000 
fxus66 klox 231010 
afdlox 


Area forecast discussion 
National Weather Service Los Angeles/Oxnard California 
310 am PDT Mon Oct 23 2017 


Synopsis... 
gusty offshore winds will strengthen and become more widespread 
through Tuesday as many locations have record heat on Monday and 
Tuesday. Winds ease on Wednesday and temperatures begin to cool 
and possibly drop to near normal by Friday. 


&& 


Short term...(tdy-wed) 


High pressure aloft will dominate the weather through Wednesday. 
Hgts will be around 594 dm today and Tuesday and will fall to 591 
dm on Wednesday as the ridge weakens. The high pressure and 
offshore flow will keep skies clear through the period. 


The offshore flow will be the major story for the next 3 days. 
Current gradients are -5.4 mb from kdag and a healthy -7.5 mb from 
kbfl. On Tuesday the east to west kdag gradient peaks at -8.3 
while the north to south kbfl gradient weakens some to -4.8 mb. 
This will switch the winds to more of an easterly direction. On 
Wednesday both grads weaken to -6 mb from the east and -3 mb from 
the north. No real winds yet but they will start in the mtns in a 
few hours and then mix down to the vlys then the coasts during the dawn 
to mid morning period. Winds will peak Tuesday. Fortunately there 
is zero thermal support and only a little upper support so this 
will be a gradient driven event which for the most part can not 
reach warning levels...only strong advisory levels (50 to 55 mph 
gusts). There will be a few warning level gusts across the 
ridgetops but thats about it. The winds will diminish Wednesday 
but will remain at advisory levels 


The very high hgts (15 dm higher than normal) and offshore flow 
will combine to bring record heat both today and Tuesday (highs 
95-105 common) and somewhat uncomfortably warm nights (lows 65-75 
common). This heat poses a concern for heat-related illnesses, 
especially for the elderly and children. Heat warnings/advisories 
are in effect for much of the area. Please see the product 
laxnpwlox for a detailed description of all heat and wind 
warnings and advisories. Major fire concerns exist as well (see 
fire weather section below). 


Weaker offshore flow Wednesday along with lowering heights will 
bring cooling to most areas, most significant north of Point 
Conception and near the coast. However, temperatures will remain 
well above normal with widespread 80s and 90s. 


Long term...(thu-sun) 


Bad news for people hoping for a cool down both the GFS and the ec 
now agree that a tall and skinny 588 dm ridge will set up on 
Thursday and persist into Friday only to be replaced by a smaller 
588 dm ridge poking in from the SW over the weekend. The only good 
news is that there will only be weak offshore flow in the morning 
and weak onshore flow during the afternoon so Max temps will not 
be anywhere as warm as they will be early this week still Max 
temps will be 6 to 12 degrees above normal over much of the area. 
Where there was once hope of some marine layer clouds now it looks 
like clear skies will prevail as there is no eddy forecast or any 
other low cloud formation mechanisms. 


&& 


Aviation... 


23/0830z 


At 0830z, there was a surface-based inversion at klax. The top of 
the inversion was 1300 feet with a temperature of 30 degrees 
celsius. 


Moderate to strong northeast wind will develop today and continue 
through Tuesday. Gusty surface winds and/or low level wind shear will impact ksbp, 
koxr, kcma, klgb, kbur and kvny. Conditions will remain VFR 
through the taf period. 


Klax...high confidence in 12z taf. There is a 20% chance of 
a 9 knot east wind 12z-17z. 


Kbur...high confidence in 12z taf. Low level wind shear/light turbulence will be 
likely 12z-22z. There is a 30% chance of north to northeast winds 
surfacing 12z-18z. 


&& 


Marine... 


23/130 am 


For the outer waters, high confidence in current forecast. Winds 
and seas are expected to remain below Small Craft Advisory (sca) 
levels through Friday for pzz670/673. For pzz676, there is a 40% 
chance of Small Craft Advisory level northeast winds today and Tuesday. 


For the inner waters, high confidence in current forecast. For the 
waters north of Point Sal, winds and seas will remain below Small Craft Advisory 
levels through Friday. For the waters south of Point Conception, 
Small Craft Advisory level winds are likely from Ventura south to Santa Monica 
today through Wednesday with the strongest winds in the morning to 
early afternoon hours. OH Tuesday morning, there is a 40% chance 
of gale force gusts, but the coverage of these gusts are expected 
to be localized. 


There is a chance that the northeast winds will reach Avalon and 
Two Harbors on Tuesday, but since this is a hot Santa Ana event 
the likelihood of significant winds out that far is small. 30 
percent chance of 10-20 knots winds in the harbors, 10 percent chance 
of 15-25 knots. 


&& 


Fire weather... 


22/400 PM 


From today through Wednesday, a prolonged duration of gusty Santa 
Ana winds with hot and very dry conditions is expected. Northeast 
winds are expected to gust between 30 and 45 mph across wind 
favored passes and canyons of Los Angeles and Ventura through 
tonight. The Santa Ana winds are expected to increase in areal 
coverage and intensity Monday into Tuesday, with strongest winds 
on Tuesday gusting between 45 and 60 mph across wind favored 
portions of Los Angeles and Ventura counties. During the peak of 
the offshore wind event on Tuesday, the lax-Daggett gradient is 
projected to peak at around -7.5 mb with better upper level wind 
support up to 850 mb level. Moderate offshore winds and low 
humidities are now expected to continue Tuesday night into 
Wednesday morning, prompting the extension of the red flag warning 
through Wednesday. The hottest and driest conditions are expected 
on Monday and Tuesday, when triple digit heat and humidities 
lowering into single digits and lower teens will be common across 
coastal and valley areas. Northeast to east winds gusting between 
25 and 40 mph will also bring elevated to brief critical fire 
weather concerns to portions of San Luis Obispo and Santa Barbara 
counties through Tuesday, especially across the central coast. Of 
particular concern will be Monday when the gusty offshore winds 
combine with humidities lowering into the teens(locally single 
digits) and temperatures rising to between 90 and 100 degrees 
along the central coast. 


Very warm and dry conditions during the overnight hours in the 
mountains, foothills, and wind prone areas will add to this long 
duration fire weather threat. The duration, strength, and 
widespread nature of this Santa Ana wind event combined with the 
extreme heat and very dry fuels will bring the most dangerous fire 
weather conditions that southwest California has seen in the past 
few years. If fire ignition occurs, there will be the potential 
for very rapid spread of wildfire with long range spotting and 
extreme fire behavior that could lead to a threat to life and 
property. 


&& 


Lox watches/warnings/advisories... 
California...heat advisory in effect from 10 am this morning to 8 PM PDT 
Tuesday for zones 34>36-39-88. (See laxnpwlox). 
Wind Advisory in effect until 2 PM PDT Wednesday for zones 
40-41-44>46-53-54-88-547. (See laxnpwlox). 
Excessive heat warning in effect from 10 am this morning to 8 
PM PDT Tuesday for zones 40-41-44>46-87-547. (See laxnpwlox). 
Red flag warning in effect until 6 PM PDT Wednesday for zones 
240-241-244>246-253-254-288-547-548. (See laxrfwlox). 
Pz...Small Craft Advisory in effect until 3 PM PDT Tuesday for 
zones 650-655. (See laxmwwlox). 


&& 


Hazard potential outlook...(wed-sun) 
heat advisory level temperatures may continue for many areas into 
Wednesday. Gusty northeast winds will likely impact wind prone 
areas of Los Angeles and Ventura counties through early 
Wednesday. Hot, dry and windy conditions will likely bring 
continued critical fire weather conditions to some areas 
Wednesday. 


&& 


$$ 


Public...rorke 
aviation...rat 



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