In Paraguay, the climate is subtropical, with very mild winters from mid-May to mid-August (dry in the north-west and rainy in the south-east), and long hot summers, from November to March, with possible showers and thunderstorms in the afternoon throughout the country. However, the country is exposed to different air masses, therefore to rapid changes in temperature.
Being in the Southern Hemisphere, the seasons in Paraguay are reversed compared with North America or Europe.
In the northwestern part of the country, sparsely populated, we find the region called Chaco Boreal, ie the northern part of the Gran Chaco, a plain occupied by savannah, which extends into neighbouring countries such as Brazil, Argentina and Bolivia, while the central-eastern part is more humid and often marshy. The rains increase proceeding from the north-west to the south-east: the Gran Chaco is the driest area, where precipitation drops below 1,000 millimetres (40 inches) per year, while the rainiest area is that of the Paraná River, covered by forest, where the annual precipitation approaches 2,000 mm (80 in).
The main differences in rainfall are found in winter, which is dry in the Chaco, while in the south-east of the country it's rainy; so the south-east, being rainy even in winter, has no dry season. During winter, in fact, the eastern and southern part of the country are affected by weather fronts, which usually spare the north.
Although winter in Paraguay is mild, the country, especially in the south, may be affected by cold air outbreaks from May to September (the cold wind blowing from Argentina is called Pampero), which can lead to nighttime temperatures around freezing (0 °C or 32 °F), but sometimes also a little below. In Paraguay, however, snow is virtually unknown, and daytime temperatures are mild even in these circumstances.
Paraguay is exposed throughout the year also to warm air masses, which can bring warm days even in winter, with peaks above 30 °C (86 °F). During summer, however, the heat is permanent, although it is generally torrid in the north-west, with peaks above 40 °C (104 °F), and more humid (therefore more uncomfortable) in the eastern and southern regions.
As we can see from the mean temperatures of Mariscal Estigarribia, the Gran Chaco is really hot in summer, and it's still warm in winter, at least during the day.
Average temperatures - M. Estigarribia

M. Estigarribia	Jan	Feb	Mar	Apr	May	Jun	Jul	Aug	Sep	Oct	Nov	Dec
M. Estigarribia	J	F	M	A	M	J	J	A	S	O	N	D
Min (°C)	23	22	22	19	16	14	13	14	17	20	21	22
Max (°C)	35	35	33	30	27	25	26	29	31	34	34	35
Min (°F)	73	72	72	66	61	57	55	57	63	68	70	72
Max (°F)	95	95	91	86	81	77	79	84	88	93	93	95

As mentioned, in this northern area the rainfall is lower than 1,000 mm (40 in) per year, and winter is dry. Here is the average rainfall.
Average precipitation - M. Estigarribia

M. Estigarribia	Jan	Feb	Mar	Apr	May	Jun	Jul	Aug	Sep	Oct	Nov	Dec	Year
M. Estigarribia	J	F	M	A	M	J	J	A	S	O	N	D	Y
Prec. (mm)	130	95	140	75	40	25	10	15	20	55	95	120	825
Prec.(in)	5.1	3.7	5.5	3	1.6	1	0.4	0.6	0.8	2.2	3.7	4.7	32.5
Days	8	6	8	6	5	3	2	2	3	5	7	7	62

In the far north, near the border with Bolivia, the average daily temperature rises above 20 °C (68 °F) even in the coldest months, so that the climate can be called tropical.
In the east, the city of Pedro Juan Caballero is less hot in summer and cooler in winter, because it's located at 600 metres (2,000 feet) above sea level.
In the capital Asunción, the average daily temperature goes from 28 °C (82 °F) in January and February, to 18 °C (64 °F) in June and July.
Average temperatures - Asunción

Asunción	Jan	Feb	Mar	Apr	May	Jun	Jul	Aug	Sep	Oct	Nov	Dec
Asunción	J	F	M	A	M	J	J	A	S	O	N	D
Min (°C)	23	22	21	19	16	14	13	14	16	19	20	22
Max (°C)	34	33	32	28	25	23	23	25	26	29	31	32
Min (°F)	73	72	70	66	61	57	55	57	61	66	68	72
Max (°F)	93	91	90	82	77	73	73	77	79	84	88	90

Precipitation amounts to nearly 1,400 mm (55 in) per year, including more than 100 mm (4 in) per month from October to May, while there's a remarkable decrease in winter, when it drops to 40/50 mm (1.6/2 in) per month. In fact, looking at the map above, we can see that the capital is located in the centre of the country, halfway between the north-west which has a dry winter, and the south-east which is rainy also in winter. Here is the average precipitation.
Average precipitation - Asunción

Asunción	Jan	Feb	Mar	Apr	May	Jun	Jul	Aug	Sep	Oct	Nov	Dec	Year
Asunción	J	F	M	A	M	J	J	A	S	O	N	D	Y
Prec. (mm)	145	130	120	165	115	80	40	50	90	130	165	150	1380
Prec.(in)	5.7	5.1	4.7	6.5	4.5	3.1	1.6	2	3.5	5.1	6.5	5.9	54.3
Days	8	7	7	8	7	7	4	5	6	8	8	8	83

In the far south-east, in Encarnación, the temperature is a few degrees lower throughout the year, and as mentioned in this area the rains are more frequent, without a dry season.
Average temperatures - Encarnación

Encarnación	Jan	Feb	Mar	Apr	May	Jun	Jul	Aug	Sep	Oct	Nov	Dec
Encarnación	J	F	M	A	M	J	J	A	S	O	N	D
Min (°C)	21	20	19	15	12	10	10	11	13	15	17	19
Max (°C)	33	32	31	27	24	22	22	24	25	28	30	32
Min (°F)	70	68	66	59	54	50	50	52	55	59	63	66
Max (°F)	91	90	88	81	75	72	72	75	77	82	86	90

In addition, in Encarnación the rains are more abundant, so that they exceed 100 mm (4 in) per month even in winter, and there's no dry season. Here is the average rainfall.
Average precipitation - Encarnación

Encarnación	Jan	Feb	Mar	Apr	May	Jun	Jul	Aug	Sep	Oct	Nov	Dec	Year
Encarnación	J	F	M	A	M	J	J	A	S	O	N	D	Y
Prec. (mm)	155	165	135	175	150	150	105	105	150	215	160	180	1850
Prec.(in)	6.1	6.5	5.3	6.9	5.9	5.9	4.1	4.1	5.9	8.5	6.3	7.1	72.8
Days	9	8	7	8	7	8	7	7	8	10	8	8	95

Despite the thunderstorms, the amount of sunshine in Paraguay is good in summer, while in winter, sunny days alternate with cloudy days. Spring and autumn are rainy as well. However, the rains in countries having a tropical or sub-tropical climate are irregular: weeks may well pass without rain, and then maybe in a few days, heavy showers or downpours can occur, discharging large amounts of water on the ground.
Here are the sunshine hours in Asunción.
Sunshine - Asunción

Asunción	Jan	Feb	Mar	Apr	May	Jun	Jul	Aug	Sep	Oct	Nov	Dec
Asunción	J	F	M	A	M	J	J	A	S	O	N	D
Sun (hours)	9	9	8	8	7	6	6	7	7	8	9	10

The best time to visit Paraguay is from April to October. In fact, summer, from November to March is the sunniest season, but it's uncomfortably hot and has some chance of thunderstorms: it is probably the worst season.
Winter, from mid-May to mid-August, is typically mild or pleasantly warm, and is the driest season in much of the country, except in the south-east, but sometimes it can be a bit cold and windy for a few days; in the south-east, and sometimes even in Asunción, weather disturbances in winter can bring some cloudy and rainy days.
You may therefore prefer spring and autumn (April to mid-May and September-October), at least in Asunción and in the south, bearing in mind that there is a moderate amount of showers and thunderstorms, while in the Chaco, given that in winter there is practically no risk of rainfall, while spring and autumn can be hot as well, if you want to avoid the heat you will have to focus on the period from April to August, or even better, June and July, which are the ones in which hot days are less frequent and intense.


In winter (mid-May to mid-August): clothes for spring and autumn, light for the day, sweater and jacket for the evening. Raincoat or umbrella for the south.
In summer (November-March): lightweight clothes, of natural fibres, sun hat, light raincoat or umbrella, light sweatshirt for the evening in the south.