Butter Pot Park
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Butter Pot Park clear sky chart from 2005-11-06 to 2025-11-18.

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	18% 16% 6% 11% 6% 5% 5% 3 5% 6% 21%	126951
	Night	18% 16% 6% 12% 6% 5% 5% 4 5% 5% 19%	123648
Transparency	Day	65% 5% 11% 14% 5%	130434
	Night	65% 6% 11% 13% 5%	128280
Seeing	Day	27% 17% 30% 18% 6% 1	19599
	Night	27% 16% 32% 19% 5%	26130

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	17% 20% 9% 16% 5% 4 4 2 3 5% 14%	3176
	11th to 20th	Day	14% 20% 11% 16% 6% 4 4 3 3 4 14%	3530
	21st to end	Day	10% 16% 8% 20% 6% 5% 5% 3 5% 5% 16%	3982
February	1st to 10th	Day	16% 15% 7% 15% 9% 7% 5% 4 4 5% 13%	1756
	11th to 20th	Day	18% 18% 7% 14% 6% 5% 5% 4 4 6% 12%	1758
	21st to end	Day	13% 16% 8% 17% 8% 6% 6% 4 4 5% 15%	1650
March	1st to 10th	Day	19% 15% 6% 16% 8% 7% 6% 3 4 4 13%	4537
	11th to 20th	Day	19% 17% 9% 14% 6% 5% 4 3 4 4 16%	4980
	21st to end	Day	17% 20% 10% 15% 6% 5% 4 3 4 5% 13%	5467
April	1st to 10th	Day	17% 20% 8% 12% 8% 5% 4 3 4 4 15%	2407
	11th to 20th	Day	19% 22% 6% 8% 5% 4 4 3 4 4 20%	2571
	21st to end	Day	22% 21% 6% 8% 5% 4 4 3 4 4 19%	2600
May	1st to 10th	Day	22% 26% 6% 9% 4 4 3 3 3 4 17%	5885
	11th to 20th	Day	20% 18% 5% 11% 5% 5% 4 3 4 5% 20%	6316
	21st to end	Day	18% 21% 5% 9% 5% 5% 4 3 4 6% 20%	7428
June	1st to 10th	Day	26% 16% 5% 9% 6% 5% 4 3 4 4 17%	3000
	11th to 20th	Day	22% 13% 3 8% 5% 4 5% 4 6% 7% 24%	3000
	21st to end	Day	21% 11% 3 9% 6% 6% 5% 4 6% 7% 23%	3000
July	1st to 10th	Day	21% 12% 5% 9% 6% 5% 5% 4 5% 7% 22%	6800
	11th to 20th	Day	14% 9% 4 10% 7% 7% 6% 4 6% 7% 28%	6762
	21st to end	Day	16% 8% 3 8% 5% 5% 5% 4 6% 8% 32%	6927
August	1st to 10th	Day	20% 10% 4 11% 6% 6% 5% 3 5% 7% 23%	4287
	11th to 20th	Day	20% 9% 3 9% 6% 5% 5% 5% 6% 7% 26%	4176
	21st to end	Day	20% 10% 3 7% 5% 5% 5% 4 5% 8% 30%	4675
September	1st to 10th	Day	18% 9% 4 8% 5% 4 5% 3 5% 8% 31%	2390
	11th to 20th	Day	21% 9% 3 8% 5% 5% 4 4 5% 6% 30%	2200
	21st to end	Day	16% 10% 3 8% 5% 5% 4 3 7% 8% 31%	2200
October	1st to 10th	Day	22% 12% 3 8% 5% 5% 4 3 5% 7% 27%	2091
	11th to 20th	Day	22% 16% 4 8% 6% 5% 5% 4 4 5% 23%	1969
	21st to end	Day	22% 18% 4 8% 7% 5% 4 4 5% 6% 17%	1980
November	1st to 10th	Day	16% 19% 5% 10% 5% 5% 5% 3 5% 6% 22%	1814
	11th to 20th	Day	18% 17% 5% 9% 6% 6% 5% 4 6% 7% 16%	1656
	21st to end	Day	20% 21% 7% 9% 5% 4 5% 3 4 5% 16%	1565
December	1st to 10th	Day	16% 18% 5% 9% 5% 5% 6% 4 5% 8% 19%	2290
	11th to 20th	Day	13% 22% 9% 12% 5% 3 3 3 4 5% 20%	2628
	21st to end	Day	17% 21% 8% 15% 7% 5% 5% 3 4 4 11%	3498
January	1st to 10th	Night	15% 21% 9% 14% 7% 6% 4 3 4 4 13%	6789
	11th to 20th	Night	14% 20% 10% 19% 6% 5% 4 3 4 4 12%	6358
	21st to end	Night	10% 13% 8% 19% 8% 5% 5% 3 5% 5% 18%	6996
February	1st to 10th	Night	18% 13% 6% 16% 9% 5% 5% 4 5% 4 14%	2642
	11th to 20th	Night	19% 16% 6% 14% 8% 6% 5% 3 4 5% 14%	2526
	21st to end	Night	12% 15% 8% 15% 8% 8% 4 3 5% 5% 17%	1980
March	1st to 10th	Night	18% 14% 7% 15% 6% 5% 5% 4 6% 4 16%	5303
	11th to 20th	Night	16% 16% 8% 18% 7% 5% 4 3 4 4 14%	4979
	21st to end	Night	21% 18% 9% 13% 5% 4 5% 3 4 4 14%	5465
April	1st to 10th	Night	20% 19% 7% 10% 5% 4 4 3 4 5% 17%	1987
	11th to 20th	Night	21% 18% 6% 8% 4 4 4 3 4 4 23%	1778
	21st to end	Night	21% 21% 5% 10% 6% 4 4 3 4 4 19%	1800
May	1st to 10th	Night	26% 20% 7% 9% 4 4 4 2 4 4 16%	4075
	11th to 20th	Night	23% 20% 5% 11% 5% 4 3 3 4 5% 19%	3592
	21st to end	Night	20% 22% 6% 8% 5% 5% 4 3 5% 5% 17%	3468
June	1st to 10th	Night	24% 16% 4 9% 6% 5% 5% 3 4 5% 19%	1400
	11th to 20th	Night	22% 12% 3 8% 5% 5% 5% 4 7% 8% 20%	1400
	21st to end	Night	21% 12% 4 8% 5% 4 5% 4 7% 8% 22%	1400
July	1st to 10th	Night	27% 12% 4 9% 6% 5% 5% 4 6% 7% 16%	3179
	11th to 20th	Night	17% 10% 3 7% 6% 6% 7% 6% 8% 9% 21%	3214
	21st to end	Night	15% 7% 4 8% 6% 6% 5% 5% 6% 7% 32%	3948
August	1st to 10th	Night	20% 10% 3 8% 5% 5% 5% 5% 7% 7% 25%	2858
	11th to 20th	Night	23% 9% 3 7% 5% 4 5% 4 6% 8% 27%	2881
	21st to end	Night	24% 9% 3 7% 5% 4 5% 4 5% 7% 28%	3234
September	1st to 10th	Night	17% 8% 3 7% 5% 6% 5% 5% 6% 8% 29%	2005
	11th to 20th	Night	22% 13% 3 8% 4 5% 4 3 5% 7% 26%	2200
	21st to end	Night	19% 12% 3 8% 4 4 4 3 4 6% 31%	2200
October	1st to 10th	Night	21% 12% 3 8% 5% 5% 4 3 6% 6% 27%	2308
	11th to 20th	Night	22% 16% 4 9% 6% 4 4 4 5% 6% 22%	2430
	21st to end	Night	22% 18% 4 9% 5% 4 5% 4 4 5% 21%	2860
November	1st to 10th	Night	19% 18% 4 9% 5% 4 5% 4 5% 6% 21%	2702
	11th to 20th	Night	19% 16% 5% 10% 6% 5% 5% 4 5% 6% 18%	2899
	21st to end	Night	17% 19% 5% 11% 5% 4 5% 4 6% 6% 18%	2831
December	1st to 10th	Night	13% 19% 6% 10% 5% 5% 5% 3 5% 5% 24%	4900
	11th to 20th	Night	14% 22% 6% 14% 7% 5% 4 4 4 5% 16%	5581
	21st to end	Night	18% 21% 8% 12% 6% 5% 4 3 4 4 15%	7480

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	71% 6% 5% 10% 6% 1	3177
	11th to 20th	Day	73% 4 8% 9% 5% 1	3559
	21st to end	Day	67% 5% 8% 12% 8%	3982
February	1st to 10th	Day	72% 6% 7% 7% 7% 1	1756
	11th to 20th	Day	71% 6% 9% 8% 4 1	1765
	21st to end	Day	70% 5% 10% 7% 7% 2	1650
March	1st to 10th	Day	73% 5% 8% 9% 5% 1	4542
	11th to 20th	Day	71% 5% 9% 9% 4 2	4980
	21st to end	Day	77% 4 6% 9% 4 1	5467
April	1st to 10th	Day	73% 5% 6% 10% 6%	2407
	11th to 20th	Day	67% 5% 8% 11% 8% 1	2571
	21st to end	Day	69% 5% 8% 10% 8% 1	2600
May	1st to 10th	Day	70% 6% 7% 11% 5% 1	5897
	11th to 20th	Day	67% 6% 9% 14% 4	6320
	21st to end	Day	65% 6% 9% 16% 4	7428
June	1st to 10th	Day	72% 5% 7% 11% 5% 1	3000
	11th to 20th	Day	61% 7% 12% 14% 6%	3000
	21st to end	Day	61% 8% 10% 16% 5%	3000
July	1st to 10th	Day	62% 5% 13% 16% 4	6725
	11th to 20th	Day	56% 5% 17% 15% 7%	6680
	21st to end	Day	50% 5% 20% 20% 4	6730
August	1st to 10th	Day	62% 5% 11% 17% 5%	4273
	11th to 20th	Day	58% 6% 13% 19% 4	4215
	21st to end	Day	54% 6% 15% 22% 3	4675
September	1st to 10th	Day	52% 6% 11% 23% 9%	2390
	11th to 20th	Day	54% 5% 12% 17% 11%	2200
	21st to end	Day	51% 6% 15% 20% 8%	2200
October	1st to 10th	Day	64% 6% 10% 14% 5%	3409
	11th to 20th	Day	58% 7% 12% 16% 7%	3195
	21st to end	Day	66% 5% 9% 14% 6%	3191
November	1st to 10th	Day	64% 6% 14% 11% 5%	1814
	11th to 20th	Day	67% 7% 9% 11% 5% 1	1656
	21st to end	Day	71% 6% 10% 9% 4	1565
December	1st to 10th	Day	62% 6% 14% 12% 6%	2290
	11th to 20th	Day	67% 5% 11% 10% 6%	2627
	21st to end	Day	74% 6% 8% 9% 3	3498
January	1st to 10th	Night	70% 7% 8% 7% 6% 2	6789
	11th to 20th	Night	73% 6% 11% 7% 4	6404
	21st to end	Night	62% 6% 12% 13% 6% 1	6996
February	1st to 10th	Night	70% 6% 8% 9% 6% 1	2642
	11th to 20th	Night	69% 7% 10% 10% 4 1	2530
	21st to end	Night	66% 5% 11% 11% 7% 1	1980
March	1st to 10th	Night	67% 6% 9% 12% 5%	5311
	11th to 20th	Night	70% 7% 10% 8% 5% 1	4980
	21st to end	Night	75% 4 8% 9% 3	5465
April	1st to 10th	Night	68% 5% 7% 10% 8% 1	1987
	11th to 20th	Night	64% 5% 8% 14% 9% 1	1778
	21st to end	Night	71% 4 7% 10% 8% 1	1800
May	1st to 10th	Night	72% 5% 6% 13% 3	4080
	11th to 20th	Night	69% 5% 6% 13% 7%	3593
	21st to end	Night	67% 7% 9% 12% 5%	3469
June	1st to 10th	Night	70% 7% 6% 12% 5%	1400
	11th to 20th	Night	61% 8% 13% 13% 5%	1400
	21st to end	Night	59% 6% 12% 18% 5%	1400
July	1st to 10th	Night	69% 6% 10% 11% 3	3146
	11th to 20th	Night	61% 6% 14% 16% 3	3172
	21st to end	Night	52% 5% 17% 23% 3	3831
August	1st to 10th	Night	58% 7% 16% 16% 4 1	2847
	11th to 20th	Night	57% 6% 15% 19% 4	2908
	21st to end	Night	56% 6% 13% 21% 3	3233
September	1st to 10th	Night	51% 8% 12% 20% 8% 1	2005
	11th to 20th	Night	59% 6% 13% 14% 8% 1	2200
	21st to end	Night	55% 5% 12% 19% 9% 1	2200
October	1st to 10th	Night	64% 5% 13% 14% 4	3776
	11th to 20th	Night	59% 6% 15% 14% 7%	3953
	21st to end	Night	61% 6% 10% 16% 6%	4610
November	1st to 10th	Night	63% 7% 13% 11% 6%	2702
	11th to 20th	Night	67% 6% 11% 11% 4 1	2899
	21st to end	Night	64% 6% 13% 11% 6% 1	2831
December	1st to 10th	Night	62% 6% 9% 16% 8%	4900
	11th to 20th	Night	70% 5% 12% 9% 4	5583
	21st to end	Night	69% 7% 9% 11% 4	7480

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	27% 23% 33% 13% 3 1	400
	11th to 20th	Day	27% 24% 32% 13% 4 1	400
	21st to end	Day	26% 23% 33% 16% 2	440
February	1st to 10th	Day	25% 26% 29% 17% 4 1	400
	11th to 20th	Day	29% 29% 31% 9% 3	396
	21st to end	Day	18% 27% 35% 16% 3	331
March	1st to 10th	Day	27% 28% 32% 10% 3	400
	11th to 20th	Day	25% 24% 30% 16% 3 3	400
	21st to end	Day	29% 23% 30% 12% 5% 1	440
April	1st to 10th	Day	30% 26% 28% 11% 4 1	525
	11th to 20th	Day	32% 20% 28% 12% 7% 1	689
	21st to end	Day	31% 18% 28% 17% 4 1	700
May	1st to 10th	Day	31% 20% 26% 16% 7% 1	703
	11th to 20th	Day	25% 13% 34% 19% 7% 1	724
	21st to end	Day	26% 13% 35% 19% 6% 1	790
June	1st to 10th	Day	37% 12% 28% 16% 6% 1	730
	11th to 20th	Day	28% 13% 32% 19% 6% 2	730
	21st to end	Day	26% 10% 29% 25% 8% 2	730
July	1st to 10th	Day	24% 10% 37% 21% 7% 1	720
	11th to 20th	Day	22% 8% 34% 25% 9% 1	718
	21st to end	Day	25% 10% 31% 25% 9% 1	795
August	1st to 10th	Day	22% 10% 32% 25% 10% 2	725
	11th to 20th	Day	22% 11% 26% 29% 10% 2	717
	21st to end	Day	26% 12% 26% 25% 11% 1	803
September	1st to 10th	Day	23% 9% 30% 25% 11% 1	565
	11th to 20th	Day	27% 15% 30% 21% 6% 1	420
	21st to end	Day	24% 15% 33% 20% 7% 1	420
October	1st to 10th	Day	27% 12% 33% 22% 6%	420
	11th to 20th	Day	29% 17% 30% 15% 7% 2	420
	21st to end	Day	28% 22% 27% 17% 4 2	462
November	1st to 10th	Day	28% 23% 29% 15% 4 1	425
	11th to 20th	Day	33% 21% 26% 14% 6%	421
	21st to end	Day	31% 25% 28% 12% 4 1	400
December	1st to 10th	Day	28% 21% 30% 16% 6%	400
	11th to 20th	Day	28% 31% 26% 13% 3	400
	21st to end	Day	25% 22% 32% 15% 4 1	440
January	1st to 10th	Night	26% 22% 33% 14% 4	900
	11th to 20th	Night	26% 19% 35% 16% 4 1	900
	21st to end	Night	25% 22% 34% 17% 2	990
February	1st to 10th	Night	25% 25% 33% 15% 2	900
	11th to 20th	Night	28% 24% 34% 12% 2	878
	21st to end	Night	22% 19% 34% 20% 5%	660
March	1st to 10th	Night	25% 22% 34% 15% 3	775
	11th to 20th	Night	21% 21% 30% 23% 6%	600
	21st to end	Night	31% 17% 32% 18% 2	660
April	1st to 10th	Night	29% 21% 29% 15% 6% 1	600
	11th to 20th	Night	31% 16% 31% 16% 5%	594
	21st to end	Night	30% 17% 32% 17% 5% 1	600
May	1st to 10th	Night	31% 12% 30% 20% 7% 1	600
	11th to 20th	Night	28% 11% 32% 21% 8% 1	592
	21st to end	Night	27% 12% 33% 22% 5% 1	649
June	1st to 10th	Night	35% 9% 30% 20% 7% 1	600
	11th to 20th	Night	27% 12% 31% 23% 8% 1	600
	21st to end	Night	28% 10% 32% 23% 7% 1	600
July	1st to 10th	Night	25% 7% 36% 25% 5% 1	586
	11th to 20th	Night	25% 7% 35% 26% 6%	582
	21st to end	Night	24% 7% 34% 27% 7%	656
August	1st to 10th	Night	24% 5% 31% 29% 9% 1	598
	11th to 20th	Night	26% 6% 31% 29% 9% 1	592
	21st to end	Night	26% 9% 30% 27% 8%	660
September	1st to 10th	Night	20% 9% 33% 29% 9% 1	600
	11th to 20th	Night	28% 13% 29% 25% 6% 1	600
	21st to end	Night	27% 11% 31% 24% 7% 1	600
October	1st to 10th	Night	26% 12% 33% 23% 6%	661
	11th to 20th	Night	29% 15% 31% 18% 6% 1	740
	21st to end	Night	30% 18% 27% 20% 5%	1001
November	1st to 10th	Night	30% 19% 30% 17% 4	930
	11th to 20th	Night	29% 18% 29% 19% 5%	936
	21st to end	Night	27% 22% 33% 15% 4	900
December	1st to 10th	Night	26% 21% 31% 16% 5%	900
	11th to 20th	Night	31% 25% 30% 11% 3	900
	21st to end	Night	25% 19% 32% 18% 5% 1	990

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