Sprinklers or Not?

Temperatures should be in the 60′s Halloween evening with calm conditions.  Early morning temperatures will continue to dip into the 50s with cool daytime highs (70s) through Friday.  Saturday, another offshore event will begin, raising temperatures.

Next Santa Ana Wind event: Saturday afternoon/evening through Monday (at least).

After a brief, moderate Santa Ana event this past Friday (peak gusts around 25mph for inland Irvine) and a hot weekend (highs near 90F on Saturday), temperatures will cool through the week.  Halloween, highs during the day will struggle to make it into the 70′s with temperatures in the low-60′s Halloween evening.

Offshore flow has started in the Santa Clarita Valley as of Thursday night.  I am calling this a moderate Santa Ana event as I don’t expect the winds to be stronger than 35mph in inland Irvine. Also, this will be a brief event for most Orange County areas with winds subsiding during the afternoon on Friday.  However, very dry and warm conditions will prevail through Saturday.

Outlook: Offshore winds could arrive in OC after midnight and exceed 30mph near the foothills of the Santa Ana Mountains.  Winds should peak around 10am to noon on Friday and decrease during the afternoon hours.  More winds are possible Friday night although not as widespread or fast.    Extremely dry conditions with warm temperatures (mid to upper 80s) will persist for most of OC through Saturday.

Our first moderate Santa Ana event could occur this Thursday night/Friday morning.  Wind gusts could exceed 30mph for inland Irvine (50mph for mountains).  Stay tuned…

Wednesday will be the hottest day of the week.  Temperatures will soar WELL into the 90s for inland Irvine on Wednesday.  Significant warming in the lower atmosphere near the surface relative to Tuesday and a weak offshore flow will combine to bring hot temperatures to the southland on Wednesday.

This morning’s sounding is showing some cooling below 925mb with warming above.  Weak northeasterly winds near the surface with stronger winds aloft.  A trough moving through to our north (Washington state) will flatten the ridge over the west coast on Tuesday.  This will weaken any remaining offshore gradients and allow for a stronger sea breeze during the afternoon hours.

So, high temperatures could be limited to the upper-80s on Tuesday for inland Irvine with an afternoon sea breeze.  Offshore gradients quickly return on Wednesday and Thursday with the possibility for some offshore winds in inland Irvine Wednesday evening/Thursday morning.  Max wind gusts could top 20mph for areas near the foothills Thursday morning.  I expect a jump in temperatures on Wednesday afternoon as well (back into the 90s).

Highs on Sunday reached to 90F for inland Irvine as expected.  Monday could be warmer with highs potentially reaching into the low 90s.

Discussion: Warming has occurred throughout all lower levels on Monday with a weaker surface inversion.  Thicknesses are:

time:12101412_OBS 500-1000mb thick=5705 850-1000mb thick=1404

time:12101512_OBS 500-1000mb thick=5745 Change=40m 850-1000mb thick=1418 Change=14m

Weak easterly winds are observed for all levels below 700mb.  These winds have weakened from Sunday and could allow a stronger sea breeze on Monday.  This could offset some of the warming potential on Monday.  So, expect highs Monday near or above 90F once again.

After a nice cool evening with lows dipping into the low-50s, temperatures will sky-rocket to near 90F for inland Irvine on Sunday.  Monday, temperatures could be warmer!  Offshore winds with very dry conditions could reach our location on Thursday morning.

Why the hot temperatures?  We are in the middle of a weak offshore flow which will continue into the week ahead.  In fact, hot temperatures will prevail until Friday with dry conditions.

It may not be much, but, as Scott mentioned a few days ago, it does look like we will get a dusting of rain here in Southern California today! A spinning upper low off the coast has been inching closer all week, and a quick look at the radar today reveals some showers spreading into the area:

The showers are VERY convective in nature – that is, they are being fueled mostly by goings-on aloft (very cold air, some vorticity) and will not be as organized as a regular rain event. That means some areas may see a good dumping, while others just see a dusting of rain. We’ll keep our eyes peeled for anything significant. In the meantime, prepare for on-and-off showers throughout the day, with totals across the basin probably anywhere between 0.1-0.25″, but not exceeding 0.5″

-Mike

As mentioned previously, our first rain of the fall could occur this week.  As of now, the rain chances increase on Wednesday evening (drizzle/light rain) through Thursday night (light/moderate rain).  Very cold temperatures will follow on Friday. Welcome fall!

Periods of high clouds are likely on Tuesday for most areas with a stronger onshore flow and mild temperatures.  Partly cloudy skies Wednesday morning with breezy conditions.  Mostly cloudy with showers possible Thursday. Windy conditions are expected on Friday morning and early afternoon.  Stay tuned!