Palomar East
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Palomar East clear sky chart from 2005-11-06 to 2026-02-16.

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	16% 6% 2 6% 4 4 4 4 5% 7% 40%	130947
	Night	16% 7% 2 6% 4 4 4 3 5% 6% 43%	129866
Transparency	Day	41% 6% 12% 22% 16% 3	134462
	Night	40% 6% 11% 23% 17% 3	134424
Seeing	Day	22% 16% 29% 21% 10% 3	16539
	Night	20% 13% 31% 27% 9% 1	25916

By Month

Percentage Cloud Cover NE (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	13% 6% 2 6% 4 4 4 3 5% 5% 47%	4661
	11th to 20th	Day	15% 8% 3 7% 5% 4 4 3 4 5% 44%	4747
	21st to end	Day	16% 6% 2 6% 5% 5% 5% 4 5% 6% 40%	5780
February	1st to 10th	Day	16% 6% 3 7% 5% 4 4 4 6% 6% 39%	1890
	11th to 20th	Day	17% 8% 2 7% 5% 4 4 3 5% 6% 39%	1952
	21st to end	Day	18% 9% 4 6% 4 3 4 3 5% 5% 39%	1650
March	1st to 10th	Day	21% 5% 2 5% 4 4 3 3 4 5% 44%	4476
	11th to 20th	Day	12% 6% 2 6% 5% 4 4 3 5% 7% 44%	4970
	21st to end	Day	18% 6% 2 6% 4 4 4 3 4 6% 43%	5804
April	1st to 10th	Day	17% 7% 3 7% 5% 4 4 3 6% 6% 39%	2400
	11th to 20th	Day	15% 7% 3 6% 4 4 4 3 5% 7% 40%	2374
	21st to end	Day	15% 6% 2 7% 5% 4 4 4 6% 7% 40%	2400
May	1st to 10th	Day	27% 7% 2 6% 4 4 5% 3 6% 8% 29%	5833
	11th to 20th	Day	24% 8% 3 6% 4 4 4 3 5% 7% 32%	6318
	21st to end	Day	20% 6% 2 6% 4 4 5% 4 6% 9% 35%	6949
June	1st to 10th	Day	13% 6% 2 6% 5% 5% 6% 4 7% 9% 38%	2800
	11th to 20th	Day	13% 7% 2 6% 5% 5% 6% 4 7% 8% 37%	2800
	21st to end	Day	11% 6% 2 5% 4 4 6% 5% 6% 10% 41%	2800
July	1st to 10th	Day	9% 6% 2 7% 5% 5% 6% 5% 6% 10% 38%	6360
	11th to 20th	Day	11% 7% 3 8% 5% 6% 6% 5% 8% 10% 32%	6360
	21st to end	Day	11% 7% 3 6% 5% 4 5% 4 6% 9% 40%	6847
August	1st to 10th	Day	20% 5% 2 7% 4 5% 5% 4 6% 7% 35%	4234
	11th to 20th	Day	13% 6% 2 6% 4 4 4 4 6% 8% 43%	3851
	21st to end	Day	11% 5% 2 5% 3 4 4 3 5% 8% 49%	4312
September	1st to 10th	Day	14% 6% 2 6% 4 4 5% 3 6% 6% 45%	2400
	11th to 20th	Day	13% 5% 2 4 3 3 3 3 6% 8% 50%	2363
	21st to end	Day	18% 7% 3 7% 5% 5% 4 3 5% 6% 37%	2200
October	1st to 10th	Day	17% 6% 2 5% 2 4 4 4 5% 6% 44%	2010
	11th to 20th	Day	15% 6% 2 4 4 4 4 3 5% 7% 48%	2000
	21st to end	Day	18% 6% 2 5% 3 3 3 3 5% 6% 46%	2118
November	1st to 10th	Day	12% 7% 2 5% 3 3 3 3 4 6% 53%	1851
	11th to 20th	Day	16% 5% 2 6% 3 3 3 4 5% 6% 47%	1890
	21st to end	Day	15% 7% 3 5% 3 3 3 4 5% 8% 44%	1753
December	1st to 10th	Day	14% 8% 2 5% 4 4 4 4 5% 7% 43%	2680
	11th to 20th	Day	21% 8% 2 4 3 3 3 2 4 6% 43%	3066
	21st to end	Day	17% 6% 2 6% 4 5% 5% 4 6% 7% 38%	4048
January	1st to 10th	Night	12% 7% 3 7% 4 4 4 3 5% 6% 46%	8234
	11th to 20th	Night	15% 8% 2 6% 4 3 4 3 4 6% 46%	8136
	21st to end	Night	15% 9% 2 5% 4 3 4 3 4 6% 46%	8401
February	1st to 10th	Night	15% 9% 2 6% 4 4 4 4 4 6% 41%	2730
	11th to 20th	Night	18% 8% 3 5% 4 4 4 3 5% 6% 41%	2443
	21st to end	Night	18% 8% 3 6% 4 3 3 4 4 6% 42%	1980
March	1st to 10th	Night	19% 8% 2 6% 3 3 3 3 4 5% 44%	5364
	11th to 20th	Night	12% 8% 3 6% 4 3 3 3 4 5% 50%	4986
	21st to end	Night	16% 8% 2 6% 4 4 4 3 5% 5% 43%	5113
April	1st to 10th	Night	18% 6% 2 7% 5% 5% 3 4 5% 6% 39%	2000
	11th to 20th	Night	16% 6% 2 7% 6% 3 4 4 5% 6% 41%	1975
	21st to end	Night	18% 6% 2 5% 3 3 3 3 5% 8% 44%	2000
May	1st to 10th	Night	23% 9% 3 7% 4 4 4 4 6% 8% 29%	4134
	11th to 20th	Night	23% 9% 3 7% 4 4 3 3 5% 7% 33%	3575
	21st to end	Night	22% 6% 2 6% 3 4 3 3 6% 8% 37%	3926
June	1st to 10th	Night	16% 6% 2 6% 5% 4 4 3 5% 8% 42%	1600
	11th to 20th	Night	12% 6% 3 5% 5% 5% 5% 4 5% 8% 41%	1600
	21st to end	Night	11% 4 3 6% 4 5% 5% 5% 7% 9% 43%	1600
July	1st to 10th	Night	9% 6% 2 7% 6% 5% 5% 4 7% 9% 39%	3600
	11th to 20th	Night	14% 8% 3 8% 5% 5% 5% 4 7% 9% 31%	3600
	21st to end	Night	12% 6% 2 6% 4 4 5% 4 6% 8% 43%	3988
August	1st to 10th	Night	22% 7% 3 5% 4 4 4 4 6% 8% 33%	2915
	11th to 20th	Night	13% 7% 3 6% 4 4 4 3 6% 7% 41%	3162
	21st to end	Night	11% 5% 2 5% 4 3 4 4 6% 7% 50%	3586
September	1st to 10th	Night	15% 6% 2 6% 4 4 4 3 4 6% 46%	2000
	11th to 20th	Night	11% 6% 2 6% 3 3 3 3 4 6% 53%	2036
	21st to end	Night	18% 7% 2 6% 4 4 4 4 5% 7% 39%	2200
October	1st to 10th	Night	18% 6% 2 5% 4 4 3 3 4 5% 45%	2386
	11th to 20th	Night	16% 5% 1 4 3 3 3 3 4 6% 51%	2400
	21st to end	Night	17% 7% 2 5% 3 2 3 3 5% 5% 48%	2720
November	1st to 10th	Night	11% 6% 2 4 3 3 3 3 4 6% 54%	2667
	11th to 20th	Night	17% 6% 2 5% 3 3 4 3 4 5% 48%	2730
	21st to end	Night	14% 6% 2 5% 5% 4 4 4 6% 7% 44%	2861
December	1st to 10th	Night	13% 7% 2 6% 3 4 4 3 5% 6% 47%	4720
	11th to 20th	Night	22% 7% 2 5% 3 3 4 3 4 6% 41%	5348
	21st to end	Night	19% 8% 3 6% 4 4 4 3 5% 5% 41%	7150

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	37% 5% 9% 27% 19% 2	4662
	11th to 20th	Day	41% 5% 9% 21% 18% 6%	4777
	21st to end	Day	43% 5% 12% 23% 16% 1	5780
February	1st to 10th	Day	43% 6% 14% 24% 11% 2	1890
	11th to 20th	Day	45% 5% 9% 23% 15% 2	1961
	21st to end	Day	46% 6% 11% 23% 12% 3	1650
March	1st to 10th	Day	40% 6% 9% 22% 15% 7%	4479
	11th to 20th	Day	36% 6% 12% 28% 13% 5%	4970
	21st to end	Day	42% 5% 10% 15% 23% 5%	5804
April	1st to 10th	Day	43% 7% 10% 20% 15% 5%	2400
	11th to 20th	Day	41% 6% 12% 21% 16% 4	2374
	21st to end	Day	41% 6% 12% 20% 18% 4	2400
May	1st to 10th	Day	51% 8% 14% 17% 9% 1	5843
	11th to 20th	Day	50% 7% 9% 21% 12% 1	6322
	21st to end	Day	43% 8% 11% 23% 14% 2	6949
June	1st to 10th	Day	39% 10% 13% 22% 15% 1	2800
	11th to 20th	Day	41% 9% 14% 23% 11% 2	2800
	21st to end	Day	36% 9% 14% 23% 16% 1	2800
July	1st to 10th	Day	39% 10% 14% 19% 16% 2	6290
	11th to 20th	Day	44% 9% 17% 20% 10% 1	6285
	21st to end	Day	40% 6% 11% 20% 23% 1	6650
August	1st to 10th	Day	46% 9% 12% 23% 10%	4221
	11th to 20th	Day	37% 7% 12% 29% 14% 1	3887
	21st to end	Day	33% 6% 10% 27% 22% 2	4312
September	1st to 10th	Day	38% 7% 12% 20% 21% 3	2400
	11th to 20th	Day	32% 5% 11% 25% 23% 4	2363
	21st to end	Day	48% 5% 9% 17% 19% 2	2200
October	1st to 10th	Day	36% 5% 9% 18% 27% 5%	3270
	11th to 20th	Day	26% 4 11% 25% 27% 6%	3240
	21st to end	Day	25% 4 13% 24% 29% 4	3395
November	1st to 10th	Day	34% 4 13% 25% 21% 4	1851
	11th to 20th	Day	37% 5% 11% 24% 20% 3	1890
	21st to end	Day	38% 5% 14% 30% 12% 2	1753
December	1st to 10th	Day	40% 4 16% 27% 11% 2	2680
	11th to 20th	Day	43% 4 11% 29% 11% 2	3066
	21st to end	Day	42% 8% 11% 22% 16% 2	4048
January	1st to 10th	Night	38% 5% 13% 24% 17% 4	8234
	11th to 20th	Night	40% 4 11% 21% 17% 7%	8181
	21st to end	Night	41% 3 9% 24% 21% 3	8401
February	1st to 10th	Night	43% 5% 12% 25% 11% 2	2730
	11th to 20th	Night	45% 5% 9% 20% 18% 4	2445
	21st to end	Night	43% 5% 8% 22% 18% 4	1980
March	1st to 10th	Night	41% 5% 9% 23% 12% 9%	5374
	11th to 20th	Night	35% 6% 15% 25% 14% 5%	4987
	21st to end	Night	43% 5% 7% 16% 24% 5%	5113
April	1st to 10th	Night	44% 6% 11% 19% 16% 4	2000
	11th to 20th	Night	42% 6% 10% 19% 19% 3	1975
	21st to end	Night	39% 6% 10% 21% 19% 5%	2000
May	1st to 10th	Night	52% 8% 11% 16% 10% 2	4140
	11th to 20th	Night	50% 8% 11% 16% 13% 1	3576
	21st to end	Night	44% 8% 12% 22% 13% 2	3927
June	1st to 10th	Night	40% 7% 11% 21% 19% 2	1600
	11th to 20th	Night	39% 9% 13% 24% 13% 1	1600
	21st to end	Night	34% 10% 16% 24% 15% 2	1600
July	1st to 10th	Night	41% 9% 16% 18% 15% 2	3560
	11th to 20th	Night	47% 8% 16% 18% 9% 1	3552
	21st to end	Night	37% 7% 13% 22% 20% 1	3870
August	1st to 10th	Night	47% 8% 18% 16% 10% 1	2904
	11th to 20th	Night	40% 7% 13% 25% 14% 1	3192
	21st to end	Night	33% 6% 10% 29% 21% 2	3586
September	1st to 10th	Night	39% 6% 11% 20% 21% 3	2000
	11th to 20th	Night	33% 5% 11% 22% 26% 4	2036
	21st to end	Night	43% 6% 9% 20% 20% 2	2200
October	1st to 10th	Night	40% 5% 10% 21% 21% 2	3906
	11th to 20th	Night	25% 4 10% 29% 28% 4	3899
	21st to end	Night	27% 4 11% 31% 24% 4	4380
November	1st to 10th	Night	32% 5% 13% 24% 21% 5%	2667
	11th to 20th	Night	39% 4 9% 23% 20% 5%	2730
	21st to end	Night	39% 5% 12% 26% 16% 2	2861
December	1st to 10th	Night	39% 4 12% 30% 13% 2	4720
	11th to 20th	Night	44% 5% 10% 25% 13% 4	5348
	21st to end	Night	44% 6% 10% 20% 17% 3	7150

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	28% 28% 30% 10% 2 1	220
	11th to 20th	Day	38% 24% 30% 7% 1	237
	21st to end	Day	29% 29% 28% 11% 4	363
February	1st to 10th	Day	28% 28% 33% 9% 3	330
	11th to 20th	Day	33% 23% 34% 10% 1	470
	21st to end	Day	30% 24% 31% 12% 2	414
March	1st to 10th	Day	30% 21% 31% 15% 4	500
	11th to 20th	Day	25% 25% 32% 14% 2 1	500
	21st to end	Day	28% 24% 30% 12% 5% 1	550
April	1st to 10th	Day	30% 23% 29% 13% 5% 1	500
	11th to 20th	Day	24% 26% 29% 13% 6% 2	492
	21st to end	Day	23% 21% 33% 18% 4 1	500
May	1st to 10th	Day	29% 19% 30% 15% 6% 2	503
	11th to 20th	Day	24% 14% 31% 22% 7% 2	527
	21st to end	Day	20% 10% 27% 26% 14% 3	573
June	1st to 10th	Day	16% 14% 30% 25% 12% 2	530
	11th to 20th	Day	18% 12% 28% 27% 11% 3	530
	21st to end	Day	16% 12% 29% 29% 12% 2	530
July	1st to 10th	Day	11% 7% 24% 31% 20% 6%	525
	11th to 20th	Day	10% 4 26% 33% 24% 4	524
	21st to end	Day	13% 7% 28% 33% 14% 3	576
August	1st to 10th	Day	12% 5% 27% 33% 17% 6%	526
	11th to 20th	Day	14% 6% 21% 35% 19% 6%	519
	21st to end	Day	13% 8% 26% 30% 16% 7%	583
September	1st to 10th	Day	17% 11% 25% 25% 16% 6%	530
	11th to 20th	Day	15% 5% 26% 30% 14% 9%	530
	21st to end	Day	24% 13% 23% 24% 11% 5%	530
October	1st to 10th	Day	22% 9% 27% 22% 12% 7%	530
	11th to 20th	Day	19% 17% 30% 22% 9% 2	530
	21st to end	Day	22% 18% 31% 17% 10% 2	537
November	1st to 10th	Day	20% 13% 33% 22% 10% 2	425
	11th to 20th	Day	23% 20% 33% 20% 4	430
	21st to end	Day	25% 22% 34% 15% 4	293
December	1st to 10th	Day	30% 26% 30% 9% 5%	220
	11th to 20th	Day	35% 24% 26% 10% 4	220
	21st to end	Day	28% 21% 31% 14% 6%	242
January	1st to 10th	Night	21% 22% 35% 19% 3	840
	11th to 20th	Night	25% 19% 32% 21% 3	840
	21st to end	Night	19% 22% 37% 21% 1	924
February	1st to 10th	Night	21% 17% 39% 21% 1	840
	11th to 20th	Night	27% 22% 35% 15% 1	804
	21st to end	Night	23% 20% 39% 16% 2	660
March	1st to 10th	Night	24% 20% 33% 20% 3	800
	11th to 20th	Night	23% 20% 35% 18% 4	800
	21st to end	Night	22% 16% 39% 19% 5%	880
April	1st to 10th	Night	22% 20% 38% 16% 4	800
	11th to 20th	Night	19% 17% 37% 21% 5%	791
	21st to end	Night	21% 14% 35% 25% 5%	800
May	1st to 10th	Night	23% 14% 33% 24% 6%	641
	11th to 20th	Night	21% 9% 39% 26% 6%	394
	21st to end	Night	18% 7% 25% 37% 12% 1	433
June	1st to 10th	Night	17% 6% 30% 36% 12%	400
	11th to 20th	Night	11% 7% 30% 40% 12% 1	400
	21st to end	Night	10% 5% 27% 48% 11%	400
July	1st to 10th	Night	12% 3 24% 44% 17% 1	390
	11th to 20th	Night	9% 3 22% 43% 21% 2	388
	21st to end	Night	8% 2 27% 42% 19% 2	463
August	1st to 10th	Night	14% 1 16% 45% 21% 2	597
	11th to 20th	Night	13% 4 19% 37% 25% 2	767
	21st to end	Night	15% 4 19% 38% 22% 2	880
September	1st to 10th	Night	17% 4 25% 36% 16% 2	800
	11th to 20th	Night	13% 5% 22% 36% 20% 4	800
	21st to end	Night	22% 5% 22% 32% 17% 1	800
October	1st to 10th	Night	21% 8% 26% 25% 17% 4	800
	11th to 20th	Night	19% 11% 27% 31% 12%	800
	21st to end	Night	20% 14% 32% 25% 8%	880
November	1st to 10th	Night	17% 10% 35% 28% 11% 1	820
	11th to 20th	Night	22% 18% 28% 25% 7%	840
	21st to end	Night	18% 17% 34% 25% 6%	840
December	1st to 10th	Night	25% 17% 33% 19% 5% 1	840
	11th to 20th	Night	23% 15% 34% 23% 4	840
	21st to end	Night	22% 17% 33% 25% 3	924

Page generated at 2026-02-13 01:42:14. Version ac07

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