Strawberry Hill Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Strawberry Hill Observatory clear sky chart from 2005-11-06 to 2025-01-07.

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	14% 12% 5% 9% 5% 4 4 3 5% 6% 31%	104440
	Night	14% 14% 5% 11% 5% 5% 4 3 4 5% 29%	104662
Transparency	Day	53% 6% 10% 20% 11% 1	107997
	Night	56% 6% 11% 18% 9% 1	109246
Seeing	Day	21% 16% 30% 21% 9% 3	15861
	Night	20% 13% 30% 26% 9% 1	25769

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	12% 23% 12% 21% 6% 6% 3 2 3 2 9%	2575
	11th to 20th	Day	13% 18% 8% 19% 11% 11% 5% 2 3 3 6%	2530
	21st to end	Day	18% 22% 11% 13% 6% 4 5% 3 4 5% 10%	2783
February	1st to 10th	Day	11% 18% 7% 14% 13% 6% 4 3 4 5% 15%	1652
	11th to 20th	Day	11% 16% 8% 17% 11% 7% 5% 3 4 4 16%	1838
	21st to end	Day	12% 19% 7% 13% 8% 5% 4 3 4 4 20%	1570
March	1st to 10th	Day	12% 13% 6% 11% 6% 4 4 4 4 5% 30%	3120
	11th to 20th	Day	10% 12% 7% 17% 5% 4 4 3 5% 6% 26%	3408
	21st to end	Day	18% 14% 7% 13% 6% 5% 5% 3 4 4 23%	3928
April	1st to 10th	Day	18% 16% 5% 9% 5% 4 3 3 4 6% 28%	2280
	11th to 20th	Day	20% 13% 3 6% 4 3 4 3 4 5% 34%	2357
	21st to end	Day	16% 12% 4 9% 5% 4 4 3 6% 7% 31%	2470
May	1st to 10th	Day	15% 9% 3 6% 5% 4 5% 3 5% 6% 38%	4082
	11th to 20th	Day	12% 8% 2 6% 4 4 4 4 5% 6% 45%	4171
	21st to end	Day	13% 6% 2 6% 5% 4 4 4 5% 8% 43%	4824
June	1st to 10th	Day	14% 7% 2 6% 4 4 4 4 6% 8% 41%	2717
	11th to 20th	Day	13% 7% 2 6% 4 4 5% 4 6% 9% 40%	2850
	21st to end	Day	15% 6% 3 6% 4 4 5% 4 7% 7% 38%	2698
July	1st to 10th	Day	16% 7% 2 7% 5% 4 4 4 6% 8% 36%	4440
	11th to 20th	Day	10% 5% 2 5% 4 4 6% 5% 7% 9% 44%	4440
	21st to end	Day	9% 5% 2 6% 4 4 5% 5% 7% 9% 43%	4813
August	1st to 10th	Day	10% 5% 2 7% 5% 5% 6% 5% 7% 9% 37%	4204
	11th to 20th	Day	14% 6% 2 6% 5% 4 4 4 5% 7% 44%	4044
	21st to end	Day	13% 6% 3 7% 5% 4 5% 4 5% 6% 42%	4354
September	1st to 10th	Day	15% 5% 2 6% 4 4 5% 4 6% 8% 40%	2242
	11th to 20th	Day	14% 6% 1 6% 4 3 4 3 5% 6% 47%	2090
	21st to end	Day	16% 8% 2 7% 4 4 6% 4 6% 7% 36%	2090
October	1st to 10th	Day	18% 9% 3 7% 4 3 4 3 4 6% 38%	2090
	11th to 20th	Day	23% 15% 4 10% 5% 5% 4 3 5% 6% 21%	1810
	21st to end	Day	23% 19% 4 8% 6% 5% 4 4 5% 5% 18%	1881
November	1st to 10th	Day	17% 18% 4 7% 4 5% 3 3 6% 6% 28%	1762
	11th to 20th	Day	13% 22% 8% 11% 5% 5% 4 3 4 6% 18%	1800
	21st to end	Day	17% 24% 9% 11% 6% 4 3 2 4 5% 16%	1714
December	1st to 10th	Day	12% 28% 10% 17% 6% 5% 4 2 4 2 8%	2280
	11th to 20th	Day	13% 22% 11% 16% 10% 6% 4 2 3 2 11%	2625
	21st to end	Day	20% 25% 9% 15% 6% 4 4 2 3 4 10%	3908
January	1st to 10th	Night	14% 19% 11% 20% 6% 5% 3 2 3 4 13%	4513
	11th to 20th	Night	11% 17% 7% 18% 12% 12% 4 3 3 3 9%	4440
	21st to end	Night	16% 21% 9% 19% 8% 6% 5% 3 3 3 9%	4884
February	1st to 10th	Night	10% 16% 7% 15% 12% 8% 6% 3 3 4 15%	2527
	11th to 20th	Night	12% 14% 7% 17% 8% 5% 4 4 5% 4 18%	2225
	21st to end	Night	14% 16% 5% 14% 8% 5% 4 3 4 5% 22%	1884
March	1st to 10th	Night	14% 10% 4 8% 4 4 4 3 4 6% 38%	3733
	11th to 20th	Night	9% 14% 6% 9% 5% 4 4 3 4 6% 35%	3550
	21st to end	Night	15% 14% 7% 11% 5% 4 4 4 4 5% 28%	3732
April	1st to 10th	Night	16% 14% 5% 8% 5% 4 4 3 5% 6% 31%	1900
	11th to 20th	Night	20% 11% 3 6% 4 3 4 3 5% 5% 35%	1770
	21st to end	Night	15% 12% 4 6% 5% 4 3 3 5% 6% 37%	1710
May	1st to 10th	Night	15% 9% 2 6% 5% 4 4 4 5% 7% 39%	2813
	11th to 20th	Night	14% 8% 3 6% 5% 3 4 3 5% 7% 42%	2723
	21st to end	Night	18% 6% 3 5% 3 3 3 3 5% 7% 44%	2743
June	1st to 10th	Night	14% 6% 2 6% 5% 4 4 3 5% 7% 43%	1454
	11th to 20th	Night	10% 4 3 6% 4 4 5% 4 6% 9% 44%	1330
	21st to end	Night	11% 7% 3 6% 4 4 3 3 6% 7% 46%	1471
July	1st to 10th	Night	13% 7% 2 6% 4 4 4 4 6% 9% 41%	2530
	11th to 20th	Night	7% 4 1 5% 4 3 4 4 6% 6% 54%	2530
	21st to end	Night	8% 6% 2 6% 4 4 4 4 5% 7% 50%	2750
August	1st to 10th	Night	11% 5% 2 6% 4 5% 6% 4 6% 7% 43%	2728
	11th to 20th	Night	15% 6% 1 4 3 3 3 3 5% 7% 50%	2785
	21st to end	Night	13% 6% 2 5% 4 4 5% 4 5% 7% 46%	3298
September	1st to 10th	Night	13% 5% 2 5% 4 3 4 3 5% 6% 51%	1919
	11th to 20th	Night	13% 6% 2 5% 3 3 4 3 5% 6% 50%	2090
	21st to end	Night	18% 6% 3 6% 4 4 3 3 6% 7% 39%	2090
October	1st to 10th	Night	17% 10% 3 6% 4 3 3 3 4 6% 42%	2090
	11th to 20th	Night	20% 12% 3 8% 4 5% 5% 4 4 6% 29%	2365
	21st to end	Night	25% 15% 3 7% 4 4 4 3 4 5% 26%	2717
November	1st to 10th	Night	13% 14% 3 8% 6% 5% 5% 4 5% 7% 31%	2536
	11th to 20th	Night	15% 20% 7% 11% 5% 5% 4 3 4 5% 21%	2600
	21st to end	Night	16% 23% 9% 11% 4 4 4 3 5% 5% 17%	2678
December	1st to 10th	Night	12% 19% 10% 18% 6% 5% 5% 3 5% 4 12%	4910
	11th to 20th	Night	12% 25% 9% 18% 7% 4 3 3 4 4 12%	5582
	21st to end	Night	22% 25% 8% 13% 4 3 4 3 3 3 12%	7062

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	84% 4 6% 4 2	2576
	11th to 20th	Day	86% 5% 4 4 1	2530
	21st to end	Day	79% 6% 9% 4 1	2783
February	1st to 10th	Day	74% 4 9% 10% 3	1652
	11th to 20th	Day	72% 6% 8% 9% 4	1848
	21st to end	Day	69% 4 9% 15% 3	1570
March	1st to 10th	Day	56% 5% 9% 21% 9%	3120
	11th to 20th	Day	58% 5% 12% 17% 7% 1	3408
	21st to end	Day	65% 5% 8% 15% 6% 1	3928
April	1st to 10th	Day	58% 5% 10% 17% 10%	2280
	11th to 20th	Day	53% 4 9% 20% 14% 1	2357
	21st to end	Day	52% 6% 10% 15% 14% 3	2470
May	1st to 10th	Day	44% 7% 8% 21% 18% 2	4120
	11th to 20th	Day	38% 6% 10% 28% 17% 2	4175
	21st to end	Day	39% 6% 10% 22% 20% 2	4837
June	1st to 10th	Day	40% 6% 12% 26% 15% 2	2717
	11th to 20th	Day	40% 6% 12% 23% 18% 1	2850
	21st to end	Day	43% 6% 13% 24% 13% 1	2698
July	1st to 10th	Day	44% 7% 12% 21% 14% 1	4371
	11th to 20th	Day	31% 8% 12% 33% 14% 1	4365
	21st to end	Day	34% 9% 11% 27% 18% 1	4662
August	1st to 10th	Day	39% 8% 13% 26% 13% 1	4189
	11th to 20th	Day	39% 6% 10% 29% 14% 1	4083
	21st to end	Day	42% 7% 10% 28% 12% 1	4353
September	1st to 10th	Day	40% 6% 12% 25% 15% 1	2242
	11th to 20th	Day	37% 5% 14% 29% 14% 1	2090
	21st to end	Day	45% 7% 13% 24% 10%	2090
October	1st to 10th	Day	35% 4 9% 33% 18% 1	3480
	11th to 20th	Day	54% 5% 9% 19% 12%	2987
	21st to end	Day	63% 6% 11% 16% 4	3081
November	1st to 10th	Day	58% 5% 10% 20% 8%	1762
	11th to 20th	Day	68% 5% 12% 10% 5%	1800
	21st to end	Day	73% 5% 11% 9% 2	1714
December	1st to 10th	Day	81% 6% 7% 5% 1	2280
	11th to 20th	Day	80% 4 7% 8% 1	2621
	21st to end	Day	80% 4 5% 8% 3	3908
January	1st to 10th	Night	78% 4 7% 9% 2	4513
	11th to 20th	Night	82% 5% 6% 5% 2	4440
	21st to end	Night	81% 5% 7% 5% 1	4884
February	1st to 10th	Night	74% 4 7% 11% 4	2527
	11th to 20th	Night	69% 5% 9% 13% 4	2226
	21st to end	Night	64% 5% 12% 14% 5%	1884
March	1st to 10th	Night	47% 5% 16% 23% 9%	3733
	11th to 20th	Night	50% 5% 13% 23% 9% 1	3550
	21st to end	Night	58% 5% 10% 19% 7% 1	3732
April	1st to 10th	Night	55% 5% 9% 19% 11% 1	1900
	11th to 20th	Night	52% 5% 8% 20% 14% 2	1770
	21st to end	Night	48% 4 12% 19% 14% 2	1710
May	1st to 10th	Night	43% 7% 11% 18% 17% 4	2840
	11th to 20th	Night	42% 6% 8% 28% 15% 1	2724
	21st to end	Night	40% 6% 13% 20% 16% 4	2751
June	1st to 10th	Night	40% 6% 10% 26% 17% 1	1454
	11th to 20th	Night	35% 5% 15% 26% 17% 2	1330
	21st to end	Night	37% 5% 13% 26% 17% 2	1471
July	1st to 10th	Night	39% 6% 13% 25% 13% 5%	2490
	11th to 20th	Night	29% 6% 13% 33% 18% 1	2482
	21st to end	Night	33% 8% 13% 25% 19% 1	2662
August	1st to 10th	Night	39% 7% 14% 27% 12% 1	2719
	11th to 20th	Night	34% 6% 15% 29% 16%	2812
	21st to end	Night	36% 7% 13% 24% 19% 1	3298
September	1st to 10th	Night	33% 6% 13% 29% 18% 2	1919
	11th to 20th	Night	36% 5% 14% 30% 14% 1	2090
	21st to end	Night	44% 6% 15% 25% 9% 1	2090
October	1st to 10th	Night	38% 5% 11% 32% 13%	3480
	11th to 20th	Night	47% 6% 9% 24% 14%	3927
	21st to end	Night	55% 5% 12% 23% 5%	4467
November	1st to 10th	Night	53% 7% 13% 18% 8% 1	2536
	11th to 20th	Night	66% 6% 11% 11% 6% 1	2600
	21st to end	Night	71% 6% 12% 10% 1	2678
December	1st to 10th	Night	75% 8% 9% 7% 1	4910
	11th to 20th	Night	76% 5% 7% 8% 3	5585
	21st to end	Night	78% 6% 7% 6% 4	7062

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	23% 22% 39% 14% 4	288
	11th to 20th	Day	29% 18% 40% 11% 2	270
	21st to end	Day	27% 18% 35% 17% 3	297
February	1st to 10th	Day	22% 30% 34% 9% 4 2	270
	11th to 20th	Day	23% 31% 33% 11% 1	270
	21st to end	Day	29% 33% 32% 5% 1	225
March	1st to 10th	Day	25% 32% 32% 10% 1	270
	11th to 20th	Day	25% 20% 34% 15% 5% 1	414
	21st to end	Day	30% 16% 27% 18% 7% 1	506
April	1st to 10th	Day	27% 21% 32% 15% 4 1	460
	11th to 20th	Day	31% 20% 27% 13% 7% 2	452
	21st to end	Day	28% 17% 28% 18% 8% 2	460
May	1st to 10th	Day	26% 21% 28% 16% 6% 3	463
	11th to 20th	Day	18% 16% 31% 24% 7% 4	538
	21st to end	Day	14% 16% 30% 27% 10% 3	734
June	1st to 10th	Day	16% 17% 31% 24% 10% 3	680
	11th to 20th	Day	16% 14% 34% 24% 10% 3	680
	21st to end	Day	17% 13% 31% 29% 9% 3	680
July	1st to 10th	Day	12% 11% 27% 29% 14% 6%	671
	11th to 20th	Day	13% 10% 28% 29% 14% 5%	668
	21st to end	Day	11% 7% 33% 27% 16% 5%	739
August	1st to 10th	Day	11% 8% 30% 25% 17% 9%	548
	11th to 20th	Day	14% 7% 23% 30% 18% 9%	479
	21st to end	Day	17% 9% 25% 28% 16% 5%	539
September	1st to 10th	Day	18% 8% 27% 24% 16% 7%	490
	11th to 20th	Day	12% 10% 23% 29% 19% 7%	490
	21st to end	Day	22% 12% 21% 26% 13% 6%	490
October	1st to 10th	Day	25% 16% 27% 19% 11% 2	490
	11th to 20th	Day	31% 16% 34% 17% 2	395
	21st to end	Day	32% 23% 32% 10% 3 1	330
November	1st to 10th	Day	30% 21% 29% 18% 3	300
	11th to 20th	Day	25% 27% 36% 11% 2	300
	21st to end	Day	29% 30% 27% 11% 2	262
December	1st to 10th	Day	32% 23% 29% 11% 5% 1	200
	11th to 20th	Day	27% 29% 33% 11% 1 1	200
	21st to end	Day	27% 29% 34% 6% 3 1	313
January	1st to 10th	Night	21% 19% 35% 20% 5% 1	981
	11th to 20th	Night	25% 18% 33% 19% 5%	950
	21st to end	Night	19% 12% 39% 24% 5%	1045
February	1st to 10th	Night	18% 18% 37% 22% 6%	817
	11th to 20th	Night	22% 20% 31% 23% 4	743
	21st to end	Night	25% 19% 32% 21% 3	628
March	1st to 10th	Night	18% 15% 35% 23% 8% 1	760
	11th to 20th	Night	20% 19% 33% 23% 5% 1	760
	21st to end	Night	21% 16% 31% 24% 7% 1	789
April	1st to 10th	Night	25% 13% 33% 24% 5% 1	570
	11th to 20th	Night	25% 14% 32% 21% 7% 1	563
	21st to end	Night	21% 11% 31% 28% 7% 1	570
May	1st to 10th	Night	18% 11% 34% 29% 7% 1	570
	11th to 20th	Night	18% 10% 33% 29% 9%	561
	21st to end	Night	15% 8% 27% 38% 12%	617
June	1st to 10th	Night	16% 9% 30% 35% 9% 1	504
	11th to 20th	Night	10% 9% 30% 40% 10% 1	380
	21st to end	Night	14% 7% 28% 36% 15% 1	521
July	1st to 10th	Night	10% 3 21% 42% 21% 2	555
	11th to 20th	Night	9% 5% 24% 36% 23% 2	552
	21st to end	Night	12% 4 23% 37% 22% 1	624
August	1st to 10th	Night	10% 3 24% 41% 21% 2	567
	11th to 20th	Night	11% 6% 18% 37% 26% 4	564
	21st to end	Night	15% 6% 19% 40% 19% 1	627
September	1st to 10th	Night	14% 4 25% 32% 21% 4	589
	11th to 20th	Night	16% 6% 22% 35% 18% 3	760
	21st to end	Night	21% 9% 25% 29% 14% 3	760
October	1st to 10th	Night	20% 12% 28% 29% 10% 1	760
	11th to 20th	Night	27% 15% 26% 24% 6% 1	760
	21st to end	Night	31% 16% 27% 20% 5%	836
November	1st to 10th	Night	23% 14% 33% 22% 6% 1	780
	11th to 20th	Night	25% 20% 34% 18% 3	800
	21st to end	Night	26% 16% 36% 19% 3	806
December	1st to 10th	Night	22% 20% 36% 19% 4	1000
	11th to 20th	Night	24% 20% 36% 16% 4 1	1000
	21st to end	Night	28% 19% 32% 18% 2	1100

Page generated at 2025-01-04 03:24:03. Version ac07

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