Sturk Road Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Sturk Road Observatory clear sky chart from 2005-11-06 to 2025-01-22.

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% 13% 4 9% 5% 4 4 3 5% 6% 28%	105550
	Night	18% 14% 5% 11% 6% 4 4 3 4 5% 25%	103875
Transparency	Day	59% 3 10% 19% 10% 1	109132
	Night	61% 3 10% 18% 8% 1	108383
Seeing	Day	26% 19% 31% 17% 6% 1	17239
	Night	26% 18% 30% 20% 5%	24917

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	15% 21% 6% 16% 10% 6% 3 2 3 3 16%	2311
	11th to 20th	Day	15% 18% 7% 27% 5% 5% 4 2 3 3 10%	2775
	21st to end	Day	17% 15% 8% 15% 9% 6% 4 2 3 5% 15%	3133
February	1st to 10th	Day	18% 18% 6% 14% 12% 5% 4 3 3 4 13%	1710
	11th to 20th	Day	16% 19% 6% 14% 11% 6% 4 3 3 4 16%	1663
	21st to end	Day	11% 17% 7% 11% 7% 5% 3 3 3 5% 28%	1446
March	1st to 10th	Day	23% 19% 5% 8% 6% 6% 3 3 3 4 20%	3420
	11th to 20th	Day	13% 23% 5% 11% 6% 5% 4 2 4 4 23%	3480
	21st to end	Day	25% 18% 6% 12% 4 4 3 2 2 3 20%	3816
April	1st to 10th	Day	22% 18% 4 8% 4 4 3 3 4 4 26%	2240
	11th to 20th	Day	19% 14% 3 6% 4 4 4 2 4 6% 35%	2371
	21st to end	Day	21% 14% 3 6% 4 5% 4 3 4 6% 30%	2470
May	1st to 10th	Day	22% 19% 3 7% 4 4 4 3 5% 6% 22%	4133
	11th to 20th	Day	19% 11% 3 7% 5% 4 5% 4 5% 7% 32%	4398
	21st to end	Day	15% 9% 3 7% 4 4 5% 3 7% 8% 34%	4836
June	1st to 10th	Day	25% 9% 3 6% 5% 4 5% 4 6% 6% 28%	2698
	11th to 20th	Day	21% 8% 2 7% 5% 4 4 4 5% 7% 33%	2850
	21st to end	Day	24% 11% 3 7% 5% 4 4 4 5% 5% 27%	2850
July	1st to 10th	Day	21% 8% 3 6% 4 4 5% 3 6% 8% 33%	4760
	11th to 20th	Day	19% 9% 2 6% 4 4 4 4 7% 7% 34%	4518
	21st to end	Day	14% 8% 3 8% 5% 5% 5% 5% 7% 8% 33%	4594
August	1st to 10th	Day	21% 10% 3 7% 5% 4 5% 3 5% 6% 29%	4105
	11th to 20th	Day	13% 7% 3 7% 5% 5% 5% 4 6% 8% 37%	4045
	21st to end	Day	11% 6% 2 5% 4 5% 4 4 5% 8% 47%	4412
September	1st to 10th	Day	19% 6% 2 5% 4 3 3 3 5% 6% 44%	2280
	11th to 20th	Day	17% 7% 2 6% 4 4 4 2 3 6% 44%	2158
	21st to end	Day	18% 8% 3 5% 4 3 3 3 5% 6% 42%	2061
October	1st to 10th	Day	18% 9% 3 6% 5% 3 4 3 6% 7% 37%	1900
	11th to 20th	Day	20% 12% 3 6% 4 3 4 3 5% 7% 33%	1900
	21st to end	Day	20% 15% 3 8% 5% 3 4 3 4 5% 31%	2085
November	1st to 10th	Day	20% 16% 3 8% 5% 4 4 2 4 6% 27%	1622
	11th to 20th	Day	18% 21% 9% 9% 5% 4 4 2 3 5% 20%	1600
	21st to end	Day	19% 22% 7% 12% 6% 4 3 3 3 4 17%	1600
December	1st to 10th	Day	18% 18% 9% 21% 6% 4 3 2 3 4 11%	2610
	11th to 20th	Day	22% 18% 7% 17% 8% 4 3 3 2 3 14%	2996
	21st to end	Day	18% 18% 10% 16% 8% 4 3 3 4 4 15%	3704
January	1st to 10th	Night	14% 16% 8% 21% 9% 5% 3 3 4 3 15%	4857
	11th to 20th	Night	15% 20% 7% 21% 7% 5% 4 2 3 4 12%	4410
	21st to end	Night	16% 13% 6% 16% 12% 5% 4 3 5% 5% 15%	4546
February	1st to 10th	Night	18% 16% 7% 16% 10% 6% 3 3 4 4 14%	2470
	11th to 20th	Night	17% 16% 5% 14% 10% 6% 3 4 4 4 17%	2403
	21st to end	Night	11% 16% 6% 12% 7% 6% 4 4 4 5% 25%	2004
March	1st to 10th	Night	21% 17% 4 13% 8% 6% 3 2 3 3 20%	3420
	11th to 20th	Night	15% 22% 8% 11% 7% 5% 4 3 4 4 17%	3479
	21st to end	Night	25% 15% 7% 11% 6% 4 3 2 2 3 23%	3816
April	1st to 10th	Night	22% 17% 5% 6% 5% 4 3 3 4 4 27%	1939
	11th to 20th	Night	21% 13% 3 7% 4 3 3 3 4 7% 31%	1755
	21st to end	Night	21% 14% 3 6% 6% 4 3 3 4 5% 31%	1710
May	1st to 10th	Night	20% 20% 4 6% 5% 3 4 3 5% 6% 24%	2807
	11th to 20th	Night	20% 9% 3 6% 5% 4 4 4 6% 7% 31%	2506
	21st to end	Night	16% 10% 3 9% 4 5% 5% 4 6% 7% 30%	2749
June	1st to 10th	Night	25% 8% 3 6% 5% 5% 4 3 5% 8% 27%	1496
	11th to 20th	Night	22% 8% 3 7% 5% 4 4 3 4 6% 34%	1330
	21st to end	Night	22% 8% 3 6% 6% 5% 5% 5% 5% 7% 29%	1330
July	1st to 10th	Night	18% 12% 3 8% 4 5% 5% 4 6% 7% 28%	2210
	11th to 20th	Night	19% 8% 3 6% 4 4 5% 5% 7% 9% 31%	2402
	21st to end	Night	13% 8% 2 6% 4 4 5% 4 7% 9% 39%	2960
August	1st to 10th	Night	22% 11% 2 6% 3 4 4 3 6% 7% 31%	2825
	11th to 20th	Night	15% 7% 3 6% 5% 4 7% 4 7% 9% 34%	2782
	21st to end	Night	13% 6% 2 5% 4 3 4 3 5% 7% 47%	3243
September	1st to 10th	Night	16% 6% 2 5% 4 3 4 4 6% 6% 44%	1900
	11th to 20th	Night	18% 6% 3 6% 3 3 3 3 4 6% 44%	2019
	21st to end	Night	17% 8% 2 7% 4 3 4 4 5% 7% 38%	2118
October	1st to 10th	Night	18% 7% 2 7% 4 4 4 3 5% 7% 40%	2280
	11th to 20th	Night	18% 10% 3 8% 4 4 4 3 5% 7% 34%	2280
	21st to end	Night	25% 13% 4 8% 4 3 4 2 4 5% 29%	2511
November	1st to 10th	Night	21% 14% 3 9% 4 4 3 3 4 5% 30%	2674
	11th to 20th	Night	18% 22% 6% 10% 5% 5% 3 3 4 4 21%	2800
	21st to end	Night	19% 21% 6% 11% 5% 3 3 3 4 5% 20%	2800
December	1st to 10th	Night	14% 20% 9% 21% 6% 4 3 3 4 4 12%	4580
	11th to 20th	Night	16% 18% 7% 17% 7% 5% 3 2 3 3 18%	5213
	21st to end	Night	21% 19% 6% 14% 7% 3 3 2 3 3 18%	7251

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	76% 1 13% 8% 2	2312
	11th to 20th	Day	81% 2 5% 10% 3	2775
	21st to end	Day	73% 2 8% 10% 7%	3133
February	1st to 10th	Day	76% 2 7% 8% 6% 1	1710
	11th to 20th	Day	74% 3 7% 11% 5%	1671
	21st to end	Day	60% 3 9% 19% 8% 2	1446
March	1st to 10th	Day	70% 1 6% 15% 6% 1	3424
	11th to 20th	Day	68% 1 8% 14% 8% 1	3480
	21st to end	Day	74% 1 3 12% 8% 1	3816
April	1st to 10th	Day	64% 2 6% 14% 11% 2	2240
	11th to 20th	Day	53% 2 6% 23% 13% 1	2371
	21st to end	Day	57% 2 8% 18% 12% 3	2470
May	1st to 10th	Day	65% 1 9% 17% 7% 1	4147
	11th to 20th	Day	55% 2 12% 21% 10%	4402
	21st to end	Day	50% 2 15% 20% 13% 1	4836
June	1st to 10th	Day	58% 3 8% 22% 8%	2698
	11th to 20th	Day	52% 3 12% 21% 11% 1	2850
	21st to end	Day	60% 2 9% 17% 10% 1	2850
July	1st to 10th	Day	51% 3 12% 20% 12% 1	4685
	11th to 20th	Day	48% 4 13% 26% 9%	4439
	21st to end	Day	48% 6% 14% 22% 9% 1	4448
August	1st to 10th	Day	57% 4 9% 19% 10%	4092
	11th to 20th	Day	46% 5% 13% 24% 12%	4084
	21st to end	Day	36% 5% 12% 28% 18% 1	4412
September	1st to 10th	Day	42% 3 12% 27% 14% 2	2280
	11th to 20th	Day	44% 2 11% 24% 17% 2	2158
	21st to end	Day	44% 2 8% 28% 17% 1	2061
October	1st to 10th	Day	46% 5% 10% 25% 12%	3160
	11th to 20th	Day	48% 2 9% 26% 15%	3140
	21st to end	Day	49% 3 13% 22% 13% 1	3411
November	1st to 10th	Day	61% 2 9% 18% 8% 1	1622
	11th to 20th	Day	68% 3 11% 14% 4 1	1600
	21st to end	Day	72% 4 9% 12% 3	1600
December	1st to 10th	Day	77% 3 6% 12% 2	2610
	11th to 20th	Day	77% 2 5% 11% 5%	2995
	21st to end	Day	75% 2 9% 8% 5%	3704
January	1st to 10th	Night	75% 2 8% 13% 2	4857
	11th to 20th	Night	78% 2 6% 9% 4	4410
	21st to end	Night	72% 3 7% 13% 4	4546
February	1st to 10th	Night	74% 3 7% 9% 6% 1	2470
	11th to 20th	Night	71% 2 8% 12% 5% 1	2406
	21st to end	Night	62% 3 8% 18% 8% 1	2004
March	1st to 10th	Night	71% 1 5% 13% 8% 1	3429
	11th to 20th	Night	72% 1 7% 12% 7% 1	3480
	21st to end	Night	70% 2 6% 14% 8% 1	3816
April	1st to 10th	Night	63% 2 7% 13% 12% 3	1939
	11th to 20th	Night	55% 3 7% 20% 14% 1	1755
	21st to end	Night	58% 3 8% 16% 12% 2	1710
May	1st to 10th	Night	63% 2 12% 16% 7% 1	2813
	11th to 20th	Night	55% 2 13% 24% 6% 1	2507
	21st to end	Night	53% 2 16% 22% 5% 1	2750
June	1st to 10th	Night	56% 3 12% 23% 6%	1496
	11th to 20th	Night	52% 4 11% 23% 9% 1	1330
	21st to end	Night	56% 5% 11% 17% 9% 2	1330
July	1st to 10th	Night	53% 5% 14% 18% 10% 1	2175
	11th to 20th	Night	48% 5% 19% 18% 10%	2358
	21st to end	Night	41% 5% 16% 25% 12% 1	2867
August	1st to 10th	Night	52% 5% 14% 23% 7%	2813
	11th to 20th	Night	45% 5% 17% 25% 8%	2809
	21st to end	Night	34% 5% 15% 28% 16% 1	3242
September	1st to 10th	Night	41% 3 9% 30% 15% 2	1900
	11th to 20th	Night	42% 2 10% 30% 16% 1	2019
	21st to end	Night	47% 3 9% 26% 14% 1	2118
October	1st to 10th	Night	49% 3 10% 25% 12% 1	3800
	11th to 20th	Night	44% 3 12% 25% 16%	3779
	21st to end	Night	48% 2 11% 24% 14%	4135
November	1st to 10th	Night	57% 3 11% 18% 9%	2674
	11th to 20th	Night	68% 3 9% 14% 6%	2800
	21st to end	Night	67% 3 13% 13% 3	2800
December	1st to 10th	Night	73% 4 8% 12% 2	4580
	11th to 20th	Night	70% 3 8% 14% 4	5215
	21st to end	Night	72% 2 7% 13% 5%	7251

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% 28% 29% 11%	221
	11th to 20th	Day	32% 25% 28% 13% 3 1	400
	21st to end	Day	24% 24% 38% 11% 2	410
February	1st to 10th	Day	27% 28% 31% 12% 2	370
	11th to 20th	Day	31% 29% 28% 9% 2	366
	21st to end	Day	23% 27% 35% 12% 3	323
March	1st to 10th	Day	29% 27% 32% 11% 2	460
	11th to 20th	Day	27% 27% 33% 11% 2	460
	21st to end	Day	29% 28% 27% 11% 4	506
April	1st to 10th	Day	35% 27% 27% 8% 3	460
	11th to 20th	Day	27% 28% 30% 11% 3	452
	21st to end	Day	25% 22% 30% 16% 6%	460
May	1st to 10th	Day	30% 26% 26% 13% 3 1	477
	11th to 20th	Day	25% 16% 29% 23% 7% 1	674
	21st to end	Day	26% 18% 35% 17% 4 1	735
June	1st to 10th	Day	30% 14% 30% 20% 6% 1	680
	11th to 20th	Day	23% 16% 34% 19% 8% 1	680
	21st to end	Day	29% 10% 33% 20% 7% 1	680
July	1st to 10th	Day	21% 9% 37% 23% 9% 1	670
	11th to 20th	Day	20% 8% 35% 26% 10% 1	668
	21st to end	Day	22% 8% 35% 26% 9%	607
August	1st to 10th	Day	16% 8% 36% 28% 11% 1	486
	11th to 20th	Day	19% 11% 32% 24% 11% 2	479
	21st to end	Day	17% 12% 30% 26% 11% 3	539
September	1st to 10th	Day	20% 10% 34% 26% 9% 1	490
	11th to 20th	Day	21% 15% 29% 23% 11% 1	490
	21st to end	Day	20% 16% 31% 20% 12% 1	474
October	1st to 10th	Day	21% 17% 28% 22% 9% 3	390
	11th to 20th	Day	27% 21% 26% 18% 7% 1	390
	21st to end	Day	26% 24% 29% 17% 4 1	429
November	1st to 10th	Day	27% 24% 29% 15% 3 1	395
	11th to 20th	Day	37% 24% 24% 12% 4 1	400
	21st to end	Day	31% 29% 31% 8% 2 1	400
December	1st to 10th	Day	34% 23% 30% 12% 2	400
	11th to 20th	Day	38% 30% 21% 10% 1	400
	21st to end	Day	31% 28% 31% 8% 2 1	318
January	1st to 10th	Night	28% 27% 30% 13% 2	900
	11th to 20th	Night	28% 25% 29% 14% 4	847
	21st to end	Night	22% 28% 33% 14% 3	841
February	1st to 10th	Night	30% 27% 27% 15% 2	760
	11th to 20th	Night	31% 27% 28% 12% 2	743
	21st to end	Night	21% 25% 33% 19% 3	628
March	1st to 10th	Night	27% 24% 31% 14% 3	760
	11th to 20th	Night	24% 22% 31% 18% 4 1	760
	21st to end	Night	26% 21% 33% 14% 4	836
April	1st to 10th	Night	34% 19% 29% 15% 2	609
	11th to 20th	Night	29% 19% 31% 17% 4	564
	21st to end	Night	29% 15% 31% 20% 4 1	570
May	1st to 10th	Night	29% 13% 33% 19% 5% 1	570
	11th to 20th	Night	27% 10% 32% 26% 4	562
	21st to end	Night	21% 12% 38% 22% 5%	616
June	1st to 10th	Night	29% 10% 32% 23% 6%	546
	11th to 20th	Night	24% 7% 33% 29% 6% 1	380
	21st to end	Night	25% 7% 34% 27% 7% 1	380
July	1st to 10th	Night	19% 5% 35% 33% 7%	370
	11th to 20th	Night	16% 6% 38% 30% 10%	480
	21st to end	Night	20% 5% 30% 37% 9%	623
August	1st to 10th	Night	19% 7% 27% 39% 8%	568
	11th to 20th	Night	17% 7% 29% 32% 13% 1	562
	21st to end	Night	18% 6% 30% 31% 15% 1	627
September	1st to 10th	Night	17% 8% 32% 32% 10% 1	570
	11th to 20th	Night	19% 11% 30% 28% 11% 1	689
	21st to end	Night	22% 13% 30% 24% 10% 1	760
October	1st to 10th	Night	20% 12% 33% 26% 9% 1	760
	11th to 20th	Night	25% 15% 33% 19% 7% 1	760
	21st to end	Night	33% 21% 24% 19% 4	836
November	1st to 10th	Night	31% 18% 29% 16% 5% 1	850
	11th to 20th	Night	32% 24% 26% 14% 4	900
	21st to end	Night	33% 22% 27% 16% 2	900
December	1st to 10th	Night	32% 23% 31% 12% 2	900
	11th to 20th	Night	33% 27% 27% 11% 2	900
	21st to end	Night	32% 24% 26% 15% 3	990

Page generated at 2025-01-19 04:06:43. Version ac07

Copyright © 2025 Attilla Danko.