Mongolia has an extreme continental climate and being so far inland with no sea to moderate it, you could be in for a surprise. It is said that Mongolia can experience four seasons in a single day.
The travel season begins in mid-May. Ger camps start opening their doors and more travellers are around to share vehicles. The weather is generally fair although early May can still see snowfall, especially in the north. June weather is fine and generally dry throughout the central and southern regions. The mountains and northern areas can still be cold. July is the time to see the Naadam Festival. Unfortunately, this is also the peak tourist season when Ulaanbaatar's accommodation can become inadequate and city transport load stretched to breaking point. It's a good time to look for travel partners and get out of the city. Gobi temperatures this month can hit above 40°C.
The Mongolian unit of currency is the tögrög (T), which comes in notes of T5, T10, T20, T50, T100, T500, T1000, T5000, T10,000 and T20,000. (T1 notes are basically souvenirs and have practically no monetary value.) The highest-value note the T20,000 is worth around US$15 (as of Jan 2011). Banks and exchange offices in Ulaanbaatar will change money with relative efficiency and no extra commission charges. Banks in provincial centres are also fine; but since they are so remote it's still a good idea to leave the capital with enough cash just in case.