Heartwood Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Heartwood 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	15% 9% 3 7% 5% 4 5% 4 6% 7% 35%	101533
	Night	16% 9% 3 7% 5% 4 4 4 5% 7% 35%	97488
Transparency	Day	46% 7% 13% 22% 11% 1	105105
	Night	47% 7% 13% 21% 11% 1	102004
Seeing	Day	20% 15% 31% 21% 10% 3	14483
	Night	20% 12% 30% 26% 10% 1	23714

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	16% 16% 4 9% 5% 4 3 3 4 6% 31%	2517
	11th to 20th	Day	12% 18% 6% 12% 7% 6% 4 3 5% 4 21%	2529
	21st to end	Day	19% 20% 6% 11% 6% 5% 4 3 4 4 19%	3124
February	1st to 10th	Day	13% 16% 4 11% 7% 5% 5% 4 6% 5% 24%	1710
	11th to 20th	Day	12% 14% 5% 12% 7% 6% 4 3 5% 5% 28%	1663
	21st to end	Day	19% 13% 4 10% 6% 6% 4 4 4 6% 27%	1508
March	1st to 10th	Day	21% 12% 4 7% 5% 4 3 3 4 6% 31%	3308
	11th to 20th	Day	10% 15% 4 9% 6% 5% 5% 3 5% 6% 32%	3480
	21st to end	Day	14% 8% 2 6% 4 3 4 3 5% 6% 45%	3896
April	1st to 10th	Day	19% 12% 3 7% 6% 4 3 3 5% 5% 32%	2280
	11th to 20th	Day	21% 8% 3 6% 4 4 4 2 4 6% 38%	2254
	21st to end	Day	20% 9% 3 8% 6% 4 5% 3 5% 6% 33%	2441
May	1st to 10th	Day	18% 9% 3 7% 4 5% 4 4 5% 6% 34%	4296
	11th to 20th	Day	15% 9% 3 8% 4 5% 5% 4 5% 8% 33%	4398
	21st to end	Day	12% 5% 2 6% 5% 4 5% 4 6% 9% 43%	4837
June	1st to 10th	Day	17% 8% 2 7% 4 5% 5% 5% 7% 8% 33%	2660
	11th to 20th	Day	12% 6% 2 5% 5% 5% 5% 5% 7% 10% 39%	2660
	21st to end	Day	15% 8% 3 6% 4 4 4 5% 7% 8% 37%	2660
July	1st to 10th	Day	10% 5% 2 6% 5% 5% 5% 5% 6% 10% 41%	4440
	11th to 20th	Day	11% 4 2 5% 4 4 5% 4 7% 10% 45%	4440
	21st to end	Day	7% 5% 2 6% 5% 5% 6% 5% 8% 9% 42%	4767
August	1st to 10th	Day	15% 7% 3 6% 4 4 5% 4 5% 8% 38%	4104
	11th to 20th	Day	13% 7% 3 6% 4 4 5% 4 7% 9% 38%	4044
	21st to end	Day	10% 5% 2 6% 4 4 5% 5% 7% 9% 42%	4226
September	1st to 10th	Day	12% 6% 3 5% 4 4 4 4 6% 8% 44%	2280
	11th to 20th	Day	11% 4 2 5% 4 4 4 3 6% 8% 50%	2280
	21st to end	Day	15% 7% 2 7% 4 4 4 4 5% 7% 41%	1987
October	1st to 10th	Day	17% 8% 3 8% 4 4 6% 4 5% 7% 35%	1900
	11th to 20th	Day	19% 9% 3 7% 5% 5% 5% 4 6% 6% 32%	1900
	21st to end	Day	23% 10% 3 8% 5% 5% 4 4 5% 6% 27%	2053
November	1st to 10th	Day	14% 9% 3 8% 5% 5% 5% 3 6% 7% 35%	1653
	11th to 20th	Day	15% 11% 3 9% 5% 4 4 5% 6% 6% 32%	1520
	21st to end	Day	20% 12% 4 8% 6% 4 5% 4 6% 6% 26%	1520
December	1st to 10th	Day	18% 16% 5% 10% 6% 5% 4 4 4 6% 23%	1520
	11th to 20th	Day	18% 15% 4 8% 4 5% 4 3 5% 5% 28%	1906
	21st to end	Day	29% 14% 3 8% 5% 4 4 3 4 5% 20%	2772
January	1st to 10th	Night	18% 14% 6% 9% 5% 5% 5% 3 5% 5% 24%	4429
	11th to 20th	Night	15% 12% 5% 11% 8% 7% 6% 4 5% 5% 22%	4427
	21st to end	Night	20% 14% 6% 10% 5% 5% 4 3 4 5% 23%	4532
February	1st to 10th	Night	14% 15% 4 10% 6% 5% 5% 4 5% 5% 26%	2470
	11th to 20th	Night	14% 13% 5% 9% 5% 5% 5% 4 6% 6% 28%	2403
	21st to end	Night	16% 10% 4 8% 5% 4 5% 4 6% 7% 31%	1945
March	1st to 10th	Night	19% 10% 3 8% 5% 5% 4 3 5% 5% 31%	3515
	11th to 20th	Night	15% 13% 3 9% 5% 5% 4 4 6% 6% 30%	3479
	21st to end	Night	16% 8% 2 5% 3 3 3 3 5% 6% 45%	3735
April	1st to 10th	Night	19% 10% 3 7% 4 4 4 3 5% 6% 35%	1900
	11th to 20th	Night	18% 8% 2 8% 4 4 4 3 5% 6% 37%	1875
	21st to end	Night	19% 7% 2 7% 4 4 4 4 6% 6% 35%	1757
May	1st to 10th	Night	20% 9% 3 6% 4 5% 5% 4 5% 6% 35%	2643
	11th to 20th	Night	15% 8% 3 7% 4 4 4 4 6% 8% 37%	2495
	21st to end	Night	10% 6% 2 5% 4 4 4 4 6% 7% 47%	2738
June	1st to 10th	Night	13% 6% 2 7% 5% 5% 5% 3 6% 8% 38%	1520
	11th to 20th	Night	10% 5% 2 7% 5% 4 4 5% 6% 8% 43%	1520
	21st to end	Night	12% 8% 3 7% 5% 4 4 4 6% 6% 42%	1520
July	1st to 10th	Night	8% 5% 2 7% 5% 5% 6% 4 7% 8% 44%	2520
	11th to 20th	Night	11% 6% 3 4 4 4 4 4 5% 7% 49%	2520
	21st to end	Night	9% 5% 1 5% 4 4 4 4 6% 8% 50%	2770
August	1st to 10th	Night	10% 6% 2 6% 4 4 4 3 6% 8% 46%	2825
	11th to 20th	Night	12% 6% 2 5% 3 3 4 4 5% 8% 46%	2785
	21st to end	Night	8% 4 2 5% 4 4 5% 5% 7% 10% 47%	3398
September	1st to 10th	Night	11% 6% 2 6% 4 4 4 4 6% 8% 46%	1900
	11th to 20th	Night	11% 4 1 5% 3 3 4 3 5% 7% 53%	1900
	21st to end	Night	16% 6% 2 6% 4 4 4 3 4 6% 43%	2190
October	1st to 10th	Night	16% 6% 3 7% 4 4 4 4 6% 7% 38%	2280
	11th to 20th	Night	20% 8% 3 8% 5% 5% 4 3 6% 6% 33%	2280
	21st to end	Night	21% 9% 4 8% 5% 4 5% 3 4 7% 30%	2543
November	1st to 10th	Night	18% 7% 3 5% 5% 4 4 4 4 6% 39%	2522
	11th to 20th	Night	17% 10% 3 6% 5% 5% 5% 4 6% 7% 32%	2660
	21st to end	Night	21% 10% 2 7% 5% 5% 5% 4 6% 7% 27%	2660
December	1st to 10th	Night	20% 13% 5% 8% 5% 4 5% 4 5% 6% 25%	2660
	11th to 20th	Night	18% 14% 4 9% 4 5% 4 4 5% 5% 28%	3288
	21st to end	Night	30% 15% 3 8% 4 4 4 4 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	54% 7% 16% 15% 7% 2	2518
	11th to 20th	Day	64% 8% 11% 10% 6%	2529
	21st to end	Day	69% 6% 10% 10% 5% 1	3124
February	1st to 10th	Day	60% 7% 12% 15% 5% 1	1710
	11th to 20th	Day	57% 6% 11% 15% 10% 1	1672
	21st to end	Day	59% 6% 11% 14% 9% 1	1508
March	1st to 10th	Day	53% 6% 13% 18% 9% 1	3311
	11th to 20th	Day	51% 6% 17% 15% 10% 2	3480
	21st to end	Day	40% 6% 9% 26% 17% 3	3896
April	1st to 10th	Day	52% 5% 10% 19% 10% 3	2280
	11th to 20th	Day	48% 4 10% 22% 16% 1	2254
	21st to end	Day	52% 6% 10% 18% 13% 2	2441
May	1st to 10th	Day	47% 7% 11% 21% 12% 2	4308
	11th to 20th	Day	46% 9% 14% 20% 10% 1	4402
	21st to end	Day	35% 8% 14% 25% 15% 3	4837
June	1st to 10th	Day	45% 8% 14% 18% 13% 1	2660
	11th to 20th	Day	38% 8% 14% 24% 14% 2	2660
	21st to end	Day	41% 8% 14% 22% 13% 1	2660
July	1st to 10th	Day	36% 6% 15% 29% 14% 1	4370
	11th to 20th	Day	32% 7% 16% 35% 10%	4365
	21st to end	Day	34% 9% 16% 29% 12%	4615
August	1st to 10th	Day	43% 7% 15% 23% 12% 1	4091
	11th to 20th	Day	39% 7% 16% 28% 9%	4083
	21st to end	Day	36% 7% 13% 33% 10% 1	4226
September	1st to 10th	Day	36% 8% 15% 29% 12% 1	2280
	11th to 20th	Day	31% 6% 15% 32% 15% 1	2280
	21st to end	Day	42% 8% 13% 28% 9%	1987
October	1st to 10th	Day	39% 6% 13% 29% 12% 1	3160
	11th to 20th	Day	40% 7% 17% 24% 11% 1	3140
	21st to end	Day	49% 6% 14% 21% 9%	3367
November	1st to 10th	Day	46% 7% 17% 20% 10% 1	1653
	11th to 20th	Day	50% 9% 15% 17% 10% 1	1520
	21st to end	Day	57% 9% 13% 13% 8%	1520
December	1st to 10th	Day	62% 7% 13% 13% 5%	1520
	11th to 20th	Day	58% 8% 13% 13% 7%	1906
	21st to end	Day	66% 7% 10% 12% 5%	2772
January	1st to 10th	Night	60% 8% 14% 13% 5%	4429
	11th to 20th	Night	60% 11% 13% 12% 4 1	4427
	21st to end	Night	63% 7% 12% 12% 6%	4532
February	1st to 10th	Night	59% 6% 12% 17% 5% 1	2470
	11th to 20th	Night	54% 6% 12% 19% 9%	2405
	21st to end	Night	50% 7% 13% 21% 9% 1	1945
March	1st to 10th	Night	53% 6% 10% 21% 10% 1	3525
	11th to 20th	Night	51% 8% 14% 17% 10% 1	3480
	21st to end	Night	39% 4 10% 25% 19% 2	3735
April	1st to 10th	Night	49% 5% 10% 21% 13% 2	1900
	11th to 20th	Night	47% 6% 10% 18% 17% 1	1875
	21st to end	Night	46% 7% 12% 17% 16% 3	1757
May	1st to 10th	Night	48% 8% 11% 16% 15% 2	2650
	11th to 20th	Night	44% 7% 14% 23% 10% 2	2496
	21st to end	Night	34% 8% 14% 20% 21% 2	2739
June	1st to 10th	Night	42% 7% 12% 23% 14% 2	1520
	11th to 20th	Night	35% 7% 14% 21% 20% 3	1520
	21st to end	Night	41% 7% 13% 23% 14% 2	1520
July	1st to 10th	Night	35% 7% 14% 24% 20% 1	2480
	11th to 20th	Night	34% 6% 12% 33% 14%	2472
	21st to end	Night	31% 7% 16% 33% 11% 2	2681
August	1st to 10th	Night	36% 5% 13% 30% 15% 2	2814
	11th to 20th	Night	35% 7% 17% 28% 12% 1	2812
	21st to end	Night	30% 8% 13% 37% 12% 1	3398
September	1st to 10th	Night	34% 7% 16% 27% 14% 1	1900
	11th to 20th	Night	30% 8% 13% 32% 17% 1	1900
	21st to end	Night	42% 6% 11% 27% 13% 1	2190
October	1st to 10th	Night	35% 6% 10% 28% 21% 1	3800
	11th to 20th	Night	42% 5% 15% 29% 9%	3779
	21st to end	Night	45% 5% 14% 26% 9%	4179
November	1st to 10th	Night	44% 7% 13% 23% 11% 1	2522
	11th to 20th	Night	49% 8% 13% 18% 10% 2	2660
	21st to end	Night	53% 10% 16% 15% 5% 1	2660
December	1st to 10th	Night	59% 8% 13% 15% 5%	2660
	11th to 20th	Night	57% 7% 13% 16% 6% 1	3288
	21st to end	Night	69% 7% 11% 10% 4	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	25% 23% 30% 14% 7% 1	180
	11th to 20th	Day	28% 22% 32% 15% 3 1	184
	21st to end	Day	27% 23% 30% 16% 4 1	297
February	1st to 10th	Day	28% 28% 30% 12% 2	270
	11th to 20th	Day	25% 26% 39% 9% 1	270
	21st to end	Day	33% 21% 34% 10% 1	320
March	1st to 10th	Day	23% 19% 37% 16% 4	460
	11th to 20th	Day	24% 22% 32% 18% 3	460
	21st to end	Day	30% 18% 32% 13% 6% 1	506
April	1st to 10th	Day	26% 22% 32% 12% 7% 1	460
	11th to 20th	Day	28% 22% 23% 15% 8% 3	452
	21st to end	Day	26% 20% 32% 15% 6% 2	460
May	1st to 10th	Day	24% 14% 32% 19% 8% 4	463
	11th to 20th	Day	17% 12% 34% 24% 10% 3	487
	21st to end	Day	14% 13% 31% 26% 12% 4	529
June	1st to 10th	Day	18% 14% 33% 25% 9% 2	490
	11th to 20th	Day	12% 13% 33% 26% 13% 3	490
	21st to end	Day	19% 11% 31% 25% 11% 3	490
July	1st to 10th	Day	9% 9% 28% 32% 18% 5%	485
	11th to 20th	Day	14% 8% 29% 27% 17% 5%	484
	21st to end	Day	9% 8% 33% 33% 12% 4	532
August	1st to 10th	Day	13% 6% 30% 29% 16% 7%	486
	11th to 20th	Day	12% 6% 26% 30% 20% 6%	479
	21st to end	Day	12% 8% 31% 27% 14% 8%	539
September	1st to 10th	Day	12% 9% 30% 28% 13% 8%	490
	11th to 20th	Day	9% 8% 26% 25% 18% 14%	490
	21st to end	Day	15% 13% 28% 24% 15% 5%	490
October	1st to 10th	Day	20% 17% 26% 18% 14% 6%	490
	11th to 20th	Day	22% 18% 32% 18% 8% 2	490
	21st to end	Day	29% 18% 28% 21% 4	519
November	1st to 10th	Day	25% 16% 26% 22% 9% 1	323
	11th to 20th	Day	24% 22% 34% 16% 3 1	180
	21st to end	Day	24% 22% 34% 14% 4 1	180
December	1st to 10th	Day	28% 16% 36% 14% 6%	180
	11th to 20th	Day	28% 27% 30% 13% 2 1	180
	21st to end	Day	36% 19% 32% 12% 2	198
January	1st to 10th	Night	27% 18% 30% 20% 4	760
	11th to 20th	Night	27% 17% 31% 19% 6%	760
	21st to end	Night	23% 14% 34% 23% 5%	836
February	1st to 10th	Night	23% 18% 38% 19% 2	760
	11th to 20th	Night	21% 19% 36% 18% 4	743
	21st to end	Night	24% 19% 34% 20% 3	628
March	1st to 10th	Night	21% 16% 36% 24% 3	760
	11th to 20th	Night	23% 18% 32% 22% 4 1	760
	21st to end	Night	21% 14% 33% 24% 7% 1	836
April	1st to 10th	Night	23% 13% 36% 24% 3	760
	11th to 20th	Night	22% 16% 32% 22% 9% 1	751
	21st to end	Night	22% 12% 31% 24% 10% 1	617
May	1st to 10th	Night	22% 7% 29% 28% 13% 1	458
	11th to 20th	Night	14% 7% 35% 34% 10%	374
	21st to end	Night	11% 6% 34% 34% 15% 1	411
June	1st to 10th	Night	15% 4 36% 32% 13% 1	380
	11th to 20th	Night	11% 7% 29% 36% 17% 1	380
	21st to end	Night	14% 6% 28% 37% 14% 1	380
July	1st to 10th	Night	6% 6% 27% 42% 18% 1	370
	11th to 20th	Night	10% 2 26% 38% 22% 1	368
	21st to end	Night	10% 2 26% 43% 17% 1	435
August	1st to 10th	Night	11% 4 18% 40% 25% 3	567
	11th to 20th	Night	9% 5% 20% 37% 25% 3	564
	21st to end	Night	9% 4 27% 36% 22% 2	784
September	1st to 10th	Night	13% 5% 28% 32% 19% 3	760
	11th to 20th	Night	14% 4 20% 29% 27% 6%	760
	21st to end	Night	19% 8% 21% 30% 19% 4	760
October	1st to 10th	Night	19% 9% 29% 24% 16% 3	760
	11th to 20th	Night	23% 13% 29% 25% 9% 1	760
	21st to end	Night	25% 14% 32% 23% 6%	836
November	1st to 10th	Night	23% 14% 25% 29% 9% 1	760
	11th to 20th	Night	23% 16% 32% 22% 6% 1	760
	21st to end	Night	28% 15% 31% 19% 7%	760
December	1st to 10th	Night	30% 17% 31% 19% 3	760
	11th to 20th	Night	25% 18% 34% 19% 4	760
	21st to end	Night	34% 14% 33% 17% 2	836

Page generated at 2024-11-03 02:11:07. Version ac07

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