Pattern I've noticed regarding start of monsoon (Phoenix: 2015, schools)

[FirebirdCamaro1220]

Anyone else notice that the monsoon seems to start after 8 consecutive days with highs 104+ with at least 1 of them 109+ (I have).

Last 15 years:

2001=June 16-23 (monsoon started Jun 20)
2002=June 13-20 (monsoon started July 9,but the 80's for lows really kicked off Jun 20)
2003=June 26-Jul 3 (monsoon started July 18, but again, much warmer nights after Jul 3)
2004=June 22-29 (monsoon started July 13, only delayed by a late season trough which dived into the west around 4th of July weekend)
2005=June 19-26 (monsoon started July 18, but there was some subtropical style rain during the Jun 19-26 period)
2006=Jun 1-8 (monsoon started Jul 2)
2007=Jun 13-20 (monsoon started Jul 19)
2008=Jun 13-20 (monsoon started Jul 3)
2009=Jul 3-10 (monsoon started Jun 30)
2010=Jun 16-23 (monsoon started Jul 9)
2011=Jun 21-28 (monsoon started Jul 3)
2012=Jun 16-23 (monsoon started Jul 3)
2013=Jun 1-8 (monsoon started Jul 5)
2014=May 30-Jun 6 (monsoon started Jul 3)
2015=Jun 12-19 (monsoon started Jun 26)

As noted earlier, even if the actual monsoon didn't start right after these waves, they were the start of the "hot mornings" every year except 2004, due to a late season trough of low pressure

[locolobo13]

Not specifically. But have noticed that the higher temps seem to bring in more moisture. More moisture brings in the monsoons. Monsoons lower the temp but now you have higher humidity. Until they drop that moisture somewhere.


Then the sun starts baking the desert again. The temps go higher.. The cycle repeats several times thru the summer.


Maybe I'm wrong. Just seems that way to me.

[ScottsdaleMark]

I really appreciate the thread topic, and the thought / research you put into it.

I don't think you could tie it down to anything as specific as "104 degrees" ... but I do think you need it to get hot before you have any good hope of setting up a monsoonal flow, since generally you need the environment and atmosphere to get heated up, to get that four corners high and, lastly, to get that Mexican moisture moving north.

I don't think the heat is the cause of it, but rather a reflection of the existence of the sort of conditions that occur during the monsoon, e.g. high pressure anticyclone in the region...and the more/longer we have that sort of setup going on, the better the chances of the monsoon kicking off early.

I do think your data shows a number of times where there was no link at all, e.g. 2005-2007 and 2014 there was a delay of basically a full month according to your data. That doesn't mean there's no correlation, though ... just that it isn't a sure fire correlation. Maybe in those cases you had a temporary monsoonal-type setup, but it got disrupted by other weather factors moving through and it took some weeks before a solid monsoonal setup was again established?

[Ponderosa]

The sub tropical high that brings the scorching temps is the engine that drives the monsoon. I worked with an old school (before modeling) meteorologist once who said that it takes three consecutive days of 110 plus for the monsoon to start. He also said that when clouds form over the Bradshaws by 10 am, Phoenix is most likely to see rain. I live by those rules except I have raised the three days of 110 to 115 to reflect higher temps of recent years.

[ScottsdaleMark]

Originally Posted by Ponderosa

The sub tropical high that brings the scorching temps is the engine that drives the monsoon. I worked with an old school (before modeling) meteorologist once who said that it takes three consecutive days of 110 plus for the monsoon to start. He also said that when clouds form over the Bradshaws by 10 am, Phoenix is most likely to see rain. I live by those rules except I have raised the three days of 110 to 115 to reflect higher temps of recent years.

Thanks for this info, that sort of old-school guidance is stuff the layperson can use...whereas the NWS forecast discussions, when they start talking about, "Well, the GFS says..." or "the Euro model predicts..." that's not stuff I can put into practice in my every day life. But I can look at the sky and basic weather data that we all can access, so I appreciate tips like that.

Anyone else have any old schools tips or tricks? I'd love to hear them.

One thing I seem to have learned that I do look out for, you do not want it to be TOO cloudy TOO early...or it won't get hot enough to fire off the good monsoonal storms, and it will be too stable an atmosphere to get all the updrafts/downdrafts that you need to build a big thunderhead. You need relatively clear morning skies to get hot and get the convective winds going up and down and that forms the afternoon clouds.

So I always look for that. I also look to see how tall the clouds are getting and what sort of shape they have, e.g. if they are slanting or changing shape or if they just are billowing straight up. As sometimes that can give a clue to it there are different winds at different altitudes, I believe.

<One thing I do find interesting is the occasional -- and seemingly increasingly rare -- morning showers you sometimes get during the monsoon. Those seem to happen so rarely anymore that I don't have much of a grasp on them but it's always nice to start the day with rain.>

[FirebirdCamaro1220]

Originally Posted by Ponderosa

The sub tropical high that brings the scorching temps is the engine that drives the monsoon. I worked with an old school (before modeling) meteorologist once who said that it takes three consecutive days of 110 plus for the monsoon to start. He also said that when clouds form over the Bradshaws by 10 am, Phoenix is most likely to see rain. I live by those rules except I have raised the three days of 110 to 115 to reflect higher temps of recent years.

If you used 115, then 1999,2002,2004&2010 wouldn't have had a monsoon per logic, and in 2001,2009 and 2014 the monsoon started prior to the 1st 115

[ajonesaz]

Originally Posted by FirebirdCamaro1220

As noted earlier, even if the actual monsoon didn't start right after these waves, they were the start of the "hot mornings" every year except 2004, due to a late season trough of low pressure

Hot mornings are because of the increased dew point and humidity, which is the moisture working its way up from the South. Because we aren't cooling off as much, days can get hotter too. The old school way of determining the start of monsoon season is 3 days of a dew point higher than 55

[FirebirdCamaro1220]

Originally Posted by ajonesaz

Hot mornings are because of the increased dew point and humidity, which is the moisture working its way up from the South. Because we aren't cooling off as much, days can get hotter too. The old school way of determining the start of monsoon season is 3 days of a dew point higher than 55

That is the measure I used, I don't like the new 6/15-9/30, I still use the 3 days DP 55+, for the end of the monsoon, there was never a consensus (though some sources used 3 days DP 54 or lower), I consider the end of the monsoon 5 days with DP 49 or lower AND 3 days with morning lows below 75

[BIG CATS]

Monsoon season begins when there is a certain number of days with a dew point of a certain degree or higher. Youll have to forgive me as I dont remember the specifics. Hence the reason it varies every year.

[Ponderosa]

One of the heralds of monsoon that I have noticed is the singing of the cicadas and the flight of the big black bugs. I haven't heard or seen either this year yet, though all my neighbors douse everything with pesticides so that might be the reason.