Prognostic Meteorological Discussion
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000
FXSA20 KWBC 281525
PMDSA

SOUTH AMERICA FORECAST DISCUSSION - INTERNATIONAL DESKS
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1125 AM EDT TUE JUL 28 2015

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

MODEL DISCUSSION (VALID FROM JUL 28 AT 0000 UTC): THERE IS GOOD
AGREEMENT AMONG THE GLOBAL MODELS THROUGH THE MEDIUM RANGE PERIOD.
THIS FORECAST IS WELL SUPPORTED BY THE GLOBAL ENSEMBLE MEMBERS...
AS A RESULT FORECAST CONFIDENCE IS HIGH THROUGH 108-120 HRS.
DURING THE SHORT RANGE PERIOD...AS A MID LEVEL TROUGH CROSSES
ARGENTINA...THERE IS A THREAT OF SEVERE CONVECTION ON THE BUENOS
AIRES PROVINCE-ENTRE RIOS-PORTIONS OF URUGUAY...WITH MODERATE TO
HEAVY CONVECTION LIKELY.

A BROAD MID/UPPER LEVEL TROUGH IS TO DOMINATE THE FLOW ACROSS THE
EASTERN PACIFIC-SOUTHERN CONE OF SOUTH AMERICA OVER THE NEXT
THREE.  AS IT MEANDERS OVER THE SOUTHERN CONE...SUCCESSIVE SHORT
WAVE PERTURBATIONS ARE TO REVOLVE AROUND THE LONG WAVE AXIS. THESE
ARE TO FOCUS SHORT WAVE ENERGY AND SUBTROPICAL MOISTURE ACROSS
CENTRAL-SOUTHERN REGIONS OF CHILE. MOST INTENSE IS TO ENTER
CENTRAL CHILE 48-60 HRS....AND ACROSS CENTRAL ARGENTINA BY 78-84
HRS. AT LOW LEVELS THIS IS TO SUSTAIN A BROAD TROUGH ACROSS THE
EASTERN PACIFIC/SOUTHERN CONE...WITH POLAR FRONTS TO STREAM ACROSS
CHILE/ARGENTINA. THESE ARE TO GENERALLY STALL OVER RIO DE LA PLATA
BASIN-CENTRAL CHILE...WHERE IN A NORTHERLY LOW LEVEL FLOW DEEP
MOISTURE IS TO CONVERGE. ACROSS CENTRAL CHILE...INFLOW OF SHORT
WAVE ENERGY ON DAY 02 AND INCREASE IN SUBTROPICAL MOISTURE IS TO
SUSTAIN SCATTERED CONVECTION WITH MAXIMA TO PEAK AT 15-20MM. ON
THE CENTRAL ANDES THIS IS TO FAVOR LIGHT TO MODERATE SNOWFALL
AMOUNTS WITH ACCUMULATION OF 15-20MM. ON THE SOUTHERN REGIONS OF
CHILE THE DAILY MAXIMA IS TO MEANWHILE PEAK AT 05-10MM. OVER
ARGENTINA...MEANDERING SURFACE FRONT IS TO SUSTAIN SCATTERED
CONVECTION ACROSS RIO DE LA PLATA BASIN WITH ACCUMULATION OF
05-10MM/DAY. ON DAY 03...AS MID LEVEL TROUGH PULLS ACROSS THE
CONTINENT AND UNDER FAVORABLE JET DYNAMICS...THIS INCREASES TO
25-50MM IN POTENTIALLY SEVERE CONVECTION.

CONSISTENT WITH PREVIOUS FORECASTS A DEEPENING MID LEVEL TROUGH IS
TO THEN PROPAGATE ACROSS THE EASTERN PACIFIC TO THE SOUTHERN CONE
BY 84-108 HRS. THE TROUGH IS TO THEN GRADUALLY WEAKEN THROUGH 144
HRS AS SHORT WAVE ENERGY SHEARS ACROSS CHILE-ARGENTINA TO THE
WESTERN ATLANTIC. AT LOW LEVELS THIS WILL SUSTAIN A DEEP OCCLUDED
LOW OFF THE COAST OF CHILE BY 84-96 HRS...WITH SYSTEM TO RAPIDLY
PUSH EAST ACROSS CHILE TO PATAGONIA IN ARGENTINA LATER IN THE
FORECAST CYCLE. BY 96-108 HRS THIS IS TO ENHANCE MOISTURE
CONVERGENCE OVER SOUTHERN CHILE BETWEEN CONCEPCION-ISLA DE
CHILOE...TO RESULT IN RAINFALL MAXIMA OF 15-30MM IN SCATTERED
CONVECTION. THROUGH 120-132 HRS THIS INCREASES TO 20-35MM WHILE
SPREADING NORTH INTO CENTRAL REGIONS OF CHILE.

NORTH OVER THE CONTINENT...AT 200 HPA...MODELS CONTINUE TO
FORECAST A NEAR ZONAL WESTERLY FLOW IS TO PREVAIL ON CONTINENTAL
AREA TO THE NORTH OF 10S. THIS IS TO VENT 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
10-15MM/DAY OVER THE NEXT COUPLE OF DAYS...DECREASING TO
05-10MM/DAY THEREAFTER. 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 10-15MM.

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




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