Gittins Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Gittins Observatory clear sky chart from 2005-11-06 to 2026-08-15.

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	11% 8% 3 7% 4 4 4 4 6% 8% 41%	143980
	Night	12% 8% 3 7% 4 4 4 3 5% 7% 42%	138205
Transparency	Day	40% 5% 12% 24% 16% 2	147560
	Night	41% 5% 11% 24% 17% 2	142704
Seeing	Day	16% 12% 28% 26% 15% 4	18149
	Night	16% 11% 30% 29% 12% 1	27892

By Month

Percentage Cloud Cover SE (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	12% 11% 6% 13% 5% 4 4 3 4 6% 32%	4691
	11th to 20th	Day	7% 9% 3 8% 7% 7% 5% 4 5% 6% 39%	5102
	21st to end	Day	16% 14% 6% 8% 6% 4 3 2 3 4 35%	5812
February	1st to 10th	Day	15% 11% 3 9% 5% 4 4 3 6% 7% 34%	1890
	11th to 20th	Day	14% 10% 3 8% 5% 6% 5% 4 5% 7% 35%	1977
	21st to end	Day	14% 11% 3 6% 5% 3 4 4 4 6% 39%	1730
March	1st to 10th	Day	16% 10% 3 5% 3 2 3 2 3 5% 48%	4717
	11th to 20th	Day	8% 7% 2 5% 3 4 5% 4 5% 8% 50%	5090
	21st to end	Day	14% 9% 3 8% 5% 5% 5% 4 6% 7% 34%	5835
April	1st to 10th	Day	14% 8% 2 7% 5% 5% 4 3 5% 6% 40%	2520
	11th to 20th	Day	15% 9% 3 6% 4 4 4 2 5% 7% 41%	2494
	21st to end	Day	17% 7% 3 7% 4 4 5% 3 6% 8% 36%	2520
May	1st to 10th	Day	14% 7% 3 8% 5% 5% 4 4 7% 8% 35%	7309
	11th to 20th	Day	13% 8% 2 7% 4 4 4 4 5% 7% 41%	8222
	21st to end	Day	14% 8% 3 8% 5% 5% 5% 4 6% 7% 35%	9047
June	1st to 10th	Day	7% 5% 2 6% 4 4 5% 5% 7% 10% 46%	2940
	11th to 20th	Day	8% 4 2 5% 4 5% 5% 4 8% 9% 47%	2940
	21st to end	Day	7% 4 2 6% 6% 5% 5% 4 7% 10% 45%	2940
July	1st to 10th	Day	9% 5% 2 5% 3 4 4 4 7% 10% 46%	8280
	11th to 20th	Day	6% 5% 2 7% 5% 5% 5% 4 7% 10% 44%	8280
	21st to end	Day	9% 5% 2 6% 4 4 5% 5% 8% 11% 39%	8538
August	1st to 10th	Day	5% 4 2 5% 4 5% 5% 5% 7% 10% 49%	4364
	11th to 20th	Day	11% 6% 2 5% 4 5% 5% 4 7% 9% 42%	3965
	21st to end	Day	5% 4 2 5% 4 4 4 4 7% 11% 50%	4312
September	1st to 10th	Day	12% 5% 2 4 3 3 4 3 5% 6% 53%	2400
	11th to 20th	Day	9% 4 2 5% 3 4 4 4 6% 8% 51%	2397
	21st to end	Day	7% 5% 2 6% 4 3 4 4 5% 8% 52%	2150
October	1st to 10th	Day	10% 5% 2 5% 3 3 3 4 4 6% 54%	2000
	11th to 20th	Day	14% 6% 3 5% 3 3 3 3 4 7% 49%	2000
	21st to end	Day	17% 9% 3 5% 3 3 3 2 4 5% 45%	2190
November	1st to 10th	Day	11% 6% 2 4 4 4 4 3 4 5% 54%	1852
	11th to 20th	Day	14% 8% 3 7% 3 3 4 3 4 5% 45%	1890
	21st to end	Day	17% 11% 4 8% 4 3 2 3 4 6% 39%	1738
December	1st to 10th	Day	7% 10% 3 5% 4 3 4 3 5% 6% 50%	2690
	11th to 20th	Day	13% 8% 5% 10% 5% 5% 4 3 4 6% 36%	3088
	21st to end	Day	22% 17% 5% 11% 5% 4 3 3 4 4 21%	4070
January	1st to 10th	Night	12% 12% 5% 11% 5% 4 4 3 4 5% 35%	8232
	11th to 20th	Night	9% 10% 4 12% 6% 4 6% 4 4 5% 36%	7883
	21st to end	Night	15% 13% 5% 10% 5% 4 3 3 4 5% 33%	8402
February	1st to 10th	Night	14% 12% 5% 9% 5% 4 4 3 4 6% 34%	2730
	11th to 20th	Night	15% 8% 4 7% 5% 4 5% 3 4 6% 39%	2529
	21st to end	Night	15% 9% 3 6% 3 4 4 2 5% 5% 44%	2076
March	1st to 10th	Night	19% 11% 3 5% 4 3 3 2 3 4 43%	5399
	11th to 20th	Night	12% 8% 2 5% 3 3 3 3 4 6% 51%	5090
	21st to end	Night	16% 10% 4 8% 5% 4 4 4 5% 7% 34%	5322
April	1st to 10th	Night	13% 7% 3 6% 5% 4 4 3 5% 7% 44%	2100
	11th to 20th	Night	13% 7% 2 5% 4 3 4 4 5% 8% 45%	2075
	21st to end	Night	18% 7% 2 7% 4 4 4 3 5% 6% 41%	2100
May	1st to 10th	Night	16% 8% 3 7% 4 5% 5% 4 5% 7% 36%	5520
	11th to 20th	Night	12% 7% 2 6% 4 4 4 4 5% 8% 45%	4670
	21st to end	Night	14% 7% 3 7% 4 4 5% 4 6% 9% 37%	5139
June	1st to 10th	Night	8% 4 2 5% 3 4 4 3 6% 9% 51%	1680
	11th to 20th	Night	7% 5% 2 5% 5% 3 5% 5% 6% 7% 51%	1680
	21st to end	Night	6% 4 1 5% 4 5% 4 4 7% 9% 51%	1680
July	1st to 10th	Night	7% 5% 2 6% 4 5% 4 4 6% 9% 47%	4708
	11th to 20th	Night	5% 4 2 6% 4 5% 5% 4 6% 9% 50%	4707
	21st to end	Night	7% 5% 2 7% 4 4 5% 4 7% 11% 43%	5551
August	1st to 10th	Night	6% 3 1 4 3 4 3 3 5% 8% 59%	3016
	11th to 20th	Night	10% 5% 2 6% 3 4 4 4 6% 7% 50%	3173
	21st to end	Night	5% 3 1 4 3 4 4 3 7% 10% 56%	3586
September	1st to 10th	Night	12% 5% 2 4 2 3 3 4 6% 6% 55%	2000
	11th to 20th	Night	8% 5% 2 5% 3 4 5% 4 6% 8% 51%	2000
	21st to end	Night	7% 5% 2 5% 3 4 3 3 6% 7% 55%	2226
October	1st to 10th	Night	8% 4 2 5% 3 3 3 3 4 7% 58%	2400
	11th to 20th	Night	13% 5% 2 5% 3 2 3 3 5% 6% 53%	2400
	21st to end	Night	18% 7% 2 5% 3 4 3 3 4 5% 46%	2649
November	1st to 10th	Night	9% 7% 2 5% 4 3 3 3 5% 7% 53%	2666
	11th to 20th	Night	12% 6% 3 6% 4 4 3 3 5% 6% 49%	2730
	21st to end	Night	16% 10% 3 6% 4 4 3 3 4 5% 41%	2877
December	1st to 10th	Night	10% 9% 3 7% 5% 3 4 3 5% 5% 46%	4720
	11th to 20th	Night	14% 9% 4 7% 4 3 4 3 5% 7% 40%	5339
	21st to end	Night	24% 18% 5% 9% 6% 4 4 2 4 4 21%	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	53% 4 10% 21% 9% 1	4692
	11th to 20th	Day	45% 4 12% 21% 15% 3	5102
	21st to end	Day	55% 2 9% 18% 12% 3	5812
February	1st to 10th	Day	50% 5% 12% 22% 10% 1	1890
	11th to 20th	Day	49% 5% 11% 19% 14% 2	1986
	21st to end	Day	46% 4 9% 25% 14% 3	1730
March	1st to 10th	Day	41% 3 6% 24% 24% 2	4717
	11th to 20th	Day	33% 4 10% 27% 23% 4	5090
	21st to end	Day	47% 7% 15% 24% 7% 1	5837
April	1st to 10th	Day	44% 6% 10% 24% 15% 1	2520
	11th to 20th	Day	44% 5% 9% 26% 13% 3	2494
	21st to end	Day	46% 6% 12% 21% 13% 1	2520
May	1st to 10th	Day	45% 6% 12% 23% 13%	7344
	11th to 20th	Day	43% 5% 9% 24% 17% 2	8226
	21st to end	Day	46% 6% 9% 21% 16% 1	9061
June	1st to 10th	Day	32% 7% 15% 28% 16% 2	2940
	11th to 20th	Day	31% 7% 13% 26% 21% 3	2940
	21st to end	Day	32% 9% 15% 24% 16% 3	2940
July	1st to 10th	Day	32% 6% 14% 28% 18% 1	8211
	11th to 20th	Day	35% 7% 15% 24% 18% 2	8205
	21st to end	Day	36% 7% 19% 29% 7% 1	8352
August	1st to 10th	Day	29% 7% 15% 35% 14% 1	4350
	11th to 20th	Day	37% 6% 14% 27% 15% 1	4002
	21st to end	Day	27% 7% 16% 32% 14% 3	4311
September	1st to 10th	Day	31% 6% 11% 25% 22% 5%	2400
	11th to 20th	Day	31% 5% 10% 29% 22% 4	2397
	21st to end	Day	30% 5% 11% 26% 25% 3	2150
October	1st to 10th	Day	20% 4 6% 18% 47% 6%	3260
	11th to 20th	Day	25% 3 7% 20% 37% 8%	3240
	21st to end	Day	37% 3 8% 25% 26% 2	3516
November	1st to 10th	Day	34% 4 12% 26% 20% 4	1852
	11th to 20th	Day	41% 4 9% 24% 18% 4	1890
	21st to end	Day	48% 4 10% 25% 12%	1738
December	1st to 10th	Day	36% 4 16% 29% 15%	2690
	11th to 20th	Day	49% 5% 11% 23% 11% 1	3085
	21st to end	Day	67% 4 11% 12% 5% 1	4070
January	1st to 10th	Night	53% 4 13% 23% 8%	8233
	11th to 20th	Night	50% 3 7% 23% 15% 3	7883
	21st to end	Night	55% 3 10% 19% 12% 2	8402
February	1st to 10th	Night	52% 5% 11% 21% 11% 2	2730
	11th to 20th	Night	46% 4 10% 23% 15% 2	2530
	21st to end	Night	43% 3 11% 26% 14% 3	2076
March	1st to 10th	Night	47% 3 6% 22% 21% 1	5399
	11th to 20th	Night	36% 4 8% 25% 22% 6%	5090
	21st to end	Night	49% 6% 10% 23% 9% 2	5322
April	1st to 10th	Night	39% 6% 11% 24% 16% 3	2100
	11th to 20th	Night	38% 5% 12% 23% 18% 4	2075
	21st to end	Night	45% 5% 9% 22% 17% 2	2100
May	1st to 10th	Night	46% 6% 13% 23% 11% 1	5550
	11th to 20th	Night	37% 6% 12% 25% 16% 3	4671
	21st to end	Night	43% 6% 12% 20% 18% 2	5149
June	1st to 10th	Night	29% 7% 15% 28% 18% 3	1680
	11th to 20th	Night	30% 7% 11% 23% 25% 3	1680
	21st to end	Night	27% 7% 17% 26% 17% 6%	1680
July	1st to 10th	Night	33% 6% 12% 30% 18% 1	4670
	11th to 20th	Night	30% 7% 13% 29% 19% 2	4662
	21st to end	Night	33% 7% 21% 30% 9% 1	5426
August	1st to 10th	Night	23% 5% 17% 36% 17% 1	3006
	11th to 20th	Night	33% 5% 12% 28% 21% 1	3202
	21st to end	Night	24% 5% 17% 32% 17% 4	3586
September	1st to 10th	Night	29% 5% 10% 24% 25% 7%	2000
	11th to 20th	Night	30% 6% 9% 25% 25% 5%	2000
	21st to end	Night	29% 5% 8% 25% 27% 4	2226
October	1st to 10th	Night	18% 4 6% 20% 47% 5%	3920
	11th to 20th	Night	23% 3 8% 23% 35% 7%	3899
	21st to end	Night	33% 4 8% 25% 26% 4	4273
November	1st to 10th	Night	32% 5% 12% 26% 20% 6%	2666
	11th to 20th	Night	36% 4 9% 28% 19% 3	2730
	21st to end	Night	45% 4 11% 24% 14% 2	2877
December	1st to 10th	Night	41% 3 10% 32% 12% 1	4720
	11th to 20th	Night	44% 4 12% 23% 16% 1	5341
	21st to end	Night	68% 4 12% 11% 5% 1	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	22% 22% 33% 18% 4	330
	11th to 20th	Day	25% 25% 36% 13% 1	330
	21st to end	Day	18% 25% 40% 14% 2	363
February	1st to 10th	Day	26% 18% 40% 13% 2	330
	11th to 20th	Day	26% 24% 33% 13% 3	330
	21st to end	Day	25% 21% 39% 14% 1	273
March	1st to 10th	Day	22% 24% 40% 13% 1	330
	11th to 20th	Day	28% 19% 33% 16% 3	330
	21st to end	Day	30% 19% 35% 13% 3	473
April	1st to 10th	Day	24% 15% 38% 18% 5% 1	540
	11th to 20th	Day	23% 19% 31% 18% 8% 1	532
	21st to end	Day	19% 19% 36% 20% 4 1	540
May	1st to 10th	Day	16% 17% 35% 24% 6% 1	587
	11th to 20th	Day	17% 14% 30% 25% 13% 1	775
	21st to end	Day	14% 10% 30% 27% 13% 6%	844
June	1st to 10th	Day	9% 6% 27% 30% 21% 7%	780
	11th to 20th	Day	9% 6% 25% 36% 19% 4	780
	21st to end	Day	8% 7% 29% 37% 16% 3	780
July	1st to 10th	Day	10% 3 15% 32% 29% 11%	771
	11th to 20th	Day	7% 4 18% 37% 27% 6%	768
	21st to end	Day	9% 3 19% 35% 28% 6%	849
August	1st to 10th	Day	8% 3 20% 37% 24% 8%	776
	11th to 20th	Day	9% 3 17% 35% 27% 8%	579
	21st to end	Day	9% 2 16% 33% 32% 8%	583
September	1st to 10th	Day	12% 5% 18% 26% 30% 9%	530
	11th to 20th	Day	8% 2 17% 33% 28% 12%	530
	21st to end	Day	11% 9% 22% 28% 21% 9%	480
October	1st to 10th	Day	12% 9% 28% 30% 16% 5%	330
	11th to 20th	Day	18% 20% 30% 22% 10%	330
	21st to end	Day	26% 19% 33% 17% 4	363
November	1st to 10th	Day	15% 13% 39% 22% 8% 2	330
	11th to 20th	Day	22% 17% 36% 19% 5% 1	330
	21st to end	Day	29% 15% 32% 20% 4 1	330
December	1st to 10th	Day	14% 19% 42% 17% 6% 2	330
	11th to 20th	Day	21% 19% 39% 16% 4	330
	21st to end	Day	26% 25% 33% 14% 2	363
January	1st to 10th	Night	18% 17% 38% 21% 5%	1050
	11th to 20th	Night	21% 20% 35% 19% 4	1050
	21st to end	Night	19% 18% 39% 22% 2	1155
February	1st to 10th	Night	21% 17% 37% 23% 2	1050
	11th to 20th	Night	22% 18% 36% 22% 2	894
	21st to end	Night	21% 21% 36% 20% 2	692
March	1st to 10th	Night	22% 18% 38% 20% 3	798
	11th to 20th	Night	23% 12% 34% 25% 5%	630
	21st to end	Night	24% 14% 35% 23% 4	693
April	1st to 10th	Night	16% 19% 37% 25% 3	630
	11th to 20th	Night	17% 15% 35% 25% 8% 1	623
	21st to end	Night	20% 11% 39% 25% 5%	630
May	1st to 10th	Night	16% 8% 34% 33% 8% 1	630
	11th to 20th	Night	16% 9% 29% 33% 12% 1	621
	21st to end	Night	13% 5% 25% 37% 18% 2	683
June	1st to 10th	Night	8% 4 24% 41% 22% 1	630
	11th to 20th	Night	9% 3 25% 42% 19% 2	630
	21st to end	Night	5% 3 27% 43% 21% 1	630
July	1st to 10th	Night	10% 2 12% 35% 36% 5%	615
	11th to 20th	Night	6% 2 16% 43% 29% 4	612
	21st to end	Night	7% 1 15% 43% 32% 2	690
August	1st to 10th	Night	9% 2 10% 44% 32% 3	627
	11th to 20th	Night	8% 2 14% 40% 33% 4	606
	21st to end	Night	6% 1 15% 37% 39% 3	660
September	1st to 10th	Night	13% 3 17% 36% 26% 5%	600
	11th to 20th	Night	10% 2 17% 35% 32% 5%	600
	21st to end	Night	11% 7% 22% 33% 23% 4	781
October	1st to 10th	Night	9% 6% 28% 32% 22% 3	800
	11th to 20th	Night	16% 11% 33% 28% 12% 1	800
	21st to end	Night	23% 14% 32% 25% 6%	880
November	1st to 10th	Night	13% 11% 40% 27% 9%	820
	11th to 20th	Night	17% 14% 38% 26% 5%	840
	21st to end	Night	22% 15% 35% 22% 5%	987
December	1st to 10th	Night	20% 15% 37% 23% 4 1	1050
	11th to 20th	Night	22% 15% 33% 25% 5%	1050
	21st to end	Night	26% 16% 34% 21% 2	1155

Page generated at 2026-08-12 02:37:17. Version ac07

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