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 2025-04-11.

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	12% 8% 3 7% 4 4 4 4 5% 7% 42%	113545
	Night	13% 9% 3 7% 4 4 4 3 5% 6% 42%	114945
Transparency	Day	40% 6% 11% 24% 17% 2	117166
	Night	41% 5% 10% 24% 17% 3	119466
Seeing	Day	16% 12% 28% 26% 14% 4	16173
	Night	17% 11% 30% 29% 12% 1	26171

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	13% 11% 6% 14% 5% 4 4 3 4 6% 29%	3617
	11th to 20th	Day	9% 10% 3 9% 6% 7% 5% 4 5% 5% 36%	3914
	21st to end	Day	17% 13% 7% 8% 6% 4 3 2 3 4 33%	4488
February	1st to 10th	Day	15% 12% 3 9% 5% 4 4 3 6% 6% 33%	1800
	11th to 20th	Day	14% 10% 3 8% 5% 5% 5% 4 5% 6% 35%	1880
	21st to end	Day	15% 11% 3 6% 4 3 4 4 4 6% 39%	1650
March	1st to 10th	Day	15% 10% 3 5% 3 2 3 2 3 5% 49%	4614
	11th to 20th	Day	8% 7% 2 5% 3 4 5% 4 5% 8% 50%	4980
	21st to end	Day	14% 9% 3 8% 5% 5% 5% 4 6% 7% 34%	5709
April	1st to 10th	Day	14% 8% 2 7% 5% 5% 4 4 5% 6% 40%	2400
	11th to 20th	Day	16% 9% 3 6% 4 4 4 2 4 7% 41%	2254
	21st to end	Day	19% 7% 2 7% 4 4 5% 3 6% 8% 36%	2280
May	1st to 10th	Day	13% 8% 3 8% 5% 5% 5% 5% 7% 9% 33%	3930
	11th to 20th	Day	17% 8% 2 6% 5% 4 4 4 5% 7% 38%	4399
	21st to end	Day	10% 6% 2 6% 4 4 4 4 6% 7% 47%	4824
June	1st to 10th	Day	7% 5% 2 6% 4 4 5% 4 7% 10% 47%	2660
	11th to 20th	Day	8% 3 2 5% 4 5% 5% 4 7% 8% 49%	2660
	21st to end	Day	6% 4 2 5% 6% 5% 5% 4 7% 10% 46%	2660
July	1st to 10th	Day	13% 6% 3 6% 3 4 5% 4 8% 10% 39%	4440
	11th to 20th	Day	5% 4 2 6% 5% 4 5% 4 6% 10% 49%	4440
	21st to end	Day	7% 5% 2 6% 5% 5% 6% 5% 8% 11% 40%	4571
August	1st to 10th	Day	5% 4 2 5% 4 5% 5% 5% 7% 10% 49%	4104
	11th to 20th	Day	12% 6% 2 5% 5% 5% 5% 4 7% 9% 42%	3793
	21st to end	Day	5% 4 2 5% 4 4 4 4 7% 11% 50%	4180
September	1st to 10th	Day	13% 4 2 4 3 3 4 3 5% 6% 53%	2280
	11th to 20th	Day	10% 4 2 5% 3 4 4 4 6% 7% 51%	2277
	21st to end	Day	8% 5% 2 6% 4 3 4 4 5% 9% 51%	2043
October	1st to 10th	Day	10% 5% 2 5% 3 3 3 3 4 6% 54%	1900
	11th to 20th	Day	15% 6% 3 5% 3 3 3 3 4 6% 49%	1900
	21st to end	Day	17% 9% 2 6% 3 4 3 2 4 5% 45%	2081
November	1st to 10th	Day	12% 6% 2 4 4 4 4 3 4 6% 53%	1762
	11th to 20th	Day	14% 9% 3 7% 3 3 3 3 5% 6% 45%	1800
	21st to end	Day	16% 11% 4 7% 4 3 2 3 5% 5% 39%	1655
December	1st to 10th	Day	7% 9% 3 5% 4 3 4 3 5% 6% 51%	2610
	11th to 20th	Day	13% 8% 6% 10% 5% 5% 4 3 4 6% 36%	3008
	21st to end	Day	22% 17% 5% 11% 5% 4 3 3 4 4 21%	3982
January	1st to 10th	Night	14% 12% 6% 11% 5% 4 5% 3 4 4 31%	6348
	11th to 20th	Night	11% 11% 4 13% 5% 5% 6% 5% 4 5% 30%	6061
	21st to end	Night	17% 14% 5% 9% 4 3 3 3 5% 6% 31%	6490
February	1st to 10th	Night	15% 12% 5% 9% 5% 4 4 3 4 6% 33%	2600
	11th to 20th	Night	15% 8% 4 7% 5% 4 4 3 4 6% 39%	2406
	21st to end	Night	15% 9% 3 6% 3 4 4 2 5% 5% 44%	1980
March	1st to 10th	Night	19% 11% 3 5% 4 3 3 2 3 4 43%	5281
	11th to 20th	Night	12% 8% 2 5% 3 3 3 3 4 6% 51%	4980
	21st to end	Night	16% 10% 4 8% 5% 4 4 4 5% 7% 34%	5206
April	1st to 10th	Night	13% 7% 3 6% 5% 4 4 3 5% 7% 45%	2000
	11th to 20th	Night	13% 7% 2 5% 4 3 5% 4 4 7% 45%	1881
	21st to end	Night	18% 7% 2 7% 4 4 4 3 5% 5% 41%	1900
May	1st to 10th	Night	16% 8% 3 6% 4 4 5% 4 6% 8% 37%	2964
	11th to 20th	Night	14% 8% 2 6% 4 4 4 3 5% 7% 42%	2506
	21st to end	Night	9% 5% 2 6% 4 3 4 4 6% 10% 48%	2743
June	1st to 10th	Night	7% 4 2 5% 3 4 4 3 7% 9% 51%	1520
	11th to 20th	Night	6% 5% 1 5% 5% 3 4 5% 6% 7% 52%	1520
	21st to end	Night	6% 3 1 5% 4 5% 4 4 7% 9% 51%	1520
July	1st to 10th	Night	11% 7% 3 6% 4 5% 5% 4 6% 8% 42%	2530
	11th to 20th	Night	4 3 1 4 3 3 4 3 5% 9% 60%	2530
	21st to end	Night	8% 6% 2 7% 5% 5% 5% 4 7% 10% 42%	2988
August	1st to 10th	Night	6% 3 1 4 3 4 3 3 5% 9% 60%	2836
	11th to 20th	Night	10% 5% 2 6% 4 4 4 4 5% 7% 50%	3037
	21st to end	Night	5% 3 1 4 3 4 4 3 7% 10% 55%	3476
September	1st to 10th	Night	12% 5% 2 3 2 3 3 4 6% 6% 55%	1900
	11th to 20th	Night	8% 5% 2 5% 3 4 4 4 6% 8% 51%	1900
	21st to end	Night	7% 5% 2 5% 3 4 3 3 6% 7% 55%	2115
October	1st to 10th	Night	9% 4 2 5% 3 3 3 3 4 7% 58%	2280
	11th to 20th	Night	13% 5% 2 5% 3 2 3 3 4 6% 53%	2280
	21st to end	Night	17% 7% 2 5% 4 4 3 3 4 5% 46%	2516
November	1st to 10th	Night	10% 7% 2 5% 3 3 3 3 4 6% 54%	2536
	11th to 20th	Night	12% 6% 3 6% 4 4 3 3 5% 5% 49%	2600
	21st to end	Night	16% 10% 3 6% 4 4 3 4 4 5% 42%	2740
December	1st to 10th	Night	10% 9% 3 7% 5% 3 4 3 5% 5% 46%	4580
	11th to 20th	Night	14% 9% 3 7% 4 3 4 3 5% 7% 40%	5199
	21st to end	Night	24% 18% 5% 9% 6% 4 4 2 4 4 20%	6996

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	56% 4 10% 19% 10% 1	3618
	11th to 20th	Day	48% 5% 12% 18% 14% 4	3914
	21st to end	Day	57% 3 8% 16% 14% 3	4488
February	1st to 10th	Day	51% 5% 12% 20% 10% 1	1800
	11th to 20th	Day	49% 5% 11% 18% 14% 2	1889
	21st to end	Day	46% 4 9% 24% 14% 3	1650
March	1st to 10th	Day	41% 3 6% 24% 24% 2	4614
	11th to 20th	Day	32% 4 10% 27% 23% 4	4980
	21st to end	Day	47% 7% 15% 23% 7% 1	5711
April	1st to 10th	Day	43% 6% 10% 25% 15% 1	2400
	11th to 20th	Day	44% 5% 9% 26% 14% 3	2254
	21st to end	Day	46% 6% 12% 21% 14% 1	2280
May	1st to 10th	Day	44% 9% 14% 23% 10% 1	3965
	11th to 20th	Day	46% 7% 10% 26% 11% 1	4403
	21st to end	Day	35% 7% 10% 24% 23% 1	4837
June	1st to 10th	Day	30% 8% 15% 29% 15% 3	2660
	11th to 20th	Day	30% 7% 12% 26% 21% 3	2660
	21st to end	Day	31% 10% 15% 24% 17% 3	2660
July	1st to 10th	Day	39% 7% 11% 28% 13% 2	4371
	11th to 20th	Day	30% 6% 14% 29% 19% 2	4365
	21st to end	Day	34% 9% 19% 26% 11% 1	4427
August	1st to 10th	Day	29% 7% 15% 35% 14% 1	4090
	11th to 20th	Day	38% 6% 13% 27% 15% 1	3830
	21st to end	Day	27% 7% 16% 32% 14% 4	4179
September	1st to 10th	Day	31% 7% 11% 25% 22% 5%	2280
	11th to 20th	Day	31% 5% 9% 28% 22% 4	2277
	21st to end	Day	30% 5% 12% 27% 23% 3	2043
October	1st to 10th	Day	20% 4 6% 18% 47% 6%	3160
	11th to 20th	Day	24% 3 7% 20% 38% 8%	3140
	21st to end	Day	36% 3 7% 26% 25% 2	3407
November	1st to 10th	Day	34% 4 12% 25% 20% 4	1762
	11th to 20th	Day	40% 4 9% 23% 19% 5%	1800
	21st to end	Day	47% 5% 10% 26% 12%	1655
December	1st to 10th	Day	35% 4 17% 29% 16%	2610
	11th to 20th	Day	49% 5% 11% 22% 11% 1	3005
	21st to end	Day	67% 4 12% 12% 5% 1	3982
January	1st to 10th	Night	57% 3 10% 22% 7% 1	6348
	11th to 20th	Night	56% 3 8% 19% 11% 2	6061
	21st to end	Night	55% 3 8% 19% 13% 2	6490
February	1st to 10th	Night	53% 5% 10% 19% 11% 2	2600
	11th to 20th	Night	47% 4 10% 22% 15% 2	2407
	21st to end	Night	44% 3 11% 25% 14% 3	1980
March	1st to 10th	Night	47% 3 6% 22% 21% 1	5281
	11th to 20th	Night	35% 4 7% 26% 22% 6%	4980
	21st to end	Night	50% 6% 10% 23% 9% 2	5206
April	1st to 10th	Night	39% 6% 11% 24% 17% 4	2000
	11th to 20th	Night	38% 6% 10% 23% 18% 4	1881
	21st to end	Night	45% 5% 8% 22% 18% 2	1900
May	1st to 10th	Night	43% 8% 16% 20% 12% 1	2994
	11th to 20th	Night	41% 7% 12% 27% 13%	2507
	21st to end	Night	31% 7% 14% 21% 23% 3	2751
June	1st to 10th	Night	28% 7% 15% 28% 19% 4	1520
	11th to 20th	Night	29% 7% 11% 23% 26% 4	1520
	21st to end	Night	27% 7% 17% 25% 18% 6%	1520
July	1st to 10th	Night	38% 7% 10% 31% 12% 2	2490
	11th to 20th	Night	21% 6% 11% 37% 22% 2	2482
	21st to end	Night	35% 7% 17% 26% 14% 1	2893
August	1st to 10th	Night	22% 6% 17% 36% 18% 1	2826
	11th to 20th	Night	33% 5% 11% 28% 22% 1	3066
	21st to end	Night	24% 5% 18% 32% 17% 4	3476
September	1st to 10th	Night	29% 5% 10% 24% 25% 7%	1900
	11th to 20th	Night	30% 6% 9% 24% 26% 5%	1900
	21st to end	Night	29% 6% 8% 26% 27% 4	2115
October	1st to 10th	Night	18% 4 6% 20% 47% 5%	3800
	11th to 20th	Night	23% 3 7% 23% 36% 7%	3779
	21st to end	Night	33% 4 8% 25% 26% 4	4140
November	1st to 10th	Night	32% 5% 12% 26% 20% 6%	2536
	11th to 20th	Night	37% 4 9% 27% 20% 4	2600
	21st to end	Night	45% 4 11% 24% 15% 2	2740
December	1st to 10th	Night	40% 4 10% 33% 13% 1	4580
	11th to 20th	Night	44% 4 12% 23% 16% 1	5201
	21st to end	Night	68% 4 12% 11% 5% 1	6996

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	24% 22% 32% 18% 4	300
	11th to 20th	Day	27% 23% 35% 14% 1	300
	21st to end	Day	18% 24% 40% 15% 3	330
February	1st to 10th	Day	27% 18% 40% 13% 2	300
	11th to 20th	Day	27% 24% 32% 13% 3	300
	21st to end	Day	26% 20% 38% 14% 2	249
March	1st to 10th	Day	20% 25% 40% 14% 1	300
	11th to 20th	Day	29% 19% 33% 17% 3	300
	21st to end	Day	32% 18% 33% 14% 3	435
April	1st to 10th	Day	23% 15% 37% 18% 6% 1	500
	11th to 20th	Day	23% 17% 31% 20% 8% 1	452
	21st to end	Day	20% 20% 36% 20% 4 1	460
May	1st to 10th	Day	17% 16% 36% 23% 7% 1	503
	11th to 20th	Day	19% 12% 29% 26% 13% 1	675
	21st to end	Day	14% 10% 30% 27% 13% 6%	734
June	1st to 10th	Day	8% 6% 26% 31% 22% 7%	680
	11th to 20th	Day	9% 5% 25% 37% 20% 4	680
	21st to end	Day	7% 7% 31% 37% 15% 3	680
July	1st to 10th	Day	11% 4 15% 32% 27% 11%	671
	11th to 20th	Day	6% 4 20% 38% 26% 6%	668
	21st to end	Day	9% 2 20% 34% 28% 6%	739
August	1st to 10th	Day	8% 3 20% 36% 25% 8%	676
	11th to 20th	Day	10% 3 18% 34% 26% 8%	519
	21st to end	Day	9% 2 15% 34% 31% 8%	539
September	1st to 10th	Day	13% 4 18% 27% 29% 9%	490
	11th to 20th	Day	9% 3 18% 34% 27% 10%	490
	21st to end	Day	11% 9% 24% 29% 20% 7%	443
October	1st to 10th	Day	12% 10% 29% 29% 14% 5%	300
	11th to 20th	Day	19% 20% 31% 22% 8%	300
	21st to end	Day	26% 19% 32% 18% 5%	330
November	1st to 10th	Day	15% 12% 38% 23% 9% 2	300
	11th to 20th	Day	23% 16% 35% 19% 6% 1	300
	21st to end	Day	27% 15% 33% 20% 4 1	300
December	1st to 10th	Day	14% 19% 42% 17% 7% 2	300
	11th to 20th	Day	21% 20% 39% 16% 4	300
	21st to end	Day	26% 25% 32% 15% 2	330
January	1st to 10th	Night	19% 17% 38% 21% 5%	1000
	11th to 20th	Night	22% 19% 35% 19% 5%	1000
	21st to end	Night	19% 18% 39% 22% 2	1100
February	1st to 10th	Night	22% 17% 37% 23% 2	1000
	11th to 20th	Night	22% 18% 36% 22% 2	851
	21st to end	Night	22% 20% 36% 20% 2	660
March	1st to 10th	Night	21% 18% 38% 20% 3	760
	11th to 20th	Night	23% 11% 35% 25% 6%	600
	21st to end	Night	25% 14% 34% 23% 4	660
April	1st to 10th	Night	16% 19% 36% 26% 4	600
	11th to 20th	Night	16% 15% 34% 27% 8% 1	565
	21st to end	Night	21% 11% 39% 25% 5%	570
May	1st to 10th	Night	16% 8% 34% 33% 8% 1	570
	11th to 20th	Night	16% 9% 28% 33% 13% 1	561
	21st to end	Night	12% 5% 26% 36% 19% 2	617
June	1st to 10th	Night	7% 4 25% 41% 22% 1	570
	11th to 20th	Night	8% 3 25% 42% 20% 2	570
	21st to end	Night	5% 2 27% 43% 21% 1	570
July	1st to 10th	Night	11% 2 13% 35% 33% 5%	555
	11th to 20th	Night	6% 2 17% 45% 27% 3	552
	21st to end	Night	7% 1 15% 43% 32% 2	624
August	1st to 10th	Night	9% 2 9% 44% 32% 3	567
	11th to 20th	Night	8% 2 15% 39% 32% 4	564
	21st to end	Night	6% 1 15% 37% 39% 3	627
September	1st to 10th	Night	13% 3 17% 36% 26% 5%	570
	11th to 20th	Night	10% 2 18% 36% 30% 5%	570
	21st to end	Night	11% 7% 23% 33% 23% 4	742
October	1st to 10th	Night	9% 6% 29% 31% 21% 3	760
	11th to 20th	Night	16% 11% 34% 28% 11% 1	760
	21st to end	Night	23% 14% 32% 25% 6%	836
November	1st to 10th	Night	14% 11% 40% 26% 10%	780
	11th to 20th	Night	17% 14% 38% 25% 5% 1	800
	21st to end	Night	21% 15% 36% 22% 5%	940
December	1st to 10th	Night	20% 16% 36% 23% 4 1	1000
	11th to 20th	Night	23% 14% 32% 25% 5%	1000
	21st to end	Night	26% 17% 34% 21% 2	1100

Page generated at 2025-04-08 08:17:25. Version ac07

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