Stillwell
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Stillwell 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	16% 11% 3 8% 5% 5% 5% 4 6% 7% 32%	100829
	Night	16% 11% 4 8% 5% 4 4 3 5% 6% 34%	98218
Transparency	Day	51% 3 10% 22% 12% 2	104518
	Night	50% 3 10% 23% 13% 2	102655
Seeing	Day	22% 14% 28% 20% 11% 4	14732
	Night	22% 11% 27% 26% 13% 2	24997

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	19% 21% 5% 12% 5% 3 4 3 5% 6% 17%	2836
	11th to 20th	Day	16% 22% 8% 12% 5% 5% 5% 2 5% 5% 16%	2840
	21st to end	Day	27% 22% 9% 10% 6% 4 2 3 3 3 11%	3124
February	1st to 10th	Day	19% 17% 5% 11% 5% 4 4 3 3 4 24%	1710
	11th to 20th	Day	16% 13% 5% 14% 6% 4 5% 2 4 5% 25%	1766
	21st to end	Day	17% 16% 5% 10% 5% 4 4 2 3 4 30%	1570
March	1st to 10th	Day	22% 16% 5% 8% 5% 4 4 3 4 5% 24%	3330
	11th to 20th	Day	13% 11% 5% 9% 5% 4 4 3 4 5% 36%	3480
	21st to end	Day	21% 10% 4 7% 4 4 4 3 4 6% 32%	3815
April	1st to 10th	Day	15% 15% 2 8% 5% 4 4 4 4 7% 32%	2091
	11th to 20th	Day	18% 11% 3 7% 4 4 4 3 5% 6% 35%	2434
	21st to end	Day	19% 9% 3 8% 6% 4 4 4 5% 5% 32%	2470
May	1st to 10th	Day	21% 10% 3 8% 5% 5% 5% 3 5% 6% 28%	4082
	11th to 20th	Day	22% 8% 3 7% 4 4 4 3 5% 7% 34%	4081
	21st to end	Day	13% 6% 2 7% 5% 5% 5% 5% 8% 9% 36%	4476
June	1st to 10th	Day	12% 6% 3 7% 6% 5% 5% 5% 7% 7% 36%	2470
	11th to 20th	Day	12% 7% 3 8% 5% 6% 5% 5% 6% 8% 35%	2470
	21st to end	Day	11% 6% 2 5% 5% 6% 5% 5% 9% 10% 36%	2470
July	1st to 10th	Day	10% 7% 2 7% 5% 6% 5% 4 7% 9% 37%	4120
	11th to 20th	Day	9% 5% 2 6% 5% 5% 5% 5% 7% 10% 41%	4120
	21st to end	Day	11% 7% 3 7% 5% 5% 6% 5% 7% 9% 37%	4466
August	1st to 10th	Day	13% 7% 3 7% 5% 5% 6% 5% 7% 10% 34%	4104
	11th to 20th	Day	10% 6% 2 7% 5% 6% 7% 5% 8% 9% 35%	4044
	21st to end	Day	7% 4 2 6% 5% 6% 6% 4 7% 10% 42%	4479
September	1st to 10th	Day	13% 5% 2 5% 4 4 4 4 5% 8% 45%	2123
	11th to 20th	Day	9% 5% 2 6% 4 5% 6% 5% 7% 8% 44%	2090
	21st to end	Day	21% 7% 3 6% 4 4 4 2 4 6% 39%	2090
October	1st to 10th	Day	13% 7% 3 7% 5% 4 5% 4 5% 7% 42%	1994
	11th to 20th	Day	15% 9% 2 7% 5% 4 5% 3 6% 6% 39%	1900
	21st to end	Day	21% 11% 3 6% 4 4 4 3 5% 5% 34%	2073
November	1st to 10th	Day	11% 8% 3 8% 4 3 4 4 5% 6% 44%	1735
	11th to 20th	Day	18% 14% 3 8% 5% 4 4 3 5% 5% 33%	1710
	21st to end	Day	19% 15% 4 10% 4 4 4 4 4 6% 28%	1644
December	1st to 10th	Day	20% 20% 6% 10% 5% 3 5% 3 4 5% 20%	1520
	11th to 20th	Day	19% 17% 6% 11% 5% 3 4 3 5% 5% 21%	1978
	21st to end	Day	24% 25% 5% 10% 5% 4 3 2 4 4 12%	3124
January	1st to 10th	Night	17% 22% 8% 11% 4 4 4 3 4 4 19%	4109
	11th to 20th	Night	16% 20% 7% 16% 5% 5% 6% 4 4 4 14%	4120
	21st to end	Night	27% 20% 7% 13% 4 3 3 2 3 3 15%	4532
February	1st to 10th	Night	20% 16% 4 10% 6% 4 4 3 4 4 24%	2470
	11th to 20th	Night	18% 14% 4 11% 6% 5% 4 3 4 6% 24%	2296
	21st to end	Night	20% 15% 5% 9% 6% 5% 4 3 4 4 24%	1884
March	1st to 10th	Night	22% 15% 4 6% 4 3 3 2 5% 5% 32%	3523
	11th to 20th	Night	15% 11% 3 6% 4 3 4 4 5% 6% 38%	3480
	21st to end	Night	19% 10% 3 7% 4 4 4 3 4 6% 38%	3817
April	1st to 10th	Night	17% 12% 3 6% 5% 4 4 4 4 7% 35%	2087
	11th to 20th	Night	16% 8% 2 7% 5% 4 5% 4 6% 6% 36%	1711
	21st to end	Night	15% 10% 2 7% 5% 5% 4 3 6% 7% 38%	1710
May	1st to 10th	Night	28% 10% 3 7% 5% 4 4 3 5% 6% 26%	2813
	11th to 20th	Night	19% 7% 3 7% 4 4 4 3 4 7% 39%	2812
	21st to end	Night	10% 5% 2 5% 5% 4 4 4 7% 10% 43%	3079
June	1st to 10th	Night	9% 6% 2 7% 6% 4 5% 4 5% 8% 44%	1710
	11th to 20th	Night	9% 6% 2 5% 4 5% 4 4 7% 11% 42%	1710
	21st to end	Night	10% 5% 2 5% 5% 4 5% 4 6% 9% 44%	1710
July	1st to 10th	Night	11% 5% 2 7% 3 4 4 4 7% 8% 44%	2840
	11th to 20th	Night	9% 4 2 5% 4 4 5% 4 7% 8% 48%	2840
	21st to end	Night	7% 6% 2 6% 4 5% 6% 5% 6% 9% 43%	3087
August	1st to 10th	Night	11% 6% 3 7% 5% 5% 5% 5% 8% 8% 36%	2825
	11th to 20th	Night	11% 8% 3 7% 4 4 4 3 5% 7% 43%	2785
	21st to end	Night	6% 4 2 6% 4 5% 6% 5% 7% 8% 48%	3144
September	1st to 10th	Night	13% 5% 2 5% 3 3 4 3 4 7% 52%	2054
	11th to 20th	Night	9% 4 2 4 3 3 4 3 6% 8% 56%	2090
	21st to end	Night	17% 7% 3 5% 4 3 3 3 5% 6% 44%	2090
October	1st to 10th	Night	12% 5% 2 5% 3 4 4 3 6% 8% 47%	2185
	11th to 20th	Night	15% 9% 2 7% 5% 4 4 3 5% 6% 41%	2280
	21st to end	Night	22% 9% 3 6% 4 4 4 3 4 6% 36%	2522
November	1st to 10th	Night	14% 7% 3 6% 4 4 3 3 5% 6% 45%	2504
	11th to 20th	Night	18% 11% 4 6% 4 4 4 3 5% 6% 34%	2470
	21st to end	Night	19% 13% 5% 8% 5% 4 5% 3 5% 5% 29%	2530
December	1st to 10th	Night	22% 17% 5% 10% 4 3 4 4 4 5% 22%	2660
	11th to 20th	Night	18% 17% 7% 9% 4 4 3 3 5% 6% 25%	3207
	21st to end	Night	25% 21% 6% 9% 5% 4 4 2 4 5% 15%	4532

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	70% 2 8% 15% 5%	2837
	11th to 20th	Day	73% 1 8% 11% 6%	2840
	21st to end	Day	81% 1 6% 9% 2 1	3124
February	1st to 10th	Day	65% 2 8% 16% 8% 1	1710
	11th to 20th	Day	63% 2 7% 17% 10% 1	1775
	21st to end	Day	60% 1 9% 19% 8% 2	1570
March	1st to 10th	Day	64% 1 7% 22% 5%	3330
	11th to 20th	Day	52% 1 8% 27% 11% 1	3480
	21st to end	Day	56% 1 9% 22% 12% 1	3815
April	1st to 10th	Day	54% 2 11% 19% 12% 2	2091
	11th to 20th	Day	52% 2 11% 18% 15% 2	2434
	21st to end	Day	54% 3 9% 21% 12% 2	2470
May	1st to 10th	Day	58% 1 10% 22% 8% 1	4120
	11th to 20th	Day	52% 2 11% 23% 12% 1	4085
	21st to end	Day	44% 3 12% 23% 13% 5%	4489
June	1st to 10th	Day	45% 3 11% 25% 14% 1	2470
	11th to 20th	Day	46% 4 12% 23% 14% 1	2470
	21st to end	Day	41% 4 14% 23% 15% 3	2470
July	1st to 10th	Day	43% 5% 11% 24% 15% 2	4055
	11th to 20th	Day	35% 6% 12% 27% 19% 1	4051
	21st to end	Day	42% 6% 12% 19% 18% 3	4324
August	1st to 10th	Day	43% 7% 13% 24% 12%	4091
	11th to 20th	Day	41% 6% 11% 30% 12% 1	4083
	21st to end	Day	35% 6% 14% 31% 12% 3	4479
September	1st to 10th	Day	38% 4 12% 23% 20% 4	2123
	11th to 20th	Day	37% 4 12% 27% 18% 3	2090
	21st to end	Day	49% 2 8% 22% 18% 1	2090
October	1st to 10th	Day	30% 4 10% 32% 23% 1	3306
	11th to 20th	Day	40% 5% 10% 24% 17% 4	3140
	21st to end	Day	40% 3 12% 27% 17% 1	3399
November	1st to 10th	Day	42% 3 10% 27% 17% 2	1735
	11th to 20th	Day	55% 2 7% 22% 10% 3	1710
	21st to end	Day	59% 3 10% 19% 8% 1	1644
December	1st to 10th	Day	70% 1 9% 16% 4	1520
	11th to 20th	Day	66% 2 8% 19% 6%	1974
	21st to end	Day	78% 2 10% 7% 3	3124
January	1st to 10th	Night	72% 1 7% 15% 4	4109
	11th to 20th	Night	77% 1 9% 11% 3	4120
	21st to end	Night	77% 1 6% 12% 3	4532
February	1st to 10th	Night	64% 2 9% 17% 8% 1	2470
	11th to 20th	Night	63% 2 8% 18% 8% 1	2298
	21st to end	Night	64% 2 8% 14% 9% 2	1884
March	1st to 10th	Night	57% 1 8% 23% 9%	3523
	11th to 20th	Night	48% 2 9% 30% 9% 2	3480
	21st to end	Night	50% 1 8% 28% 12% 1	3817
April	1st to 10th	Night	50% 2 10% 21% 15% 2	2087
	11th to 20th	Night	48% 2 11% 18% 18% 3	1711
	21st to end	Night	47% 2 11% 22% 16% 2	1710
May	1st to 10th	Night	60% 2 7% 21% 8% 2	2840
	11th to 20th	Night	48% 2 10% 26% 12% 2	2813
	21st to end	Night	37% 3 13% 29% 15% 3	3087
June	1st to 10th	Night	38% 4 11% 25% 18% 3	1710
	11th to 20th	Night	36% 3 16% 25% 17% 3	1710
	21st to end	Night	37% 5% 13% 26% 18% 2	1710
July	1st to 10th	Night	37% 5% 12% 23% 18% 5%	2795
	11th to 20th	Night	32% 5% 13% 32% 16% 1	2786
	21st to end	Night	37% 6% 12% 22% 20% 3	2988
August	1st to 10th	Night	42% 6% 14% 23% 14% 1	2814
	11th to 20th	Night	40% 5% 9% 26% 19% 1	2812
	21st to end	Night	31% 6% 14% 31% 15% 2	3144
September	1st to 10th	Night	34% 3 11% 27% 20% 6%	2054
	11th to 20th	Night	28% 3 11% 29% 26% 3	2090
	21st to end	Night	43% 3 9% 22% 22% 1	2090
October	1st to 10th	Night	30% 3 7% 31% 29% 1	3640
	11th to 20th	Night	35% 3 12% 26% 19% 5%	3779
	21st to end	Night	36% 3 9% 30% 21% 2	4146
November	1st to 10th	Night	41% 2 11% 26% 18% 3	2504
	11th to 20th	Night	52% 3 8% 23% 13% 2	2470
	21st to end	Night	58% 2 11% 22% 6% 1	2530
December	1st to 10th	Night	66% 2 9% 17% 6%	2660
	11th to 20th	Night	62% 2 10% 20% 5%	3210
	21st to end	Night	75% 1 9% 12% 3	4532

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	31% 24% 30% 9% 5% 1	270
	11th to 20th	Day	38% 21% 33% 7% 1	270
	21st to end	Day	31% 28% 30% 10% 1	297
February	1st to 10th	Day	33% 25% 30% 8% 4	270
	11th to 20th	Day	30% 33% 31% 5% 1	270
	21st to end	Day	33% 33% 29% 4	225
March	1st to 10th	Day	29% 24% 31% 15% 3	389
	11th to 20th	Day	32% 19% 31% 12% 6% 1	460
	21st to end	Day	35% 17% 29% 16% 3	506
April	1st to 10th	Day	28% 19% 30% 15% 7% 2	460
	11th to 20th	Day	29% 18% 26% 16% 7% 3	452
	21st to end	Day	28% 17% 32% 15% 6% 2	460
May	1st to 10th	Day	29% 18% 27% 16% 6% 4	463
	11th to 20th	Day	26% 10% 31% 20% 9% 4	487
	21st to end	Day	12% 12% 28% 25% 17% 6%	529
June	1st to 10th	Day	16% 10% 32% 26% 13% 4	490
	11th to 20th	Day	17% 11% 26% 28% 14% 5%	490
	21st to end	Day	14% 10% 32% 25% 12% 6%	490
July	1st to 10th	Day	16% 6% 20% 26% 21% 12%	485
	11th to 20th	Day	13% 5% 26% 29% 18% 9%	484
	21st to end	Day	11% 5% 25% 30% 20% 8%	532
August	1st to 10th	Day	14% 4 20% 31% 20% 10%	486
	11th to 20th	Day	14% 7% 25% 29% 17% 8%	479
	21st to end	Day	8% 5% 21% 31% 25% 10%	539
September	1st to 10th	Day	14% 5% 23% 27% 22% 9%	490
	11th to 20th	Day	10% 3 17% 31% 27% 11%	490
	21st to end	Day	25% 9% 22% 23% 16% 5%	490
October	1st to 10th	Day	13% 9% 29% 26% 18% 5%	490
	11th to 20th	Day	20% 17% 31% 20% 9% 3	490
	21st to end	Day	29% 14% 32% 18% 7% 1	522
November	1st to 10th	Day	16% 19% 35% 18% 10% 2	291
	11th to 20th	Day	33% 15% 30% 16% 6% 1	270
	21st to end	Day	30% 21% 38% 10% 2	239
December	1st to 10th	Day	26% 27% 32% 10% 3 2	180
	11th to 20th	Day	26% 26% 35% 11% 3 1	200
	21st to end	Day	36% 20% 31% 13% 1	297
January	1st to 10th	Night	30% 19% 33% 16% 3	760
	11th to 20th	Night	30% 19% 31% 16% 3	760
	21st to end	Night	30% 19% 30% 19% 3	836
February	1st to 10th	Night	30% 17% 32% 19% 2	760
	11th to 20th	Night	29% 19% 33% 17% 2	743
	21st to end	Night	32% 18% 32% 16% 2	628
March	1st to 10th	Night	26% 18% 30% 22% 4	760
	11th to 20th	Night	26% 18% 29% 21% 6%	760
	21st to end	Night	28% 14% 32% 20% 6%	836
April	1st to 10th	Night	25% 14% 34% 21% 5% 1	760
	11th to 20th	Night	24% 11% 32% 23% 10% 1	587
	21st to end	Night	21% 11% 36% 25% 6% 1	570
May	1st to 10th	Night	24% 8% 28% 29% 11% 1	570
	11th to 20th	Night	22% 6% 24% 31% 15% 1	561
	21st to end	Night	10% 5% 23% 37% 23% 2	617
June	1st to 10th	Night	12% 3 27% 38% 19% 1	570
	11th to 20th	Night	13% 5% 21% 39% 21% 2	570
	21st to end	Night	12% 4 22% 37% 24% 1	570
July	1st to 10th	Night	10% 3 16% 38% 27% 6%	555
	11th to 20th	Night	9% 2 20% 35% 29% 5%	552
	21st to end	Night	11% 3 16% 37% 30% 3	624
August	1st to 10th	Night	8% 2 13% 42% 31% 4	567
	11th to 20th	Night	12% 2 15% 40% 26% 5%	564
	21st to end	Night	9% 3 18% 31% 33% 6%	634
September	1st to 10th	Night	16% 4 18% 31% 27% 5%	760
	11th to 20th	Night	11% 3 14% 36% 31% 5%	760
	21st to end	Night	20% 7% 23% 28% 19% 3	760
October	1st to 10th	Night	15% 6% 23% 33% 20% 3	760
	11th to 20th	Night	20% 10% 31% 26% 12% 1	760
	21st to end	Night	28% 11% 28% 25% 8%	836
November	1st to 10th	Night	20% 9% 29% 28% 13% 1	771
	11th to 20th	Night	26% 14% 29% 21% 9% 1	760
	21st to end	Night	27% 14% 29% 23% 6% 1	760
December	1st to 10th	Night	35% 13% 32% 17% 4	760
	11th to 20th	Night	27% 17% 31% 21% 4	760
	21st to end	Night	33% 14% 30% 20% 3	836

Page generated at 2024-11-05 08:15:53. Version ac07

Copyright © 2024 Attilla Danko.