Prognostic Meteorological Discussion
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FXSA20 KWBC 041709
PMDSA

SOUTH AMERICA FORECAST DISCUSSION - INTERNATIONAL DESKS
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
109 PM EDT TUE AUG 04 2015

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

NOTE: RISK FOR WIDESPREAD MODERATE AND LOCALLY HEAVY RAINS IN
CENTRAL CHILE CONTINUES WITH PEAK DEVELOPING BETWEEN WEDNESDAY
EVENING AND FRIDAY EVENING. NOW THERE IS ALSO A RISK LARGE
RAINFALL AMOUNTS IN THE RIO DE LA PLATA BASIN DUE TO THE
PERSISTENCE OF ISOLATED TO SCATTERED HEAVY THUNDERSTORMS STARTING
WEDNESDAY INTO THE WEEKEND NEAR/ALONG SLOW MOVING FRONT. THIS
COULD LEAD TO AREAS WITH RAINFALL ACCUMULATIONS APPROACHING 150MM
IN THREE DAYS. ALSO NOTE THAT THE RISK FOR SEVERE CONVECTION IS
MODERATE ON WEDNESDAY AND ISOLATED RAINFALL TOTALS EXCEEDING MODEL
GUIDANCE ARE POSSIBLE.

MODEL DISCUSSION (VALID FROM AUG 04 AT 0000 UTC): GLOBAL MODELS
AND ENSEMBLE MEMBERS CONTINUE GENERALLY GOOD AGREEMENT THROUGH
108-120 HRS. THE ONLY MODEL MAKING SEVERAL CORRECTIONS IS THE
UKMET. CONFIDENCE ON THE SOLUTIONS OF THE GFS AND ECMWF MODELS IS
HIGH THROUGH 108-120 HRS ON THE LONG WAVE. SOME PROBLEMS ARISE IN
NORTHERN PATAGONIA AND THE SOUTHERN CONE BY 96-108 HRS.

TRANSITION INTO A HIGHLY AMPLIFIED AND SLOW-PROGRESSING LONG WAVE
PATTERN CONTINUES...WITH A LARGE TROUGH TO DOMINATE CHILE/EASTERN
PACIFIC AND A RIDGE TO THE EAST FROM BOLIVIA/PARAGUAY INTO
URUGUAY/SOUTH BRASIL AND THE SOUTH ATLANTIC INTO THE WEEKEND. THIS
WILL LEAD TO MOST ACTIVE CONVECTION CONSTRAINING TO MOST OF CHILE
AND CENTRAL ARGENTINA WHILE SEASONALLY QUIET CONDITIONS DOMINATE
TROPICAL SOUTH AMERICA.

UPPER JETS ARE SETTING NEAR 30S IN THE EASTERN PACIFIC. THIS IS
ALLOWING THE PROGRESSION OF SEVERAL SHORT WAVES ALONG THESE
LATITUDES...SOME OF WHICH WILL PLAY AN IMPORTANT ROLE IN ENHANCING
PRECIPITATION IN CENTRAL CHILE...STARTING WEDNESDAY INTO FRIDAY.
FIRST TROUGH TO ENHANCE ACTIVITY WILL ARRIVE IN SOUTHERN CHILE
LATE ON TUESDAY. THIS TROUGH WILL ARRIVE ACCOMPANIED WITH AN
ELONGATED FRONT AND A SUBTROPICAL MOISTURE CONNECTION TO PRODUCE
MODERATE RAINS BETWEEN TEMUCO AND LOS LAGOS WITH AMOUNTS OF
25-50MM/DAY THROUGH EARLY WEDNESDAY. TROUGH WILL THEN DIG AS IT
MOVES NORTHEASTWARD INTO CENTRAL. AS THE TROUGH DIGS AND SURFACE
FRONT MEANDERS NORTHWARD...A MOISTURE POOL WITH PRECIPITABLE WATER
NEARING 35MM WILL BE DRAWN FROM THE WEST INTO CENTRAL CHILE. THIS
WILL SETUP THE BEGINNING OF THE AFOREMENTIONED HEAVY RAINFALL
EVENT. DURING WEDNESDAY INTO EARLY THURSDAY THE BULK OF THE RAINS
WILL CONCENTRATE BETWEEN CONCEPCION AND CHILLAN/TALCA WITH MAXIMUM
ACCUMULATIONS OF 35-70MM/DAY. HEAVY RAINS WILL START TO AFFECT THE
VALPARAISO REGION LATE ON WEDNESDAY TO PRODUCE MAXIMA OF
20-35MM/DAY BY EARLY THURSDAY. ALSO DURING THIS PERIOD...EXPECTING
MAXIMA OF 20-35MM/DAY BETWEEN TEMUCO AND PUERTO MONTT. BY THURSDAY
INTO EARLY FRIDAY...HEAVIEST RAINS ARE EXPECTED BETWEEN TALCA AND
JUST TO THE SOUTH OF LA SERENA WHERE EXPECTING MAXIMA OF
50-100MM/DAY. NOTE THAT LARGEST ACCUMULATIONS ARE EXPECTED IN
NORTHWESTERN SLOPES DUE TO OROGRAPHIC ENHANCEMENT. TO THE SOUTH
BETWEEN CHILLAN AND VALDIVIA EXPECTING MAXIMA OF 20-35MM/DAY.
AMOUNTS WILL DECREASE DURING FRIDAY. BY FRIDAY INTO EARLY SATURDAY
EXPECTING MAXIMA OF 15-25MM/DAY IN THE COQUIMBO REGION...AND
MAXIMA OF 05-10MM/DAY IN INLAND LOCATIONS BETWEEN THE VALPARAISO
AND LOS LAGOS REGION. MOUNTAIN SNOWFALL IN CENTRAL CHILE WILL ALSO
BE AN ISSUE. EXPECTING HEAVY SNOWFALL TO DEVELOP DURING WEDNESDAY
LEADING TO MAXIMA OF 50-100CM/DAY INTO EARLY THURSDAY ACROSS THE
CENTRAL ANDES. DURING THURSDAY INTO EARLY FRIDAY EXPECTING MAXIMA
OF 100-150CM. AMOUNTS WILL START DECREASING AFTER AS SNOWFALL
SHIFTS INTO THE COQUIMBO/ATACAMA REGIONS WITH DAILY MAXIMA IN THE
ORDER OF 15-30CM.

AS TROUGH AMPLIFIES AND SLOWLY CROSSES THE ANDES INTO
ARGENTINA...THE ADVECTION OF CYCLONIC VORTICITY WILL AID
CONVECTIVE DEVELOPMENT. MOISTURE WILL BE SLOWLY RETURNING AS THE
PATTERN WILL FAVOR DE DEVELOPMENT OF A LOW-LEVEL JET FROM BOLIVIA
SOUTH INTO NORTHERN PATAGONIA AND THE SOUTHWESTERN ATLANTIC.
INITIALLY...EXPECTING STRONG THUNDERSTORMS TO DEVELOP DURING
TUESDAY ALONG A STATIONARY FRONT LINGERING ACROSS RIO GRANDE DO
SUL-SOUTHERN CORRIENTES. THIS WILL PRODUCE ACCUMULATIONS OF
25-50MM/DAY. CONFIDENCE ON THE EXACT LOCATION OF THE STRONGEST
CONVECTION HAS IMPROVED SLIGHTLY WITH RESPECT TO YESTERDAY.
EXPECTING SEVERE THUNDERSTORMS TO DEVELOP IN THE BUENOS AIRES
PROVINCE/LA PAMPA DURING WEDNESDAY TO PRODUCE  MAXIMA OF
25-50MM/DAY DURING WEDNESDAY INTO EARLY THURSDAY. ACTIVE
CONVECTION WILL MEANDER NORTHWARD INTO THE RIO DE LA PLATA BASIN
BY THURSDAY WHERE IT WILL PRODUCE MAXIMA OF 20-45MM/DAY. A NEW
STRENGTHENING IS EXPECTED DURING FRIDAY WHERE MAXIMA IN THE RIO DE
LA PLATA REGION WILL INCREASE TO 30-60MM/DAY. AMOUNTS ARE TO
PERSIST INTO SATURDAY AS SURFACE FRONT MOVES VERY LITTLE INTO
SOUTHERN URUGUAY.

NORTH OVER THE CONTINENT SEASONALLY QUIET PATTERN WILL DOMINATE
THE DOMAIN WITH ACTIVITY CONSTRAINING TO THE NORTHEASTERN COAST OF
BRASIL IN TRADE WIND CONVERGENCE...AND TO THE NORTHERN AMAZON
NORTH OF 02S. EXPECTING LIGHT RAINFALL DEVELOPING ACROSS ESPIRITO
SANTO IN BRASIL ON FRIDAY INTO EARLY SATURDAY NEAR THE TAIL OF A
SURFACE FRONT TO REMAIN GENERALLY OFFSHORE. FOCUS FOR ACTIVITY
WILL MEANDER NORTHWARD TO AFFECT AREAS BETWEEN ESPIRITO SANTO AND
BAHIA ON SATURDAY WITH ISOLATED MAXIMA OF 10-15MM/DAY IN TRADE
WIND CONVECTION.

ROMERO...DMC (CHILE)
FARINA...DMH (PARAGUAY)
GALVEZ...WPC (USA)
$$





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