20/229 PM.
Below normal temperatures will continue through the weekend, with a deep marine layer, as well as gusty winds over the interior. A significant warming trend will start Monday and peak around Wednesday. A push of moisture midweek will bring at least a low chance for rain.
(Sat-Tue), 20/905 PM.
***UPDATE***
Marine layer clouds were fairly widespread for many areas this morning, especially north of Point Conception. However, good clearing allowed for a warming trend today with high temperatures in the 70s to 80s for much of the region. Lower confidence in the coverage of marine layer clouds tonight, and in general thinking the best chance for marine layer clouds will be north of Point Conception. However, a decent inversion still exists, and eddy circulations in the Santa Barbara Channel and south of the Channel Islands could help bolster cloud development. Things still look on track for warming into this coming week as high pressure builds. Current forecast looks on track in general, but decreased the coverage of marine layer clouds and fog slightly.
***From Previous Discussion***
Models are in good agreement showing zonal flow over the area through this weekend before a building strong high pressure to the east-southeast over the Desert Southwest starts nudging into the area during the start of the coming workweek.
Moderate to strong onshore flow is forecast to continue through the short term, through the transition from zonal flow to anticyclonic flow. However, a slight lowering trend of the marine layer depth is anticipated as onshore pressure gradients are forecast to slowly weaken. There were notably less marine layer stratus this morning south of Point Conception, where a noticeable N-NW wind in the cloud motions was present. Hi-res guidance indicates similar conditions can be expected again Sunday and Monday, but with the weakening onshore flow, the marine stratus should exhibit a decrease in areal extent tonight through at least Monday. Other than the marine layer stratus, skies should remain mostly clear through Monday.
As for temperatures today, midday temperatures were running 5-10 degrees warmer than the same time yesterday for many areas, largely due to less morning stratus coverage and quicker clearing. Overall though, highs this afternoon should be within a few degrees of yesterday. For Sunday, all areas will see a few degrees of warming, especially away from the coast. The area-wide warming trend will continue Monday and Tuesday, as the ridge noses in, with coastal temperatures in the 70s and inland areas topping out in the 80s and 90s.
As for winds, the strong onshore pressure gradients will continue to generate gusty southwesterly winds across interior sections in the afternoon and evening hours. However, at this time, expect any advisory-level gusts to remain localized in the Antelope Valley foothills. So, no wind products are expected at this time.
(Wed-Sat), 20/228 PM.
For the extended, models continue to exhibit good synoptic agreement. At upper levels, high pressure, over Arizona and New Mexico, peaks in strength on Tuesday then gradually weakens Wednesday through Friday. At the surface, moderate to strong onshore pressure gradients will continue with some continued weak northerly offshore gradients.
Forecast-wise, main concern in the extended will be the heat. With H5 heights peaking Tuesday and 925mb temps peaking Wednesday, the warmest temperatures in the forecast are expected to be on Tuesday and Wednesday, with guidance still continuing the heat through Thursday. High temperatures Tuesday through Thursday are forecast around 3-6 degrees above seasonal normals for coastal areas and 5-10 degrees above normal for valleys/interior sections. For Wednesday, there will also be an increase in mid-level moisture which may add to the heat impact and stress. A gradual cooling trend is likely to begin on Thursday or Friday. Widespread Minor and areas of Moderate Heat Risk is expected with the forecast temperatures midweek with a slight improvement into the end of the week. Given the influx of visitors to the area and plenty of outdoor activities, will continue with the Extreme Heat Watch for the Los Angeles county valleys and mountains.
Secondary concern for the extended forecast will be the potential for some precipitation on Wednesday. Ensembles indicate increasing PWATs (100-150% of normal) moving into the area on Wednesday, with high chances of PWATs greater than 1.00 inch. However, most of this moisture looks to be confined to 700 mb and above and the best moisture may stay just east and southeast of the area. So, at this time, there is a 5-15% chance of showers/high based thunderstorms on Wednesday just about anywhere, but with best chances over the higher terrain. This will need to be monitored closely over the coming days.
21/0410z.
At 0400Z at KLAX, the marine layer was 1200 feet deep. The top of the inversion was 5000 feet with a temperature of 19 degrees Celsius.
For the 06Z TAF package, high confidence in KSBA, KBUR, KVNY, KPMD and KWJF.
For all other sites, low to moderate confidence in 06Z TAF. There is a 40-50% chance that CIG restrictions do not develop overnight. Additionally, if CIGs do develop, equal chances of IFR or MVFR levels.
KLAX, Low confidence in 06Z TAF. There is a 40% chance that CIGs do not develop Sunday morning. If CIGs do develop, there are equal chances of IFR or MVFR CIGs. No significant easterly wind component is expected.
KBUR, High confidence in 06Z TAF as CAVU conditions are expected through the period.
20/914 PM.
High confidence in the winds and seas remaining below Small Craft Advisory (SCA) criteria into the middle of the week. Localized gusty winds up to 25 kts are possible in the western Santa Barbara channel tonight. The typically gusty winds of 15 to 20 kts are expected each afternoon and evening over portions of the waters Sunday and Monday, mainly between Point Conception to San Nicolas Island and into the western SBA Channel. There is a 40% chance they become widespread enough to warrant a SCA.
Ca, Extreme Heat Watch in effect from Tuesday morning through Thursday evening for zones 88-368-372-373-379-380-548. (See LAXNPWLOX). PZ, NONE.
