Lenore and Walter Hawley Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Lenore and Walter Hawley Observatory clear sky chart from 2005-11-06 to 2025-10-19.

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% 7% 3 7% 5% 4 4 4 5% 7% 37%	126430
	Night	17% 8% 3 6% 4 4 4 4 5% 6% 39%	123269
Transparency	Day	45% 6% 11% 21% 14% 2	129937
	Night	44% 6% 11% 22% 15% 2	127849
Seeing	Day	25% 17% 29% 19% 8% 2	16167
	Night	22% 14% 30% 25% 7% 1	25009

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	13% 7% 4 10% 6% 5% 5% 4 6% 5% 34%	3597
	11th to 20th	Day	12% 8% 4 8% 4 3 4 3 5% 7% 41%	3570
	21st to end	Day	13% 10% 3 7% 5% 4 4 3 4 5% 42%	3960
February	1st to 10th	Day	16% 9% 2 6% 5% 6% 5% 5% 5% 6% 35%	1807
	11th to 20th	Day	12% 8% 3 9% 5% 4 5% 4 6% 7% 38%	1948
	21st to end	Day	16% 10% 3 9% 5% 4 4 2 5% 6% 36%	1650
March	1st to 10th	Day	20% 11% 4 8% 5% 4 5% 4 4 4 31%	4476
	11th to 20th	Day	17% 9% 3 7% 5% 4 4 4 5% 6% 36%	4743
	21st to end	Day	25% 8% 2 6% 4 4 3 3 5% 7% 32%	5822
April	1st to 10th	Day	19% 9% 3 7% 4 4 4 4 4 5% 37%	2400
	11th to 20th	Day	18% 6% 2 7% 5% 5% 4 4 6% 6% 37%	2391
	21st to end	Day	21% 7% 3 7% 5% 4 4 4 4 6% 35%	2600
May	1st to 10th	Day	33% 9% 2 7% 5% 4 4 3 5% 6% 23%	5886
	11th to 20th	Day	19% 8% 3 9% 6% 5% 5% 3 5% 7% 29%	6106
	21st to end	Day	19% 7% 2 6% 5% 4 5% 4 6% 8% 35%	6949
June	1st to 10th	Day	19% 7% 3 7% 5% 5% 4 3 6% 8% 32%	2800
	11th to 20th	Day	16% 6% 3 7% 4 5% 5% 4 6% 8% 37%	2800
	21st to end	Day	18% 7% 2 6% 5% 5% 5% 4 6% 8% 34%	2800
July	1st to 10th	Day	15% 6% 2 7% 5% 5% 5% 5% 6% 10% 33%	6360
	11th to 20th	Day	9% 6% 2 7% 5% 5% 6% 5% 7% 9% 39%	6360
	21st to end	Day	14% 5% 2 6% 4 4 4 4 6% 8% 42%	6926
August	1st to 10th	Day	14% 6% 3 7% 5% 5% 6% 4 6% 8% 36%	4367
	11th to 20th	Day	14% 8% 3 6% 5% 5% 5% 4 6% 8% 37%	4125
	21st to end	Day	8% 4 2 6% 4 5% 5% 4 7% 9% 45%	4312
September	1st to 10th	Day	12% 5% 2 5% 4 4 4 5% 6% 7% 47%	2400
	11th to 20th	Day	14% 5% 2 5% 3 3 2 2 5% 6% 53%	2211
	21st to end	Day	16% 5% 2 5% 3 4 4 3 5% 7% 45%	2200
October	1st to 10th	Day	21% 7% 2 6% 3 4 4 3 5% 5% 40%	2200
	11th to 20th	Day	17% 6% 2 5% 4 4 4 4 4 7% 44%	1906
	21st to end	Day	23% 7% 3 5% 4 4 4 3 3 6% 38%	1881
November	1st to 10th	Day	14% 7% 2 5% 4 4 3 3 5% 6% 48%	1761
	11th to 20th	Day	18% 6% 2 5% 3 3 3 4 4 5% 47%	1800
	21st to end	Day	20% 8% 2 5% 4 4 4 3 4 6% 40%	1770
December	1st to 10th	Day	15% 8% 3 7% 5% 4 5% 3 5% 7% 37%	2600
	11th to 20th	Day	20% 6% 2 6% 4 4 4 3 5% 4 42%	2986
	21st to end	Day	21% 9% 3 7% 4 4 4 3 4 5% 36%	3960
January	1st to 10th	Night	13% 7% 3 7% 5% 5% 5% 4 6% 6% 39%	6349
	11th to 20th	Night	12% 9% 3 10% 6% 5% 5% 3 5% 6% 36%	6315
	21st to end	Night	15% 10% 3 7% 4 5% 4 4 5% 5% 37%	6996
February	1st to 10th	Night	15% 9% 3 7% 5% 4 5% 3 5% 6% 37%	2587
	11th to 20th	Night	13% 9% 2 7% 4 5% 5% 4 7% 6% 38%	2338
	21st to end	Night	15% 9% 2 6% 5% 5% 5% 4 5% 7% 39%	1980
March	1st to 10th	Night	23% 8% 2 6% 4 4 4 4 6% 6% 34%	5364
	11th to 20th	Night	15% 11% 3 7% 5% 4 5% 3 5% 6% 36%	5215
	21st to end	Night	27% 8% 2 5% 3 3 4 4 6% 6% 32%	5105
April	1st to 10th	Night	20% 8% 3 7% 4 4 4 4 5% 6% 36%	2000
	11th to 20th	Night	21% 8% 2 6% 4 4 4 4 4 5% 39%	1956
	21st to end	Night	19% 7% 2 6% 4 4 3 4 5% 5% 39%	1800
May	1st to 10th	Night	35% 9% 2 6% 4 3 4 3 5% 5% 24%	4054
	11th to 20th	Night	15% 9% 3 9% 6% 6% 5% 4 6% 7% 29%	3817
	21st to end	Night	21% 7% 3 7% 5% 5% 4 4 5% 7% 32%	3926
June	1st to 10th	Night	20% 8% 3 7% 5% 3 4 3 5% 6% 37%	1600
	11th to 20th	Night	19% 6% 2 5% 4 5% 5% 3 6% 9% 36%	1600
	21st to end	Night	17% 7% 3 5% 5% 5% 4 4 5% 8% 38%	1600
July	1st to 10th	Night	12% 6% 2 6% 5% 4 5% 4 7% 9% 41%	3600
	11th to 20th	Night	11% 7% 2 6% 5% 4 5% 4 7% 8% 39%	3600
	21st to end	Night	11% 5% 2 4 4 3 5% 4 5% 6% 51%	3926
August	1st to 10th	Night	21% 6% 3 7% 5% 4 5% 3 5% 6% 36%	2751
	11th to 20th	Night	13% 8% 3 7% 5% 5% 5% 3 6% 8% 38%	2905
	21st to end	Night	9% 4 2 5% 3 3 4 3 5% 10% 53%	3586
September	1st to 10th	Night	12% 6% 2 5% 3 3 3 3 4 7% 51%	2000
	11th to 20th	Night	14% 6% 1 4 3 2 3 2 5% 6% 53%	2188
	21st to end	Night	15% 6% 2 5% 4 3 3 3 5% 6% 48%	2200
October	1st to 10th	Night	21% 6% 3 6% 4 4 3 3 4 5% 42%	2200
	11th to 20th	Night	16% 6% 2 5% 4 4 4 4 6% 8% 43%	2448
	21st to end	Night	22% 7% 2 6% 4 4 4 3 5% 6% 37%	2717
November	1st to 10th	Night	15% 7% 3 7% 4 3 4 2 4 6% 46%	2537
	11th to 20th	Night	16% 6% 3 6% 4 4 4 3 5% 5% 46%	2600
	21st to end	Night	17% 8% 2 5% 4 4 4 3 5% 7% 41%	2625
December	1st to 10th	Night	16% 10% 3 8% 5% 4 4 3 5% 6% 36%	4580
	11th to 20th	Night	22% 8% 3 6% 3 3 3 3 4 5% 39%	5208
	21st to end	Night	19% 11% 2 7% 4 4 3 3 5% 5% 38%	6996

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% 5% 10% 24% 12%	3598
	11th to 20th	Day	41% 5% 14% 22% 15% 3	3600
	21st to end	Day	43% 5% 8% 22% 18% 4	3960
February	1st to 10th	Day	49% 5% 12% 21% 11% 2	1807
	11th to 20th	Day	44% 6% 13% 20% 14% 3	1957
	21st to end	Day	49% 4 9% 21% 14% 2	1650
March	1st to 10th	Day	55% 4 9% 13% 10% 8%	4479
	11th to 20th	Day	45% 8% 14% 21% 11% 2	4743
	21st to end	Day	50% 4 7% 17% 17% 5%	5822
April	1st to 10th	Day	49% 5% 8% 19% 15% 4	2400
	11th to 20th	Day	46% 6% 11% 18% 17% 3	2391
	21st to end	Day	50% 5% 8% 17% 17% 3	2600
May	1st to 10th	Day	62% 7% 9% 13% 8% 1	5897
	11th to 20th	Day	53% 8% 13% 16% 9% 2	6110
	21st to end	Day	45% 8% 12% 21% 13% 1	6949
June	1st to 10th	Day	49% 7% 12% 20% 12%	2800
	11th to 20th	Day	44% 7% 11% 19% 16% 3	2800
	21st to end	Day	48% 7% 11% 19% 13% 1	2800
July	1st to 10th	Day	47% 6% 12% 20% 14% 1	6290
	11th to 20th	Day	40% 7% 14% 23% 15% 1	6285
	21st to end	Day	40% 5% 11% 26% 17% 1	6728
August	1st to 10th	Day	44% 7% 15% 22% 11% 1	4353
	11th to 20th	Day	44% 7% 14% 25% 9% 1	4164
	21st to end	Day	34% 7% 12% 28% 17% 2	4312
September	1st to 10th	Day	36% 6% 13% 25% 19% 2	2400
	11th to 20th	Day	33% 5% 9% 27% 24% 2	2211
	21st to end	Day	39% 6% 9% 25% 19% 3	2200
October	1st to 10th	Day	44% 5% 8% 23% 18% 2	3590
	11th to 20th	Day	35% 5% 10% 28% 20% 3	3083
	21st to end	Day	36% 3 8% 31% 18% 3	3081
November	1st to 10th	Day	38% 4 13% 25% 17% 2	1761
	11th to 20th	Day	39% 4 11% 22% 22% 3	1800
	21st to end	Day	46% 4 16% 21% 12% 1	1770
December	1st to 10th	Day	46% 6% 14% 26% 8% 1	2600
	11th to 20th	Day	44% 5% 12% 17% 18% 4	2986
	21st to end	Day	51% 4 9% 18% 14% 5%	3960
January	1st to 10th	Night	42% 5% 11% 28% 11% 2	6349
	11th to 20th	Night	47% 6% 13% 21% 11% 2	6360
	21st to end	Night	47% 4 9% 17% 17% 5%	6996
February	1st to 10th	Night	46% 7% 12% 21% 13% 2	2587
	11th to 20th	Night	44% 6% 11% 21% 15% 3	2340
	21st to end	Night	43% 6% 10% 23% 13% 4	1980
March	1st to 10th	Night	50% 4 10% 15% 15% 6%	5374
	11th to 20th	Night	47% 7% 15% 17% 12% 2	5216
	21st to end	Night	50% 5% 6% 14% 21% 5%	5105
April	1st to 10th	Night	49% 5% 10% 17% 16% 2	2000
	11th to 20th	Night	47% 5% 7% 22% 18% 1	1956
	21st to end	Night	45% 6% 11% 18% 17% 3	1800
May	1st to 10th	Night	62% 6% 10% 13% 7% 1	4060
	11th to 20th	Night	51% 9% 14% 16% 9% 1	3818
	21st to end	Night	50% 8% 14% 18% 9% 1	3927
June	1st to 10th	Night	48% 6% 11% 21% 13% 1	1600
	11th to 20th	Night	44% 9% 13% 20% 12% 2	1600
	21st to end	Night	44% 9% 12% 22% 12% 1	1600
July	1st to 10th	Night	39% 7% 15% 25% 13% 1	3560
	11th to 20th	Night	41% 8% 14% 20% 16%	3552
	21st to end	Night	33% 6% 12% 34% 14% 1	3809
August	1st to 10th	Night	49% 8% 11% 20% 11% 1	2741
	11th to 20th	Night	44% 9% 15% 21% 11% 1	2932
	21st to end	Night	28% 5% 17% 31% 18% 1	3586
September	1st to 10th	Night	34% 6% 13% 27% 20% 1	2000
	11th to 20th	Night	32% 5% 10% 28% 22% 2	2188
	21st to end	Night	37% 6% 9% 28% 18% 2	2200
October	1st to 10th	Night	42% 5% 14% 23% 14% 2	3590
	11th to 20th	Night	32% 5% 11% 26% 24% 3	4010
	21st to end	Night	37% 4 10% 31% 15% 2	4467
November	1st to 10th	Night	40% 5% 10% 25% 18% 2	2537
	11th to 20th	Night	40% 4 10% 24% 19% 3	2600
	21st to end	Night	43% 5% 14% 25% 12% 1	2625
December	1st to 10th	Night	49% 5% 10% 26% 9%	4580
	11th to 20th	Night	48% 4 12% 15% 20% 2	5208
	21st to end	Night	49% 4 9% 21% 15% 3	6996

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	32% 26% 24% 17% 3	200
	11th to 20th	Day	30% 24% 32% 12% 2 2	200
	21st to end	Day	23% 30% 30% 14% 4	220
February	1st to 10th	Day	33% 25% 27% 13% 2	352
	11th to 20th	Day	34% 26% 25% 13% 1	496
	21st to end	Day	30% 24% 29% 14% 2	414
March	1st to 10th	Day	32% 19% 32% 15% 2	500
	11th to 20th	Day	32% 26% 26% 11% 4 1	500
	21st to end	Day	34% 20% 28% 12% 4 2	550
April	1st to 10th	Day	37% 19% 27% 11% 5% 2	500
	11th to 20th	Day	34% 21% 27% 12% 5% 2	492
	21st to end	Day	30% 20% 30% 12% 6% 2	500
May	1st to 10th	Day	35% 19% 26% 15% 4 1	503
	11th to 20th	Day	20% 20% 35% 17% 5% 2	527
	21st to end	Day	21% 14% 33% 23% 7% 1	573
June	1st to 10th	Day	21% 13% 37% 19% 8% 1	530
	11th to 20th	Day	19% 17% 32% 21% 9% 2	530
	21st to end	Day	19% 17% 32% 22% 7% 3	530
July	1st to 10th	Day	17% 9% 33% 26% 12% 2	525
	11th to 20th	Day	14% 9% 33% 29% 12% 4	524
	21st to end	Day	14% 11% 33% 29% 10% 3	576
August	1st to 10th	Day	12% 10% 30% 30% 15% 3	526
	11th to 20th	Day	17% 9% 28% 27% 14% 6%	519
	21st to end	Day	11% 10% 32% 27% 14% 5%	583
September	1st to 10th	Day	17% 11% 25% 24% 16% 7%	530
	11th to 20th	Day	16% 13% 27% 18% 17% 10%	530
	21st to end	Day	19% 12% 29% 22% 12% 6%	530
October	1st to 10th	Day	26% 12% 23% 21% 12% 5%	530
	11th to 20th	Day	25% 14% 29% 19% 11% 3	463
	21st to end	Day	31% 14% 27% 21% 6%	429
November	1st to 10th	Day	25% 17% 27% 22% 9% 1	395
	11th to 20th	Day	33% 17% 26% 19% 5% 1	400
	21st to end	Day	32% 19% 27% 16% 5% 1	370
December	1st to 10th	Day	26% 26% 27% 17% 5%	200
	11th to 20th	Day	35% 21% 31% 11% 3 1	200
	21st to end	Day	33% 18% 28% 15% 6%	220
January	1st to 10th	Night	23% 22% 33% 19% 3	800
	11th to 20th	Night	28% 19% 31% 19% 3	800
	21st to end	Night	22% 19% 36% 20% 3	880
February	1st to 10th	Night	23% 17% 36% 21% 2	800
	11th to 20th	Night	24% 21% 35% 18% 2	783
	21st to end	Night	24% 20% 30% 22% 3	660
March	1st to 10th	Night	28% 18% 34% 18% 3	800
	11th to 20th	Night	26% 20% 29% 21% 4	800
	21st to end	Night	28% 18% 32% 19% 4	880
April	1st to 10th	Night	28% 18% 30% 20% 4	800
	11th to 20th	Night	27% 18% 32% 18% 5%	772
	21st to end	Night	26% 16% 33% 22% 3	600
May	1st to 10th	Night	27% 12% 35% 21% 6% 1	600
	11th to 20th	Night	21% 14% 32% 28% 5%	506
	21st to end	Night	22% 9% 29% 33% 8%	433
June	1st to 10th	Night	19% 9% 34% 30% 8% 1	400
	11th to 20th	Night	18% 10% 28% 35% 10% 1	400
	21st to end	Night	18% 9% 28% 38% 8%	400
July	1st to 10th	Night	15% 4 28% 43% 9% 1	390
	11th to 20th	Night	12% 5% 24% 42% 15% 2	388
	21st to end	Night	15% 4 27% 41% 12% 1	438
August	1st to 10th	Night	17% 4 22% 42% 14%	498
	11th to 20th	Night	16% 8% 28% 32% 15% 1	612
	21st to end	Night	15% 6% 23% 36% 18% 2	880
September	1st to 10th	Night	15% 7% 30% 31% 17% 1	800
	11th to 20th	Night	15% 7% 27% 29% 18% 3	800
	21st to end	Night	18% 8% 29% 29% 14% 2	800
October	1st to 10th	Night	23% 12% 23% 28% 13% 1	800
	11th to 20th	Night	19% 11% 32% 25% 11% 1	793
	21st to end	Night	25% 15% 29% 24% 6%	836
November	1st to 10th	Night	19% 14% 33% 26% 7% 1	780
	11th to 20th	Night	22% 18% 30% 22% 7% 1	800
	21st to end	Night	25% 18% 29% 22% 6%	800
December	1st to 10th	Night	26% 18% 32% 19% 4	800
	11th to 20th	Night	27% 19% 32% 19% 3	800
	21st to end	Night	27% 18% 31% 21% 4	880

Page generated at 2025-10-16 01:50:25. Version ac07

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