WHS Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the WHS Observatory clear sky chart from 2005-11-06 to 2024-02-10.

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	12% 7% 3 6% 5% 3 4 4 5% 7% 43%	78421
	Night	12% 7% 3 6% 4 3 4 4 4 7% 47%	80600
Transparency	Day	41% 5% 13% 25% 15% 2	78144
	Night	38% 5% 12% 26% 17% 3	80397
Seeing	Day	15% 7% 27% 29% 17% 4	14608
	Night	14% 7% 31% 34% 13% 1	24650

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	15% 9% 5% 9% 6% 2 4 4 4 7% 35%	2847
	11th to 20th	Day	10% 11% 4 9% 6% 4 8% 4 3 4 37%	2850
	21st to end	Day	13% 15% 6% 10% 5% 3 4 3 5% 6% 30%	3135
February	1st to 10th	Day	14% 10% 4 7% 6% 3 4 4 5% 6% 37%	1701
	11th to 20th	Day	12% 10% 5% 6% 5% 3 4 4 4 7% 40%	1574
	21st to end	Day	12% 10% 4 6% 4 3 3 4 5% 7% 42%	1518
March	1st to 10th	Day	12% 10% 4 6% 5% 2 4 4 4 7% 42%	1980
	11th to 20th	Day	20% 10% 3 7% 5% 2 3 4 4 7% 35%	1980
	21st to end	Day	19% 13% 4 7% 6% 3 4 3 4 5% 30%	2178
April	1st to 10th	Day	15% 8% 3 5% 4 2 3 4 5% 7% 44%	2078
	11th to 20th	Day	15% 10% 2 6% 6% 2 5% 4 4 7% 39%	2134
	21st to end	Day	20% 7% 3 5% 5% 3 4 5% 6% 6% 36%	2304
May	1st to 10th	Day	18% 8% 3 6% 6% 3 4 5% 4 7% 36%	2340
	11th to 20th	Day	15% 6% 3 7% 5% 3 5% 4 5% 6% 40%	2302
	21st to end	Day	14% 8% 3 6% 6% 3 5% 6% 5% 8% 36%	2610
June	1st to 10th	Day	7% 3 1 4 4 3 5% 5% 6% 10% 49%	2520
	11th to 20th	Day	8% 4 2 5% 4 3 6% 5% 5% 9% 50%	2520
	21st to end	Day	7% 3 2 5% 4 4 5% 5% 6% 10% 50%	2520
July	1st to 10th	Day	9% 4 2 5% 5% 3 6% 6% 6% 9% 46%	2364
	11th to 20th	Day	5% 3 2 5% 6% 3 5% 5% 7% 8% 51%	2340
	21st to end	Day	9% 4 2 4 5% 3 5% 5% 7% 9% 47%	2546
August	1st to 10th	Day	6% 5% 2 5% 6% 4 6% 5% 7% 11% 44%	2328
	11th to 20th	Day	9% 5% 2 5% 4 2 4 4 5% 8% 51%	2301
	21st to end	Day	8% 4 2 4 4 3 5% 4 5% 8% 53%	2440
September	1st to 10th	Day	12% 5% 2 4 4 2 4 4 5% 7% 52%	2160
	11th to 20th	Day	10% 4 2 5% 5% 4 4 5% 5% 7% 50%	1994
	21st to end	Day	8% 4 2 4 3 3 4 4 5% 5% 58%	1972
October	1st to 10th	Day	13% 5% 2 5% 4 2 3 4 4 7% 51%	1800
	11th to 20th	Day	12% 5% 2 5% 4 2 3 3 4 5% 54%	1800
	21st to end	Day	15% 7% 2 5% 4 2 3 3 4 7% 48%	1980
November	1st to 10th	Day	9% 4 2 4 4 3 4 3 4 7% 55%	1839
	11th to 20th	Day	14% 6% 2 3 4 2 3 4 4 5% 52%	1625
	21st to end	Day	15% 9% 3 5% 3 2 3 3 4 5% 47%	1520
December	1st to 10th	Day	10% 6% 4 6% 5% 3 5% 5% 5% 6% 44%	1520
	11th to 20th	Day	12% 9% 4 6% 6% 3 4 4 4 6% 41%	1918
	21st to end	Day	17% 14% 7% 13% 6% 2 4 4 4 5% 25%	2883
January	1st to 10th	Night	9% 8% 3 14% 7% 4 4 4 4 6% 37%	4108
	11th to 20th	Night	11% 10% 4 7% 5% 4 7% 5% 4 5% 38%	4120
	21st to end	Night	16% 12% 6% 10% 5% 3 4 4 4 5% 33%	4532
February	1st to 10th	Night	12% 11% 4 7% 5% 3 4 4 5% 6% 39%	2464
	11th to 20th	Night	12% 8% 4 6% 5% 3 4 4 5% 7% 42%	2273
	21st to end	Night	12% 7% 3 5% 4 3 4 4 5% 4 47%	1753
March	1st to 10th	Night	12% 7% 3 5% 4 2 3 4 5% 6% 49%	1980
	11th to 20th	Night	16% 8% 3 5% 4 3 4 3 5% 6% 42%	1980
	21st to end	Night	21% 10% 3 6% 6% 3 4 4 4 6% 34%	2178
April	1st to 10th	Night	10% 7% 3 5% 4 3 4 4 5% 8% 50%	1882
	11th to 20th	Night	14% 8% 2 5% 3 2 5% 4 3 6% 47%	1775
	21st to end	Night	17% 7% 2 5% 5% 3 4 3 5% 7% 42%	1652
May	1st to 10th	Night	16% 5% 2 6% 5% 3 5% 5% 4 7% 41%	1620
	11th to 20th	Night	14% 5% 2 5% 4 3 3 4 5% 8% 47%	1593
	21st to end	Night	10% 5% 2 6% 4 3 4 5% 5% 8% 47%	1663
June	1st to 10th	Night	5% 2 1 3 3 3 4 6% 6% 9% 57%	1440
	11th to 20th	Night	5% 3 2 4 3 4 5% 5% 7% 11% 51%	1440
	21st to end	Night	4 3 1 3 3 1 4 3 5% 9% 63%	1440
July	1st to 10th	Night	7% 4 2 3 4 3 5% 5% 6% 10% 51%	1591
	11th to 20th	Night	3 2 1 3 2 2 4 3 8% 9% 62%	1620
	21st to end	Night	5% 4 2 5% 4 3 4 5% 7% 10% 50%	1772
August	1st to 10th	Night	3 2 2 4 4 3 5% 6% 6% 9% 55%	1611
	11th to 20th	Night	6% 5% 1 4 3 3 4 4 5% 8% 57%	1600
	21st to end	Night	6% 3 2 3 4 3 4 3 5% 8% 60%	1915
September	1st to 10th	Night	10% 5% 2 3 4 3 3 3 4 7% 56%	1800
	11th to 20th	Night	9% 3 2 4 3 2 3 5% 6% 7% 55%	1963
	21st to end	Night	7% 3 1 5% 4 3 4 4 4 5% 60%	1980
October	1st to 10th	Night	12% 5% 2 3 4 2 3 3 3 6% 56%	2150
	11th to 20th	Night	14% 4 2 4 3 2 2 3 4 6% 56%	2160
	21st to end	Night	15% 8% 2 4 4 2 3 3 3 4 52%	2376
November	1st to 10th	Night	8% 4 2 3 3 2 3 3 4 7% 62%	2237
	11th to 20th	Night	10% 6% 2 4 3 2 3 4 4 6% 55%	2553
	21st to end	Night	15% 7% 3 4 3 2 2 4 3 5% 52%	2660
December	1st to 10th	Night	11% 9% 2 4 5% 3 4 4 5% 6% 47%	2660
	11th to 20th	Night	12% 7% 3 6% 4 2 4 4 4 6% 46%	3279
	21st to end	Night	20% 17% 6% 9% 5% 2 3 3 3 4 29%	4780

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	49% 4 12% 24% 11% 1	2848
	11th to 20th	Day	53% 3 14% 20% 10% 1	2850
	21st to end	Day	56% 4 11% 17% 11% 1	3135
February	1st to 10th	Day	49% 3 13% 21% 10% 3	1701
	11th to 20th	Day	45% 4 14% 23% 13% 2	1583
	21st to end	Day	43% 3 13% 24% 15% 3	1518
March	1st to 10th	Day	44% 4 11% 24% 14% 3	1980
	11th to 20th	Day	51% 4 9% 22% 13% 2	1980
	21st to end	Day	57% 4 13% 17% 7% 1	2178
April	1st to 10th	Day	40% 5% 14% 23% 16% 2	2078
	11th to 20th	Day	45% 4 13% 22% 15% 1	2134
	21st to end	Day	48% 6% 11% 25% 10% 1	2304
May	1st to 10th	Day	49% 6% 10% 21% 12% 1	2340
	11th to 20th	Day	44% 6% 13% 23% 13%	2306
	21st to end	Day	45% 9% 13% 20% 11% 2	2610
June	1st to 10th	Day	29% 8% 15% 31% 15% 2	2520
	11th to 20th	Day	30% 8% 14% 29% 18% 1	2520
	21st to end	Day	29% 7% 15% 31% 15% 3	2520
July	1st to 10th	Day	32% 7% 16% 26% 14% 4	2300
	11th to 20th	Day	29% 7% 14% 26% 19% 4	2271
	21st to end	Day	31% 6% 14% 32% 17% 1	2405
August	1st to 10th	Day	32% 9% 18% 27% 12% 2	2314
	11th to 20th	Day	32% 5% 12% 33% 17% 2	2301
	21st to end	Day	29% 6% 12% 26% 20% 6%	2440
September	1st to 10th	Day	33% 5% 12% 27% 17% 6%	2160
	11th to 20th	Day	33% 6% 11% 25% 21% 3	1994
	21st to end	Day	28% 5% 9% 32% 23% 3	1972
October	1st to 10th	Day	34% 4 13% 28% 20% 2	1800
	11th to 20th	Day	34% 4 7% 27% 24% 5%	1800
	21st to end	Day	39% 4 11% 24% 18% 5%	1980
November	1st to 10th	Day	30% 4 13% 29% 19% 4	1839
	11th to 20th	Day	35% 3 11% 28% 20% 3	1625
	21st to end	Day	40% 3 9% 27% 19% 1	1520
December	1st to 10th	Day	40% 5% 13% 26% 14% 1	1520
	11th to 20th	Day	45% 4 15% 27% 8% 1	1915
	21st to end	Day	63% 4 10% 15% 7% 1	2883
January	1st to 10th	Night	48% 5% 13% 21% 12% 1	4108
	11th to 20th	Night	49% 3 13% 22% 12% 1	4120
	21st to end	Night	55% 4 14% 17% 9% 1	4532
February	1st to 10th	Night	47% 4 12% 21% 14% 3	2464
	11th to 20th	Night	43% 4 12% 22% 16% 3	2274
	21st to end	Night	41% 3 10% 22% 18% 6%	1753
March	1st to 10th	Night	36% 4 11% 26% 18% 4	1980
	11th to 20th	Night	44% 5% 10% 22% 15% 3	1980
	21st to end	Night	52% 5% 12% 19% 10% 2	2178
April	1st to 10th	Night	34% 6% 12% 24% 21% 4	1882
	11th to 20th	Night	39% 6% 9% 27% 16% 3	1775
	21st to end	Night	43% 5% 10% 25% 17% 1	1652
May	1st to 10th	Night	43% 7% 12% 23% 14% 2	1620
	11th to 20th	Night	37% 6% 13% 25% 18% 1	1594
	21st to end	Night	35% 7% 16% 27% 12% 2	1664
June	1st to 10th	Night	22% 8% 17% 33% 17% 3	1440
	11th to 20th	Night	26% 7% 15% 30% 21% 2	1440
	21st to end	Night	19% 5% 15% 37% 21% 4	1440
July	1st to 10th	Night	26% 8% 14% 31% 17% 4	1546
	11th to 20th	Night	18% 5% 16% 34% 23% 4	1566
	21st to end	Night	26% 6% 12% 36% 19% 1	1673
August	1st to 10th	Night	23% 7% 19% 33% 16% 2	1601
	11th to 20th	Night	26% 5% 12% 33% 23% 1	1600
	21st to end	Night	23% 5% 12% 29% 24% 7%	1915
September	1st to 10th	Night	29% 5% 10% 28% 21% 7%	1800
	11th to 20th	Night	27% 6% 11% 27% 25% 4	1963
	21st to end	Night	27% 4 8% 29% 28% 4	1980
October	1st to 10th	Night	31% 4 9% 27% 24% 5%	2150
	11th to 20th	Night	32% 4 7% 27% 23% 8%	2160
	21st to end	Night	38% 4 9% 21% 26% 3	2376
November	1st to 10th	Night	25% 4 14% 28% 24% 6%	2237
	11th to 20th	Night	31% 4 10% 29% 22% 4	2553
	21st to end	Night	37% 3 10% 28% 19% 3	2660
December	1st to 10th	Night	39% 5% 12% 28% 16% 1	2660
	11th to 20th	Night	39% 4 12% 30% 13% 1	3281
	21st to end	Night	61% 4 7% 18% 8% 1	4780

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% 11% 34% 28% 6%	270
	11th to 20th	Day	25% 13% 38% 20% 4	270
	21st to end	Day	18% 12% 42% 24% 3	297
February	1st to 10th	Day	24% 16% 37% 20% 2	267
	11th to 20th	Day	20% 18% 43% 11% 8%	240
	21st to end	Day	19% 20% 38% 18% 5% 1	198
March	1st to 10th	Day	20% 13% 44% 20% 3	240
	11th to 20th	Day	29% 8% 33% 22% 6% 1	240
	21st to end	Day	35% 16% 27% 18% 2 2	264
April	1st to 10th	Day	24% 13% 36% 21% 6% 1	338
	11th to 20th	Day	20% 11% 37% 23% 9%	412
	21st to end	Day	25% 11% 34% 20% 10% 1	564
May	1st to 10th	Day	21% 10% 33% 24% 9% 2	603
	11th to 20th	Day	21% 7% 29% 27% 13% 3	625
	21st to end	Day	18% 4 29% 27% 19% 4	679
June	1st to 10th	Day	6% 5% 19% 34% 26% 10%	630
	11th to 20th	Day	8% 3 23% 38% 22% 6%	630
	21st to end	Day	7% 4 33% 38% 16% 3	630
July	1st to 10th	Day	11% 1 13% 33% 30% 12%	621
	11th to 20th	Day	6% 1 18% 39% 28% 8%	618
	21st to end	Day	10% 1 13% 40% 29% 7%	684
August	1st to 10th	Day	8% 1 14% 41% 31% 6%	626
	11th to 20th	Day	9% 2 16% 37% 30% 7%	615
	21st to end	Day	10% 1 13% 33% 32% 11%	559
September	1st to 10th	Day	14% 2 16% 32% 30% 6%	450
	11th to 20th	Day	5% 2 22% 37% 26% 8%	284
	21st to end	Day	15% 4 27% 33% 15% 6%	270
October	1st to 10th	Day	16% 5% 27% 27% 20% 6%	270
	11th to 20th	Day	12% 15% 46% 19% 7% 1	270
	21st to end	Day	22% 13% 35% 22% 7% 1	297
November	1st to 10th	Day	17% 7% 35% 30% 9% 3	270
	11th to 20th	Day	18% 14% 34% 23% 9% 2	270
	21st to end	Day	23% 10% 34% 22% 10%	270
December	1st to 10th	Day	8% 14% 38% 29% 9% 2	270
	11th to 20th	Day	21% 10% 36% 25% 7% 1	270
	21st to end	Day	20% 16% 42% 20% 1	297
January	1st to 10th	Night	12% 13% 37% 30% 8%	950
	11th to 20th	Night	17% 13% 37% 27% 6% 1	950
	21st to end	Night	16% 9% 39% 32% 4	1045
February	1st to 10th	Night	17% 11% 41% 26% 4	948
	11th to 20th	Night	16% 12% 37% 29% 5%	879
	21st to end	Night	19% 10% 43% 22% 6% 1	569
March	1st to 10th	Night	15% 11% 42% 26% 6%	540
	11th to 20th	Night	21% 8% 35% 29% 6% 1	540
	21st to end	Night	25% 9% 36% 25% 4	594
April	1st to 10th	Night	14% 10% 40% 31% 5%	540
	11th to 20th	Night	19% 10% 34% 32% 5%	533
	21st to end	Night	21% 6% 36% 28% 7% 1	540
May	1st to 10th	Night	17% 8% 30% 35% 9% 1	540
	11th to 20th	Night	15% 5% 31% 36% 12% 1	531
	21st to end	Night	11% 5% 29% 39% 15% 2	584
June	1st to 10th	Night	6% 2 19% 45% 26% 1	540
	11th to 20th	Night	7% 2 24% 45% 19% 2	540
	21st to end	Night	6% 2 28% 48% 16%	540
July	1st to 10th	Night	8% 1 10% 44% 34% 4	525
	11th to 20th	Night	5% 1 14% 47% 31% 2	522
	21st to end	Night	6% 1 10% 49% 32% 2	591
August	1st to 10th	Night	4 1 14% 48% 32% 1	537
	11th to 20th	Night	8% 1 11% 46% 31% 3	534
	21st to end	Night	8% 1 11% 42% 35% 4	594
September	1st to 10th	Night	14% 1 16% 40% 25% 4	540
	11th to 20th	Night	9% 1 20% 43% 24% 3	540
	21st to end	Night	9% 4 22% 43% 20% 2	540
October	1st to 10th	Night	15% 5% 28% 32% 18% 2	710
	11th to 20th	Night	17% 7% 38% 31% 8%	720
	21st to end	Night	20% 8% 33% 30% 8%	792
November	1st to 10th	Night	10% 9% 35% 35% 10% 1	757
	11th to 20th	Night	14% 12% 36% 29% 8%	950
	21st to end	Night	19% 9% 33% 30% 8%	950
December	1st to 10th	Night	16% 11% 34% 33% 7% 1	950
	11th to 20th	Night	20% 7% 37% 29% 6%	950
	21st to end	Night	20% 13% 35% 27% 4	1045

Page generated at 2024-02-07 05:11:56. Version ac07

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