August 15, 2020 Excessive Heat Warning - Los Angeles County San Gabriel Valley (California)
Temp
 
104.4 °F
 
Heat Idx
 
110.2 °F
 
Dew Pt.
 
64.7 °F
 
Humidity
 
28%
 
Pressure
 
1008.0 hPa 
  falling slowly
Wind
 
0.0 mph 
    W
Rain
 
0.00 in 
  0.00 in/hr
UV index
 
---  
 
Solar rad.
 
100 W/m²
 
This
Afternoon
This Afternoon: Mostly sunny and hot, with a high near 108. West southwest wind around 15 mph, with gusts as high as 20 mph.
Hot
Tonight

Tonight: Partly cloudy, with a low around 74. Southwest wind 5 to 10 mph becoming light  in the evening.
Partly Cloudy
Hi 108 °F Lo 74 °F
000
FXUS66 KLOX 151913
AFDLOX

Area Forecast Discussion
National Weather Service Los Angeles/Oxnard CA
1213 PM PDT Sat Aug 15 2020

Updated Aviation and Marine Sections

.SYNOPSIS...15/925 AM.

Very hot conditions will continue into the middle of next week,as
well as very warm nights, especially for valley and interior
areas. There is a slight chance of thunderstorms through at least
Tuesday.

&&

.SHORT TERM (TDY-TUE)...15/923 AM.

Impressive line of elevated convection developing from the western
Channel Islands north through western SB/SLO Counties. Difficult
to pinpoint what`s triggering this in that specific location but
it`s generating a ton of lightning from Santa Cruz Island north to
Gaviota, through the highway 101 corridor up through Buellton and
eastern parts of Santa Maria, Sisquoc, and Nipomo. The expectation
is that this will settle down for coastal areas as we move into
the afternoon but a chance of convection will continue across the
interior. This is all very high based and not a lot of precip
reaching the ground so the biggest threat is dry lighting and
gusty winds for boaters and anyone outdoors in this area.

Going into tonight and Sunday models continue to show a chance of
elevated convection but aren`t singling out any specific areas so
given what`s occurring this morning it may be prudent to add
thunderstorms chances to most of the area, though again the
threats would focus on dry lightning and gusty winds with minimal
precip.

The rest of the forecast looks on track. Models still showing
increasing onshore flow Sunday and Monday which should bring some
relief to coastal areas and possibly even a very shallow marine
layer and dense fog in a few places. Though any convective
activity would likely minimize that potential.

***From Previous Discussion***

There will continue to be very hot conditions across much of the
forecast area away from the coast over the next several days. For
today, high temps will trend up 2-5 more degrees, except for
significant cooling across the Central Coast as there will be a
sea breeze influence later this morning, yet highs will reach
still the mid 80s to low 90s. A far cry from the 100 degree mark
reached at Lompoc. There will be a chance at a few hi temperatures
to be broken today. Excessive Heat Warnings remain in place for
valleys and interior locations today, and will continue into next
week. A Heat Advisory will remain in effect for the L.A. County
Coast and Santa Ynez Valley through early this evening.

An eddy develops tonight across SoCal Bight and low clouds are
expected to move up from Orange County into LA/VTU and possibly
into the eastern portion of the Santa Barbara South Coast. This
will cause a deepening of the marine layer which will help to
cool down coastal areas and help bring 4-8 degrees of cooling to
some coastal valleys as well on Sunday, except for a few degrees
of warming across the Central Coast. Highs will still remain well
above normal with triple digit heat continuing across most inland
valleys and interior locations. Not much change for Monday,
possibly a few degrees of cooling.

Minimum temperatures will remain quite warm only lowering to the
70s to mid 80s over the next few nights with the continued heat
remaining over the region, especially in the lower mountain
elevations and elevated valley locations and Antelope Valley.

As far as monsoonal moisture goes for today through Monday, there
will be a slight chance to chance for thunderstorms across the
L.A./Ventura/ Santa Barbara Mtns and the Antelope Valley this
afternoon and early evening hours, as well as Sunday and Monday
during the same time periods. Instability over the mountains with
LIs ranging from -3 to -5 with CAPE up to 1200 j/kg and K values
in the high 30s. Moisture will be somewhat limited over the next
few days between 500-700 MB. However, if thunderstorms do develop,
they will have no problem growing vertically due to great lift in
the atmosphere. With the atmosphere continuing to remain unstable
each afternoon, fire weather concerns will continue as well with
plume dominated fires, including the Ranch and Lake Fires. If
thunderstorms develop near active fires, some chaotic gusty
outflow winds will be possible due to the strong downward wind
motion. Dry lightning will also be a concern over the next few
afternoons.

.LONG TERM (WED-SAT)...15/411 AM.

Both the GFS and EC models remain in good agreement with large
scale features through the long term period. There will be only
minor fluctuations of movement with the 598-600 DM high over
NV/AZ/UT through Wednesday. The placement of the high will
continue to be conducive to draw in monsoonal mid level moisture
bringing a continued chance of afternoon and evening showers or
thunderstorms across the Antelope Valley and adjacent mountains.
By Wednesday, the Upper High becomes slightly elongated west to
east, which if there is moisture to tap into, an easterly wave
could bring the potential for a few showers into the coastal
valleys and even coastal areas. However, it is too far out to put
in the forecast. By Thursday, the upper high continues to expand over
southern California into the Ern Pacific which would shunt the
chance of monsoonal moisture over the region and keep chances of
showers east of the forecast area over SE Calif and AZ.

High temperatures will continue to remain well above normal with
very warm nights across the foothills, elevated valley locations
and the high desert. Excessive Heat Warnings or heat advisories
are likely to continue Tue into Wed before more cooling occurs
inland to more typical for this time of year on Thursday.

&&

.AVIATION...15/1841Z.

At 17Z, at KLAX there was no marine layer. A strong inversion
extended up to 2000 feet and 34 degrees Celsius.

Moderate confidence in VCTS at KSMX KSBP KPRB ending around 20Z
today. VCTS possible at KWJF KPMD 21-03Z. Moderate confidence of
TS in the region tonight through Sunday morning. Low confidence
on exactly when and where they will occur, with a possibility
practically anywhere, but with the best chances over KSBA KSMX
KSBP KPRB. Gusty erratic winds are likely near any thunderstorm.
There is also a 20-30 percent chance of IFR CIGS at KLGB KLAX KSMO
10-16Z Sunday.

KLAX...High confidence in TAF through 06Z, with VFR conditions.
Low confidence after. Moderate confidence in SE winds 09-18Z, with
a 30 percent chance of exceeding 8 KT (primarily between 12Z and
17Z). 20 percent chance of IFR CIGS 10-16Z Sunday, as well as a 20
percent chance of TS. If TS forms, rain unlikely but gusty and
erratic winds possible.

KBUR...High confidence in TAF through 08Z, with VFR conditions and
stronger and longer-lasting SE winds. 20 percent chance of TS
10-18Z, and if TS forms rain unlikely but gusty and erratic winds
possible.

&&

.MARINE...15/1158 AM.

Thunderstorms will remain possible this morning north of San
Nicolas Island, but the chances will be decreasing in the
afternoon. The chances will increase again tonight, and possible
nearly anywhere through Sunday morning. Any thunderstorm that does
form will bring a potential for strong gusty winds.

Moderate confidence of low-end Small Craft Advisory (SCA) winds
for the outer waters from the Central Coast to San Nicolas Island
tonight. These winds could persist well off the Central Coast in
Sunday morning, then expand again over the same areas Sunday night
and could persist through Friday. There is a chance of Gale Force
Winds off the Central Coast starting Tuesday night. All of these
winds will create a persistent source of short period seas over
most of the coastal waters.

Southeast winds will increase tonight through Sunday south of
Point Conception, including the Santa Barbara Channel and the San
Pedro Channel. There is a chance for winds to locally reach 20 KT,
especially around Anacapa and Catalina Islands.

There is also a chance for dense fog south of Point Conception
early next week, as early as Sunday.

A tropical storm is expected to form south of Baja over the next
few days. Some projections show this forming into a strong storm
with large seas. This brings a chance of a significant south to
southeast swell toward the middle to end of next week.

&&

.FIRE WEATHER...15/1034 AM.

Strong high pressure across the western states will
maintain very hot conditions across the area, especially inland, through
at least the middle of next week. Daytime high temperatures will
generally range between 100 and 110 degrees for valleys, lower
mountains, and deserts through at least Wednesday with a few record
highs possible. Nighttime lows will also be near record territory in
the 70s to lower 80s for many inland and foothill communities. The hot and
unstable conditions will continue to create a very favorable pattern
for large vertical plume growth each afternoon for existing or new
wildfires, bringing elevated to brief critical fire weather conditions.
Mixing heights of 15,000 to 20,000 feet are expected this
afternoon across the interior. The significant vertical plume
activity will bring the threat of extreme fire behavior at times,
capable of strong downdrafts with rapid and large fire growth.
Minimum humidities each day will generally be in the teens and 20s
across inland areas, along with poor humidity recoveries in the
mountains and foothills.

A weak upper level disturbance is bringing isolated showers and
thunderstorms this morning to portions of Santa Barbara and San Luis
Obispo counties, with the main threats being isolated dry lightning
strikes and gusty erratic winds. As of 1030 am, 5 small brush
fires have been reported across Santa Barbara county due to
lightning. Mid level monsoonal moisture will continue to bring a
threat of thunderstorms through Tuesday, mainly during the
afternoon and evening hours across, and mainly focused across
interior areas. The main threats with these thunderstorms will
continue to be isolated dry lightning strikes and gusty erratic
winds.

&&

.LOX WATCHES/WARNINGS/ADVISORIES...
CA...Excessive Heat Warning in effect until 9 PM PDT this evening
      for zone 36. (See LAXNPWLOX).
     Heat Advisory in effect from 9 PM this evening to 9 PM PDT
      Sunday for zone 36. (See LAXNPWLOX).
     Excessive Heat Warning in effect until 9 PM PDT Wednesday for
      zones 37-38-44>46-51>54-88-547. (See LAXNPWLOX).
     Heat Advisory in effect until 9 PM PDT Sunday for zone 41. (See LAXNPWLOX).
     Excessive Heat Warning in effect until 9 PM PDT Thursday for
      zone 59. (See LAXNPWLOX).
PZ...Small Craft Advisory in effect until 3 AM PDT Sunday for
      zones 670-673-676. (See LAXMWWLOX).

&&

.HAZARD POTENTIAL OUTLOOK (TUE-SAT).

Triple digit high temperatures and very warm nights will bring
the potential for excessive heat over many areas into Tuesday or
longer. There is a slight chance of afternoon thunderstorms through
Tuesday.

&&

$$

PUBLIC...MW/Kaplan
AVIATION...Kittell
MARINE...Kittell
FIRE...Gomberg
SYNOPSIS...MW/Kaplan

weather.gov/losangeles

NWS LOX Office Area Forecast Discussion