Map from Google - Aragon

In Aragon, autonomous community and province of Spain, there are the following climatic zones:
- the Pyrenean range in the far north, on the border with France, characterized by an alpine climate (cold mountain climate);
- the pre-Pyrenean range to the north, in valleys or slopes at hill or low-mountain altitudes (see Jaca, Bielsa), where the weather is cold in winter and mild in summer, with some hot days, and relatively abundant rainfall;
- all the center-south, at medium-low altitudes, is characterized by an arid or semi-arid climate, and more or less warm depending on altitude, so we have a transitional Mediterranean (slightly continental) climate in the Ebro Valley (see Zaragoza), with quite mild winters, and hot summers, often torrid, while above 600 metres (2,000 feet), there's a semi-continental climate, similar to that of the central plateau (meseta);
- in the center-south, there is a mountain range as well, called Iberian System (Sistema Ibérico): here the climate becomes colder with increasing altitude, while rain (and snow in winter) becomes more abundant, so that the mountains are covered with forests.

Bielsa

In the far north, on the border with France, we find the chain of the Pyrenees; the highest peak of the entire chain, Pico de Aneto, 3,404 metres (11,168 feet) high, is located in Aragon. Above 2,700 meters (9,000 feet) there are glaciers, which are among the most southern in Europe (together with the small Calderone glacier in Abruzzo, Italy, and the glaciers of Caucasus).
In the Pyrenean area we find the Ordesa y Monte Perdido National Park.
In the area at the foot of the Pyrenees, at the same altitude, the climate is cooler than in the south-central region; in addition this area is exposed to cold air outbreaks, with strong winds, in winter.
In Jaca, located at the foot of the Pyrenees, at 800 metres (2,600 feet) above sea level, the average temperature goes from 2.5 °C (36.5 °F) in January, to 17.5 °C (63.5 °F) in July and August, therefore winter is cold, and sometimes there can be heavy snowfalls. Although the averages are not high, in summer there can be some hot days.
Here are the average temperatures.
Average temperatures - Jaca
JacaJanFebMarAprMayJunJulAugSepOctNovDec
JacaJFMAMJJASOND
Min (°C)-2-1136912111062-1
Max (°C)681113162024242016107
Min (°F)283034374348545250433630
Max (°F)434652556168757568615045

In Jaca, 780 millimetres (30.5 inches) of rain or snow fall, well distributed throughout the year, with a maximum in May of 85 mm (3.3 in), and a minimum in July of 45 mm (1.8 in), not very pronounced, since even in summer a few Atlantic fronts can pass, or some thunderstorms can erupt in the afternoon.

In Huesca, located in the center-north, at no great distance from the Pyrenees and at 450 meters (1,475 ft) of altitude, we already enter in the semi-arid zone, with hot summers. Here the average of January is 5 °C (41 °F), that of July and August is 24 °C (75 °F). In winter there can be cold spells, with night frosts, and when the weather is stable, cold and foggy periods may occur; in summer, days with an intense heat are possible, although the air is dry and nights remain cool.
Here are the average temperatures.
Average temperatures - Huesca
HuescaJanFebMarAprMayJunJulAugSepOctNovDec
HuescaJFMAMJJASOND
Min (°C)125610141717141052
Max (°C)9121618222832312620139
Min (°F)343641435057636357504136
Max (°F)485461647282908879685548

In Huesca, 485 mm (19 in) of rain per year fall, with two maxima in spring and autumn, and quite poor rains, but not entirely absent, in winter (when they are a bit more common but not abundant), and in summer (when rare thunderstorms can break out).
Here is the average precipitation.
Average precipitation - Huesca
HuescaJanFebMarAprMayJunJulAugSepOctNovDecYear
HuescaJFMAMJJASONDY
Prec. (mm)303030555535203050605045485
Prec. (in)1.21.21.22.22.21.40.81.222.421.819.1
Days55467433576662

Zaragoza, bridge on the Ebro and basilica

Further to the south, we find Zaragoza, located in the Ebro Valley, 250 meters (820 feet) above sea level, therefore, in the area where the altitude is lower, and the climate can be described as transitional Mediterranean. Here the average temperature goes from 6.5 °C (43.5 °F) in January to 25.5 °C (78 °F) in July and August. In winter, nights are often cold, with possible slight frosts. In summer, hot days are frequent, however, the air is dry, and at night the temperature drops a lot.
Here are the average temperatures.
Average temperatures - Zaragoza
ZaragozaJanFebMarAprMayJunJulAugSepOctNovDec
ZaragozaJFMAMJJASOND
Min (°C)336812161818151163
Max (°C)111317202429323227211511
Min (°F)373743465461646459524337
Max (°F)525563687584909081705952

In Zaragoza, just 330 mm of precipitation fall annually; winter is particularly dry, given that only 20 mm (0.8 in) of rain fall each month.
Here is the average precipitation.
Average precipitation - Zaragoza
ZaragozaJanFebMarAprMayJunJulAugSepOctNovDecYear
ZaragozaJFMAMJJASONDY
Prec. (mm)202020404525201530353020330
Prec. (in)0.80.80.81.61.810.80.61.21.41.20.813
Days44467432355552

The amount of sunshine in Zaragoza is never bad, because some sunny day can occur all year round, although it is better, as happens in Mediterranean climates, in late spring and summer, especially from May to August, when sunny days prevail.
Sunshine - Zaragoza
ZaragozaJanFebMarAprMayJunJulAugSepOctNovDec
ZaragozaJFMAMJJASOND
Sun (hours)467891011108654

East of Zaragoza we find the Monegros Desert (which is actually a semi-desert zone), where rainfall drops below 300 mm (12 in) per year.

Monegros Desert

In the center-south of Aragon the altitude rises again for the presence of the mountain chain called Sistema Ibérico, whose highest point is Moncayo (or San Miguel), 2,314 meters (7,592 feet) high.
In Molina de Aragon, at 1,050 metres (3,450 feet), the average temperature goes from 2.5 °C (36.5 °F) in January to 20 °C (68 °F) in July and August. You can notice the cold nights in the winter months, and the wide temperature range in summer, when nights remain very cool.
Here are the average temperatures.
Average temperatures - Molina de A.
Molina de A.JanFebMarAprMayJunJulAugSepOctNovDec
Molina de A.JFMAMJJASOND
Min (°C)-4-3-11591111740-3
Max (°C)9111416202630292418129
Min (°F)252730344148525245393227
Max (°F)485257616879868475645448

In Molina de Aragon, average precipitation (rain or snow) amounts to 485 mm (19 in) per year, with a peak in spring, and a small amount in winter.
Here is the average precipitation.
Average precipitation - Molina de A.
Molina de A.JanFebMarAprMayJunJulAugSepOctNovDecYear
Molina de A.JFMAMJJASONDY
Prec. (mm)303030557050202550504040485
Prec. (in)1.21.21.22.22.820.81221.61.619.1
Days666910734587777

Further to the south-east, in Teruel, capital of the province, 900 meters (2,950 feet) above sea level, the average temperature goes from 3.5 °C (38.5 °F) in January, to 22.5 °C (72.5 °F) in July.
Here are the average temperatures.
Average temperatures - Teruel
TeruelJanFebMarAprMayJunJulAugSepOctNovDec
TeruelJFMAMJJASOND
Min (°C)-2-21371113131061-1
Max (°C)101216172227313125191310
Min (°F)282834374552555550433430
Max (°F)505461637281888877665550

In an average year, in Teruel 390 mm (15.3 in) of rain fall. The driest season here is even winter.
Here is the average precipitation.
Average precipitation - Teruel
TeruelJanFebMarAprMayJunJulAugSepOctNovDecYear
TeruelJFMAMJJASONDY
Prec. (mm)201520406045254035502520390
Prec. (in)0.80.60.81.62.41.811.61.4210.815.4
Days43478634565559

When to go

The best time to visit the Pyrenees and the valleys at the foot of the mountains is summer, being the warmest (or mildest) and the sunniest of the year.
In areas at low altitude of central and southern Aragon (see Huesca, Zaragoza), since the summer is hot, you may prefer spring and autumn (although the rains are more frequent), especially in May, and from mid-September to mid-October.
Those who can stand the heat can choose July and August also in the center-south, but they should be ready to stroll around the cities in hot weather. Given the high temperature range, except perhaps in Zaragoza, even in the center-south in summer it's better to bring a sweatshirt for the evening.