The Bruce M. Bedow Memorial Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the The Bruce M. Bedow Memorial Observatory clear sky chart from 2005-11-06 to 2024-11-02.

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% 11% 4 8% 5% 5% 5% 4 5% 7% 29%	101223
	Night	18% 12% 4 9% 5% 4 4 3 5% 6% 30%	97689
Transparency	Day	53% 6% 11% 19% 10% 1	101027
	Night	55% 6% 11% 18% 10% 1	97555
Seeing	Day	24% 15% 27% 20% 10% 3	14638
	Night	24% 13% 27% 25% 10% 1	24192

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	20% 22% 10% 13% 4 4 3 2 2 4 15%	2677
	11th to 20th	Day	12% 22% 10% 16% 8% 5% 3 2 3 4 16%	2840
	21st to end	Day	26% 20% 9% 15% 6% 4 3 2 3 3 9%	3124
February	1st to 10th	Day	18% 20% 5% 12% 7% 5% 3 3 3 4 19%	1710
	11th to 20th	Day	16% 16% 5% 15% 6% 5% 5% 4 4 4 20%	1663
	21st to end	Day	21% 16% 4 11% 5% 4 4 3 4 5% 22%	1541
March	1st to 10th	Day	21% 11% 5% 8% 5% 3 4 3 5% 6% 27%	3435
	11th to 20th	Day	13% 15% 6% 9% 6% 5% 4 3 4 5% 29%	3480
	21st to end	Day	20% 11% 3 9% 5% 4 5% 3 4 6% 30%	3815
April	1st to 10th	Day	17% 15% 3 7% 6% 4 4 3 4 6% 30%	2218
	11th to 20th	Day	20% 13% 3 7% 4 4 4 3 5% 6% 32%	2275
	21st to end	Day	22% 11% 3 6% 5% 4 3 4 5% 6% 32%	2470
May	1st to 10th	Day	23% 10% 3 7% 5% 4 4 4 5% 6% 28%	4082
	11th to 20th	Day	20% 10% 3 7% 5% 5% 5% 4 6% 7% 27%	4160
	21st to end	Day	13% 6% 3 7% 5% 4 5% 4 6% 8% 39%	4823
June	1st to 10th	Day	17% 7% 3 7% 6% 5% 6% 4 6% 8% 33%	2660
	11th to 20th	Day	14% 8% 3 7% 5% 6% 5% 4 6% 9% 34%	2660
	21st to end	Day	16% 6% 2 5% 5% 5% 5% 4 7% 10% 35%	2660
July	1st to 10th	Day	10% 7% 2 7% 5% 5% 6% 4 7% 10% 37%	4440
	11th to 20th	Day	12% 6% 2 6% 5% 5% 6% 4 7% 8% 39%	4187
	21st to end	Day	11% 6% 2 7% 6% 5% 6% 5% 7% 8% 37%	4466
August	1st to 10th	Day	17% 9% 3 8% 5% 5% 6% 4 6% 8% 29%	4104
	11th to 20th	Day	13% 8% 3 7% 5% 6% 6% 5% 7% 8% 32%	4044
	21st to end	Day	11% 6% 3 8% 4 5% 6% 5% 7% 9% 37%	4292
September	1st to 10th	Day	17% 8% 2 6% 3 4 4 3 5% 6% 42%	2280
	11th to 20th	Day	12% 8% 2 6% 4 4 5% 4 7% 7% 41%	2139
	21st to end	Day	20% 8% 4 7% 4 5% 4 4 4 6% 33%	2064
October	1st to 10th	Day	18% 8% 2 7% 4 4 4 4 6% 7% 35%	1900
	11th to 20th	Day	22% 10% 3 7% 5% 5% 4 3 5% 6% 32%	1900
	21st to end	Day	24% 11% 3 8% 5% 4 4 3 6% 7% 26%	2090
November	1st to 10th	Day	12% 10% 3 8% 5% 4 5% 3 5% 7% 37%	1782
	11th to 20th	Day	18% 15% 3 9% 5% 4 3 4 6% 5% 28%	1520
	21st to end	Day	20% 20% 5% 8% 4 4 4 4 4 6% 21%	1520
December	1st to 10th	Day	20% 24% 7% 11% 6% 4 4 3 3 4 14%	1520
	11th to 20th	Day	19% 19% 7% 13% 5% 4 4 3 4 6% 17%	1910
	21st to end	Day	27% 25% 6% 11% 6% 4 2 2 3 3 12%	2772
January	1st to 10th	Night	17% 23% 10% 15% 5% 4 3 2 3 4 14%	4265
	11th to 20th	Night	16% 19% 9% 17% 6% 6% 5% 3 4 4 12%	4120
	21st to end	Night	28% 18% 9% 13% 4 3 3 2 3 3 13%	4532
February	1st to 10th	Night	18% 17% 5% 12% 8% 6% 3 3 4 3 21%	2470
	11th to 20th	Night	18% 15% 5% 13% 6% 5% 6% 3 5% 4 20%	2403
	21st to end	Night	21% 12% 5% 13% 6% 4 4 3 4 4 23%	1909
March	1st to 10th	Night	22% 14% 4 7% 4 4 3 3 4 6% 30%	3418
	11th to 20th	Night	18% 13% 8% 8% 4 3 3 3 4 5% 30%	3480
	21st to end	Night	17% 11% 4 8% 4 4 3 3 4 5% 37%	3817
April	1st to 10th	Night	18% 14% 4 7% 5% 4 4 3 4 6% 31%	1961
	11th to 20th	Night	18% 10% 2 7% 4 4 4 3 5% 6% 36%	1870
	21st to end	Night	15% 11% 3 8% 5% 4 4 3 5% 8% 35%	1710
May	1st to 10th	Night	27% 9% 2 6% 5% 4 4 3 4 7% 30%	2813
	11th to 20th	Night	19% 10% 3 7% 5% 4 4 3 5% 7% 33%	2731
	21st to end	Night	13% 6% 2 5% 4 4 4 4 6% 10% 42%	2732
June	1st to 10th	Night	9% 6% 2 6% 6% 5% 4 5% 6% 9% 42%	1520
	11th to 20th	Night	12% 6% 3 6% 5% 5% 4 4 6% 9% 41%	1520
	21st to end	Night	13% 6% 2 7% 4 4 4 4 6% 10% 40%	1520
July	1st to 10th	Night	12% 8% 3 7% 5% 4 5% 4 5% 7% 40%	2520
	11th to 20th	Night	11% 6% 2 6% 4 4 5% 3 7% 9% 44%	2768
	21st to end	Night	11% 7% 2 6% 5% 4 5% 4 6% 7% 43%	3087
August	1st to 10th	Night	15% 9% 3 8% 4 4 5% 4 5% 7% 36%	2825
	11th to 20th	Night	15% 7% 3 7% 4 5% 5% 4 5% 8% 38%	2785
	21st to end	Night	10% 4 2 6% 4 4 6% 4 6% 9% 45%	3330
September	1st to 10th	Night	14% 6% 2 6% 3 4 4 3 5% 6% 47%	1900
	11th to 20th	Night	11% 5% 2 5% 3 4 3 4 5% 8% 50%	2038
	21st to end	Night	20% 7% 3 7% 5% 4 4 3 4 6% 37%	2114
October	1st to 10th	Night	15% 7% 2 6% 4 3 4 3 5% 7% 42%	2280
	11th to 20th	Night	19% 8% 2 7% 5% 4 4 4 5% 6% 36%	2280
	21st to end	Night	24% 11% 3 6% 4 4 4 3 5% 6% 31%	2508
November	1st to 10th	Night	14% 10% 3 7% 4 4 4 3 5% 7% 39%	2314
	11th to 20th	Night	18% 16% 3 8% 5% 4 5% 3 4 6% 27%	2660
	21st to end	Night	20% 17% 5% 8% 5% 4 4 3 5% 6% 24%	2660
December	1st to 10th	Night	22% 19% 7% 11% 6% 5% 4 3 5% 4 15%	2660
	11th to 20th	Night	19% 19% 7% 12% 5% 4 4 2 3 5% 20%	3285
	21st to end	Night	25% 22% 7% 11% 5% 5% 4 3 4 4 11%	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	76% 3 7% 10% 5%	2678
	11th to 20th	Day	76% 2 8% 11% 3	2840
	21st to end	Day	82% 3 7% 6% 2	3124
February	1st to 10th	Day	70% 4 8% 12% 6%	1710
	11th to 20th	Day	67% 5% 8% 14% 6%	1672
	21st to end	Day	65% 5% 9% 14% 6% 1	1541
March	1st to 10th	Day	57% 6% 10% 23% 5%	3435
	11th to 20th	Day	56% 5% 15% 17% 5% 1	3480
	21st to end	Day	54% 5% 9% 20% 11% 1	3815
April	1st to 10th	Day	55% 5% 11% 16% 12% 1	2218
	11th to 20th	Day	53% 5% 10% 18% 12% 2	2275
	21st to end	Day	53% 6% 10% 19% 11% 2	2470
May	1st to 10th	Day	55% 6% 9% 22% 7% 1	4120
	11th to 20th	Day	53% 8% 11% 20% 8% 1	4164
	21st to end	Day	40% 8% 13% 22% 14% 3	4837
June	1st to 10th	Day	47% 8% 11% 21% 12% 1	2660
	11th to 20th	Day	46% 7% 13% 19% 13% 1	2660
	21st to end	Day	42% 8% 11% 26% 12% 1	2660
July	1st to 10th	Day	41% 8% 12% 23% 15% 2	4370
	11th to 20th	Day	39% 8% 12% 25% 16%	4115
	21st to end	Day	41% 9% 12% 21% 17% 1	4324
August	1st to 10th	Day	51% 8% 13% 21% 7%	4091
	11th to 20th	Day	44% 10% 14% 24% 8% 1	4083
	21st to end	Day	39% 8% 13% 26% 11% 1	4292
September	1st to 10th	Day	43% 7% 10% 22% 16% 2	2280
	11th to 20th	Day	41% 6% 12% 24% 16% 1	2139
	21st to end	Day	51% 6% 11% 20% 12%	2064
October	1st to 10th	Day	45% 8% 12% 20% 14% 1	1900
	11th to 20th	Day	53% 6% 11% 20% 8% 1	1900
	21st to end	Day	57% 6% 12% 16% 9% 1	2090
November	1st to 10th	Day	46% 7% 12% 18% 15% 2	1782
	11th to 20th	Day	57% 4 12% 18% 7% 2	1520
	21st to end	Day	64% 6% 11% 14% 5% 1	1520
December	1st to 10th	Day	75% 4 10% 8% 3	1520
	11th to 20th	Day	70% 5% 9% 13% 3	1906
	21st to end	Day	80% 3 8% 8% 1	2772
January	1st to 10th	Night	75% 4 7% 11% 3	4265
	11th to 20th	Night	77% 5% 8% 9% 2	4120
	21st to end	Night	78% 3 6% 9% 3	4532
February	1st to 10th	Night	68% 4 8% 15% 5%	2470
	11th to 20th	Night	67% 5% 8% 14% 6%	2405
	21st to end	Night	65% 4 9% 14% 8% 1	1909
March	1st to 10th	Night	57% 4 9% 23% 6%	3418
	11th to 20th	Night	56% 6% 13% 18% 6% 1	3480
	21st to end	Night	49% 5% 7% 23% 15% 2	3817
April	1st to 10th	Night	55% 5% 9% 18% 12% 1	1961
	11th to 20th	Night	48% 6% 10% 19% 14% 2	1870
	21st to end	Night	47% 6% 11% 22% 11% 3	1710
May	1st to 10th	Night	55% 5% 9% 18% 11% 2	2840
	11th to 20th	Night	49% 7% 11% 22% 9% 1	2732
	21st to end	Night	35% 8% 14% 24% 15% 4	2739
June	1st to 10th	Night	38% 8% 13% 26% 14% 1	1520
	11th to 20th	Night	40% 8% 13% 24% 14% 2	1520
	21st to end	Night	39% 8% 13% 22% 17%	1520
July	1st to 10th	Night	43% 8% 10% 20% 18% 1	2480
	11th to 20th	Night	34% 7% 16% 26% 16% 1	2717
	21st to end	Night	40% 7% 10% 18% 23% 1	2988
August	1st to 10th	Night	46% 8% 13% 23% 11% 1	2814
	11th to 20th	Night	42% 8% 12% 29% 9% 1	2812
	21st to end	Night	33% 8% 16% 29% 12% 2	3330
September	1st to 10th	Night	38% 7% 11% 25% 17% 3	1900
	11th to 20th	Night	31% 6% 13% 27% 21% 1	2038
	21st to end	Night	48% 6% 11% 19% 15% 1	2114
October	1st to 10th	Night	42% 5% 14% 22% 16% 1	2280
	11th to 20th	Night	47% 6% 13% 21% 11% 2	2280
	21st to end	Night	54% 5% 11% 18% 11% 1	2508
November	1st to 10th	Night	44% 6% 11% 23% 13% 3	2314
	11th to 20th	Night	58% 5% 9% 17% 8% 3	2660
	21st to end	Night	61% 5% 10% 18% 4 1	2660
December	1st to 10th	Night	72% 5% 10% 10% 3	2660
	11th to 20th	Night	69% 3 11% 13% 3	3288
	21st to end	Night	77% 5% 9% 8% 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	32% 31% 25% 9% 3	225
	11th to 20th	Day	36% 29% 25% 7% 2 1	270
	21st to end	Day	33% 27% 31% 7% 2	297
February	1st to 10th	Day	33% 26% 33% 7%	270
	11th to 20th	Day	37% 27% 27% 7% 1	270
	21st to end	Day	41% 23% 28% 8%	268
March	1st to 10th	Day	30% 23% 30% 14% 2	460
	11th to 20th	Day	33% 20% 33% 10% 3 2	460
	21st to end	Day	35% 20% 27% 14% 4 1	506
April	1st to 10th	Day	30% 23% 26% 16% 5% 1	460
	11th to 20th	Day	29% 21% 25% 15% 8% 3	452
	21st to end	Day	30% 19% 30% 15% 5% 1	460
May	1st to 10th	Day	30% 18% 26% 16% 7% 3	463
	11th to 20th	Day	24% 14% 29% 20% 10% 3	487
	21st to end	Day	16% 11% 27% 26% 15% 5%	529
June	1st to 10th	Day	20% 14% 30% 25% 10% 2	490
	11th to 20th	Day	18% 13% 25% 28% 13% 2	490
	21st to end	Day	18% 15% 30% 23% 10% 2	490
July	1st to 10th	Day	12% 6% 25% 29% 20% 7%	485
	11th to 20th	Day	12% 7% 29% 27% 18% 7%	484
	21st to end	Day	13% 7% 30% 27% 17% 6%	532
August	1st to 10th	Day	15% 6% 25% 27% 21% 7%	486
	11th to 20th	Day	16% 5% 26% 28% 14% 10%	479
	21st to end	Day	15% 7% 24% 30% 17% 8%	539
September	1st to 10th	Day	21% 7% 20% 26% 18% 8%	490
	11th to 20th	Day	13% 6% 23% 29% 19% 10%	490
	21st to end	Day	26% 12% 24% 22% 12% 4	490
October	1st to 10th	Day	20% 9% 29% 22% 16% 4	490
	11th to 20th	Day	26% 17% 30% 17% 8% 2	490
	21st to end	Day	33% 15% 28% 18% 5%	539
November	1st to 10th	Day	23% 17% 30% 18% 9% 2	379
	11th to 20th	Day	33% 22% 26% 13% 4 1	180
	21st to end	Day	24% 30% 36% 9% 1	180
December	1st to 10th	Day	37% 26% 25% 7% 2 2	180
	11th to 20th	Day	36% 18% 34% 8% 3	180
	21st to end	Day	33% 25% 29% 11% 2	198
January	1st to 10th	Night	30% 23% 33% 11% 3	760
	11th to 20th	Night	33% 22% 28% 15% 2	760
	21st to end	Night	26% 22% 32% 17% 2	836
February	1st to 10th	Night	32% 18% 29% 19% 1	760
	11th to 20th	Night	30% 22% 33% 14% 1	743
	21st to end	Night	30% 22% 29% 16% 2	628
March	1st to 10th	Night	26% 18% 35% 19% 3	760
	11th to 20th	Night	29% 18% 27% 19% 6%	760
	21st to end	Night	27% 16% 34% 18% 5% 1	836
April	1st to 10th	Night	27% 16% 31% 20% 6%	760
	11th to 20th	Night	26% 13% 31% 21% 8% 1	746
	21st to end	Night	21% 10% 37% 26% 5% 1	570
May	1st to 10th	Night	25% 10% 21% 32% 11% 1	570
	11th to 20th	Night	20% 10% 27% 33% 9%	519
	21st to end	Night	12% 4 28% 34% 19% 2	411
June	1st to 10th	Night	10% 6% 30% 39% 15%	380
	11th to 20th	Night	13% 6% 25% 40% 16%	380
	21st to end	Night	14% 4 29% 36% 17% 1	380
July	1st to 10th	Night	11% 3 19% 44% 19% 4	370
	11th to 20th	Night	11% 4 19% 39% 25% 3	509
	21st to end	Night	13% 3 16% 43% 24% 1	624
August	1st to 10th	Night	12% 1 17% 43% 25% 2	567
	11th to 20th	Night	14% 4 13% 38% 27% 4	564
	21st to end	Night	12% 4 21% 33% 26% 4	742
September	1st to 10th	Night	16% 5% 22% 31% 23% 3	760
	11th to 20th	Night	13% 5% 18% 34% 27% 4	760
	21st to end	Night	22% 9% 23% 26% 17% 3	760
October	1st to 10th	Night	20% 7% 25% 27% 19% 2	760
	11th to 20th	Night	23% 11% 31% 24% 9% 1	760
	21st to end	Night	30% 13% 27% 25% 5%	836
November	1st to 10th	Night	21% 12% 29% 27% 11%	745
	11th to 20th	Night	29% 16% 27% 20% 6% 1	760
	21st to end	Night	31% 17% 29% 19% 4	760
December	1st to 10th	Night	34% 20% 27% 15% 3	760
	11th to 20th	Night	29% 23% 28% 16% 4	760
	21st to end	Night	31% 19% 30% 17% 2	836

Page generated at 2024-10-30 01:22:55. Version ac07

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