Prognostic Meteorological Discussion
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000
FXSA20 KWBC 071555
PMDSA

SOUTH AMERICA FORECAST DISCUSSION - INTERNATIONAL DESKS
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1155 AM EDT TUE JUL 07 2015

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

MODEL DISCUSSION (VALID FROM JUL 07 AT 0000 UTC): CONFIDENCE IN
THE FORECAST IS HIGH THROUGH 84 HRS...WITH THE GLOBAL AND ENSEMBLE
MEMBERS AGREEING ON THE SHORT RANGE EVOLUTION. THEY...HOWEVER...
DEVELOP TIMING AND AMPLITUDE DIFFERENCES DURING THE MEDIUM
RANGE...WITH THE EUROPEAN MEMBERS FAVORING A STRONGER/DEEPER
TROUGH TO MAKE LANDFALL OVER CENTRAL CHILE THAN WHAT THE GFS
SUGGESTS...WITH THE ENSEMBLE MEMBERS TRENDING TOWARDS THE DEEPER
EUROPEAN MODELS. AS A COMPROMISE...WE MADE ADJUSTMENTS TO THE
GFS...SHOWING A SLIGHTLY DEEPER PERTURBATION TO MAKE LANDFALL.
BUT...NOT AS INTENSE AS FORECASTED BY THE EUROPEAN MODELS.

CONSISTENT WITH PREVIOUS FORECASTS A MID/UPPER LEVEL TROUGH MOVES
ACROSS NORTHWEST ARGENTINA/BOLIVIA TO PARAGUAY-SOUTHERN BRASIL
THROUGH 36-48 HRS. AS IT MOVES ACROSS PARAGUAY TO SOUTHERN BRASIL
THIS IS TO INDUCE HEIGHT FALLS OF 50-75GPM. THIS IS TO ALSO FAVOR
A DIVERGENT PATTERN ALOFT AS A SUBTROPICAL JET MAXIMA ROUNDS THE
BASE OF THE UPPER TROUGH. AT LOW LEVEL THE TROUGH IS INTERACTING
WITH A SURFACE FRONT OVER SOUTHERN BRASIL-BOLIVIA...AND THIS IS TO
FAVOR CYCLOGENESIS OVER PARAGUAY EARLY IN THE CYCLE. THE LOW IS
FORECAST TO RAPIDLY DEEPEN AND GRADUALLY OCCLUDE AS IT MOVES
ACROSS SOUTHERN BRASIL BY 36-48 HRS. THROUGH 84-96 HRS THE LOW IS
TO MIGRATE TO THE SOUTHEAST INTO THE SOUTH ATLANTIC...WHILE
SURFACE FRONT MEANDERS OVER SOUTHEASTERN BRASIL-PARAGUAY.
SCATTERED DEEP CONVECTION IS TO AFFECT CENTRAL
BOLIVIA-PARAGUAY-SOUTHERN BRASIL THROUGH 36 HRS...WITH RAINFALL
MAXIMA TO PEAK AT 30-60MM. SIMILAR AMOUNTS ARE EXPECTED ACROSS RIO
GRANDE DO SUL/SANTA CATARINA IN SOUTHERN BRASIL BY 36-60
HRS...WHERE COUPLED JETS ALOFT ARE TO VENT ORGANIZED CONVECTION.
ACTIVITY IS TO THEN WANE ALONG THE MEANDERING FRONT...WITH A SURGE
IN ACTIVITY EXPECTED BY 96-108 HRS WHEN ANOTHER MID/UPPER LEVEL
SHORT WAVE TROUGH INTERACTS WITH THE FRONT TO SUSTAIN MAXIMA OF
25-50MM IN POTENTIALLY SEVERE CONVECTION.

SIMULTANEOUSLY...PROGRESSIVE SHORT WAVE TROUGH ON THE SOUTHERN
STREAM IS TO MOVE TO THE ANTARCTIC PENINSULA/DRAKE PASSAGE BY
30-360 HRS. AS IT NEARS TIERRA DEL FUEGO THIS IS TO PHASE WITH A
SHORT WAVE TROUGH TO THE NORTH...WITH SYSTEMS TO COMBINE INTO A
DEEP MID LEVEL TROUGH OVER SOUTHERN CHILE/PATAGONIA IN ARGENTINA
BY 36-48 HRS. THIS TROUGH IS TO SUSTAIN A SUBTROPICAL CONNECTION
AS IT NEARS SOUTHERN PORTIONS OF CHILE...WITH MOISTURE TO CONVERGE
BETWEEN ISLA DE CHILOE AND CONCEPCION. THIS IS TO ALSO SUSTAIN
BOUNDARY LAYER WINDS OF 40-45KT ACROSS CENTRAL/SOUTHERN CHILE.
THIS...IN-TURN...IS TO ENHANCE TOPOGRAPHICALLY INDUCED
CONVECTION...TO RESULT IN RAINFALL MAXIMA OF 35-70MM. NOTE THAT
DUE TO ABOVE NORMAL SEA SURFACE TEMPERATURES THERE IS A RISK OF
THUNDERSTORMS AS THE FRONT MAKES LANDFALL OVER SOUTHERN CHILE.
ACROSS PATAGONIA THE DEEP OCCLUDED LOW IS TO ALSO FAVOR SCATTERED
CONVECTION BY 48-60 HRS...WITH ACCUMULATION OF 05-10MM IN MIXED
PRECIPITATION.

FARTHER WEST OVER THE PACIFIC...A 500 HPA LOW NEAR 40S 110W IS TO
ANCHOR A TROUGH BETWEEN 130W-90W. AS IT MEANDERS TO THE
WEST...THIS TROUGH IS TO SHEAR SHORT WAVE VORTICES EASTWARD
TOWARDS THE CONTINENT. DEEP SUBTROPICAL MOISTURE IS TO ACCOMPANY
THESE PERTURBATIONS AS THEY ENTER CENTRAL PORTIONS OF CHILE...TO
FAVOR SCATTERED SNOWFALL OVER THE ANDES. IN THIS PATTERN EXPECTING
A STRONG SHORT WAVE PERTURBATION TO PULL ACROSS 85W BY 72
HRS...AND THROUGH 96-108 HRS IT IS TO REACH CENTRAL PORTIONS OF
CHILE. ALTHOUGH THE GLOBAL MODELS DISAGREE ON INTENSITY OF THIS
PERTURBATION...THEY AGREE ON POTENTIAL FOR ORGANIZED CONVECTION AS
IT ENTERS CENTRAL PORTIONS OF CHILE. FAVORABLE UPPER JET DYNAMICS
ARE TO PROVIDE THE VENTILATION ALOFT TO CONVECTIVE ACTIVITY IN
THIS AREA. THIS WILL COMBINE WITH INFLOW OF SHORT WAVE ENERGY AND
SUBTROPICAL MOISTURE TO FAVOR MODERATE TO HEAVY CONVECTION ACROSS
CENTRAL CHILE ON DAY 05 (FRIDAY-SATURDAY). ACROSS CENTRAL CHILE
THIS IS TO PRODUCE MODERATE TO HEAVY CONVECTION...WITH
ACCUMULATION OF 20-45MM...WHILE OVER THE ANDES EXPECTING SNOWFALL
ACCUMULATION OF 75-150CM.

NORTH OVER THE CONTINENT...AT 200 HPA...A NEAR ZONAL WESTERLY FLOW
IS TO PREVAIL TO THE NORTH OF 10S. IN THIS PATTERN DIURNAL
CONVECTION IS TO CONFINE TO SOUTHERN COLOMBIA-EASTERN
ECUADOR-NORTHERN PERU-NORTHERN AMAZONAS IN BRASIL...WITH RAINFALL
MAXIMA IN TIS AREA TO PEAK AT 10-15MM/DAY. ACROSS PARA-AMAZON
DELTA REGION LESSER AMOUNTS ARE EXPECTED...WITH MAXIMA TO PEAK AT
05-10MM/DAY.

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





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