I have checked the Argentine national official weather forecasting service web-site and extracted/adapted some info that might be useful (see below). The info is for reference (unusual phenomena like for instance a very heavy hail last winter and a snowfall occurred here just one week ago).
 
http://www.smn.gov.ar/?mod=clima&id=30&provincia=Capital%20Federal&ciudad=Buenos%20Aires
 
Extreme Data values (1961-1990 Period)

Statistical Data(1981-1990 Period)

Month    Temperature (°C)    Relative Humidity
(%)    Mean Wind Speed
(km/h)    Number of days with    Precipitation
monthly (mm)
mean Maximum    Mean    mean minimum    Clear sky    Covered sky    Precipitation
Jan    30.4    25.1    20.4    65    11.5    11    6    9    121.6
Feb    28.7    23.7    19.4    70    10.8    11    6    9    122.6
Mar    26.4    21.4    17.0    72    10    13    6    9    153.9
Apr    22.7    17.7    13.7    77    8.9    11    6    9    106.9
May    19.0    14.3    10.3    76    9    9    8    8    92.1
Jun    15.6    11.2    7.6    79    8.4    9    10    6    50.0
Jul    14.9    10.9    7.4    79    9.7    10    10    7    52.9
Aug    17.3    12.7    8.9    74    10.3    9    9    8    63.2
Sep    18.9    14.2    9.9    71    11.7    10    8    7    77.7
Oct    22.5    17.7    13.0    69    11.5    11    7    10    139.3
Nov    25.3    20.6    15.9    68    11.6    10    7    10    131.2
Dec    28.1    23.2    18.4    64    11.8    10    6    9    103.2
 
 
http://www.smn.gov.ar/?mod=clima&id=17
 
October in Buenos Aires city

In October the weather is generally pleasant, with shiny days and fresh or even cold nights. However, in this part of the year sporadic incursions of cold air might occur, associated with frontal systems coming from the south. Following them, the "Pampero", a southwestern fresh and dry wind, might blow for several days. Occasionally these cold fronts can stay in the northern Rio de la Plata, generating low pressure systems that may originate precipitation, which could persist for several days with cloud-cover and strong southeastern winds ("sudestada") over the city.

During this month the mean temperature in Buenos Aires is about 17 degrees Celsius, the maximum-mean 22 and the minimum-mean 13C. Regarding extreme values, the maximum might exceed 30 degrees Celsius (as occurred on last October 24th, 2006) and the minimum might descend to -2 deg. C, as registered on October 2nd, 1911.

Regarding precipitation, the monthly mean rainfall is 119 mm, distributed among 10 days in the month (average). On a daily basis, exceptionally, there might fall more that 80 mm in 24 hours as occurred on Ocober 3rd, 1976 (84 mm).

The mean relative humidity is of about 70%. After October it starts to drop, as well as the mean frequency of foggy days does (which amounts 0.3 days). The average amount of stormy days is 5. That frequency increases in mid spring.

As far as cloud-cover is concerned, in October there are 10 days of cloud-free- and 8 with cloud-covered skies expected (average).

Regarding the mean frequency of strong windy days (=> 43 km/h), this amounts 4 days in the month. The maximum wind intensity may exceed 100 km/h (as occurred in October 1978, when a maximum wind speed of 116 km/h was registered).
 
* * *
Posted via e-mail on July 16, 2007 by:

 
Andrés F. Zakrajsek
Geodesy / Geophysics - Earth Sciences
Instituto Antártico Argentino - Dirección Nacional del Antártico
Cerrito 1248 - (C1010AAZ) Buenos Aires - Argentina
Phone: +54 11 4812 6313     Fax: +54 11 4813 7807
E-mail: afz@dna.gov.ar          afz@mail.abaconet.com.ar