Tucker Creek Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Tucker Creek Observatory clear sky chart from 2005-11-06 to 2026-05-17.

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% 7% 2 6% 4 4 4 4 6% 7% 44%	131805
	Night	13% 8% 2 6% 4 4 4 3 5% 6% 45%	131261
Transparency	Day	38% 5% 11% 25% 18% 4	135400
	Night	38% 4 11% 24% 19% 4	135744
Seeing	Day	17% 12% 28% 25% 14% 5%	17544
	Night	17% 12% 29% 26% 13% 2	27438

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% 10% 3 8% 5% 5% 4 3 4 6% 40%	4691
	11th to 20th	Day	8% 7% 3 7% 4 3 4 3 5% 6% 50%	5207
	21st to end	Day	17% 8% 3 7% 3 4 4 3 4 5% 42%	5812
February	1st to 10th	Day	15% 12% 3 7% 5% 3 3 3 4 5% 39%	1924
	11th to 20th	Day	15% 9% 3 7% 5% 3 3 3 5% 6% 40%	2048
	21st to end	Day	13% 11% 3 6% 4 3 4 4 6% 6% 39%	1730
March	1st to 10th	Day	16% 11% 3 5% 3 4 4 3 3 4 44%	4622
	11th to 20th	Day	10% 7% 2 4 3 3 3 3 4 7% 54%	5090
	21st to end	Day	13% 8% 3 7% 4 4 5% 3 5% 7% 40%	5908
April	1st to 10th	Day	12% 7% 3 6% 3 4 4 4 6% 7% 44%	2520
	11th to 20th	Day	15% 9% 2 7% 4 4 4 3 4 7% 41%	2494
	21st to end	Day	16% 8% 3 6% 5% 4 5% 4 5% 7% 38%	2520
May	1st to 10th	Day	14% 8% 3 9% 6% 6% 5% 5% 7% 8% 30%	5609
	11th to 20th	Day	17% 9% 3 7% 4 5% 4 4 6% 8% 33%	6156
	21st to end	Day	15% 7% 3 7% 5% 4 4 4 5% 6% 41%	6935
June	1st to 10th	Day	10% 5% 2 6% 5% 4 4 4 7% 8% 45%	2800
	11th to 20th	Day	5% 5% 2 5% 4 5% 5% 4 7% 8% 48%	2800
	21st to end	Day	4 4 2 5% 5% 5% 6% 4 8% 11% 47%	2800
July	1st to 10th	Day	8% 5% 2 6% 5% 5% 5% 4 7% 9% 45%	6360
	11th to 20th	Day	5% 4 2 6% 5% 5% 6% 5% 8% 12% 43%	6360
	21st to end	Day	6% 5% 2 7% 5% 6% 7% 6% 8% 10% 39%	6478
August	1st to 10th	Day	4 3 2 5% 3 4 5% 5% 6% 11% 53%	4117
	11th to 20th	Day	11% 6% 2 5% 4 4 5% 3 6% 9% 46%	3849
	21st to end	Day	5% 5% 1 5% 4 4 4 4 6% 8% 54%	4312
September	1st to 10th	Day	10% 5% 2 5% 4 3 4 4 6% 8% 49%	2400
	11th to 20th	Day	9% 6% 2 5% 3 4 4 4 6% 9% 47%	2358
	21st to end	Day	11% 6% 2 4 3 3 4 3 5% 7% 52%	2200
October	1st to 10th	Day	7% 4 2 4 3 3 3 3 5% 6% 58%	2027
	11th to 20th	Day	12% 5% 2 5% 3 3 3 3 4 6% 54%	2000
	21st to end	Day	17% 9% 2 5% 3 3 3 2 4 5% 47%	2193
November	1st to 10th	Day	11% 6% 2 5% 2 4 3 3 4 5% 55%	1852
	11th to 20th	Day	12% 7% 3 6% 4 3 3 3 5% 8% 46%	1890
	21st to end	Day	17% 10% 2 6% 3 3 3 3 4 4 43%	1890
December	1st to 10th	Day	9% 9% 2 6% 4 3 3 3 4 6% 51%	2695
	11th to 20th	Day	14% 10% 3 7% 4 3 3 3 5% 6% 42%	3088
	21st to end	Day	21% 17% 4 8% 4 4 4 3 3 4 28%	4070
January	1st to 10th	Night	15% 10% 3 8% 4 4 4 3 4 5% 38%	8232
	11th to 20th	Night	10% 8% 2 8% 5% 4 4 3 4 5% 46%	7767
	21st to end	Night	17% 9% 3 7% 5% 5% 3 3 4 5% 40%	8402
February	1st to 10th	Night	17% 11% 4 8% 4 4 3 3 4 6% 37%	2693
	11th to 20th	Night	15% 8% 4 7% 4 4 4 2 4 5% 42%	2458
	21st to end	Night	16% 7% 3 7% 4 3 4 4 4 5% 42%	2076
March	1st to 10th	Night	17% 12% 3 7% 4 4 4 3 4 4 39%	5493
	11th to 20th	Night	11% 7% 2 6% 3 4 4 4 5% 6% 48%	5090
	21st to end	Night	14% 6% 2 8% 5% 4 4 3 5% 7% 40%	5262
April	1st to 10th	Night	10% 6% 2 5% 4 4 4 4 5% 8% 48%	2100
	11th to 20th	Night	13% 7% 2 7% 4 5% 4 3 5% 6% 45%	2075
	21st to end	Night	19% 7% 3 5% 5% 4 4 3 5% 6% 41%	2100
May	1st to 10th	Night	17% 9% 3 7% 5% 4 5% 4 6% 7% 34%	4501
	11th to 20th	Night	14% 8% 3 8% 4 4 5% 3 6% 8% 39%	3877
	21st to end	Night	16% 8% 2 7% 4 4 4 4 5% 7% 38%	3942
June	1st to 10th	Night	9% 5% 2 6% 4 4 5% 5% 6% 10% 45%	1600
	11th to 20th	Night	6% 4 2 4 3 4 4 4 6% 10% 55%	1600
	21st to end	Night	4 3 1 3 3 4 5% 5% 7% 10% 56%	1600
July	1st to 10th	Night	8% 4 2 6% 4 4 4 4 5% 9% 50%	3618
	11th to 20th	Night	5% 5% 2 6% 4 4 5% 4 7% 10% 48%	3617
	21st to end	Night	6% 6% 2 5% 4 4 4 4 7% 11% 46%	4376
August	1st to 10th	Night	4 3 1 4 3 3 4 4 6% 9% 59%	3036
	11th to 20th	Night	8% 6% 2 6% 3 4 4 3 5% 9% 50%	3200
	21st to end	Night	4 3 1 5% 3 3 4 3 6% 9% 59%	3586
September	1st to 10th	Night	10% 6% 2 5% 4 3 3 3 5% 6% 53%	2000
	11th to 20th	Night	8% 6% 2 4 3 4 5% 4 5% 7% 53%	2020
	21st to end	Night	10% 5% 2 4 3 4 4 4 5% 7% 53%	2200
October	1st to 10th	Night	6% 4 1 4 2 3 3 3 5% 5% 64%	2370
	11th to 20th	Night	12% 5% 2 4 3 3 3 2 4 5% 57%	2400
	21st to end	Night	18% 7% 2 5% 3 3 4 2 3 5% 48%	2645
November	1st to 10th	Night	10% 6% 2 4 3 2 3 2 5% 6% 57%	2666
	11th to 20th	Night	13% 6% 2 5% 4 3 3 2 4 6% 52%	2730
	21st to end	Night	18% 9% 3 5% 3 3 2 2 4 5% 47%	2730
December	1st to 10th	Night	13% 9% 2 6% 4 4 3 3 4 5% 47%	4710
	11th to 20th	Night	14% 9% 3 6% 4 4 4 3 4 6% 44%	5339
	21st to end	Night	22% 13% 4 8% 4 3 4 3 4 5% 30%	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	45% 3 13% 26% 11% 2	4692
	11th to 20th	Day	35% 3 6% 29% 21% 6%	5207
	21st to end	Day	45% 2 9% 20% 14% 9%	5812
February	1st to 10th	Day	48% 4 12% 22% 14% 1	1924
	11th to 20th	Day	46% 4 11% 21% 14% 5%	2058
	21st to end	Day	44% 4 9% 22% 14% 5%	1730
March	1st to 10th	Day	46% 3 5% 21% 17% 8%	4622
	11th to 20th	Day	32% 3 7% 29% 22% 7%	5090
	21st to end	Day	42% 5% 13% 27% 12% 1	5910
April	1st to 10th	Day	38% 5% 11% 24% 19% 2	2520
	11th to 20th	Day	44% 4 11% 21% 16% 5%	2494
	21st to end	Day	45% 6% 11% 23% 14% 1	2520
May	1st to 10th	Day	48% 8% 12% 19% 12% 1	5644
	11th to 20th	Day	48% 6% 11% 21% 12% 1	6160
	21st to end	Day	43% 5% 9% 22% 18% 3	6949
June	1st to 10th	Day	34% 7% 15% 25% 17% 2	2800
	11th to 20th	Day	31% 7% 12% 27% 21% 3	2800
	21st to end	Day	28% 8% 18% 24% 17% 5%	2800
July	1st to 10th	Day	35% 5% 12% 26% 20% 3	6291
	11th to 20th	Day	32% 6% 18% 31% 12% 1	6285
	21st to end	Day	38% 5% 17% 29% 10% 1	6294
August	1st to 10th	Day	24% 6% 14% 34% 21% 1	4103
	11th to 20th	Day	35% 5% 13% 27% 17% 3	3885
	21st to end	Day	27% 4 14% 35% 17% 3	4311
September	1st to 10th	Day	32% 5% 13% 26% 19% 5%	2400
	11th to 20th	Day	33% 6% 10% 25% 25% 2	2358
	21st to end	Day	31% 5% 8% 27% 27% 3	2200
October	1st to 10th	Day	16% 3 6% 20% 44% 11%	3300
	11th to 20th	Day	23% 2 6% 22% 37% 9%	3240
	21st to end	Day	31% 3 5% 28% 28% 5%	3519
November	1st to 10th	Day	32% 4 11% 27% 20% 6%	1852
	11th to 20th	Day	38% 4 8% 23% 21% 6%	1890
	21st to end	Day	44% 3 8% 24% 19% 2	1890
December	1st to 10th	Day	36% 3 8% 36% 16% 1	2695
	11th to 20th	Day	44% 4 8% 25% 17% 2	3085
	21st to end	Day	61% 4 10% 14% 9% 2	4070
January	1st to 10th	Night	47% 3 12% 25% 12% 1	8233
	11th to 20th	Night	38% 4 6% 25% 23% 4	7767
	21st to end	Night	46% 3 9% 21% 17% 3	8402
February	1st to 10th	Night	48% 4 9% 22% 14% 2	2693
	11th to 20th	Night	45% 3 10% 21% 17% 3	2459
	21st to end	Night	43% 5% 7% 23% 18% 5%	2076
March	1st to 10th	Night	49% 3 5% 19% 17% 6%	5493
	11th to 20th	Night	37% 5% 8% 22% 19% 9%	5090
	21st to end	Night	42% 5% 13% 27% 12% 1	5262
April	1st to 10th	Night	33% 5% 13% 25% 19% 3	2100
	11th to 20th	Night	39% 6% 11% 21% 19% 4	2075
	21st to end	Night	45% 4 9% 24% 15% 2	2100
May	1st to 10th	Night	47% 7% 16% 20% 10% 1	4531
	11th to 20th	Night	44% 6% 13% 21% 13% 2	3878
	21st to end	Night	44% 6% 10% 22% 15% 3	3950
June	1st to 10th	Night	34% 7% 13% 24% 19% 2	1600
	11th to 20th	Night	24% 6% 13% 29% 23% 5%	1600
	21st to end	Night	21% 7% 16% 30% 18% 8%	1600
July	1st to 10th	Night	32% 6% 12% 26% 22% 3	3580
	11th to 20th	Night	31% 6% 17% 30% 14% 2	3572
	21st to end	Night	30% 4 24% 28% 14% 1	4249
August	1st to 10th	Night	21% 5% 19% 32% 22% 1	3026
	11th to 20th	Night	32% 5% 16% 26% 17% 4	3230
	21st to end	Night	22% 4 12% 39% 19% 3	3586
September	1st to 10th	Night	31% 7% 8% 29% 20% 6%	2000
	11th to 20th	Night	30% 6% 10% 27% 25% 3	2020
	21st to end	Night	30% 6% 9% 22% 28% 5%	2200
October	1st to 10th	Night	14% 3 6% 17% 45% 16%	3877
	11th to 20th	Night	22% 2 6% 20% 39% 11%	3899
	21st to end	Night	32% 2 7% 25% 28% 7%	4269
November	1st to 10th	Night	30% 4 10% 27% 23% 6%	2666
	11th to 20th	Night	34% 3 9% 24% 24% 6%	2730
	21st to end	Night	41% 3 8% 26% 20% 2	2730
December	1st to 10th	Night	41% 3 8% 29% 18% 1	4710
	11th to 20th	Night	42% 4 12% 21% 20% 2	5341
	21st to end	Night	56% 4 11% 19% 9% 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	28% 20% 35% 15% 2 1	330
	11th to 20th	Day	27% 25% 37% 10% 1	330
	21st to end	Day	22% 27% 37% 12% 2	363
February	1st to 10th	Day	25% 22% 40% 11% 2	330
	11th to 20th	Day	31% 30% 29% 8% 1 1	330
	21st to end	Day	32% 23% 34% 8% 2	273
March	1st to 10th	Day	25% 21% 39% 13% 2	330
	11th to 20th	Day	31% 22% 34% 11% 2	330
	21st to end	Day	27% 22% 36% 13% 3	507
April	1st to 10th	Day	22% 21% 35% 17% 4 1	540
	11th to 20th	Day	26% 21% 27% 18% 7% 1	532
	21st to end	Day	21% 14% 39% 18% 7% 1	540
May	1st to 10th	Day	19% 19% 34% 21% 6% 1	543
	11th to 20th	Day	20% 12% 29% 23% 12% 3	638
	21st to end	Day	12% 8% 34% 27% 14% 5%	789
June	1st to 10th	Day	13% 5% 25% 26% 24% 7%	730
	11th to 20th	Day	7% 3 24% 39% 21% 6%	730
	21st to end	Day	5% 4 30% 36% 18% 7%	730
July	1st to 10th	Day	10% 3 18% 31% 25% 14%	721
	11th to 20th	Day	6% 2 20% 37% 25% 9%	718
	21st to end	Day	7% 4 18% 36% 27% 8%	794
August	1st to 10th	Day	8% 2 17% 38% 25% 9%	661
	11th to 20th	Day	13% 3 19% 29% 29% 7%	519
	21st to end	Day	9% 2 15% 33% 30% 11%	583
September	1st to 10th	Day	10% 3 19% 35% 24% 9%	530
	11th to 20th	Day	10% 4 15% 32% 29% 11%	530
	21st to end	Day	15% 8% 22% 29% 18% 8%	530
October	1st to 10th	Day	11% 7% 27% 39% 11% 4	357
	11th to 20th	Day	20% 12% 34% 25% 7% 1	330
	21st to end	Day	31% 14% 37% 15% 3	363
November	1st to 10th	Day	18% 14% 38% 21% 7% 2	330
	11th to 20th	Day	19% 21% 34% 18% 7% 1	330
	21st to end	Day	29% 18% 32% 15% 5%	330
December	1st to 10th	Day	21% 21% 36% 15% 6% 2	330
	11th to 20th	Day	29% 18% 35% 15% 2	330
	21st to end	Day	27% 20% 40% 9% 3	363
January	1st to 10th	Night	22% 21% 35% 19% 3	1050
	11th to 20th	Night	24% 26% 32% 15% 3	1050
	21st to end	Night	21% 19% 40% 19% 1	1155
February	1st to 10th	Night	23% 21% 37% 17% 2	1013
	11th to 20th	Night	23% 23% 36% 17% 2	823
	21st to end	Night	23% 20% 37% 18% 1	692
March	1st to 10th	Night	24% 18% 36% 19% 2	840
	11th to 20th	Night	24% 14% 38% 22% 3	630
	21st to end	Night	23% 15% 34% 23% 5%	693
April	1st to 10th	Night	14% 19% 39% 24% 4	630
	11th to 20th	Night	20% 15% 30% 24% 11%	623
	21st to end	Night	22% 11% 36% 22% 8%	630
May	1st to 10th	Night	17% 11% 35% 27% 9% 1	630
	11th to 20th	Night	18% 6% 32% 28% 14% 2	609
	21st to end	Night	12% 4 27% 36% 19% 4	650
June	1st to 10th	Night	11% 4 20% 36% 26% 2	600
	11th to 20th	Night	7% 2 20% 46% 24% 1	600
	21st to end	Night	5% 3 22% 41% 28% 1	600
July	1st to 10th	Night	8% 2 12% 36% 35% 8%	585
	11th to 20th	Night	7% 2 13% 40% 32% 6%	582
	21st to end	Night	7% 2 14% 40% 33% 5%	657
August	1st to 10th	Night	7% 1 14% 39% 35% 5%	597
	11th to 20th	Night	9% 2 12% 36% 37% 4	594
	21st to end	Night	7% 2 12% 36% 37% 7%	660
September	1st to 10th	Night	12% 3 16% 31% 33% 6%	600
	11th to 20th	Night	11% 2 15% 32% 35% 6%	620
	21st to end	Night	13% 6% 22% 30% 25% 5%	800
October	1st to 10th	Night	8% 6% 25% 35% 23% 4	800
	11th to 20th	Night	15% 9% 32% 27% 16% 1	800
	21st to end	Night	23% 13% 31% 26% 7%	880
November	1st to 10th	Night	14% 10% 38% 27% 10% 1	820
	11th to 20th	Night	19% 13% 33% 26% 8%	840
	21st to end	Night	25% 13% 32% 23% 7%	840
December	1st to 10th	Night	22% 16% 36% 21% 5%	1040
	11th to 20th	Night	23% 13% 37% 23% 4	1050
	21st to end	Night	26% 17% 37% 18% 3	1155

Page generated at 2026-05-14 00:58:54. Version ac07

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