXIMA OF 15-25MM.

DEEPENING MID LEVEL TROUGH IS TO THEN LIFT ACROSS THE SOUTHEAST
PACIFIC THROUGH 36-48 HRS...WITH PERTURBATION TO THEN RAPIDLY
DEEPEN AS IT APPROACHES SOUTHERN CHILE BY 72-84 HRS. BUT AS IT
ENTERS THE SOUTHERN CONE THE TROUGH IS FORECAST TO SHEAR EAST
ACROSS SOUTHERN CHILE-ARGENTINA. AT LOW LEVELS THIS IS TO SUSTAIN
A BROAD/DEEP OCCLUDED LOW OFF THE SOUTH COAST OF CHILE BY 60-66
HRS...TO MEANDER EAST ACROSS THE SOUTHERN CONE THROUGH 108 HRS.
THE SLOW TO EVOLVE SYSTEM IS TO FOCUS MOISTURE AND ENERGY ACROSS
SOUTHERN-CENTRAL CHILE. FOCUS OF MOST INTENSE IS EXPECTED BETWEEN
CONCEPCION AND ISLA DE CHILOE...WITH MAXIMA OF 15-30MM ON DAY
03...AND 20-35MM ON DAY 04. ACROSS CENTRAL CHILE MOST INTENSE IS
EXPECTED ON DAY 04 WHEN THE MAXIMA IS TO PEAK AT 15-20MM.

AT 200 HPA...A WESTERLY NEAR ZONAL FLOW IS TO ENVELOP CONTINENTAL
AREA TO THE NORTH OF 10S. THIS PATTERN IS TO REMAIN UNCHANGED OVER
THE NEXT FIVE DAYS. THIS WILL CONTINUE VENTING DIURNAL CONVECTION
ACROSS EQUATORIAL SOUTH AMERICA...WITH MOST INTENSE OVER NORTHERN
AMAZONAS IN BRASIL-SOUTHERN AMAZONIA IN COLOMBIA-NORTHERN JUNGLE
OF PERU TO EASTERN ECUADOR. RAINFALL MAXIMA IS TO PEAK AT
15-20MM/DAY EARLY IN THE CYCLE...TO THEN DECREASE TO 05-10MM/DAY
ON THURSDAY AND ONWARD. OVER NORTHEAST BRASIL...TRADE WIND
EASTERLY CONVERGENCE IS TO ENHANCE COASTAL CONVECTION BETWEEN
ESPIRITO SANTO AND PERNAMBUCO. MOST ACTIVE IS EXPECTED BETWEEN
SALVADOR AND RECIFE...WITH DAILY MAXIMA OF 15-20MM EXPECTED
THROUGH 36 HRS...AND 05-10MM/DAY THEREAFTER.

CHARPENTIER...DMC (CHILE)
ROMERO...DMC (CHILE)
DAVISON...WPC (USA)
$$




USA.gov is the U.S. government's official web portal to all federal, state and local government web resources and services.