Howe Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Howe Observatory clear sky chart from 2005-11-06 to 2024-11-04.

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% 8% 3 6% 4 4 4 4 5% 7% 37%	101246
	Night	17% 8% 3 6% 4 4 4 3 5% 6% 38%	97766
Transparency	Day	44% 7% 12% 22% 14% 2	104784
	Night	43% 7% 13% 22% 14% 2	102317
Seeing	Day	23% 18% 31% 18% 7% 2	14988
	Night	22% 17% 34% 21% 6% 1	23930

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	14% 8% 3 6% 5% 4 4 3 5% 5% 43%	2517
	11th to 20th	Day	16% 9% 4 8% 5% 5% 4 4 5% 5% 36%	2520
	21st to end	Day	20% 13% 3 7% 4 4 4 3 4 5% 32%	2772
February	1st to 10th	Day	17% 8% 3 7% 5% 5% 5% 4 5% 7% 34%	1771
	11th to 20th	Day	14% 7% 3 8% 6% 5% 4 4 5% 7% 37%	1848
	21st to end	Day	19% 11% 3 7% 4 4 3 3 4 5% 36%	1570
March	1st to 10th	Day	21% 15% 4 8% 4 4 4 3 3 4 31%	3116
	11th to 20th	Day	12% 8% 3 8% 5% 5% 5% 5% 6% 7% 36%	3278
	21st to end	Day	20% 9% 3 6% 4 4 5% 3 6% 6% 34%	4120
April	1st to 10th	Day	18% 10% 3 7% 5% 4 4 3 5% 6% 36%	2280
	11th to 20th	Day	18% 8% 2 5% 5% 4 4 3 5% 7% 39%	2254
	21st to end	Day	20% 7% 2 7% 4 5% 5% 3 5% 7% 35%	2441
May	1st to 10th	Day	24% 10% 3 8% 5% 5% 5% 3 4 6% 28%	4106
	11th to 20th	Day	22% 8% 3 7% 4 4 3 3 4 7% 33%	4238
	21st to end	Day	14% 6% 2 5% 4 4 4 3 6% 8% 43%	4837
June	1st to 10th	Day	17% 7% 3 6% 5% 4 4 4 7% 9% 34%	2660
	11th to 20th	Day	16% 7% 3 6% 4 5% 4 4 7% 9% 36%	2660
	21st to end	Day	17% 7% 2 7% 5% 5% 5% 4 6% 8% 33%	2660
July	1st to 10th	Day	13% 6% 2 7% 5% 5% 5% 5% 7% 9% 35%	4440
	11th to 20th	Day	13% 6% 2 6% 4 5% 5% 5% 7% 10% 38%	4440
	21st to end	Day	19% 8% 2 7% 4 5% 4 4 6% 8% 33%	4814
August	1st to 10th	Day	16% 8% 3 7% 5% 5% 5% 4 7% 8% 32%	4233
	11th to 20th	Day	13% 6% 3 7% 5% 5% 5% 4 6% 8% 38%	3890
	21st to end	Day	8% 5% 2 6% 4 4 5% 5% 7% 9% 44%	4180
September	1st to 10th	Day	13% 6% 2 5% 5% 4 5% 3 6% 6% 44%	2280
	11th to 20th	Day	14% 7% 3 4 3 2 3 2 5% 6% 50%	2119
	21st to end	Day	17% 6% 2 5% 4 3 5% 3 5% 7% 42%	2090
October	1st to 10th	Day	21% 8% 3 5% 4 3 4 3 4 6% 38%	2090
	11th to 20th	Day	15% 7% 2 5% 3 3 4 3 5% 7% 46%	1844
	21st to end	Day	20% 8% 2 6% 5% 3 4 3 5% 6% 38%	1881
November	1st to 10th	Day	13% 9% 2 7% 4 3 3 3 4 5% 48%	1698
	11th to 20th	Day	19% 7% 3 4 3 3 3 3 4 6% 43%	1710
	21st to end	Day	17% 8% 2 5% 4 5% 3 4 5% 6% 42%	1691
December	1st to 10th	Day	19% 8% 2 7% 6% 4 4 3 5% 5% 36%	1520
	11th to 20th	Day	21% 7% 2 6% 4 3 4 3 4 5% 41%	1906
	21st to end	Day	20% 12% 3 6% 4 5% 4 4 4 6% 30%	2772
January	1st to 10th	Night	17% 7% 2 5% 3 4 4 3 5% 7% 43%	4429
	11th to 20th	Night	16% 9% 4 8% 5% 4 4 3 6% 6% 36%	4440
	21st to end	Night	21% 14% 4 7% 5% 4 4 3 4 5% 30%	4884
February	1st to 10th	Night	16% 9% 3 6% 4 4 5% 4 5% 6% 37%	2405
	11th to 20th	Night	13% 9% 2 8% 4 5% 5% 4 6% 7% 38%	2218
	21st to end	Night	17% 10% 2 7% 5% 5% 4 3 4 5% 38%	1884
March	1st to 10th	Night	24% 12% 2 5% 4 4 4 3 5% 5% 30%	3724
	11th to 20th	Night	11% 8% 3 6% 6% 5% 4 4 6% 8% 39%	3681
	21st to end	Night	22% 10% 3 5% 4 4 4 3 6% 6% 33%	3508
April	1st to 10th	Night	19% 7% 3 7% 6% 4 5% 4 5% 5% 34%	1900
	11th to 20th	Night	20% 7% 2 6% 4 4 4 4 4 6% 38%	1875
	21st to end	Night	21% 8% 2 7% 4 4 3 4 4 6% 39%	1738
May	1st to 10th	Night	24% 9% 3 8% 4 4 4 4 6% 7% 26%	2834
	11th to 20th	Night	18% 10% 3 9% 5% 5% 5% 4 6% 7% 27%	2669
	21st to end	Night	16% 6% 2 5% 4 4 4 3 6% 8% 41%	2738
June	1st to 10th	Night	16% 8% 3 7% 6% 4 4 4 5% 6% 37%	1520
	11th to 20th	Night	18% 9% 2 6% 4 3 4 3 6% 8% 37%	1520
	21st to end	Night	15% 6% 2 5% 4 4 4 4 5% 8% 41%	1520
July	1st to 10th	Night	14% 6% 2 6% 6% 5% 5% 5% 7% 9% 35%	2520
	11th to 20th	Night	17% 7% 2 6% 3 4 4 4 6% 9% 38%	2520
	21st to end	Night	16% 7% 3 8% 5% 4 4 4 5% 6% 37%	2739
August	1st to 10th	Night	22% 6% 3 7% 5% 5% 4 4 5% 7% 32%	2663
	11th to 20th	Night	13% 8% 3 8% 5% 4 5% 4 5% 7% 38%	2932
	21st to end	Night	8% 4 1 5% 4 3 3 3 5% 7% 58%	3476
September	1st to 10th	Night	13% 8% 2 5% 4 3 4 3 5% 7% 46%	1900
	11th to 20th	Night	12% 7% 2 5% 4 3 3 3 5% 6% 52%	2060
	21st to end	Night	16% 8% 2 5% 4 3 4 3 5% 6% 44%	2090
October	1st to 10th	Night	20% 7% 2 7% 4 3 4 3 4 6% 40%	2090
	11th to 20th	Night	15% 6% 2 5% 3 4 4 3 5% 6% 46%	2332
	21st to end	Night	21% 8% 3 6% 4 4 3 3 4 6% 39%	2717
November	1st to 10th	Night	14% 6% 2 6% 3 3 4 3 5% 6% 48%	2453
	11th to 20th	Night	18% 6% 3 5% 5% 4 4 3 4 5% 43%	2470
	21st to end	Night	15% 8% 2 6% 4 4 4 3 5% 7% 42%	2485
December	1st to 10th	Night	19% 10% 2 6% 5% 4 4 3 5% 6% 38%	2660
	11th to 20th	Night	20% 7% 3 6% 4 4 5% 4 5% 5% 37%	3288
	21st to end	Night	21% 11% 4 6% 4 4 4 3 5% 5% 32%	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	41% 5% 10% 33% 9% 2	2518
	11th to 20th	Day	48% 7% 11% 23% 10% 1	2520
	21st to end	Day	54% 6% 9% 20% 10% 1	2772
February	1st to 10th	Day	47% 6% 15% 18% 12% 2	1771
	11th to 20th	Day	45% 7% 11% 21% 14% 3	1857
	21st to end	Day	51% 5% 10% 19% 13% 2	1570
March	1st to 10th	Day	56% 5% 12% 14% 11% 2	3119
	11th to 20th	Day	38% 9% 18% 23% 10% 2	3278
	21st to end	Day	48% 5% 7% 19% 18% 4	4120
April	1st to 10th	Day	49% 5% 10% 20% 14% 3	2280
	11th to 20th	Day	44% 6% 12% 19% 17% 3	2254
	21st to end	Day	49% 6% 9% 18% 15% 3	2441
May	1st to 10th	Day	55% 9% 12% 13% 10% 1	4120
	11th to 20th	Day	50% 8% 13% 18% 9% 1	4242
	21st to end	Day	35% 8% 13% 25% 17% 2	4837
June	1st to 10th	Day	45% 8% 13% 23% 10% 1	2660
	11th to 20th	Day	43% 7% 15% 20% 13% 1	2660
	21st to end	Day	46% 9% 12% 21% 12% 1	2660
July	1st to 10th	Day	44% 8% 11% 21% 14% 1	4370
	11th to 20th	Day	39% 8% 17% 23% 12% 1	4365
	21st to end	Day	48% 7% 13% 19% 13% 2	4661
August	1st to 10th	Day	48% 9% 15% 20% 8% 1	4219
	11th to 20th	Day	41% 8% 16% 26% 8% 1	3929
	21st to end	Day	33% 7% 13% 30% 15% 1	4180
September	1st to 10th	Day	39% 7% 11% 24% 18% 1	2280
	11th to 20th	Day	35% 5% 9% 26% 22% 3	2119
	21st to end	Day	41% 6% 10% 22% 19% 2	2090
October	1st to 10th	Day	40% 6% 10% 23% 19% 3	3480
	11th to 20th	Day	32% 5% 9% 26% 25% 3	3034
	21st to end	Day	34% 5% 13% 28% 17% 3	3081
November	1st to 10th	Day	39% 5% 12% 25% 16% 2	1698
	11th to 20th	Day	41% 5% 11% 23% 18% 2	1710
	21st to end	Day	43% 5% 14% 25% 11% 2	1691
December	1st to 10th	Day	49% 5% 14% 16% 14% 2	1520
	11th to 20th	Day	44% 5% 15% 19% 16% 2	1906
	21st to end	Day	53% 5% 13% 19% 10%	2772
January	1st to 10th	Night	39% 5% 13% 29% 11% 3	4429
	11th to 20th	Night	46% 6% 14% 21% 10% 2	4440
	21st to end	Night	56% 6% 10% 17% 10% 2	4884
February	1st to 10th	Night	45% 7% 13% 21% 11% 2	2405
	11th to 20th	Night	45% 5% 11% 20% 15% 3	2220
	21st to end	Night	48% 5% 9% 22% 12% 4	1884
March	1st to 10th	Night	53% 6% 10% 20% 9% 2	3734
	11th to 20th	Night	40% 9% 15% 20% 13% 2	3682
	21st to end	Night	48% 5% 8% 15% 18% 5%	3508
April	1st to 10th	Night	49% 5% 10% 19% 15% 3	1900
	11th to 20th	Night	46% 7% 9% 19% 18% 2	1875
	21st to end	Night	46% 5% 10% 19% 14% 5%	1738
May	1st to 10th	Night	52% 11% 12% 15% 8% 1	2840
	11th to 20th	Night	53% 11% 13% 13% 8% 2	2670
	21st to end	Night	39% 9% 15% 23% 14% 1	2739
June	1st to 10th	Night	46% 7% 12% 23% 12% 1	1520
	11th to 20th	Night	45% 8% 13% 22% 12% 1	1520
	21st to end	Night	38% 11% 14% 23% 14%	1520
July	1st to 10th	Night	43% 9% 14% 20% 13% 1	2480
	11th to 20th	Night	42% 7% 16% 22% 12%	2472
	21st to end	Night	47% 6% 13% 18% 15% 1	2651
August	1st to 10th	Night	51% 10% 11% 19% 8% 1	2653
	11th to 20th	Night	44% 8% 15% 24% 8%	2959
	21st to end	Night	26% 6% 16% 32% 19% 1	3476
September	1st to 10th	Night	38% 8% 11% 24% 18% 1	1900
	11th to 20th	Night	34% 6% 10% 24% 25% 2	2060
	21st to end	Night	40% 6% 8% 24% 18% 3	2090
October	1st to 10th	Night	39% 5% 14% 24% 15% 2	3480
	11th to 20th	Night	28% 5% 12% 25% 27% 3	3881
	21st to end	Night	34% 4 14% 30% 16% 2	4467
November	1st to 10th	Night	37% 7% 11% 22% 19% 4	2453
	11th to 20th	Night	42% 5% 13% 21% 17% 3	2470
	21st to end	Night	40% 6% 16% 26% 11% 1	2485
December	1st to 10th	Night	47% 6% 13% 21% 12% 1	2660
	11th to 20th	Night	44% 7% 15% 17% 15% 2	3288
	21st to end	Night	50% 6% 11% 23% 10% 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	27% 26% 27% 17% 3	180
	11th to 20th	Day	29% 31% 29% 8% 2	180
	21st to end	Day	22% 30% 34% 11% 4	198
February	1st to 10th	Day	34% 27% 27% 10% 1	343
	11th to 20th	Day	30% 30% 30% 9% 1	456
	21st to end	Day	34% 21% 32% 10% 3	382
March	1st to 10th	Day	31% 22% 34% 10% 3	460
	11th to 20th	Day	30% 28% 28% 11% 3	460
	21st to end	Day	30% 25% 30% 9% 4 2	506
April	1st to 10th	Day	33% 22% 29% 10% 5% 1	460
	11th to 20th	Day	31% 21% 31% 11% 5% 1	452
	21st to end	Day	30% 22% 30% 13% 4 2	460
May	1st to 10th	Day	31% 22% 28% 13% 5% 1	463
	11th to 20th	Day	23% 18% 37% 17% 5%	487
	21st to end	Day	19% 14% 35% 21% 9% 2	529
June	1st to 10th	Day	17% 16% 35% 22% 8% 2	490
	11th to 20th	Day	17% 14% 38% 21% 8% 2	490
	21st to end	Day	17% 17% 34% 21% 9% 2	490
July	1st to 10th	Day	17% 9% 31% 28% 12% 3	485
	11th to 20th	Day	14% 8% 31% 32% 13% 2	484
	21st to end	Day	14% 10% 36% 30% 9% 2	532
August	1st to 10th	Day	12% 9% 32% 34% 10% 2	486
	11th to 20th	Day	15% 10% 31% 27% 13% 4	479
	21st to end	Day	12% 13% 32% 25% 15% 4	539
September	1st to 10th	Day	18% 11% 30% 22% 13% 6%	490
	11th to 20th	Day	19% 10% 30% 19% 13% 9%	490
	21st to end	Day	20% 15% 32% 20% 10% 4	490
October	1st to 10th	Day	27% 15% 25% 20% 10% 4	490
	11th to 20th	Day	21% 19% 29% 22% 6% 2	455
	21st to end	Day	26% 19% 30% 18% 6% 1	429
November	1st to 10th	Day	22% 18% 32% 18% 9% 1	374
	11th to 20th	Day	29% 24% 26% 16% 3 1	370
	21st to end	Day	27% 23% 29% 16% 5%	351
December	1st to 10th	Day	24% 32% 28% 13% 4	180
	11th to 20th	Day	38% 23% 31% 7% 2	180
	21st to end	Day	29% 28% 30% 9% 3 1	198
January	1st to 10th	Night	23% 23% 40% 13% 2	760
	11th to 20th	Night	30% 21% 33% 14% 2	760
	21st to end	Night	22% 24% 34% 17% 2	836
February	1st to 10th	Night	24% 22% 37% 16% 1	760
	11th to 20th	Night	23% 27% 38% 10% 1	743
	21st to end	Night	29% 22% 34% 13% 2	628
March	1st to 10th	Night	25% 23% 35% 15% 2	760
	11th to 20th	Night	21% 26% 36% 15% 2	760
	21st to end	Night	27% 21% 31% 17% 4	836
April	1st to 10th	Night	25% 20% 36% 16% 3	760
	11th to 20th	Night	24% 22% 32% 19% 4	751
	21st to end	Night	24% 20% 34% 18% 3	598
May	1st to 10th	Night	29% 17% 32% 18% 3	570
	11th to 20th	Night	18% 18% 41% 20% 4	483
	21st to end	Night	18% 9% 39% 27% 6%	411
June	1st to 10th	Night	17% 12% 36% 29% 7%	380
	11th to 20th	Night	21% 8% 39% 26% 7%	380
	21st to end	Night	14% 6% 38% 35% 7%	380
July	1st to 10th	Night	15% 6% 31% 39% 9%	370
	11th to 20th	Night	16% 3 28% 40% 13% 1	368
	21st to end	Night	12% 6% 32% 40% 10%	416
August	1st to 10th	Night	11% 4 34% 39% 10% 1	470
	11th to 20th	Night	13% 7% 28% 37% 13% 1	647
	21st to end	Night	14% 6% 27% 36% 16% 2	836
September	1st to 10th	Night	17% 6% 34% 31% 10% 1	760
	11th to 20th	Night	14% 10% 28% 29% 18% 2	760
	21st to end	Night	19% 10% 32% 27% 11% 2	760
October	1st to 10th	Night	24% 12% 27% 25% 10% 2	760
	11th to 20th	Night	20% 15% 34% 21% 10% 1	760
	21st to end	Night	27% 18% 32% 19% 5%	836
November	1st to 10th	Night	18% 17% 36% 21% 7% 1	755
	11th to 20th	Night	23% 23% 32% 16% 6% 1	760
	21st to end	Night	21% 22% 36% 17% 4	760
December	1st to 10th	Night	28% 19% 34% 15% 4	760
	11th to 20th	Night	25% 23% 34% 15% 2	760
	21st to end	Night	26% 23% 36% 13% 2	836

Page generated at 2024-11-01 22:47:30. Version ac07

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