Weather forecast for Monday April 18

April 18, 2011

By JOHN LINDSEY from PG&E

A 1,022-millibar Eastern Pacific High is parked about 600 miles to the west-southwest of San Luis Obispo and will gradually weaken and move westward over the next 48 hours.

This condition will allow a series of weak and relatively warm low pressure systems to move into Northern California this week.

The first is this series is an 1,011 millibar low currently off Cape Mendocino. This system will move eastward towards Nevada and will spread rain southward toward Monterey Bay
today. The associated cold front will pass the Central Coast later today with areas of drizzle and a few sprinkles, especially along the coastline. In other words, today will be dreary but mild with high temperatures mostly in the 60s.

Little change is expected on Tuesday, except we should see a greater amount of Sun during the afternoon hours.

Another, but slightly stronger 1,009-millibar low-pressure system will approach the Central Coast later Tuesday, producing night and morning coastal low clouds and fog. As the system moves over the Central Coast on Wednesday, it’s expected to produce gentle southerly winds and mostly cloudy conditions with a few sprinkles or light rain showers.

Both of these systems will have little in the way of any upper-level support and most Central Coast locations shouldn’t have any measurable rainfall.

A return to dry and warmer weather along with strong- to gale-force northwesterly winds along the coastline is expected Thursday through next weekend.

Yesterday’s         Today’s          Tomorrow’s
Min    Max        Min    Max         Min     Max
52.4°   56.8°     49.1°   60.0°      52.0°    61.0°

PG&E San Francisco Met Office predicted temps:

Inland Temperatures, Paso Robles

Actual                    Predicted

Sun        Mon   Tue   Wed   Thu   Fri   Sat   Sun   Mon
54 80      50 72 46 73 43 67 41 66 39 70 42 74 49 80 45 81

Coastal Valleys Temperatures, San Luis Obispo

Sun        Mon   Tue   Wed   Thu   Fri   Sat   Sun   Mon
52 71      48 65 46 66 45 63 47 65 46 67 45 70 49 75 48 75

SEA/SWELL:

Today’s 3- to 5-foot northwesterly (295-degree deep-water) sea and swell (with a 7- to 15-second period) will continue at this height through Tuesday morning, building to 4- to 6-feet
(with a 7- to 13-second period) Tuesday afternoon and night.

A 3- to 4-foot west-northwesterly (280-degree deep-water) swell (with an 8- to 12-second period) is forecast along our coastline on Wednesday through Thursday morning.

Another round of strong to gale force (25- to 38-mph) northwesterly winds Thursday afternoon, will produce a 5- to 7-foot northwesterly (310-degree deep-water) sea and swell
(with a 7- to 11-second period) Thursday afternoon through Friday, decreasing to 3- to 5-feet on Saturday through Sunday.

Arriving from the southern hemisphere:

A 1- to 2-foot southern hemisphere (205-degree deep-water) swell (with a 16- to 18-second period) will arrive along our coastline Tuesday, increasing to 2- to 3-feet (with a 14- to
16-second period) on Wednesday.

Another, but longer period southern hemisphere swell will overlap the first wave train, and will continue to produce a 2- to 3-foot southern hemisphere (205-degree deep-water)
swell (with a 13- to 20-second period) on Thursday. This 2- to 3-feet swell will continue at this height but with a gradually shorter period through Sunday.

WINDS:

Today’s moderate to fresh (13 to 24-mph) northwesterly winds will continue at this level through Tuesday, shifting and decreasing out of the south on Wednesday.

Strong to gale force (25- to 38-mph) northwesterly winds are forecast on Thursday through Saturday, decreasing on Sunday.

DIABLO CANYON METEOROLOGICAL TOWER WIND DATA:

Today’s winds:

Max peak winds:      NW       19.5 mph at    6:30 a.m.
Max sustained wind:  NW       13.0 mph at    6:30 a.m.

Yesterday’s Maximum Winds:

Max peak winds:      NW       29.3 mph at    1:45 p.m.
Max sustained wind:  NW       21.5 mph at    2:00 p.m.

SEAWATER TEMPERATURES:

The Diablo Canyon waverider buoy is reporting a sea surface temperature of 55.0 degrees while the Nortek AWAC current meter is reporting 49.8 degrees.

Intake seawater temperatures will range between 49- and 51 -degrees through Friday.

OCEAN CURRENTS:

Both the DCPP Cal Poly CODAR stations and the DCPP Nortek AWAC meter are indicating a southerly (offshore) flowing current today.

This southerly (offshore) current will continue to flow southward through Friday.

SEAWATER VISIBILITY:

Seawater visibility was 20- to 22-feet at the Diablo Canyon Intake.

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24-Hour Ocean Condition Outlook for Monday 04/18 to Tuesday 04/19

Sea/Swell       DIR. NW      HT.   3-5   PER.   7-15  This morning
Remaining  at:  DIR. NW      HT.   3-5   PER.   7-14  This afternoon
Remaining  at:  DIR. NW      HT.   3-5   PER.   7-13  Tonight

WINDS:          DIR. NW      SPEED 10-15              This morning
Increasing to:  DIR. NW      SPEED 15-20 + 25         This afternoon
Decreasing to:  DIR. NW      SPEED 10-15              Tonight
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48-Hour Ocean Condition Outlook for Tuesday 04/19 to Wednesday 04/20

Sea/Swell       DIR. NW      HT.   3-5   PER.   7-13  Tuesday morning
Increasing to:  DIR. NW      HT.   4-6   PER.   7-13  Tuesday afternoon
Remaining  at:  DIR. NW      HT.   4-6   PER.   7-13  Tuesday night

WINDS:          DIR. NW      SPEED 10-15              Tuesday morning
Increasing to:  DIR. NW      SPEED 15-20 + 25         Tuesday afternoon
Decreasing to:  DIR. VAR.    SPEED  5-10              Tuesday night
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Extended Ocean Condition Outlook:

Gentle southerly winds are forecast on Wednesday.

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The 24 – Hour Ocean Data From The Diablo Canyon Wave rider Buoy
MONTH  DAY  TIME  SIG.HEIGHT   PERIOD   SWELL DIRECTION     SST
04    14    0512     5.0       12            275          51.6
04    15    1212     4.9       11            285          52.7
04    16    0442     4.8        8            288          55.0
04    17    1912     5.8        7            279          52.5
04    18    0612     4.7       15            220          52.2

(cm) (sec)  22+   20    17    15    13     11    9    7
———————————————————————
04 14  0512  154    4     1     4    28    30   102   262   211  432
04 15  1212  150   11     1     5    15    21    79   476   253  181
04 16  0442  146    7     1     5     4    20    81   154   260  439
04 17  1912  176    7     3     9    81    53    22   154   185  670
04 18  0612  143    4     2    19    20   108    20    68   163  446

Daily Swell Inspection Program

NAME                      DAY   TIME    HEIGHT   PERIOD     SST
(PST)   (FEET)  (SECONDS) (DEG. F)
# 166  Ocean Station Papa      18    0402       4       13       42.6
# 06   SE Papa                 18    0650      10       10       51.3
# 59   California Buoy         18 0650 7 8 55.8
# 01   Point Reyes Waverider   18 0646 4 8 53.4
# 15   Monterey Waverider Buoy 18    0650       4       16       51.6
# 28   Cape San Martin, Ca     18    0650       6       15       54.5
# 50   DCPP Waverider Buoy, Ca 18    0612       5       15       52.2
# 63   Harvest Buoy            18 0620 7 8 50.7
# 01   NW Hawaii               18    0650       5       10       74.5

* Note: Height (significant swell height) is the average height of the waves in the top third of the wave record. Maximum wave height may be up to TWICE the height in the data shown in the above table.

Precipitation at the Diablo Canyon Ocean Lab.

Saturday  1500 through Sunday      1500   0.00 inches
Sunday    1500 through Monday      1500   0.00 inches

Precipitation this rain season (July 1 – June 30): 25.84 inches
Average season rainfall at DIP to date:            23.67 inches

Ocean Lab Barometer:  29.99 in/Hg or 1015.5 mb  +1.2 mb (Rising)
Sunrise and Sunset

Today’s         Sunrise 6:27 AM      Sunset 7:38  PM
Tomorrow’s      Sunrise 6:26 AM      Sunset 7:39  PM

Tides:
Low Tide                 High Tide
AM          PM           AM          PM
18 Monday      4:58 -1.2    4:34  1.2   11:19 4.3   10:46  6.3
19 Tuesday     5:49 -1.3    5:16  1.6  (12:18 4.1)  11:28  6.2
20 Wednesday   6:42 -1.3    6:02  2.0   —– —    1:20  3.8
21 Thursday    7:39 -1.1    6:55  2.4   12:14 5.9    2:29  3.6
22 Friday      8:40 -0.7    8:02  2.6    1:05 5.4    3:46  3.5
23 Saturday    9:45 -0.4    9:32  2.7    2:04 4.9    5:03  3.6
24 Sunday     10:50 -0.1   11:09  2.5    3:15 4.4    6:06  3.8
25 Monday     11:50  0.1   —–  —    4:36 4.1    6:53  4.0
26 Tuesday    12:29  2.1   12:40  0.4    5:55 3.9    7:29  4.2
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This day in weather history

1906 – A severe earthquake shook San Francisco, and unusual easterly winds spread fires destroying the city. 1989. (David Ludlum)

1944 – California experienced its worst hailstorm of record. Damage mounted to two million dollars as two consecutive storms devastated the Sacramento Valley destroying the fruit
crop.

1970 – Rapid City, SD, received a record 22 inches of snow in 24 hours. (17th-18th)

1989 – Thunderstorms produced large hail and damaging winds in Texas, Oklahoma and Arkansas. A thunderstorm in Pecos County of southwest Texas produced wind gusts to 90 mph at Imperial. (Storm Data) (The National Weather Summary)

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I want to personally thank those who came out Saturday to help us with the Earth Day projects at Montaña de Oro State Park. I would especially like to thank Tom Esser for
organizing this wonderful event over the years.

It’s remarkable how much good can be accomplished by a motivated group of volunteers.

This weather forecast is a service provided by Pacific Gas and Electric Company (PG&E) to our energy customers. The forecast is valid only for the Diablo Canyon Power Plant coastline area (approximately a one-half mile radius surrounding the plant). Some of the information in this forecast is provided by Pacific Weather Analysis, with their permission.

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