15/237 PM.
Night through morning marine layer clouds will continue for the coast and valleys, shrinking in coverage each day into next week. Cooler than normal temperatures continue through this weekend, then warmer than normal temperatures return next week, with widespread moderate Heat Risk potentially occurring away from the immediate coast.
(Sat-Tue), 15/705 PM.
***UPDATE***
Very minor changes made regarding cloud cover and temperatures in the short-term. Still expecting hot and dry conditions with heat impacts and fire weather concerns starting on Monday. 40-60% chance of heat advisory for portions of the valleys, mountains, and interior coast. Warmest in San Fernando & Antelope valleys where 100 F readings are likely. There is potential for Downtown LA to climb into the 90-95 F range during the Wednesday through Friday timeframe. Otherwise, the forecast remains on track.
***From Previous Discussion***
Weak upper level trough of low pressure off the coast of California today combined with moderate onshore flow has resulted in another deep marine layer this morning, along with cooler than normal daytime temperatures. The marine layer depth was between 2500 and 3000 feet this morning. Other than a few cloud build-ups over the local mountains each afternoon this weekend, looking for all thunderstorm activity to remain well south and east of our area.
The main story over the next seven days is the warming and drying trend, with increasing confidence that heat will likely peak in the Tuesday through Friday time frame. The large area of high pressure will continue to expand west over the next few days, nudging in higher 500 mb heights each day, reaching 596 dm by Tuesday. In addition, we will get slight weakening of the onshore pressure gradient by Monday or Tuesday, along with the marine layer depth becoming more shallow with time. Temperatures are expected to ramp up by Tuesday, when many valley, lower mountain, and desert locations could reach 90-102 degrees, leading to a moderate chance of a heat advisory.
An increase in northwest to northerly winds is likely as soon as Sunday afternoon/evening as the north-south pressure gradient strengthens. We will see increasing gusty winds over southwest Santa Barbara County and interior mountains (especially through the Grapevine) and the Antelope Valley. At this point winds aren't expected to be widespread advisory levels, however, there is a moderate chance for advisory level winds across southwest Santa Barbara County by Monday evening, as the Santa Barbara-Santa Maria gradient is expected to peak around -4 mb. The focus of the winds each evening will be from Gaviota to San Marcos Pass, with isolated gusts up to 45 mph near Gaviota/Refugio on Monday evening.
(Wed-Sat), 15/236 PM.
There is now good agreement amongst models that the upper level ridging will remain over the Western US, bringing hot and dry conditions to Southwest California Wednesday through Friday. Boundary layer temperatures continue to edge upward during this period, with further weakening of the onshore pressure gradients. During this time period, there is increasing confidence that high temperatures will peak in the 93-105 degree range for valleys, lower mountains, and deserts. In addition, the weakening of the onshore gradients will likely allow heat to expand into the inland portions of the coastal plain. Downtown LA will likely climb in the 90 to 95 degree range during this time. With these projected temperatures, there is moderate confidence that heat advisories will be issued for many areas away from the immediate coast at some point between Tuesday and Friday. Ensemble data shows less certainty in the upper level pattern and resultant temperatures for next weekend. There is still the potential for the hot and dry pattern to extend into next weekend, but definitely less confidence than Tuesday-Friday. Overnight lows will also start to warm in the extended period, especially in the foothills and lower mountains, which will add to the heat discomfort.
This long duration of hot and dry weather will bring widespread elevated fire weather conditions away from the coast next week, with the potential for large vertical plume growth across the interior. The marine layer is expected to be fairly shallow,thus dense fog may become an issue in some coastal areas. The north- south pressure gradient will allow for weak to potentially moderate Sundowner winds across southwest Santa Barbara county, with Friday night likely being the best chance for moderate winds. Aside from gusty winds across southwest Santa Barbara County, interior mountains and desert will likely see an uptick in northwest to north winds overnight.
16/0150z.
At 2346Z at KLAX, the marine layer was at 1500 feet deep. The top of the inversion was near 3900 feet with a temperature of 22 C.
High confidence in VFR TAFs for KPMD & KWJF.
Moderate confidence in remaining TAFs. Arrival of CIGs tonight may be off +/- 3 hours and KSBA may remain VFR. Low chance for brief LIFR cigs at KSBP/KSMX/KPRB. There is a 30% chance of IFR conds at KLAX, KSMO, KLGB, KBUR, and KVNY 08Z-16Z Sun.
KLAX, Moderate confidence in TAF. CIG arrival time may be between 05Z-10Z and there is a 30% chance for brief IFR conditions after 08Z. No significant east wind component expected.
KBUR, Moderate confidence in TAF. There is a 30% chance for BKN008 conds 09-15Z Sun.
15/230 PM.
Moderate to high confidence in forecast. There is a 40-60 percent chance of Small Craft Advisory (SCA) level winds developing over the outer waters from near Point Conception southward to San Nicolas Island and in the vicinity of the Channel Islands this afternoon through late night. Further north over PZZ670, there is a 30-40 percent chance of SCA gusts from late this afternoon through late tonight.
There is a better chance of SCA level winds developing Sunday afternoon from near Point Conception and southward over the outer waters, and over the nearshore waters inside the S CA Bight. These nearshore winds are likely to subside early Monday morning, but with SCA winds continuing over the two southern outer zones PZZ673-676. By late Monday afternoon or evening, SCA winds are likely to expand northward to the outer and nearshore waters north of Pt. Sal, and into the Santa Barbara Channel. Local gusts to 25 knots may affect portions of PZZ655 Monday evening.
Strong SCA winds are likely to persist over the outer waters Tuesday and Wednesday, affecting the nearshore areas in the afternoon and evening hours. Local gale force gusts will be possible during this time. In addition, building short period seas are expected, likely rising to around 8 feet over the outer waters.
Ca, NONE. PZ, Small Craft Advisory in effect until 3 AM PDT Sunday for zones 673-676. (See LAXMWWLOX).
