Howell Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Howell Observatory clear sky chart from 2005-11-06 to 2024-11-08.

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	11% 6% 2 6% 5% 5% 5% 4 6% 7% 43%	100880
	Night	12% 6% 2 6% 4 4 4 3 5% 7% 46%	98210
Transparency	Day	37% 7% 11% 21% 19% 6%	104669
	Night	35% 6% 10% 20% 21% 8%	102561
Seeing	Day	13% 7% 19% 24% 23% 13%	15034
	Night	14% 6% 21% 31% 23% 5%	24723

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	16% 12% 2 6% 3 3 3 3 4 6% 41%	2631
	11th to 20th	Day	16% 6% 3 7% 4 4 3 3 4 4 46%	2850
	21st to end	Day	21% 10% 2 5% 3 3 2 2 3 5% 44%	3441
February	1st to 10th	Day	16% 8% 3 6% 4 4 4 4 5% 7% 40%	1900
	11th to 20th	Day	21% 9% 3 6% 4 3 3 3 4 4 41%	1848
	21st to end	Day	20% 8% 3 7% 5% 3 3 2 4 5% 40%	1570
March	1st to 10th	Day	21% 9% 3 8% 4 4 4 3 5% 7% 31%	3120
	11th to 20th	Day	13% 7% 2 6% 4 4 4 4 6% 7% 41%	3346
	21st to end	Day	13% 8% 3 8% 5% 5% 4 4 5% 6% 41%	4152
April	1st to 10th	Day	12% 5% 2 5% 4 4 4 3 7% 7% 46%	2280
	11th to 20th	Day	14% 6% 2 5% 3 4 4 4 5% 7% 45%	2254
	21st to end	Day	8% 5% 2 6% 5% 4 5% 3 6% 7% 49%	2280
May	1st to 10th	Day	10% 5% 2 6% 5% 4 5% 5% 6% 9% 45%	3765
	11th to 20th	Day	13% 5% 2 7% 5% 5% 5% 3 6% 9% 41%	4037
	21st to end	Day	10% 5% 2 6% 4 5% 5% 5% 7% 9% 41%	4476
June	1st to 10th	Day	8% 5% 2 6% 6% 6% 6% 4 7% 10% 38%	2511
	11th to 20th	Day	5% 3 1 6% 5% 6% 6% 5% 8% 9% 46%	2660
	21st to end	Day	6% 3 2 5% 6% 5% 7% 6% 7% 11% 43%	2660
July	1st to 10th	Day	6% 6% 2 8% 7% 6% 8% 6% 9% 10% 33%	4440
	11th to 20th	Day	8% 5% 2 7% 6% 7% 7% 7% 9% 11% 30%	4283
	21st to end	Day	10% 9% 4 9% 7% 7% 7% 5% 7% 9% 26%	4123
August	1st to 10th	Day	3 3 1 5% 4 4 5% 4 6% 7% 59%	3785
	11th to 20th	Day	4 4 2 6% 5% 6% 5% 5% 8% 9% 46%	3729
	21st to end	Day	7% 3 2 5% 5% 5% 5% 4 7% 9% 48%	4180
September	1st to 10th	Day	10% 5% 2 6% 5% 5% 5% 5% 6% 7% 45%	2280
	11th to 20th	Day	12% 5% 2 6% 5% 5% 6% 3 5% 5% 45%	2155
	21st to end	Day	10% 5% 2 5% 3 4 4 3 6% 7% 51%	2090
October	1st to 10th	Day	7% 4 2 7% 3 3 3 3 5% 5% 58%	2090
	11th to 20th	Day	10% 4 1 5% 4 3 4 2 4 6% 57%	1919
	21st to end	Day	12% 4 1 4 3 3 4 3 4 5% 55%	2090
November	1st to 10th	Day	9% 6% 2 4 3 3 4 3 4 5% 56%	1745
	11th to 20th	Day	11% 5% 2 6% 3 4 3 3 3 5% 55%	1710
	21st to end	Day	15% 7% 2 4 4 3 5% 3 5% 7% 45%	1710
December	1st to 10th	Day	16% 9% 3 6% 5% 4 4 4 4 5% 41%	1710
	11th to 20th	Day	14% 8% 4 8% 4 4 4 3 4 5% 43%	2153
	21st to end	Day	13% 8% 3 8% 5% 4 4 3 5% 6% 40%	2907
January	1st to 10th	Night	18% 10% 2 5% 3 3 3 3 4 5% 42%	4321
	11th to 20th	Night	17% 7% 3 6% 4 3 3 2 3 4 47%	4120
	21st to end	Night	22% 10% 3 5% 4 3 3 2 2 3 44%	4211
February	1st to 10th	Night	17% 8% 3 6% 4 4 4 3 5% 6% 41%	2280
	11th to 20th	Night	21% 7% 2 5% 3 3 3 3 3 4 44%	2218
	21st to end	Night	20% 7% 3 6% 4 4 4 3 5% 5% 39%	1884
March	1st to 10th	Night	21% 11% 3 6% 4 3 3 3 4 6% 36%	3733
	11th to 20th	Night	13% 7% 2 5% 5% 4 3 3 5% 8% 46%	3641
	21st to end	Night	18% 7% 3 6% 4 4 4 3 5% 5% 41%	3477
April	1st to 10th	Night	11% 6% 2 5% 4 4 5% 4 5% 7% 48%	1900
	11th to 20th	Night	12% 6% 2 5% 3 3 4 4 5% 7% 50%	1875
	21st to end	Night	10% 5% 2 5% 4 4 4 3 6% 7% 51%	1900
May	1st to 10th	Night	11% 5% 2 6% 4 4 4 3 6% 8% 46%	3130
	11th to 20th	Night	15% 6% 2 6% 4 3 4 4 6% 7% 44%	2854
	21st to end	Night	8% 4 2 6% 4 5% 6% 4 7% 10% 43%	3079
June	1st to 10th	Night	8% 5% 2 6% 5% 5% 6% 4 6% 10% 44%	1663
	11th to 20th	Night	4 3 1 3 4 4 4 5% 7% 10% 54%	1520
	21st to end	Night	4 3 2 5% 4 4 4 5% 7% 11% 49%	1520
July	1st to 10th	Night	5% 5% 2 7% 5% 6% 6% 6% 9% 12% 38%	2530
	11th to 20th	Night	7% 4 2 6% 4 5% 5% 5% 10% 12% 40%	2681
	21st to end	Night	8% 9% 4 10% 7% 6% 6% 5% 7% 10% 28%	3425
August	1st to 10th	Night	3 2 1 3 3 3 4 4 6% 9% 64%	3144
	11th to 20th	Night	3 2 1 4 3 4 4 4 8% 12% 53%	3100
	21st to end	Night	5% 3 2 6% 4 4 5% 5% 7% 9% 50%	3476
September	1st to 10th	Night	9% 4 2 6% 5% 4 5% 4 6% 7% 49%	1900
	11th to 20th	Night	11% 5% 2 5% 4 4 4 4 7% 9% 46%	2004
	21st to end	Night	8% 5% 2 4 3 3 4 4 5% 7% 56%	2090
October	1st to 10th	Night	7% 3 1 3 3 3 4 2 5% 6% 63%	2090
	11th to 20th	Night	10% 5% 1 5% 3 2 4 3 4 7% 55%	2256
	21st to end	Night	15% 6% 2 4 3 2 2 2 4 5% 57%	2508
November	1st to 10th	Night	11% 5% 2 4 3 3 3 3 5% 6% 55%	2490
	11th to 20th	Night	13% 5% 2 4 4 3 3 2 4 5% 54%	2470
	21st to end	Night	15% 5% 2 5% 4 4 3 3 4 5% 49%	2470
December	1st to 10th	Night	17% 7% 3 7% 4 3 4 3 5% 5% 44%	2470
	11th to 20th	Night	15% 6% 3 6% 4 3 3 3 4 5% 49%	3042
	21st to end	Night	16% 9% 3 6% 4 4 5% 4 6% 6% 37%	4738

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	44% 4 5% 21% 22% 4	2632
	11th to 20th	Day	41% 4 6% 23% 23% 3	2850
	21st to end	Day	45% 3 8% 18% 20% 6%	3441
February	1st to 10th	Day	43% 5% 9% 19% 17% 6%	1900
	11th to 20th	Day	47% 3 4 19% 18% 7%	1858
	21st to end	Day	47% 4 6% 14% 20% 8%	1570
March	1st to 10th	Day	52% 5% 8% 11% 16% 8%	3120
	11th to 20th	Day	40% 6% 8% 21% 18% 6%	3346
	21st to end	Day	43% 5% 9% 18% 19% 5%	4152
April	1st to 10th	Day	36% 5% 10% 21% 20% 8%	2280
	11th to 20th	Day	37% 5% 7% 19% 24% 7%	2254
	21st to end	Day	32% 6% 10% 25% 23% 3	2280
May	1st to 10th	Day	34% 8% 12% 28% 15% 3	3800
	11th to 20th	Day	38% 8% 12% 26% 14% 1	4041
	21st to end	Day	35% 9% 13% 29% 12% 2	4489
June	1st to 10th	Day	37% 10% 12% 22% 16% 2	2511
	11th to 20th	Day	30% 9% 15% 25% 19% 3	2660
	21st to end	Day	32% 9% 17% 23% 16% 4	2660
July	1st to 10th	Day	40% 12% 18% 22% 6% 2	4371
	11th to 20th	Day	40% 11% 21% 21% 5% 1	4208
	21st to end	Day	51% 10% 13% 19% 6%	3992
August	1st to 10th	Day	21% 8% 11% 31% 28% 1	3773
	11th to 20th	Day	30% 9% 16% 28% 15% 2	3765
	21st to end	Day	31% 8% 14% 20% 22% 4	4179
September	1st to 10th	Day	35% 10% 12% 19% 18% 6%	2280
	11th to 20th	Day	40% 6% 10% 15% 22% 6%	2155
	21st to end	Day	31% 6% 10% 23% 21% 9%	2090
October	1st to 10th	Day	19% 3 6% 15% 26% 31%	3480
	11th to 20th	Day	17% 2 4 14% 38% 24%	3172
	21st to end	Day	24% 3 5% 19% 35% 14%	3428
November	1st to 10th	Day	31% 4 7% 21% 26% 10%	1745
	11th to 20th	Day	33% 3 7% 19% 26% 12%	1710
	21st to end	Day	39% 5% 6% 17% 25% 8%	1710
December	1st to 10th	Day	46% 4 9% 16% 19% 6%	1710
	11th to 20th	Day	44% 4 7% 18% 23% 5%	2150
	21st to end	Day	43% 5% 8% 19% 23% 2	2907
January	1st to 10th	Night	44% 4 6% 16% 27% 3	4321
	11th to 20th	Night	43% 4 4 22% 20% 8%	4120
	21st to end	Night	47% 3 3 20% 22% 5%	4211
February	1st to 10th	Night	44% 3 7% 17% 20% 8%	2280
	11th to 20th	Night	45% 4 5% 17% 19% 10%	2219
	21st to end	Night	46% 6% 6% 14% 18% 10%	1884
March	1st to 10th	Night	50% 4 8% 13% 15% 9%	3733
	11th to 20th	Night	36% 6% 8% 20% 20% 10%	3641
	21st to end	Night	45% 4 7% 19% 21% 4	3477
April	1st to 10th	Night	35% 6% 9% 21% 20% 9%	1900
	11th to 20th	Night	34% 4 8% 21% 23% 10%	1875
	21st to end	Night	32% 6% 10% 23% 24% 6%	1900
May	1st to 10th	Night	35% 7% 13% 23% 19% 3	3160
	11th to 20th	Night	37% 7% 11% 28% 15% 2	2855
	21st to end	Night	32% 10% 13% 26% 17% 3	3087
June	1st to 10th	Night	34% 9% 15% 21% 18% 3	1663
	11th to 20th	Night	23% 9% 15% 29% 19% 6%	1520
	21st to end	Night	27% 8% 19% 22% 20% 4	1520
July	1st to 10th	Night	34% 12% 24% 19% 9% 2	2490
	11th to 20th	Night	31% 11% 24% 26% 6% 1	2633
	21st to end	Night	48% 10% 17% 17% 7% 1	3316
August	1st to 10th	Night	16% 7% 14% 33% 27% 3	3132
	11th to 20th	Night	21% 10% 22% 30% 15% 3	3130
	21st to end	Night	28% 8% 14% 21% 22% 6%	3476
September	1st to 10th	Night	32% 6% 14% 23% 18% 6%	1900
	11th to 20th	Night	33% 9% 13% 16% 23% 7%	2004
	21st to end	Night	28% 6% 8% 26% 22% 11%	2090
October	1st to 10th	Night	16% 3 7% 16% 27% 31%	3480
	11th to 20th	Night	19% 3 4 17% 29% 29%	3742
	21st to end	Night	21% 2 6% 19% 31% 20%	4120
November	1st to 10th	Night	30% 5% 8% 18% 27% 12%	2490
	11th to 20th	Night	33% 3 7% 18% 26% 13%	2470
	21st to end	Night	37% 4 6% 21% 23% 10%	2470
December	1st to 10th	Night	42% 5% 8% 19% 21% 5%	2470
	11th to 20th	Night	40% 3 7% 18% 27% 6%	3044
	21st to end	Night	43% 7% 8% 16% 23% 3	4738

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	23% 20% 30% 21% 5% 1	270
	11th to 20th	Day	23% 20% 34% 14% 8% 2	270
	21st to end	Day	22% 20% 35% 19% 4 1	297
February	1st to 10th	Day	23% 15% 34% 19% 9%	270
	11th to 20th	Day	34% 14% 31% 17% 3 1	270
	21st to end	Day	30% 19% 34% 13% 4	225
March	1st to 10th	Day	19% 17% 32% 22% 9%	270
	11th to 20th	Day	19% 16% 38% 21% 4 1	270
	21st to end	Day	19% 14% 31% 23% 12%	493
April	1st to 10th	Day	17% 16% 27% 26% 12% 2	460
	11th to 20th	Day	20% 11% 30% 23% 14% 2	452
	21st to end	Day	9% 14% 27% 30% 17% 3	460
May	1st to 10th	Day	16% 9% 18% 33% 19% 6%	463
	11th to 20th	Day	11% 5% 20% 31% 21% 12%	487
	21st to end	Day	10% 4 19% 28% 22% 16%	529
June	1st to 10th	Day	9% 3 14% 28% 28% 18%	531
	11th to 20th	Day	6% 2 11% 27% 32% 22%	680
	21st to end	Day	8% 2 10% 25% 33% 22%	680
July	1st to 10th	Day	7% 2 7% 21% 38% 25%	671
	11th to 20th	Day	7% 1 6% 20% 32% 34%	668
	21st to end	Day	7% 1 7% 20% 36% 31%	537
August	1st to 10th	Day	5% 2 6% 21% 36% 30%	486
	11th to 20th	Day	8% 1 8% 22% 32% 29%	479
	21st to end	Day	13% 2 6% 20% 31% 29%	539
September	1st to 10th	Day	9% 3 8% 24% 37% 19%	490
	11th to 20th	Day	12% 1 11% 20% 34% 22%	490
	21st to end	Day	10% 3 10% 29% 33% 15%	490
October	1st to 10th	Day	9% 3 17% 30% 29% 13%	490
	11th to 20th	Day	10% 8% 28% 27% 22% 7%	319
	21st to end	Day	16% 9% 23% 28% 17% 6%	330
November	1st to 10th	Day	15% 8% 25% 30% 17% 5%	291
	11th to 20th	Day	13% 11% 33% 33% 8% 2	270
	21st to end	Day	14% 16% 32% 22% 13% 4	270
December	1st to 10th	Day	22% 11% 35% 21% 9% 1	270
	11th to 20th	Day	18% 13% 35% 19% 13% 2	270
	21st to end	Day	21% 13% 36% 21% 7% 1	297
January	1st to 10th	Night	21% 11% 33% 28% 7%	950
	11th to 20th	Night	21% 11% 32% 28% 8%	950
	21st to end	Night	20% 12% 36% 29% 4	854
February	1st to 10th	Night	21% 10% 31% 31% 7%	760
	11th to 20th	Night	26% 11% 29% 30% 4	743
	21st to end	Night	21% 14% 34% 28% 3	628
March	1st to 10th	Night	18% 11% 30% 33% 7%	760
	11th to 20th	Night	17% 8% 35% 30% 9%	666
	21st to end	Night	15% 9% 32% 30% 13% 1	627
April	1st to 10th	Night	12% 11% 31% 32% 14%	570
	11th to 20th	Night	12% 7% 30% 34% 15% 2	563
	21st to end	Night	10% 7% 32% 36% 13% 2	570
May	1st to 10th	Night	11% 4 24% 39% 21% 2	570
	11th to 20th	Night	12% 3 17% 36% 28% 4	561
	21st to end	Night	9% 1 12% 37% 34% 7%	617
June	1st to 10th	Night	8% 3 7% 38% 37% 7%	570
	11th to 20th	Night	5% 1 7% 28% 46% 12%	570
	21st to end	Night	5% 1 8% 28% 46% 12%	570
July	1st to 10th	Night	4 1 5% 23% 52% 16%	555
	11th to 20th	Night	5% 1 4 24% 45% 21%	552
	21st to end	Night	6% 1 6% 23% 48% 16%	624
August	1st to 10th	Night	5% 3 21% 51% 20%	567
	11th to 20th	Night	6% 3 25% 51% 15%	564
	21st to end	Night	9% 1 6% 21% 48% 15%	627
September	1st to 10th	Night	11% 2 7% 30% 43% 7%	570
	11th to 20th	Night	12% 3 10% 26% 43% 7%	674
	21st to end	Night	9% 3 11% 32% 41% 5%	760
October	1st to 10th	Night	9% 2 13% 34% 36% 6%	760
	11th to 20th	Night	13% 4 18% 39% 24% 1	760
	21st to end	Night	16% 5% 21% 32% 24% 2	836
November	1st to 10th	Night	13% 5% 18% 39% 22% 4	771
	11th to 20th	Night	13% 6% 28% 35% 16% 1	760
	21st to end	Night	18% 7% 25% 34% 15% 1	760
December	1st to 10th	Night	21% 9% 26% 33% 11%	760
	11th to 20th	Night	21% 8% 29% 31% 12%	760
	21st to end	Night	23% 9% 31% 29% 7%	964

Page generated at 2024-11-05 07:15:49. Version ac07

Copyright © 2024 Attilla Danko.