The HomCav Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the The HomCav Observatory clear sky chart from 2005-11-06 to 2024-11-05.

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	17% 11% 4 9% 5% 5% 5% 4 6% 7% 29%	101502
	Night	18% 11% 4 9% 5% 5% 4 4 5% 6% 30%	97534
Transparency	Day	52% 7% 12% 20% 9% 1	105051
	Night	53% 6% 12% 19% 9% 1	102075
Seeing	Day	25% 16% 28% 18% 9% 3	14738
	Night	23% 14% 28% 24% 10% 1	23950

By Month

Percentage Cloud Cover NE (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	14% 20% 10% 12% 5% 4 4 3 4 5% 20%	2517
	11th to 20th	Day	14% 17% 8% 16% 8% 6% 4 3 4 4 16%	2520
	21st to end	Day	18% 19% 9% 13% 8% 5% 4 3 4 4 14%	3124
February	1st to 10th	Day	17% 15% 5% 13% 8% 5% 5% 4 5% 4 18%	1710
	11th to 20th	Day	13% 15% 6% 14% 8% 5% 5% 4 5% 5% 21%	1715
	21st to end	Day	22% 13% 4 12% 8% 4 3 4 4 5% 24%	1570
March	1st to 10th	Day	24% 16% 5% 10% 5% 4 3 2 3 4 24%	3180
	11th to 20th	Day	11% 16% 7% 11% 6% 4 4 3 4 5% 28%	3480
	21st to end	Day	19% 12% 4 11% 5% 4 4 3 4 5% 29%	3995
April	1st to 10th	Day	18% 14% 4 8% 5% 4 5% 3 4 6% 29%	2280
	11th to 20th	Day	19% 11% 4 7% 5% 4 5% 3 5% 5% 33%	2254
	21st to end	Day	19% 12% 3 8% 5% 4 3 3 5% 6% 32%	2280
May	1st to 10th	Day	25% 9% 3 7% 3 4 4 3 5% 6% 32%	4340
	11th to 20th	Day	20% 8% 3 8% 6% 5% 6% 4 6% 7% 27%	4398
	21st to end	Day	13% 7% 2 6% 4 4 5% 4 7% 9% 40%	4837
June	1st to 10th	Day	17% 7% 4 6% 5% 4 5% 4 6% 9% 33%	2660
	11th to 20th	Day	15% 7% 2 6% 6% 5% 5% 4 7% 9% 34%	2660
	21st to end	Day	14% 7% 2 7% 6% 5% 5% 5% 7% 9% 33%	2660
July	1st to 10th	Day	10% 6% 3 6% 5% 6% 6% 5% 8% 12% 34%	4440
	11th to 20th	Day	8% 6% 2 8% 6% 5% 7% 6% 8% 11% 34%	4440
	21st to end	Day	12% 6% 3 7% 5% 6% 6% 5% 7% 8% 33%	4801
August	1st to 10th	Day	20% 6% 3 8% 4 5% 5% 5% 6% 8% 30%	4104
	11th to 20th	Day	17% 6% 3 7% 5% 6% 6% 6% 8% 10% 27%	3894
	21st to end	Day	18% 6% 2 6% 4 5% 5% 4 7% 8% 36%	4180
September	1st to 10th	Day	17% 6% 3 6% 5% 4 4 4 5% 8% 38%	2280
	11th to 20th	Day	14% 6% 2 6% 4 4 5% 3 5% 7% 43%	2280
	21st to end	Day	19% 8% 3 7% 5% 4 4 5% 6% 7% 33%	2031
October	1st to 10th	Day	18% 9% 3 7% 4 5% 5% 4 6% 7% 32%	1900
	11th to 20th	Day	20% 9% 4 7% 5% 4 4 3 5% 6% 32%	1900
	21st to end	Day	22% 13% 2 9% 5% 4 5% 3 4 6% 26%	2016
November	1st to 10th	Day	14% 12% 2 8% 4 4 5% 3 5% 7% 35%	1708
	11th to 20th	Day	16% 14% 4 11% 5% 4 4 3 5% 6% 28%	1630
	21st to end	Day	19% 16% 4 9% 6% 5% 4 4 4 7% 21%	1520
December	1st to 10th	Day	20% 17% 7% 12% 5% 3 4 4 5% 6% 17%	1520
	11th to 20th	Day	22% 16% 7% 11% 4 4 3 3 4 5% 23%	1906
	21st to end	Day	24% 21% 8% 11% 5% 4 3 3 3 4 14%	2772
January	1st to 10th	Night	17% 14% 6% 16% 6% 5% 5% 4 5% 6% 17%	4429
	11th to 20th	Night	14% 15% 6% 14% 8% 6% 4 4 4 5% 18%	4438
	21st to end	Night	23% 14% 6% 14% 9% 5% 3 3 4 3 15%	4532
February	1st to 10th	Night	16% 13% 4 11% 8% 6% 6% 4 5% 6% 23%	2470
	11th to 20th	Night	14% 13% 5% 13% 8% 6% 6% 4 5% 5% 21%	2351
	21st to end	Night	19% 11% 3 13% 6% 5% 4 4 6% 6% 24%	1884
March	1st to 10th	Night	21% 13% 5% 10% 5% 4 3 3 4 5% 27%	3646
	11th to 20th	Night	14% 16% 5% 9% 6% 4 4 3 5% 6% 27%	3479
	21st to end	Night	17% 13% 3 10% 6% 5% 4 3 4 5% 31%	3636
April	1st to 10th	Night	20% 13% 4 7% 5% 4 3 3 5% 6% 30%	1900
	11th to 20th	Night	20% 11% 3 7% 5% 3 4 3 5% 6% 35%	1875
	21st to end	Night	19% 9% 3 5% 5% 4 4 3 6% 6% 36%	1900
May	1st to 10th	Night	27% 8% 2 7% 4 4 4 3 4 5% 30%	2628
	11th to 20th	Night	18% 9% 3 7% 4 4 5% 4 6% 6% 33%	2495
	21st to end	Night	12% 7% 3 7% 6% 5% 5% 5% 6% 8% 38%	2738
June	1st to 10th	Night	16% 8% 2 6% 4 3 4 4 5% 9% 39%	1520
	11th to 20th	Night	14% 7% 2 5% 5% 4 4 5% 6% 9% 39%	1520
	21st to end	Night	12% 4 2 6% 5% 5% 6% 3 6% 9% 42%	1520
July	1st to 10th	Night	9% 7% 3 9% 4 5% 5% 4 7% 8% 40%	2520
	11th to 20th	Night	11% 6% 2 5% 5% 5% 5% 4 6% 10% 42%	2520
	21st to end	Night	14% 7% 2 7% 5% 5% 4 4 6% 7% 40%	2739
August	1st to 10th	Night	19% 6% 3 7% 4 5% 5% 3 6% 6% 35%	2822
	11th to 20th	Night	17% 8% 2 6% 5% 5% 3 4 4 6% 40%	2903
	21st to end	Night	14% 6% 2 6% 4 5% 4 4 5% 9% 42%	3476
September	1st to 10th	Night	14% 7% 2 5% 4 4 4 4 5% 7% 43%	1900
	11th to 20th	Night	13% 5% 2 5% 4 4 4 3 5% 6% 49%	1900
	21st to end	Night	18% 6% 2 6% 5% 4 5% 4 5% 8% 37%	2146
October	1st to 10th	Night	18% 8% 3 9% 4 5% 4 4 5% 6% 35%	2280
	11th to 20th	Night	20% 8% 3 7% 4 4 4 3 5% 6% 36%	2280
	21st to end	Night	23% 12% 3 8% 5% 4 3 2 5% 6% 27%	2579
November	1st to 10th	Night	13% 10% 4 9% 5% 4 4 4 5% 6% 37%	2470
	11th to 20th	Night	20% 10% 3 8% 5% 4 5% 4 5% 6% 30%	2546
	21st to end	Night	15% 14% 5% 7% 6% 5% 5% 5% 7% 7% 25%	2660
December	1st to 10th	Night	20% 14% 6% 11% 6% 5% 4 4 5% 6% 19%	2660
	11th to 20th	Night	20% 14% 5% 12% 5% 5% 5% 4 4 5% 20%	3288
	21st to end	Night	27% 15% 6% 9% 4 4 4 3 5% 5% 17%	4884

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	68% 4 10% 14% 4	2518
	11th to 20th	Day	71% 5% 9% 10% 5% 1	2520
	21st to end	Day	72% 5% 10% 9% 3	3124
February	1st to 10th	Day	67% 6% 10% 13% 5%	1710
	11th to 20th	Day	64% 6% 7% 17% 6%	1724
	21st to end	Day	63% 4 10% 16% 6% 1	1570
March	1st to 10th	Day	65% 4 9% 16% 6% 1	3183
	11th to 20th	Day	56% 5% 13% 16% 8% 1	3480
	21st to end	Day	57% 4 8% 18% 12% 1	3995
April	1st to 10th	Day	55% 5% 8% 21% 9% 2	2280
	11th to 20th	Day	53% 5% 10% 17% 13% 2	2254
	21st to end	Day	52% 5% 9% 18% 13% 3	2280
May	1st to 10th	Day	53% 5% 10% 19% 11% 2	4354
	11th to 20th	Day	53% 8% 11% 20% 7% 1	4402
	21st to end	Day	38% 8% 14% 24% 15% 1	4837
June	1st to 10th	Day	47% 8% 12% 20% 14% 1	2660
	11th to 20th	Day	44% 8% 14% 23% 10% 1	2660
	21st to end	Day	44% 9% 14% 22% 11% 1	2660
July	1st to 10th	Day	39% 9% 17% 25% 10% 1	4370
	11th to 20th	Day	38% 10% 15% 26% 10%	4365
	21st to end	Day	45% 8% 14% 20% 11% 1	4648
August	1st to 10th	Day	51% 8% 13% 18% 10%	4091
	11th to 20th	Day	48% 10% 15% 21% 6%	3933
	21st to end	Day	44% 7% 11% 31% 7% 1	4180
September	1st to 10th	Day	44% 6% 11% 25% 13% 1	2280
	11th to 20th	Day	41% 6% 11% 23% 19% 1	2280
	21st to end	Day	49% 7% 11% 21% 11% 1	2031
October	1st to 10th	Day	46% 7% 10% 23% 13% 1	3160
	11th to 20th	Day	46% 5% 11% 22% 15% 1	3140
	21st to end	Day	42% 5% 16% 25% 10% 1	3306
November	1st to 10th	Day	47% 6% 13% 20% 12% 1	1708
	11th to 20th	Day	56% 4 12% 17% 8% 2	1630
	21st to end	Day	61% 6% 13% 15% 5%	1520
December	1st to 10th	Day	67% 6% 11% 12% 4	1520
	11th to 20th	Day	66% 6% 13% 11% 4	1906
	21st to end	Day	75% 4 7% 11% 3	2772
January	1st to 10th	Night	67% 6% 13% 10% 4	4429
	11th to 20th	Night	66% 6% 10% 13% 4	4438
	21st to end	Night	74% 4 7% 11% 4	4532
February	1st to 10th	Night	61% 6% 12% 14% 7%	2470
	11th to 20th	Night	65% 5% 9% 13% 6% 1	2353
	21st to end	Night	59% 6% 11% 15% 8% 1	1884
March	1st to 10th	Night	60% 5% 10% 17% 8%	3656
	11th to 20th	Night	57% 5% 13% 19% 6%	3480
	21st to end	Night	56% 4 8% 20% 10% 2	3636
April	1st to 10th	Night	55% 5% 10% 19% 10% 2	1900
	11th to 20th	Night	50% 6% 11% 18% 15%	1875
	21st to end	Night	47% 6% 11% 19% 13% 3	1900
May	1st to 10th	Night	55% 6% 8% 19% 9% 2	2634
	11th to 20th	Night	47% 10% 15% 18% 9% 1	2496
	21st to end	Night	41% 10% 13% 19% 15% 2	2739
June	1st to 10th	Night	41% 7% 12% 25% 15%	1520
	11th to 20th	Night	40% 8% 15% 24% 11% 2	1520
	21st to end	Night	38% 9% 14% 26% 13% 1	1520
July	1st to 10th	Night	41% 7% 15% 21% 15% 1	2480
	11th to 20th	Night	37% 7% 16% 26% 14%	2472
	21st to end	Night	42% 8% 12% 22% 16% 1	2651
August	1st to 10th	Night	48% 8% 14% 22% 8%	2812
	11th to 20th	Night	44% 7% 14% 25% 9%	2930
	21st to end	Night	39% 7% 11% 32% 11% 1	3476
September	1st to 10th	Night	40% 7% 13% 23% 15% 1	1900
	11th to 20th	Night	35% 7% 11% 28% 18% 1	1900
	21st to end	Night	45% 7% 11% 22% 14% 1	2146
October	1st to 10th	Night	51% 7% 9% 22% 10% 1	3800
	11th to 20th	Night	42% 6% 13% 21% 14% 3	3779
	21st to end	Night	43% 5% 15% 27% 9% 1	4239
November	1st to 10th	Night	47% 7% 12% 19% 14% 2	2470
	11th to 20th	Night	53% 5% 12% 18% 9% 2	2546
	21st to end	Night	55% 8% 15% 18% 5%	2660
December	1st to 10th	Night	64% 7% 12% 13% 3	2660
	11th to 20th	Night	64% 6% 11% 14% 5%	3288
	21st to end	Night	69% 6% 11% 13% 2	4884

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	30% 22% 32% 12% 3 1	180
	11th to 20th	Day	38% 24% 28% 7% 2 1	180
	21st to end	Day	26% 30% 30% 10% 4	297
February	1st to 10th	Day	31% 29% 31% 8% 1	270
	11th to 20th	Day	35% 32% 27% 6% 1	322
	21st to end	Day	38% 22% 28% 10% 2	382
March	1st to 10th	Day	34% 20% 30% 11% 4 1	460
	11th to 20th	Day	34% 23% 27% 12% 4	460
	21st to end	Day	32% 26% 26% 10% 3 2	506
April	1st to 10th	Day	36% 19% 26% 14% 5% 1	460
	11th to 20th	Day	29% 25% 26% 10% 6% 3	452
	21st to end	Day	33% 17% 28% 15% 5% 2	460
May	1st to 10th	Day	31% 18% 29% 13% 7% 4	463
	11th to 20th	Day	23% 16% 30% 18% 9% 3	487
	21st to end	Day	18% 12% 30% 23% 13% 4	529
June	1st to 10th	Day	20% 16% 30% 20% 10% 3	490
	11th to 20th	Day	19% 12% 26% 26% 14% 2	490
	21st to end	Day	19% 11% 36% 23% 8% 3	490
July	1st to 10th	Day	14% 8% 30% 26% 17% 6%	485
	11th to 20th	Day	12% 8% 27% 31% 17% 5%	484
	21st to end	Day	14% 7% 34% 28% 13% 3	532
August	1st to 10th	Day	15% 9% 26% 24% 20% 7%	486
	11th to 20th	Day	18% 9% 23% 27% 16% 7%	479
	21st to end	Day	14% 12% 25% 24% 14% 10%	539
September	1st to 10th	Day	20% 11% 24% 21% 17% 7%	490
	11th to 20th	Day	16% 9% 22% 23% 20% 11%	490
	21st to end	Day	23% 12% 27% 20% 12% 5%	490
October	1st to 10th	Day	23% 13% 25% 18% 14% 6%	490
	11th to 20th	Day	24% 17% 30% 20% 7% 2	490
	21st to end	Day	32% 16% 28% 18% 5%	499
November	1st to 10th	Day	25% 18% 24% 21% 10% 2	378
	11th to 20th	Day	33% 19% 26% 15% 7%	290
	21st to end	Day	33% 24% 31% 8% 3	180
December	1st to 10th	Day	36% 21% 28% 12% 3 1	180
	11th to 20th	Day	39% 21% 26% 12% 2	180
	21st to end	Day	39% 19% 31% 9% 2	198
January	1st to 10th	Night	25% 24% 33% 15% 2	760
	11th to 20th	Night	28% 19% 30% 20% 4	760
	21st to end	Night	22% 22% 36% 17% 3	836
February	1st to 10th	Night	27% 19% 34% 19% 1	760
	11th to 20th	Night	27% 23% 33% 16% 1	743
	21st to end	Night	32% 19% 30% 16% 3	628
March	1st to 10th	Night	26% 21% 30% 20% 3	760
	11th to 20th	Night	27% 20% 31% 17% 5%	760
	21st to end	Night	25% 21% 30% 17% 7%	836
April	1st to 10th	Night	29% 18% 30% 19% 3	760
	11th to 20th	Night	27% 17% 29% 19% 7%	751
	21st to end	Night	25% 14% 29% 25% 6%	760
May	1st to 10th	Night	27% 9% 25% 29% 9%	455
	11th to 20th	Night	18% 10% 33% 29% 9% 1	374
	21st to end	Night	14% 8% 27% 36% 15%	411
June	1st to 10th	Night	17% 9% 28% 34% 12% 1	380
	11th to 20th	Night	18% 6% 25% 35% 16% 1	380
	21st to end	Night	12% 7% 27% 42% 12% 1	380
July	1st to 10th	Night	9% 5% 21% 43% 20% 2	370
	11th to 20th	Night	11% 4 22% 41% 22% 1	368
	21st to end	Night	13% 5% 19% 44% 18% 2	416
August	1st to 10th	Night	12% 4 23% 35% 25% 2	564
	11th to 20th	Night	15% 5% 17% 32% 28% 4	630
	21st to end	Night	16% 4 18% 34% 26% 2	836
September	1st to 10th	Night	18% 6% 24% 31% 19% 2	760
	11th to 20th	Night	15% 7% 20% 29% 25% 4	760
	21st to end	Night	20% 11% 24% 26% 17% 2	760
October	1st to 10th	Night	22% 11% 24% 24% 16% 2	760
	11th to 20th	Night	25% 12% 26% 28% 7% 1	760
	21st to end	Night	31% 13% 27% 22% 5%	836
November	1st to 10th	Night	20% 15% 30% 27% 8% 1	760
	11th to 20th	Night	27% 15% 31% 20% 6% 1	760
	21st to end	Night	24% 18% 32% 21% 5%	760
December	1st to 10th	Night	29% 22% 28% 18% 3	760
	11th to 20th	Night	28% 22% 31% 17% 3	760
	21st to end	Night	31% 20% 30% 17% 2	836

Page generated at 2024-11-03 02:11:22. Version ac07

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