Fall brings big changes to our Valley weather

Fall is one of the most beautiful times to be in the Valley of the Sun.

After our scorching summer highs at 110 or above, with lows in the 80s and sometimes even 90s, relief finally arrives.

Triple digit heat may stick around for the first week or so of fall, but then temperatures really take a dive.

On average, we only see one triple digit day in October.

October begins with an average high of 94 degrees and ends with an average high of 83.  Lows start out in the low 70s and typically fall to the upper 50s by Halloween.

November brings an even bigger cool down before temperatures even out through December.  Our average high temperature in Phoenix drops from 82 degrees November 1st to only 69 degrees by November 30th with lows dropping from the upper 50s to the upper 40s.

With La Nina intensifying now, we are expecting to see a warmer than usual fall and winter here in the Valley and a drier one too.

Typically, the jet stream starts to shift farther south as we head into fall, bringing Pacific storms through the Great Basin. Those storms, passing to our north, work to dry us out and cool us off. 

Usually by November and December, the jet stream is far enough south to bring Pacific storms right through Arizona dumping rain in the Valley and snow in the high country.

But, when La Nina conditions are present, the jet stream does not dip far enough south for that to happen.  So, the storm track stays to our north and we miss out on the precipitation and the cooler air those Pacific systems bring.

That is exactly what happened last year and what's expected to happen again this year.

Here's a look at how things stacked up last year:

October:

Average High: 88.7 (+1.0 from normal)

Average Low: 66.7 (+4.6 from normal) 

Rainfall: 0.66" (-0.13" from normal)

November:

Average High: 74.7 (-0.3 from normal)

Average Low: 51.3 (+0.9 from normal)

Rainfall: 0.01" (-0.72" from normal)

December:

Average High: 70.4 (+3.3 from normal)

Average Low: 48.7 (+4.8 from normal)

Rainfall:  1.07" (+0.15" from normal)