Humane Animal Hospital Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Humane Animal Hospital Observatory clear sky chart from 2005-11-06 to 2025-01-07.

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% 5% 2 5% 4 4 4 3 5% 7% 51%	105301
	Night	11% 5% 2 4 3 3 3 3 5% 6% 55%	103870
Transparency	Day	32% 5% 9% 25% 22% 7%	109031
	Night	29% 4 9% 23% 25% 10%	108267
Seeing	Day	12% 6% 21% 28% 25% 9%	15379
	Night	12% 7% 27% 35% 17% 2	25333

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	11% 6% 2 5% 3 3 2 2 4 6% 54%	2901
	11th to 20th	Day	11% 5% 1 3 2 2 2 2 3 5% 62%	2850
	21st to end	Day	20% 8% 3 7% 3 3 2 2 3 3 46%	3135
February	1st to 10th	Day	17% 7% 3 7% 5% 3 3 3 3 5% 45%	1788
	11th to 20th	Day	17% 7% 2 5% 3 3 3 3 4 6% 47%	1849
	21st to end	Day	21% 7% 2 5% 2 2 2 2 2 3 51%	1610
March	1st to 10th	Day	15% 7% 2 5% 3 3 3 2 5% 6% 50%	3436
	11th to 20th	Day	17% 6% 2 6% 4 4 4 4 5% 5% 42%	3480
	21st to end	Day	15% 7% 3 6% 4 4 5% 4 6% 6% 41%	3814
April	1st to 10th	Day	12% 6% 2 5% 4 4 4 3 5% 6% 48%	2090
	11th to 20th	Day	13% 7% 2 6% 4 4 3 4 5% 6% 45%	2187
	21st to end	Day	13% 5% 2 5% 4 4 4 4 5% 5% 48%	2396
May	1st to 10th	Day	18% 7% 3 7% 5% 4 4 3 5% 6% 39%	4082
	11th to 20th	Day	14% 6% 2 6% 4 4 4 3 5% 7% 46%	4082
	21st to end	Day	16% 7% 3 7% 4 5% 5% 4 6% 7% 35%	4477
June	1st to 10th	Day	6% 3 1 5% 4 5% 6% 4 7% 10% 48%	2470
	11th to 20th	Day	5% 4 2 4 5% 4 4 4 7% 8% 53%	2470
	21st to end	Day	4 3 1 4 3 4 6% 4 7% 9% 56%	2470
July	1st to 10th	Day	6% 4 2 5% 3 5% 5% 4 5% 7% 52%	4120
	11th to 20th	Day	3 2 1 3 3 4 4 4 6% 10% 61%	4120
	21st to end	Day	5% 5% 2 6% 5% 4 6% 5% 7% 11% 44%	4465
August	1st to 10th	Day	2 2 1 3 3 3 3 3 5% 8% 69%	4104
	11th to 20th	Day	4 2 1 3 3 3 4 4 6% 10% 59%	4041
	21st to end	Day	3 3 1 4 4 4 5% 4 6% 10% 56%	4125
September	1st to 10th	Day	9% 4 2 4 4 3 4 3 6% 8% 53%	2090
	11th to 20th	Day	10% 4 2 7% 4 4 5% 4 5% 7% 49%	2090
	21st to end	Day	7% 4 2 4 3 3 4 4 5% 7% 59%	2090
October	1st to 10th	Day	6% 2 1 4 4 3 3 3 4 6% 63%	2019
	11th to 20th	Day	12% 4 2 3 2 2 2 2 3 6% 62%	1900
	21st to end	Day	15% 4 2 4 2 2 3 2 3 3 60%	2090
November	1st to 10th	Day	13% 5% 1 4 3 4 3 2 4 5% 56%	1958
	11th to 20th	Day	8% 4 2 4 3 4 4 3 3 6% 62%	1883
	21st to end	Day	15% 6% 2 4 3 2 3 2 3 5% 55%	1800
December	1st to 10th	Day	18% 5% 2 5% 3 3 3 2 4 5% 52%	2940
	11th to 20th	Day	18% 7% 2 6% 3 4 3 3 4 4 47%	3391
	21st to end	Day	20% 8% 2 4 2 3 2 2 3 4 48%	4488
January	1st to 10th	Night	13% 5% 2 4 3 2 3 3 4 6% 55%	4187
	11th to 20th	Night	11% 4 1 3 3 2 2 2 3 4 64%	4120
	21st to end	Night	20% 7% 2 5% 2 3 2 2 4 4 48%	4532
February	1st to 10th	Night	15% 7% 2 6% 3 4 3 3 3 5% 50%	2409
	11th to 20th	Night	15% 8% 2 4 3 3 4 3 4 5% 50%	2218
	21st to end	Night	19% 5% 2 4 2 2 3 2 3 4 54%	1842
March	1st to 10th	Night	15% 7% 3 6% 4 4 4 4 5% 6% 44%	3419
	11th to 20th	Night	14% 6% 2 5% 3 3 4 3 5% 7% 47%	3480
	21st to end	Night	14% 6% 2 6% 4 3 4 3 5% 5% 48%	3817
April	1st to 10th	Night	10% 5% 2 4 3 3 4 3 5% 7% 53%	2090
	11th to 20th	Night	12% 6% 2 5% 4 3 3 3 5% 5% 50%	1942
	21st to end	Night	11% 5% 2 5% 3 3 3 3 4 6% 54%	1780
May	1st to 10th	Night	19% 8% 3 6% 4 4 4 3 4 6% 39%	2823
	11th to 20th	Night	11% 6% 2 6% 4 3 4 3 4 7% 50%	2823
	21st to end	Night	10% 5% 2 5% 3 4 5% 4 6% 9% 45%	3090
June	1st to 10th	Night	4 3 2 5% 3 3 4 3 7% 10% 56%	1710
	11th to 20th	Night	3 3 1 3 3 3 3 4 6% 8% 62%	1710
	21st to end	Night	2 3 1 3 3 3 3 3 6% 10% 62%	1710
July	1st to 10th	Night	4 3 1 3 3 3 4 4 5% 10% 59%	2850
	11th to 20th	Night	3 2 1 2 3 2 3 2 6% 10% 66%	2850
	21st to end	Night	4 3 2 4 4 4 5% 4 7% 9% 55%	3098
August	1st to 10th	Night	1 1 1 1 1 2 3 3 4 9% 74%	2836
	11th to 20th	Night	3 2 1 3 1 2 2 3 6% 11% 67%	2798
	21st to end	Night	2 2 1 3 2 3 4 4 6% 9% 63%	3527
September	1st to 10th	Night	7% 4 2 4 3 3 2 3 5% 8% 58%	2090
	11th to 20th	Night	10% 5% 2 5% 3 3 3 4 5% 7% 53%	2090
	21st to end	Night	6% 3 1 3 3 3 3 2 5% 7% 64%	2090
October	1st to 10th	Night	6% 3 1 4 3 3 3 3 4 6% 65%	2141
	11th to 20th	Night	11% 3 2 3 2 2 2 2 4 4 64%	2280
	21st to end	Night	15% 5% 1 3 2 3 2 2 3 4 61%	2508
November	1st to 10th	Night	10% 4 2 5% 4 3 3 2 3 4 61%	2340
	11th to 20th	Night	7% 4 2 4 3 3 3 3 5% 6% 61%	2514
	21st to end	Night	14% 5% 2 5% 3 3 3 3 4 5% 54%	2600
December	1st to 10th	Night	14% 6% 2 4 3 3 3 3 3 5% 54%	4250
	11th to 20th	Night	17% 6% 2 5% 4 2 3 2 3 4 51%	4816
	21st to end	Night	15% 7% 2 5% 3 3 2 2 4 5% 52%	6490

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	32% 4 6% 22% 31% 4	2902
	11th to 20th	Day	27% 3 9% 24% 32% 6%	2850
	21st to end	Day	45% 2 4 18% 22% 8%	3135
February	1st to 10th	Day	44% 4 6% 18% 20% 8%	1788
	11th to 20th	Day	41% 3 7% 21% 20% 8%	1859
	21st to end	Day	40% 3 4 16% 26% 11%	1610
March	1st to 10th	Day	35% 4 7% 17% 27% 10%	3436
	11th to 20th	Day	43% 5% 10% 22% 16% 4	3480
	21st to end	Day	42% 6% 9% 20% 19% 4	3814
April	1st to 10th	Day	36% 5% 9% 21% 19% 10%	2090
	11th to 20th	Day	39% 5% 9% 17% 20% 9%	2187
	21st to end	Day	35% 7% 9% 22% 23% 4	2396
May	1st to 10th	Day	45% 6% 8% 21% 15% 4	4120
	11th to 20th	Day	37% 6% 9% 25% 21% 1	4086
	21st to end	Day	46% 8% 11% 19% 11% 5%	4489
June	1st to 10th	Day	29% 9% 15% 28% 17% 3	2470
	11th to 20th	Day	27% 8% 13% 28% 19% 5%	2470
	21st to end	Day	23% 8% 12% 30% 23% 3	2470
July	1st to 10th	Day	29% 7% 15% 37% 13% 1	4056
	11th to 20th	Day	17% 6% 10% 42% 23% 2	4051
	21st to end	Day	31% 8% 13% 33% 15%	4325
August	1st to 10th	Day	14% 5% 12% 28% 33% 8%	4090
	11th to 20th	Day	19% 6% 15% 40% 18% 2	4080
	21st to end	Day	22% 8% 19% 36% 13% 2	4124
September	1st to 10th	Day	29% 5% 12% 23% 19% 12%	2090
	11th to 20th	Day	34% 7% 10% 19% 22% 7%	2090
	21st to end	Day	24% 5% 9% 22% 29% 11%	2090
October	1st to 10th	Day	15% 3 6% 14% 34% 29%	3357
	11th to 20th	Day	17% 2 5% 20% 34% 21%	3140
	21st to end	Day	25% 3 5% 31% 26% 9%	3428
November	1st to 10th	Day	31% 4 7% 22% 26% 10%	1958
	11th to 20th	Day	26% 3 10% 20% 29% 12%	1883
	21st to end	Day	34% 3 6% 20% 28% 10%	1800
December	1st to 10th	Day	37% 3 5% 29% 23% 4	2940
	11th to 20th	Day	42% 3 4 13% 27% 10%	3389
	21st to end	Day	41% 3 5% 23% 21% 7%	4488
January	1st to 10th	Night	31% 3 7% 20% 31% 8%	4187
	11th to 20th	Night	26% 3 8% 21% 30% 12%	4120
	21st to end	Night	41% 3 6% 16% 26% 8%	4532
February	1st to 10th	Night	38% 3 8% 18% 22% 10%	2409
	11th to 20th	Night	37% 4 7% 18% 25% 9%	2218
	21st to end	Night	36% 3 7% 15% 23% 15%	1842
March	1st to 10th	Night	41% 6% 7% 14% 21% 12%	3419
	11th to 20th	Night	37% 6% 10% 21% 20% 7%	3480
	21st to end	Night	37% 6% 9% 18% 26% 4	3817
April	1st to 10th	Night	30% 5% 11% 21% 19% 14%	2090
	11th to 20th	Night	35% 6% 8% 20% 18% 13%	1942
	21st to end	Night	31% 4 11% 23% 26% 5%	1780
May	1st to 10th	Night	45% 8% 9% 18% 14% 7%	2850
	11th to 20th	Night	34% 6% 13% 20% 25% 2	2824
	21st to end	Night	33% 9% 15% 25% 13% 6%	3099
June	1st to 10th	Night	22% 7% 16% 32% 20% 5%	1710
	11th to 20th	Night	19% 6% 13% 33% 21% 8%	1710
	21st to end	Night	18% 6% 14% 31% 26% 5%	1710
July	1st to 10th	Night	21% 7% 15% 39% 16% 2	2805
	11th to 20th	Night	15% 4 10% 43% 26% 3	2796
	21st to end	Night	24% 7% 15% 36% 18% 1	2999
August	1st to 10th	Night	10% 3 9% 32% 40% 6%	2826
	11th to 20th	Night	13% 4 13% 41% 22% 6%	2825
	21st to end	Night	17% 6% 20% 35% 19% 3	3527
September	1st to 10th	Night	26% 5% 10% 22% 25% 11%	2090
	11th to 20th	Night	29% 6% 10% 20% 23% 11%	2090
	21st to end	Night	21% 3 8% 24% 28% 16%	2090
October	1st to 10th	Night	13% 3 5% 14% 32% 34%	3570
	11th to 20th	Night	16% 2 4 18% 35% 26%	3779
	21st to end	Night	26% 2 3 26% 26% 15%	4120
November	1st to 10th	Night	29% 4 7% 21% 25% 15%	2340
	11th to 20th	Night	25% 4 7% 20% 28% 15%	2514
	21st to end	Night	33% 3 8% 17% 28% 11%	2600
December	1st to 10th	Night	35% 3 6% 23% 27% 7%	4250
	11th to 20th	Night	39% 3 6% 14% 25% 14%	4817
	21st to end	Night	37% 3 6% 20% 26% 9%	6490

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	16% 15% 34% 26% 9%	288
	11th to 20th	Day	18% 16% 35% 22% 7% 2	270
	21st to end	Day	20% 10% 38% 21% 10% 1	297
February	1st to 10th	Day	21% 14% 37% 20% 8%	270
	11th to 20th	Day	21% 14% 41% 18% 5%	270
	21st to end	Day	30% 11% 43% 13% 2	225
March	1st to 10th	Day	19% 16% 34% 25% 6%	270
	11th to 20th	Day	19% 20% 37% 17% 5% 1	270
	21st to end	Day	13% 14% 45% 20% 7% 1	297
April	1st to 10th	Day	12% 16% 36% 29% 6% 2	270
	11th to 20th	Day	16% 12% 37% 26% 9%	385
	21st to end	Day	16% 11% 37% 26% 8% 2	576
May	1st to 10th	Day	16% 8% 30% 35% 10% 1	653
	11th to 20th	Day	16% 5% 28% 32% 15% 4	675
	21st to end	Day	15% 6% 23% 34% 18% 4	734
June	1st to 10th	Day	7% 2 12% 37% 34% 9%	680
	11th to 20th	Day	6% 2 17% 36% 31% 8%	680
	21st to end	Day	5% 1 12% 33% 36% 14%	680
July	1st to 10th	Day	5% 2 8% 30% 40% 15%	671
	11th to 20th	Day	3 1 6% 28% 44% 18%	668
	21st to end	Day	3 1 4 26% 47% 18%	739
August	1st to 10th	Day	3 3 27% 50% 17%	676
	11th to 20th	Day	8% 1 3 30% 43% 14%	665
	21st to end	Day	5% 5% 23% 40% 27%	510
September	1st to 10th	Day	8% 3 15% 45% 29%	300
	11th to 20th	Day	3 1 6% 26% 39% 26%	300
	21st to end	Day	9% 3 9% 25% 36% 18%	300
October	1st to 10th	Day	3 18% 31% 36% 12%	300
	11th to 20th	Day	11% 6% 24% 32% 23% 4	300
	21st to end	Day	22% 10% 22% 23% 21% 2	330
November	1st to 10th	Day	19% 7% 31% 26% 13% 5%	300
	11th to 20th	Day	13% 9% 30% 29% 16% 4	300
	21st to end	Day	18% 13% 32% 25% 9% 3	300
December	1st to 10th	Day	19% 9% 29% 30% 11% 2	300
	11th to 20th	Day	20% 8% 39% 26% 7%	300
	21st to end	Day	21% 12% 34% 26% 7% 1	330
January	1st to 10th	Night	13% 10% 36% 33% 7%	981
	11th to 20th	Night	16% 14% 34% 30% 6% 1	950
	21st to end	Night	15% 9% 37% 32% 6%	1045
February	1st to 10th	Night	19% 10% 37% 28% 5%	889
	11th to 20th	Night	19% 11% 38% 28% 4	744
	21st to end	Night	21% 15% 39% 22% 3	586
March	1st to 10th	Night	17% 11% 38% 28% 6%	570
	11th to 20th	Night	17% 9% 38% 30% 6%	570
	21st to end	Night	13% 12% 39% 29% 6%	627
April	1st to 10th	Night	12% 11% 42% 30% 5%	570
	11th to 20th	Night	15% 10% 40% 28% 6%	563
	21st to end	Night	13% 9% 39% 28% 10% 1	570
May	1st to 10th	Night	12% 8% 36% 35% 8% 1	570
	11th to 20th	Night	11% 4 33% 36% 15% 1	561
	21st to end	Night	8% 3 29% 40% 17% 2	617
June	1st to 10th	Night	6% 1 14% 43% 33% 4	570
	11th to 20th	Night	4 2 20% 52% 22% 1	570
	21st to end	Night	2 2 12% 44% 34% 5%	570
July	1st to 10th	Night	5% 1 8% 43% 39% 5%	555
	11th to 20th	Night	3 5% 42% 46% 4	552
	21st to end	Night	2 4 43% 45% 6%	624
August	1st to 10th	Night	2 1 3 44% 46% 5%	567
	11th to 20th	Night	7% 1 4 42% 42% 5%	564
	21st to end	Night	4 4 40% 46% 6%	627
September	1st to 10th	Night	8% 1 9% 36% 42% 5%	570
	11th to 20th	Night	12% 1 6% 38% 38% 4	570
	21st to end	Night	8% 1 13% 41% 33% 5%	570
October	1st to 10th	Night	7% 2 18% 43% 27% 3	621
	11th to 20th	Night	13% 4 23% 41% 17% 2	760
	21st to end	Night	17% 7% 29% 31% 15% 1	836
November	1st to 10th	Night	12% 3 29% 39% 16% 1	780
	11th to 20th	Night	9% 10% 32% 36% 13% 1	914
	21st to end	Night	17% 9% 34% 31% 9% 1	1000
December	1st to 10th	Night	15% 9% 33% 35% 7%	1000
	11th to 20th	Night	19% 9% 33% 33% 7%	1000
	21st to end	Night	19% 8% 36% 29% 6%	1100

Page generated at 2025-01-04 02:24:03. Version ac07

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