Darke Sky Ranch
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Darke Sky Ranch clear sky chart from 2005-11-06 to 2024-01-27.

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% 9% 4 7% 6% 3 5% 5% 5% 7% 35%	75111
	Night	15% 9% 4 7% 6% 3 5% 4 5% 7% 36%	74937
Transparency	Day	48% 6% 11% 21% 12% 2	74824
	Night	47% 6% 11% 21% 14% 2	74744
Seeing	Day	18% 9% 26% 24% 16% 8%	14346
	Night	18% 8% 27% 30% 15% 2	24253

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	17% 14% 6% 10% 7% 5% 6% 4 5% 6% 22%	1517
	11th to 20th	Day	17% 14% 8% 10% 8% 4 5% 4 4 4 21%	1563
	21st to end	Day	16% 15% 7% 12% 8% 4 5% 4 4 6% 19%	1836
February	1st to 10th	Day	20% 14% 7% 10% 7% 3 5% 4 3 5% 23%	1692
	11th to 20th	Day	15% 11% 5% 12% 8% 5% 5% 4 5% 6% 24%	1748
	21st to end	Day	18% 12% 5% 10% 7% 3 4 2 3 5% 30%	1480
March	1st to 10th	Day	18% 11% 5% 7% 6% 4 3 5% 5% 6% 30%	1806
	11th to 20th	Day	17% 11% 5% 8% 7% 3 4 4 4 6% 30%	1980
	21st to end	Day	21% 12% 5% 8% 6% 3 4 4 5% 6% 26%	2178
April	1st to 10th	Day	14% 11% 4 8% 7% 4 4 5% 4 7% 33%	2132
	11th to 20th	Day	16% 9% 3 7% 5% 3 5% 4 5% 7% 37%	2194
	21st to end	Day	19% 8% 3 7% 6% 3 5% 4 6% 7% 32%	2340
May	1st to 10th	Day	18% 9% 4 6% 6% 4 4 5% 5% 7% 32%	2340
	11th to 20th	Day	20% 8% 3 5% 6% 3 5% 5% 5% 7% 33%	2301
	21st to end	Day	9% 5% 3 7% 7% 4 6% 6% 8% 8% 36%	2531
June	1st to 10th	Day	13% 6% 2 5% 6% 4 5% 6% 5% 8% 40%	2416
	11th to 20th	Day	10% 5% 3 5% 5% 3 5% 6% 6% 10% 42%	2520
	21st to end	Day	9% 4 3 6% 6% 4 5% 7% 7% 10% 40%	2520
July	1st to 10th	Day	10% 5% 2 7% 5% 4 7% 6% 7% 10% 38%	2520
	11th to 20th	Day	8% 4 2 5% 5% 3 5% 6% 7% 11% 43%	2502
	21st to end	Day	9% 5% 2 5% 6% 3 6% 6% 7% 10% 42%	2547
August	1st to 10th	Day	7% 5% 2 5% 6% 3 6% 6% 8% 9% 43%	2327
	11th to 20th	Day	9% 5% 3 6% 6% 5% 7% 5% 8% 10% 39%	2303
	21st to end	Day	8% 4 3 5% 6% 3 5% 6% 7% 10% 43%	2418
September	1st to 10th	Day	12% 6% 2 4 5% 4 4 5% 5% 6% 47%	2057
	11th to 20th	Day	10% 5% 2 5% 5% 3 4 4 5% 8% 47%	1980
	21st to end	Day	14% 5% 2 5% 5% 3 4 3 5% 6% 48%	1980
October	1st to 10th	Day	12% 5% 2 6% 6% 3 5% 5% 5% 6% 44%	1980
	11th to 20th	Day	14% 7% 2 4 5% 3 4 4 5% 8% 44%	1819
	21st to end	Day	19% 10% 3 7% 6% 3 4 4 6% 8% 31%	1824
November	1st to 10th	Day	9% 8% 3 5% 4 3 3 4 5% 7% 49%	1672
	11th to 20th	Day	15% 11% 4 8% 6% 3 4 4 4 6% 35%	1710
	21st to end	Day	18% 12% 4 7% 6% 3 4 4 5% 6% 32%	1710
December	1st to 10th	Day	18% 15% 7% 10% 6% 4 4 3 5% 5% 23%	1710
	11th to 20th	Day	15% 14% 7% 11% 6% 3 5% 5% 4 5% 25%	2153
	21st to end	Day	22% 20% 9% 10% 7% 4 4 4 4 5% 11%	2805
January	1st to 10th	Night	17% 11% 6% 11% 8% 4 6% 4 4 4 24%	2648
	11th to 20th	Night	18% 16% 7% 10% 8% 3 4 3 4 5% 22%	2611
	21st to end	Night	17% 15% 6% 10% 7% 4 4 4 4 6% 23%	2664
February	1st to 10th	Night	21% 13% 5% 8% 7% 3 5% 3 3 6% 26%	2267
	11th to 20th	Night	14% 11% 5% 7% 8% 4 5% 5% 4 6% 30%	2098
	21st to end	Night	20% 12% 6% 9% 5% 3 5% 3 4 6% 28%	1776
March	1st to 10th	Night	17% 8% 5% 7% 6% 3 4 5% 4 5% 36%	2153
	11th to 20th	Night	14% 10% 3 6% 6% 3 5% 4 5% 7% 38%	1980
	21st to end	Night	20% 10% 4 7% 5% 3 4 3 3 6% 33%	2178
April	1st to 10th	Night	13% 8% 4 6% 6% 2 5% 6% 6% 7% 37%	1841
	11th to 20th	Night	16% 8% 3 5% 5% 3 5% 5% 6% 8% 38%	1713
	21st to end	Night	18% 6% 3 6% 5% 3 5% 4 5% 8% 36%	1620
May	1st to 10th	Night	18% 10% 4 6% 5% 4 5% 5% 6% 8% 30%	1620
	11th to 20th	Night	18% 7% 3 4 5% 3 4 4 5% 7% 40%	1592
	21st to end	Night	7% 5% 2 5% 4 3 5% 5% 8% 12% 43%	1744
June	1st to 10th	Night	9% 4 3 5% 5% 3 5% 4 6% 8% 49%	1539
	11th to 20th	Night	8% 4 2 4 6% 3 5% 4 6% 10% 48%	1440
	21st to end	Night	7% 5% 2 4 4 3 5% 7% 7% 9% 47%	1440
July	1st to 10th	Night	9% 4 2 5% 6% 4 5% 5% 5% 8% 46%	1440
	11th to 20th	Night	7% 4 2 5% 5% 2 4 6% 6% 9% 51%	1457
	21st to end	Night	8% 5% 2 5% 4 3 5% 4 6% 8% 49%	1771
August	1st to 10th	Night	6% 4 2 5% 6% 3 6% 6% 7% 10% 46%	1611
	11th to 20th	Night	6% 5% 2 6% 5% 4 5% 5% 7% 8% 48%	1598
	21st to end	Night	5% 4 2 5% 5% 3 5% 5% 6% 9% 51%	1934
September	1st to 10th	Night	13% 4 2 3 4 3 4 4 5% 9% 49%	1885
	11th to 20th	Night	9% 5% 2 3 3 2 3 5% 5% 8% 55%	1980
	21st to end	Night	12% 5% 2 4 5% 3 4 4 5% 7% 50%	1980
October	1st to 10th	Night	10% 5% 2 5% 5% 3 4 4 5% 6% 51%	1980
	11th to 20th	Night	16% 8% 2 6% 6% 3 4 5% 4 6% 41%	2139
	21st to end	Night	19% 8% 3 5% 5% 3 4 4 4 6% 39%	2528
November	1st to 10th	Night	12% 8% 2 5% 5% 2 4 4 5% 7% 47%	2406
	11th to 20th	Night	16% 8% 4 7% 6% 2 4 4 4 8% 37%	2470
	21st to end	Night	18% 11% 5% 7% 7% 3 6% 4 5% 6% 29%	2470
December	1st to 10th	Night	19% 12% 5% 8% 6% 3 4 4 5% 7% 26%	2470
	11th to 20th	Night	17% 14% 6% 9% 4 3 5% 5% 5% 6% 27%	3042
	21st to end	Night	22% 18% 8% 9% 7% 4 4 4 4 4 16%	4852

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	63% 5% 7% 16% 8%	1518
	11th to 20th	Day	67% 4 11% 13% 5%	1563
	21st to end	Day	67% 5% 8% 14% 5% 1	1836
February	1st to 10th	Day	66% 4 10% 12% 8% 1	1692
	11th to 20th	Day	62% 4 9% 16% 7%	1758
	21st to end	Day	59% 4 10% 18% 9% 1	1480
March	1st to 10th	Day	54% 5% 10% 22% 8% 1	1806
	11th to 20th	Day	55% 5% 11% 18% 10% 1	1980
	21st to end	Day	59% 5% 11% 19% 5% 1	2178
April	1st to 10th	Day	50% 6% 12% 19% 12% 1	2132
	11th to 20th	Day	47% 5% 13% 19% 13% 3	2194
	21st to end	Day	50% 5% 11% 20% 10% 2	2340
May	1st to 10th	Day	51% 6% 12% 20% 10% 1	2340
	11th to 20th	Day	50% 6% 13% 19% 11% 1	2305
	21st to end	Day	43% 8% 15% 22% 11% 1	2531
June	1st to 10th	Day	41% 6% 11% 24% 15% 3	2416
	11th to 20th	Day	36% 8% 14% 24% 17% 1	2520
	21st to end	Day	38% 9% 14% 22% 14% 4	2520
July	1st to 10th	Day	39% 9% 14% 21% 14% 3	2451
	11th to 20th	Day	33% 7% 14% 26% 17% 2	2427
	21st to end	Day	35% 8% 15% 24% 15% 3	2405
August	1st to 10th	Day	33% 9% 14% 29% 14% 2	2314
	11th to 20th	Day	38% 8% 13% 27% 13% 1	2303
	21st to end	Day	33% 8% 12% 24% 17% 5%	2418
September	1st to 10th	Day	36% 6% 12% 23% 20% 3	2057
	11th to 20th	Day	34% 6% 11% 25% 21% 2	1980
	21st to end	Day	38% 3 10% 25% 22% 1	1980
October	1st to 10th	Day	39% 6% 10% 25% 18% 2	1980
	11th to 20th	Day	39% 5% 9% 25% 19% 2	1819
	21st to end	Day	52% 4 11% 20% 11% 2	1824
November	1st to 10th	Day	35% 4 11% 28% 19% 3	1672
	11th to 20th	Day	51% 4 10% 21% 12% 3	1710
	21st to end	Day	53% 5% 10% 21% 10% 1	1710
December	1st to 10th	Day	64% 4 10% 15% 6% 1	1710
	11th to 20th	Day	61% 5% 8% 18% 7%	2150
	21st to end	Day	76% 5% 6% 7% 5%	2805
January	1st to 10th	Night	63% 6% 7% 16% 8%	2648
	11th to 20th	Night	66% 4 9% 15% 6%	2611
	21st to end	Night	63% 4 9% 16% 8% 1	2664
February	1st to 10th	Night	62% 4 10% 15% 7% 1	2267
	11th to 20th	Night	55% 4 10% 19% 12% 1	2099
	21st to end	Night	60% 4 10% 16% 9% 2	1776
March	1st to 10th	Night	49% 5% 10% 22% 13% 1	2153
	11th to 20th	Night	47% 5% 12% 22% 12% 3	1980
	21st to end	Night	53% 5% 8% 24% 9% 1	2178
April	1st to 10th	Night	44% 7% 12% 24% 12% 1	1841
	11th to 20th	Night	44% 6% 11% 18% 18% 4	1713
	21st to end	Night	46% 5% 12% 22% 11% 3	1620
May	1st to 10th	Night	51% 7% 11% 18% 9% 3	1620
	11th to 20th	Night	44% 7% 12% 21% 13% 2	1593
	21st to end	Night	31% 8% 17% 27% 13% 4	1745
June	1st to 10th	Night	33% 7% 11% 25% 22% 2	1539
	11th to 20th	Night	31% 8% 14% 25% 17% 4	1440
	21st to end	Night	31% 9% 16% 23% 17% 4	1440
July	1st to 10th	Night	36% 8% 13% 21% 18% 5%	1400
	11th to 20th	Night	29% 8% 13% 30% 19% 2	1409
	21st to end	Night	31% 7% 14% 28% 18% 3	1672
August	1st to 10th	Night	31% 8% 14% 27% 17% 2	1600
	11th to 20th	Night	32% 8% 12% 28% 19% 1	1598
	21st to end	Night	28% 8% 15% 21% 23% 5%	1934
September	1st to 10th	Night	34% 5% 13% 24% 18% 6%	1885
	11th to 20th	Night	28% 5% 11% 28% 26% 2	1980
	21st to end	Night	34% 6% 10% 23% 25% 3	1980
October	1st to 10th	Night	33% 4 11% 26% 23% 2	1980
	11th to 20th	Night	44% 5% 7% 24% 19% 1	2139
	21st to end	Night	47% 5% 8% 23% 15% 3	2528
November	1st to 10th	Night	38% 4 10% 23% 21% 3	2406
	11th to 20th	Night	45% 5% 9% 22% 16% 3	2470
	21st to end	Night	56% 5% 10% 20% 9% 1	2470
December	1st to 10th	Night	59% 5% 10% 17% 8% 1	2470
	11th to 20th	Night	57% 7% 9% 20% 7% 1	3044
	21st to end	Night	71% 5% 8% 11% 4	4852

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	22% 18% 33% 20% 6%	270
	11th to 20th	Day	26% 16% 36% 19% 3	270
	21st to end	Day	31% 15% 31% 18% 4 1	282
February	1st to 10th	Day	32% 17% 33% 14% 4	240
	11th to 20th	Day	26% 20% 33% 15% 6%	240
	21st to end	Day	24% 15% 46% 13% 2	198
March	1st to 10th	Day	26% 17% 35% 19% 3	246
	11th to 20th	Day	25% 11% 35% 19% 7% 1	420
	21st to end	Day	31% 12% 32% 18% 7%	462
April	1st to 10th	Day	18% 15% 33% 21% 10% 3	420
	11th to 20th	Day	21% 15% 27% 22% 10% 5%	412
	21st to end	Day	25% 11% 33% 20% 9% 2	420
May	1st to 10th	Day	25% 10% 29% 24% 8% 4	423
	11th to 20th	Day	22% 6% 29% 23% 12% 7%	447
	21st to end	Day	12% 5% 26% 25% 18% 14%	485
June	1st to 10th	Day	13% 5% 24% 31% 19% 8%	526
	11th to 20th	Day	11% 6% 24% 30% 21% 8%	630
	21st to end	Day	11% 6% 25% 30% 19% 10%	630
July	1st to 10th	Day	12% 3 15% 25% 26% 19%	621
	11th to 20th	Day	9% 2 19% 29% 27% 16%	600
	21st to end	Day	11% 2 14% 26% 26% 19%	488
August	1st to 10th	Day	11% 4 10% 22% 33% 20%	446
	11th to 20th	Day	11% 3 17% 26% 31% 13%	439
	21st to end	Day	10% 4 12% 26% 32% 17%	495
September	1st to 10th	Day	12% 3 13% 27% 28% 17%	450
	11th to 20th	Day	10% 2 14% 26% 31% 18%	450
	21st to end	Day	16% 9% 20% 24% 21% 10%	450
October	1st to 10th	Day	11% 6% 24% 30% 18% 11%	450
	11th to 20th	Day	17% 14% 28% 25% 13% 2	450
	21st to end	Day	26% 13% 35% 20% 6% 1	339
November	1st to 10th	Day	14% 14% 31% 26% 10% 5%	270
	11th to 20th	Day	23% 17% 27% 18% 12% 3	270
	21st to end	Day	26% 11% 39% 21% 4	270
December	1st to 10th	Day	20% 18% 36% 18% 8% 1	270
	11th to 20th	Day	21% 14% 40% 18% 6%	270
	21st to end	Day	31% 19% 29% 18% 4	297
January	1st to 10th	Night	22% 16% 34% 22% 5% 1	950
	11th to 20th	Night	28% 14% 35% 20% 4	901
	21st to end	Night	24% 11% 37% 24% 4	820
February	1st to 10th	Night	27% 9% 35% 26% 2	720
	11th to 20th	Night	22% 15% 35% 25% 2	703
	21st to end	Night	27% 11% 36% 22% 3	592
March	1st to 10th	Night	22% 11% 33% 28% 6% 1	720
	11th to 20th	Night	18% 15% 33% 28% 6% 1	720
	21st to end	Night	27% 9% 29% 27% 8% 1	792
April	1st to 10th	Night	19% 11% 34% 29% 7% 1	581
	11th to 20th	Night	19% 10% 31% 27% 11% 1	533
	21st to end	Night	20% 6% 39% 23% 11% 1	540
May	1st to 10th	Night	22% 6% 31% 29% 10% 1	540
	11th to 20th	Night	21% 4 24% 33% 17% 1	531
	21st to end	Night	8% 2 23% 37% 27% 3	584
June	1st to 10th	Night	10% 1 22% 42% 24% 1	540
	11th to 20th	Night	11% 3 19% 40% 26% 1	540
	21st to end	Night	8% 2 22% 39% 27% 2	540
July	1st to 10th	Night	11% 1 13% 34% 34% 7%	525
	11th to 20th	Night	8% 2 12% 39% 31% 7%	522
	21st to end	Night	11% 3 9% 41% 35% 2	591
August	1st to 10th	Night	7% 1 10% 40% 36% 4	537
	11th to 20th	Night	7% 1 11% 42% 34% 5%	534
	21st to end	Night	6% 2 12% 35% 39% 6%	594
September	1st to 10th	Night	13% 6% 13% 31% 33% 5%	625
	11th to 20th	Night	10% 2 13% 33% 37% 5%	720
	21st to end	Night	14% 4 21% 33% 25% 3	720
October	1st to 10th	Night	12% 4 26% 32% 22% 5%	720
	11th to 20th	Night	20% 9% 28% 30% 12% 1	720
	21st to end	Night	24% 10% 31% 27% 8%	792
November	1st to 10th	Night	16% 8% 32% 27% 16% 1	740
	11th to 20th	Night	20% 14% 31% 27% 7% 1	760
	21st to end	Night	23% 12% 28% 29% 7% 1	760
December	1st to 10th	Night	25% 11% 33% 24% 5% 1	760
	11th to 20th	Night	25% 9% 35% 26% 5% 1	760
	21st to end	Night	29% 12% 32% 23% 4	1026

Page generated at 2024-01-24 09:37:31. Version ac07

Copyright 2024 Attilla Danko