Area Forecast Discussion
Issued by NWS Los Angeles, CA
Issued by NWS Los Angeles, CA
Versions:
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
770 FXUS66 KLOX 120004 AFDLOX Area Forecast Discussion...UPDATED National Weather Service Los Angeles/Oxnard CA 504 PM PDT Tue Jun 11 2024 .SYNOPSIS...11/205 PM. Low clouds, along with patchy overnight and morning fog, are expected each day through the remainder of this week over coastal areas and coastal valleys. This will result in a wide range of temperatures each day, from the 60s near the coast to the 80s and 90s over the interior areas. Gusty southwest winds are expected over the Antelope Valley through late this week. Winds will turn more northwest to north Friday night into the weekend over much of the area, with moderate to locally strong winds over the higher terrain. Temperatures this weekend will warm by at least a few degrees all the way to the coast, where skies will mostly clear. && .SHORT TERM (TDY-FRI)...11/205 PM. Visible satellite imagery this afternoon indicates marine stratus continuing to remain entrenched over coastal areas and coastal valleys south of Point Conception. This has been supported by continued strong onshore pressure gradients -- around 8-9 mb from LAX to DAG -- maintaining an influx of the marine layer beneath midlevel heights that have increased behind an upper low. Water vapor loops show that the upper low has moved well south- southwest of the region, now centered off the coast of Baja California. From tonight through Wednesday night, the upper low will gradually edge northward before turning more eastward into Thursday, spreading weak height falls over the region. Correspondingly, the marine layer will lift and deepen to some extent through Wednesday night, causing an increase in the coverage of low clouds along with night/morning fog over the coasts and coastal valleys, extending toward some of the nearby foothills. The potential for drizzle will accompany the marine layer Wednesday night into Thursday morning, when midlevel height falls maximize -- albeit still remaining modest in magnitude. With marine stratus likely remaining entrenched over coastal locations, and only partially clearing elsewhere across the coastal valleys and nearby foothills each afternoon, there will be a large range in high temperatures between the coast and interior sections each day through Thursday. These temperatures will range from the middle and upper 60s over the coast, to the 70s over coastal valleys, to the 80s and 90s over the foothills and interior valleys. However, a cooling trend by around 5 degrees is expected across interior locations from Wednesday into Thursday, in response to cooling aloft ahead of the approaching upper low. Later on Thursday, the center of the upper low is expected to come in closest proximity to the forecast area along its eastward track south of the area. This is when cooling aloft will have the greatest chance to erode the top of the inversion surmounting the marine layer, which could disrupt the structure of the marine- layer thermal profile and clear out low stratus over the coasts and coastal valleys. If this were to occur, greater diurnal heating over coastal areas and coastal valleys on Thursday could result in warmer temperatures than currently anticipated -- specifically around a 30% chance of high temperatures reaching into the upper 70s to lower 80s close to the coast. However, continued significant onshore pressure gradients limit confidence in both substantial clearing of marine stratus and significantly warmer temperatures materializing. Then on Friday, the upper low will accelerate east-northeastward toward the central Rockies, with midlevel heights rebounding in its wake. The marine layer will likely remain entrenched at the coasts and coastal valleys, as the inversion aloft is reinforced by rebounding midlevel heights, and onshore pressure gradients continue. Thus, temperature gradients across the forecast area will once again increase -- ranging from the middle 60s close to the coast, to near 100 degrees in the Antelope Valley. Regarding other weather elements, aside from a few areas of afternoon cumulus build-ups over the higher terrain, midlevel tropospheric conditions will be too dry for precipitation development through the period. The onshore pressure gradients will maximize during the afternoon hours, when wind gusts -- generally from the southwest to west-southwest -- could reach 30-40 mph over interior areas, perhaps locally to 45 mph over the Antelope Valley. However, without more appreciable upper support, wind headlines are unlikely at this time through Friday (less than 20% chance). Late Friday will feature the onset of a significant change in the wind pattern across the area, which will also usher in warmer conditions and clearing skies all the way to the coast for this weekend. Also late this week, the southern periphery of enhanced cyclonic flow aloft, south of a compact upper low approaching the Pacific Northwest coast, will begin to graze the region. Surface high pressure, resulting from subsidence upstream of the upper low, will build north of the area causing SBA-SMX and SBA-BFL pressure gradients to transition decidedly offshore Friday night, specifically around 4.0-4.5 mb offshore gradients. Winds will become northwesterly to northerly and strengthen from the Santa Ynez Range and adjacent foothills to the I-5 Corridor vicinity and western Antelope Valley and Foothills. And with modest upper support given enhanced midlevel flow, Wind Advisories will be likely (60-80% chance), and there is a small but non-zero chance for High Wind Watches/Warnings (20% chance) over the Santa Ynez range and surrounding foothills. In addition, the influence of the strengthening offshore flow will cause the marine layer to retreat toward the coast, or even offshore particularly for the Santa Barbara County South Coast, by late Friday night. .LONG TERM (SAT-TUE)...11/205 PM. Offshore flow will continue for the Santa Barbara County South Coast vicinity through a large portion of the weekend, in response to the enhanced offshore pressure gradients being maintained for SBA-BFL and SBA-SMX. Moderate to locally strong northwest to north winds will continue over the higher terrain through at least the first part of the weekend -- enhanced by nocturnal drainage flow during the evening, overnight, and early morning hours. However, gusty winds will likely persist into the daytime hours, aided by the modest upper support. The strongest winds are expected over the Santa Ynez range and surrounding foothills, where High Wind Watch/Warning chances are low but non- zero (around 20% chance) into the weekend. Otherwise, at least Wind Advisories will be likely from these areas through the I-5 Corridor and western Antelope Valley and Foothills into the weekend. Any night/morning marine stratus and fog are expected to clear during the day, especially in areas where offshore flow is strongest -- specifically Santa Barbara South Coast and vicinity. This will correspond to a moderate to strong warming trend on Saturday, with high temperatures reaching the middle 70s to middle 80s across many coastal locations and coastal valleys. Where local sea-breeze circulations form -- such as the beaches around Santa Monica Bay in LA County -- and amid a weak onshore-flow component for SLO County and SBA County Central Coast, high temperatures may only remain in the middle and upper 60s this weekend. Also of note, the combination of the enhanced Sundowner winds and reduced humidity from downslope-flow drying could increase the fire-weather risk this weekend especially in southern Santa Barbara County. Please reference the Fire Weather Planning Forecast for additional information. Through the day Sunday, the trough surrounding the aforementioned Pacific Coast upper low is expected to be amplifying, causing midlevel heights to fall over the forecast area. Corresponding surface pressure falls north of the area will cause offshore pressure gradients to weaken, and temperatures will cool by a few to several degrees going into Sunday -- largest cooling trends over interior sections. Then for early next week, the trough will remain over the area and is expected to lose organization, as the associated upper low moves well north of the CONUS. Offshore gradients pressure gradients are expected to be further weakening, though light to locally moderate northwest to north winds will continue over many interior areas, with diurnally-enhanced onshore winds returning to most coastal areas and vicinity. This will have the potential to bring more widespread marine stratus and fog, along with cooler temperatures, for coastal locations and coastal valleys early next week. && .AVIATION...12/0003Z. At 2300Z at KLAX, the marine layer was 1700 ft deep. The top of the inversion was at 3900 ft with a temperature of 26 C. High confidence in VFR conds and winds for KPRB, KPMD and KWJF. For the remainder of the sites, low to moderate confidence. The arrival times of CIGs may differ by up to 2 hours from TAF times, and there is lower confidence in flight categories. Generally low IFR conds expected for the Central Coast sites, with a 30 percent chance of LIFR conds. Further south, IFR to low MVFR conds expected with a better chance of afternoon clearing by 21-23Z. Low confidence in KBUR and KVNY with a 30 percent chance that VFR conds persist through the period. KLAX...Moderate confidence in the 00Z TAF. There is a 20-30 percent chance that conds remain in MVFR category overnight through Wed morning. There is a 30 percent chance that CIGs do not clear Wed afternoon. No significant easterly wind component is expected. KBUR...Low confidence in the 00Z TAF. There is a 30-40 percent chance that VFR conds prevail through the period. Otherwise, lower confidence in the onset time and dissipation time of CIGs. && .MARINE...11/125 PM. Good confidence in current forecast through Thursday afternoon with Small Craft Advisories (SCA) not expected. Moderate confidence the forecast for the nearshore waters along the Central Coast. SCA conditions are likely (60 percent chance) between Friday afternoon and Sunday. There is a chance (30 percent) of GALE force winds Saturday afternoon through Sunday evening. Wave heights will likely peak between 9 and 13 feet. For the outer waters, SCA winds will likely (60-70 percent) develop Thursday night over most of the area. GALE force winds are likely (60-70 percent chance) Friday through Sunday. If GALES do not develop there will be strong SCA conditions. An extended period of steep, short period hazardous seas with overall wave heights of 10 to 15 feet are likely between Friday and Sunday. For the western Santa Barbara channel SCA winds and seas will likely develop on Friday and continue through Sunday. There is a 30-40 percent of a period of GALE force winds focused Saturday afternoon and evening. For the inner waters, including the eastern Santa Barbara Channel, wave heights along with steep choppy seas will build Friday and continue into the weekend with a 20-30 percent chance of SCA winds or seas. && .LOX WATCHES/WARNINGS/ADVISORIES... CA...NONE. PZ...NONE. && $$ PUBLIC...Cohen AVIATION...Smith MARINE...Munroe/Rorke SYNOPSIS...Cohen weather.gov/losangeles Experimental Graphical Hazardous Weather Outlook at: https://www.weather.gov/erh/ghwo?wfo=lox