Stock Dr/Savery
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Stock Dr/Savery clear sky chart from 2005-11-06 to 2024-01-13.

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	6% 10% 4 6% 5% 3 4 4 5% 7% 45%	74736
	Night	7% 11% 4 6% 5% 3 4 4 5% 6% 46%	75032
Transparency	Day	38% 5% 12% 21% 17% 7%	74448
	Night	38% 6% 12% 22% 16% 6%	74842
Seeing	Day	14% 17% 31% 24% 12% 2	14454
	Night	13% 11% 29% 32% 14% 2	24666

By Month

Percentage Cloud Cover SW (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	8% 18% 5% 11% 5% 2 3 3 4 5% 35%	1518
	11th to 20th	Day	8% 19% 7% 8% 5% 2 4 4 4 4 34%	1586
	21st to end	Day	6% 21% 8% 12% 6% 2 3 3 4 4 32%	1782
February	1st to 10th	Day	8% 21% 8% 11% 5% 2 3 4 3 5% 29%	1620
	11th to 20th	Day	8% 20% 9% 10% 5% 2 3 3 3 4 31%	1584
	21st to end	Day	5% 17% 8% 13% 7% 3 4 4 4 6% 29%	1480
March	1st to 10th	Day	6% 15% 7% 10% 5% 3 4 3 4 6% 36%	1905
	11th to 20th	Day	4 13% 5% 6% 5% 3 5% 5% 6% 7% 41%	1980
	21st to end	Day	7% 18% 7% 9% 6% 3 4 5% 4 7% 30%	2219
April	1st to 10th	Day	8% 16% 4 6% 6% 3 5% 4 6% 6% 36%	2160
	11th to 20th	Day	8% 16% 5% 8% 6% 3 5% 5% 5% 5% 34%	2131
	21st to end	Day	7% 13% 4 7% 5% 3 5% 5% 5% 6% 40%	2180
May	1st to 10th	Day	10% 12% 4 7% 7% 3 6% 5% 6% 7% 34%	2358
	11th to 20th	Day	8% 8% 2 6% 6% 4 6% 5% 7% 9% 38%	2478
	21st to end	Day	8% 7% 3 6% 6% 4 7% 5% 7% 9% 38%	2724
June	1st to 10th	Day	5% 5% 2 4 4 3 4 5% 7% 8% 52%	2520
	11th to 20th	Day	5% 3 2 4 4 2 5% 5% 6% 7% 57%	2520
	21st to end	Day	3 2 1 3 3 3 4 4 5% 7% 64%	2520
July	1st to 10th	Day	4 3 1 3 4 3 5% 5% 7% 8% 57%	2520
	11th to 20th	Day	2 3 2 4 6% 3 6% 5% 6% 9% 53%	2520
	21st to end	Day	3 4 2 4 6% 3 6% 6% 7% 9% 50%	2590
August	1st to 10th	Day	3 3 2 5% 6% 4 5% 6% 8% 9% 47%	2328
	11th to 20th	Day	4 3 2 4 4 3 6% 5% 5% 8% 56%	2273
	21st to end	Day	4 3 2 4 5% 3 4 5% 6% 8% 57%	2376
September	1st to 10th	Day	5% 3 1 3 4 2 4 5% 5% 6% 62%	2160
	11th to 20th	Day	6% 5% 1 4 4 2 4 4 5% 6% 58%	2160
	21st to end	Day	7% 5% 2 3 3 2 4 3 5% 5% 61%	1907
October	1st to 10th	Day	9% 8% 3 5% 5% 3 4 4 5% 6% 49%	1800
	11th to 20th	Day	11% 9% 3 3 4 2 2 3 4 7% 52%	1800
	21st to end	Day	9% 12% 3 4 4 2 3 3 3 6% 50%	1980
November	1st to 10th	Day	9% 10% 4 6% 3 2 3 4 5% 8% 47%	1701
	11th to 20th	Day	11% 11% 6% 6% 5% 2 3 3 5% 5% 43%	1596
	21st to end	Day	6% 11% 6% 9% 5% 3 2 3 3 6% 46%	1520
December	1st to 10th	Day	8% 19% 6% 11% 7% 2 3 4 4 5% 31%	1520
	11th to 20th	Day	8% 17% 6% 10% 6% 2 3 3 3 6% 36%	1926
	21st to end	Day	7% 17% 7% 10% 7% 3 3 3 4 6% 33%	2794
January	1st to 10th	Night	8% 19% 6% 9% 6% 3 3 2 4 4 36%	2647
	11th to 20th	Night	7% 19% 6% 8% 6% 3 3 3 3 5% 37%	2452
	21st to end	Night	7% 21% 8% 10% 6% 2 3 2 3 4 34%	2574
February	1st to 10th	Night	8% 17% 8% 13% 6% 4 3 3 4 5% 29%	2340
	11th to 20th	Night	6% 17% 8% 10% 5% 3 3 3 4 5% 34%	2262
	21st to end	Night	5% 17% 8% 11% 7% 3 4 3 4 6% 33%	1776
March	1st to 10th	Night	8% 14% 5% 9% 5% 3 4 4 4 6% 39%	2052
	11th to 20th	Night	5% 12% 4 5% 4 3 4 6% 5% 7% 45%	1980
	21st to end	Night	6% 16% 4 7% 6% 3 5% 4 5% 5% 38%	2136
April	1st to 10th	Night	8% 15% 4 6% 4 3 4 4 4 7% 42%	1800
	11th to 20th	Night	9% 12% 4 7% 6% 3 5% 5% 5% 6% 38%	1777
	21st to end	Night	9% 12% 3 5% 4 3 4 4 6% 6% 44%	1777
May	1st to 10th	Night	10% 10% 3 5% 5% 3 5% 6% 5% 7% 41%	1599
	11th to 20th	Night	8% 7% 2 6% 4 4 5% 6% 7% 8% 43%	1417
	21st to end	Night	6% 7% 2 6% 5% 4 6% 5% 7% 9% 44%	1552
June	1st to 10th	Night	5% 4 1 4 3 3 4 6% 6% 10% 55%	1440
	11th to 20th	Night	5% 4 2 4 5% 3 4 5% 6% 6% 58%	1440
	21st to end	Night	2 3 1 3 3 3 3 3 4 6% 69%	1440
July	1st to 10th	Night	4 3 2 4 4 3 5% 5% 8% 9% 55%	1440
	11th to 20th	Night	2 3 1 3 4 3 4 5% 7% 10% 58%	1440
	21st to end	Night	2 3 2 5% 5% 4 6% 7% 7% 9% 52%	1725
August	1st to 10th	Night	3 5% 2 3 4 3 5% 6% 6% 10% 53%	1611
	11th to 20th	Night	3 3 1 4 3 2 4 4 6% 9% 62%	1628
	21st to end	Night	3 3 1 3 4 3 4 5% 6% 10% 57%	1980
September	1st to 10th	Night	5% 4 1 3 3 2 2 4 5% 7% 64%	1800
	11th to 20th	Night	6% 5% 1 4 3 3 4 4 5% 6% 60%	1800
	21st to end	Night	6% 3 1 2 3 1 3 3 4 5% 67%	2049
October	1st to 10th	Night	9% 9% 2 4 3 2 3 3 4 6% 56%	2160
	11th to 20th	Night	7% 7% 2 3 3 2 3 3 4 6% 59%	2160
	21st to end	Night	7% 11% 3 6% 4 1 3 4 3 5% 53%	2376
November	1st to 10th	Night	10% 10% 3 4 3 1 3 4 5% 6% 50%	2359
	11th to 20th	Night	10% 12% 4 7% 4 3 3 4 5% 6% 44%	2579
	21st to end	Night	6% 13% 6% 7% 4 2 3 3 4 7% 45%	2660
December	1st to 10th	Night	9% 17% 5% 8% 5% 3 3 3 4 6% 37%	2660
	11th to 20th	Night	8% 14% 6% 8% 5% 2 3 4 4 6% 38%	3271
	21st to end	Night	5% 15% 6% 9% 7% 2 4 4 5% 6% 36%	4873

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	52% 6% 16% 16% 7% 2	1519
	11th to 20th	Day	53% 6% 14% 18% 8% 2	1586
	21st to end	Day	58% 4 16% 14% 7% 1	1782
February	1st to 10th	Day	59% 6% 12% 16% 7%	1620
	11th to 20th	Day	57% 4 13% 17% 7% 2	1593
	21st to end	Day	57% 5% 14% 15% 8% 1	1480
March	1st to 10th	Day	50% 4 13% 23% 10% 1	1905
	11th to 20th	Day	41% 6% 15% 24% 12% 1	1980
	21st to end	Day	53% 7% 12% 18% 8% 2	2219
April	1st to 10th	Day	47% 6% 13% 16% 14% 4	2160
	11th to 20th	Day	48% 6% 12% 19% 12% 1	2134
	21st to end	Day	43% 6% 11% 27% 13%	2180
May	1st to 10th	Day	47% 6% 11% 21% 14% 1	2358
	11th to 20th	Day	39% 8% 15% 24% 12% 1	2482
	21st to end	Day	39% 7% 12% 25% 16% 2	2724
June	1st to 10th	Day	28% 6% 13% 23% 23% 8%	2520
	11th to 20th	Day	23% 5% 10% 17% 27% 17%	2520
	21st to end	Day	18% 4 6% 20% 33% 19%	2520
July	1st to 10th	Day	22% 6% 9% 18% 27% 19%	2451
	11th to 20th	Day	25% 5% 11% 18% 21% 19%	2445
	21st to end	Day	27% 7% 12% 20% 20% 14%	2446
August	1st to 10th	Day	29% 7% 12% 20% 19% 12%	2313
	11th to 20th	Day	24% 5% 10% 20% 24% 16%	2273
	21st to end	Day	23% 5% 9% 21% 28% 13%	2376
September	1st to 10th	Day	21% 4 8% 17% 28% 22%	2160
	11th to 20th	Day	25% 4 10% 22% 25% 14%	2160
	21st to end	Day	25% 3 7% 27% 31% 6%	1907
October	1st to 10th	Day	35% 4 12% 24% 19% 5%	1800
	11th to 20th	Day	33% 4 12% 28% 18% 5%	1800
	21st to end	Day	37% 4 13% 28% 14% 3	1980
November	1st to 10th	Day	36% 6% 12% 28% 17% 1	1701
	11th to 20th	Day	44% 6% 15% 21% 14% 1	1596
	21st to end	Day	41% 4 14% 26% 13% 1	1520
December	1st to 10th	Day	56% 6% 16% 13% 8% 2	1520
	11th to 20th	Day	49% 6% 10% 28% 6%	1924
	21st to end	Day	51% 6% 12% 20% 10% 1	2794
January	1st to 10th	Night	52% 5% 13% 19% 7% 3	2647
	11th to 20th	Night	51% 5% 13% 20% 8% 3	2452
	21st to end	Night	57% 4 13% 16% 8% 2	2574
February	1st to 10th	Night	58% 6% 12% 15% 7% 1	2340
	11th to 20th	Night	52% 5% 12% 20% 9% 2	2263
	21st to end	Night	52% 4 13% 18% 11% 2	1776
March	1st to 10th	Night	46% 5% 13% 22% 12% 1	2052
	11th to 20th	Night	38% 6% 14% 25% 15% 3	1980
	21st to end	Night	46% 7% 13% 23% 9% 1	2136
April	1st to 10th	Night	42% 6% 15% 17% 16% 4	1800
	11th to 20th	Night	44% 7% 13% 21% 14% 2	1777
	21st to end	Night	40% 6% 13% 25% 16% 1	1777
May	1st to 10th	Night	39% 8% 14% 23% 14% 2	1599
	11th to 20th	Night	35% 7% 16% 27% 12% 3	1418
	21st to end	Night	35% 7% 12% 28% 16% 2	1552
June	1st to 10th	Night	23% 6% 15% 25% 22% 9%	1440
	11th to 20th	Night	25% 6% 11% 16% 23% 19%	1440
	21st to end	Night	16% 4 6% 19% 31% 23%	1440
July	1st to 10th	Night	23% 7% 10% 18% 24% 18%	1400
	11th to 20th	Night	19% 6% 11% 21% 21% 22%	1392
	21st to end	Night	24% 8% 13% 22% 18% 15%	1629
August	1st to 10th	Night	25% 6% 14% 25% 19% 12%	1602
	11th to 20th	Night	19% 5% 11% 19% 28% 18%	1628
	21st to end	Night	21% 6% 10% 18% 29% 15%	1980
September	1st to 10th	Night	20% 5% 7% 18% 27% 24%	1800
	11th to 20th	Night	23% 6% 9% 22% 24% 15%	1800
	21st to end	Night	19% 4 7% 26% 35% 8%	2049
October	1st to 10th	Night	31% 4 9% 26% 21% 8%	2160
	11th to 20th	Night	27% 4 9% 32% 23% 5%	2160
	21st to end	Night	35% 4 12% 28% 17% 3	2376
November	1st to 10th	Night	34% 5% 13% 24% 21% 2	2359
	11th to 20th	Night	41% 6% 14% 24% 13% 3	2579
	21st to end	Night	40% 4 12% 28% 14% 2	2660
December	1st to 10th	Night	50% 6% 16% 16% 11% 2	2660
	11th to 20th	Night	46% 6% 14% 26% 9%	3272
	21st to end	Night	48% 6% 14% 20% 11% 1	4873

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	26% 22% 24% 20% 8% 1	270
	11th to 20th	Day	20% 25% 33% 17% 5%	248
	21st to end	Day	18% 28% 40% 13% 2	264
February	1st to 10th	Day	28% 34% 28% 10%	240
	11th to 20th	Day	27% 28% 26% 18% 1	240
	21st to end	Day	22% 30% 35% 11% 3	198
March	1st to 10th	Day	20% 33% 31% 13% 3	345
	11th to 20th	Day	14% 29% 36% 17% 5%	420
	21st to end	Day	21% 29% 36% 11% 2	462
April	1st to 10th	Day	20% 31% 30% 16% 3	420
	11th to 20th	Day	23% 32% 30% 12% 4	412
	21st to end	Day	21% 21% 27% 22% 8% 1	420
May	1st to 10th	Day	16% 20% 36% 19% 7% 1	441
	11th to 20th	Day	18% 9% 28% 24% 18% 2	625
	21st to end	Day	15% 12% 29% 23% 17% 3	679
June	1st to 10th	Day	7% 11% 27% 30% 21% 5%	630
	11th to 20th	Day	9% 15% 33% 28% 13% 1	630
	21st to end	Day	6% 9% 30% 31% 20% 3	630
July	1st to 10th	Day	4 5% 25% 38% 25% 4	621
	11th to 20th	Day	3 6% 29% 34% 23% 5%	618
	21st to end	Day	5% 4 25% 41% 22% 5%	532
August	1st to 10th	Day	6% 6% 38% 34% 14% 3	447
	11th to 20th	Day	3 6% 32% 36% 18% 4	437
	21st to end	Day	5% 7% 34% 32% 19% 4	495
September	1st to 10th	Day	8% 11% 30% 28% 17% 5%	450
	11th to 20th	Day	11% 13% 35% 24% 15% 3	450
	21st to end	Day	12% 18% 27% 26% 12% 5%	346
October	1st to 10th	Day	15% 15% 27% 25% 14% 4	270
	11th to 20th	Day	19% 21% 29% 22% 7% 1	270
	21st to end	Day	19% 22% 34% 20% 5% 1	297
November	1st to 10th	Day	22% 28% 29% 14% 7% 1	270
	11th to 20th	Day	21% 24% 35% 17% 3 1	270
	21st to end	Day	14% 24% 41% 17% 3 1	270
December	1st to 10th	Day	24% 26% 26% 18% 5% 1	270
	11th to 20th	Day	19% 28% 36% 14% 3	270
	21st to end	Day	24% 24% 32% 16% 4 1	297
January	1st to 10th	Night	19% 15% 32% 26% 8% 1	950
	11th to 20th	Night	17% 16% 35% 24% 7% 1	805
	21st to end	Night	15% 15% 39% 25% 6% 1	792
February	1st to 10th	Night	17% 17% 41% 20% 5% 1	720
	11th to 20th	Night	15% 15% 37% 27% 5%	704
	21st to end	Night	14% 18% 39% 24% 5%	592
March	1st to 10th	Night	16% 14% 33% 28% 8% 1	720
	11th to 20th	Night	11% 9% 31% 39% 9% 1	720
	21st to end	Night	12% 12% 38% 28% 8% 1	750
April	1st to 10th	Night	16% 15% 32% 31% 7%	540
	11th to 20th	Night	16% 16% 32% 26% 9% 1	533
	21st to end	Night	15% 11% 25% 34% 13% 2	540
May	1st to 10th	Night	15% 9% 28% 32% 15% 1	540
	11th to 20th	Night	13% 3 20% 42% 19% 3	531
	21st to end	Night	13% 7% 21% 38% 19% 2	584
June	1st to 10th	Night	6% 6% 22% 37% 26% 3	540
	11th to 20th	Night	7% 6% 29% 43% 16%	540
	21st to end	Night	4 3 17% 48% 26% 2	540
July	1st to 10th	Night	6% 2 13% 41% 36% 3	525
	11th to 20th	Night	5% 2 13% 45% 33% 3	522
	21st to end	Night	3 1 7% 46% 40% 3	591
August	1st to 10th	Night	6% 1 12% 48% 31% 1	537
	11th to 20th	Night	4 2 14% 46% 33% 2	534
	21st to end	Night	6% 1 12% 43% 32% 6%	594
September	1st to 10th	Night	7% 2 17% 44% 24% 5%	540
	11th to 20th	Night	8% 4 20% 40% 24% 4	540
	21st to end	Night	8% 5% 22% 33% 24% 7%	686
October	1st to 10th	Night	14% 7% 24% 36% 17% 2	720
	11th to 20th	Night	10% 12% 25% 38% 13% 2	720
	21st to end	Night	14% 11% 30% 32% 10% 2	792
November	1st to 10th	Night	15% 15% 34% 25% 10% 1	879
	11th to 20th	Night	16% 17% 38% 23% 5%	950
	21st to end	Night	13% 13% 38% 30% 6%	950
December	1st to 10th	Night	19% 16% 35% 24% 5%	950
	11th to 20th	Night	16% 18% 38% 21% 6%	950
	21st to end	Night	19% 20% 36% 19% 5% 1	1045

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