Prognostic Meteorological Discussion
Issued by NWS

Home | Current Version | Previous Version | Text Only | Print | Product List | Glossary On
Versions: 1 2
000
FXSA20 KWBC 231903
PMDSA

SOUTH AMERICA FORECAST DISCUSSION - INTERNATIONAL DESKS
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
202 PM EST THU FEB 23 2017

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

MODEL DISCUSSION (VALID FROM FEBRUARY 23 AT 0000 UTC): GLOBAL
MODELS AND ENSEMBLE MEMBERS ARE IN AGREEMENT THROUGH 84-96 HRS.
FORECAST CONFIDENCE DECREASES GRADUALLY AFTER...ESPECIALLY TO THE
SOUTH OF 40-45S.

PREVIOUSLY ACTIVE PATTERN IN SOUTHERN CHILE IS EVOLVING INTO A
MORE QUIET ONE UNDER THE INFLUENCE OF A BUILDING RIDGE OVER THE
EASTERN PACIFIC. YET...EXPECTING DIURNAL CONVECTION TO PERSIST IN
HIGH ELEVATIONS OF THE CORDILLERA FROM CENTRAL CHILE NORTH INTO
THE ALTIPLANO. ENHANCED INSTABILITY IN THE REGION WILL SUSTAIN
MAXIMUM ACCUMULATIONS OF 10-15MM/DAY...ESPECIALLY ON THE
ANTOFAGASTA AND ATACAMA REGIONS.

AN UPPER RIDGE IS BUILDING OVER NORTHERN CHILE/CENTRAL ARGENTINA
AND INTO THE SOUTHERN CONE. THIS IS LIMITING THE PASSAGE OF STRONG
PERTURBATIONS AND FRONTS INTO CENTRAL AND NORTHERN PARTS OF
ARGENTINA. TOGETHER WITH POSITIVE SEA SURFACE TEMPERATURE
ANOMALIES ALONG THE RIO DE LA PLATA/URUGUAY AND THE COAST OF
SOUTHERN BRASIL...THIS IS LEADING TO ABOVE AVERAGE TEMPERATURES
ACROSS MOST OF ARGENTINA...AND ELEVATED DEW POINTS IN THE RIO DE
LA PLATA REGION. UNDER LIMITED SYNOPTIC FORCING BUT ENHANCED
LOW-LEVEL INSTABILITY...THE PATTERN IS SUSTAINING ISOLATED TO
SCATTERED AIR MASS THUNDERSTORMS IN THE REGION. THE NEXT PERIOD
WITH ORGANIZED CONVECTION IS EXPECTED ON FRIDAY AS A SURFACE FRONT
APPROACHES THE RIO COLORADO REGION. THIS WILL TRIGGER A FEW STRONG
THUNDERSTORMS THAT ARE TO PRODUCE MAXIMA OF 15-30MM/DAY ACROSS
NORTHERN PATAGONIA INTO LA PAMPA AND THE SOUTHERN BUENOS AIRES
PROVINCE. ACTIVITY IS TO DECREASE ON SATURDAY. THE NEXT ROUND OF
CONVECTION IS EXPECTED ON SUNDAY...WHEN A SHORT WAVE TROUGH
INTERACTS WITH AN UNSTABLE AIR MASS BREEDING IN CENTRAL/NORTHERN
PATAGONIA. THIS WILL SUSTAIN STRONG THUNDERSTORMS THAT ARE TO
PRODUCE MAXIMA OF 25-50MM/DAY. ACTIVITY IS TO DECREASE ON
MONDAY...YET THUNDERSTORMS ARE TO STILL PRODUCE ACCUMULATIONS
PEAKING AT 20-30MM/DAY.

CONVECTION IN SOUTHEASTERN BRASIL IS TO GRADUALLY ACTIVATE DUE TO
THE INFLUENCE OF THE STRENGTHENING BOLIVIAN HIGH/SUBTROPICAL RIDGE
TO THE WEST. THIS WILL UNDULATE/DEEPEN AN UPPER TROUGH THAT WILL
EXTEND ACROSS SAO PAULO/PARANA BY SUNDAY-MONDAY...LYING IN THE
EASTERN PERIPHERY OF THE SUBTROPICAL RIDGE. IN INTERACTION WITH AN
UNSTABLE AIR MASS TO ITS EAST/NORTHEAST...EXPECTING A GRADUAL
INCREASE IN DIURNAL CONVECTION IN THE REGION. THIS WILL LEAD TO
MAXIMA IN THE ORDER OF 25-50MM/DAY BY SUNDAY-TUESDAY.

NORTH ACROSS THE CONTINENT...VERY ACTIVE CONVECTION IS OCCURRING
IN THE WESTERN AMAZON. A SURFACE AND MID-LEVEL LOW CONTINUES
SLOWLY RETROGRESSING ACROSS ACRE/CENTRAL PERU. THIS LOW IS
MODULATING THE EASTERLY TRADES AND PRODUCING SEVERAL REGIONS OF
LOW-LEVEL MOISTURE CONVERGENCE IN THE REGION. AIDED BY UPPER
VENTILATION IN THE NORTHERN PERIPHERY OF THE SUBTROPICAL
RIDGE...EXPECTING DAILY RAINFALL TOTALS IN THE ORDER OF
30-70MM/DAY THROUGH SUNDAY. LARGEST ACCUMULATIONS ARE TO RELOCATE
TO THE NORTH INTO SOUTHERN COLOMBIA/NORTHERN BRASIL FROM SUNDAY
THROUGH TUESDAY.

ALSO IN TROPICAL SOUTH AMERICA...SEASONALLY ACTIVE CONVECTION WILL
CONTINUE ACROSS THE ALTIPLANO AND PERUVIAN/ECUADORIAN ANDES.
ACTIVITY IS FAVORED BY VERY MOIST MID-LEVELS AIDED BY ACTIVE
AMAZONIAN CONVECTION...BY PLENTIFUL MOISTURE IN THE PACIFIC BASIN
IN ASSOCIATION WITH ABOVE-AVERAGE SEA SURFACE TEMPERATURES...AND
ENHANCED UPPER VENTILATION IN ASSOCIATION WITH THE BOLIVIAN
HIGH/SUBTROPICAL RIDGE. EXPECTING RAINFALL ACCUMULATIONS IN THE
ORDER OF 15-30MM/DAY. ANOTHER REGION WITH ACTIVE CONVECTION WILL
CONTINUE BEING THE NORTHERN COAST OF PERU/SOUTHERN ECUADOR...WHERE
ENHANCED CONVECTIVE INSTABILITY IN ASSOCIATION WITH SEA SURFACE
TEMPERATURES EXCEEDING 28C...AND THE ACTIVE SECOND BAND OF THE
ITCZ WILL LEAD TO STRONG EVENING THUNDERSTORMS WITH ACCUMULATIONS
EXCEEDING 50MM ON A QUASI-DAILY BASIS.

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





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