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 2024-11-08.

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	19% 15% 5% 11% 6% 5% 5% 4 5% 6% 20%	101635
	Night	20% 15% 6% 11% 6% 5% 5% 4 5% 5% 19%	97585
Transparency	Day	64% 6% 11% 13% 5%	105136
	Night	64% 6% 11% 12% 5% 1	102200
Seeing	Day	27% 17% 30% 19% 6% 1	18169
	Night	27% 16% 32% 20% 5%	24707

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% 14% 9% 19% 4 4 4 3 4 5% 17%	2216
	11th to 20th	Day	16% 16% 7% 18% 7% 5% 4 3 3 4 16%	2482
	21st to end	Day	14% 18% 8% 19% 5% 4 4 3 4 5% 15%	2783
February	1st to 10th	Day	17% 15% 7% 15% 9% 7% 5% 4 4 5% 13%	1668
	11th to 20th	Day	18% 18% 7% 14% 6% 5% 5% 4 4 6% 12%	1667
	21st to end	Day	13% 16% 8% 16% 8% 6% 6% 4 4 5% 15%	1570
March	1st to 10th	Day	24% 16% 6% 14% 7% 6% 4 2 3 4 15%	3163
	11th to 20th	Day	18% 19% 11% 15% 6% 5% 4 3 4 3 12%	3480
	21st to end	Day	20% 19% 9% 15% 5% 4 4 3 4 5% 12%	3817
April	1st to 10th	Day	17% 20% 7% 12% 8% 5% 4 3 4 4 15%	2287
	11th to 20th	Day	19% 22% 6% 9% 5% 4 4 3 4 4 19%	2441
	21st to end	Day	21% 20% 6% 8% 5% 4 4 3 4 4 20%	2470
May	1st to 10th	Day	23% 24% 7% 8% 4 4 3 3 4 5% 14%	4105
	11th to 20th	Day	23% 17% 5% 12% 5% 4 5% 3 5% 5% 15%	4402
	21st to end	Day	19% 19% 5% 9% 5% 5% 4 3 5% 5% 19%	5173
June	1st to 10th	Day	27% 17% 5% 9% 6% 5% 4 3 4 4 16%	2850
	11th to 20th	Day	22% 13% 3 8% 5% 4 5% 4 6% 7% 23%	2850
	21st to end	Day	21% 11% 3 9% 6% 6% 5% 4 6% 7% 22%	2850
July	1st to 10th	Day	24% 12% 4 9% 5% 4 4 4 5% 6% 23%	4750
	11th to 20th	Day	15% 10% 4 11% 7% 6% 6% 4 6% 7% 25%	4725
	21st to end	Day	15% 8% 3 7% 5% 5% 5% 4 6% 7% 35%	4815
August	1st to 10th	Day	20% 10% 4 12% 6% 6% 5% 3 5% 7% 21%	4155
	11th to 20th	Day	20% 9% 3 9% 6% 5% 5% 5% 6% 7% 25%	4046
	21st to end	Day	20% 10% 3 7% 5% 5% 5% 4 5% 8% 30%	4532
September	1st to 10th	Day	18% 9% 4 8% 5% 4 5% 4 5% 9% 29%	2271
	11th to 20th	Day	21% 9% 3 8% 5% 5% 4 4 5% 6% 31%	2090
	21st to end	Day	16% 10% 3 8% 5% 5% 4 3 7% 8% 31%	2090
October	1st to 10th	Day	23% 11% 3 8% 5% 5% 4 4 5% 7% 26%	1987
	11th to 20th	Day	22% 14% 4 8% 6% 5% 5% 4 5% 5% 22%	1871
	21st to end	Day	22% 19% 5% 8% 7% 5% 4 4 5% 6% 17%	1881
November	1st to 10th	Day	16% 18% 5% 10% 6% 5% 5% 4 5% 6% 23%	1701
	11th to 20th	Day	18% 18% 6% 9% 6% 6% 5% 4 5% 7% 17%	1520
	21st to end	Day	19% 21% 8% 9% 5% 4 5% 3 4 5% 17%	1487
December	1st to 10th	Day	20% 19% 7% 12% 5% 4 5% 3 4 6% 15%	1330
	11th to 20th	Day	15% 24% 8% 12% 6% 4 4 3 4 5% 15%	1668
	21st to end	Day	16% 21% 7% 12% 7% 5% 5% 4 5% 4 12%	2442
January	1st to 10th	Night	15% 18% 10% 15% 8% 6% 4 3 4 4 13%	4739
	11th to 20th	Night	14% 13% 7% 22% 7% 6% 5% 3 4 4 14%	4471
	21st to end	Night	12% 16% 8% 18% 8% 5% 5% 3 5% 4 15%	4884
February	1st to 10th	Night	18% 13% 6% 16% 9% 5% 5% 4 5% 4 14%	2510
	11th to 20th	Night	19% 16% 6% 14% 7% 6% 5% 3 5% 5% 13%	2397
	21st to end	Night	13% 16% 8% 15% 8% 8% 4 3 5% 5% 17%	1884
March	1st to 10th	Night	22% 14% 6% 13% 5% 4 5% 3 4 4 19%	3677
	11th to 20th	Night	14% 15% 8% 18% 7% 5% 5% 4 4 5% 14%	3479
	21st to end	Night	26% 19% 8% 12% 5% 3 4 3 3 3 14%	3815
April	1st to 10th	Night	20% 20% 7% 9% 5% 4 4 3 4 5% 18%	1888
	11th to 20th	Night	22% 18% 6% 8% 4 4 4 3 4 4 22%	1688
	21st to end	Night	21% 21% 5% 9% 6% 4 4 3 4 4 20%	1710
May	1st to 10th	Night	25% 24% 8% 8% 4 4 4 2 4 4 14%	2845
	11th to 20th	Night	24% 20% 5% 12% 5% 4 3 3 4 5% 16%	2496
	21st to end	Night	22% 17% 6% 9% 5% 5% 4 4 5% 5% 17%	2412
June	1st to 10th	Night	25% 16% 4 9% 6% 5% 5% 3 4 5% 19%	1330
	11th to 20th	Night	23% 12% 3 8% 4 5% 5% 4 7% 8% 20%	1330
	21st to end	Night	22% 12% 4 8% 5% 3 5% 4 7% 8% 21%	1330
July	1st to 10th	Night	32% 11% 3 8% 5% 4 4 3 5% 7% 18%	2220
	11th to 20th	Night	19% 11% 3 9% 7% 6% 7% 5% 9% 8% 16%	2241
	21st to end	Night	15% 7% 3 7% 5% 5% 4 5% 6% 7% 35%	2750
August	1st to 10th	Night	21% 10% 3 8% 5% 5% 5% 5% 7% 7% 24%	2770
	11th to 20th	Night	23% 9% 3 7% 5% 4 5% 4 6% 8% 26%	2791
	21st to end	Night	25% 9% 3 7% 5% 4 5% 4 5% 7% 28%	3135
September	1st to 10th	Night	18% 9% 3 7% 5% 6% 5% 5% 6% 7% 29%	1905
	11th to 20th	Night	23% 12% 3 7% 4 5% 4 3 5% 7% 27%	2090
	21st to end	Night	19% 13% 3 8% 4 4 5% 3 4 7% 30%	2090
October	1st to 10th	Night	21% 12% 3 8% 5% 5% 4 4 6% 6% 26%	2192
	11th to 20th	Night	21% 15% 4 9% 6% 4 4 4 5% 6% 22%	2308
	21st to end	Night	22% 18% 4 9% 5% 4 5% 4 4 5% 21%	2717
November	1st to 10th	Night	19% 16% 5% 9% 5% 4 5% 4 5% 6% 21%	2536
	11th to 20th	Night	19% 16% 6% 10% 6% 5% 4 4 5% 6% 19%	2660
	21st to end	Night	16% 17% 5% 11% 5% 4 6% 4 6% 6% 18%	2689
December	1st to 10th	Night	18% 19% 6% 12% 6% 5% 5% 3 5% 4 16%	2850
	11th to 20th	Night	19% 22% 8% 14% 7% 4 4 4 4 4 11%	3531
	21st to end	Night	18% 20% 7% 11% 5% 5% 4 3 4 4 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	65% 8% 6% 12% 7% 2	2217
	11th to 20th	Day	68% 4 10% 9% 7% 1	2482
	21st to end	Day	69% 4 7% 11% 8%	2783
February	1st to 10th	Day	72% 6% 7% 7% 7% 1	1668
	11th to 20th	Day	71% 6% 9% 9% 4 1	1674
	21st to end	Day	69% 5% 11% 7% 7% 2	1570
March	1st to 10th	Day	71% 5% 8% 11% 5% 1	3168
	11th to 20th	Day	73% 6% 9% 8% 3	3480
	21st to end	Day	75% 4 8% 9% 2 1	3817
April	1st to 10th	Day	73% 5% 6% 10% 6% 1	2287
	11th to 20th	Day	68% 5% 8% 11% 8% 1	2441
	21st to end	Day	68% 5% 8% 10% 9% 1	2470
May	1st to 10th	Day	70% 7% 8% 10% 4	4120
	11th to 20th	Day	70% 8% 9% 10% 3	4406
	21st to end	Day	63% 8% 9% 14% 6%	5173
June	1st to 10th	Day	73% 5% 6% 11% 4 1	2850
	11th to 20th	Day	62% 7% 12% 13% 6%	2850
	21st to end	Day	61% 8% 10% 16% 5%	2850
July	1st to 10th	Day	63% 6% 12% 15% 5%	4675
	11th to 20th	Day	59% 6% 17% 13% 5%	4643
	21st to end	Day	47% 6% 20% 21% 6%	4662
August	1st to 10th	Day	63% 5% 11% 17% 4	4141
	11th to 20th	Day	59% 6% 13% 19% 4	4085
	21st to end	Day	53% 6% 15% 23% 3	4532
September	1st to 10th	Day	52% 6% 11% 22% 8%	2271
	11th to 20th	Day	54% 5% 11% 18% 11%	2090
	21st to end	Day	51% 7% 15% 19% 7%	2090
October	1st to 10th	Day	65% 6% 10% 14% 5%	3305
	11th to 20th	Day	58% 7% 13% 15% 7%	3097
	21st to end	Day	66% 5% 8% 14% 6%	3092
November	1st to 10th	Day	62% 6% 15% 12% 5%	1701
	11th to 20th	Day	66% 7% 9% 12% 6% 1	1520
	21st to end	Day	69% 6% 10% 9% 5%	1487
December	1st to 10th	Day	70% 7% 8% 11% 5%	1330
	11th to 20th	Day	71% 5% 10% 8% 5%	1667
	21st to end	Day	72% 6% 9% 10% 3	2442
January	1st to 10th	Night	65% 9% 10% 8% 7% 2	4739
	11th to 20th	Night	66% 7% 13% 9% 5%	4471
	21st to end	Night	66% 5% 14% 9% 4 1	4884
February	1st to 10th	Night	70% 6% 9% 9% 5% 1	2510
	11th to 20th	Night	69% 7% 10% 10% 4	2401
	21st to end	Night	65% 6% 11% 11% 7% 1	1884
March	1st to 10th	Night	64% 7% 10% 14% 5%	3685
	11th to 20th	Night	67% 9% 11% 9% 4	3480
	21st to end	Night	73% 4 8% 10% 4 1	3815
April	1st to 10th	Night	67% 5% 8% 10% 8% 1	1888
	11th to 20th	Night	65% 5% 7% 13% 9% 1	1688
	21st to end	Night	70% 4 7% 11% 8% 1	1710
May	1st to 10th	Night	72% 7% 7% 10% 4	2850
	11th to 20th	Night	71% 6% 5% 12% 5%	2497
	21st to end	Night	64% 9% 9% 11% 6%	2413
June	1st to 10th	Night	71% 7% 6% 11% 5%	1330
	11th to 20th	Night	61% 8% 13% 12% 5%	1330
	21st to end	Night	60% 7% 12% 16% 5%	1330
July	1st to 10th	Night	67% 7% 8% 13% 4	2186
	11th to 20th	Night	66% 7% 14% 9% 4	2199
	21st to end	Night	50% 5% 18% 23% 4	2663
August	1st to 10th	Night	59% 7% 16% 16% 3	2759
	11th to 20th	Night	57% 6% 15% 18% 4	2818
	21st to end	Night	56% 6% 13% 22% 3	3134
September	1st to 10th	Night	52% 8% 12% 20% 8% 1	1905
	11th to 20th	Night	58% 6% 12% 14% 9% 1	2090
	21st to end	Night	56% 6% 12% 19% 8%	2090
October	1st to 10th	Night	64% 5% 13% 14% 4	3660
	11th to 20th	Night	58% 6% 15% 14% 7%	3831
	21st to end	Night	61% 6% 10% 16% 6%	4467
November	1st to 10th	Night	62% 7% 13% 11% 6%	2536
	11th to 20th	Night	65% 7% 11% 12% 5% 1	2660
	21st to end	Night	63% 6% 13% 11% 6% 1	2689
December	1st to 10th	Night	69% 6% 7% 12% 5%	2850
	11th to 20th	Night	75% 5% 8% 7% 5%	3533
	21st to end	Night	64% 8% 11% 13% 4	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	27% 24% 32% 14% 3 1	370
	11th to 20th	Day	27% 24% 32% 12% 4 1	370
	21st to end	Day	26% 21% 34% 16% 2	407
February	1st to 10th	Day	25% 25% 29% 17% 4 1	370
	11th to 20th	Day	28% 28% 31% 9% 3	366
	21st to end	Day	17% 29% 36% 16% 3	307
March	1st to 10th	Day	26% 28% 32% 10% 3	370
	11th to 20th	Day	24% 23% 30% 17% 3 3	370
	21st to end	Day	29% 24% 29% 13% 5% 1	407
April	1st to 10th	Day	29% 25% 29% 12% 4 1	485
	11th to 20th	Day	32% 20% 28% 13% 7% 1	639
	21st to end	Day	30% 19% 30% 17% 4	650
May	1st to 10th	Day	30% 20% 25% 16% 7% 1	653
	11th to 20th	Day	25% 13% 34% 19% 8% 1	674
	21st to end	Day	26% 13% 34% 20% 6% 1	735
June	1st to 10th	Day	39% 11% 27% 16% 6% 1	680
	11th to 20th	Day	29% 12% 31% 20% 6% 2	680
	21st to end	Day	26% 9% 29% 25% 8% 2	680
July	1st to 10th	Day	25% 9% 36% 23% 7% 1	670
	11th to 20th	Day	23% 8% 33% 26% 9% 1	668
	21st to end	Day	25% 9% 30% 26% 9% 1	740
August	1st to 10th	Day	23% 10% 32% 25% 10% 1	675
	11th to 20th	Day	23% 10% 26% 29% 10% 2	667
	21st to end	Day	24% 11% 25% 27% 12% 1	748
September	1st to 10th	Day	23% 9% 30% 25% 11% 2	526
	11th to 20th	Day	27% 15% 29% 21% 6% 1	390
	21st to end	Day	23% 15% 33% 21% 7% 1	390
October	1st to 10th	Day	27% 12% 33% 21% 7%	390
	11th to 20th	Day	28% 16% 29% 16% 8% 2	390
	21st to end	Day	28% 24% 26% 17% 4 1	429
November	1st to 10th	Day	26% 23% 30% 16% 5% 1	386
	11th to 20th	Day	29% 22% 26% 15% 7%	370
	21st to end	Day	28% 26% 28% 12% 4 1	370
December	1st to 10th	Day	28% 21% 30% 15% 6%	370
	11th to 20th	Day	28% 31% 25% 13% 2	370
	21st to end	Day	25% 24% 32% 15% 3 1	407
January	1st to 10th	Night	26% 22% 34% 14% 4	850
	11th to 20th	Night	27% 20% 35% 16% 3	850
	21st to end	Night	25% 21% 34% 18% 2	935
February	1st to 10th	Night	25% 25% 33% 15% 2	850
	11th to 20th	Night	28% 23% 34% 12% 3	829
	21st to end	Night	22% 19% 35% 20% 5%	628
March	1st to 10th	Night	25% 22% 35% 15% 3	736
	11th to 20th	Night	20% 20% 30% 23% 6%	570
	21st to end	Night	31% 16% 32% 19% 2	627
April	1st to 10th	Night	28% 20% 29% 15% 6% 1	570
	11th to 20th	Night	32% 16% 31% 16% 5%	564
	21st to end	Night	28% 17% 32% 17% 5% 1	570
May	1st to 10th	Night	31% 11% 29% 20% 8% 1	570
	11th to 20th	Night	28% 11% 32% 21% 8% 1	562
	21st to end	Night	28% 12% 33% 22% 5% 1	616
June	1st to 10th	Night	35% 9% 29% 20% 7% 1	570
	11th to 20th	Night	28% 11% 30% 23% 8% 1	570
	21st to end	Night	28% 9% 31% 23% 8% 1	570
July	1st to 10th	Night	25% 7% 37% 25% 6% 1	556
	11th to 20th	Night	25% 7% 35% 26% 7%	552
	21st to end	Night	24% 7% 33% 27% 8%	623
August	1st to 10th	Night	25% 5% 31% 29% 9% 1	568
	11th to 20th	Night	26% 6% 31% 28% 9% 1	562
	21st to end	Night	26% 8% 29% 28% 8%	627
September	1st to 10th	Night	20% 8% 33% 28% 9% 1	570
	11th to 20th	Night	27% 13% 29% 25% 6% 1	570
	21st to end	Night	27% 11% 31% 24% 7% 1	570
October	1st to 10th	Night	26% 12% 33% 22% 6%	625
	11th to 20th	Night	28% 15% 31% 19% 7% 1	698
	21st to end	Night	30% 18% 27% 19% 5%	946
November	1st to 10th	Night	27% 19% 31% 17% 4	868
	11th to 20th	Night	27% 19% 29% 20% 5%	850
	21st to end	Night	25% 23% 33% 15% 4	850
December	1st to 10th	Night	26% 22% 31% 16% 6%	850
	11th to 20th	Night	31% 25% 30% 10% 3	850
	21st to end	Night	24% 20% 32% 18% 4 1	935

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