Baghdad in Iraq has an average maximum and minimum temperature in July and August of 43 deg. C. and 24 deg. C. respectively (giving a mean of 34.5 deg. C., about 94 deg. Fahrenheit) so even if the means dropped by 5 deg. C., by British temperatures it would still be extremely hot. These figures are from "Weather to Travel" by Maria Harding, published by "Tomorrow's Guides" in 2001; it does not state which period this refers to.
While I am sure the documents referred to would no doubt be interesting, one should perhaps be wary of reading too much into them, or extrapolating from them about climate in the Middle East or in larger areas during these times.
I think snow has been recorded in Baghdad (certainly in other places in the Middle East and North Africa - I think Tripoli in Libya recorded snow earlier this month) so the fact that it occurred 3 times in 100 years does not necessarily mean that it was more frequent, only that it was considered uncommon enough to be mentioned in the 10th century. Obviously if it was an annual occurrence there would have been no particular reason to mention it. Harding 2001 above states that winters are mild in Southern Iraq but grow colder the further north you go, while Kurdistan (in the north) has heavy snows (the latter of course has mountains, reaching up to over 11,000 feet - see http://en.wikipedia....raq#Geography0.
The average maximum and minimum in Baghdad in December, January and February are 18 deg. C./6 deg. c. (Dec), 16 deg. C/4 deg C. (Jan), and 18 deg. C./6 deg. C. respectively, which is actually only about 2 deg. C. warmer on average for mean temperature in the warmest parts of the British Isles in January. The minimum temperatures would imply that air frost must occasionally occur as it would only need to be 4 deg. C. cooler than normal at night, and presumably ground frost is even more frequent. The average annual rainfall at Baghdad is only 140 mm, with no rain from June to September inclusive.
In Harding (2001) above, equivalent figures for Eilat and Jerusalem in Israel are:
EILAT January 21 deg. C./9 deg. C.; February 23 deg. C./11 deg. C.; June 38 deg. C./24 deg. C.; July 40 deg. C./25 deg. C.; August 40 deg. C./25 deg. C.; December 22 deg. C./11 deg. C.
JERUSALEM January 12 deg. C./4 deg. C.; February 13 deg. C./5 deg. C.; June 28 deg. C./15 deg. C.; July 29 deg. C./15 deg. C.; August 29 deg. C./15 deg. C.; December 14 deg. C./6 deg. C. Eilat has an annual rainfall of 31 mm (maximum 6 mm in December) while Jerusalem has an annual average of 588 mm (maximum 143 mm in December compared with 5 mm at Eilat, with 113 mm in February and 110 mm in December, and none from June to September, as does Eilat). Perhaps surprisingly, the difference in average maxima between Jerusalem and Eilat is actually higher in July and August (11 deg. C.) than in December (8 deg. C.) and January (9 deg. C.). As can be seen from looking at a map, Israel is a smallish country, although Eilat is in the extreme south and Jerusalem in the middle; Eilat lies at an altitude of 40 feet and Jerusalem 2,500 feet (Baghdad is at 110 feet.
Aden in Yemen (10 feet above sea level), which is much further south, has an average maximum and minimum in January of 28 deg. C. and 22 deg. C. respectively, much warmer than Baghdad, but is actually cooler in July than Baghdad (36 deg. C./28 deg. C.). It is even drier with an annual total of only 23 mm, though suprisingly July (5 mm) is the joint wettest month of the year along with January, March and December; August also averages 3 mm but all other months have zero. This all seems a bit strange and if the figures are correct I wonder if they refer to only a few years.