18/209 AM.
A significant cool down is expected across southwest California through the middle part of the week. Widespread rain is likely Wednesday and Thursday with a slight chance of thunderstorms.
(tdy-Tue), 18/714 AM.
***UPDATE***
No significant changes needed. The forecast remains on track.
***From Previous Discussion***
Today will kick off a 4-5 day stretch of cooling. It will still be quite warm today with pockets of moderate heat risk (NO heat products needed) with widespread highs in the 80s to near 90. The heat will be just a memory by Tuesday with seasonal temperatures in the 70s.
One last morning of decent offshore mountain to canyon winds are anticipated before onshore trends support prevailing afternoon to evening onshore winds with light winds at night by Tuesday as pressure gradients slowly turn onshore.
There is a 20-50 percent chance of night to morning low clouds and fog returning by Monday morning, highest along the Central Coast with more widespread coverage likely by Tuesday morning. Mid to high clouds may be on the increase late Tuesday, a harbinger of our upcoming storm.
(Wed-Sat), 18/452 AM.
Above normal confidence in widespread rain at times Wednesday into Thursday in particular (yes is a bit delayed from earlier thinking). Despite fairly good agreement among guidance, confidence in forecast details remain below normal due guidance historically performing poorly with cut-off closed lows such as this system. Two scenarios remain very much in play.
Scenario 1 (60-70 percent chance): Cold low pressure that passes through the region. This scenario is more dynamic with increased potential for bands of moderate to heavy rain with rainfall totals 0.5-1.5 inches except local 1-3 inches southwest facing mountain slopes and foothills. Los Angeles, Ventura, and southern Santa Barbara County may be on the higher end of these ranges. There is about a 20 percent chance of thunderstorms in this scenario. Flood and debris flow concerns would be enhanced, especially near recent burn scars.
Scenario 2 (20-30 percent chance): The system slows and peaks in intensity far offshore and weakens considerably while moving over southern California or tracks to our south. Rain chances more sporadic and less guaranteed with this scenario with around 0.25 inches of rain (0.5-1 inch in the mountains). The lower totals are related to less near storm dynamics and low pressure to our south inducing weak offshore flow. Historically this type of pattern has cut into rainfall totals, especially near the coast. The risk for thunderstorms or flooding would be MUCH diminished.
Both scenarios would be chilly, especially compared to our current weather pattern with highs only in the 60s and 70s.
By Friday and Saturday, the upper low will have moved eastward. In its wake, weak to moderate offshore flow is likely. So, expect dry and locally breezy conditions along with a warming trend.
Our (CPC) week two (Oct 25-31) outlook favors above normal rain and near normal temperatures. So we may be heading into a pattern supportive of additional rain towards the end of the month.
18/1758z.
At 17Z at KLAX, there was a weak inversion with a base at 2600 ft. The top of the inversion was at 3400 ft with a temp of 21 deg C.
High confidence in VFR TAFs for most airfields. Lower confidence for TAFs at KSBP, KSMX and KLGB due to uncertainties with the timing and extent of low clouds and IFR/LIFR/VLIFR conds late tonight into Mon morning. Timing of onset/dissipation/flight cat changes could be off +/- 1-2 hours.
KLAX, Generally hi confidence in VFR TAF. However, there is a 10-20 percent chance of IFR cigs/vsbys 12Z-16Z Mon. Any east wind component is expected to be 6 kt or less thru the period.
KBUR, High confidence in VFR TAF.
18/831 AM.
Small Craft Advisory (SCA) NW winds will increase this afternoon through late tonight over the outer waters, increasing first in the northern section, with stronger winds pushing southward over the outer waters through around midnight. The SCA winds will persist through Tuesday evening or late Tuesday night. SCA winds may return to portions of the waters Thursday evening. Finally, there is a 40% chance of SCA winds in the western Santa Barbara Channel Monday night (as well as Thursday night).
A moderate-strength storm system is becoming more likely in the Tuesday through Thursday timeframe with a 10-20 percent chance of thunderstorms.
Ca, Beach Hazards Statement in effect through Tuesday morning for zones 354-362-366. (See LAXCFWLOX). PZ, Small Craft Advisory in effect from 3 PM this afternoon to 9 PM PDT Monday for zone 670. (See LAXMWWLOX). Small Craft Advisory in effect from 9 PM this evening to 3 AM PDT Tuesday for zone 673. (See LAXMWWLOX). Small Craft Advisory in effect from midnight tonight to 3 AM PDT Tuesday for zone 676. (See LAXMWWLOX).
