National Weather Service Weather Forecast Office

• Home
• Site Map
• News
• Organization
• Search for: NWS All NOAA 

000
FXSA20 KWBC 231604
PMDSA

SOUTH AMERICA FORECAST DISCUSSION - INTERNATIONAL DESKS
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1204 PM EDT THU MAY 23 2013

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

MODEL COMPARISON (VALID FROM 00 UTC MAY 23): MODELS ARE IN
EXCELLENT AGREEMENT IN FORECAST EVOLUTION THROUGH THE CYCLE.
FORECAST CONFIDENCE IS HIGH.

LONG WAVE TROUGH OVER THE ANTARCTIC PENINSULA HAS SEVERAL SHORT
WAVE VORTICES REVOLVING RAPIDLY AROUND MAIN AXIS. THIS WILL LEAD
TO WINDY SHOWERY CONDITIONS ACROSS THE SOUTHERN CONE EARLY UN THE
CYCLE. FURTHER NORTH...RAINFALL WILL CLUSTER BETWEEN PUERTO MONTT
AND TEMUCO WITH ISOLATED MAXIMA PEAKING AT 10-15MM/DAY.

MODELS CONTINUE FORECASTING LONG WAVE RIDGE BUILDING OVER THE
EASTERN PACIFIC THROUGH MID CYCLE. THIS WILL HELP AMPLIFY LONG
WAVE TROUGH TO THE EAST. AT LOW LEVELS...THIS WILL SUSTAIN A DEEP
POLAR TROUGH OVER THE WESTERN ATLANTIC WITH ASSOCIATED FRONT TO
RACE ACROSS RIO DE LA PLATA TO URUGUAY-CORDOBA IN ARGENTINA BY 48
HRS. THROUGH 72 HRS THE FRONT WILL MOVE FARTHER NORTH ACROSS THE
SOUTHERN STATES OF BRASIL TO SAO PAULO-PARAGUAY. AS THE FRONT
SURGES NORTH...A POLAR RIDGE IS TO THEN BUILD ACROSS ARGENTINA.
THIS WILL SUSTAIN A COLD ADVECTIVE PATTERN INTO MID SECTIONS OF
SOUTH AMERICA. ACCUMULATIONS WITH THIS SYSTEM WILL BE GENERALLY
LIGHT...AS HIGH PRECIPITABLE WATER WILL REMAIN BLOCKED TO THE
NORTH OF 10/15S.

TO THE NORTH...A ZONALLY-ORIENTED SUBTROPICAL UPPER JET WILL
DOMINATE MID SECTIONS OF THE CONTINENT. A FEW WEAK PERTURBATIONS
WILL PROPAGATE EASTWARD IN THE REGION ENHANCING ACCUMULATIONS
LOCALLY ALONG PERSISTENT STATIONARY FRONT. INITIALLY...HIGHEST
ACCUMULATIONS ARE EXPECTED ALONG EASTERN RIO DO
JANEIRO/SOUTHEASTERN MINAS GERAIS/SOUTHERN ESPIRITO SANTO...WHERE
EXPECTING MAXIMA OF 15-20MM/DAY THROUGH 36 HRS. AMOUNTS ARE TO
START DECREASING AFTERWARDS LEADING TO 10-15MM/DAY ON DAY 02.
OTHER REGION OF ACTIVATING CONVECTION WILL BE THE BOLIVIAN
YUNGAS/SOUTHEASTERN PERU IN DAY 02...WHERE LOW-LEVEL MOISTURE
CONVERGENCE WILL INTERACT WITH UPPER TROUGH MOVING EASTWARD. THIS
WILL LEAD TO LOCALIZED THUNDERSTORMS WITH ACCUMULATIONS OF
15-20MM/DAY BY 36-60 HRS.

ALONG TROPICAL SOUTH AMERICA...EXPECTING A REACTIVATION ACROSS THE
NORDESTE ASSOCIATED WITH INCREASING LOW-LEVEL EASTERLIES AND UPPER
VENTILATION. EXPECTING MAXIMA OF 15-20MM/DAY INCREASING TOWARDS
DAY 04 BETWEEN SALVADOR/MACEIO NORTHWARD INTO NATAL AND FORTALEZA.
OTHER REGION OF ACTIVE CONVECTION WILL BE AMAPA/GUIANAS ON DAY
01...AS TROPICAL WAVE ARRIVES. EXPECTING ACCUMULATIONS OF
20-40MM/DAY. FURTHER WEST...SEASONALLY QUIET PATTERN WILL
DOMINATE. MODELS ARE STILL REFORMING SUBTROPICAL HIGH OVER THE
WEST/CENTRAL AMAZON BASIN. THIS SHOULD VENTILATE A FEW STORMS OVER
ECUADOR/COLOMBIA AND NORTHWESTERN BRASIL. EXPECTING ACCUMULATIONS
IN THE 15-30MM/DAY RANGE IN ISOLATED TO SCATTERED DIURNAL STORMS.

A SYSTEM OF CONCERN IS A POTENT TROUGH ESTABLISHING OVER THE
EASTERN PACIFIC ON DAYS 04 AND 05. MODELS ARE GAINING CONFIDENCE
ON A DEEP AND SLOW-MOVING SYSTEM. THIS TROUGH WILL BE ACCOMPANIED
BY COUPLED UPPER JETS AND FORMIDABLE DIVERGENCE ACROSS
SOUTH-CENTRAL CHILE INTO NORTHERN PATAGONIA. ALTHOUGH
BOUNDARY-LAYER MOISTURE WILL BE SOMEWHAT LIMITED ACROSS
CHILE...FAVORABLE DYNAMICS AND SLOW DEVELOPMENT/MOTION WILL LEAD
TO MODERATE TO HEAVY RAINS. SO FAR...EXPECTING AMOUNTS IN THE
20-40MM/DAY RANGE ACROSS SOUTH-CENTRAL CHILE BETWEEN
RANCAGUA/CURICO SOUTHWARD INTO PUERTO MONTT ON DAY 05. ADJUSTMENTS
WILL BE NEEDED ONCE THE SITUATION BECOMES MORE CLEAR IN FUTURE
MODEL RUNS. EVOLVING UPPER TROUGH WILL INTERACT WITH LOW-LEVEL JET
AND INCREASING LOW-LEVEL MOISTURE IN MID SECTIONS OF THE
CONTINENT. THIS WILL ACTIVATE DEEP CONVECTION ACROSS PARAGUAY INTO
SOUTHEASTERN BRASIL BY LATE CYCLE. EXPECTING AMOUNTS OF
20-45MM/DAY WITH THIS SYSTEM ON DAY 05.

MAQUEDA...DINAC (PARAGUAY)
SILVA DE SOUZA...INMET (BRASIL)
DAVISON...WPC (USA)
GALVEZ...WPC (USA)
$$