"Way The Held Out" Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the "Way The Held Out" Observatory clear sky chart from 2005-11-06 to 2024-08-30.

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% 13% 4 9% 5% 4 4 3 5% 7% 29%	95493
	Night	18% 14% 5% 9% 5% 4 4 3 4 6% 28%	93459
Transparency	Day	54% 6% 11% 18% 9% 1	95261
	Night	57% 6% 11% 16% 9% 1	93296
Seeing	Day	24% 17% 29% 19% 9% 3	14317
	Night	25% 15% 27% 23% 9% 1	23913

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	19% 24% 11% 13% 5% 5% 3 2 4 4 11%	2723
	11th to 20th	Day	13% 26% 8% 16% 7% 5% 3 2 3 4 13%	2840
	21st to end	Day	25% 21% 10% 18% 6% 3 3 2 2 2 7%	3124
February	1st to 10th	Day	17% 21% 6% 15% 9% 4 3 2 3 4 16%	1710
	11th to 20th	Day	16% 17% 8% 15% 8% 4 4 3 4 4 16%	1663
	21st to end	Day	19% 18% 4 14% 4 4 3 4 5% 5% 21%	1537
March	1st to 10th	Day	21% 13% 7% 9% 5% 3 4 3 4 6% 25%	3435
	11th to 20th	Day	12% 20% 6% 11% 4 4 3 3 4 5% 29%	3480
	21st to end	Day	22% 14% 5% 10% 4 3 3 3 4 5% 28%	3815
April	1st to 10th	Day	18% 15% 3 7% 4 4 4 3 5% 6% 30%	2190
	11th to 20th	Day	21% 13% 3 6% 4 4 3 4 5% 6% 32%	2337
	21st to end	Day	21% 13% 3 7% 4 3 3 2 4 6% 33%	2470
May	1st to 10th	Day	21% 9% 3 8% 5% 4 4 4 5% 6% 31%	4082
	11th to 20th	Day	19% 10% 3 7% 4 4 5% 3 6% 7% 30%	4081
	21st to end	Day	12% 6% 3 7% 5% 5% 5% 4 6% 8% 41%	4823
June	1st to 10th	Day	16% 7% 2 7% 5% 4 5% 5% 6% 8% 35%	2660
	11th to 20th	Day	14% 7% 3 7% 5% 5% 5% 4 6% 8% 36%	2660
	21st to end	Day	15% 6% 2 6% 5% 5% 5% 4 6% 9% 38%	2660
July	1st to 10th	Day	10% 6% 2 6% 5% 5% 5% 4 6% 10% 40%	4426
	11th to 20th	Day	12% 5% 2 6% 5% 5% 4 4 7% 9% 41%	4120
	21st to end	Day	11% 6% 2 7% 5% 5% 6% 5% 6% 8% 40%	4466
August	1st to 10th	Day	11% 6% 2 8% 5% 5% 5% 5% 6% 10% 38%	2457
	11th to 20th	Day	12% 8% 2 8% 6% 5% 7% 4 8% 9% 32%	2433
	21st to end	Day	13% 6% 3 7% 5% 4 6% 4 6% 9% 38%	2602
September	1st to 10th	Day	17% 7% 2 7% 5% 4 5% 3 6% 8% 36%	2159
	11th to 20th	Day	13% 6% 3 7% 5% 4 4 3 5% 8% 41%	1980
	21st to end	Day	19% 9% 2 8% 5% 4 4 3 4 6% 35%	1980
October	1st to 10th	Day	18% 7% 3 6% 4 5% 6% 4 6% 7% 34%	1805
	11th to 20th	Day	23% 10% 3 8% 6% 5% 5% 3 5% 6% 27%	1800
	21st to end	Day	28% 15% 3 8% 4 4 4 4 4 5% 22%	1980
November	1st to 10th	Day	14% 15% 4 8% 6% 4 4 3 5% 6% 32%	1726
	11th to 20th	Day	19% 20% 4 9% 5% 3 3 3 4 6% 23%	1547
	21st to end	Day	20% 24% 6% 9% 5% 4 4 3 5% 5% 15%	1520
December	1st to 10th	Day	18% 30% 9% 10% 4 4 3 3 3 3 12%	1520
	11th to 20th	Day	18% 23% 10% 14% 4 3 4 3 4 5% 13%	1910
	21st to end	Day	26% 26% 8% 12% 4 3 3 2 3 3 10%	2772
January	1st to 10th	Night	17% 26% 11% 17% 5% 4 3 2 3 3 10%	4205
	11th to 20th	Night	16% 22% 10% 19% 5% 5% 4 3 3 4 11%	4120
	21st to end	Night	27% 22% 9% 15% 5% 3 3 1 3 3 10%	4532
February	1st to 10th	Night	19% 20% 5% 12% 8% 4 4 3 4 4 17%	2470
	11th to 20th	Night	16% 18% 7% 15% 7% 5% 4 3 3 5% 17%	2403
	21st to end	Night	20% 14% 5% 16% 5% 4 3 3 3 5% 21%	1911
March	1st to 10th	Night	22% 16% 4 9% 4 3 3 3 4 5% 28%	3418
	11th to 20th	Night	17% 18% 8% 8% 4 3 3 2 4 5% 29%	3480
	21st to end	Night	18% 13% 4 9% 4 3 4 3 3 3 35%	3817
April	1st to 10th	Night	18% 17% 4 6% 5% 4 5% 3 5% 5% 29%	1990
	11th to 20th	Night	20% 9% 3 6% 5% 5% 5% 4 5% 7% 31%	1809
	21st to end	Night	15% 11% 4 7% 5% 4 5% 4 5% 7% 33%	1710
May	1st to 10th	Night	25% 9% 3 7% 4 3 3 3 5% 6% 31%	2813
	11th to 20th	Night	16% 10% 3 8% 5% 4 4 3 4 8% 35%	2795
	21st to end	Night	13% 5% 2 4 3 3 3 4 6% 11% 45%	2732
June	1st to 10th	Night	10% 7% 2 8% 5% 5% 5% 4 7% 9% 40%	1520
	11th to 20th	Night	11% 6% 3 8% 5% 4 5% 4 6% 8% 42%	1520
	21st to end	Night	13% 6% 2 6% 4 5% 4 4 7% 8% 41%	1520
July	1st to 10th	Night	12% 7% 3 7% 5% 4 4 3 5% 8% 42%	2520
	11th to 20th	Night	12% 6% 2 5% 4 4 4 3 6% 9% 45%	2836
	21st to end	Night	9% 5% 2 7% 4 5% 5% 5% 7% 7% 44%	3087
August	1st to 10th	Night	9% 6% 2 6% 4 5% 5% 3 6% 8% 46%	1701
	11th to 20th	Night	11% 6% 3 6% 4 5% 5% 4 6% 9% 41%	1688
	21st to end	Night	12% 6% 2 5% 4 4 4 5% 6% 8% 44%	1943
September	1st to 10th	Night	14% 6% 2 5% 4 3 4 5% 5% 8% 45%	1800
	11th to 20th	Night	13% 5% 2 5% 4 3 4 3 6% 6% 48%	1979
	21st to end	Night	17% 7% 2 6% 5% 4 4 3 6% 7% 38%	1980
October	1st to 10th	Night	19% 7% 2 6% 4 3 4 3 4 7% 41%	2154
	11th to 20th	Night	21% 10% 3 7% 5% 5% 5% 3 5% 6% 30%	2160
	21st to end	Night	28% 12% 3 7% 4 4 4 3 4 5% 26%	2376
November	1st to 10th	Night	16% 12% 3 7% 5% 4 4 4 5% 7% 33%	2350
	11th to 20th	Night	18% 19% 4 8% 6% 4 4 3 5% 5% 23%	2631
	21st to end	Night	20% 22% 5% 9% 5% 3 4 3 4 6% 19%	2660
December	1st to 10th	Night	22% 26% 8% 9% 6% 3 3 2 4 4 14%	2660
	11th to 20th	Night	17% 25% 8% 13% 6% 3 3 2 3 4 15%	3285
	21st to end	Night	25% 25% 8% 11% 5% 4 4 3 4 4 9%	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	78% 5% 8% 8% 2	2724
	11th to 20th	Day	77% 4 8% 9% 2	2840
	21st to end	Day	85% 3 6% 4 1	3124
February	1st to 10th	Day	75% 3 8% 9% 4	1710
	11th to 20th	Day	72% 5% 8% 10% 5%	1672
	21st to end	Day	65% 5% 10% 13% 5% 2	1537
March	1st to 10th	Day	59% 6% 9% 22% 4	3435
	11th to 20th	Day	57% 6% 16% 14% 5% 1	3480
	21st to end	Day	59% 5% 7% 18% 10% 1	3815
April	1st to 10th	Day	53% 7% 13% 15% 12% 1	2190
	11th to 20th	Day	52% 5% 11% 18% 11% 2	2337
	21st to end	Day	53% 5% 10% 19% 11% 3	2470
May	1st to 10th	Day	52% 7% 9% 22% 9% 1	4120
	11th to 20th	Day	50% 8% 11% 21% 8% 1	4085
	21st to end	Day	39% 8% 13% 21% 15% 4	4837
June	1st to 10th	Day	44% 7% 13% 23% 12% 1	2660
	11th to 20th	Day	44% 8% 13% 21% 13% 1	2660
	21st to end	Day	42% 6% 12% 25% 14% 1	2660
July	1st to 10th	Day	38% 7% 13% 24% 16% 2	4356
	11th to 20th	Day	37% 7% 12% 26% 17% 1	4051
	21st to end	Day	40% 8% 13% 21% 16% 1	4324
August	1st to 10th	Day	40% 8% 16% 25% 11%	2444
	11th to 20th	Day	45% 10% 14% 22% 8% 2	2433
	21st to end	Day	40% 8% 14% 22% 14% 2	2602
September	1st to 10th	Day	45% 7% 14% 20% 12% 2	2159
	11th to 20th	Day	40% 7% 14% 23% 14% 1	1980
	21st to end	Day	48% 7% 12% 22% 11% 1	1980
October	1st to 10th	Day	47% 7% 15% 18% 12% 1	1805
	11th to 20th	Day	57% 6% 14% 16% 7% 1	1800
	21st to end	Day	65% 5% 11% 12% 6% 1	1980
November	1st to 10th	Day	52% 6% 11% 18% 11% 2	1726
	11th to 20th	Day	63% 5% 10% 13% 6% 2	1547
	21st to end	Day	70% 6% 9% 10% 5%	1520
December	1st to 10th	Day	77% 5% 7% 9% 1	1520
	11th to 20th	Day	75% 6% 7% 10% 2	1906
	21st to end	Day	82% 4 7% 7% 1	2772
January	1st to 10th	Night	81% 3 7% 7% 2	4205
	11th to 20th	Night	79% 4 8% 7% 1	4120
	21st to end	Night	82% 3 6% 7% 1	4532
February	1st to 10th	Night	72% 4 10% 11% 4	2470
	11th to 20th	Night	70% 5% 9% 11% 4	2405
	21st to end	Night	67% 5% 9% 12% 7% 1	1911
March	1st to 10th	Night	58% 5% 11% 19% 6%	3418
	11th to 20th	Night	57% 6% 13% 16% 7% 1	3480
	21st to end	Night	54% 5% 10% 17% 13% 1	3817
April	1st to 10th	Night	57% 5% 10% 16% 11% 1	1990
	11th to 20th	Night	51% 6% 11% 17% 12% 2	1809
	21st to end	Night	49% 6% 12% 19% 10% 4	1710
May	1st to 10th	Night	53% 5% 11% 18% 10% 3	2840
	11th to 20th	Night	47% 7% 11% 22% 11% 2	2796
	21st to end	Night	32% 8% 15% 26% 16% 2	2739
June	1st to 10th	Night	39% 8% 13% 24% 14% 2	1520
	11th to 20th	Night	38% 8% 13% 23% 16% 2	1520
	21st to end	Night	39% 9% 14% 22% 16% 1	1520
July	1st to 10th	Night	41% 6% 11% 22% 19% 3	2480
	11th to 20th	Night	36% 6% 11% 28% 17% 2	2783
	21st to end	Night	36% 9% 13% 20% 22% 1	2988
August	1st to 10th	Night	35% 7% 12% 30% 14% 2	1690
	11th to 20th	Night	38% 9% 15% 26% 11% 1	1688
	21st to end	Night	36% 8% 14% 25% 15% 3	1943
September	1st to 10th	Night	37% 8% 14% 24% 14% 3	1800
	11th to 20th	Night	35% 7% 14% 24% 19% 1	1979
	21st to end	Night	45% 6% 13% 21% 15% 1	1980
October	1st to 10th	Night	43% 7% 12% 21% 17% 1	2154
	11th to 20th	Night	53% 7% 13% 17% 10% 1	2160
	21st to end	Night	60% 5% 11% 14% 7% 2	2376
November	1st to 10th	Night	50% 6% 14% 19% 9% 3	2350
	11th to 20th	Night	63% 5% 9% 14% 6% 3	2631
	21st to end	Night	68% 5% 10% 13% 3 1	2660
December	1st to 10th	Night	76% 5% 8% 8% 2	2660
	11th to 20th	Night	75% 4 10% 9% 2	3288
	21st to end	Night	80% 6% 8% 6% 1	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	36% 25% 27% 10% 2	240
	11th to 20th	Day	34% 30% 27% 6% 3	270
	21st to end	Day	29% 36% 27% 7% 2	297
February	1st to 10th	Day	34% 24% 35% 7%	270
	11th to 20th	Day	36% 29% 28% 7% 1	270
	21st to end	Day	41% 27% 26% 6%	226
March	1st to 10th	Day	32% 22% 32% 10% 3	460
	11th to 20th	Day	31% 22% 32% 12% 2 1	460
	21st to end	Day	36% 21% 25% 15% 2	506
April	1st to 10th	Day	27% 27% 27% 14% 4 1	460
	11th to 20th	Day	32% 21% 24% 13% 8% 2	452
	21st to end	Day	30% 19% 32% 14% 4 1	460
May	1st to 10th	Day	28% 18% 30% 17% 5% 2	463
	11th to 20th	Day	22% 16% 31% 20% 9% 2	487
	21st to end	Day	16% 12% 30% 27% 12% 4	529
June	1st to 10th	Day	20% 14% 31% 24% 8% 3	490
	11th to 20th	Day	18% 10% 30% 27% 14% 2	490
	21st to end	Day	16% 12% 37% 23% 11% 1	490
July	1st to 10th	Day	11% 8% 27% 29% 19% 6%	485
	11th to 20th	Day	15% 8% 30% 27% 15% 5%	484
	21st to end	Day	11% 9% 34% 27% 15% 5%	532
August	1st to 10th	Day	12% 9% 28% 27% 17% 7%	486
	11th to 20th	Day	17% 8% 24% 29% 13% 9%	479
	21st to end	Day	13% 9% 27% 28% 17% 6%	532
September	1st to 10th	Day	17% 8% 26% 26% 17% 6%	450
	11th to 20th	Day	13% 6% 26% 29% 20% 7%	450
	21st to end	Day	21% 14% 28% 21% 12% 4	450
October	1st to 10th	Day	20% 12% 30% 20% 15% 3	450
	11th to 20th	Day	28% 20% 32% 14% 5% 1	450
	21st to end	Day	39% 18% 28% 13% 2	495
November	1st to 10th	Day	29% 19% 29% 15% 7% 1	324
	11th to 20th	Day	41% 23% 23% 10% 3	192
	21st to end	Day	33% 22% 37% 8%	180
December	1st to 10th	Day	39% 28% 25% 4 3 1	180
	11th to 20th	Day	34% 27% 29% 8% 1	180
	21st to end	Day	35% 26% 30% 8% 1	198
January	1st to 10th	Night	34% 24% 30% 10% 2	760
	11th to 20th	Night	37% 21% 27% 13% 2	760
	21st to end	Night	29% 23% 31% 15% 2	836
February	1st to 10th	Night	34% 20% 29% 15% 1	760
	11th to 20th	Night	28% 24% 33% 14% 2	743
	21st to end	Night	31% 22% 30% 15% 1	628
March	1st to 10th	Night	26% 19% 33% 18% 3	760
	11th to 20th	Night	27% 20% 29% 19% 4 1	760
	21st to end	Night	27% 17% 31% 19% 5% 1	836
April	1st to 10th	Night	27% 18% 31% 20% 4	760
	11th to 20th	Night	27% 14% 32% 20% 7% 1	685
	21st to end	Night	20% 14% 32% 28% 5% 1	570
May	1st to 10th	Night	25% 9% 25% 31% 9% 1	570
	11th to 20th	Night	20% 8% 29% 33% 9% 1	557
	21st to end	Night	13% 6% 30% 30% 19% 2	411
June	1st to 10th	Night	12% 6% 34% 34% 14%	380
	11th to 20th	Night	13% 8% 23% 42% 13%	380
	21st to end	Night	12% 7% 28% 35% 17%	380
July	1st to 10th	Night	11% 3 19% 43% 19% 5%	370
	11th to 20th	Night	12% 4 21% 35% 24% 4	549
	21st to end	Night	11% 4 18% 41% 24% 2	624
August	1st to 10th	Night	11% 4 18% 39% 24% 4	567
	11th to 20th	Night	13% 5% 16% 34% 28% 4	564
	21st to end	Night	14% 6% 22% 31% 25% 3	695
September	1st to 10th	Night	17% 7% 20% 30% 22% 4	720
	11th to 20th	Night	14% 6% 19% 32% 24% 5%	720
	21st to end	Night	19% 11% 23% 26% 17% 4	720
October	1st to 10th	Night	21% 9% 26% 24% 17% 2	720
	11th to 20th	Night	28% 15% 28% 23% 6% 1	720
	21st to end	Night	35% 16% 30% 17% 2	792
November	1st to 10th	Night	23% 16% 28% 24% 8% 1	740
	11th to 20th	Night	32% 20% 29% 13% 5% 1	760
	21st to end	Night	34% 19% 31% 13% 4	760
December	1st to 10th	Night	38% 20% 28% 11% 4	760
	11th to 20th	Night	30% 29% 26% 13% 2	760
	21st to end	Night	34% 22% 30% 12% 1	836

Page generated at 2024-08-27 09:49:43. Version ac07

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