Thursday, October 11, 2012

entrenched pattern... (pm.11.oct.12)>

Thursday's stats:

Early morning low temp: 59.2F (15.1C)
Afternoon high temp: 70.0F (21.1C)
Rainfall: trace

I think we're all getting pretty used to our recent weather pattern.  Although it's been quite nice, it has become very very predictable.  Sunshine has been dominating the morning hours... with cumulus clouds rapidly developing over the mountains by noon.  Then, isolated thundershower action has been occurring mainly above town during the mid- to late afternoons... with clearing and beautiful sunsets during the evenings.  At my house, humidity has been averaging about 55-60%.

So often I talk about "instability", and I realized yesterday that maybe I should take some time to explain what that important term actually means.  If you are familiar at all with the laws of thermodynamics, you know that warmer air likes to rise, whereas, parcels of colder air will sink.  We say that the atmosphere is "unstable" when there is enough warming of the air mass in the lower levels to force it to rise into relatively colder air aloft.  When that happens, all of the latent moisture in the air condenses out in the form of clouds... and if there is any dynamic circulation in the atmosphere, those clouds will continue developing into thundershowers/storms.  The greater the difference between temperatures at the surface and the mid/upper-levels of the atmosphere, the greater the instability.

Lately, we've had a weak trough of low pressure up around 12-20,000ft, which is the result a persistent pool of colder air up there.  Abundant sunshine has caused the surface to heat up nicely during the first half of the day, thus creating the instability necessary to produce random thundershowers in the mountains.  It appears that this scenario is well-entrenched, with no major changes expected during the coming few days at least.

THURSDAY NIGHT:
becoming mostly clear.  pleasantly cool.
low: 15C (59F)

FRIDAY:
morning sunshine.  some clouds developing by noon, with a thundershower or two in the area during the PM.
high: 21C (70F)

FRIDAY NIGHT:
any clouds giving way to mostly clear skies.
low: 14C (58F)

SATURDAY:
mostly sunny in the morning.  partly cloudy in the afternoon with an isolated thundershower possible.
high: 21C (69F)

SUNDAY:
sunny to partly cloudy skies.  risk of a brief PM thundershower.
morning low: 14C (58F)
daytime high: 21C (69F)

MONDAY:
sunny in the morning.  partly cloudy in the afternoon with a chance of a thundershower.
morning low: 15C (59F)
daytime high: 21C (69F)

TUESDAY:
morning sun giving way to some afternoon clouds.  a period of PM thundershowers possible.
morning low: 16C (60F)
daytime high: 20C (68F)