19/802 PM.
Below normal temperatures will continue through the weekend, with a deep marine layer and a few spots of drizzle, 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.
(Fri-Mon), 19/818 PM.
***UPDATE***
A cool but clear evening and night remains on tap. The low clouds cleared in a similar fashion this afternoon as it did yesterday, but is much slower in its redevelopment. Everything points to a similar setup on Saturday as today, but this slow redevelopment is both puzzling and a damper on any low cloud timing and coverage confidence we might otherwise have. Otherwise, the forecast is on track, with well below normal temperatures continuing through the weekend, before temperatures start trending up on Monday. The Extreme Heat Watch remains in effect for portions of Los Angeles County for Tuesday through Thursday. The basis of this hazard is certainly the warmer conditions, but also the potential impacts with so many outdoor events scheduled and the fact that several heat-related illness issues popped up during last weeks events with cooler conditions that next week.
***From Previous Discussion***
June Gloom conditions will continue through this weekend, with model guidance supporting a small weakening of onshore flow and likely a gradual lowering of the marine layer depth as a result. Morning low stratus should continue to push far inland, into many of the valleys, through the weekend with at least moderate or strong onshore flow. Marine layer clouds this morning were similar to yesterday, with cloud tops mostly in the 3000-3500 ft range. Cloud depth and forcing was enough for scattered drizzle across many coastal areas, with measurements up to 0.01-0.04". Hi-res ensembles, which did fairly well identifying the drizzle this morning, support potential for drizzle again Saturday morning favoring primarily areas north of Point Conception and the coastal areas of LA County. The hi-res keeps drizzle over the ocean for Sunday.
Temperatures this afternoon are forecast to be similar to yesterday for most coastal areas and a few degrees cooler for interior valleys, with 60s for the beaches and 70s for most coastal areas away from the beaches. These highs are mostly 5-10 degrees below normal.
A shortwave trough will move through the area this afternoon, imparting a brief enhancement to the southwesterly flow and contributing to the below normal temperatures. With the enhanced southwesterlies, a slight uptick in wind is expected, especially across mountain tops and northeast-facing slopes. A Wind Advisory is in effect this afternoon for western Antelope Valley, where gusts up to 45 mph are possible. Winds will again be quite breezy across the Antelope Valley Saturday afternoon, but not as strong as today, and then winds will calm down further Sunday and Monday as the onshore flow weakens and weak zonal flow develops aloft following today's shortwave.
There will be a small degree of warming this weekend, 1-3 degrees each day, with the zonal flow and lowering marine layer, but afternoon temperatures are forecast to remain below normal. Better warming should then begin on Monday as heights rise over the area with a building high to the southeast. Highs will be closer to daily averages Monday.
(Tue-Fri), 19/200 PM.
Warming temperatures will continue through the middle of next week as high pressure continues to strengthen and spread further over the area. Hgts will slowly rise over the area, with global models still showing hgts peaking around 593-595 dam late-Tuesday or Wednesday, which is about 8-9 dam higher than normal. Hgts of this value will squish the marine layer down to 1000 ft or less which will greatly reduce the amount of low clouds in the vlys. It will, however, strengthen the marine inversion which will make coastal clearing more difficult. Mdt to stg onshore flow will continue although there will be weaker onshore flow to the north in the morning. These onshore gradients and the strong capping inversion will bring plenty of low clouds to the csts and some lower vlys. The marine layer will moderate the cstl warming and only 1 or 2 degrees of warming is likely each day there. For the vlys and further inland areas, however, the absence of a marine layer and building hgts will allow for 3 to 6 locally 8 degrees of warming each day. By Tuesday triple digit heat is likely in the Antelope Vly while the vlys will warm into the upper 80s and lower 90s.
The warmest days will likely be Wednesday and Thursday. Vly temps will likely end up in the upper 80s to mid 90s. There is even a low chance (5-10%) of eclipsing 100 in the San Fernando and Santa Clarita valleys. These abnormally warm temperatures will lead to pockets of moderate HeatRisk for some inland valleys. With the potential for moderate HeatRisk in parts of the LA Basin, and the consideration of the influx of visitors, an Extreme Heat Watch is in effect for next Tue-Thu. This chc of heat warning will be continuously monitored over the next three days.
In addition to the warming temps with the strong high pressure, models point to a decent push of moisture up from Baja CA midweek, with PWATs climbing up to 150% of normal. This moisture flux will increase chances for rain showers and storms (5-10% chance). An increase in mid and upper level clouds may also help alleviate some of the heat impacts.
20/0015z.
At 23Z at KLAX, the marine layer was 3000 ft deep. The top of the inversion was near 4500 ft with a temperature of 19 Celsius.
High confidence in KPMD & KWJF staying VFR with gusty southwest winds.
Moderate confidence in ceilings at all other airports. High confidence in flight categories (MVFR-VFR), with a small chance of brief IFR. Low confidence in timing (+/- 5 hours).
KLAX, High confidence in MVFR ceilings forming tonight. Low confidence in timing (+/- 5 hours). No significant east wind component expected.
KBUR, High confidence in MVFR ceilings forming tonight with slightly stronger than usual onshore winds in the afternoon and evening hours. There is a small chance of brief IFR.
19/806 PM.
Fairly high confidence in winds and seas staying below Small Craft Advisory (SCA) criteria through early next week, but typically gusty winds of 15 to 20 knots will form each afternoon and evening over portions of the nearshore waters as well as around the Channel Islands. Very localized gusts to 25 may be possible at times in those areas.
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.
