San Pasqual Battlefield State Historic Park
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the San Pasqual Battlefield State Historic Park clear sky chart from 2005-11-06 to 2025-10-04.

This page is a summary of past forecasts. Even though it's based only on forecasts, some people use these pages as clue to a site's climate. But climate data based on actual observation should be preferred (if you can find it!).

Cloud, Transparency and Seeing forecasts are summarized individually. But because good observing conditions require a combination of minimum cloud cover, transparency and seeing, the individual forecast summaries can be difficult to interpret. The observing conditions section counts the combinations of conditions needed for common types of astronomical observation.

Observing Conditions

The following tables count the occurrence of the combinations of forecast and darkness conditions needed for different observations. Conditions are rated by by what percentage of the hours the observation would likely be attempted are usable.

Observation Type	Minimum conditions for hour to be usable				Out of hours
	Clear of Clouds	Transparency	Seeing	Sky Brightness
Planetary:	50%	(no limit)	Average	(no limit)	Nighttime Hours
Deep Sky:	70%	Average	(no limit)	5.9	Nighttime Hours
CCD Imaging:	70%	Below Average	Poor	(no limit)	Nighttime Hours

Percentages are of nighttime hours per month, or per year, when a particular observing conditions was met. Deep Sky percentages never exceed 50% because the moon is up half the time. Deep sky percentages are much lower for charts at high latitudes because of fewer dark hours in the summer.

Overall

By Month

Individual Forecasts

The length of each colored bar in the "occurrence of each Forecast" column is proportional to the number of times the chart forecast that color. The percentages are of the total number of hours per month, or per year, with a particular forecast. The colors as the same as those used in clear sky charts.

Note: Transparency probabilities are only counted for those hours that have 30% or less cloud cover. Seeing probabilities are only counted for those hours that have 80% or less cloud cover. If that's too tricky, try Observing Conditions instead.

Overall

		Occurrence of each Forecast	Data Points
Cloud Cover	Day	5% 3 1 3 2 2 3 2 4 6% 67%	134944
	Night	7% 6% 2 4 2 2 3 2 5% 6% 60%	132076
Transparency	Day	20% 2 3 17% 28% 30%	130039
	Night	27% 2 4 15% 24% 28%	127954
Seeing	Day	8% 6% 25% 36% 19% 6%	17004
	Night	9% 3 8% 35% 35% 10%	27339

By Month

Percentage Cloud Cover SW (2006-)
Color Meanings: Overcast 90% covered 80% covered 70% covered 60% covered 50% covered 40% covered 30% covered 20% covered 10% covered Clear
Month	Days in Month		Occurrence of each Forecast	Data Points
January	1st to 10th	Day	6% 3 1 3 3 2 3 2 3 4 70%	4098
	11th to 20th	Day	6% 4 1 3 2 2 3 2 4 6% 68%	4348
	21st to end	Day	11% 5% 2 4 3 4 4 4 6% 8% 48%	5016
February	1st to 10th	Day	10% 5% 2 5% 3 4 3 3 3 5% 57%	2000
	11th to 20th	Day	10% 7% 1 4 3 2 4 3 5% 6% 54%	1950
	21st to end	Day	12% 6% 2 6% 4 4 4 4 5% 5% 49%	1650
March	1st to 10th	Day	10% 8% 2 6% 4 4 4 4 8% 8% 41%	4518
	11th to 20th	Day	11% 5% 2 4 3 3 3 3 5% 7% 54%	4777
	21st to end	Day	11% 6% 2 4 3 3 3 3 5% 6% 54%	5749
April	1st to 10th	Day	8% 6% 2 4 3 3 4 3 5% 7% 56%	2400
	11th to 20th	Day	5% 4 1 4 3 3 3 3 5% 6% 62%	2369
	21st to end	Day	7% 5% 1 2 2 2 3 3 4 8% 62%	2400
May	1st to 10th	Day	6% 5% 2 4 2 2 2 2 4 5% 66%	5721
	11th to 20th	Day	3 5% 2 3 2 2 3 3 6% 9% 61%	5841
	21st to end	Day	3 5% 2 4 2 3 2 2 4 7% 65%	6423
June	1st to 10th	Day	4 5% 1 4 2 2 3 2 5% 6% 66%	2600
	11th to 20th	Day	3 3 1 3 2 2 2 2 3 4 76%	2600
	21st to end	Day	1 2 1 2 2 2 2 2 4 4 78%	2600
July	1st to 10th	Day	1 1 1 1 1 1 1 2 4 87%	5879
	11th to 20th	Day	1 1 1 2 2 2 2 2 6% 7% 75%	5880
	21st to end	Day	1 1 1 1 1 1 2 2 4 5% 81%	6144
August	1st to 10th	Day	1 1 1 1 1 2 2 3 5% 84%	5346
	11th to 20th	Day	1 1 1 1 1 1 1 3 4 87%	5364
	21st to end	Day	2 1 2 1 2 2 2 4 4 79%	5984
September	1st to 10th	Day	2 2 1 2 2 2 3 2 4 5% 75%	2378
	11th to 20th	Day	3 2 1 2 1 1 2 1 3 4 80%	2200
	21st to end	Day	3 3 1 3 1 2 2 2 3 6% 76%	2200
October	1st to 10th	Day	2 2 1 2 2 1 2 2 3 4 78%	3524
	11th to 20th	Day	3 3 1 3 2 2 2 2 4 5% 75%	3469
	21st to end	Day	3 3 1 3 2 2 2 3 5% 6% 71%	3283
November	1st to 10th	Day	5% 3 1 2 2 2 3 3 5% 6% 68%	1764
	11th to 20th	Day	5% 3 1 3 2 3 2 3 4 5% 69%	1800
	21st to end	Day	8% 4 2 4 2 3 4 4 5% 7% 58%	1800
December	1st to 10th	Day	5% 3 1 2 2 1 3 2 5% 8% 68%	2950
	11th to 20th	Day	9% 4 2 3 4 4 5% 4 6% 7% 52%	3409
	21st to end	Day	9% 5% 2 5% 4 5% 5% 5% 7% 8% 45%	4510
January	1st to 10th	Night	6% 4 1 3 2 3 3 2 4 6% 66%	5867
	11th to 20th	Night	6% 5% 1 4 3 3 3 2 4 6% 62%	5639
	21st to end	Night	14% 9% 2 4 3 3 4 3 4 6% 48%	5984
February	1st to 10th	Night	11% 6% 2 5% 3 2 3 3 4 5% 57%	2400
	11th to 20th	Night	11% 7% 2 5% 3 3 3 2 4 5% 54%	2338
	21st to end	Night	13% 8% 2 4 3 2 3 3 4 6% 51%	1980
March	1st to 10th	Night	20% 13% 3 6% 2 3 2 2 4 5% 39%	5376
	11th to 20th	Night	12% 13% 2 5% 3 3 3 3 4 6% 47%	5221
	21st to end	Night	12% 14% 3 6% 3 3 3 2 4 6% 44%	5209
April	1st to 10th	Night	10% 9% 2 5% 3 2 3 3 5% 7% 51%	2000
	11th to 20th	Night	8% 10% 3 4 3 2 3 3 4 5% 54%	1979
	21st to end	Night	9% 9% 2 5% 3 3 3 3 4 7% 53%	2000
May	1st to 10th	Night	10% 10% 3 4 2 3 2 2 5% 5% 56%	4249
	11th to 20th	Night	7% 13% 3 6% 3 3 3 2 5% 10% 46%	4074
	21st to end	Night	5% 14% 4 6% 3 3 3 2 4 6% 51%	4474
June	1st to 10th	Night	4 10% 3 5% 4 3 3 3 6% 8% 52%	1800
	11th to 20th	Night	3 5% 1 3 2 3 3 2 5% 7% 65%	1800
	21st to end	Night	2 2 1 3 1 2 4 2 6% 6% 70%	1800
July	1st to 10th	Night	2 1 1 1 1 1 4 5% 83%	4100
	11th to 20th	Night	2 1 4 2 2 3 2 8% 10% 67%	4100
	21st to end	Night	1 3 1 2 2 2 2 2 5% 6% 74%	4737
August	1st to 10th	Night	1 1 1 1 1 1 1 1 3 6% 83%	4486
	11th to 20th	Night	1 1 1 1 1 2 2 7% 6% 78%	4506
	21st to end	Night	2 2 1 1 1 2 2 5% 7% 76%	5015
September	1st to 10th	Night	2 4 1 4 2 2 3 2 5% 6% 69%	2020
	11th to 20th	Night	4 5% 1 3 2 2 2 2 4 4 72%	2200
	21st to end	Night	3 5% 1 3 1 1 2 1 5% 5% 73%	2200
October	1st to 10th	Night	3 3 1 2 1 2 2 2 3 5% 77%	3523
	11th to 20th	Night	5% 8% 2 4 2 3 2 1 5% 5% 63%	3469
	21st to end	Night	4 4 1 3 2 2 3 3 4 6% 68%	4276
November	1st to 10th	Night	6% 4 1 3 2 3 2 3 4 7% 66%	2535
	11th to 20th	Night	4 4 1 4 2 3 3 2 4 6% 66%	2600
	21st to end	Night	7% 5% 2 4 4 4 4 4 5% 7% 55%	2600
December	1st to 10th	Night	5% 3 1 3 2 2 3 2 5% 6% 67%	4240
	11th to 20th	Night	10% 7% 2 4 3 3 4 4 7% 8% 50%	4811
	21st to end	Night	8% 8% 2 6% 3 3 3 4 6% 10% 46%	6468

Transparency (when cloud cover <= 30%)
Color Meanings: Too cloudy to forecast Poor Below Average Average Above average Transparent
Month	Days in Month		Occurrence of each Forecast	Data Points
January	1st to 10th	Day	21% 2 2 17% 26% 32%	4099
	11th to 20th	Day	21% 1 6% 19% 21% 32%	4348
	21st to end	Day	32% 3 4 10% 27% 23%	5016
February	1st to 10th	Day	32% 2 3 13% 21% 29%	2000
	11th to 20th	Day	31% 2 5% 15% 27% 20%	1960
	21st to end	Day	38% 2 4 15% 19% 22%	1650
March	1st to 10th	Day	37% 3 4 21% 21% 14%	4518
	11th to 20th	Day	31% 2 7% 26% 22% 12%	4777
	21st to end	Day	31% 2 8% 33% 16% 10%	5749
April	1st to 10th	Day	29% 3 6% 24% 25% 14%	2400
	11th to 20th	Day	24% 2 4 21% 28% 20%	2372
	21st to end	Day	22% 2 5% 24% 34% 12%	2400
May	1st to 10th	Day	23% 2 4 21% 37% 13%	5721
	11th to 20th	Day	21% 3 3 21% 40% 12%	5844
	21st to end	Day	21% 3 3 19% 41% 14%	6424
June	1st to 10th	Day	21% 3 3 22% 32% 19%	2600
	11th to 20th	Day	15% 2 1 11% 30% 41%	2600
	21st to end	Day	12% 2 1 7% 24% 54%	2600
July	1st to 10th	Day	6% 1 1 5% 18% 70%	5816
	11th to 20th	Day	10% 2 3 15% 39% 31%	5811
	21st to end	Day	8% 1 4 20% 28% 38%	5967
August	1st to 10th	Day	10% 2 3 18% 40% 28%	3890
	11th to 20th	Day	8% 2 3 12% 26% 50%	3880
	21st to end	Day	8% 2 1 7% 25% 56%	4311
September	1st to 10th	Day	14% 3 2 8% 35% 38%	2378
	11th to 20th	Day	12% 2 7% 36% 43%	2200
	21st to end	Day	14% 2 1 12% 31% 40%	2200
October	1st to 10th	Day	12% 2 1 9% 18% 58%	3524
	11th to 20th	Day	14% 2 1 14% 29% 40%	3469
	21st to end	Day	15% 2 1 10% 32% 40%	3283
November	1st to 10th	Day	18% 2 4 15% 22% 38%	1764
	11th to 20th	Day	19% 2 4 12% 22% 41%	1800
	21st to end	Day	26% 2 5% 13% 21% 33%	1800
December	1st to 10th	Day	17% 1 4 12% 25% 40%	2950
	11th to 20th	Day	31% 2 6% 14% 24% 22%	3408
	21st to end	Day	37% 2 6% 24% 23% 9%	4510
January	1st to 10th	Night	22% 2 3 14% 30% 30%	5867
	11th to 20th	Night	25% 2 6% 19% 16% 31%	5639
	21st to end	Night	39% 2 3 9% 23% 23%	5984
February	1st to 10th	Night	31% 2 4 14% 21% 28%	2400
	11th to 20th	Night	35% 2 5% 12% 23% 23%	2339
	21st to end	Night	36% 2 3 15% 21% 22%	1980
March	1st to 10th	Night	49% 2 5% 14% 17% 13%	5376
	11th to 20th	Night	40% 2 5% 24% 20% 9%	5221
	21st to end	Night	44% 2 7% 19% 16% 11%	5209
April	1st to 10th	Night	33% 3 6% 22% 21% 15%	2000
	11th to 20th	Night	32% 3 4 18% 23% 19%	1979
	21st to end	Night	35% 3 5% 21% 23% 14%	2000
May	1st to 10th	Night	33% 2 4 22% 27% 11%	4246
	11th to 20th	Night	41% 2 3 16% 29% 9%	4075
	21st to end	Night	38% 2 2 17% 28% 12%	4474
June	1st to 10th	Night	32% 4 4 15% 28% 16%	1800
	11th to 20th	Night	22% 3 1 10% 28% 36%	1800
	21st to end	Night	16% 5% 2 5% 24% 49%	1800
July	1st to 10th	Night	6% 2 1 5% 19% 67%	4055
	11th to 20th	Night	13% 3 3 18% 41% 22%	4046
	21st to end	Night	13% 2 3 20% 29% 32%	4602
August	1st to 10th	Night	9% 2 3 19% 42% 26%	3256
	11th to 20th	Night	9% 3 4 14% 24% 46%	3256
	21st to end	Night	9% 3 1 7% 25% 55%	3608
September	1st to 10th	Night	18% 4 2 10% 27% 40%	2020
	11th to 20th	Night	18% 2 1 8% 31% 40%	2200
	21st to end	Night	16% 2 1 11% 35% 35%	2200
October	1st to 10th	Night	14% 2 2 10% 18% 55%	3523
	11th to 20th	Night	25% 2 2 10% 20% 41%	3469
	21st to end	Night	20% 2 1 9% 25% 43%	4276
November	1st to 10th	Night	21% 2 3 15% 19% 39%	2535
	11th to 20th	Night	21% 2 2 13% 19% 41%	2600
	21st to end	Night	29% 2 5% 15% 17% 31%	2600
December	1st to 10th	Night	20% 2 4 13% 23% 39%	4240
	11th to 20th	Night	33% 2 5% 12% 20% 27%	4811
	21st to end	Night	35% 2 8% 24% 21% 11%	6468

Seeing (when cloud cover <= 80%)
Color Meanings: Too cloudy to forecast Bad 1/5 Poor 2/5 Average 3/5 Good 4/5 Excellent 5/5
Month	Days in Month		Occurrence of each Forecast	Data Points
January	1st to 10th	Day	17% 5% 25% 34% 18% 2	300
	11th to 20th	Day	13% 7% 25% 38% 15% 3	405
	21st to end	Day	15% 9% 29% 33% 11% 3	550
February	1st to 10th	Day	14% 8% 32% 30% 13% 3	500
	11th to 20th	Day	14% 12% 30% 31% 11% 2	495
	21st to end	Day	17% 11% 37% 27% 7% 1	414
March	1st to 10th	Day	16% 12% 32% 28% 10% 2	500
	11th to 20th	Day	16% 9% 32% 30% 10% 3	500
	21st to end	Day	10% 15% 38% 25% 10% 1	550
April	1st to 10th	Day	11% 12% 30% 27% 15% 5%	500
	11th to 20th	Day	7% 12% 36% 31% 10% 3	492
	21st to end	Day	9% 11% 28% 29% 16% 6%	500
May	1st to 10th	Day	13% 9% 30% 29% 14% 6%	503
	11th to 20th	Day	9% 8% 29% 34% 16% 4	528
	21st to end	Day	8% 9% 28% 33% 18% 4	573
June	1st to 10th	Day	4 5% 23% 33% 27% 8%	530
	11th to 20th	Day	5% 2 26% 38% 22% 7%	530
	21st to end	Day	3 2 22% 41% 24% 9%	530
July	1st to 10th	Day	2 1 13% 41% 31% 12%	526
	11th to 20th	Day	2 8% 44% 30% 16%	524
	21st to end	Day	2 7% 48% 28% 15%	575
August	1st to 10th	Day	1 1 12% 46% 26% 14%	527
	11th to 20th	Day	2 1 9% 49% 24% 16%	517
	21st to end	Day	2 2 13% 45% 26% 12%	583
September	1st to 10th	Day	4 1 19% 46% 19% 10%	530
	11th to 20th	Day	5% 4 25% 44% 17% 5%	530
	21st to end	Day	4 7% 27% 34% 19% 8%	530
October	1st to 10th	Day	5% 6% 29% 35% 21% 4	503
	11th to 20th	Day	7% 6% 28% 40% 17% 3	490
	21st to end	Day	7% 4 27% 35% 22% 5%	439
November	1st to 10th	Day	8% 4 21% 39% 23% 5%	300
	11th to 20th	Day	7% 4 23% 41% 21% 4	300
	21st to end	Day	11% 5% 28% 36% 14% 5%	300
December	1st to 10th	Day	10% 4 25% 36% 22% 2	300
	11th to 20th	Day	7% 4 24% 38% 21% 5%	300
	21st to end	Day	19% 5% 24% 35% 15% 3	330
January	1st to 10th	Night	12% 2 19% 38% 22% 8%	800
	11th to 20th	Night	10% 2 15% 42% 24% 7%	800
	21st to end	Night	15% 2 16% 42% 21% 3	880
February	1st to 10th	Night	14% 3 12% 41% 23% 7%	800
	11th to 20th	Night	15% 3 13% 40% 22% 6%	784
	21st to end	Night	16% 2 16% 40% 21% 4	660
March	1st to 10th	Night	18% 2 14% 42% 22% 2	800
	11th to 20th	Night	15% 3 10% 40% 25% 8%	800
	21st to end	Night	13% 3 11% 41% 26% 5%	880
April	1st to 10th	Night	13% 4 8% 45% 25% 5%	800
	11th to 20th	Night	12% 5% 11% 39% 27% 6%	791
	21st to end	Night	13% 5% 8% 36% 31% 9%	800
May	1st to 10th	Night	12% 6% 8% 38% 31% 5%	671
	11th to 20th	Night	12% 5% 8% 28% 39% 7%	591
	21st to end	Night	11% 7% 8% 33% 37% 4	650
June	1st to 10th	Night	8% 5% 7% 34% 40% 7%	600
	11th to 20th	Night	4 2 6% 37% 44% 7%	600
	21st to end	Night	3 2 4 35% 49% 7%	600
July	1st to 10th	Night	1 2 1 23% 61% 12%	585
	11th to 20th	Night	1 1 1 17% 67% 14%	582
	21st to end	Night	3 2 16% 60% 20%	769
August	1st to 10th	Night	2 2 20% 57% 19%	796
	11th to 20th	Night	2 2 14% 58% 25%	792
	21st to end	Night	2 2 14% 58% 23%	880
September	1st to 10th	Night	5% 2 1 19% 58% 15%	800
	11th to 20th	Night	7% 3 2 29% 49% 11%	800
	21st to end	Night	5% 2 4 35% 40% 13%	800
October	1st to 10th	Night	6% 2 5% 42% 38% 8%	772
	11th to 20th	Night	9% 4 7% 36% 34% 11%	760
	21st to end	Night	8% 2 8% 36% 32% 14%	836
November	1st to 10th	Night	8% 1 8% 42% 31% 10%	780
	11th to 20th	Night	7% 1 10% 43% 28% 12%	800
	21st to end	Night	10% 2 13% 42% 25% 9%	800
December	1st to 10th	Night	11% 2 15% 42% 22% 8%	800
	11th to 20th	Night	16% 3 14% 41% 21% 6%	800
	21st to end	Night	14% 2 15% 40% 22% 7%	880

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