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 2026-05-02.

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% 10% 6% 5% 4 3 5% 6% 30%	130909
	Night	14% 13% 5% 12% 6% 5% 4 3 4 5% 28%	131823
Transparency	Day	53% 6% 10% 20% 11% 1	134421
	Night	57% 6% 11% 17% 9% 1	136386
Seeing	Day	21% 17% 30% 20% 9% 3	17620
	Night	20% 14% 30% 26% 9% 1	27568

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% 20% 10% 25% 9% 5% 3 2 3 2 9%	4691
	11th to 20th	Day	10% 17% 9% 24% 13% 9% 5% 2 2 2 5%	4710
	21st to end	Day	11% 14% 9% 16% 8% 8% 7% 3 4 5% 15%	5156
February	1st to 10th	Day	10% 17% 7% 14% 15% 6% 4 3 4 5% 15%	1826
	11th to 20th	Day	11% 15% 8% 18% 11% 7% 5% 3 4 4 15%	2038
	21st to end	Day	11% 20% 7% 14% 9% 5% 4 3 4 4 19%	1730
March	1st to 10th	Day	11% 11% 5% 13% 6% 5% 4 4 5% 5% 31%	4580
	11th to 20th	Day	12% 12% 6% 13% 4 4 4 4 6% 8% 26%	4988
	21st to end	Day	22% 12% 7% 15% 5% 4 4 3 3 4 21%	5756
April	1st to 10th	Day	17% 17% 5% 9% 5% 4 3 3 4 6% 27%	2520
	11th to 20th	Day	20% 14% 3 6% 4 3 3 3 4 5% 34%	2609
	21st to end	Day	15% 12% 4 8% 5% 4 5% 4 6% 7% 31%	2730
May	1st to 10th	Day	17% 10% 3 6% 4 4 4 3 4 7% 39%	5875
	11th to 20th	Day	11% 11% 2 7% 4 4 4 4 5% 6% 41%	5993
	21st to end	Day	14% 9% 3 7% 5% 4 4 3 5% 7% 40%	6935
June	1st to 10th	Day	14% 6% 2 6% 4 4 4 4 6% 8% 41%	2860
	11th to 20th	Day	13% 7% 2 6% 5% 4 5% 5% 6% 9% 39%	3000
	21st to end	Day	14% 7% 3 7% 4 4 5% 5% 7% 7% 38%	2840
July	1st to 10th	Day	15% 6% 2 6% 4 4 4 3 6% 9% 41%	6360
	11th to 20th	Day	11% 5% 2 6% 4 4 5% 4 6% 8% 45%	6360
	21st to end	Day	9% 5% 2 6% 4 4 5% 4 7% 10% 44%	6924
August	1st to 10th	Day	10% 5% 2 7% 5% 5% 6% 5% 7% 8% 38%	4337
	11th to 20th	Day	14% 6% 2 6% 5% 4 4 4 5% 7% 44%	4174
	21st to end	Day	13% 6% 3 7% 5% 4 5% 4 5% 6% 42%	4492
September	1st to 10th	Day	15% 5% 2 6% 5% 4 5% 4 6% 8% 40%	2360
	11th to 20th	Day	14% 6% 2 6% 4 3 4 3 5% 6% 47%	2200
	21st to end	Day	16% 8% 2 7% 5% 5% 6% 4 6% 7% 36%	2200
October	1st to 10th	Day	18% 9% 2 7% 4 3 4 3 5% 6% 39%	2200
	11th to 20th	Day	22% 15% 4 10% 5% 5% 4 3 5% 6% 22%	1905
	21st to end	Day	22% 18% 4 8% 6% 4 4 4 5% 5% 19%	1980
November	1st to 10th	Day	16% 17% 4 7% 4 5% 3 3 5% 7% 28%	1852
	11th to 20th	Day	13% 23% 8% 11% 5% 4 4 3 5% 6% 18%	1890
	21st to end	Day	17% 24% 8% 12% 6% 5% 3 2 4 5% 16%	1799
December	1st to 10th	Day	12% 27% 11% 18% 7% 5% 4 2 4 2 8%	2350
	11th to 20th	Day	13% 21% 11% 16% 10% 6% 4 2 3 2 11%	2695
	21st to end	Day	20% 25% 9% 16% 6% 4 4 2 3 3 10%	3994
January	1st to 10th	Night	12% 17% 9% 26% 9% 5% 3 2 3 3 11%	8232
	11th to 20th	Night	9% 19% 9% 19% 12% 11% 5% 3 3 3 7%	8280
	21st to end	Night	9% 15% 8% 20% 11% 8% 7% 3 4 4 11%	9058
February	1st to 10th	Night	10% 17% 7% 15% 12% 7% 6% 3 3 4 15%	2793
	11th to 20th	Night	12% 14% 7% 16% 8% 5% 4 4 5% 5% 19%	2465
	21st to end	Night	14% 16% 6% 14% 8% 5% 4 3 4 5% 22%	2076
March	1st to 10th	Night	14% 11% 4 9% 7% 4 3 3 4 6% 35%	5493
	11th to 20th	Night	12% 13% 5% 9% 4 4 4 4 5% 7% 32%	5190
	21st to end	Night	19% 13% 6% 11% 4 4 3 3 4 5% 29%	5459
April	1st to 10th	Night	16% 14% 5% 9% 5% 3 4 3 5% 6% 30%	2100
	11th to 20th	Night	20% 12% 4 7% 4 3 4 3 4 5% 35%	1958
	21st to end	Night	15% 11% 4 6% 5% 4 3 3 5% 6% 37%	1890
May	1st to 10th	Night	14% 9% 3 6% 5% 4 4 4 5% 8% 39%	4042
	11th to 20th	Night	13% 12% 3 7% 5% 4 4 3 5% 6% 39%	3904
	21st to end	Night	18% 7% 3 5% 3 3 3 3 5% 6% 44%	3942
June	1st to 10th	Night	13% 6% 2 6% 5% 5% 4 3 5% 7% 43%	1530
	11th to 20th	Night	10% 4 3 7% 5% 4 5% 4 6% 9% 43%	1400
	21st to end	Night	12% 7% 3 6% 4 4 3 4 5% 7% 45%	1549
July	1st to 10th	Night	13% 7% 2 6% 4 4 4 4 6% 8% 42%	3618
	11th to 20th	Night	9% 6% 2 4 4 3 4 4 6% 6% 53%	3617
	21st to end	Night	9% 6% 2 5% 4 4 4 4 5% 7% 51%	3947
August	1st to 10th	Night	11% 5% 2 6% 4 5% 6% 4 6% 7% 44%	2815
	11th to 20th	Night	15% 6% 1 4 3 3 3 4 5% 7% 49%	2875
	21st to end	Night	13% 6% 2 5% 4 4 5% 4 5% 7% 46%	3402
September	1st to 10th	Night	13% 5% 2 5% 4 3 4 3 5% 6% 51%	2020
	11th to 20th	Night	13% 6% 2 5% 3 3 4 3 5% 6% 50%	2200
	21st to end	Night	18% 6% 3 6% 4 4 3 3 6% 7% 39%	2200
October	1st to 10th	Night	16% 10% 3 6% 4 3 3 3 4 6% 43%	2200
	11th to 20th	Night	20% 12% 3 8% 4 4 4 4 4 6% 29%	2490
	21st to end	Night	24% 15% 3 7% 4 4 4 3 4 5% 27%	2860
November	1st to 10th	Night	13% 14% 4 8% 6% 5% 5% 3 5% 7% 31%	2666
	11th to 20th	Night	14% 20% 7% 11% 5% 5% 4 3 4 5% 21%	2730
	21st to end	Night	16% 23% 9% 11% 4 4 4 3 4 5% 16%	2813
December	1st to 10th	Night	12% 19% 10% 18% 6% 5% 5% 3 5% 4 12%	5060
	11th to 20th	Night	12% 25% 9% 19% 7% 4 3 3 4 4 12%	5732
	21st to end	Night	22% 24% 8% 14% 4 3 3 3 3 3 12%	7217

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% 5% 2	4692
	11th to 20th	Day	86% 5% 4 4 1	4710
	21st to end	Day	72% 6% 9% 10% 3	5156
February	1st to 10th	Day	74% 4 8% 10% 3	1826
	11th to 20th	Day	72% 6% 8% 10% 4	2048
	21st to end	Day	69% 4 8% 15% 3	1730
March	1st to 10th	Day	54% 5% 13% 17% 9% 2	4580
	11th to 20th	Day	56% 5% 13% 17% 8% 1	4988
	21st to end	Day	68% 4 8% 14% 6%	5758
April	1st to 10th	Day	59% 5% 10% 16% 10%	2520
	11th to 20th	Day	53% 4 8% 21% 13% 1	2609
	21st to end	Day	52% 6% 10% 16% 13% 3	2730
May	1st to 10th	Day	45% 6% 7% 21% 17% 4	5910
	11th to 20th	Day	43% 5% 8% 24% 17% 2	5997
	21st to end	Day	44% 5% 8% 21% 20% 2	6949
June	1st to 10th	Day	40% 6% 11% 26% 15% 2	2860
	11th to 20th	Day	41% 7% 12% 23% 17% 1	3000
	21st to end	Day	43% 6% 13% 24% 13% 1	2840
July	1st to 10th	Day	39% 6% 11% 26% 16% 1	6291
	11th to 20th	Day	33% 7% 11% 34% 14% 1	6285
	21st to end	Day	32% 8% 12% 31% 16% 1	6728
August	1st to 10th	Day	39% 8% 13% 26% 13% 1	4322
	11th to 20th	Day	39% 6% 10% 29% 14% 1	4213
	21st to end	Day	41% 7% 10% 29% 12% 1	4491
September	1st to 10th	Day	41% 7% 13% 24% 15% 1	2360
	11th to 20th	Day	37% 5% 14% 29% 14% 1	2200
	21st to end	Day	45% 7% 13% 24% 11%	2200
October	1st to 10th	Day	34% 4 9% 33% 18% 1	3590
	11th to 20th	Day	54% 5% 9% 20% 12%	3082
	21st to end	Day	62% 6% 11% 16% 4	3180
November	1st to 10th	Day	57% 5% 10% 20% 8%	1852
	11th to 20th	Day	67% 5% 12% 10% 4	1890
	21st to end	Day	74% 5% 11% 9% 2	1799
December	1st to 10th	Day	82% 6% 7% 5% 1	2350
	11th to 20th	Day	80% 4 7% 8% 1	2691
	21st to end	Day	80% 4 5% 8% 2	3994
January	1st to 10th	Night	79% 5% 7% 7% 2	8233
	11th to 20th	Night	82% 5% 6% 5% 2	8280
	21st to end	Night	75% 6% 7% 9% 3	9058
February	1st to 10th	Night	74% 4 7% 11% 4	2793
	11th to 20th	Night	67% 5% 9% 14% 4	2466
	21st to end	Night	64% 5% 12% 14% 5%	2076
March	1st to 10th	Night	51% 5% 16% 19% 9%	5493
	11th to 20th	Night	51% 5% 18% 19% 7% 1	5190
	21st to end	Night	58% 5% 10% 17% 9% 1	5459
April	1st to 10th	Night	55% 5% 9% 20% 10% 1	2100
	11th to 20th	Night	53% 5% 7% 19% 14% 2	1958
	21st to end	Night	48% 4 13% 20% 14% 2	1890
May	1st to 10th	Night	43% 6% 11% 18% 19% 4	4069
	11th to 20th	Night	45% 6% 7% 25% 16% 1	3905
	21st to end	Night	42% 5% 11% 22% 15% 4	3950
June	1st to 10th	Night	40% 6% 10% 26% 17% 1	1530
	11th to 20th	Night	37% 5% 15% 26% 16% 2	1400
	21st to end	Night	39% 6% 13% 25% 16% 2	1549
July	1st to 10th	Night	38% 6% 13% 26% 14% 4	3580
	11th to 20th	Night	31% 6% 11% 32% 18% 1	3572
	21st to end	Night	32% 7% 15% 28% 17% 1	3832
August	1st to 10th	Night	38% 6% 14% 27% 12% 1	2806
	11th to 20th	Night	34% 6% 15% 29% 15%	2902
	21st to end	Night	36% 7% 13% 25% 18% 1	3402
September	1st to 10th	Night	33% 6% 14% 28% 17% 2	2020
	11th to 20th	Night	35% 6% 14% 31% 14% 1	2200
	21st to end	Night	44% 6% 14% 25% 10% 1	2200
October	1st to 10th	Night	38% 5% 11% 32% 13%	3590
	11th to 20th	Night	47% 6% 9% 24% 14%	4052
	21st to end	Night	55% 5% 12% 23% 6%	4610
November	1st to 10th	Night	54% 7% 13% 18% 9% 1	2666
	11th to 20th	Night	65% 6% 11% 12% 5% 1	2730
	21st to end	Night	71% 6% 12% 9% 1	2813
December	1st to 10th	Night	75% 8% 9% 7% 1	5060
	11th to 20th	Night	76% 5% 7% 8% 3	5735
	21st to end	Night	77% 6% 7% 6% 4	7217

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% 23% 39% 12% 3	330
	11th to 20th	Day	28% 20% 41% 10% 2	330
	21st to end	Day	26% 19% 36% 15% 3	363
February	1st to 10th	Day	22% 31% 33% 8% 4 2	330
	11th to 20th	Day	25% 30% 33% 11% 1	330
	21st to end	Day	31% 33% 31% 4 1	273
March	1st to 10th	Day	28% 31% 32% 9% 1	330
	11th to 20th	Day	29% 21% 31% 14% 5% 1	490
	21st to end	Day	33% 18% 27% 16% 6% 1	594
April	1st to 10th	Day	28% 21% 32% 14% 4 1	540
	11th to 20th	Day	31% 20% 27% 13% 7% 2	532
	21st to end	Day	27% 17% 29% 18% 8% 1	540
May	1st to 10th	Day	26% 20% 30% 15% 6% 3	507
	11th to 20th	Day	18% 16% 31% 24% 7% 3	581
	21st to end	Day	17% 17% 29% 25% 10% 2	789
June	1st to 10th	Day	16% 18% 32% 22% 9% 2	730
	11th to 20th	Day	16% 14% 34% 24% 9% 3	730
	21st to end	Day	17% 13% 32% 27% 8% 2	730
July	1st to 10th	Day	12% 11% 29% 29% 14% 6%	721
	11th to 20th	Day	13% 11% 29% 29% 13% 5%	718
	21st to end	Day	11% 8% 34% 28% 15% 4	794
August	1st to 10th	Day	10% 8% 30% 26% 18% 9%	591
	11th to 20th	Day	14% 7% 22% 31% 18% 9%	519
	21st to end	Day	17% 9% 25% 28% 16% 5%	583
September	1st to 10th	Day	18% 8% 27% 24% 15% 7%	530
	11th to 20th	Day	11% 9% 22% 29% 20% 9%	530
	21st to end	Day	21% 12% 21% 27% 14% 6%	530
October	1st to 10th	Day	23% 15% 27% 20% 12% 2	530
	11th to 20th	Day	30% 16% 35% 17% 2	430
	21st to end	Day	30% 23% 32% 11% 4 1	363
November	1st to 10th	Day	30% 21% 29% 16% 3	330
	11th to 20th	Day	27% 26% 34% 11% 2	330
	21st to end	Day	31% 30% 26% 11% 2	288
December	1st to 10th	Day	32% 23% 27% 11% 5% 1	220
	11th to 20th	Day	30% 28% 31% 10% 1	220
	21st to end	Day	29% 29% 32% 6% 2 1	344
January	1st to 10th	Night	21% 19% 35% 19% 5% 1	1050
	11th to 20th	Night	24% 19% 35% 18% 5%	1050
	21st to end	Night	19% 13% 40% 23% 5%	1155
February	1st to 10th	Night	18% 18% 37% 21% 5%	903
	11th to 20th	Night	22% 21% 30% 23% 4	823
	21st to end	Night	25% 19% 33% 21% 3	692
March	1st to 10th	Night	19% 16% 35% 22% 8% 1	840
	11th to 20th	Night	22% 20% 32% 22% 4	840
	21st to end	Night	22% 16% 32% 24% 6% 1	872
April	1st to 10th	Night	26% 14% 31% 23% 5% 1	630
	11th to 20th	Night	27% 15% 30% 21% 7% 1	623
	21st to end	Night	21% 12% 31% 29% 6% 1	630
May	1st to 10th	Night	17% 12% 33% 30% 7%	603
	11th to 20th	Night	18% 11% 32% 30% 9%	591
	21st to end	Night	16% 9% 26% 38% 11%	650
June	1st to 10th	Night	16% 9% 30% 35% 9% 1	530
	11th to 20th	Night	10% 9% 31% 40% 10% 1	400
	21st to end	Night	15% 7% 28% 35% 15% 1	549
July	1st to 10th	Night	10% 3 22% 42% 21% 2	585
	11th to 20th	Night	10% 5% 24% 37% 23% 2	582
	21st to end	Night	11% 4 24% 38% 21% 1	657
August	1st to 10th	Night	10% 3 23% 41% 21% 2	597
	11th to 20th	Night	11% 6% 18% 37% 25% 3	594
	21st to end	Night	15% 6% 19% 39% 19% 1	660
September	1st to 10th	Night	14% 4 25% 31% 21% 4	620
	11th to 20th	Night	15% 5% 21% 36% 19% 4	800
	21st to end	Night	21% 9% 25% 28% 15% 3	800
October	1st to 10th	Night	19% 12% 29% 29% 10% 1	800
	11th to 20th	Night	27% 15% 27% 24% 7% 1	800
	21st to end	Night	31% 16% 27% 21% 5%	880
November	1st to 10th	Night	24% 14% 32% 22% 6% 1	820
	11th to 20th	Night	25% 19% 34% 18% 4	840
	21st to end	Night	27% 16% 35% 19% 3	847
December	1st to 10th	Night	22% 20% 36% 19% 4	1050
	11th to 20th	Night	24% 20% 35% 16% 4 1	1050
	21st to end	Night	28% 19% 32% 18% 2	1155

Page generated at 2026-04-29 02:21:45. Version ac07

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