Need An Average By Year Of An Average By Month

I have a temp_max column and a temp_min column with data for every day for 60 years. I want the average temp for jan of yr1 through yr60, averaged...
I.E. the avg temp for Jan of yr1 is 20 and the avg temp for Jan of yr2 is 30, then the overall average is 25.
The complexity lies within calculating a daily average by month, THEN a yearly average by month, in one statement.
?confused?

Here's the original query.
accept platformId CHAR format a6 prompt 'Enter Platform Id (capital letters in ''): '

SELECT name, country_cd from weather_station where platformId=&&platformId;

SELECT to_char(datetime,'MM') as MO, max(temp_max) as max_T, round(avg((temp_max+temp_min)/2),2) as avg_T, min(temp_min) as min_temTp, count(unique(to_char(datetime, 'yyyy'))) as TOTAL_YEARS
FROM daily
WHERE platformId=&&platformId and platformId = platformId and platformId = platformId and datetime=datetime and datetime=datetime
GROUP BY to_char(datetime,'MM')
ORDER BY to_char(datetime,'MM');

with a result of:

NAME_________________CO
-------------------- --
OFFUTT AFB___________US

MO______MAX_T _____AVG_T__MIN_TEMTP_TOTAL_YEARS
-- ---------- ---------- ---------- -----------
01_________21______-5.31________-30__________60
02_________26______-2.19______-28.3__________61
03_______31.1_______3.61______-26.1__________60
04_______35.6______11.07______-12.2__________60
05_______37.2_______17.2_______-3.3__________60
06_______41.1______22.44__________5__________60
07_______43.3______24.92________7.2__________60
08_______40.6______23.71________5.6__________60
09_________40______18.84_______-2.2__________59
10_______34.4_______12.5_______-8.9__________59
11_________29_______4.13______-23.9__________60
12_________21______-2.52______-28.3__________60