Heilwood
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Heilwood 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	16% 12% 4 9% 5% 4 4 4 5% 7% 30%	101431
	Night	16% 13% 5% 9% 5% 4 4 3 5% 6% 30%	98036
Transparency	Day	53% 5% 11% 20% 10% 1	105073
	Night	53% 5% 10% 19% 11% 2	102534
Seeing	Day	26% 16% 27% 19% 9% 3	14801
	Night	25% 16% 26% 23% 9% 1	24378

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% 21% 10% 18% 5% 3 3 2 3 4 15%	2654
	11th to 20th	Day	11% 19% 10% 21% 9% 5% 3 2 3 3 14%	2840
	21st to end	Day	24% 19% 10% 13% 8% 4 3 2 3 3 11%	3124
February	1st to 10th	Day	16% 20% 6% 13% 8% 5% 4 2 3 4 19%	1710
	11th to 20th	Day	16% 15% 8% 15% 6% 5% 4 3 5% 5% 19%	1663
	21st to end	Day	18% 18% 4 14% 5% 4 3 3 3 5% 22%	1552
March	1st to 10th	Day	18% 12% 8% 9% 4 3 4 3 5% 6% 28%	3435
	11th to 20th	Day	13% 15% 6% 12% 5% 4 4 3 5% 5% 28%	3480
	21st to end	Day	16% 12% 3 8% 5% 4 4 3 6% 6% 32%	3815
April	1st to 10th	Day	16% 16% 3 9% 5% 4 4 4 5% 5% 29%	2245
	11th to 20th	Day	16% 14% 4 7% 4 4 4 3 5% 6% 33%	2254
	21st to end	Day	20% 11% 3 7% 4 4 5% 4 4 7% 30%	2422
May	1st to 10th	Day	25% 10% 3 8% 5% 4 4 4 5% 6% 26%	4082
	11th to 20th	Day	21% 10% 3 7% 5% 6% 5% 4 6% 7% 26%	4190
	21st to end	Day	13% 7% 3 6% 4 5% 5% 4 7% 9% 37%	4823
June	1st to 10th	Day	17% 8% 3 6% 6% 5% 5% 4 7% 8% 32%	2660
	11th to 20th	Day	16% 6% 3 8% 5% 5% 5% 5% 7% 9% 32%	2660
	21st to end	Day	15% 7% 2 6% 6% 5% 5% 4 8% 10% 33%	2660
July	1st to 10th	Day	11% 7% 2 7% 5% 5% 6% 5% 6% 8% 38%	4440
	11th to 20th	Day	11% 7% 2 6% 5% 5% 5% 4 7% 10% 38%	4201
	21st to end	Day	14% 7% 3 8% 5% 5% 5% 4 6% 7% 36%	4466
August	1st to 10th	Day	18% 9% 3 8% 5% 6% 6% 4 7% 8% 27%	4104
	11th to 20th	Day	14% 7% 3 7% 5% 6% 6% 5% 6% 8% 33%	4044
	21st to end	Day	11% 5% 2 6% 5% 5% 6% 5% 7% 10% 38%	4222
September	1st to 10th	Day	17% 6% 3 4 4 4 4 4 5% 7% 42%	2280
	11th to 20th	Day	15% 5% 2 6% 4 4 4 4 5% 8% 43%	2185
	21st to end	Day	21% 9% 4 6% 5% 4 5% 3 5% 7% 33%	2037
October	1st to 10th	Day	17% 8% 2 7% 5% 4 5% 3 5% 7% 37%	1900
	11th to 20th	Day	19% 12% 3 7% 5% 4 4 3 5% 5% 34%	1900
	21st to end	Day	22% 14% 3 5% 5% 3 3 3 4 6% 31%	2090
November	1st to 10th	Day	13% 12% 3 6% 5% 3 4 4 4 6% 39%	1915
	11th to 20th	Day	16% 17% 5% 8% 4 4 5% 4 6% 5% 27%	1600
	21st to end	Day	18% 19% 7% 9% 5% 4 3 3 4 5% 22%	1576
December	1st to 10th	Day	19% 20% 10% 12% 6% 3 3 3 4 4 16%	1520
	11th to 20th	Day	17% 22% 7% 12% 5% 3 3 2 4 6% 19%	1910
	21st to end	Day	23% 24% 9% 11% 5% 3 3 2 3 4 14%	2772
January	1st to 10th	Night	13% 22% 9% 16% 5% 4 4 3 4 4 16%	4287
	11th to 20th	Night	14% 18% 9% 17% 7% 6% 4 2 3 4 14%	4120
	21st to end	Night	23% 18% 8% 12% 10% 3 3 2 3 3 15%	4532
February	1st to 10th	Night	16% 16% 6% 14% 7% 4 3 3 4 4 23%	2470
	11th to 20th	Night	16% 16% 5% 13% 8% 5% 4 3 4 6% 21%	2403
	21st to end	Night	17% 15% 6% 13% 7% 4 3 3 5% 4 25%	1897
March	1st to 10th	Night	21% 13% 4 8% 4 4 4 3 4 6% 30%	3418
	11th to 20th	Night	14% 12% 9% 9% 5% 4 3 3 4 6% 30%	3480
	21st to end	Night	14% 12% 4 9% 4 3 3 3 4 5% 37%	3817
April	1st to 10th	Night	15% 16% 4 8% 4 4 4 3 5% 6% 30%	1934
	11th to 20th	Night	16% 11% 2 6% 4 3 5% 3 6% 7% 35%	1875
	21st to end	Night	15% 11% 3 8% 5% 5% 5% 3 4 6% 35%	1773
May	1st to 10th	Night	27% 11% 3 7% 4 5% 4 3 4 6% 27%	2813
	11th to 20th	Night	18% 12% 3 7% 5% 4 4 5% 5% 6% 31%	2699
	21st to end	Night	14% 10% 2 6% 4 5% 4 3 6% 9% 35%	2732
June	1st to 10th	Night	13% 5% 2 5% 4 5% 5% 5% 6% 8% 42%	1520
	11th to 20th	Night	13% 7% 2 6% 5% 4 5% 4 7% 10% 38%	1520
	21st to end	Night	14% 6% 2 6% 4 4 4 4 6% 11% 40%	1520
July	1st to 10th	Night	13% 8% 3 8% 5% 4 5% 5% 6% 7% 37%	2520
	11th to 20th	Night	11% 6% 2 5% 5% 4 4 4 6% 9% 42%	2741
	21st to end	Night	14% 8% 3 8% 4 5% 4 3 6% 6% 40%	3087
August	1st to 10th	Night	18% 9% 3 6% 4 4 5% 4 6% 7% 34%	2825
	11th to 20th	Night	16% 7% 2 6% 4 4 4 4 6% 7% 40%	2785
	21st to end	Night	9% 5% 2 5% 4 5% 5% 4 7% 9% 45%	3402
September	1st to 10th	Night	15% 6% 2 6% 3 4 4 4 5% 6% 46%	1900
	11th to 20th	Night	11% 5% 2 5% 3 3 4 3 6% 8% 50%	1990
	21st to end	Night	18% 8% 3 7% 4 4 4 4 5% 6% 39%	2142
October	1st to 10th	Night	17% 8% 1 6% 4 3 4 3 5% 7% 42%	2280
	11th to 20th	Night	18% 10% 2 6% 4 4 4 3 5% 6% 39%	2280
	21st to end	Night	24% 13% 2 5% 4 3 3 3 5% 5% 33%	2508
November	1st to 10th	Night	11% 12% 4 6% 4 3 3 3 4 6% 43%	2378
	11th to 20th	Night	18% 15% 5% 8% 5% 4 4 3 5% 5% 28%	2800
	21st to end	Night	18% 17% 6% 8% 4 4 4 3 4 5% 26%	2759
December	1st to 10th	Night	19% 21% 8% 12% 5% 4 4 3 4 4 16%	2660
	11th to 20th	Night	18% 18% 7% 14% 6% 4 3 3 3 4 20%	3285
	21st to end	Night	19% 22% 8% 11% 6% 5% 4 3 4 4 13%	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	73% 6% 6% 11% 4 1	2655
	11th to 20th	Day	76% 3 6% 10% 3 1	2840
	21st to end	Day	79% 4 6% 7% 3	3124
February	1st to 10th	Day	71% 4 8% 12% 6%	1710
	11th to 20th	Day	67% 6% 8% 13% 6%	1672
	21st to end	Day	65% 4 9% 14% 6% 1	1552
March	1st to 10th	Day	57% 4 11% 22% 6%	3435
	11th to 20th	Day	56% 6% 13% 18% 6% 1	3480
	21st to end	Day	51% 6% 11% 20% 11% 1	3815
April	1st to 10th	Day	55% 5% 10% 17% 10% 2	2245
	11th to 20th	Day	52% 5% 10% 17% 15% 2	2254
	21st to end	Day	54% 4 9% 21% 10% 1	2422
May	1st to 10th	Day	58% 5% 9% 20% 8% 1	4120
	11th to 20th	Day	54% 8% 11% 19% 7% 1	4194
	21st to end	Day	40% 8% 15% 23% 12% 2	4837
June	1st to 10th	Day	48% 7% 12% 23% 10%	2660
	11th to 20th	Day	46% 6% 15% 20% 12% 1	2660
	21st to end	Day	44% 7% 13% 25% 11%	2660
July	1st to 10th	Day	43% 6% 12% 24% 12% 3	4370
	11th to 20th	Day	40% 6% 15% 26% 13% 1	4129
	21st to end	Day	46% 5% 10% 22% 17% 1	4324
August	1st to 10th	Day	53% 6% 14% 21% 6%	4091
	11th to 20th	Day	47% 4 12% 27% 9%	4083
	21st to end	Day	40% 5% 14% 27% 12% 2	4222
September	1st to 10th	Day	42% 7% 8% 23% 17% 3	2280
	11th to 20th	Day	38% 6% 11% 27% 17% 1	2185
	21st to end	Day	51% 4 12% 19% 12% 1	2037
October	1st to 10th	Day	38% 5% 10% 28% 19% 1	3160
	11th to 20th	Day	46% 5% 10% 22% 11% 7%	3140
	21st to end	Day	40% 3 11% 28% 18% 1	3428
November	1st to 10th	Day	45% 5% 11% 19% 16% 3	1915
	11th to 20th	Day	57% 4 11% 16% 10% 2	1600
	21st to end	Day	65% 3 11% 15% 6% 1	1576
December	1st to 10th	Day	73% 4 9% 10% 4	1520
	11th to 20th	Day	68% 3 8% 17% 3	1906
	21st to end	Day	76% 3 7% 11% 2	2772
January	1st to 10th	Night	72% 4 7% 12% 5%	4287
	11th to 20th	Night	74% 6% 9% 10% 2	4120
	21st to end	Night	76% 4 6% 12% 3	4532
February	1st to 10th	Night	65% 4 8% 16% 7%	2470
	11th to 20th	Night	66% 4 8% 15% 7%	2405
	21st to end	Night	63% 4 8% 16% 9% 1	1897
March	1st to 10th	Night	55% 5% 12% 20% 7%	3418
	11th to 20th	Night	51% 10% 14% 19% 6% 1	3480
	21st to end	Night	48% 5% 10% 21% 15% 2	3817
April	1st to 10th	Night	55% 5% 10% 17% 12% 1	1934
	11th to 20th	Night	47% 6% 12% 18% 14% 2	1875
	21st to end	Night	50% 6% 8% 22% 12% 2	1773
May	1st to 10th	Night	58% 5% 8% 17% 10% 2	2840
	11th to 20th	Night	52% 8% 12% 19% 8% 1	2700
	21st to end	Night	42% 8% 13% 22% 11% 4	2739
June	1st to 10th	Night	39% 7% 12% 27% 13% 1	1520
	11th to 20th	Night	39% 8% 14% 24% 12% 2	1520
	21st to end	Night	39% 7% 15% 25% 14%	1520
July	1st to 10th	Night	46% 5% 11% 21% 14% 3	2480
	11th to 20th	Night	38% 6% 16% 24% 16% 1	2691
	21st to end	Night	44% 6% 10% 19% 20% 1	2988
August	1st to 10th	Night	48% 7% 14% 22% 9%	2814
	11th to 20th	Night	43% 6% 11% 29% 11% 1	2812
	21st to end	Night	34% 6% 15% 31% 13% 2	3402
September	1st to 10th	Night	38% 6% 10% 24% 18% 3	1900
	11th to 20th	Night	31% 6% 12% 29% 21% 1	1990
	21st to end	Night	46% 4 13% 21% 15% 1	2142
October	1st to 10th	Night	38% 5% 10% 26% 20% 1	3800
	11th to 20th	Night	40% 4 11% 22% 14% 9%	3779
	21st to end	Night	41% 3 10% 26% 19% 1	4120
November	1st to 10th	Night	43% 5% 11% 21% 17% 4	2378
	11th to 20th	Night	58% 4 8% 18% 10% 3	2800
	21st to end	Night	61% 4 10% 18% 6% 1	2759
December	1st to 10th	Night	72% 4 9% 10% 4	2660
	11th to 20th	Night	69% 3 8% 16% 4	3288
	21st to end	Night	74% 4 9% 10% 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	37% 25% 24% 9% 5%	220
	11th to 20th	Day	41% 33% 20% 4 2	270
	21st to end	Day	34% 29% 29% 8% 1	297
February	1st to 10th	Day	31% 30% 31% 6% 2	270
	11th to 20th	Day	42% 26% 27% 4 1	270
	21st to end	Day	37% 28% 28% 7% 1	310
March	1st to 10th	Day	34% 22% 27% 12% 3	460
	11th to 20th	Day	35% 22% 27% 11% 4 1	460
	21st to end	Day	34% 24% 24% 15% 3 1	506
April	1st to 10th	Day	32% 24% 28% 13% 4	460
	11th to 20th	Day	26% 22% 30% 12% 7% 3	452
	21st to end	Day	32% 18% 31% 14% 4 2	460
May	1st to 10th	Day	34% 15% 27% 16% 6% 2	463
	11th to 20th	Day	26% 15% 30% 18% 8% 3	487
	21st to end	Day	17% 11% 29% 25% 13% 4	529
June	1st to 10th	Day	22% 14% 27% 23% 12% 2	490
	11th to 20th	Day	22% 12% 27% 22% 14% 4	490
	21st to end	Day	19% 12% 30% 26% 11% 2	490
July	1st to 10th	Day	15% 9% 25% 25% 17% 8%	485
	11th to 20th	Day	13% 9% 28% 32% 12% 6%	484
	21st to end	Day	17% 7% 28% 28% 14% 6%	532
August	1st to 10th	Day	16% 7% 25% 27% 19% 6%	486
	11th to 20th	Day	19% 7% 24% 26% 16% 8%	479
	21st to end	Day	14% 9% 24% 29% 16% 9%	539
September	1st to 10th	Day	20% 9% 20% 26% 17% 8%	490
	11th to 20th	Day	15% 3 22% 34% 18% 8%	490
	21st to end	Day	28% 12% 23% 22% 11% 5%	490
October	1st to 10th	Day	21% 13% 23% 24% 15% 2	490
	11th to 20th	Day	26% 17% 27% 21% 8% 1	490
	21st to end	Day	33% 15% 30% 17% 5%	539
November	1st to 10th	Day	24% 17% 28% 21% 8% 1	471
	11th to 20th	Day	32% 21% 34% 11% 3 1	200
	21st to end	Day	31% 26% 35% 8% 1	194
December	1st to 10th	Day	37% 26% 27% 7% 2 1	180
	11th to 20th	Day	38% 21% 31% 8% 2	180
	21st to end	Day	41% 22% 25% 9% 3	198
January	1st to 10th	Night	33% 26% 27% 11% 3	760
	11th to 20th	Night	33% 25% 28% 12% 2	760
	21st to end	Night	30% 26% 30% 13% 2	836
February	1st to 10th	Night	32% 22% 29% 15% 2	760
	11th to 20th	Night	31% 29% 30% 9% 1	743
	21st to end	Night	32% 24% 28% 14% 1	628
March	1st to 10th	Night	29% 20% 31% 18% 2	760
	11th to 20th	Night	29% 24% 26% 15% 6%	760
	21st to end	Night	26% 21% 32% 16% 4 1	836
April	1st to 10th	Night	29% 18% 31% 18% 4	760
	11th to 20th	Night	24% 18% 31% 19% 7%	751
	21st to end	Night	21% 16% 31% 27% 5%	633
May	1st to 10th	Night	25% 12% 26% 30% 6% 1	570
	11th to 20th	Night	22% 9% 30% 31% 7%	500
	21st to end	Night	12% 6% 27% 31% 21% 2	411
June	1st to 10th	Night	13% 6% 31% 36% 14% 1	380
	11th to 20th	Night	15% 7% 26% 36% 15% 1	380
	21st to end	Night	14% 5% 30% 36% 14% 1	380
July	1st to 10th	Night	15% 3 18% 43% 17% 3	370
	11th to 20th	Night	12% 5% 19% 40% 21% 3	496
	21st to end	Night	14% 4 19% 40% 21% 1	624
August	1st to 10th	Night	12% 4 19% 42% 22% 2	567
	11th to 20th	Night	14% 5% 15% 37% 26% 3	564
	21st to end	Night	13% 5% 18% 39% 21% 4	788
September	1st to 10th	Night	17% 6% 20% 33% 20% 4	760
	11th to 20th	Night	12% 5% 19% 35% 24% 5%	760
	21st to end	Night	21% 11% 23% 26% 16% 3	760
October	1st to 10th	Night	20% 9% 25% 28% 16% 2	760
	11th to 20th	Night	25% 15% 30% 21% 8% 1	760
	21st to end	Night	33% 13% 27% 22% 5%	836
November	1st to 10th	Night	20% 15% 30% 27% 8% 1	780
	11th to 20th	Night	30% 19% 26% 19% 5% 1	800
	21st to end	Night	32% 19% 29% 16% 4	789
December	1st to 10th	Night	37% 22% 24% 13% 3	760
	11th to 20th	Night	34% 25% 25% 14% 3	760
	21st to end	Night	30% 25% 29% 15% 1	836

Page generated at 2024-11-25 00:22:19. Version ac07

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