Three dog Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Three dog Observatory clear sky chart from 2005-11-06 to 2024-12-06.

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	21% 14% 5% 9% 5% 5% 4 3 5% 6% 23%	102059
	Night	21% 14% 5% 9% 5% 4 4 3 5% 6% 23%	97813
Transparency	Day	61% 7% 11% 14% 5%	105504
	Night	61% 7% 13% 14% 5% 1	102481
Seeing	Day	29% 15% 29% 19% 7% 1	18224
	Night	29% 15% 31% 19% 5%	25009

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	12% 17% 7% 14% 7% 5% 4 3 5% 5% 20%	2216
	11th to 20th	Day	17% 15% 6% 14% 6% 6% 6% 4 5% 5% 17%	2508
	21st to end	Day	10% 14% 6% 11% 8% 6% 7% 4 5% 6% 22%	2783
February	1st to 10th	Day	16% 15% 4 11% 7% 5% 6% 4 6% 7% 19%	1520
	11th to 20th	Day	18% 20% 4 13% 7% 4 4 4 4 5% 16%	1709
	21st to end	Day	13% 14% 5% 13% 7% 7% 5% 4 4 5% 23%	1570
March	1st to 10th	Day	16% 15% 5% 14% 8% 5% 4 3 4 5% 21%	3114
	11th to 20th	Day	22% 21% 8% 11% 7% 5% 4 3 4 3 13%	3379
	21st to end	Day	27% 18% 8% 9% 4 4 3 2 3 4 18%	3970
April	1st to 10th	Day	19% 19% 7% 11% 6% 5% 5% 3 4 5% 16%	2280
	11th to 20th	Day	23% 17% 5% 8% 3 4 2 3 5% 5% 24%	2428
	21st to end	Day	21% 20% 6% 8% 4 4 4 3 4 5% 21%	2470
May	1st to 10th	Day	29% 23% 7% 8% 3 3 3 2 3 4 14%	4260
	11th to 20th	Day	24% 18% 6% 9% 5% 4 4 3 4 5% 19%	4539
	21st to end	Day	28% 17% 4 6% 4 4 3 3 4 5% 21%	5173
June	1st to 10th	Day	33% 15% 4 7% 5% 4 4 4 4 4 16%	2850
	11th to 20th	Day	28% 12% 3 7% 4 5% 4 3 5% 5% 24%	2850
	21st to end	Day	24% 11% 3 6% 6% 5% 5% 4 5% 7% 24%	2850
July	1st to 10th	Day	20% 12% 4 9% 5% 5% 5% 4 5% 7% 25%	4750
	11th to 20th	Day	14% 8% 3 9% 5% 6% 6% 5% 7% 9% 28%	4693
	21st to end	Day	15% 7% 2 6% 5% 5% 5% 4 7% 8% 36%	4815
August	1st to 10th	Day	20% 10% 3 8% 6% 5% 6% 4 6% 7% 23%	4424
	11th to 20th	Day	18% 9% 3 6% 4 4 4 3 6% 6% 37%	4054
	21st to end	Day	20% 8% 2 7% 4 4 4 3 6% 8% 33%	4532
September	1st to 10th	Day	22% 7% 3 6% 4 4 5% 4 5% 8% 32%	2280
	11th to 20th	Day	28% 9% 3 7% 4 4 5% 3 4 6% 28%	2090
	21st to end	Day	19% 11% 4 8% 4 5% 4 3 4 8% 30%	2090
October	1st to 10th	Day	23% 11% 3 7% 4 4 4 3 4 7% 30%	2049
	11th to 20th	Day	23% 14% 2 8% 5% 4 5% 3 6% 7% 22%	1734
	21st to end	Day	26% 18% 4 6% 6% 4 5% 3 5% 4 20%	1881
November	1st to 10th	Day	23% 17% 4 8% 6% 5% 6% 3 4 5% 19%	1760
	11th to 20th	Day	22% 17% 5% 8% 4 4 5% 3 4 6% 22%	1563
	21st to end	Day	24% 18% 5% 9% 5% 3 4 3 3 5% 20%	1400
December	1st to 10th	Day	20% 18% 7% 10% 6% 5% 3 4 5% 5% 17%	1365
	11th to 20th	Day	23% 15% 6% 12% 6% 6% 4 4 4 6% 15%	1668
	21st to end	Day	22% 19% 6% 13% 6% 4 4 3 5% 4 14%	2442
January	1st to 10th	Night	12% 17% 7% 13% 6% 6% 4 4 4 5% 22%	4739
	11th to 20th	Night	12% 14% 6% 14% 6% 5% 5% 4 6% 6% 22%	4460
	21st to end	Night	10% 12% 6% 12% 8% 7% 6% 4 5% 6% 24%	4884
February	1st to 10th	Night	17% 13% 5% 12% 8% 5% 5% 4 5% 5% 21%	2660
	11th to 20th	Night	19% 17% 5% 11% 6% 5% 5% 4 4 4 19%	2352
	21st to end	Night	14% 14% 4 10% 7% 5% 4 3 5% 6% 27%	1884
March	1st to 10th	Night	20% 15% 3 12% 6% 4 4 4 6% 6% 20%	3726
	11th to 20th	Night	19% 19% 6% 13% 7% 5% 5% 5% 4 4 14%	3580
	21st to end	Night	26% 14% 5% 10% 4 3 4 3 3 6% 22%	3658
April	1st to 10th	Night	24% 18% 6% 7% 4 4 3 3 4 5% 22%	1900
	11th to 20th	Night	25% 16% 4 7% 4 3 4 2 4 5% 25%	1702
	21st to end	Night	26% 17% 5% 7% 4 4 2 3 4 6% 24%	1710
May	1st to 10th	Night	33% 20% 7% 7% 3 2 2 2 4 5% 13%	2688
	11th to 20th	Night	26% 18% 8% 12% 4 4 3 2 3 4 16%	2363
	21st to end	Night	30% 14% 5% 6% 3 4 4 3 4 6% 20%	2412
June	1st to 10th	Night	35% 14% 3 6% 4 4 4 3 5% 5% 17%	1330
	11th to 20th	Night	31% 10% 3 5% 4 4 4 4 5% 7% 24%	1330
	21st to end	Night	23% 13% 4 7% 6% 6% 4 2 5% 6% 24%	1330
July	1st to 10th	Night	23% 10% 4 8% 5% 4 5% 3 6% 6% 26%	2220
	11th to 20th	Night	14% 11% 4 9% 6% 5% 5% 5% 6% 7% 30%	2273
	21st to end	Night	16% 9% 2 6% 5% 4 4 3 5% 7% 38%	2750
August	1st to 10th	Night	15% 8% 3 8% 6% 4 5% 4 6% 8% 32%	2516
	11th to 20th	Night	17% 9% 3 7% 4 3 4 4 5% 6% 38%	2782
	21st to end	Night	21% 8% 3 6% 4 4 5% 3 4 7% 36%	3135
September	1st to 10th	Night	24% 8% 2 6% 4 3 3 3 5% 5% 37%	1897
	11th to 20th	Night	25% 11% 2 6% 4 4 4 3 4 6% 31%	2090
	21st to end	Night	22% 11% 3 7% 4 4 4 4 5% 6% 30%	2090
October	1st to 10th	Night	25% 11% 3 7% 4 4 3 3 5% 6% 29%	2130
	11th to 20th	Night	25% 12% 3 7% 5% 4 4 3 4 6% 27%	2444
	21st to end	Night	29% 16% 3 7% 4 3 4 3 4 5% 23%	2717
November	1st to 10th	Night	21% 16% 4 8% 6% 5% 4 4 5% 6% 19%	2538
	11th to 20th	Night	25% 14% 5% 8% 5% 4 4 3 5% 6% 21%	2835
	21st to end	Night	21% 18% 5% 9% 5% 4 4 3 6% 6% 19%	3000
December	1st to 10th	Night	19% 18% 6% 12% 6% 5% 4 3 5% 5% 17%	2932
	11th to 20th	Night	25% 18% 6% 14% 6% 4 4 2 3 4 14%	3531
	21st to end	Night	22% 15% 6% 11% 5% 4 4 4 5% 6% 18%	5225

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	63% 9% 14% 9% 4 1	2217
	11th to 20th	Day	63% 12% 11% 9% 6%	2508
	21st to end	Day	57% 9% 12% 13% 6% 3	2783
February	1st to 10th	Day	63% 8% 12% 10% 6% 1	1520
	11th to 20th	Day	68% 7% 10% 11% 4	1716
	21st to end	Day	61% 7% 10% 14% 8% 1	1570
March	1st to 10th	Day	63% 7% 10% 13% 6% 1	3118
	11th to 20th	Day	76% 7% 7% 7% 4	3379
	21st to end	Day	70% 6% 8% 12% 4	3970
April	1st to 10th	Day	70% 6% 9% 10% 4 1	2280
	11th to 20th	Day	62% 6% 9% 14% 7% 1	2428
	21st to end	Day	66% 6% 8% 12% 8%	2470
May	1st to 10th	Day	73% 7% 9% 8% 3	4275
	11th to 20th	Day	66% 8% 9% 12% 5%	4543
	21st to end	Day	64% 7% 9% 14% 6%	5173
June	1st to 10th	Day	70% 7% 8% 11% 4	2850
	11th to 20th	Day	61% 8% 11% 16% 5%	2850
	21st to end	Day	59% 10% 11% 13% 7% 1	2850
July	1st to 10th	Day	58% 5% 12% 18% 6%	4675
	11th to 20th	Day	52% 7% 17% 19% 5%	4611
	21st to end	Day	44% 7% 17% 26% 5%	4662
August	1st to 10th	Day	59% 8% 15% 16% 3	4410
	11th to 20th	Day	47% 6% 14% 20% 11% 1	4093
	21st to end	Day	49% 6% 15% 25% 5%	4532
September	1st to 10th	Day	49% 8% 12% 22% 8% 2	2280
	11th to 20th	Day	58% 7% 13% 17% 6%	2090
	21st to end	Day	52% 7% 17% 17% 6%	2090
October	1st to 10th	Day	59% 5% 12% 17% 6%	3403
	11th to 20th	Day	61% 5% 11% 17% 5%	2869
	21st to end	Day	67% 5% 9% 10% 8% 1	3092
November	1st to 10th	Day	67% 8% 12% 10% 3	1760
	11th to 20th	Day	63% 7% 11% 12% 6% 1	1563
	21st to end	Day	67% 7% 12% 8% 5% 1	1400
December	1st to 10th	Day	68% 7% 11% 10% 3	1365
	11th to 20th	Day	69% 7% 14% 7% 2	1667
	21st to end	Day	71% 8% 11% 9% 2	2442
January	1st to 10th	Night	60% 9% 14% 12% 3	4739
	11th to 20th	Night	57% 10% 13% 13% 6%	4460
	21st to end	Night	57% 10% 14% 11% 5% 3	4884
February	1st to 10th	Night	62% 7% 12% 12% 6% 1	2660
	11th to 20th	Night	67% 7% 10% 12% 4	2356
	21st to end	Night	55% 7% 13% 16% 9% 1	1884
March	1st to 10th	Night	62% 8% 11% 13% 5% 1	3735
	11th to 20th	Night	70% 10% 8% 8% 4 1	3581
	21st to end	Night	62% 7% 13% 13% 5% 1	3658
April	1st to 10th	Night	64% 6% 8% 13% 8% 1	1900
	11th to 20th	Night	63% 5% 9% 16% 7% 1	1702
	21st to end	Night	62% 6% 9% 13% 9% 1	1710
May	1st to 10th	Night	74% 5% 10% 8% 3	2693
	11th to 20th	Night	71% 6% 7% 11% 4	2364
	21st to end	Night	63% 8% 10% 13% 5%	2413
June	1st to 10th	Night	68% 8% 11% 9% 4	1330
	11th to 20th	Night	58% 9% 14% 15% 5%	1330
	21st to end	Night	60% 9% 10% 14% 7% 1	1330
July	1st to 10th	Night	58% 6% 14% 19% 4	2186
	11th to 20th	Night	53% 7% 16% 16% 7%	2231
	21st to end	Night	46% 6% 17% 26% 5%	2663
August	1st to 10th	Night	47% 9% 18% 22% 4	2505
	11th to 20th	Night	46% 6% 16% 22% 9% 1	2809
	21st to end	Night	49% 5% 15% 26% 5%	3134
September	1st to 10th	Night	48% 7% 14% 21% 9% 1	1897
	11th to 20th	Night	54% 7% 13% 17% 9% 1	2090
	21st to end	Night	54% 7% 14% 17% 7%	2090
October	1st to 10th	Night	61% 5% 15% 13% 5% 1	3559
	11th to 20th	Night	59% 5% 15% 14% 7%	4058
	21st to end	Night	59% 4 12% 16% 8% 1	4467
November	1st to 10th	Night	65% 9% 11% 11% 4	2538
	11th to 20th	Night	64% 7% 13% 13% 3	2835
	21st to end	Night	65% 8% 12% 10% 5% 1	3000
December	1st to 10th	Night	68% 8% 10% 12% 3	2932
	11th to 20th	Night	75% 7% 9% 7% 2	3533
	21st to end	Night	66% 9% 14% 10% 2	5225

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% 35% 14% 5%	370
	11th to 20th	Day	23% 24% 35% 16% 3	370
	21st to end	Day	28% 19% 31% 17% 4	407
February	1st to 10th	Day	26% 26% 28% 16% 4	370
	11th to 20th	Day	27% 24% 34% 11% 2 1	366
	21st to end	Day	20% 23% 37% 15% 3 1	307
March	1st to 10th	Day	24% 21% 39% 12% 4 1	370
	11th to 20th	Day	28% 16% 28% 17% 8% 2	370
	21st to end	Day	37% 21% 22% 15% 3 2	450
April	1st to 10th	Day	29% 21% 30% 17% 3	460
	11th to 20th	Day	34% 13% 28% 19% 5% 1	626
	21st to end	Day	32% 17% 30% 18% 3	650
May	1st to 10th	Day	38% 12% 24% 17% 6% 2	653
	11th to 20th	Day	30% 13% 28% 18% 9% 2	674
	21st to end	Day	34% 13% 30% 19% 4 1	735
June	1st to 10th	Day	41% 11% 24% 15% 9% 1	680
	11th to 20th	Day	33% 11% 25% 20% 9% 1	680
	21st to end	Day	28% 10% 27% 22% 11% 3	680
July	1st to 10th	Day	29% 10% 26% 23% 9% 3	670
	11th to 20th	Day	21% 11% 28% 28% 10% 1	668
	21st to end	Day	23% 10% 25% 31% 10% 1	740
August	1st to 10th	Day	25% 9% 28% 25% 10% 2	675
	11th to 20th	Day	22% 7% 28% 24% 16% 2	667
	21st to end	Day	24% 8% 27% 25% 12% 3	748
September	1st to 10th	Day	25% 12% 31% 23% 9% 1	492
	11th to 20th	Day	36% 12% 28% 20% 4 1	390
	21st to end	Day	23% 20% 34% 16% 5% 2	390
October	1st to 10th	Day	25% 19% 33% 17% 5% 2	390
	11th to 20th	Day	35% 11% 26% 18% 7% 3	390
	21st to end	Day	33% 21% 25% 14% 6% 1	429
November	1st to 10th	Day	37% 18% 30% 13% 2	395
	11th to 20th	Day	35% 22% 23% 15% 5% 1	400
	21st to end	Day	39% 20% 29% 12% 1	400
December	1st to 10th	Day	26% 16% 33% 18% 6% 1	385
	11th to 20th	Day	30% 25% 29% 13% 3	370
	21st to end	Day	24% 21% 31% 18% 5% 1	407
January	1st to 10th	Night	26% 20% 31% 18% 5% 1	850
	11th to 20th	Night	23% 24% 34% 16% 3	850
	21st to end	Night	24% 20% 38% 15% 3	935
February	1st to 10th	Night	26% 20% 35% 16% 3	850
	11th to 20th	Night	29% 22% 34% 12% 2	802
	21st to end	Night	21% 15% 40% 16% 6% 1	628
March	1st to 10th	Night	28% 19% 34% 14% 5% 1	760
	11th to 20th	Night	24% 16% 29% 23% 7%	632
	21st to end	Night	32% 17% 29% 17% 4	627
April	1st to 10th	Night	32% 19% 28% 16% 4 1	570
	11th to 20th	Night	32% 11% 33% 18% 5% 1	564
	21st to end	Night	32% 12% 34% 19% 2	570
May	1st to 10th	Night	36% 10% 24% 22% 7% 1	570
	11th to 20th	Night	35% 11% 27% 19% 9%	562
	21st to end	Night	35% 11% 31% 18% 5%	616
June	1st to 10th	Night	40% 10% 22% 24% 3	570
	11th to 20th	Night	38% 8% 24% 24% 6% 1	570
	21st to end	Night	29% 9% 31% 22% 8%	570
July	1st to 10th	Night	25% 8% 33% 27% 7% 1	556
	11th to 20th	Night	22% 9% 31% 33% 5%	552
	21st to end	Night	24% 7% 30% 32% 7%	623
August	1st to 10th	Night	23% 6% 30% 30% 10%	568
	11th to 20th	Night	23% 6% 30% 31% 10%	562
	21st to end	Night	24% 8% 28% 31% 9% 1	627
September	1st to 10th	Night	27% 7% 34% 25% 6%	570
	11th to 20th	Night	29% 13% 31% 24% 3	570
	21st to end	Night	31% 12% 32% 21% 4	570
October	1st to 10th	Night	32% 11% 32% 21% 4 1	592
	11th to 20th	Night	33% 11% 29% 20% 7%	834
	21st to end	Night	38% 15% 25% 16% 5% 1	946
November	1st to 10th	Night	32% 20% 30% 14% 3	880
	11th to 20th	Night	35% 15% 30% 14% 5% 1	900
	21st to end	Night	34% 20% 30% 14% 2	900
December	1st to 10th	Night	28% 18% 34% 15% 4 1	878
	11th to 20th	Night	33% 21% 32% 11% 2	850
	21st to end	Night	24% 20% 33% 17% 4 1	935

Page generated at 2024-12-03 07:45:08. Version ac07

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