FXUS66 KEKA 222135
AREA FORECAST DISCUSSION
National Weather Service Eureka CA
235 PM PDT Tue May 22 2018
.SYNOPSIS...A mix of mild temperatures, coastal stratus, and
afternoon thunderstorms will continue over the next few days.
There will be a chance for light showers across most of
northwest California for Thursday and Friday. Then building high
pressure will bring warmer and drier weather for Memorial Weekend.
.DISCUSSION...Weak ridging will break down today as an upper trough
dives down from the Gulf of Alaska. Although brief, the impacts from
high pressure were still noticed with clear skies and warmer
temperatures approaching 80 degrees across inland areas. This
surface heating will also make conditions more conducive for
thunderstorm development primarily across the Trinity Alps and Yolla
Bolly Mountains through early this evening.
The chance for afternoon thunderstorms will persist through the rest
of the work week as a closed low pressure system develops offshore
of the California coast and tracks over central California. This
will additionally bring a chance for more widespread showers across
northwest California Thursday and Friday. Cloud cover will also
thicken and increase in areal coverage resulting in noticeably
cooler afternoon highs over the interior later this week. Building
high pressure will bring warmer and drier weather conditions to
inland areas for Memorial weekend with stratus and seasonal
temperatures expected along the coast. /KML
.AVIATION...A persistent marine layer remained in place again
today. Well- entrenched stratus clouds extended far into local
river valleys... as well as over some neighboring coastal ranges
in Humboldt and Mendocino Counties. The result has been up/down
MVFR-IFR conditions at coastal airports/airfields...specifically
ACV & CEC terminals. UKI and generally nearly all inland locales
remained VFR. Stratus could not top over the coastal ranges this
morning, and there was not enough of a deeper layer to advect low
clouds into UKI from the south. Any airfields over the Trinity
Alps and Yolla Bolla could experience the threat of convective
activity into evening. Through the Tuesday afternoon 24 hour TAF
period, will keep with continuity through tomorrow as model
guidance maintains stratus clouds at coastal airports...with
possibly some afternoon breaks. Guidance is also predicting some
MVFR Cigs rolling into UKI in the morning. /TA
.MARINE...Light to moderate winds will persist through the work week
as a surface low located offshore maintains a generally weak
pressure gradient across the coastal waters. Southerly winds will
develop across parts of the coastal waters Thursday and Friday
before building high pressure brings increasing north winds on
Saturday. Long range models suggest 20 to 30 kt northerlies may
develop across the outer waters late memorial weekend with moderate
confidence in the strength and duration this far in advance.
Meanwhile, steep waves will subside today and then multiple swells
will dominate the sea state through the remainder of the week
including a long period south swell and a northwesterly mid period
wave system. Wind driven waves will develop over Memorial weekend
but we will know more once we become more confident in the wind
NORTHWEST CALIFORNIA COASTAL WATERS...Small Craft Advisory until 3 AM PDT Wednesday for PZZ470-475.
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FXUS66 KHNX 222235
Area Forecast Discussion
National Weather Service San Joaquin Valley - Hanford CA
335 PM PDT Tue May 22 2018
Low pressure over the region will move east today with a brief
ridge of high pressure over the area Wednesday and Thursday. This
weekend, another Pacific low pressure system will move into the
region bringing additional cooling.
Another day of unsettled conditions over the Sierra Nevada and
Mojave desert as the associated upper low drifts pass Las Vegas.
While orographic lift is supporting widespread showers over the
mountains, a more northerly orientation of the flow aloft is
keeping much of the valley clear as the blow-off from today's
convection heads southeastward. In addition, with the marine layer
(as observed on the Fort Ord profiler) was reaching up around
3000 feet msl and spilling into the San Joaquin Valley – as
observed on visible satellite imagery. Furthermore, surface
observation from the higher elevations of the Western side the
district were blowing in the 15 to 25 mph range as cool air
filters in the region. Therefore, the air-mass over the valley may
be too stable for significant afternoon convection. Yet, while
thunderstorms are not very likely over the San Joaquin Valley,
some clouds could still drift into the area with a possible
sprinkle over the east side of the valley before sunset tonight.
Afterward, upper low lifts toward the Northern Rockies and allows
a weak short-wave ridge to push in ahead of the next disturbance.
Models continue to show higher uncertainty levels with the next
disturbance, even at the 48 hour time frame, while still
indicating that a disturbance will form over the Eastern Pacific
at that time. Ensemble model uncertainty is more with the
amplitude of the disturbance than the phase(timing). Therefore,
with models showing good consensus of having the axis of the
disturbance about 525 miles west of the bay area by Wednesday
evening, the problem is more with how deep the disturbance will be
before shifting onshore by the end of the week. Models come into
better agreement by Thursday afternoon as the position of the low
may be about 300 miles due west of the bay area. At that point,
weak difluent flow aloft may support the Sierra Nevada's
orographic lift as showers continue over the higher terrain. By
Friday, enough lift may exist for possible valley convection north
of Fresno County as the low moves closer to shore and vort max
energy moves into the region. With the GFS/ECMWF/ Canadian and
NOGAPS showing reduced uncertainty in their solution of the upper
lows position toward Friday night, will have higher confidence
levels have precipitation may occur over the region until the vort
max energy exits the region toward Saturday.
The bulk of the energy from disturbance passing through around the
end of the week will be east of the district by Saturday night. By
that time, will expect lingering showers over the Sierra Nevada as
wrap around moves vort lobes through the area until Monday
morning. While models show no significant surges of moisture into
the area, enough moisture should exist over the region to pop-up a
few light to moderate showers during each event. Afterward,
ridging returns to the region near the middle of next week. Again,
just like the first short-wave ridge in the short term, the second
will be short-lived as models continue to show a very uncertain
long term prognosis. With the amount of error in the long term,
will introduce the ridge and hold off on allowing the ridge to
exit the region until after day seven. In the meanwhile, will keep
temperatures and winds on a roller-coaster ride of warm or cool
and strong or light during the forecast period.
A slight chance of possible thunderstorms with local MVFR/IFR
conditions may occur over the higher elevations of the Southern
Sierra Nevada until 03Z Wednesday. Otherwise...VFR conditions
will prevail across the Central CA Interior during the next 24
.AIR QUALITY ISSUES...
The level of certainty for days 1 and 2 is high.
The level of certainty for days 3 through 7 is medium.
Certainty levels include low...medium...and high. Please visit
www.weather.gov/hnx/certainty.php for additional information
an/or to provide feedback.
FXUS66 KLOX 222129
Area Forecast Discussion
National Weather Service Los Angeles/Oxnard CA
229 PM PDT Tue May 22 2018
An upper level trough continues to move east of California
bringing continued onshore flow and below normal temperatures
throughout the week. Night to morning low clouds will continue
through the weekend for the coast and valley areas.
.SHORT TERM (TDY-FRI)...22/206 PM.
Latest satellite imagery showed low clouds hanging tough across
many coastal and valley areas south of Point Conception. It seems
LA County will hang onto the low clouds the longest. Low clouds
off the Central Coast continue to stream in from the northwest.
Isolated cumulus clouds have developed due to limited moisture and
instability across the northern Ventura County mountains near
Lockwood Valley and the San Gabriel mountains in eastern LA
County. Can't completely rule out a few sprinkles or a shower with
this development, however at this time vertical development of the
clouds has been limited.
A weak pop up ridge is expected over the region with 500 mb
heights rising from around 571 dm today to around 578 dm by
Wednesday afternoon. A piece of energy is expected to pinch off a
trough of low pressure currently positioned over the Gulf of
Alaska and move into Central California Friday. Southwesterly flow
aloft ahead of this feature Thursday will support a modest
increase in onshore flow with lowering heights north of Point
Conception. The increase in onshore flow will likely maintain low
clouds well into Thursday afternoon for many coastal and valley
areas. A 100+ knot jet streak at 300 mb may help provide enough
lift for drizzle or a few light showers for coastal and valley
areas north of Point Conception (especially SLO County). Have
opted to leave out of the forecast for now (tho did bump up PoPs)
as there remains some uncertainty of the eventual track of the
system. Drizzle can't be ruled out further south either,
especially the climatologically favored foothills and lower
coastal slopes of eastern LA County.
Temperatures will warm some, especially away from the marine layer
through Wednesday before gradually cooling through Friday, first
due to increasing onshore flow, then lowering 500 mb heights.
Locally gusty onshore winds will continue for the foothills of the
Antelope Valley each afternoon and early evening.
.LONG TERM (SAT-TUE)...22/227 PM.
Moderate confidence exists in the extended forecast mainly due to
uncertainty with the exact position and associated impacts of a
trough of low pressure expected to pass through the region.
The fastest model solutions have trended the core of the upper
level low closer to southwest California. Temperatures were
trended downward slightly (and could be lowered further by future
shifts) as a result of the low's proximity. This is unusually cold
feature for this time of year. Night to morning low clouds may
have trouble forming over the weekend as a result, especially
north of Point Conception. Will also keep an eye on the potential
for a few showers or thunderstorms over the mountains mainly
Saturday due to the low's proximity. Advisory level Sundowner
winds are possible for western portions of the SBA South Coast
this weekend with gusty also possible in the LA and VTA mountains
near the I-5 corridor.
The trough of low pressure is expected to exit into the Four
Corners by early next week. This will support increasing 500 mb
heights and weakening onshore flow, especially from the south. The
resulting lower marine layer and likely better clearing with
support a gradual warming trend with widespread 80s away from the
At 17Z, there is a weak marine inversion at KLAX based at 4200
feet. The top of the inversion was 5400 feet with a temperature
of 12 degrees Celsius.
Overall, moderate confidence in coastal/valley TAFs and high
confidence in desert TAFs. The trends in the marine inversion will
be lowering through tonight with a shallower layer that is likely
to burn off quicker Wednesday morning. Lingering MVFR CIGs for
portions of the central coast and valleys south of Pt Conception
this afternoon with some SCT between 22-04Z. MVFR CIGs with patchy
IFR likely to return after 06Z for all coastal and valley TAFs.
KLAX...Moderate confidence in 18Z TAF. BKN VFR conditions through
21Z then SCT-BKN from 21-06Z. MVFR CIGs are likely to return
07-17Z Wednesday with a 20% chance of IFR CIGs occurring.
KBUR...Moderate confidence in 18Z TAF. BKN VFR conditions through
06Z then MVFR CIGs are likely to return 07-17Z Wednesday with a
50% chance of IFR CIGs occurring.
For the Outer Waters, high confidence in current forecast. Winds
and seas will remain below Small Craft Advisory (SCA) levels
through Thursday. By late Friday into Saturday, there is a 70%
chance of SCA level northwest winds. There will be a mixed swell
with shorter periods from the NW and long periods from the S.
For the Inner Waters, moderate to high confidence in current
forecast. For the waters north of Point Sal, winds and seas will
remain below SCA levels through Thursday then there is a 60%
chance of SCA level winds beginning late Friday into Saturday.
For the waters south of Point Conception, winds and seas will
remain below SCA levels through Thursday. Late Friday into
Saturday, there is a 50% chance of SCA level winds, especially
across western sections.
A long period southerly swell will continue to move across the
coastal waters through Thursday. Locally rough conditions may
occur at local harbor entrances, especially those with southerly
CA...Beach Hazards Statement in effect through Thursday evening
for zones 40-41-87. (See LAXCFWLOX).
.HAZARD POTENTIAL OUTLOOK (FRI-TUE).
Strong rip currents and elevated surf will linger at south-facing
beaches across Los Angeles and Ventura Counties through Thursday.
Advisory level Sundowner winds are possible for western portions
of the SBA South Coast this weekend.
FXUS66 KSTO 222054
Area Forecast Discussion
National Weather Service Sacramento CA
154 PM PDT Tue May 22 2018
Afternoon and evening thunderstorms possible mainly over higher
terrain this week. These may extend through the Valley late in the
week. Slightly cooler than normal temperatures continue across
most of the region this week warming to above normal early next
A low pressure area centered over Nevada continues to drift
northward during the day. Easterly flow continues to dominate
aloft, so afternoon mountains activity during the day will be
trying to push towards the valley once again with the best chances
in the valley during the evening hours over the central and
northern Sacramento valley. The Delta breeze is expected to remain
moderate to locally strong this evening and tonight. Temperatures
will remain on the cool side of normal as a result near the delta
influence areas. The only exception will be over the north end of
the valley which will warm well into the 80s. Some stratus will
possibly advect into the valley the next couple of mornings.
Wednesday will still have a decent Delta breeze in place and
temperatures are expected to be slightly cooler across the region.
Unstable air over the mountains will continue with possible
afternoon and evening thunderstorm activity.
The low pressure area to our Northwest will continue to move
closer to the region Thursday and Friday moving through Friday
night. This low will have cooler air associated with it so expect
temperatures to remain below normal for the latter part of the
week and unstable conditions each day. Snow levels may drop to
around pass levels during the day and below Friday night. At this
time though precipitation amounts look light but 1 to 3 inches of
snow across elevations higher than 8000 feet looks possible.
There should be an increase in shower activity as the low moves
closer and through the region Friday and Friday night.
.EXTENDED DISCUSSION (Saturday THROUGH Tuesday)
A low pressure system will continue to move east through the area
during the morning hours on Saturday and into Nevada by late
Saturday. Colder air associated with the low may bring some snow
down around pass levels. However, since showers are expected to
be scattered enough to not produce much precipitation, we are not
expecting much snow at or below pass levels at this time. Precipitation
should be winding down by Saturday night as the low moves further
to the east, though could see some lingering mountain showers
through very early Sunday. Behind the system northerly winds will
develop Sunday into Monday. Ridging begins to build early next
week, causing temperatures to rise significantly beginning Sunday.
Most valley locations could see temperatures in the 90s by Monday.
Showers and thunderstorms have formed over the mountains, will
continue through the evening. Local MVFR/IFR conditions possible
in storms. Otherwise, mainly VFR conditions over interior NorCal
next 24 hours except small chance of stratus near Sacramento TAF
sites after 10Z Wednesday. Winds up to 15 kts in the valley with
gusts up to 35kts in Delta. HEC
FXUS66 KSGX 222048
Area Forecast Discussion
National Weather Service San Diego CA
200 PM PDT Tue May 22 2018
A deep upper level trough will move northeast out of the area this
afternoon and tonight, resulting in a gradual decrease in cloud
cover through Wednesday. Another area of low pressure will through
the region Friday through Sunday, so the below normal daytime
temperatures will continue through the weekend with periodic low
clouds west of the mountains. More marine layer low clouds are
likely early next week as well.
.DISCUSSION...FOR EXTREME SOUTHWESTERN CALIFORNIA INCLUDING ORANGE...
SAN DIEGO...WESTERN RIVERSIDE AND SOUTHWESTERN SAN BERNARDINO
Marine layer depth ranged from 4000 feet above sea level in San
Diego County to 5000 feet farther north this morning, with aircraft
soundings showing a slight lowering this afternoon. We had partial
clearing today, with greatest remaining stratus extent over Orange
County and northern parts of the Inland Empire. Some cumulus were
over the Big Bear area and the high deserts.
The upper low will move to the northeast mainly tonight and weaken
while some ridging forms over the interior southwestern US. Some
lowering of the marine layer will occur, with better afternoon
clearing Wednesday, especially inland. With onshore flow continuing
as well as the peak stratus season, we will still have a lot of
stratus around, especially nights and mornings, most of the week. An
upper level low will move into California Friday/Friday night, and
this will bring more cooling to inland areas, though the marine
layer effects here will depend partly on if we have a coastal eddy.
Right now, the GFS is saying no to the eddy until Sunday, so we may
end up with a decrease in stratus Friday/Saturday, especially with
cooling above the marine inversion. Models are inconsistent for
early next week, except for one thing--no significant ridging, and
yes to continued onshore flow. Thus, coastal low clouds are likely
to occur then, with temperatures at or a little below normal.
222030Z...Coast/Valleys/Coastal Mountain Slopes...Stratus deck
hanging on at KSNA/KONT/KSBD while significant clearing has
developed elsewhere. Expect continued erosion of the cloud cover
with several hours of SCT conditions at the terminals through early
this evening. The marine layer will be much shallower
tonight/Wednesday morning. Expect low clouds to fill in again
beginning 03-05Z coastal terminals and 06-10Z inland terminals with
BKN IFR/MVFR conditions at the terminals thereafter. Will see bases
900-1300 feet MSL and tops 1500-2500 feet late tonight/ Wednesday
morning. Expect cloud deck to scatter out early Wednesday afternoon.
Mountain Crests/Desert Mountain Slopes/Deserts...VFR conditions with
clear skies through the period. Local west winds 15-25 kt with gusts
25-35 kt will occur on the desert mountain slopes and through San
Gorgonio Pass, with the strongest gusts late this afternoon and
No hazardous marine conditions are expected through Friday. Wind
gusts over 20 knots are likely over the outer waters Friday night
through Saturday night.
A long-period swell from 200 degrees and resulting surf on south
facing beaches will peak today through Wednesday before subsiding
slowly Thursday and Friday. Check the beach hazard statement for all
Skywarn activation is not requested. However weather spotters are
encouraged to report significant weather conditions.
CA...Beach Hazards Statement through Thursday afternoon for Orange
County Coastal Areas.
FXUS66 KMTR 222034
Area Forecast Discussion
National Weather Service San Francisco Bay Area
134 PM PDT Tue May 22 2018
.SYNOPSIS...Cool weather and morning low clouds will continue
through most of the week with inland temperatures remaining below
normal for this time of year as a deep marine layer continues to
influence the region. A late season cold front will approach
California late Thursday into Friday bringing a slight chance of
showers to most of the area. Showers should end by Saturday
morning before a warming trend brings inland temperatures back to
near seasonal normals by Sunday.
.DISCUSSION...as of 1:34 PM PDT Tuesday...Visible satellite
imagery shows this morning's low clouds have dissipated for inland
areas while much of the coast remains under broken to overcast
conditions. Late clearing has slowed this afternoon's warming,
keeping temperatures across the area about 5 degrees cooler than
this time yesterday. An upper low remains near Las Vegas, allowing
for breezy onshore winds to continue this afternoon with onshore
gradients still around 2.5 mb from sfo to sac. Expect low clouds
to redevelop this evening moving inland and down the valleys
Despite some brief shortwave ridging over the eastern Pacific
tomorrow, seasonably cool temperatures will continue with many
inland locations around 5 to 10 degrees below normal as we remain
under the influence of a deep marine layer. Expect afternoon highs
along the coast in the low 60s with inland areas reaching the low
An upper level low with an associated surface cold front will then
approach the area on Thursday. This will bring chances of showers
to the region Thursday night into Friday morning. QPF totals
remain light with most areas seeing a few hundredths to just over
a tenth of an inch. The highest amounts will likely be in the
North Bay coastal hills where up to a quarter of an inch is
possible. For now, the main impact from this system would be for
the commute Friday morning when the bulk of the precipitation is
expected. The forecast was updated this afternoon to increase POPs
and QPF across the region with higher QPF totals in the North Bay
and other terrain favored locations along the coast.
Showers will remain a possibility through Saturday morning as the
core of the upper low slowly moves inland, but any remaining
showers would bring little if any additional accumulations. The
main impact will be continued unseasonably cool weather,
As the low continues to move east on Saturday, a modest warming
trend will occur starting Saturday afternoon through Memorial Day
as a ridge develops over the eastern Pacific. Inland temperatures
will rebound to near seasonal normals by Sunday with more
widespread upper 70s in the afternoon. As warming continues on
Monday, some inland locations may even be slightly above normal
with widespread afternoon highs forecast in the 80s.
.AVIATION...As of 10:31 AM PDT Tuesday for 18Z TAFs. Widespread
stratus continues to bring MVFR/IFR ceilings across the San
Francisco Bay Area. Visible satellite shows the low clouds
beginning to mix-out in the North Bay Valleys as of the 18Z TAF
publication time; however, many of the major Bay Area airports
remain blanketed. Several terminals will likely stay OVC/BKN
through the entire day, and for those that do clear, ceilings will
return again overnight.
Vicinity of KSFO...MVFR ceilings are expected to prevail through
the day as a consequence to the deep marine layer, strong onshore
gradient, and healthy stratus feed pushing through the San Bruno
Gap from the Pacific. Winds will increase in the afternoon to 15
to 20 kt with higher gusts possible. Ceilings will drop again
after sunset, perhaps flirting with IFR levels.
SFO Bridge Approach...Could see some SCT/BKN conditions just south
of the bridge, though overall expecting similar conditions to
that of the terminal.
Monterey Bay Terminals...MVFR conditions will likely prevail at
KMRY during the day. There's a chance KSNS could transition from
MVFR to VRF given sufficient mixing, though opted to take the
conservative approach in the TAF. Will continue to monitor and
amend if necessary. MVFR/IFR conditions expected overnight.
.MARINE...as of 8:15 AM PDT Tuesday...Winds will continue to
decrease through the day as high pressure over the eastern Pacific
weakens. Winds will turn southerly by Thursday morning as a weak
low pressure system approaches from the west. This low will bring
a chance of showers Thursday through Friday night. A long period
southwest swell will persist with a shorter period northwest swell
through the majority of the week.
.Tngt...SCA...SF Bay until 9 PM
PUBLIC FORECAST: AS
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