I have been on top of Whitney 11 times. 9 out of 11 of those times have been in October (all parts of October too - early, mid and late). I have seen it all with regards to weather during October summits. From 18" of snow at Outpost camp, heavy snow falling at the trail-head, sub-freezing temps (not to mention bone chilling wind chills), white outs less than a mile from the summit, crazy windstorm at trail crest.. all the way to perfect cool sunny weather the entire hike. One time on the summit in mid October, it was 10F with a wind chill that felt like death! Then a year later it was sunny and 50F!!!
So, looking back I can say that out of those 9 times that I have day hiked Whitney, 3 summits have been perfect weather.
What to expect? Well, from my data and experience there will be a 66.7% chance that you will have unfavorable weather.
Keep your eye out for weather by checking the NWS weather link on the left of this page. Be prepared for anything.
Best of luck.
