10/217 AM.
Moderate heat impacts will continue into next week, though there will be slight cooling over the weekend. Monsoonal showers and thunderstorms will be possible starting Sunday. Temperatures will rise again on Tuesday and may reach Major Heat Risk levels, with the monsoonal moisture adding to the discomfort from the heat.
(tdy-Sun), 10/1004 AM.
***UPDATE***
Cooling trends are underway across most of the area today as scheduled. Given these trends, we may be able to trim some areas closer to the coast from the heat advisory, especially for Saturday.
Monsoon shower and thunderstorm potential is on track with a 5-10 percent chance as early as Saturday night, increasing to 10-20 percent chance Sunday into much of next week. Highest probability is across interior Los Angeles and Ventura Counties, however, smaller chances do extend to coastal areas, including Santa Barbara and San Louis Obispo Counties.
***From Previous Discussion***
An upper high just to the SW of LA will slowly drift to the NE through Sunday. By Sunday afternoon it will be over Wyoming. Hgts will slowly fall from about 594 dam to 590 dam during the period. At the sfc there will be mdt to stg onshore flow both to the N and E today and Saturday. Significant offshore trends are forecast for Sunday as the east PAC high weakens.
The marine layer is about 1200 ft deep and the low clouds are much more extensive than they have been over the past few days. Most of the csts will wake up to low clouds and there is a good chance the low clouds will cover some of the vlys as well. The increased marine layer and onshore flow will bring 2 to 4 degrees of cooling to most areas today.
On Saturday the upper high will be to the NE of the state and it will bring SE flow aloft to the area. There will be plenty of mid and high level clouds in this flow and the day will be a partly to mostly cloudy one. The strong onshore push in the afternoon may well keep the majority of the nearshore area covered in low clouds as well. Most max temps will fall another 1 or 2 degrees, but it will not feel any cooling as the humidities will be on the increase.
The SE monsoon flow will increase on Sunday and the mid and high level clouds will continue to flow over the area. There will be strong offshore trends through the day and this will bring complete clearing to the beaches. The monsoon flow will moisten up the lower levels of the atmosphere to bring a 10-20 percent chc of showers or isold TSTM to the mtns of LA and VTA counties. Max temps will not change much as the cooling brought by the cloud cover should be neutralized by the reduction in onshore flow.
(Mon-Thu), 10/217 AM.
The upper high will migrate to South Dakota on Monday and then sit there for a while. It will also strengthen and push hgts over CA up from 590 dam to 594 dam. The onshore flow to the east will increase to mdt-stg on Monday and will no change much through the rest of the week. The N/S gradient is a much trickier call with many different solutions possible ranging from weak onshore to mdt offshore. Pinning down this value will be the key to getting next weeks forecast correct.
The monsoon will continue on Monday with partly to mostly cloudy skies and a 10 to 20 percent chc of showers and isold TSTMs over the mtns. The increase in onshore flow will likely bring another round of morning low clouds although there is a chc that the advection of monsoon moisture may disrupt the marine inversion. Max temps will not change much from Sunday's values and will remain above normal.
The long range mdl consensus is that the monsoon will stop on Tuesday and skies will become mostly sunny. The marine layer and temp forecast begins to get problematic due to the uncertainty in the N/S pressure gradient. Right now it looks like the best bet is for continued onshore flow which means a good chc of morning stratus and only a degree or two of warming due to the increase in sunshine.
Rising hgts and a better chc of weak onshore or even offshore flow in the N/S direction will bring 3 to 6 degrees of warming to most areas. Vly temps will likely range from 95 to 105. A heat watch is in effect to cover the good possibility of these temps.
The mdl consensus points to an increase in onshore flow to the normal next Thursday perhaps a substantial increase. This will likely increase the morning clouds and bring 3 to 6 degrees of cooling to the area. Even with this cooling max temps will remain above normal. The is also a chc of a return of the monsoon with a 10 to 20 percent chc of showers/TSTMs developing over the mtns.
10/1707z.
At 1620z at KLAX, the marine layer was 1500 ft deep. The top of the inversion was around 7300 ft deep with a temperature of 24 C.
High confidence in TAFs for KPMD and KWJF.
Low confidence in TAF for KPRB with a 40 percent chc of LIFR conds 12Z-16Z.
Moderate confidence in the remaining TAFs. Timing of flgt cat changes could be off by +/- 90 min and cig hgt off by +/- 300 ft.
KLAX, Moderate confidence in TAF. MVFR conds could arrive anytime between 03Z and 05Z. High confidence that any east wind component will be AOB 6kt.
KBUR, Moderate confidence in TAF. There is a 20 percent chc of OVC004 conds through 15Z. MVFR conds could arrive anytime between 0900Z and 1100Z.
10/217 AM.
For the outer waters, Small Craft Advisory (SCA) level NW winds are expected to continue subside from south to north through Saturday. Across the far northern outer waters there will be gusts up to 30 knots. Large short period NW seas 8 to 10 feet at 8 seconds will gradually diminish through early next week.
For the nearshore waters along the Central Coast, SCA winds are this afternoon and evening. Otherwise, mainly light winds are then expected through Tuesday morning, then increasing Tuesday afternoon and evening.
For the inner waters south of Point Conception, conditions are expected to remain below SCA levels through the period.
Ca, Heat Advisory remains in effect until 10 AM PDT Tuesday for zones 38-88-343>345-353-368-372-373-375>380-548. (See LAXNPWLOX). Extreme Heat Watch in effect from Tuesday morning through Thursday evening for zones 38-88-341>345-347>358-362-366>376-378>383-548. (See LAXNPWLOX). PZ, Small Craft Advisory in effect from 3 PM this afternoon to 9 PM PDT this evening for zone 645. (See LAXMWWLOX). Small Craft Advisory in effect until 5 PM PDT Saturday for zone 670. (See LAXMWWLOX). Small Craft Advisory in effect until 3 AM PDT Saturday for zone 673. (See LAXMWWLOX).
