Weather forecast for Thursday April 21

April 21, 2011

By JOHN LINDSEY from PG&E

A weak cold front draped over the Central Coast this morning produced gentle southerly winds, mild temperatures and low-level light steady rain along the coastline.

As this cold front moves southward, a steep pressure gradient will produce strong to gale force (25 to 38-mph) post frontal northwesterly winds and clearing skies this afternoon through Friday.

Today’s high temperatures will reach the low to mid-60s, increasing to the mid-60s to low-70s on Friday.

A 1,022 millibar Eastern Pacific High, currently located about 1,800 miles west-southwest of San Luis Obispo, will allow a eastward moving 1,008 millibar low pressure system to pass just to the north of San Luis Obispo County on Saturday. This system will produce gentle southwesterly winds and extensive night and morning low clouds and fog with drizzle on Saturday and Easter Sunday.

The Eastern Pacific High will finally move eastward and take a more normal spring time position about 500 miles to the west of San Luis Obispo. this condition will produce strong to gale force northwesterly winds along our coastline on Monday through most of next week. During this period, North County temperatures will warm to the low to mid 80s, while temperatures in the coastal valleys and a few of the southwesterly (Avila Beach and Cayucos) facing beaches will reach the high 70s to low 80s. In other words, absolutely beautiful spring weather.

Yesterday’s         Today’s          Tomorrow’s
Min    Max        Min    Max         Min     Max
49.5°   56.7°     52.8°   57.0°      50.0°    58.0°

PG&E San Francisco Met Office predicted temps:

Inland Temperatures, Paso Robles

Actual                    Predicted

Wed        Thu   Fri   Sat   Sun   Mon   Tue   Wed   Thu
46 70      55 68 42 72 41 69 44 73 48 75 45 80 50 85 45 80

Coastal Valleys Temperatures, San Luis Obispo

Wed        Thu   Fri   Sat   Sun   Mon   Tue   Wed   Thu
49 68      54 63 45 66 45 64 47 69 50 72 49 76 52 80 48 69

24 hours rainfall totals as of 6 a.m.

Arroyo Grande …………………………  0.11″
Atascadero ……………………………  Trace
Baywood Park ………………………….  0.17″
Cambria ………………………………  0.28″
Camp San Luis …………………………  0.16″
Condor Lookout Los Padres National Forest ..  0.07″
Diablo Canyon …………………………  0.10″
Islay Hill, San Luis Obispo, CA …………  0.05″
Los Osos, George’s Home ………………..  0.23″
Morro Bay, Riches’ Home ……………….  0.19″
Paso Robles Airport ……………………  Trace
Pismo Beach …………………………..  0.11″
PG&E Energy Education Center ……………  0.15″
Rocky Butte near San Simeon …………….  0.28″
Santa Margarita Fire Department …………  0.03″
San Luis Obispo Water Reclamation Facility .  0.04″
Santa Maria Public Airport ……………..  0.05″
San Luis Obispo County Airport ………….  0.05″
San Simeon, Walt’s Home ………………..  0.31″
SLOWeather.com ………………………..  0.05″

SEA/SWELL:

Fresh to strong (19- to 31-mph) northwesterly winds this afternoon will produce a 3- to 5-foot northwesterly (295-degree deep-water) sea and swell (with a 7- to 9-second period) this afternoon through tonight, increasing to 4- to 6-feet on Friday.

A 3- to 4-foot northwesterly (320-degree deep-water) swell (with an 8- to 11-second period) will develop along our coastline on Saturday and will continue at this height and period through Sunday.

Strong to gale force (25- to 38-mph) northwesterly winds will generate 4- to 6-foot (310-degree deep-water) sea and swell (with a 5- to 11-second period) on Monday, increasing to 5- to 7-feet (with a 6- to 12-second period) on Tuesday and remaining at this height and period through Friday.

Arriving from the southern hemisphere:

Today’s 2- to 3-foot southern hemisphere (200-degree deep -water) swell (with a 14- to 16-second period) will remain at this height but with a gradually shorter period through tonight.

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

WINDS:

Strong to gale force (25- to 38-mph) northwesterly winds will develop this afternoon through Friday, decreasing and shifting out of the southwest to gentle to moderate (8 to 18-mph) levels on Saturday through Sunday morning.

Increasing northwesterly winds are forecast Sunday afternoon, building to strong to gale force (25- to 38-mph) levels on Monday through most of next week.

DIABLO CANYON METEOROLOGICAL TOWER WIND DATA:

Today’s winds:

Max peak winds:      S         4.0 mph at    4:15 a.m.
Max sustained wind:  S         1.3 mph at    4:15 a.m.

Yesterday’s Maximum Winds:

Max peak winds:      NW       13.4 mph at    4:45 p.m.
Max sustained wind:  NW        9.4 mph at    4:45 p.m.

SEAWATER TEMPERATURES:

The Diablo Canyon waverider buoy is reporting a sea surface temperature of 51.4 degrees while the Nortek AWAC current meter is reporting 51.0 degrees.

Intake seawater temperatures will range between 51- and 53 -degrees through tonight.

Intake seawater temperatures will decrease to 50- and 52 -degrees on Friday and will remain at this level through Monday, decreasing to 49- and 51 degrees on Tuesday through next Friday.

OCEAN CURRENTS:

Both the DCPP Cal Poly CODAR stations and the DCPP Nortek AWAC meter are indicating a northerly (onshore) flowing current. This current will continue to flow northward through this morning.

A southerly (offshore) current will develop this afternoon and will continue to flow southward through next Friday.

SEAWATER VISIBILITY:

Seawater visibility was 18- to 20-feet at the Diablo Canyon Intake.

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24-Hour Ocean Condition Outlook for Thursday 04/21 to Friday 04/22

Sea/Swell       DIR. NW      HT.   1-3   PER.   8-11  This morning
Increasing to:  DIR. NW      HT.   3-5   PER.   7-9   This afternoon
Remaining  at:  DIR. NW      HT.   3-5   PER.   7-9   Tonight

(Combined with:  DIR. SW      HT.   2-3   PER.  13-20  All day)

WINDS:          DIR. S       SPEED  5-10              This morning
Increasing to:  DIR. NW      SPEED 25-30 + 35         This afternoon
Decreasing to:  DIR. NW      SPEED 15-20 + 25         Tonight
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48-Hour Ocean Condition Outlook for Friday 04/22 to Saturday 04/23

Sea/Swell       DIR. NW      HT.   3-5   PER.   7-11  Friday morning
Increasing to:  DIR. NW      HT.   4-6   PER.   7-11  Friday afternoon
Remaining  at:  DIR. NW      HT.   4-6   PER.   7-11  Friday night

(Combined with:  DIR. SW      HT.   2-3   PER.  13-18  All day Friday)

WINDS:          DIR. NW      SPEED 15-20 + 25         Friday morning
Increasing to:  DIR. NW      SPEED 25-30 + 35         Friday afternoon
Decreasing to:  DIR. NW      SPEED 15-20              Friday night
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Extended Ocean Condition Outlook:

The northwesterly winds will decrease on Saturday.

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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
04    19    0212     2.6       17            215          51.4
04    20    0842     3.4       15            210          56.3
04    21    0342     2.8       14            219          51.4

(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
04 19  0212   78    4     2    11    62    44    40    13    35  116
04 20  0842  105   15     1     8    35   224    66    23    42  156
04 21  0342   84   15     4    10    38   113   107    15     7  103

Daily Swell Inspection Program

NAME                      DAY   TIME    HEIGHT   PERIOD     SST
(PST)   (FEET)  (SECONDS) (DEG. F)
# 166  Ocean Station Papa      21    0002       7        9       43.5
# 06   SE Papa                 21    0350       6        7       52.2
# 59   California Buoy         21    0350       5       15       55.2
# 01   Point Reyes Waverider   21    0346       6       14       52.9
# 15   Monterey Waverider Buoy 21    0350       3       14       56.1
# 28   Cape San Martin, Ca     21    0350       3       14       56.1
# 50   DCPP Waverider Buoy, Ca 21    0342       3       14       51.4
# 63   Harvest Buoy            21    0320       3       13       52.9
# 01   NW Hawaii               21    0350       5        8       75.7

* 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.

Monday    1500 through Tuesday     1500   0.00 inches
Tuesday   1500 through Wednesday   1500   0.00 inches
Wednesday 1500 through Thursday    0600   0.10 inches

Precipitation this rain season (July 1 – June 30): 25.94 inches
Average season rainfall at DIP to date:            23.76 inches

Ocean Lab Barometer:  30.04 in/Hg or 1017.4 mb  +0.0 mb (Steady)
Sunrise and Sunset

Today’s         Sunrise 6:23 AM      Sunset 7:40  PM
Tomorrow’s      Sunrise 6:22 AM      Sunset 7:41  PM

Tides:
Low Tide                 High Tide
AM          PM           AM          PM
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
27 Wednesday   1:27  1.7    1:22  0.6    7:03 3.8    7:58  4.4
28 Thursday    2:13  1.2    1:57  0.9    8:00 3.7    8:23  4.7
29 Friday      2:52  0.8    2:27  1.1    8:49 3.7    8:47  4.9
30 Saturday    3:27  0.4    2:55  1.4    9:33 3.7    9:10  5.1
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This day in weather history

1958 – Portions of Montana were in the midst of a spring snowburst. Snowfall amounts ranged up to 55 inches at Red Lodge, 61 inches at Nye Mine, and 72 inches at Mystic Lake. (David Ludlum)

1988 – After having had just twelve rainouts in the previous twenty-six years at Dodger Stadium, a third day of heavy rain in southern California rained out a double-header at Dodger Stadium which had been scheduled due to rainouts the previous two days. (Storm Data)

2007 – The cold which passed our area early Friday morning produced 0.58 inches of rain at the Diablo Canyon Ocean Lab.

2008 – The strong to gale force (25-38 mph) northwesterly winds which have been relentlessly blowing along our coastline since last week will finally decrease on Tuesday. These
winds have produced a great amount of upwelling along our coastline giving some of the coldest (47° to 49°F) seawater temperatures on record.

2009 – The temperature at the San Luis Obispo County Airport reached  101 degrees yesterday afternoon. Cal Poly reached 100 degrees which was a record for the date but not the
month. The record for the month of April was 104 degrees on Apr. 8, 1989.

2010 – Gale force northwesterly winds along the northern and central California coastline will produce “Victory at Sea” conditions today.

This morning’s 10- to 12-foot northwesterly (300-degree deep-water) sea/swell (with a 5- to-15 second period) will build to 13- to 15-feet (with a 7- to 14-second period) this afternoon and will remain at this height through tonight.

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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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