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HAA Dark Sky Site
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the HAA Dark Sky Site 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	14% 10% 3 8% 5% 5% 5% 4 6% 7% 33%	101405
	Night	15% 10% 3 8% 5% 5% 4 4 5% 7% 34%	97643
Transparency	Day	48% 7% 13% 20% 11% 1	105011
	Night	48% 6% 13% 20% 12% 1	102125
Seeing	Day	19% 12% 28% 23% 13% 5%	14480
	Night	20% 10% 29% 28% 12% 1	23936

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% 15% 5% 10% 6% 5% 4 4 5% 6% 25%	2526
	11th to 20th	Day	11% 18% 7% 16% 9% 5% 5% 3 5% 5% 16%	2840
	21st to end	Day	21% 20% 7% 11% 6% 6% 4 3 4 4 14%	3124
February	1st to 10th	Day	16% 16% 5% 11% 7% 6% 5% 4 5% 5% 20%	1710
	11th to 20th	Day	12% 14% 6% 13% 7% 5% 5% 4 5% 5% 24%	1663
	21st to end	Day	19% 13% 5% 13% 6% 5% 5% 3 4 5% 24%	1492
March	1st to 10th	Day	18% 12% 4 9% 6% 5% 4 3 5% 6% 28%	3432
	11th to 20th	Day	10% 15% 5% 10% 6% 5% 5% 4 5% 6% 30%	3480
	21st to end	Day	16% 9% 3 8% 6% 5% 5% 3 6% 6% 33%	3815
April	1st to 10th	Day	18% 10% 4 8% 6% 5% 5% 4 5% 6% 30%	2223
	11th to 20th	Day	18% 8% 2 8% 5% 4 4 4 5% 7% 35%	2334
	21st to end	Day	18% 9% 3 8% 5% 5% 4 3 5% 5% 33%	2470
May	1st to 10th	Day	17% 8% 3 7% 5% 5% 5% 4 5% 7% 34%	4108
	11th to 20th	Day	14% 10% 4 9% 6% 5% 5% 4 6% 7% 30%	4286
	21st to end	Day	10% 6% 2 6% 4 4 4 4 6% 8% 46%	4837
June	1st to 10th	Day	12% 6% 3 6% 5% 6% 5% 4 6% 8% 39%	2660
	11th to 20th	Day	10% 6% 2 7% 5% 4 5% 5% 6% 10% 40%	2660
	21st to end	Day	13% 5% 2 6% 4 4 5% 4 6% 9% 41%	2660
July	1st to 10th	Day	9% 5% 2 6% 4 5% 6% 5% 7% 10% 42%	4440
	11th to 20th	Day	10% 6% 2 5% 5% 5% 5% 5% 8% 10% 40%	4356
	21st to end	Day	7% 5% 2 7% 5% 5% 5% 5% 8% 9% 42%	4466
August	1st to 10th	Day	17% 6% 2 6% 4 4 5% 4 6% 8% 36%	4104
	11th to 20th	Day	11% 6% 2 7% 5% 5% 6% 4 8% 10% 35%	4044
	21st to end	Day	8% 5% 2 7% 5% 5% 5% 4 7% 10% 42%	4372
September	1st to 10th	Day	12% 7% 3 7% 3 5% 5% 4 6% 7% 41%	2280
	11th to 20th	Day	9% 6% 2 5% 5% 5% 4 3 5% 9% 47%	2138
	21st to end	Day	14% 7% 3 7% 6% 5% 5% 4 7% 7% 35%	2068
October	1st to 10th	Day	18% 8% 3 7% 5% 5% 4 4 5% 7% 35%	1900
	11th to 20th	Day	17% 9% 4 8% 5% 5% 4 3 6% 7% 32%	1900
	21st to end	Day	22% 11% 3 10% 5% 4 5% 3 5% 6% 25%	2090
November	1st to 10th	Day	12% 9% 3 8% 6% 5% 5% 4 7% 7% 35%	1689
	11th to 20th	Day	13% 13% 4 9% 6% 5% 5% 4 6% 9% 27%	1520
	21st to end	Day	18% 15% 3 8% 6% 5% 4 4 7% 7% 24%	1520
December	1st to 10th	Day	15% 16% 6% 10% 7% 5% 5% 3 6% 6% 21%	1520
	11th to 20th	Day	17% 14% 5% 10% 5% 7% 6% 5% 6% 5% 21%	1906
	21st to end	Day	27% 19% 8% 12% 6% 4 3 3 4 4 11%	2772
January	1st to 10th	Night	16% 14% 5% 11% 6% 6% 5% 3 4 6% 23%	4415
	11th to 20th	Night	13% 15% 6% 12% 8% 7% 6% 5% 5% 5% 20%	4120
	21st to end	Night	22% 16% 6% 11% 5% 5% 4 4 5% 5% 18%	4532
February	1st to 10th	Night	15% 15% 5% 10% 7% 5% 4 4 6% 6% 23%	2470
	11th to 20th	Night	13% 13% 5% 10% 6% 5% 5% 4 6% 6% 27%	2403
	21st to end	Night	16% 11% 5% 10% 7% 5% 4 4 6% 7% 24%	1961
March	1st to 10th	Night	17% 10% 3 8% 5% 5% 5% 4 5% 5% 32%	3408
	11th to 20th	Night	14% 12% 3 7% 4 4 4 3 5% 7% 36%	3479
	21st to end	Night	15% 9% 3 7% 4 4 4 3 4 6% 40%	3817
April	1st to 10th	Night	17% 11% 3 8% 6% 4 4 4 5% 5% 33%	1957
	11th to 20th	Night	18% 8% 3 7% 5% 5% 4 3 6% 6% 36%	1811
	21st to end	Night	15% 8% 4 7% 6% 5% 4 3 6% 6% 36%	1710
May	1st to 10th	Night	18% 9% 3 8% 4 4 4 3 5% 7% 36%	2833
	11th to 20th	Night	14% 8% 3 9% 6% 5% 5% 4 6% 8% 32%	2605
	21st to end	Night	9% 5% 2 6% 4 4 4 3 5% 8% 49%	2738
June	1st to 10th	Night	10% 7% 2 6% 5% 5% 6% 4 7% 8% 41%	1520
	11th to 20th	Night	9% 5% 2 6% 4 6% 4 6% 7% 8% 43%	1520
	21st to end	Night	11% 6% 2 6% 4 5% 5% 4 5% 9% 44%	1520
July	1st to 10th	Night	6% 5% 2 6% 5% 4 4 4 5% 9% 50%	2520
	11th to 20th	Night	9% 5% 2 5% 3 4 4 3 6% 9% 49%	2601
	21st to end	Night	7% 6% 2 5% 4 5% 5% 4 7% 8% 49%	3087
August	1st to 10th	Night	11% 5% 2 6% 4 4 5% 4 6% 8% 44%	2825
	11th to 20th	Night	11% 6% 2 6% 4 4 4 4 6% 8% 45%	2785
	21st to end	Night	7% 5% 1 5% 4 4 4 4 6% 10% 50%	3252
September	1st to 10th	Night	11% 6% 3 6% 5% 4 4 4 6% 7% 44%	1900
	11th to 20th	Night	9% 5% 1 5% 3 4 4 3 5% 8% 53%	2039
	21st to end	Night	14% 7% 2 8% 5% 5% 4 3 6% 7% 38%	2111
October	1st to 10th	Night	16% 7% 3 6% 4 4 3 3 5% 7% 42%	2280
	11th to 20th	Night	17% 10% 3 7% 5% 4 4 4 6% 6% 35%	2280
	21st to end	Night	21% 9% 4 7% 5% 4 5% 4 5% 5% 31%	2508
November	1st to 10th	Night	15% 7% 2 6% 4 4 4 4 6% 7% 40%	2484
	11th to 20th	Night	14% 11% 4 8% 5% 5% 5% 4 5% 8% 31%	2660
	21st to end	Night	18% 11% 4 7% 5% 5% 5% 3 6% 7% 28%	2660
December	1st to 10th	Night	17% 16% 4 10% 6% 4 6% 4 5% 7% 21%	2660
	11th to 20th	Night	14% 17% 5% 10% 6% 5% 3 4 6% 6% 24%	3288
	21st to end	Night	26% 19% 7% 11% 6% 5% 4 3 4 4 12%	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	60% 9% 12% 11% 8% 1	2527
	11th to 20th	Day	72% 6% 10% 8% 4	2840
	21st to end	Day	75% 6% 9% 7% 3	3124
February	1st to 10th	Day	68% 5% 10% 12% 4 1	1710
	11th to 20th	Day	62% 5% 10% 14% 7% 1	1672
	21st to end	Day	63% 6% 10% 13% 7% 1	1492
March	1st to 10th	Day	57% 6% 11% 21% 5% 1	3435
	11th to 20th	Day	54% 6% 15% 17% 7% 1	3480
	21st to end	Day	50% 6% 12% 20% 11% 1	3815
April	1st to 10th	Day	55% 5% 11% 16% 12% 1	2223
	11th to 20th	Day	49% 6% 11% 19% 13% 2	2334
	21st to end	Day	52% 6% 10% 17% 12% 2	2470
May	1st to 10th	Day	48% 6% 13% 18% 12% 2	4120
	11th to 20th	Day	49% 10% 13% 20% 7% 1	4290
	21st to end	Day	35% 8% 12% 24% 17% 3	4837
June	1st to 10th	Day	41% 8% 11% 23% 15% 2	2660
	11th to 20th	Day	39% 9% 14% 23% 14% 1	2660
	21st to end	Day	38% 8% 15% 24% 15% 1	2660
July	1st to 10th	Day	34% 7% 13% 27% 16% 2	4370
	11th to 20th	Day	36% 8% 14% 29% 13%	4281
	21st to end	Day	35% 9% 16% 21% 18% 1	4324
August	1st to 10th	Day	43% 7% 15% 21% 13% 1	4091
	11th to 20th	Day	40% 8% 16% 25% 10% 1	4083
	21st to end	Day	35% 7% 13% 32% 12% 1	4372
September	1st to 10th	Day	40% 8% 15% 24% 13% 1	2280
	11th to 20th	Day	35% 7% 13% 29% 16% 1	2138
	21st to end	Day	44% 8% 15% 23% 9% 1	2068
October	1st to 10th	Day	38% 5% 16% 24% 17% 1	3160
	11th to 20th	Day	41% 6% 13% 24% 15% 1	3140
	21st to end	Day	49% 6% 15% 23% 8%	3428
November	1st to 10th	Day	46% 8% 14% 22% 9% 2	1689
	11th to 20th	Day	53% 8% 15% 14% 10% 1	1520
	21st to end	Day	57% 7% 16% 16% 5%	1520
December	1st to 10th	Day	63% 7% 13% 13% 4	1520
	11th to 20th	Day	63% 7% 16% 9% 5%	1906
	21st to end	Day	77% 6% 8% 8% 2	2772
January	1st to 10th	Night	61% 7% 14% 12% 5%	4415
	11th to 20th	Night	64% 7% 14% 11% 4	4120
	21st to end	Night	69% 6% 9% 12% 4	4532
February	1st to 10th	Night	62% 6% 11% 16% 5% 1	2470
	11th to 20th	Night	57% 5% 12% 17% 8% 1	2405
	21st to end	Night	59% 6% 11% 16% 7%	1961
March	1st to 10th	Night	53% 6% 11% 22% 7% 1	3418
	11th to 20th	Night	46% 6% 16% 17% 12% 2	3480
	21st to end	Night	43% 4 12% 22% 17% 2	3817
April	1st to 10th	Night	52% 6% 11% 18% 13% 1	1957
	11th to 20th	Night	50% 5% 8% 20% 15% 2	1811
	21st to end	Night	47% 6% 10% 19% 15% 3	1710
May	1st to 10th	Night	47% 5% 11% 19% 14% 4	2840
	11th to 20th	Night	46% 8% 15% 21% 8% 2	2606
	21st to end	Night	33% 7% 11% 24% 23% 2	2739
June	1st to 10th	Night	39% 8% 10% 24% 17% 2	1520
	11th to 20th	Night	37% 6% 12% 25% 18% 2	1520
	21st to end	Night	37% 7% 14% 24% 17% 2	1520
July	1st to 10th	Night	32% 5% 12% 24% 23% 4	2480
	11th to 20th	Night	32% 6% 14% 31% 16% 1	2553
	21st to end	Night	32% 7% 15% 24% 19% 2	2988
August	1st to 10th	Night	36% 6% 13% 26% 16% 3	2814
	11th to 20th	Night	36% 8% 16% 29% 11% 1	2812
	21st to end	Night	29% 6% 14% 32% 16% 1	3252
September	1st to 10th	Night	38% 7% 12% 25% 17% 2	1900
	11th to 20th	Night	30% 7% 11% 33% 19% 1	2039
	21st to end	Night	45% 7% 11% 24% 13% 1	2111
October	1st to 10th	Night	33% 5% 9% 27% 26% 1	3800
	11th to 20th	Night	42% 5% 13% 25% 14%	3779
	21st to end	Night	40% 5% 15% 26% 13% 1	4120
November	1st to 10th	Night	42% 6% 13% 25% 13% 1	2484
	11th to 20th	Night	50% 7% 13% 20% 10% 1	2660
	21st to end	Night	54% 7% 15% 18% 5%	2660
December	1st to 10th	Night	61% 8% 14% 13% 4	2660
	11th to 20th	Night	61% 8% 13% 14% 5%	3288
	21st to end	Night	74% 6% 10% 7% 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	21% 22% 32% 15% 9% 2	184
	11th to 20th	Day	24% 25% 33% 12% 3 1	270
	21st to end	Day	22% 23% 30% 20% 4 1	297
February	1st to 10th	Day	26% 19% 40% 11% 3	270
	11th to 20th	Day	22% 25% 39% 13% 1	270
	21st to end	Day	30% 27% 30% 12%	234
March	1st to 10th	Day	23% 13% 35% 21% 7%	460
	11th to 20th	Day	24% 14% 39% 16% 6% 1	460
	21st to end	Day	29% 14% 31% 18% 8% 1	506
April	1st to 10th	Day	22% 15% 33% 22% 7% 1	460
	11th to 20th	Day	24% 18% 27% 18% 8% 4	452
	21st to end	Day	23% 11% 32% 22% 9% 2	460
May	1st to 10th	Day	24% 11% 28% 23% 9% 5%	463
	11th to 20th	Day	18% 8% 27% 25% 17% 4	487
	21st to end	Day	13% 8% 26% 28% 18% 7%	529
June	1st to 10th	Day	12% 10% 33% 29% 13% 3	490
	11th to 20th	Day	13% 8% 26% 32% 18% 4	490
	21st to end	Day	17% 7% 28% 30% 14% 5%	490
July	1st to 10th	Day	9% 5% 19% 31% 25% 10%	485
	11th to 20th	Day	13% 7% 23% 27% 20% 10%	484
	21st to end	Day	9% 3 29% 33% 18% 8%	532
August	1st to 10th	Day	13% 4 20% 29% 22% 12%	486
	11th to 20th	Day	11% 5% 24% 28% 19% 13%	479
	21st to end	Day	12% 6% 22% 31% 20% 10%	539
September	1st to 10th	Day	13% 8% 22% 26% 19% 11%	490
	11th to 20th	Day	10% 6% 18% 24% 26% 17%	490
	21st to end	Day	16% 10% 26% 26% 15% 8%	490
October	1st to 10th	Day	20% 12% 25% 21% 16% 6%	490
	11th to 20th	Day	20% 15% 33% 21% 8% 3	490
	21st to end	Day	28% 15% 30% 19% 8%	539
November	1st to 10th	Day	19% 23% 31% 18% 7% 2	296
	11th to 20th	Day	22% 26% 24% 19% 7% 2	180
	21st to end	Day	26% 19% 36% 16% 3 1	180
December	1st to 10th	Day	27% 18% 31% 17% 5% 1	180
	11th to 20th	Day	26% 24% 33% 14% 3	180
	21st to end	Day	27% 20% 37% 13% 3	198
January	1st to 10th	Night	24% 16% 35% 18% 5% 1	760
	11th to 20th	Night	28% 17% 32% 18% 4	760
	21st to end	Night	20% 14% 37% 24% 5%	836
February	1st to 10th	Night	24% 19% 33% 22% 2	760
	11th to 20th	Night	22% 16% 35% 24% 4	743
	21st to end	Night	24% 16% 34% 23% 3	628
March	1st to 10th	Night	20% 11% 36% 27% 7%	760
	11th to 20th	Night	24% 13% 34% 22% 7% 1	760
	21st to end	Night	21% 10% 33% 27% 9% 1	836
April	1st to 10th	Night	23% 12% 33% 28% 4	760
	11th to 20th	Night	20% 11% 33% 25% 9% 1	687
	21st to end	Night	18% 6% 32% 34% 9%	570
May	1st to 10th	Night	22% 5% 28% 28% 16% 1	570
	11th to 20th	Night	17% 3 25% 41% 13% 1	445
	21st to end	Night	13% 6% 23% 36% 20% 1	411
June	1st to 10th	Night	13% 4 33% 36% 14%	380
	11th to 20th	Night	13% 3 27% 40% 16% 1	380
	21st to end	Night	13% 5% 24% 42% 16%	380
July	1st to 10th	Night	6% 4 21% 45% 24% 1	370
	11th to 20th	Night	12% 3 22% 42% 19% 2	410
	21st to end	Night	11% 2 18% 45% 22% 2	624
August	1st to 10th	Night	9% 4 15% 41% 28% 3	567
	11th to 20th	Night	10% 2 16% 35% 34% 3	564
	21st to end	Night	9% 3 19% 36% 30% 3	703
September	1st to 10th	Night	14% 6% 18% 33% 23% 6%	760
	11th to 20th	Night	11% 4 17% 33% 29% 6%	760
	21st to end	Night	18% 6% 22% 29% 21% 5%	760
October	1st to 10th	Night	18% 7% 27% 27% 19% 2	760
	11th to 20th	Night	22% 12% 28% 27% 9% 1	760
	21st to end	Night	26% 11% 31% 26% 6%	836
November	1st to 10th	Night	20% 11% 29% 26% 11% 2	760
	11th to 20th	Night	21% 14% 33% 21% 9% 1	760
	21st to end	Night	25% 13% 34% 21% 7%	760
December	1st to 10th	Night	28% 18% 30% 18% 6%	760
	11th to 20th	Night	24% 18% 35% 19% 5%	760
	21st to end	Night	31% 13% 33% 21% 2	836

Page generated at 2024-11-03 02:11:20. Version ac07

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