Prognostic Meteorological Discussion
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SOUTH AMERICA FORECAST DISCUSSION - INTERNATIONAL DESKS
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1128 AM EST THU JAN 19 2017

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

MODEL DISCUSSION (VALID FROM JANUARY 19 AT 0000 UTC): A BUILDING
MID/UPPER LEVEL RIDGE OVER THE PACIFIC EXTENDS SOUTH ALONG 140W TO
THE POLAR ICECAP. AS THE RIDGE HOLDS TO THE WEST...IT IS INDUCING
THE NORTHWARD AMPLIFICATION OF A TROUGH BETWEEN 120W-70W AND TO
THE SOUTH OF 30S. HIGH AMPLITUDE TROUGH IS TO THEN HOLD THROUGH
THE MEDIUM RANGE PERIOD...MEANWHILE SHEARING SHORT WAVE ENERGY
ACROSS SOUTHERN PORTIONS OF CHILE AND PATAGONIA IN ARGENTINA. AT
LOW LEVELS...THE TROUGH ALOFT SUSTAINS A DEEP OCCLUDED LOW THAT
MOVES TO THE SOUTH-SOUTHWEST OF TIERRA DEL FUEGO LATER TODAY.
THROUGH FRIDAY EVENING THE LOW/TROUGH MEANDERS EAST ACROSS THE
DRAKE PASSAGE/ NORTHERN PORTIONS OF THE ANTARCTIC PENINSULA...TO
NEARLY DISSIPATE ON THE WEDDELL SEA ON SATURDAY. POLAR FRONTS WILL
REVOLVE AROUND THIS TROUGH...WITH ONE TO MOVE ACROSS SOUTHERN
CHILE TO PATAGONIA IN ARGENTINA LATER TODAY. THE BOUNDARY IS TO
THEN MEANDER NORTH ACROSS LA PAMPA/NORTHERN PATAGONIA ON SATURDAY
TO SUNDAY. ACROSS SOUTHERN CHILE THE DEEP TROUGH WILL FAVOR STRONG
BOUNDARY LAYER WINDS DURING THE NEXT 24-30 HRS...WITH
TOPOGRAPHICALLY INDUCED CONVECTION TO AFFECT AREA TO THE SOUTH OF
40S...WITH DAILY RAINFALL MAXIMA TO PEAK AT 05-10MM IN SCATTERED
CONVECTION. THROUGH SUNDAY THIS INCREASES TO 10-15MM AS A
SECONDARY LOW MOVES INLAND OVER SOUTHERN CHILE.

A BROAD CELL OF THE SUBTROPICAL RIDGE LIES TO THE NORTH...WHILE
ANCHORING AT 500 HPA ON TWO CLOSED HIGHS...ONE OVER NORTHWEST
ARGENTINA AND THE OTHER OFF THE NORTH COAST OF CHILE TO CENTER
WEST OF LA SERENA. THIS PATTERN IS TO HOLD THROUGH THE MEDIUM
RANGE PERIOD. SHORT WAVE VORTICES ARE TO STREAM TO THE SOUTH OF
THE MID LEVEL RIDGE...TRACKING ACROSS CENTRAL CHILE INTO
ARGENTINA. AT LOW LEVELS...AN ELONGATED FRONT EXTENDS ACROSS THE
SOUTH ATLANTIC TO SOUTHERN BRASIL-ENTRE RIOS IN ARGENTINA. MID
LEVEL VORTICES WILL INTERACT WITH THIS BOUNDARY TO FAVOR SCATTERED
CONVECTION ACROSS THE BUENOS AIRES PROVINCE/CENTRAL PROVINCES IN
ARGENTINA. CONVECTION IS TO PEAK LATER TODAY RAINFALL MAXIMA OF
15-20MM. ON FRIDAY-SUNDAY THE DAILY MAXIMA IS TO PEAK AT 05-10MM.

EAST OF THE MID LEVEL RIDGE...A SHORT WAVE TROUGH EXTENDS TO THE
NORTH-NORTHWEST ACROSS SOUTHEAST BRASIL TO MATO GROSSO. AS THE
AFOREMENTIONED MID LEVEL VORTICES STREAM ACROSS CENTRAL
ARGENTINA... THEY ARE TO THEN FEED INTO THE SHORT WAVE TROUGH TO
THE EAST. THE INFLOW OF SHORT WAVE ENERGY WILL HELP SUSTAIN THE
TROUGH DURING THE NEXT FEW DAYS. THIS...IN-TURN...WILL PROVIDE THE
DYNAMICAL SUPPORT FOR CONVECTION TO DEVELOP ACROSS SAO PAULO/RIO
DE JANEIRO-MATO GROSSO DO SUL IN BRASIL. ON THE HIGH SIERRA OF SAO
PAULO THE DAILY MAXIMA IS TO PEAK AT 30-60MM THROUGH 36 HRS...AND
20-45MM/DAY THEREAFTER. OVER MATO GROSS/WESTERN SAO PAULO THE
DAILY MAXIMA IS TO PEAK AT 20-35MM OVER THE NEXT COUPLE OF
DAYS...INCREASING TO 20-45MM LATER DURING THE WEEKEND.

AT 200 HPA...THE SUBTROPICAL RIDGE IS TO ANCHOR ON A CLOSED HIGH
THAT IS TO MEANDER BETWEEN NORTHERN CHILE/NORTHWEST ARGENTINA
DURING THE NEXT COUPLE OF DAYS...MEANWHILE ANCHORING A RIDGE OVER
THE CONTINENT TO THE NORTH OF 40S AND WEST OF 55W. ON SATURDAY TO
SUNDAY THE HIGH IS EXPECTED TO MEANDER WEST TO 21N 80W...WHILE THE
RIDGE OVER THE CONTINENT WILL TEND TO WEAKEN. MEANWHILE...THIS IS
TO VENT ORGANIZED DEEP CONVECTION ACROSS CENTRAL-WESTERN PORTIONS
OF BRASIL-PERU-BOLIVIA. MOST ACTIVE IS TO DEVELOP ALONG A SURFACE
TROUGH FROM MATO GROSSO/RONDONIA IN BRASIL TO NORTHERN AMAZONAS TO
THE NORTHWEST. THROUGH FRIDAY MORNING THE MAXIMA IN THIS AREA WILL
PEAK AT 75-125MM. ON FRIDAY AND SATURDAY IT IS TO THEN PEAK AT
40-80MM/DAY WHILE BUILDING NORTH AND WEST INTO CENTRAL/NORTHERN
JUNGLE OF PERU AND EASTERN ECUADOR. THROUGH SATURDAY EVENING THE
MAXIMA DECREASES TO 25-50MM/DAY...WITH MOST INTENSE EXPECTED
ACROSS ACRE/SOUTHERN AMAZONAS IN BRASIL-CENTRAL/NORTHERN JUNGLE OF
PERU AND NORTHERN BOLIVIA. ON THE SIERRA OF PERU DIURNAL
CONVECTION IS TO FAVOR MAXIMA OF 15-30MM EARLY IN THE CYCLE.
THROUGH SATURDAY THIS WILL DECREASE TO 05-10MM/DAY. ACROSS
ECUADOR...THE EVOLVING SUBTROPICAL RIDGE PATTERN WILL SUSTAIN A
SURGE IN CONVECTION ON FRIDAY TO SATURDAY...WHERE AS ENHANCED BY A
DEEP LAYER WESTERLY LOW LEVEL FLOW THE MAXIMA IS TO PEAK AT
50-10MM.

A TUTT WILL BOUND THE EASTERN FRINGES OF THE SUBTROPICAL
RIDGE...WITH UPPER LEVEL AXIS TO MEANDER ACROSS THE NORTHEAST
STATES OF BRASIL. OVER NORTHERN BRASIL THIS IS TO FAVOR SCATTERED
DEEP CONVECTION...WITH MAXIMA OF 30-60MM EXPECTED THROUGH FRIDAY
MORNING...AND 15-20MM/DAY THEREAFTER. OTHER CONVECTION TO THE WEST
IS TO CLUSTER ALONG THE NEAR EQUATORIAL TROUGH OVER NORTHERN
PARA...WHERE THE MAXIMA IS TO PEAK AT 20-30MM/DAY...WITH LOCALLY
HIGHER AMOUNTS EXPECTED ON FRIDAY AND SATURDAY...WHEN MAXIMA IS TO
PEAK AT 20-45MM.

DURAN...SMN (ARGENTINA)
TEPES...DMC (CHILE)
DAVISON/GALVEZ...WPC (USA)
$$





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