Blackhawk Ranch
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Blackhawk Ranch clear sky chart from 2005-11-06 to 2024-11-28.

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	3 4 2 4 3 3 4 4 6% 8% 57%	105213
	Night	4 5% 2 4 3 3 3 3 5% 7% 60%	103017
Transparency	Day	21% 7% 11% 21% 25% 14%	104962
	Night	21% 7% 11% 22% 26% 14%	102858
Seeing	Day	6% 10% 30% 31% 18% 5%	15474
	Night	6% 7% 36% 36% 13% 1	25524

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	1 5% 3 5% 2 2 3 2 5% 8% 63%	2538
	11th to 20th	Day	1 3 2 3 3 3 5% 3 5% 7% 66%	2744
	21st to end	Day	3 7% 2 5% 2 3 3 3 5% 7% 59%	3146
February	1st to 10th	Day	1 5% 3 5% 3 3 3 3 4 7% 63%	1780
	11th to 20th	Day	1 4 2 4 3 2 4 3 6% 8% 63%	1849
	21st to end	Day	1 5% 3 5% 3 4 3 3 5% 7% 62%	1570
March	1st to 10th	Day	1 6% 3 3 2 2 2 3 5% 6% 67%	3130
	11th to 20th	Day	5% 12% 3 6% 4 3 3 3 4 7% 51%	3422
	21st to end	Day	3 7% 2 4 3 3 4 3 6% 7% 59%	4086
April	1st to 10th	Day	3 5% 2 4 3 3 3 4 6% 8% 59%	2280
	11th to 20th	Day	5% 7% 2 5% 3 3 4 4 6% 7% 55%	2251
	21st to end	Day	6% 7% 2 5% 3 3 4 3 6% 9% 53%	2280
May	1st to 10th	Day	6% 6% 2 4 3 3 4 3 5% 6% 59%	3914
	11th to 20th	Day	6% 5% 2 5% 3 4 5% 4 8% 7% 50%	4140
	21st to end	Day	3 2 1 2 3 3 4 5% 7% 9% 61%	4825
June	1st to 10th	Day	4 3 1 4 4 4 5% 6% 9% 10% 50%	2660
	11th to 20th	Day	3 2 1 3 2 3 5% 5% 8% 9% 58%	2660
	21st to end	Day	5% 3 2 4 4 5% 6% 5% 9% 10% 48%	2660
July	1st to 10th	Day	3 2 1 4 4 5% 6% 6% 8% 10% 51%	4430
	11th to 20th	Day	2 3 1 4 4 6% 7% 6% 10% 11% 46%	4430
	21st to end	Day	5% 3 1 5% 5% 5% 5% 5% 8% 9% 47%	4559
August	1st to 10th	Day	6% 4 1 5% 4 6% 6% 6% 10% 12% 40%	3921
	11th to 20th	Day	3 2 1 4 4 5% 6% 5% 9% 11% 49%	3726
	21st to end	Day	3 3 2 5% 4 5% 6% 6% 9% 11% 46%	4180
September	1st to 10th	Day	5% 4 1 5% 3 4 5% 4 7% 8% 54%	2280
	11th to 20th	Day	5% 3 1 3 3 3 4 4 6% 7% 60%	2235
	21st to end	Day	5% 3 1 5% 3 3 4 3 3 6% 65%	2090
October	1st to 10th	Day	3 3 1 2 2 2 3 2 4 5% 73%	3273
	11th to 20th	Day	3 3 1 3 3 2 3 4 6% 8% 65%	3150
	21st to end	Day	3 3 1 3 2 2 1 2 3 4 76%	3378
November	1st to 10th	Day	2 4 1 2 2 2 2 3 5% 6% 72%	1763
	11th to 20th	Day	1 4 1 4 3 2 2 3 4 6% 69%	1800
	21st to end	Day	3 6% 2 4 2 2 3 2 5% 6% 65%	1773
December	1st to 10th	Day	1 4 2 5% 2 2 2 3 5% 7% 67%	1570
	11th to 20th	Day	1 4 1 4 3 2 4 3 6% 8% 62%	1926
	21st to end	Day	1 6% 3 5% 3 3 3 3 5% 8% 60%	2794
January	1st to 10th	Night	1 8% 4 6% 3 3 3 3 5% 7% 57%	4417
	11th to 20th	Night	1 4 1 4 3 2 3 3 4 6% 69%	4242
	21st to end	Night	2 6% 2 5% 3 3 3 3 5% 7% 61%	4521
February	1st to 10th	Night	1 6% 2 6% 4 2 3 3 4 7% 62%	2398
	11th to 20th	Night	2 6% 3 5% 4 3 3 3 5% 7% 60%	2218
	21st to end	Night	1 6% 3 4 2 2 3 2 4 6% 67%	1884
March	1st to 10th	Night	3 7% 2 3 2 3 2 2 3 5% 68%	3734
	11th to 20th	Night	8% 10% 2 5% 3 2 3 3 5% 6% 53%	3552
	21st to end	Night	3 7% 2 5% 3 3 3 3 5% 6% 60%	3556
April	1st to 10th	Night	3 4 1 3 2 3 3 3 5% 7% 66%	1900
	11th to 20th	Night	6% 6% 3 4 2 3 3 2 5% 7% 60%	1877
	21st to end	Night	8% 7% 2 3 3 3 3 3 5% 6% 57%	1900
May	1st to 10th	Night	8% 6% 2 3 2 2 2 2 4 5% 64%	3054
	11th to 20th	Night	11% 5% 2 5% 3 3 3 4 6% 8% 51%	2749
	21st to end	Night	5% 3 2 3 3 3 4 2 5% 7% 65%	2762
June	1st to 10th	Night	4 3 1 3 3 3 3 5% 7% 10% 58%	1520
	11th to 20th	Night	3 2 1 2 3 3 3 3 8% 9% 63%	1520
	21st to end	Night	6% 4 2 5% 3 4 5% 5% 8% 10% 49%	1520
July	1st to 10th	Night	8% 3 2 5% 4 5% 5% 5% 7% 9% 47%	2540
	11th to 20th	Night	3 2 1 5% 4 5% 5% 6% 9% 12% 47%	2540
	21st to end	Night	5% 4 2 4 4 5% 6% 6% 8% 10% 47%	3000
August	1st to 10th	Night	5% 5% 3 8% 6% 7% 7% 5% 8% 11% 35%	3017
	11th to 20th	Night	4 3 2 4 3 4 6% 6% 9% 15% 45%	3113
	21st to end	Night	3 3 2 5% 5% 5% 6% 7% 10% 12% 43%	3487
September	1st to 10th	Night	5% 4 1 3 3 4 4 4 8% 9% 55%	1900
	11th to 20th	Night	5% 3 1 3 2 2 3 3 5% 8% 65%	1943
	21st to end	Night	6% 4 1 2 3 3 3 3 5% 5% 66%	2090
October	1st to 10th	Night	4 3 1 2 2 2 2 2 3 5% 73%	3690
	11th to 20th	Night	5% 3 1 3 3 2 3 3 4 6% 66%	3778
	21st to end	Night	3 4 2 3 2 2 2 2 3 4 75%	4147
November	1st to 10th	Night	3 3 1 3 2 1 2 3 4 5% 72%	2535
	11th to 20th	Night	1 3 2 4 1 2 2 2 3 5% 75%	2600
	21st to end	Night	3 6% 2 3 2 2 2 3 5% 7% 66%	2562
December	1st to 10th	Night	1 4 2 4 3 3 3 3 6% 8% 63%	2607
	11th to 20th	Night	1 4 1 4 3 3 3 3 5% 7% 64%	3271
	21st to end	Night	2 5% 2 5% 3 3 4 4 6% 7% 59%	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	17% 7% 10% 29% 31% 7%	2539
	11th to 20th	Day	15% 7% 9% 26% 35% 7%	2744
	21st to end	Day	22% 5% 11% 26% 29% 7%	3146
February	1st to 10th	Day	22% 4 9% 27% 25% 14%	1780
	11th to 20th	Day	18% 5% 8% 24% 31% 13%	1859
	21st to end	Day	21% 4 7% 19% 28% 21%	1570
March	1st to 10th	Day	17% 5% 7% 16% 37% 18%	3130
	11th to 20th	Day	29% 9% 9% 21% 26% 6%	3422
	21st to end	Day	21% 6% 9% 26% 30% 8%	4086
April	1st to 10th	Day	20% 6% 10% 23% 24% 17%	2280
	11th to 20th	Day	25% 6% 10% 22% 21% 16%	2254
	21st to end	Day	25% 7% 12% 21% 27% 9%	2280
May	1st to 10th	Day	22% 7% 12% 19% 23% 18%	3914
	11th to 20th	Day	26% 10% 15% 18% 18% 13%	4144
	21st to end	Day	13% 9% 14% 19% 19% 25%	4825
June	1st to 10th	Day	22% 10% 16% 21% 19% 12%	2660
	11th to 20th	Day	16% 8% 12% 16% 23% 24%	2660
	21st to end	Day	25% 9% 13% 20% 19% 15%	2660
July	1st to 10th	Day	21% 10% 12% 19% 23% 14%	4361
	11th to 20th	Day	22% 10% 15% 26% 20% 7%	4355
	21st to end	Day	26% 10% 13% 21% 20% 10%	4415
August	1st to 10th	Day	28% 13% 21% 21% 12% 5%	3907
	11th to 20th	Day	22% 11% 16% 19% 17% 15%	3762
	21st to end	Day	25% 10% 16% 25% 19% 6%	4179
September	1st to 10th	Day	25% 6% 11% 25% 21% 13%	2280
	11th to 20th	Day	20% 7% 10% 17% 25% 20%	2235
	21st to end	Day	20% 5% 7% 18% 33% 17%	2090
October	1st to 10th	Day	12% 4 7% 15% 35% 26%	3273
	11th to 20th	Day	16% 5% 8% 24% 31% 16%	3150
	21st to end	Day	14% 3 4 15% 40% 24%	3378
November	1st to 10th	Day	13% 3 7% 21% 33% 23%	1763
	11th to 20th	Day	16% 5% 7% 25% 32% 17%	1800
	21st to end	Day	20% 3 5% 18% 33% 21%	1773
December	1st to 10th	Day	17% 4 11% 26% 29% 13%	1570
	11th to 20th	Day	18% 6% 10% 21% 31% 14%	1924
	21st to end	Day	21% 7% 9% 21% 25% 17%	2794
January	1st to 10th	Night	23% 6% 8% 24% 30% 8%	4417
	11th to 20th	Night	16% 7% 8% 29% 31% 10%	4242
	21st to end	Night	19% 8% 11% 28% 28% 6%	4521
February	1st to 10th	Night	23% 4 8% 27% 25% 14%	2398
	11th to 20th	Night	23% 4 10% 26% 25% 13%	2218
	21st to end	Night	19% 3 6% 19% 36% 18%	1884
March	1st to 10th	Night	19% 4 6% 14% 37% 20%	3734
	11th to 20th	Night	29% 8% 11% 19% 25% 8%	3552
	21st to end	Night	21% 7% 9% 28% 29% 7%	3556
April	1st to 10th	Night	17% 4 11% 24% 28% 15%	1900
	11th to 20th	Night	23% 5% 12% 23% 23% 14%	1877
	21st to end	Night	26% 7% 13% 22% 22% 10%	1900
May	1st to 10th	Night	22% 6% 10% 17% 22% 24%	3054
	11th to 20th	Night	28% 9% 12% 25% 15% 11%	2750
	21st to end	Night	14% 10% 13% 18% 21% 24%	2762
June	1st to 10th	Night	20% 9% 14% 23% 16% 17%	1520
	11th to 20th	Night	15% 8% 11% 19% 23% 25%	1520
	21st to end	Night	26% 9% 12% 18% 20% 14%	1520
July	1st to 10th	Night	29% 10% 16% 16% 14% 16%	2500
	11th to 20th	Night	24% 9% 20% 29% 13% 4	2492
	21st to end	Night	26% 10% 15% 21% 20% 7%	2906
August	1st to 10th	Night	40% 11% 18% 16% 10% 5%	3008
	11th to 20th	Night	24% 10% 22% 21% 15% 8%	3143
	21st to end	Night	27% 10% 18% 25% 15% 5%	3487
September	1st to 10th	Night	22% 7% 12% 25% 23% 11%	1900
	11th to 20th	Night	17% 6% 10% 19% 26% 21%	1943
	21st to end	Night	18% 6% 9% 18% 32% 16%	2090
October	1st to 10th	Night	14% 4 8% 17% 35% 22%	3690
	11th to 20th	Night	18% 4 9% 22% 31% 16%	3778
	21st to end	Night	15% 4 5% 18% 36% 22%	4147
November	1st to 10th	Night	15% 3 8% 22% 32% 22%	2535
	11th to 20th	Night	14% 2 5% 26% 35% 18%	2600
	21st to end	Night	19% 4 6% 21% 31% 20%	2562
December	1st to 10th	Night	18% 5% 11% 27% 27% 11%	2607
	11th to 20th	Night	18% 5% 8% 21% 36% 12%	3272
	21st to end	Night	19% 8% 11% 21% 28% 13%	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	7% 13% 36% 30% 11% 3	270
	11th to 20th	Day	9% 12% 41% 30% 6% 2	270
	21st to end	Day	6% 9% 39% 30% 13% 3	297
February	1st to 10th	Day	4 18% 50% 21% 6% 1	270
	11th to 20th	Day	6% 13% 49% 24% 7%	270
	21st to end	Day	10% 21% 40% 28% 2	225
March	1st to 10th	Day	4 20% 37% 27% 11%	270
	11th to 20th	Day	10% 18% 33% 28% 10% 1	418
	21st to end	Day	12% 25% 36% 21% 6%	506
April	1st to 10th	Day	7% 22% 40% 24% 6% 2	460
	11th to 20th	Day	11% 21% 42% 19% 4 2	452
	21st to end	Day	11% 22% 38% 23% 5% 1	460
May	1st to 10th	Day	11% 14% 41% 25% 8% 1	525
	11th to 20th	Day	9% 10% 32% 29% 17% 3	675
	21st to end	Day	6% 11% 33% 32% 14% 4	734
June	1st to 10th	Day	5% 9% 25% 33% 23% 6%	680
	11th to 20th	Day	4 6% 31% 36% 19% 4	680
	21st to end	Day	5% 5% 28% 33% 23% 5%	680
July	1st to 10th	Day	5% 3 18% 33% 33% 7%	671
	11th to 20th	Day	3 1 10% 35% 36% 13%	668
	21st to end	Day	5% 2 10% 31% 37% 16%	597
August	1st to 10th	Day	5% 2 18% 38% 27% 10%	487
	11th to 20th	Day	4 3 21% 33% 31% 8%	477
	21st to end	Day	5% 3 18% 42% 27% 6%	539
September	1st to 10th	Day	5% 2 19% 40% 25% 9%	490
	11th to 20th	Day	6% 2 25% 37% 24% 5%	445
	21st to end	Day	8% 5% 23% 30% 27% 7%	300
October	1st to 10th	Day	7% 11% 25% 25% 24% 8%	300
	11th to 20th	Day	3 12% 31% 32% 17% 6%	300
	21st to end	Day	8% 11% 30% 31% 18% 2	330
November	1st to 10th	Day	6% 13% 34% 28% 17% 2	300
	11th to 20th	Day	5% 10% 34% 33% 13% 4	300
	21st to end	Day	8% 10% 34% 30% 14% 3	291
December	1st to 10th	Day	4 14% 41% 25% 14% 2	270
	11th to 20th	Day	6% 10% 42% 34% 6% 2	270
	21st to end	Day	8% 16% 45% 24% 6% 1	297
January	1st to 10th	Night	4 10% 42% 33% 10% 2	950
	11th to 20th	Night	6% 10% 43% 30% 9% 2	840
	21st to end	Night	5% 8% 44% 33% 10% 1	836
February	1st to 10th	Night	4 10% 49% 31% 6%	760
	11th to 20th	Night	5% 13% 51% 25% 6%	744
	21st to end	Night	5% 14% 51% 27% 3	628
March	1st to 10th	Night	6% 12% 48% 28% 6% 1	760
	11th to 20th	Night	7% 9% 38% 37% 7% 1	760
	21st to end	Night	8% 13% 47% 28% 4 1	680
April	1st to 10th	Night	5% 11% 55% 26% 3	570
	11th to 20th	Night	10% 12% 40% 33% 5%	563
	21st to end	Night	12% 9% 40% 32% 6%	570
May	1st to 10th	Night	9% 6% 41% 35% 8% 1	570
	11th to 20th	Night	13% 5% 31% 35% 14% 1	561
	21st to end	Night	9% 7% 39% 34% 11% 1	617
June	1st to 10th	Night	5% 5% 34% 37% 19% 1	570
	11th to 20th	Night	3 4 38% 44% 10% 1	570
	21st to end	Night	5% 5% 26% 41% 21% 1	570
July	1st to 10th	Night	6% 3 20% 41% 28% 2	555
	11th to 20th	Night	5% 1 14% 45% 33% 2	552
	21st to end	Night	5% 2 11% 37% 42% 3	624
August	1st to 10th	Night	6% 2 11% 42% 35% 4	567
	11th to 20th	Night	8% 1 13% 48% 28% 2	564
	21st to end	Night	4 1 16% 47% 27% 4	627
September	1st to 10th	Night	6% 3 16% 48% 24% 3	570
	11th to 20th	Night	7% 2 25% 48% 15% 3	570
	21st to end	Night	7% 5% 26% 42% 17% 3	570
October	1st to 10th	Night	8% 3 34% 39% 14% 2	689
	11th to 20th	Night	3 5% 35% 40% 16% 3	760
	21st to end	Night	7% 6% 33% 36% 15% 3	851
November	1st to 10th	Night	5% 7% 35% 40% 12% 1	975
	11th to 20th	Night	3 8% 38% 39% 10% 1	1000
	21st to end	Night	5% 10% 34% 38% 12% 1	986
December	1st to 10th	Night	2 9% 45% 33% 9% 1	950
	11th to 20th	Night	4 11% 44% 34% 7% 1	950
	21st to end	Night	6% 12% 44% 33% 5% 1	1045

Page generated at 2024-11-24 22:22:19. Version ac07

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