Humidity anyone?

WEATHER TIDBITS

The burning question for July must be discussed now that the muggiest

July since -- well, let me refer to the records real quick, let’s

see, 1996 and before that, July 1990 -- is coming to a close.

It’s 4 p.m. on Monday and here are the conditions: skies are

showing convection. Streams of altocumulus are invading the sky with

vertical uplift graduation to cumulonimbus in large numbers now

popping up like exploding popcorn on the Doppler radar. Once this

dense wave of moist unstable air does the orographic run up the

leeward slopes of first the Santa Rosa Mountains then up the chain to

the towering 10,804-foot summit of Mt. San Jacinto, onward into the

Banning Pass. Next stop, the San Bernardinos and if it’s a strong

enough “Sonoran” it’ll make it to the San Gabriels.

So back to the issue at hand -- the humidity. Of course, Tidbitter

has the numbers. Time to compare: the average max-min humidity in

July is 86-50%. This July it’s been 95-72%. Maximum humidity usually

occurs in the pre-dawn hours and minimum is usually around 1 or 2

p.m. in July. The key factor here is the deviation from normal -- 72%

at 2 p.m. instead of the usual 50%.

Then you’ve got the heat index theory becoming a big player.

With the westerlies cut off, the air is more humid and more

unstable sending dew points way up and setting the stage for

thunderstorm production.

Heat index is kind of like wind chill except it goes the other

way.

OK, take the past four summers where the average temp at 2 p.m.

was 76 degrees with humidity at about 50-52% at the same time, it’s a

very comfortable combo, do the math and it feels like 77 degrees and

your clothes aren’t sticking to you 15 minutes after you shower.

Well, this July the average temp at 2 p.m. has been almost 83

degrees with 72% humidity so it feels roughly like 93 degrees and the

dew point has been 69-70 degrees whereas the 76 and 52 combo had a

dew point of only 55 degrees and there’s a coolish west wind which

usually blows till sundown. But with this year, the south and

southeast breezes usually only blow in the morning and usually just

plain die by afternoon making it warm, moist, still and sultry.

Our maximum/minimum air temps for this July surpass the normal by

six degrees.

The instigator or main orchestrator of this most humid July is a

high pressure cell that has taken up residence over and near the Four

Corners region for pretty much the whole month.

Let’s put it this way, that high hasn’t visited Four Corners

region since ’98. This year it’s been totally running the show -- and

it looks like it’s already paid it’s rent for August too! Plus this

high is anchored solid, cause it’s teamed up with strong high cell

over Montana and Idaho. These twin highs are both working every state

from the Continental Divide westward to the whole Pacific Coast up to

Vancouver. The Four Corners high with it’s clockwise air movement

gathers warm, moist unstable tropical air and flings it west and

northwest.

As a result our surface and aloft winds are from the south,

southeast and east, cutting off the prevailing westerly flow, which

has dominated things the past four consecutive summers. The

westerlies are part of the Pacific Maritime Region, thus the air is

drier and more stable. That’s why the past four summers have been

below normal both air and water temps, it would get down to the low

50s out in the canyon on several occasions even in August. This year,

it’s a whole different ballgame. The south and southeast winds are

blowing in from a totally different climatic region. Tropical

maritime which is usually confined to states east of the Continental

Divide, hence our day and night temps increase markedly and so does

the accompanying humidity and more noticeably our local air temps and

ocean temps.

On the home front, this late bulletin the enemy struck last

Saturday and Sunday, and Monday awoke to a shocking 61-degree water

temp, plus the flattest day in three months.

But it was a nice run while it lasted. The stinkin’ westerlies

showed up and spoiled the party.

I didn’t invite ‘em -- hey, southerlies, we need some bulky

bouncers, some gang called the stinkin’ westerlies just crashed our

party. Remove them immediately.

Stay tuned!

* DENNIS McTIGHE is a Laguna Beach resident. He earned a

bachelor’s degree in earth sciences from UCSD and was a U.S. Air

Force weather forecaster at Hickman Air Force Base, Hawaii.