February 20, 2019 Freeze Watch - Los Angeles County San Gabriel Valley (California)
Temp
 
45.3 °F
 
Dew Pt.
 
42.3 °F
 
Humidity
 
89%
 
Pressure
 
1005.9 hPa 
  falling slowly
Wind
 
0.0 mph 
    NE
Rain
 
0.02 in 
  0.00 in/hr
UV index
 
---  
 
Solar rad.
 
100 W/m²
 
Tonight

Tonight: A 50 percent chance of showers.  Mostly cloudy, with a low around 38. Northwest wind around 5 mph.
Chance
Showers
Thursday

Thursday: A chance of showers, with thunderstorms also possible after 10am.  Partly sunny, with a high near 52. Light and variable wind becoming west 5 to 10 mph in the afternoon.  Chance of precipitation is 40%.
Chance
Showers
Lo 38 °F Hi 52 °F
000
FXUS66 KLOX 210615
AFDLOX

Area Forecast Discussion...UPDATED
National Weather Service Los Angeles/Oxnard CA
1015 PM PST Wed Feb 20 2019

.SYNOPSIS...20/824 PM.

A very cold storm system moves will continue to move across the
area, bringing light to moderate rain, mountain snow and a chance
of thunderstorms through Thursday. Snow levels could drop impacting
lower elevations and interior valleys. Drier conditions will
return going into the weekend, but below normal temperatures are
expected for most areas through early next week.

&&

.SHORT TERM (WED-SAT)...20/822 PM.

***UPDATE***

A somewhat moist cyclonic flow around a cold upper level trough
over srn CA this evening was generating scattered showers over
much of the forecast area, with snow showers above about 3000 to
3500 feet. However, little in the way of precip has fallen thus
far on the SBA County S coast and VTU County coast due to
downsloping off the mtns. Most areas that have had measurable
precip has received 0.10 inch or less, altho the foothills and
mtns have had up to 0.25 inch.

Little change can be expected overnight as the large upper level
trof along the W coast digs further S. Strong and gusty NW to N
winds were also noted for many areas this evening from the coast
to the mtns, with local gusts near or to advisory levels at times.
These winds should diminish some overnight. No change in the
current forecast is expected this evening.

***From Previous Discussion***

This pattern to continue through Thursday with the added
potential of thunderstorms as the air mass becomes slightly
unstable. These could generate some brief heavy downpours with
small hail or graupel just about anywhere but given the overall
lack of moisture with this system we`re not expecting rain rates
to pose any issues for burn areas.

The biggest impact locally will be the extremely low snow levels
and likely significant delays and closures of major roads through
the mountains tonight and Thursday, including Interstate 5
through the Grapevine and possibly even Highway 14 from Santa
Clarita to the Antelope Valley. Some of lower highways could even
be impacted at times including Highway 101 through Cuesta Pass in
SLO County and Highway 154 through San Marcos Pass in SB County.
Interstate 5 likely to be the biggest concern due to the
combination of strong northwest flow pushing the moisture up the
north facing slopes and very cold temps. Could see 3-6" of snow
accumulation at pass level. Thicknesses bottom out at around 526dm
which if true could result in snow down to 1000` or even slightly
lower. A Winter Weather Advisory is in effect for all the
mountains and interior valleys through Thursday evening.

Showers expected to taper off by Thursday night with dry but cold
weather Friday. Will be issuing a Freeze Watch for late Thursday
night into Friday morning for the Central Coast and the valleys of
LA/Ventura Counties as clearing should happen early enough for
temps to drop to near or below freezing in many areas.

Another cold night Friday night followed by a cool but slightly
warmer day Saturday but with temps still a good 5-10 degrees
below normal in most areas.

.LONG TERM (SUN-WED)...20/205 PM.

Pretty quiet through the middle of next week. Temps will remain
below normal through the early next week but then should be
getting very close to normal by Tue/Wed as a ridge of high
pressure sets up along the West Coast that should last at least
through Friday.

&&

.AVIATION...21/0612Z.

At 05450Z at KLAX...there was no marine layer nor was there a sfc
based inversion.

Moderate confidence overall in TAFs. A cold and showery pattern
will prevail over all airfields through mid afternoon. There is a
30 percent chc of showers over all of the TAF sites through 23Z. VFR
cigs and vis are most likely with ocnl MVFR cigs during showers.
Worse conditions for KPMD and KWJF with low MVFR cigs and more
numerous showers...snow is possible at both fields 11Z-18Z.

LAX...Moderate in TAF. There is a 30 percent chc of a shower with
cigs between 020 and 030 through 23Z. Good confidence in winds
staying out of the west.

KBUR...Moderate in TAF. There is a 40 percent chc of a shower
with cigs between 020 and 030 through 23Z. Low confidence in wind
forecast with large changes in direction likely through 23Z.

&&

.MARINE...20/808 PM.

For the Outer Waters, moderate confidence in current forecast.
High confidence in strong Small Craft Advisory (SCA) level
northwest winds through Thursday night, but there is a 40% chance
of gale force gusts becoming widespread over the waters tonight
into Thursday morning. After a lull Friday morning, there is a
70% chance of SCA level winds Friday afternoon and evening.
Finally, SCA level winds may return on Sunday.

For the Inner Waters north of Point Sal, moderate to high
confidence in current forecast. High confidence in Small Craft
Advisory (SCA) level northwest winds through tonight, and then
again Thursday late afternoon and evening. There is a 50% chance
of SCA level winds Sunday afternoon and evening.

For the Inner Waters south of Point Conception, moderate to high
confidence in current forecast of SCA level west to northwest
winds through Thursday afternoon. There is a 50% chance the SCA
winds continue through Thursday night. After a lull on Friday and
Saturday, there is a 40% chance of SCA level winds across the
western portion of the Santa Barbara Channel on Sunday.

For all waters, there is a slight chance of thunderstorms Thursday
and Thursday evening. Large steep seas will continue across the
waters tonight through Thursday.

&&

.LOX WATCHES/WARNINGS/ADVISORIES...
CA...Freeze Watch in effect from late Thursday night through
      Friday morning for zones 34>36-44>46-88-547. (See LAXNPWLOX).
     Winter Weather Advisory in effect until 10 PM PST Thursday
      for zones 37-38-51>54-59. (See LAXWSWLOX).
PZ...Small Craft Advisory in effect until 3 AM PST Thursday for
      zone 645. (See LAXMWWLOX).
     Small Craft Advisory in effect until 3 PM PST Thursday for
      zones 650-655. (See LAXMWWLOX).
     Small Craft Advisory in effect until 3 AM PST Friday for
      zones 670-673-676. (See LAXMWWLOX).

&&

.HAZARD POTENTIAL OUTLOOK (SAT-WED).

No significant hazards expected.

&&

$$

PUBLIC...MW/Sirard
AVIATION...Rorke
MARINE...Smith
SYNOPSIS...Delerme

weather.gov/losangeles

NWS LOX Office Area Forecast Discussion